1,672 research outputs found
The Metal-Insulator Transition of the Magneli phase V_4O_7: Implications for V_2O_3
The metal-insulator transition (MIT) of the Magneli phase V_4O_7 is studied
by means of electronic structure calculations using the augmented spherical
wave method. The calculations are based on density functional theory and the
local density approximation. Changes of the electronic structure at the MIT are
discussed in relation to the structural transformations occuring
simultaneously. The analysis is based on a unified point of view of the crystal
structures of all Magneli phase compounds V_nO_2n-1 (3 =< n =< 9) as well as of
VO_2 and V_2O_3. This allows to group the electronic bands into states behaving
similar to the dioxide or the sesquioxide. In addition, the relationship
between the structural and electronic properties near the MIT of these oxides
can be studied on an equal footing. For V_4O_7, a strong influence of
metal-metal bonding across octahedral faces is found for states both parallel
and perpendicular to the hexagonal c_hex axis of V_2O_3. Furthermore, the
structural changes at the MIT cause localization of those states, which mediate
in-plane metal-metal bonding via octahedral edges. This band narrowing opens
the way to an increased influence of electronic correlations, which are
regarded as playing a key role for the MIT of V_2O_3.Comment: 7 pages, 3 figures, more information at
http://www.physik.uni-augsburg.de/~eyert
The high-intensity hyperon beam at CERN
A high-intensity hyperon beam was constructed at CERN to deliver Sigma- to
experiment WA89 at the Omega facility and operated from 1989 to 1994. The setup
allowed rapid changeover between hyperon and conventional hadron beam
configurations. The beam provided a Sigma-flux of 1.4 x 10^5 per burst at mean
momenta between 330 and 345 Gev/c, produced by about 3 x 10^10 protons of 450
GeV/c . At the experiment target the beam had a Sigma-/pi- ratio close to 0.4
and a size of 1.6 x 3.7 cm^2. The beam particle trajectories and their momenta
were measured with a scintillating fibre hodoscope in the beam channel and a
silicon microstrip detector at the exit of the channel. A fast transition
radiation detector was used to identify the pion component of the beam.Comment: 20 pages, 13 figures. Submitted to Nucl. Instr. Meth.
Measurement of the Omega_c Lifetime
We present the measurement of the lifetime of the Omega_c we have performed
using three independent data samples from two different decay modes. Using a
Sigma- beam of 340 GeV/c we have obtained clean signals for the Omega_c
decaying into Xi- K- pi+ pi+ and Omega- pi+ pi- pi+, avoiding topological cuts
normally used in charm analysis. The short but measurable lifetime of the
Omega_c is demonstrated by a clear enhancement of the signals at short but
finite decay lengths. Using a continuous maximum likelihood method we
determined the lifetime to be tau(Omega_c) = 55 +13-11(stat) +18-23(syst) fs.
This makes the Omega_c the shortest living weakly decaying particle observed so
far. The short value of the lifetime confirms the predicted pattern of the
charmed baryon lifetimes and demonstrates that the strong interaction plays a
vital role in the lifetimes of charmed hadrons.Comment: 15 pages, including 7 figures; gzipped, uuencoded postscrip
Intestinal parasites from public and private latrines and the harbour canal in Roman Period Ephesus, Turkey (1st c. BCE to 6th c. CE)
To improve our knowledge of the parasite species affecting the inhabitants of Roman period Asia Minor, we analysed faecal material from Ephesus, Turkey. Mineralised material from the drain from a private house latrine (3rd c. CE), sediment samples from the sewer drain of a public communal latrine (6th c. CE), and sediment from the harbour canal (ca. 1st c. BCE to ca. 6th c. CE) were studied for the presence of intestinal parasites. Samples were viewed by light microscopy for helminth eggs, and commercial enzyme-linked immunosorbent assay (ELISA) kits were used to test for protozoal parasites that cause dysentery. Eggs of roundworm were found in the public latrine, whipworm in the house latrine, and both whipworm and roundworm in the harbour canal. Sequential sampling of the harbour core suggests that whipworm was by far the most common parasite throughout the Roman period, and there was no clear evidence for change in parasite species over the centuries. Whipworm and roundworm are both spread by the contamination of food and drink by human faeces. Despite the large number of travellers to Ephesus, as the capital of its province and a major port city in the Roman Empire, there was a surprising lack of diversity in parasite species found. This is especially apparent when we consider that ten species of intestinal parasite have been found across the Roman Empire. This is the first Roman site to be directly assessed for differences between infection in individuals using private latrines, public latrines, and mixed town effluent (in the harbour) at the same site.This research was supported by a doctoral award from the Social Sciences and Humanities Research Council of Canada [752-2016-2085] and a Tidmarsh Cambridge Scholarship from the Cambridge Commonwealth, European and International Trust and Trinity Hall Colleg
Elaia, Pergamon's maritime satellite:The rise and fall of an ancient harbour city shaped by shoreline migration
Throughout human history, communication and trade have been key to society. Because maritime trade facilitated the rapid transportation of passengers and freight at relatively low cost, harbours became hubs for traffic, trade and exchange. This general statement holds true for the Pergamenian kingdom, which ruled wide parts of today's western Turkey during Hellenistic times. Its harbour, located at the city of Elaia on the eastern Aegean shore, was used extensively for commercial and military purposes. This study reconstructs the coastal evolution in and around the ancient harbour of Elaia and compares the observed environmental modifications with archaeological and historical findings. We use micropalaeontological, sedimentological and geochemical proxies to reconstruct the palaeoenvironmental dynamics and evolution of the ancient harbour. The geoarchaeological results confirm the archaeological and historical evidence for Elaia's primacy during Hellenistic and early Roman times, and the city's gradual decline during the late Roman period. Furthermore, our study demonstrates that Elaia holds a unique position as a harbour city during ancient times in the eastern Aegean region, because it was not greatly influenced by the high sediment supply associated with river deltas. Consequently, no dredging of the harbour basins is documented, creating exceptional geo-bioarchives for palaeoenvironmental reconstructions
Coulomb corrections to low energy antiproton annihilation cross sections on protons and nuclei
We calculate, in a systematic way, the enhancement effect on
antiproton-proton and antiproton-nucleus annihilation cross sections at low
energy due to the initial state electrostatic interaction between the
projectile and the target nucleus. This calculation is aimed at future
comparisons between antineutron and antiproton annihilation rates on different
targets, for the extraction of pure isospin channels.Comment: 18 pages, 4 figures (latex format
- …