354 research outputs found
Recommended from our members
Space charge behaviour in epoxy laminates under high constant electric field
The development of space charge in insulating materials is one of the main causes of their electrical ageing. The pulsed electro-acoustic method is often used to determine space charge distribution, but the signal analysis in the case of laminate structures is much more complex to analyse. In this paper the authors describe and use a simulated signal in order to study laminates made of epoxy resin and fibre mat. The relatively large conductivity of the fibres compared with that of the resin seems to produce a rapid charge dissociation and recombination in the fibres. Under voltage the presence of fibres close to an electrode seems to promote charge injection
First Principles Investigation of Ferromagnetism and Ferroelectricity in Bismuth Manganite
We present results of local spin density approximation (LSDA) pseudopotential
calculations for the perovskite structure oxide, bismuth manganite (BiMnO3).
The origin of the differences between bismuth manganite and other perovskite
manganites is determined by first calculating total energies and band
structures of the high symmetry cubic phase, then sequentially lowering the
magnetic and structural symmetry. Our results indicate that covalent bonding
between bismuth cations and oxygen anions stabilizes different magnetic and
structural phases compared with the rare earth manganites. This is consistent
with recent experimental results showing enhancement of charge ordering in
doped bismuth manganite
Angular momentum sharing in dissipative collisions
Light charged particles emitted by the projectile-like fragment were measured
in the direct and reverse collision of Nb and Sn at 25 AMeV. The
experimental multiplicities of Hydrogen and Helium particles as a function of
the primary mass of the emitting fragment show evidence for a correlation with
net mass transfer. The ratio of Hydrogen and Helium multiplicities points to a
dependence of the angular momentum sharing on the net mass transfer.Comment: 8 pages, 2 figure
Consequences of local gauge symmetry in empirical tight-binding theory
A method for incorporating electromagnetic fields into empirical
tight-binding theory is derived from the principle of local gauge symmetry.
Gauge invariance is shown to be incompatible with empirical tight-binding
theory unless a representation exists in which the coordinate operator is
diagonal. The present approach takes this basis as fundamental and uses group
theory to construct symmetrized linear combinations of discrete coordinate
eigenkets. This produces orthogonal atomic-like "orbitals" that may be used as
a tight-binding basis. The coordinate matrix in the latter basis includes
intra-atomic matrix elements between different orbitals on the same atom.
Lattice gauge theory is then used to define discrete electromagnetic fields and
their interaction with electrons. Local gauge symmetry is shown to impose
strong restrictions limiting the range of the Hamiltonian in the coordinate
basis. The theory is applied to the semiconductors Ge and Si, for which it is
shown that a basis of 15 orbitals per atom provides a satisfactory description
of the valence bands and the lowest conduction bands. Calculations of the
dielectric function demonstrate that this model yields an accurate joint
density of states, but underestimates the oscillator strength by about 20% in
comparison to a nonlocal empirical pseudopotential calculation.Comment: 23 pages, 7 figures, RevTeX4; submitted to Phys. Rev.
A Superconducting Instability in the Infinite-U Anderson Lattice in the Presence of Crystal Electric Fields
We report evidence of a superconducting instability (of symmetry) in
the infinite-U Anderson lattice in the presence of crystal fields of cubic
symmetry. We assume a lattice of sites, each with a total angular momentum
of that is split by crystal fields into a low-lying doublet of
symmetry and an excited quartet of symmetry. Slave Bosons
on the sites create and destroy configurations and Lagrange
multipliers at each site enforce the occupancy constraint due to the
infinite Coulomb repulsion. Quasiparticle interactions are due to exchange of
density fluctuations, which are represented by fluctuations in the slave
Bosons and Lagrange multipliers. We use the so-called analytic tetrahedron
method to calculate the dressed (to order 1/N) Boson Green functions. In weak
couping, the exchange of the dressed Bosons gives rise to a superconducting
instability of , , symmetry. The , ``s-wave'',
channel has strongly repulsive interactions and hence no pairing instability.
The channel exhibits weakly repulsive interactions. Average
quasiparticle interactions in the , , , channel
fluctuate strongly as a function of the number of tetrahedra used to calculate
the Bosonic Green functions,Comment: 66 pages+ 17 postscript figures, LATE
Associations between diet and disease activity in ulcerative colitis patients using a novel method of data analysis
BACKGROUND: The relapsing nature and varying geographical prevalence of ulcerative colitis (UC) implicates environmental factors such as diet in its aetiology. METHODS: In order to determine which foods might be related to disease activity in UC a new method of dietary analysis was developed and applied. Eighty-one UC patients were recruited at all stages of the disease process. Following completion of a 7 d diet diary, clinical assessment including a sigmoidoscopic examination (scale 0 (normal mucosa) to 6 (very active disease)) was conducted. Food weights for each person were adjusted (divided) by the person's calorific intake for the week. Each food consumed was given a food sigmoidoscopy score (FSS) calculated by summing the products of the (adjusted) weight of food consumed and sigmoidoscopy score for each patient and occurrence of food and dividing by the total (adjusted) weight of the food consumed by all 81 patients. Thus, foods eaten in large quantities by patients with very active disease have high FSSs and vice versa. Foods consumed by <10 people or weighing <1 kg for the whole group were excluded, leaving 75 foods. RESULTS: High FSS foods were characterized by high levels of the anti-thiamin additive sulfite (Mann-Whitney, p < 0.001), i.e. bitter, white wine, burgers, soft drinks from concentrates, sausages, lager and red wine. Caffeine also has anti-thiamin properties and decaffeinated coffee was associated with a better clinical state than the caffeine containing version. Beneficial foods (average intake per week) included pork (210 g), breakfast cereals (200 g), lettuce (110 g), apples and pears (390 g), milk (1250 ml), melon (350 g), bananas (350 g), bacon (120 g), beef and beef products (500 g), tomatoes (240 g), soup (700 g), citrus fruits (300 g), fish (290 g), yogurt (410 g), cheese (110 g), potatoes (710 g) and legumes (120 g). CONCLUSIONS: The dietary analysis method described provides a new tool for establishing relationships between diet and disease and indicates a potentially therapeutic diet for UC
From Isotropic to Anisotropic Side Chain Representations: Comparison of Three Models for Residue Contact Estimation
The criterion to determine residue contact is a fundamental problem in deriving knowledge-based mean-force potential energy calculations for protein structures. A frequently used criterion is to require the side chain center-to-center distance or the -to- atom distance to be within a pre-determined cutoff distance. However, the spatially anisotropic nature of the side chain determines that it is challenging to identify the contact pairs. This study compares three side chain contact models: the Atom Distance criteria (ADC) model, the Isotropic Sphere Side chain (ISS) model and the Anisotropic Ellipsoid Side chain (AES) model using 424 high resolution protein structures in the Protein Data Bank. The results indicate that the ADC model is the most accurate and ISS is the worst. The AES model eliminates about 95% of the incorrectly counted contact-pairs in the ISS model. Algorithm analysis shows that AES model is the most computational intensive while ADC model has moderate computational cost. We derived a dataset of the mis-estimated contact pairs by AES model. The most misjudged pairs are Arg-Glu, Arg-Asp and Arg-Tyr. Such a dataset can be useful for developing the improved AES model by incorporating the pair-specific information for the cutoff distance
On the typology and the worship status of sacred trees with a special reference to the Middle East
This article contains the reasons for the establishment of sacred trees in Israel based on a field study. It includes 97 interviews with Muslim and Druze informants. While Muslims (Arabs and Bedouins) consider sacred trees especially as an abode of righteous figures' (Wellis') souls or as having a connection to their graves, the Druze relate sacred trees especially to the events or deeds in the lives of prophets and religious leaders. A literary review shows the existence of 24 known reasons for the establishment of sacred trees worldwide, 11 of which are known in Israel one of these is reported here for the first time. We found different trends in monotheistic and polytheistic religions concerning their current worship of sacred trees
- …