Aerial archaeology

Aerial archaeology is the study of archaeological remains by examining them from altitude. The advantages of gaining a good aerial view of the ground had been long appreciated by archaeologists as a high viewpoint permits a better appreciation of fine details and their relationships within the wider site context. Early investigators attempted to gain birdseye views of sites using hot air balloons, scaffolds or cameras attached to kites. Following the invention of the aeroplane and the military importance placed on aerial photography during the First and Second World Wars, archaeologists were able to more use the technique to discover and record archaeological sites. Photographs may be taken either vertically, from directly overhead, or obliquely, meaning that they are taken at an angle. In order to provide a three-dimensional effect, an overlapping pair of vertical photographs, taken from offset positions, can be viewed stereoscopically; the advantages of aerial photographs to archaeologists are manifold.

Large sites could for the first time be viewed in their entirety and within their landscape. This aided the production of drawn plans and inspired archaeologists to look beyond the discrete monument and to appreciate a site's role within its setting. Photos are taken vertically for the purposes of planning and spatial analysis and obliquely to emphasize certain features or give perspective. Through the process of photogrammetry, vertical photos can be converted into scaled plans. Archaeological features may be more visible from the air than on the ground. In temperate Europe, aerial reconnaissance is one of the most important ways in which new archaeological sites are discovered. Tiny differences in ground conditions caused by buried features can be emphasised by a number of factors and viewed from the air: Slight differences in ground levels will cast shadows when the sun is low and these can be seen best from an aeroplane; these are referred to as shadow marks. Buried ditches will hold more water and buried walls will hold less water than undisturbed ground, this phenomenon, amongst others, causes crops to grow better or worse, taller or shorter, over each kind of ground and therefore define buried features which are apparent as tonal or colour differences.

Such effects are called cropmarks. Frost can appear in winter on ploughed fields where water has accumulated along the lines of buried features; these are known as frostmarks. Slight differences in soil colour between natural deposits and archaeological ones can often show in ploughed fields as soilmarks Differences in levels and buried features will affect the way surface water behaves across a site and can produce a striking effect after heavy rain. In cases like the Nazca lines, the features are meaningless from the ground but visible from the air. Pioneers of aerial archaeology include Roger Agache in Northern France, Antoine Poidebard in Syria, L W B Rees in Jordan O. G. S. Crawford in England and Sir Henry Wellcome in the Sudan, Giacomo Boni in Italy. Following in the footsteps of Henry Wellcome, kite aerial photography is now being used on archaeological sites outside the visible spectrum, from the near ultra-violet through to the near and thermal infra-red. Aerial archaeology is used in the processes of investigation in aviation archaeology.

Archaeological field survey Cropmark Markus Casey Shadow marks BibliographyBourgeois, J. and Meganck, M.. Aerial Photography and Archaeology 2003. A Century of Information. Archaeological Reports Ghent University 4. Ghent: Academia Press. ISBN 90-382-0782-4 Brophy, K. and Cowley, D.. From the air: understanding aerial archaeology. London: The History Press. ISBN 0-7524-3130-7 Riley, D. N.. Air photography and archaeology. Univ of Pennsylvania. ISBN 0-8122-8087-3 Wilson, D. R.. Air photo interpretation for archaeologists, London: The History Press.. ISBN 0-7524-1498-4 Emporia State University: Aerial Archaeology Aerial and Remote Sensing Archaeology Link and Reference Site Aerial Archaeology. focuses on near-earth imaging technologies such as kite aerial photography, remote-control powered parachutes and model airplanes and helicopters. *** Off-line April 20, 2010 *** ACE Foundation Kite Aerial Photographers - Archaeology Sir Henry Wellcome Aerial Archaeology in Northern France

Elliptic flow

Relativistic heavy-ion collisions produce large numbers of subatomic particles in all directions. In such collisions, flow refers to how energy and number of these particles varies with direction, elliptic flow is a measure of how the flow is not uniform in all directions when viewed along the beam-line. Elliptic flow is strong evidence for the existence of quark–gluon plasma, has been described as one of the most important observations measured at the Relativistic Heavy Ion Collider. Elliptic flow describes the azimuthal momentum space anisotropy of particle emission from non-central heavy-ion collisions in the plane transverse to the beam direction, is defined as the second harmonic coefficient of the azimuthal Fourier decomposition of the momentum distribution. Elliptic flow is a fundamental observable since it directly reflects the initial spatial anisotropy, of the nuclear overlap region in the transverse plane, directly translated into the observed momentum distribution of identified particles.

Since the spatial anisotropy is largest at the beginning of the evolution, elliptic flow is sensitive to the early stages of system evolution. A measurement of elliptic flow thus provides access to the fundamental thermalization time scale and many more things in the early stages of a relativistic heavy-ion collision. "ALICE gets with the flow". CERN Courier. 30 March 2011. Cramer, John G. "Solving the RHIC Puzzle". Analog Science Fiction and Fact. Archived from the original on 26 January 2012. Retrieved 11 March 2012