Quantum Teleportation

A way to transfer the state of a quantum system over large distances by employing entanglement. Entanglement is a nonclassical connection between objects that Albert Einstein called "spooky."

To be able to travel from one place to another instantly and over arbitrary distances, or at least to move objects in this way, is an ancient dream. The concept of teleportation is frequently utilized in the literature of science fiction to overcome limitations imposed on space travel by the laws of physics.

In the standard science fiction approach, the sender, Alice, scans the object to be teleported in order to read out all the information needed to describe it. She then sends that information to the receiver, Bob, who uses this information to reconstitute the object, not necessarily from the same material as that of the original. However, according to quantum mechanics, it is impossible to succeed in this way. If only one individual object is at hand, it is impossible to determine its quantum state by measurement. The quantum state represents all that can be known about the object, that is, all possible (in general, probabilistic) predictions that can be made about future observations of the object.

In fact, it is quantum mechanics that comes to the rescue and makes quantum teleportation possible using a very deep feature of the theory, quantum entanglement. It is important to realize that there are significant differences between teleportation as portrayed in science fiction and quantum teleportation as realized in the laboratory. In the experiments, what is teleported is not the substance an object is made of but the information it represents.
Quantum entanglement. Entangled quantum states as used in teleportation were introduced into the discussion of the foundations of quantum mechanics by Einstein, Boris Podolsky, and Nathan Rosen in 1935. In the same year, Erwin Schrodinger introduced the notion of entanglement, which he called the essence of quantum mechanics.

In order to discuss entanglement, one specific case will be considered, and the possible experimental results will be examined . There are many possible sources that can create many different sorts of entangled states. The source under consideration will be assumed to be the one used in the first tele-portation experiments, which produced photons in a singlet polarization state. This means that neither photon enjoys a state of well-defined polarization; each one of the photons on its own is maximally unpolarized. Yet, when one of the two photons is subject to a polarization measurement, it assumes one specific polarization. That specific experimental outcome is completely random. As a consequence of the two photons being in the entangled singlet state, the other photon is instantly projected into a state orthogonal to that of the first photon. The fact that the measurement result on the second photon can be perfectly predicted on the basis of the measurement result of the first photon, even as neither one carries a well-defined quantum state, is known as the Einstein-Podolsky-Rosen paradox.

In 1964 John Bell showed that these perfect correlations cannot be understood on the basis of properties that the entangled photons carry individually before the measurement. The resulting conflict between the philosophical position of local realism and the predictions of quantum mechanics, which have been confirmed beyond reasonable doubt in experiment, is known as Bell's theorem.
From an information-theoretic point of view, the interesting feature of entanglement is that neither of the two photons carries any information on its own. All information is stored in joint properties.

Concept of quantum teleportation. It was first realized by Charles H. Bennett and his colleagues that entanglement can be utilized to make teleportation possible. Alice, who is in possession of the original teleportee photon in a quantum state not known to her, and Bob initially share an ancillary pair of entangled photons, say in the singlet state described above. Alice then subjects her teleportee photon and her member of the ancillary pair to a Bell-state measurement. A Bell-state measurement is designed in such a way that it projects the two photons into an entangled state even if they were previously unentangled. This is a very tricky procedure both conceptually and experimentally. Conceptually it means that the measurement must be performed in such a way that it is not possible, even in principle, to determine from the measurement result which photon was the teleportee and which was Alice's ancillary. They both have to lose their individuality. The result of the measurement must reveal only how the two photons relate to each other, and ignore individual properties. A Bell measurement has four possible results if the objects considered are denned in a two-dimensional Hilbert space just as is done to describe the photon's polarization. One of the four states is the singlet state discussed above. The other three states also define specific relations between the two photons, though different ones than those for the singlet state.

By the Bell-state measurement, Alice now knows how the unknown state of the teleportee photon relates to her ancillary one. She also knows in which entangled state the two ancillaries were produced, that is, how these two relate to each other. Thus she finally knows precisely how the teleportee relates to Bob's photon. More formally speaking, as a result of Alice's measurement Bob's photon is projected into a state which is uniquely related to the original state; the specific relationship is expressed by which of the four Bell states Alice obtained. Alice therefore informs Bob of her measurement result via a classical communication channel, and he, by applying a simple unitary transformation on his photon, changes it into the original state.
In one of the four cases, Alice obtains the information that her two photons have been projected into the singlet state, the same state in which the ancil-laries were produced. Then, she knows that Bob's photon is instantly projected into the original state; the transformation that Bob has to apply is an identity transformation, that is, one that makes no change to his photon. That Bob's photon then instantly becomes an exact replica of the original seems to violate relativity.

Yet, while Alice knows instantly that Bob's photon, no matter how far away, is already an exact replica, she has to inform Bob of the Bell mea-sûrement result such that he knows that his photon is already in the correct state. That classical information can arrive only at the speed of light. This requirement is also true for the other possible Bellstate measurement results. Bob has to know them in order to apply the correct transformation to his photon.
The result of the Bell measurement is not related at all to any properties that the original photon carries. Thus, that measurement does not reveal any information about its state. Therefore, the operation that Bob has to apply is also completely independent of any properties of the original photon. The reason that quantum measurement succeeds is that entanglement makes it possible to completely transfer the information that an object carries without measuring this information.
Experimental realization. An experiment therefore faces a number of challenges. They include (1) how to produce the entangled photon pairs and (2) how to perform a Bell measurement for independent photons. In the experimental realization by D. Bouwmeester and his colleagues in 1997, the entangled photons were produced in the process of spontaneous parametric downconversion.

This is a second-order nonlinear process where a suitable crystal, in the experiment beta barium borate (BBO), is pumped with a beam of ultraviolet radiation. A photon from that beam has a very small probability to decay spontaneously into two photons, which then are polarization-entangled in just the way necessary for the experiment. The more tricky part is the Bellstate measurement because, in essence, it requires that the two photons are registered such that all information about which was the teleportee photon and which the ancillary is irrevocably erased. This is a nontrivial requirement since the two photons are coming from different directions, they might arrive at different times, and so forth.
In the experiment, the Bell-state measurement was performed using a semireflecting mirror, which acted as a 50/50 beam splitter.

Two photons were incident on the beam splitter, one from its front side and one from its back, and each one had the same probability of 50% to be either reflected or transmitted. If each of the two detectors in the two outgoing beams, again one in the front and one in the back, registered a photon simultaneously, then no information existed as to which incoming photon was registered in which detector, and the two were projected into the entangled singlet state. Narrow-bandwidth filters in front of the detectors further served to erase any time information which could also serve to identify the photons.
In this experiment, only one of the four possible Bell states could be identified, the singlet state. This certainly reduced the efficiency of the procedure, though in those cases in which the two detectors at the Bell-state analyzer registered, teleportation worked with a fidelity escaping all possible classical explanation.
In another experiment, also called entanglement swapping, it was even possible to teleport a photon that was still entangled to another one. That experiment started with two entangled pairs. A joint Bellstate measurement on one photon from each pair projected the other two photons onto an entangled state. In that way, two photons that neither came from the same source nor ever interacted with one another became entangled.

What all these experiments reveal is that the quantum state is really just a representation of the information that has been acquired. In the case of entanglement, it is only information on how objects relate to each other without any information on their individual properties. And in the case of teleportation, Alice's observation changes the quantum state that Bob observes. In other words, what can be said about the situation changes due to an observation by Alice. This gives very strong support to the Copenhagen interpretation of quantum mechanics. The first experiments were done with polarization-entangled photon pairs. Since then a number of experiments teleporting other properties such as continuous variables carried by the electromagnetic field of light, instead of the discrete ones discussed above, have been performed.
Prospects. While the teleportation distance in the first experiments was of the order of 1 m (3 ft), experiments in 2004 extended the distance to the order of 600 m (2000 ft), and there are plans to perform such experiments over much larger distances and even from a satellite down to laboratories on the ground. Other important experimental steps include the teleportation of quantum states of atoms (2004) and the teleportation of the quantum state of a photon onto that of an atomic cloud (2006).

Today quantum teleportation and entanglement swapping—the teleportation of an entangled state— are considered to be key building blocks of future quantum computer networks. At present there is intense research in the development of both quantum communication networks and quantum computers. Future quantum computers would use individual quantum states, for example those of atoms, to represent information in so-called quantum bits. They are expected to allow some algorithms to be performed with significantly higher speed than any existing computers. Quantum tele-portation would allow the transfer of the quantum output of one quantum computer to the quantum input of another quantum computer.

Knossos - Minos and Minotaur

The site of Knossos is located some 5 kilometers to the southeast of Herakleion, in the Kairatos Valley on the Greek island of Crete. The earliest Neolithic settlement and the Bronze Age palace are situated on a low hill known locally as the Kephala hill, and the Roman settlement is located to the west, on the lower slopes of the Acropolis hill.

The first excavations at Knossos were by Minos Kalokairinos in 1878, on the western side of the mound of Kephala, but the main excavations were undertaken by Sir Arthur Evans between 1900 and 1931.
Knossos is the longest-inhabited settlement on Crete and was preeminent—culturally, politically, and economically—as the largest settlement on the island until the end of the Bronze Age. The Neolithic settlement at Knossos was established on the Kephala hill during the late eighth millennium b.c. or early seventh millennium b.c. by a migrant population probably from Anatolia, and it represents the earliest human occupation attested on the island. Arthur Evans first recognized the existence of a Neolithic settlement beneath the Central Court of the Bronze Age palace in 1923. This he divided into four main phases, based on changing pottery styles. Subsequent excavations by John Evans refined the sequence, with ten strata dating from the Aceramic Neolithic (so-called because of the absence of pottery containers in the material assemblage) through the Early, Middle, Late, and Final Neolithic.

Knossos was an obvious location for settlement, being a naturally protected inland site on a low hill, with a perennial spring and fertile arable land. The settlers brought with them a fully developed Neolithic economy. They reared sheep, goats, pigs, and cattle and grew wheat, barley, and lentils. Stone tools included obsidian from the volcanic island of Melos in the Cyclades as well as flint and chert. During the course of the Early Neolithic, mace-heads became a typical component of the material assemblage. The Neolithic population lived in rectilinear houses built of mud brick or pisé (rammed earth) on a stone foundation. Pottery is attested from Stratum IX (Early Neolithic): initially with incised and dot-impressed (pointillé) decoration filled with white paste and later with ripple burnished decoration.

Equipment associated with textile production (spindle whorls and loom weights) was also introduced in the Early Neolithic period. The symbolic life and religious beliefs of the earliest inhabitants of Knossos remain elusive. Although no adult burials have been found, there are infant and child burials in pits under the house floors in various strata. Figurines are attested from the earliest occupation levels, with a concentration of human and animal terra-cottas in the Early Neolithic II levels.
The Early Bronze Age (Early Minoan or Pre-Palatial) occupation of Knossos is poorly known, being largely obscured by the later construction of the palace, but it has been identified in a number of soundings throughout the site. The remains of the Early Minoan II settlement indicate that it was large and prosperous. It has been suggested that a partially excavated building beneath the West Court of the palace was the residence of an important inhabitant, possibly the ruler of Knossos. This structure was destroyed by fire and might have been superseded by a large building beneath the northwest corner of the palace in Early Minoan III. The so-called Hypoge-um, at the southern limits of the later palace, likewise probably dates to Early Minoan III. It has been suggested that this was an underground, corbel-vaulted granary. Occasional imports from the Cyc-lades and southern Greece and even stone vases from as far away as Egypt have been found at Knos-sos, indicating initial trading ventures beyond the island. Internal exchange is illustrated by the presence of significant quantities of luxury pottery imported from the Mesara region of southern Crete and by the Vasilike ware from eastern Crete.

Knossos is perhaps best known for the palace remains on the Kephala hill. Two main phases have been identified: (1) the Old Palace (Proto-Palatial) period, which comprises the Middle Minoan IB, IIA, and IIIA strata, and (2) the New Palace (Neo-Palatial) period, comprising Middle Minoan III through Late Minoan IB. The Old Palace period has traditionally been dated to c. 1900-1700 b.c. and the New Palace period to c. 1700-1425 b.c. New chronometric dates derived from radiocarbon dates from Akrotiri, a site on the nearby island of Thera (modern Santorini) destroyed in a massive eruption in Late Minoan IA, suggest that the duration of the New Palace period should be revised to c. 1690-1500 b.c. The palace at Knossos is one of several palaces identified within the Minoan landscape of Crete: the other principal palaces are at Mallia, Phaistos, and Zakros. Other possible palace structures have been identified at a number of sites in Crete. Although all the Minoan palaces conform to general underlying architectural principles and probably shared similar functions, there are distinct differences most evident in the internal configuration of space.

THE OLD PALACE PERIOD
The origins and function of the Old Palace at Knos-sos are elusive. Its architectural remains are poorly preserved, whereas those of the immediately preceding phase had been leveled. Certainly the construction of the Old Palace represents the introduction of a new social and architectural concept: a large central building and the use of repeated architectural elements to create ceremonial space. Although the exact plan of the palace is unknown, two phases of construction have been identified. In the earlier phase the palace was laid out around the Central Court (on a north-south alignment). Sir Arthur Evans believed that the palace was laid out in separate blocks of buildings, but it is now accepted that the first palace was envisaged as a single architectural complex. Components of the Old Palace include the initial construction of the Throne Room, several of the shrines along the west side of the Central Court, and the storerooms on the east and west wings of the palace. In the later phase the West Court was laid out with three large circular pits (kouloures), possibly serving as grain silos. Also dating to this phase are the Theatral Area, to the north of the palace, and the Royal Road leading west from the palace.

The Old Palace is generally viewed as an elite residence and a religious or ceremonial center. The use of monumental architecture, in particular cutstone (ashlar) masonry, was designed to impress the local populace and visiting dignitaries and also illustrates large-scale mobilization of labor. Moreover the palace appears to have played an important economic role, with control over production and redistribution of agricultural staples. In addition to the storage magazines and kouloures, the so-called Keep was possibly used to store agricultural produce. By Middle Minoan II there is evidence for the development of a sophisticated bureaucracy, in the form of clay sealings (used to seal shut containers) and "hieroglyphic" clay tablets. It is also suggested that the palace controlled the production of prestige goods. Even so there is only limited evidence for craft production, although some four hundred loom weights were found in the eastern wing of the palace, representing substantial evidence for textile production. Certainly by the New Palace period textile production is central to the Minoan economy, and New Kingdom tomb paintings indicate that woolen cloth was one of the primary Minoan exports to Egypt. Many of these activities are extrapolated from the functions of the New Palaces.

THE NEW PALACE PERIOD

The Old Palace was destroyed at the end of Middle Minoan II, and its reconstruction in Middle Mino-an III marks the zenith of Minoan palatial society. The New Palace at Knossos is the largest of the Mi-noan palaces, covering a surface area of around 13,000 square meters. Much of the extant remains date to Late Minoan IA. The focal point of the palace was the Central Court, a paved open area (54 by 27 meters) on a north-south alignment. The function of the Central Court is unclear, but it probably served as the focus of ceremonial activities, possibly associated with the cult rooms opening onto the west side of the court. These include the so-called Throne Room (possibly the principal shrine), the Tripartite Shrine, and the Temple Repository, the latter where three faience figures of possible snake goddesses were found together with a rich assortment of faience plaques (animals, drag-onflies, and richly decorated female costumes).
The ground floor of the palace was devoted to economic activities, namely craft production and storage of agricultural produce.

The storerooms (a row of eighteen long, narrow storage magazines containing large ceramic storage jars, or pithoi) are restricted to the area of the ground floor immediately behind the west facade of the palace. The walls of the storerooms are blackened by the massive fire that destroyed the palace. The storage area was accessed either via the long corridor from the north or through the Throne Room—the latter approach indicating the extent to which the Minoan economy was embedded within the ceremonial or religious aspect. This symbolic control of the agricultural wealth is reiterated by the presence of pyramidal stands for totemic double axes at the entrance to the storage magazines. To facilitate the redistribution economy, there was a flourishing bureaucracy. Economic transactions were recorded on clay tablets in the Linear A script. Workshops associated with high-status craft production are located at the northeast side of the Central Court.

The suite of rooms located to the southeast of the Central Court, at the foot of the Grand Staircase, has become known as the residential quarters of the Knossian palace elite. These quarters comprise a series of Minoan halls: each hall consists of two adjoining rooms separated by a pier-and-door partition (a polythyron) with a light well (a shaft to admit light) at one end. Most notable are the Hall of the Double Axes and the so-called Queen's Hall. The domestic quarters also include a toilet. Indeed Minoan domestic architecture is noteworthy for the development of a sophisticated sanitation system, perhaps best illustrated by the drains at Knossos. A typical feature of the palace is its lavish decoration, namely wall paintings located in both the ceremonial rooms and the private chambers. Themes include processional scenes, bull sports, and richly dressed women.

The main approach to the palace was from the west, and the western facade of the palace was grandly built with ashlar masonry and a line of gypsum orthostats. Large stone "horns of consecration" (a potent Minoan religious symbol, apparently representing stylized bulls' horns) were displayed in places of prominence in the West Court. Raised walkways led across the West Court to the ceremonial southwest entrance. The southwest entrance led into the narrow Corridor of the Procession Fresco (decorated with life-size figures carrying luxurious offerings) toward the Propylaeum and a staircase to the grand reception rooms on the upper stories of the palace and also to the Central Court. A second entrance to the palace was located on the northwest. This entrance was approached via the Royal Road (leading west to the town house known as the Little Palace) and the Theatral Area.

The palace was at the center of a large town, which reached its greatest extent in the New Palace period, possibly covering an area of around 75 hectares. The population has been estimated to have been around 12,000. Several grand town houses have been excavated, such as the South House, the Little Palace, the Unexplored Mansion, and the Royal Villa. Workshops and kilns indicate that the palace did not exclusively control craft production at Knossos. Moreover several of the large houses were decorated with wall paintings, and high-status prestige objects were also found in these buildings. Most notable is the steatite bull's-head vase found in the Little Palace.

The size and grandeur of the town and palace at Knossos indicate the preeminence of the site in Neo-Palatial Crete. The lack of city defenses and the unprotected villas and palace argue for the so-called Pax Minoica, a seemingly peaceful arrangement of political unification and centralization of Minoan Crete ruled from Knossos. In the absence of documents that can be read, this is difficult to substantiate; however, Knossos certainly played a preeminent cultural role on the island. The town was destroyed in a massive conflagration in Late Minoan IB (contemporary with the destruction of the other palace centers around Crete). An unusual discovery in the town to the west of the palace suggests ritual cannibalism of children, possibly to stave off disaster. Yet the palace at Knossos was seemingly unaffected and continued to function into Late Minoan IIIA (the fourteenth century b.c.).

THE END OF THE PALACE PERIOD

The collapse of the Minoan palace centers in Late Minoan IB is usually attributed to an invasion from the Greek mainland and the establishment of a Mycenaean ruling elite. Knossos continued to be an important center in Late Minoan II and III, alongside Khania in western Crete. Parts of the palace were rebuilt and redecorated, and the characteristic griffin decoration of the Throne Room dates to this period. Knossos appears to have been an important religious center, and the Linear B archives (written in an early form of Greek) illustrate the importance of the wool industry at the site. These texts also give the name of Knossos as ko-no-so. There is a horizon of wealthy warrior graves in the Knossian hinterland at Zapher Papoura, Ayios Ioannis, and Sellopoulo. Characteristic features include Mycenaean chamber tombs, single inhumation, and distinctive My-cenaeanizing grave goods: a preference for bronze weapons (daggers and swords) and boar's-tusk helmets, hoards of bronze vessels, and large quantities of Mycenaean-style jewelry. The date of the final destruction of the palace at Knossos is unclear due to the vagaries of Sir Arthur Evans's early excavation at the site and in particular the context of the Linear B archives.

The location of the Iron Age settlement at Knossos is unknown, but several important cemeteries have been excavated, such as Fortetsa and Teke. The site continued to be wealthy, receiving imports from Athens and Phoenicia. Most notable is a reused Minoan tholos (stone-built circular) tomb, lavishly furnished with gold jewelry. This was used in the ninth century b.c., probably by a migrant Phoenician goldsmith. A sanctuary to Demeter was established in the eighth to seventh centuries b.c. to the south of the palace, and a Hellenistic shrine dedicated to the local hero Glaukos has been found in the western part of Knossos. In 67 b.c. Knossos became a Roman colony (Colonia Julia Nobilis Cnossus), and a large Roman city was established on the lower slopes of the Acropolis hill. Most notable among the Roman remains is the imposing second-century a.d. Villa Dionysos.
Reference : Encyclopedia of the Barbarian World-Ancient Europe , 8000 B.C to A.D 1000 vol. 2

Stonehenge

Stonehenge in Wiltshire, England, is a unique Neolithic monument that combines several
episodes of construction with various monument classes. The final monument, as seen in the early twenty-first century, represents an extraordinary level of sophistication in design, material, construction, and functionrarely found at other prehistoric sites in Europe.

Stonehenge evolved slowly over a millennium or longer and was embellished and rebuilt according to changing styles, social aspirations, and beliefs in tandem with the local political landscape of Wiltshire.The various stages, which archaeology identifies in three main phases and at least eight constructional episodes, link closely with monument building and developments seen elsewhere in Britain and Europe.
Stonehenge began its development in the early third millennium B.C., a period of transition between the earlier Neolithic, with its monuments of collective long barrows and communal causewayed enclosures, and the later Neolithic world of henges, avenues, ceremonial enclosures, circles, and mega-lithic monuments.

Across Britain and western Europe, this period signaled the closure of many of the megalithic tombs and seems to indicate changes in society, from small-scale, apparently egalitarian farming groups to more hierarchical and territorially aware societies. Burial especially reflected these changes, with the abandonment of collective rites and the emergence over the third millennium B.C. of individual burials furnished with personal ornaments, weapons, and tools. Landscape also showed changes, including more open landscapes cleared of trees, growing numbers of settlements, and an apparent preoccupation with the creation of ceremonial and monumental areas incorporating numerous sites within what is described as "sacred geography," or monuments arranged intentionally to take advantage of other sites and views, creating an arena for ceremonial activities.

Toward the end of the third millennium B.C., the later Neolithic and Bell Beaker periods evidenced increasing numbers of individual burials and ritual deposits and the growing use of megalithic stones and building of henges. Early metal objects, first of copper and then of bronze and gold, appeared in burials, and these items have close parallels with material developments in western Europe and across the British Isles. The quest for metals, with a related rise in interaction between groups, is reflected in rapidly changing fashions in metalwork, ornaments, and ritual practices. Wessex and its so-called Wessex culture lay at the junction between the metal-rich west of Britain and consumers in central eastern Britain and Europe. Through political, ritual, and economic control, these communities acquired materials and fine objects for use and burial in the tombs of elites on Salisbury Plain and the chalk lands of southern Britain.
The main building phases of Stonehenge reveal the growing importance of the Stonehenge area as a focus for burial and ritual. Earlier sites either were abandoned or, as in the case of Stonehenge, were massively embellished and rebuilt; many other very large and prominent monuments were located within easy sight of Stonehenge.

Geographic Information Systems studies suggest the Stonehenge was visible to all its contemporary neighbors and thus strategically located at the center of a monumental landscape. The significance of its location may stem from Stonehenge's special function as an observatory for the study of lunar and solar movements. Without doubt, the later phases of Stonehenge's construction focused on the orientation of the structures, which aligned with observations of the solstices and equinoxes, especially the rising of the midsummer and midwinter sun. Few other prehistoric sites appear to have had comparable structures, although several were observatories, such as the passage graves at Maes Howe on Orkney, Newgrange (rising midwinter sun) and Knowth in County Meath, Ireland, and many of the stone circles across Britain and Ireland.

CONSTRUCTION SEQUENCE AND CHRONOLOGY

Stonehenge was constructed over some fifteen hundred years, with long periods between building episodes. The first stage, c. 2950-2900 B.C., included a small causewayed enclosure ditch with an inner and outer surrounding bank, which had three entrances (one aligned roughly northeast, close to the present one). At this time, the construction of the fifty-six Aubrey Holes probably took place; these manmade holes filled with rubble may have supported a line of timber posts. Deposits and bones were placed at the ends of the ditch, signifying ritual activity. At the same time, the Greater and Lesser Cursus monuments, termed "cursus" after their long, linear form, suggestive of a racetrack, were constructed to the north of the Stonehenge enclosure. Some 4 kilometers north, the causewayed enclosure of Robin Hood's Ball probably was still in use. The surrounding landscape was becoming increasingly clear of tree cover, as farming communities continued to expand across the area. Survey has identified many potential settlement sites.

The second phase of building took place over the next five hundred years, until 2400 B.C., and represented a complex series of timber settings within and around the ditched enclosure. Subsequent building has obscured the plan, but the northeastern entrance comprised a series of post-built corridors that allowed observation of the sun and blocked access to the circle. The interior included a central structure—perhaps a building—and a southern entrance with a post corridor and barriers. Cremations were inserted into the Aubrey Holes and ditch, along with distinctive bone pins. During this phase a palisade was erected between Stonehenge and the Cursus monuments to the north, dividing the landscape into northern and southern sections. To the east, 3 kilometers distant, the immense Durrington Walls Henge and the small Woodhenge site beside it, incorporating large circular buildings, seem to have represented the major ceremonial focus during this period.

The third and major phase of building lasted from 2550-2450 to about 1600 B.C., with several intermittent bursts of construction and modification. The earth avenue was completed, leading northeastward from what was by then a single northeastern entrance. Sight lines focused on two stones in the entrance area (the surviving Heel Stone and another now lost) that aligned on the Slaughter Stone and provided a direct alignment to the center of the circle. Four station stones were set up against the inner ditch on small mounds, forming a quadrangular arrangement around the main circle.
The first stone phase (stage 3i) was initiated with the erection of bluestones in a crude circle (at least twenty-five stones) at the center of the henge, but lack of evidence and the subsequent removal of the stones leave the form of the possibly unfinished structure unclear. It was followed (stage 3ii), c. 2300 B.C., by the erection of some 30 huge (4 meters high) sarsen stones, capped and held together by a continuous ring of lintels, in a circle enclosing a horseshoe-shaped inner setting of 10 stones 7 meters high. These were "dressed," or shaped, in situ with stone mauls (hammers).

This arrangement was further modified with the insertion of bluestone within the sarsen circle (stage 3iii), but it was dismantled and rearranged by c. 2000 B.C. (stage 3iv), and more than twenty of the original stones probably were dressed and set in an oval around the inner sarsen horseshoe. Another ring of rougher bluestones was assembled between this and the outer sarsen circle, and an altar stone of Welsh sandstone was set at the center. Between 1900 and 1800 B.C. there was further rearrangement (stage 3v) of the bluestone, and stones in the northern section were removed. A final stage (stage 3vi) saw the excavation of two rings of pits around the main sarsen circle—the so-called Y and Z Holes, which may have been intended for additional settings. Material at the bases dates to c. 1600 B.C., and several contained deliberate deposits of antler. In parallel with these final phases of rebuilding, Stone-henge became the main focus of burial for the area, with about five hundred Bronze Age round barrows, some of which contain prestigious grave goods.

RAW MATERIALS AND DEBATES

The raw materials that comprise Stonehenge were selected deliberately and transported over great distances, which suggests that the materials themselves were symbolically important. The sarsen stone that forms the main massive trilithons and circle derived from areas north and east of Salisbury Plain, some 20 to 30 kilometers distant. Sarsen is a very hard Tertiary sandstone, formed as a capping over the Wiltshire chalk and dispersed as shattered blocks over the Marlborough Downs and in the valleys. The shaping of this extremely hard material at Stonehenge represents a remarkable and very unusual exercise for British prehistory, when stones generally were selected in their natural form and utilized without further work. The bluestones have long been the focus of discussion, since they derive only from the Preseli Mountains of Southwest Wales, located 240 kilometers from Salisbury Plain.

Collectively, the stones are various forms of dolerite and rhyolite, occurring in large outcrops. Many theories have been proposed, and in the 1950s Richard Atkinson demonstrated the ease by which these quite small stones could be transported by raft to the Stonehenge area. Later geological study suggested that glacial ice probably transported considerable quantities of bluestone in a southeasterly direction and deposited it in central southern Britain.
The debate continues, but the carefully selected shape and size of the bluestones at Stonehenge seem to indicate that it would have been difficult to find so many similar stones deposited by natural agencies in Wiltshire. One theory suggests that the original bluestones were taken wholesale from an existing circle and removed to Stonehenge, perhaps as tribute or a gift. Other materials also have been found at Stonehenge, including the green sandstone altar stone, which may derive from the Cosheston Beds in southern Wales. Other local sites, such as West Kennet Long Barrow, include stone selected some distance away, such as Calne (Wiltshire) limestone. The interesting and complex dispersal of exotic stone axes and flint from early in the Neolithic further supports the idea that exotic materials were highly prized and had special symbolic properties.

SURROUNDING LANDSCAPE AND SITES

The landscape surrounding Stonehenge is a dry, rolling chalk plateau, with the broad Avon Valley and its floodplain to the east. The valley areas were attractive to early settlement, but perhaps because of its bleakness and lack of water, the area immediately surrounding Stonehenge was little settled. The special ritual status afforded the location also may have deterred settlement over much of prehistory. Initially (4000-3000 B.C.), the landscape at the beginning of the Neolithic was heavily wooded, and clearances made by early farmers were the main open spaces. By the transition from the earlier to the later Neolithic, c. 2900 B.C., it seems that well over half the landscape was open, and monuments such as the Cursus were widely visible. Over the next millennium, increasing clearance reduced tree cover to belts of woodland around the edge of the Avon Valley and sparse scrub, allowing Stonehenge and the surrounding monuments to be visible one from another and to gain prominence in a largely manmade landscape.

Late Mesolithic activity has been identified in the parking area of Stonehenge, where four large postholes were located. They may have demarcated an early shrine, but a relationship to activity more than four thousand years later seems remote. The two-ditched causewayed enclosure of Robin Hood's Ball represents the earliest major site in the Stonehenge landscape in the early fourth millennium B.C., alongside some ten or more long barrows in the immediate area. Such a concentration is typical of these ceremonial foci and is repeated around other causewayed enclosures. Other sites developed over the late fourth and third millennia B.C., including an enclosure on Normanton Down, which may have been a mortuary site. Contemporary with the building of the enclosure in Stonehenge phase I is the Coneybury Henge located to the southeast. It was small and oval-shaped and contained settings of some seven hundred wooden posts arranged around the inner edge and in radiating lines around a central point. Its ditches contained grooved-ware pottery, and, significantly, among the animal bone deposits was a white-tailed sea eagle, a rare bird never found inland, so its placement would appear to be intentional and ritual.
To the west of Stonehenge lies another very small henge, only about 7 meters in diameter—the Fargo Plantation, which surrounded inhumation and cremation burials. Such concerns also were reflected at Woodhenge, located 3 kilometers northeast of Stonehenge, where the central focus is on the burial of a child with Bell Beaker grave goods, who might have been killed in a ritual sacrifice. The site formed the ditched enclosure of a large structure— probably a circular building supported on six concentric rings of posts. Immediately north lies Durrington Walls, the second largest of all the henges of Britain, with a maximum diameter of 525 meters and covering some 12 hectares within an immense ditch and bank. Only a small linear area of this site had been investigated before road building took place, but this study revealed two more large, wooden, circular buildings. A great quantity of grooved-ware pottery was found together with animal remains and fine flint, suggesting offerings had been placed in the ditch and at the base of the timber posts. The henge sites all seem to have been occupied until the end of the third millennium. The Early Bronze Age saw an increasing emphasis on burial landscapes and the construction of monuments.

Over the course of only half a millennium, the five hundred or so round barrows were constructed in groups at prominent places in the Stonehenge landscape. Dramatic locales, such as the King Barrow Ridge, were chosen for linear cemeteries of as many as twenty large, round barrows. Another example, Winterbourne Stoke, west of Stonehenge, was the site of an earlier long barrow. To the south of Stonehenge, the Normanton Down cemetery, with more than twenty-five barrows, included very rich burials, such as Bush Barrow. Excavations at many sites in the nineteenth century emptied the tombs and destroyed much of the evidence; nevertheless, much artifactual information was gathered. This information formed the basis of studies by Stuart Piggott and others that helped define the Wessex culture of the Early Bronze Age, which lasted from c. 1900 to 1550 B.C.
Reference : Encyclopedia of the Barbarian World-Ancient Europe , 8000 B.C to A.D 1000 vol. 2

Cosmic rays - Extraterrestrial radiation

Cosmic rays Electrons and the nuclei of atoms—largely hydrogen—that impinge upon Earth from all directions of space with nearly the speed of light. These nuclei with relativistic speeds are often referred to as primary cosmic rays, to distinguish them from the cascade of secondary particles generated by their impact against air nuclei at the top of the terrestrial atmosphere. The secondary particles shower down through the atmosphere and are found all the way to the ground and below.

The primary cosmic rays provide the only direct sample of matter from outside the solar system. Measurement of their composition can aid in understanding which aspects of the matter making up the solar system are typical of the Milky Way Galaxy as a whole and which may be so atypical as to yield specific clues to the origin of the solar system. Cosmic rays are electrically charged; hence they are deflected by the magnetic fields which are thought to exist throughout the Galaxy, and may be used as probes to determine the nature of these fields far from Earth. Outside the solar system the energy contained in the cosmic rays is comparable to that of the magnetic field, so the cosmic rays probably play a major role in determining the structure of the field.

Collisions between the cosmic rays and the nuclei of the atoms in the tenuous gas which permeates the Galaxy change the cosmic-ray composition in a measurable way and produce gamma rays which can be detected at Earth, giving information on the distribution of this gas.
Cosmic-ray detection. All cosmic-ray detectors are sensitive only to moving electrical charges. Neutral cosmic rays (neutrons, gamma rays, and neutrinos) are studied by observing the charged particles produced in the collision of the neutral primary with some type of target. At low energies the ionization of the matter through which they pass is the principal means of detection. A single measurement of the ionization produced by a particle is usually not sufficient both to identify the particle and to determine its energy. However, since the ionization itself represents a significant energy loss to a low-energy particle, it is possible to design systems of detectors which trace the rate at which the particle slows down and thus to obtain unique identification and energy measurement.

At energies above about 500 MeV per nucleon, almost all cosmic rays will suffer a catastrophic nuclear interaction before they slow appreciably. An ionization measurement is commonly combined with measurements of physical effects which vary in a different way with mass, charge, and energy. Cerenkov detectors and the deflection of the particles in the field of large superconducting magnets or the magnetic field of the Earth itself provide the best means of studying energies up to a few hundred GeV per nucleon. Detectors employing the phenomenon of x-ray transition radiation promise to be useful for measuring composition at energies up to a few thousand GeV per nucleon.
Above about 1012 eV, direct detection of individual particles is no longer possible since they are so rare. Such particles are studied by observing the large showers of secondaries they produce in Earth's atmosphere. These showers are detected either by counting the particles which survive to strike ground-level detectors or by looking at the flashes of light the showers produce in the atmosphere with special telescopes and photomultiplier tubes.

Atmospheric cosmic rays. The primary cosmic-ray particles coming into the top of the terrestrial atmosphere make inelastic collisions with nuclei in the atmosphere. When a high-energy nucleus collides with the nucleus of an air atom, a number of things usually occur. Rapid deceleration of the incoming nucleus leads to production of pions with positive, negative, or neutral charge. A few protons and neutrons (in about equal proportions) may be knocked out with energies up to a few GeV. They are called knock-on protons and neutrons.
All these protons, neutrons, and pions generated by collision of the primary cosmic-ray nuclei with the nuclei of air atoms are the first stage in the development of the secondary cosmic-ray particles observed inside the atmosphere. Since several secondary particles are produced by each collision, the total number of energetic particles of cosmic-ray origin will increase with depth, even while the primary density is decreasing.

The uncharged n0 mesons decay into two gamma rays with a life of about 8 x 10-17 s. The two gamma rays each produce a positron-electron pair. Upon passing sufficiently close to the nucleus of an air atom deeper in the atmosphere, the electrons and positrons convert their energy into bremsstrahlung. The bremsstrahlung in turn create new positron-electron pairs, and so on. This cascade process continues until the energy of the initial n0 has been dispersed into a shower of positrons, electrons, and photons with insufficient individual energies (< 1 MeV) to continue the pair production. The electrons and photons of such showers are referred to as the soft component of the atmospheric (secondary) cosmic rays.

The n ± mesons produced by the primary collisions have a life of about 2.6 x 10-8 s before they decay into muons. Most low-energy n ± decay into muons before they have time to undergo nuclear interactions. Except at very high energy (above 500 GeV), muons interact relatively weakly with nuclei, and are too massive (207 electron masses) to produce bremsstrahlung. They lose energy mainly by the comparatively feeble process of ionizing an occasional air atom as they progress downward through the atmosphere. Because of this ability to penetrate matter, they are called the hard component.

The high-energy nucleons—the knock-on protons and neutrons—produced by the primary-particle collisions and a few pion collisions proceed down into the atmosphere. They produce nuclear interactions of the same kind as the primary nuclei, though of course with diminished energies. This cascade process constitutes the nucleonic component of the secondary cosmic rays.
Solar modulation. The cosmic-ray intensity is lower during the years of high solar activity and sunspot number, which follow an 11-year cycle. This effect has been extensively studied with ground-based and spacecraft instruments.

The primary cause of solar modulation is the solar wind, a highly ionized gas (plasma) which boils off the solar corona and propagates radially from the Sun at a velocity of about 250 mi s (400 km/s). The wind is mostly hydrogen, with typical density of 80 protons per cubic inch (5 protons per cubic centimeter). This density is too low for collisions with cosmic rays to be important. Rather, the high conductivity of the medium traps part of the solar magnetic field and carries it outward.

In addition to the bulk sweeping action, another effect of great importance occurs in the solar wind, adiabatic deceleration. Because the wind is blowing out, only those particles which chance to move upstream fast enough are able to reach Earth. However, because of the expansion of the wind, particles interacting with it lose energy. Thus, particles observed at Earth with energy of 10 MeV per nucleon actually started out with several hundred MeV per nucleon in nearby interstellar space, and those with initial energy of only 100-200 MeV per nucleon probably never reach Earth at all.

Atomic bomb - The world is not ready ...

Atomic bomb - A device for suddenly producing an explosive neutron chain reaction in a fissile material such as uranium-235 (235U) or plutonium-239 (239Pu). In a wider sense, any explosive device that derives its energy from nuclear reactions, including not only the foregoing fission weapon but also a fusion weapon, which gets its energy largely from fusion reactions of heavy hydrogen isotopes, and a fission-fusion weapon, which derives its energy from both fission and fusion.

Because an atomic bomb derives its energy from nuclear reactions, it is properly called a nuclear explosive or nuclear weapon.
of the two principal fissile materials, the cheaper but less potent 235Uispresent in natural uranium usually in the proportion of 1 part to 139 parts of 238U and is separated from it by various enrichment processes. Weapons-grade plutonium is manufactured from 238Uina special military production reactor that has enough excess neutrons for the reaction below.

U + n - 239U (23-min half-life) 239Np(2.3-day half-life) 239Pu

Weapon cores are made of very high fractions of fissile materials: highly enriched 93% uranium-235 or weapon-grade 94% plutonium-239.

A fission bomb before ignition consists of a mass of fissile material and surrounding tamper—beryllium oxide or other reflector of neutrons intended ultimately to improve the neutron multiplication factor k—arranged in a geometry so favorable to neutron leakage that k is less than 1. These materials are suddenly compressed into a geometry where k substantially exceeds 1. This is done with chemical explosives that either implode a spherical subcritical mass of fission material or else drive two subcritical sections together in a gun-barrel type of arrangement. At the same time, enough neutrons are artificially introduced to start an explosively divergent (expanding) chain reaction. Fission-explosive devices intended for military application are highly sophisticated combinations of pure materials, precise design, and reliable electronics.

The explosive energy (yield) of a nuclear weapon is usually expressed in kilotons or megatons. A kiloton is the amount of energy liberated in the explosion of 1000 tons of TNT (1012 calories or 4.18 x 1012 J), and a megaton is a thousand times as large. The fission bombs that destroyed Hiroshima (gun-barrel type) and Nagasaki (implosion type) had estimated explosive yields of 13 and 22 kilotons, respectively. Fractional kiloton yields can be obtained (tactical nuclear weapons). Fission weapons have been tested up to approximately 500 kilotons, overlapping the yield of multistage fusion explosives (strategic nuclear weapons).

The nuclear explosive energy is communicated by mechanical shock and radiative transport to the surrounding water, earth, or air, ionizing it out to a radius which, in the case of explosions in air, is known as the fireball radius (150 yd or 140 m in about 1 s after a 20-kiloton nuclear explosion). Energy goes out from such a fireball into the surrounding relatively transparent air, in not very different orders of magnitude in the form of a shock wave and in the form of heat radiation that may continue for a number of seconds.

Alzheimer's disease

A disease of the nervous system characterized by a progressive dementia that leads to profound impairment in cognition and behavior. Dementia occurs in a number of brain diseases where the impairment in cognitive abilities represents a decline from prior levels of function and interferes with the ability to perform routine daily activities (for example, balancing a checkbook or remembering appointments).

Alzheimer's disease is the most common form of dementia, affecting 5% of individuals over age 65. The onset of the dementia typically occurs in middle to late life, and the prevalence of the illness increases with advancing age to include 25-35% of individuals over age 85.
Memory loss, including difficulty in remembering recent events and learning new information, is typically the earliest clinical feature of Alzheimer's disease. As the illness progresses, memory of remote events and overlearned information (for example, date and place of birth) declines together with other cognitive abilities.

In the later stages of Alzheimer's disease, there is increasing loss of cognitive function to the point where the individual is bedridden and requires full-time assistance with basic living skills (for example, eating and bathing). Behavioral disturbances that can accompany Alzheimer's disease include agitation, aggression, depressive mood, sleep disorder, and anxiety.

The major neuropathological features of Alzheimer'sdisease include the presence of senile plaques, neurofibrillary tangles, and neuronal cell loss. Although the regional distribution ofbrain pathology varies among individuals, the areas commonly affected include the association cortical and limbic regions.
Deficits in cholinergic, serotonergic, noradrenergic, and pep-tidergic (for example, somatostatin) neurotransmitters have been demonstrated. Dysfunction of the cholinergic neurotransmitter system has been specifically implicated in the early occurrence of memory impairment in Alzheimer's disease, and it has been a target in the development of potential therapeutic agents.
A definite diagnosis of Alzheimer's disease is made only by direct examination of brain tissue obtained at autopsy or by biopsy to determine the presence of senile plaques and neurofibrillary tangles. A clinical evaluation, however, can provide a correct diagnosis in more than 80% of cases.

The clinical diagnosis of Alzheimer's disease requires a thorough evaluation to exclude all other medical, neurological, and psychiatric causes of the observed decline in memory and other cognitive abilities.
Although the cause of Alzheimer's disease is unknown, a number of factors that increase the risk of developing this form of dementia have been identified. Age is the most prominent risk factor, with the prevalence of the illness increasing twofold for each decade of life after age 60. Research in molecular genetics has shown that Alzheimer's disease is etiologically heterogeneous. Gene mutations on several different chromosomes are associated with familial inherited forms of Alzheimer's disease.

A major strategy for the treatment of Alzheimer's disease has focused on the relation between memory impairment and dysfunction of the acetylcholine neurotransmitter system. other treatment strategies to delay or diminish the progression of Alzheimer's disease are being explored. Behavioral and pharmacological interventions are also available to treat the specific behavioral disturbances that can occur in Alzheimer's disease.

Milky Way Galaxy - Our Galaxy

Milky Way Galaxy The large disk-shaped aggregation of stars, gas, and dust in which the solar system is located. The term "Milky Way" is used to refer to the diffuse band of light visible in the night sky emanating from the Milky Way Galaxy.

Although the two terms are frequently used interchangeably. Milky Way Galaxy, or simply the Galaxy, refers to the physical object rather than its appearance in the night sky.
Structure and contents. The Milky Way Galaxy contains about 2 x 10^11 solar masses of visible matter. Roughly 96% is in the form of stars, and about 4% is in the form of interstellar gas. The gas both inside the stars and in the interstellar medium is primarily hydrogen and helium with a small admixture of all of the heavier atoms.

The mass of dust is about 1 % of the interstellar gas mass and is an insignificant fraction of the total mass of the Galaxy. Its presence, however, limits the view from the Earth in the plane of the Galaxy to a small fraction of the Galaxy's diameter in most directions.
The Milky Way Galaxy contains four major structural subdivisions: the nucleus, the bulge, the disk, and the halo. The Sun is located in the disk about half way between the center and the indistinct outer edge of the disk of stars. The currently accepted value of the distance of the Sun from the galactic center is 8.5 kiloparsecs, although some measurements suggest that the distance may be as small as 7 kpc.

The nucleus of the Milky Way is a region within a few tens of parsecs of the geometric center and is totally obscured at visible wavelengths. The nucleus is the source of very energetic activity detected by means of radio waves and infrared radiation.
At the galactic center, there is a very dense cluster of hot stars observed by means of its infrared radiation. In 1997. astronomers confirmed the existence of a black hole with a mass of about 2.5 million times the mass of the Sun at the position of an unresolved source of radio emission known as Sgr A* in the middle of the central star cluster. The black hole appears to be the dynamical center of the Milky Way.

The bulge is a thick distribution of stars centered on the nucleus which extends to a distance of about 3 kpc from the center. It contains a relatively old population of stars, nearly as old as the Milky Way itself. Direct imaging with infrared satellites has demonstrated that the bulge is actually an elongated barlike structure with a length about two to three times its width. The Milky Way is thus classified as a barred spiral galaxy, a classification that includes about half of all disk-shaped galaxies.
The disk is a thin distribution of stars and gas orbiting the nucleus of the Galaxy. The disk of stars begins near the end of the bar and can be identified to about 16 kpc from the center of the Galaxy; the disk of gas can be identified to about twice this distance, about 35 kpc from the center. The faint low-mass stars make up most of the mass of the disk. There is also a thick disk of stars and gas. The thin disk of stars contains most of the mass and has a thickness relative to its diameter similar to that of a commercial compact disk. The disk is the location of the spiral arms that are characteristic of most disk-shaped galaxies, as well as most of the present-day star formation.

The halo is a rarefied spheroidal distribution of stars nearly devoid of the interstellar gas and dust that surrounds the disk. The stars found in the halo are the oldest stars in the Galaxy. The stars are found individually as "field" stars as well as in globular clusters: spherical clusters of up to about a million stars with very low abundances of elements heavier than helium. The extent of the halo is not well determined, but globular clusters with distances of about 40 kpc from the center have been identified.

Dynamical evidence suggests that the halo contains nonluminous matter in some unknown form, commonly referred to as dark matter. The dark matter contains most of the mass of the Galaxy, dominating even that in the form of stars.
Evidence suggests that the ages of the oldest stars in the Milky Way are within about 10% of the age of the universe as a whole; thus parts of the Milky Way must have formed early in the history of the universe, about 12-16 billion years ago. There is increasing evidence that the Milky Way formed as a result of the coalescence of small galaxies and protogalaxies, objects with the masses of small dwarf galaxies that are thought to have been among the first objects to form in the Univers.

All about Geomagnetism

Geomagnetism The magnetism of the Earth; also, the branch of science that deals with the Earth's magnetism. Formerly called terrestrial magnetism, geomagnetism involves any topic pertaining to the magnetic field observed near the Earth's surface, within the Earth, and extending upward to the magne-tospheric boundary.

Modern usage of the term is generally confined to historically recorded observations to distinguish it from the sciences of archeomagnetism and paleomagnetism, which deal with the ancient magnetic field frozen respectively in arche-ological artifacts and geologic structures.The primary component of the magnetic field observed at the Earth's surface is caused by electric currents flowing in its liquid core, and is called the main field. Vectorially added to this component are the crustal field of magnetized rocks, transient variations imposed from external sources, and the field from electric currents induced in the Earth from these variations.The geomagnetic field is specified at any point by its vector F. Its direction is that of a magnetized needle perfectly balanced before it is magnetized, and freely pivoted about that point, when in equilibrium. The north pole of such a needle is the one that at most places on the Earth takes the more northerly position.

Over most of the Northern Hemisphere, that pole dips downward . The elements used to describe the vector F are H, the component of the vector projected onto a horizontal plane; its north and east components X and Y. respectively; Z the vertical component; F the magnitude of the vector F; the angles I, the dip of the field vector below the horizontal; and D the magnetic declination or deviation of the compass from geographic north. By convention, Z and I are positive downward, and D is positive eastward (or may be indicated as east or west of north). These elements can be related to each other by trigonometric equations.A magnetic pole is a location where the field is vertically aligned, H = 0. Due to the presence of sometimes strong (for example, >1000 nanoteslas) magnetic anomalies at the Earth's surface, there are a number of locations where the field is locally vertical.

However, those field components that extend to sufficient altitude to control charged particles can be accurately located by using the computations from a spherical harmonic expansion using degrees up to only about n = 10. Indeed, a pole can be defined by using only the main dipole (n = 1), or many terms.The n = 1 poles are sometimes referred to as the geomagnetic poles, and those computed using higher terms as dip poles. The term geomagnetic could also refer to the eccentric geomagnetic pole, which can be computed from n = 1 and n = 2 harmonics so as to be the best representation of a dipole offset from the center of the Earth. The latter has been used as a simplified field model at distances of 3 or 4 earth radii. Due to the more rapid fall-off of the higher terms with distance from the Earth, the two principal poles approach those of the n = 1 term with increasing altitude, until the distortions due to external effects begin to predominate.

The distribution of the dip angle I over the Earth's surface can be indicated on a globe or map by contours called isoclines, along which I is constant. The isocline for which I = 0 (where a balanced magnetized needle rests horizontal) is called the dip equator. The dip equator is geophysically important because there is a region in the ionospheric E layer in which small electric fields can produce a large electric current called the equatorial electrojet.
A magnetized compass needle can be weighted so as to rest and move in a horizontal plane at the latitudes for which it is designed, thus measuring the declination D. The lines on the Earth's surface along which D is constant are called isogonic lines or isogones. The compass points true geographic north on the agonic lines where D = 0. At nonpolar latitudes. D is a useful tool for marine and aircraft navigational reference. Indeed, isogones appear on navigation charts, electronic navigational aids are referenced to D, and airport runways are marked with D/10.A runway painted with the number 11 indicates that its direction has a compass heading of 110s. The compass needle becomes less reliable in polar regions because the horizontal component H becomes smaller as the magnetic poles are approached.

The intensity of the field can also be represented by maps, and the lines of equal intensity are called isodynamic lines. The dipole dominates the patterns of magnetic intensity on Earth in that the intensity is about double at the two poles compared to the value near the Equator. However, it can also be seen that the next terms of the spherical harmonic expansion also have a significant effect in that there is a second maximum in Siberia, and an area near Brazil that is weaker than any other. This so-called Brazilian anomaly allows charged particles trapped in the magnetic field to reach a low altitude and be lost by collisions with atmospheric gases. The highest intensity of this smooth field is about 70 microteslas near the south magnetic pole in Antarctica, and the weakest is about 23 microT near the coast of Brazil.

The term magnetic anomaly has become clearer than it was previously because it is recognized that the geomagnetic field has a continuous spectrum but with two distinct contributors. Originally, the term meant a field pattern that was very local in extent; the modern definition is that portion of the field whose origin is the Earth's crust. The sizes of the strong and easily observable features are generally up to only a few tens of kilometers. Their intensity ranges typically from a few hundred nanoteslas up to several thousand, and they are highly variable depending on the geology of the region.

The electromagnetic spectrum

The electromagnetic spectrum is the full range of electromagnetic radiation and includes radio waves, heat and light rays, X rays, and gamma rays.

Electromagnetic radiation is a form of energy that travels at the velocity of light. 186.000 mi/sec (300.000km/sec). As it travels, its energy switches back and forth between electric and magnetic fields. As one field increases in strength, the other decreases. The rate at which this exchange happens is called the frequency of the radiation. Different types of electromagnetic radiation have different frequencies. Radio waves have lower frequencies than light rays, for example, and blue light has a higher frequency than red. The frequency of electromagnetic radiation, measured in hertz (Hz), is the number 61 times in one second that the electrical field reaches its maximum value.

Scientists say that electromagnetic radiation travels in waves. This is because the strengths oi the electric and magnetic fields vary continually as they travel through space. The wavelength is the distance the wave travels in the time it takes the electric field to fall from its maximum value to its minimum value and then rise back to its maximum value. Because of this, the wavelength is the speed of light divided by the frequency. The signal from a radio station whose broadcast frequency is 1,200 kilohertz, or 1,200,000 Hz, has a wavelength of around 820 feet (250m), for example.

RADIO AND MICROWAVE

Radio stations broadcast using frequencies in a range from 150,000 Hz to around 20.000,000 Hz. Each station uses a particular frequency, so receivers tunc to a given station by only accepting waves at the correct
frequency for that station. Land-based television transmitters send signals between about 70 MHz and 800 MHz. (One megahertz is one million hertz.)
Satellite TV works at even higher frequencies. These electromagnetic waves arc captured by dish-shaped antennae that point toward the satellite.
Radars bounce radio waves off planes, ships, and clouds to show their positions, which can be many miles away. They use wavelengths of about 1 inch (2.5 cm). Doppler radar measures the speed of moving objects from the minute change in the frequency of the reflected waves.
Microwave ovens use wavelengths of a few millimeters, which correspond to frequencies of billions of hertz. The radiation heats food by causing water molecules to vibrate.

INFRARED LIGHT AND BEYOND

Infrared radiation has frequencies just lower than those of visible light. Its wavelength ranges from 1 millimeter to 750 nanometers. A nanometer, or 1 nm,
is one billionth of a meter, or 1/25,000,000 of an
inch. Hot objects give off infrared radiation, which is felt as heat. Visible light is the tiny part of the electromagnetic spectrum that human eyes can sense.The spectrum of colors stretches from red light at 770 nm to violet light at 400 nm.

The energy of electromagnetic radiation increases as the wavelength becomes shorter. Invisible ultraviolet rays cause sunburn and have shorter wavelengths (100-400 nm) than visible light.
X rays have even shorter wavelengths, usually less than the diameter of an atom (0.1 nm) .They penetrate flesh and bone can be used to produce images of cracks deep inside pieces of metal.
Reference : The Kingfisher Science Encyclopedia De Charles Taylor

Volcanoes - Silent killer

A volcano is an opening in the Earth's crust through which molten lava, ash, and gases erupt. In many cases, lava and ash form a mountain around the opening.

It used to be thought that volcanoes leaked molten rock and gases directly from the Earth's core. That is not the case. As hot, solid rock rises in the mantle, the pressure drops and a small part of the rock begins to melt. This liquefied rock, called magma, is less dense than solid rock. It squeezes out from the solid like water from a sponge. The rising magma creates wide channels in the crust as it forces its way to the surface. When it breaks through the surface, the pressure drops. Gases dissolved in the magma force it to erupt through the opening as lava.

TYPES OF VOLCANOES

The behavior of a volcano depends on the type of magma that fuels it. Volcanoes such as those near Hawaii and Iceland are sitting on top of a rising plume of hot mantle rock, called a hot spot. The lava that erupts from these volcanoes comes from great depths, sometimes more than 90 mi. (150km) into the mantle. Its

composition is not the same as the mantle, because only a tiny fraction of the mantle rock melts. This lava is runny when molten and sets as dense, black basalt. Because the lava is so runny, it can pour out through fissures at vast rates and flow across the land at speeds of up to 31 mph (50kph). Where this type of volcano erupts underwater, the lava cools quickly and

builds volcanic islands as it sets. Where gas bubbles through it, the runny lava erupts in spectacular fountains. Because this type of lava flows freely, eruptions are smooth rather than explosive.
A different type of volcano is found where ocean crust dives under the edge of a continent. The ocean crust partly melts to form a sticky lava that is rich in silica and contains some water. During an eruption, the sudden drop in pressure causes the water to turn to steam. This results in an explosion of fine ash and hot gases. This mixture, which can race down the sides of a volcano at 125 mph (200kph), is called a nuée ardente, French for "glowing avalanche."

LIVING WITH VOLCANOES

With their combinations of red-hot lava, toxic gases, and suffocating ash. volcanic eruptions can be deadly phenomena. But people continue to live on the sides of volcanoes despite the danger. This is because volcanic soil is often fertile, and eruptions can be few and far between, giving a false sense of security. The consequences can be disastrous. In 1902, when Mount Pelee on the Caribbean island of Martinique erupted, a nuee ardente raced down the mountain and engulfed the port of San Pierre- More than 29,000 people were killed. The only survivor was a prisoner in an underground cell. In A.D. 79, a similar eruption from Mount Vesuvius smothered the Roman towns of Boscoreale, Herculaneum, Pompeii, and Stabiae with mud and ash.

It is possible to predict at least some eruptions by monitoring volcanic gases and measuring changes in gravity as molten lava rises inside a volcano Sometimes, the whole mountain bulges. When Mount St. Helens, in Washington, started to bulge in 1980, most people were evacuated before the mountain blew its top. A huge landslide removed part of the volcano, exposing the pressurized molten lava. The lava then exploded sideways and upward. The blast hurled about half a cubic mile of rock into the air and flattened trees up to 19 mi. (30km) away.
Reference : The Kingfisher Science Encyclopedia De Charles Taylor

Born to be a genius ?

Everyone has heard it said of somebody or other that he (or she) was born to be a genius. Can such an assertion ever be correct? A simple 'yes or no' answer has to be negative, because sophisticated inborn capabilities simply cannot exist.

Outside mythology, nobody begins life having proclivities that can guarantee the emergence of high abilities.That does not necessarily mean that the idea of being born to be a genius must be entirely false. People are not born identical, and some of the ways in which they differ at birth can have consequences that affect the course of their whole lives. One widely accepted view is that certain individuals begin life possessing innate gifts or talents that predispose a person towards exceptional attainments in a particular area of ability. Another common belief is that a person's intelligence level, which has a major role in determining the likelihood of substantial achievements, is largely fixed at birth.

This chapter examines some of the evidence that has a bearing on the possible involvement of innately-determined influences on variability, among the numerous contributing forces that combine to enable certain individuals to become exceptionally capable.All human individuals are affected in many ways by the particular combination of genetic resources they inherit. That the influences of genetic differences between people can extend to the manner in which lives are experienced is easily verified. Just watch the contrasting ways in which people at a party react to the entrance of a spectacularly beautiful individual and to a man or woman of ordinary appearance. Those differing responses will certainly affect the individuals who elicit them. Indeed, the manner in which others react to people can have an impact on many of their experiences. One beautiful woman has her education enriched as a consequence of influential people being drawn to her company; another fails to make the most of her opportunities because of repeated experiences of getting her wishes without having to make an effort. An ordinary-looking man loses out because the teacher who might have been able to help him prefers to spend time with other pupils.

Another plain man eventually thrives because his failure to gain attention fuels his determination to do well. It is not at all uncommon for the degree of success a young person experiences to be partly decided by genetic characteristics even when the genetically influenced characteristics that are crucial are ones that have no direct effects on the person's capabilities as such. In the performing arts, for example, it is not unknown for stage directors to select the prettiest of a group of equally competent young ballet dancers for a starring role. Those examples illustrate just a few of the many ways in which our lives are affected by the particular genetic material we happen to inherit. Note, however, that the eventual nature of the influences that originate in genetic variability is typically unpredictable and far being from straightforward. It is easy enough to see that people's appearances can affect how others respond to them, but it is not usually possible to predict the long-term consequences of that.

That unpredictability is highly significant, because in order to establish that there was something real in the notion of a person being 'born to be a genius' it would be necessary to go a stage beyond merely confirming that individuals are influenced by their genes, and demonstrate that a consequence of people's differing genetic compositions is to affect their abilities in a clearly predictable manner.Do differing generic materials have predictable influences on individuals' attainments, or not? In the first part of this chapter I examine evidence relating to the frequent claim that such direct influences stemming from people's genes do indeed exist, and take the form of innate talents or gifts.

These, it is often claimed, are possessed by some young people but not others. A common assumption is that a person must possess gifts or talents in order to be capable of reaching the highest levels of expertise. Afterwards, I investigate the related possibility that innate variability in general intelligence makes a big contribution to the likelihood of individuals gaining exceptional capabilities. Finally, I take a broader look at the issues, and reach some conclusions concerning possible genetic influences on the likelihood of someone becoming a genius. In the minds of many people it is a clear and simple fact, not to be questioned, that certain men and women have been born with innate talents that make them capable of high attainments. I call that viewpoint 'the talent account'.

Does it greatly matter whether the talent account is true or false? It matters immensely, not only because efforts to explain creative achievements can never succeed if they depend upon faulty assumptions about the origins of a person's unusual capabilities, but also because important practical issues are involved. The fact that the talent account is widely believed in has consequences that affect the lives of numerous young people. Within certain fields of expertise, such as music, unquestioning acceptance of the talent account is almost invariably accompanied by the belief that excellence is only attainable by those children who are innately talented. A frequent result of teachers and other influential adults having this combination of beliefs is that when scarce educational resources or opportunities are being allocated they are likely to be directed exclusively towards those young people who are thought to possess a special talent. Young children who are believed to lack innate talents are denied resources that are vital in order for a child to gain any chance of succeeding.

If the talent account was shown to be correct, it might be argued that a selection process that is based upon it makes sense, because it directs limited resources towards those individuals who are most capable oftaking advantage of them. But if the talent account is wrong, and innate talents are fictional rather than real, a policy of denying facilities to young people because they are deemed not to possess such talents is clearly wasteful and unjust. It could still be argued that those children who are selected as being talented are the ones who are most likely to succeed anyway, since their above-average early progress still may be a good predictor of eventual success even if the inference that such progress points to an innate talent being present is wrong. It makes sense, in other words, to have a selection policy that favours young people who have already done well.

Even so, a policy of totally denying learning facilities to any child who (because he or she has not yet made unusual progress) is thought to lack a vital innate talent can hardly be justified unless there are convincing reasons for assuming that such talents do indeed exist.
There is no item of evidence that single-handedly confirms or refutes the talent account, but various kinds of information have a bearing on the issue. A number of findings have been seen as offering support. First, for instance, there is some evidence that appears to show that skills appear inexplicably early in a few children. Second, some other findings seem to point to the possible existence of special inborn capacities in a smallnumber of individuals. Third, various scientific results appear to indicate the involvement of biologically transmitted mechanisms in exceptional skills.

A number of reports of extraordinarily precocious development in early childhood have appeared. These accounts are certainly consistent with the possibility that some children are born possessing special qualities that raise the likelihood of their becoming exceptionally capable. Of course, the sheer fact that a particular child turns out to be a prodigy does not in itself demonstrate that there must have been anything unusual about that child at the time of birth. However, if unusual capabilities were seen to emerge in the very earliest months of life, it would be hard to see how the child could possibly have acquired them through the kinds of learning that ordinary children are capable of. In that event the conclusion that some special innate causes were involved would seem unavoidable.

The published reports include some accounts of quite remarkable development in the first year of a child's life. One boy is reported to have begun speaking at five months of age and to have gained a fifty-word vocabulary by six months and the capacity to speak in three languages by the age of three years. Another child is said to have begun to speak in sentences at three months, hold conversations at six months, and read simple books by his first birthday.
However, the reliability of these accounts as sources of evidence is doubtful, because they are all retrospective and anecdotal. In the case of the boy who was reported to speak in sentences at three months, he was not actually seen by the psychologist who wrote about him, David Feldman, until reaching the age of three.

The parents told Feldman that they had been amazed by their son's progress in his first year, and yet Feldman himself confessed to being just as astounded by the parents' absolute dedication to accelerating the child's development and their unending quest for ways to stimulate him. In all likelihood the child's early achievements were indeed exceptional, but strong doubts about the likelihood of their emerging spontaneously and without any parental prompting are raised by the fact that all that we know about the actual circumstances comes from the testimony of parents who were extraordinarily committed to stimulating their child's progress.
Reference : "Genius Explained" De Michael J. A. Howe

Monuments and Cosmology

The architecture of public monuments, great and small, can give the archaeologist important clues about the worldviews of those who built them. One reason is that their designs may reflect the perceived cosmos, revealing associations that existed in the minds of the builders, just as the solar alignment at the passage tomb of Newgrange in Ireland reveals a perceived connection between the sun and the ancestors.

Monumental architecture may also reflect a ritually defined order of things that was relatively widespread and relatively stable, even where the nature of the society at the time was constantly changing in other ways. It is easy to see how existing monuments may have helped reinforce the perceived order of things, since they created an indelible mark on the landscape that was bound to have influenced future worldviews—if this is how the ancestors did things, people would surely have thought, then this is how we must do things too. Conversely, fundamental changes in ideology may indicate major social disruption.

This inherent stability oí the perceived world order means that associations of ideological and cosmological significance have a greater chance of leaving their mark on the material record, and thus have a greater chance ofbeing detectable by modern archaeologies, than many other, more volatile aspects of a past society. The reason is that we can expect them to be repeated over and over again. A single association, such as the solstitial alignment at Newgrange, may have meant nothing at all to the builders; it may have arisen entirely fortuitously. But it we see other, similar solstitial alignments repeated again and again, then the likelihood that they could have arisen fortuitously is rapidly diminished.

Where we find significant numbers of monuments with similar designs, similar orientation, and even consistent patterns of astronomical alignment, we can be confident that common practices prevailed over a considerable area and time.Throughout Neolithic and Bronze Age Europe we find discernible traditions of monument construction operating at various levels and scales. Some of these are remarkably widespread in space and time. In Britain, Ireland, and Brittany, for example, a propensity to build circular and linear ceremonial monuments resulted in the construction of many hundreds of stone circles and stone rows over as long as two millennia. Patterns of orientation rend to be more localized, and patterns of astronomical orientation more so still.

For example, among the recumbent stone circles, a group of stone circles of a particular form found in northeastern Scotland, and among the short stone rows of southwestern Ireland, there appear to he more specific traditions of orientation upon prominent features in the landscape or rising or setting positions of the sun or moon than in the larger area.
Reference : Ancient astronomy: an encyclopedia of cosmologies and myth De Clive L. N. Ruggles

Egyptian Temples and Tombs

During the earliest dynasties in ancient Egypt, from about 3000 B.C.E. onwards, royal burials, increased steadily in size and complexity. However, it is the construction of huge pyramids that tor most people epitomizes ancient Egyptian burial customs and captures the imagination.

Large stone architecture first appeared during the Third Dynasty (twenty-seventh century B.C.) in the form of the 77-meter- (254 foot-)high stepped pyramid at Saqqara, some ten kilometers (six miles) south of modern Cairo. Pyramid building reached its peak (after some initial shortcomings) during the fourth Dynasty lib 13-2494 B.C.E.) with the construction of the famous Pyramids of Giza. Pyramids actually formed part of complexes, typically built on the edge of the desert plateau above the fertile river valley where they would dominate the surrounding landscape yet remain inaccessible to the masses: they were enclosed, together with other sacred structures, within a high wall. The precinct interior could only be reached by means of a covered causeway leading up from a separate temple in the valley, accessible by boat.

The subsequent Fifth Dynasty is particularly characterized by the construction of temples dedicated to the sun god, Ra (or Re). The pharaoh's power depended upon sun worship, and these "sun sanctuaries" followed the design of the mortuary complexes in having two enclosed precincts on different levels linked by a causeway. Six of the nine pharaohs of the Filth Dynasty built temple complexes; the best preserved is that built by the sixth pharaoh, Neuserre, at Abu Ghurab .All of this happened during Old Kingdom limes, up to the mid-twenty-second century B.C.E. Ancient Egyptian civilization lasted for a further two millennia, its complex history including periods of political instability and social upheaval as well as two further periods of relative stability: the Middle Kingdom (mid-twenty-first century to mid-seventeenth century) and the New Kingdom (mid-sixteenth century to mid-eleventh century). Monumental tombs and temples proliferated in these later times, but they were generally more modest and not just the preserve of the kings themselves. However, the New Kingdom has left us some spectacular remains in the vicinity of its sacred capital, Thebes, some five hundred kilometers (three hundred miles) upriver to the south of Cairo, near modern Luxor. Amun (or Anion), the patron god of Thebes, had become identified with the existing sun god Ra. and the Great Temple of Anmn-Ra at Karnak provided a spectacular setting at the heart of the city for public ceremonials relating to the sun god.

On the opposite side of the river is the so-called Valley of the Kings, which contains over sixty underground pharaohs' tombs, including the famous (because it was discovered intact) tomb of Tutankhamun.
The most obvious clues to astronomical associations of temples and tombs are found in the inscriptions within them. A number of New Kingdom tombs and temples, for example, contain painted "astronomical ceilings," listing and depicting stars, constellations, and even planets. But why should these be placed inside tombs? The answer is that ancient Egyptians' understanding of the sky was framed within a worldview that bound together inextricably the gods, the otherworld Dual, the afterlife, and what was seen in the night sky. lt had long been engrained in ancient Egyptian minds that the sun god Ra traveled nightly through Duat, the world beyond the horizon, on his journey to the eastern side where the sky goddess Nut would give birth to him once again. Similarly, most of the stars in the sky disappeared from view for a period of some weeks in the year, between their heliacal set and heliacal rise; during this rime they too were understood to pass through Duat.

Likewise, the deceased were required to pass through the twelve parts of the underworld in order to join the gods in the sky. As far back as Old Kingdom times, pharaohs' tombs contained sets of spells known as pyramid texts that were designed to ensure a safe passage. Circumpolar stars, on the other hand, were immortal: ever present in the night sky, they never crossed the horizon into Duat, never died, and were never reborn. It was these stars that the human soul, striving for immortality, endeavored to join.
These beliefs, and especially the deep importance attached to the north direction with its imperishable stars, may well have given rise to a practice during Old Kingdom times of aligning tombs and temples with the cardinal directions.