1,566 research outputs found
Equivalence of two approaches for the inhomogeneous density in the canonical ensemble
In this article we show that the inhomogeneous density obtained from a
density-functional theory of classical fluids in the canonical ensemble (CE),
recently presented by White et al [Phys. Rev. Lett. 84 (2000) 1220], is
equivalent to first order to the result of the series expansion of the CE
inhomogeneous density introduced by Gonzalez et al [Phys. Rev. Lett. 79 (1997)
2466].Comment: 6 pages, RevTe
Factorization of shell-model ground-states
We present a new method that accurately approximates the shell-model
ground-state by products of suitable states. The optimal factors are determined
by a variational principle and result from the solution of rather
low-dimensional eigenvalue problems. The power of this method is demonstrated
by computations of ground-states and low-lying excitations in sd-shell and
pf-shell nuclei.Comment: 5+epsilon pages, 5 eps-figures. Main additions: wave-function
overlaps, angular momentum expectation values, application to Ni56. To be
published as Rapid Communication in PR
Topological effects at short antiferromagnetic Heisenberg chains
The manifestations of topological effects in finite antiferromagnetic
Heisenberg chains is examined by density matrix renormalization group technique
in this paper. We find that difference between integer and half-integer spin
chains shows up in ground state energy per site when length of spin chain is
longer than , where is a spin-spin correlation
length, for spin magnitude S up to 5/2. For open chains with spin magnitudes
to S=5, we verify that end states with fractional spin quantum numbers
exist and are visible even when the chain length is much smaller than the
correlation length . The end states manifest themselves in the structure
of the low energy excitation spectrum.Comment: 4 pages, 6 figure
Particle motion and stain removal during simulated abrasive tooth cleaning
Stain removal from teeth is important both to prevent decay and for appearance. This is usually achieved using a filament-based toothbrush with a toothpaste consisting of abrasive particles in a carrier fluid. This work has been carried out to examine how these abrasive particles interact with the filaments and cause material removal from a stain layer on the surface of a tooth. It is important to understand this mechanism as while maximum cleaning efficiency is required, this must not be accompanied by damage to the enamel or dentine substrate. In this work simple abrasive scratch tests were used to investigate stain removal mechanism of two abrasive particles commonly used in tooth cleaning, silica and perlite. Silica particles are granular in shape and very different to perlite particles, which are flat and have thicknesses many times smaller than their width. Initially visualisation studies were carried out with perlite particles to study how they are entrained into a filament/counterface contact. Results were compared with previous studies using silica. Reciprocating scratch tests were then run to study how many filaments have a particle trapped at one moment and are involved in the cleaning process. Stain removal tests were then carried out in a similar manner to establish cleaning rates with the two particle types. Perlite particles were found to be less abrasive than silica. This was because of their shape and how they were entrained into the filament contacts and loaded against a counterface. With both particles subsurface damage during stain removal was found to be minimal. A simple model was built to predict stain removal rates with silica particles, which gave results that correlated well with the experimental data
Evidence for genetic differences in resistance to tuberculosis in UK and Irish Holstein-Fresian populations
Charge density correlations in t-J ladders investigated by the CORE method
Using 4-site plaquette or rung basis decomposition, the CORE method is
applied to 2-leg and 4-leg t-J ladders and cylinders. Resulting range-2
effective hamiltonians are studied numerically on periodic rings taking full
advantage of the translation symmetry as well as the drastic reduction of the
Hilbert space. We investigate the role of magnetic and fermionic degrees of
freedom to obtain the most reliable representation of the underlying model.
Spin gaps, pair binding energies and charge correlations are computed and
compared to available ED and DMRG data for the full Hamiltonian. Strong
evidences for short-range diagonal stripe correlations are found in periodic
4-leg t-J ladders.Comment: Computation of Luttinger liquid parameters (charge velocity and
charge correlation exponent) adde
Change of temporomandibular joint disk configuration and clinical findings following conservative treatment
The objective of this study was to evaluate the relationship between changes in the disk status (position and reduction) and changes in the clinical findings following conservative temporomandibular joint(TMJ) treatment. The subjects consisted of 164 patients (328 joints) having TMJ disorders. Clinical examination and MR imaging were performed on all patients before and after conservative treatment. Clinical assessments included joint noise, pain and inter-incisal distance(IID). Disk position and reduction was classified as "improved", "worsened", or "unchanged" following treatment. In the 55 joints where disk position was improved, noise was improved in 37(67.2%) and worsened in 6(10.9%). In the 48 joints where disk reduction was improved, noise was improved in 34(70.8%) and worsened in 4(8.3%). There was a significant relationship between improvement in the disk status and improvement in the noise. In 55 joins where the disk position was improved, pain symptoms were disappeared in 22(40.0%) and newly occured in 4(7.3%). In the 56 joins where the pain was disappeared, disk reduction improved in 22(39.3%), but became worse in 22(39.3%) joints. In 56 joints where the pain was disappeared, disk reduction improved in 17(30.4%) joints disk reduction improved in 17(30.4%) joins but became worse in 32(57%). There was no significant relationship between improvement in the disk status and improvement in the pain. Treatment has no significant influence on IID. We conclude that there was no relationship between improvement in the disk status and improvement in the joint pain and IID after conservative treatment, but there was close relationship between disk stutus and the joint noise in their changes
Kinematic characteristics of elite men's 50 km race walking.
Race walking is an endurance event which also requires great technical ability, particularly with respect to its two distinguishing rules. The 50 km race walk is the longest event in the athletics programme at the Olympic Games. The aims of this observational study were to identify the important kinematic variables in elite men's 50 km race walking, and to measure variation in those variables at different distances. Thirty men were analysed from video data recorded during a World Race Walking Cup competition. Video data were also recorded at four distances during the European Cup Race Walking and 12 men analysed from these data. Two camcorders (50 Hz) recorded at each race for 3D analysis. The results of this study showed that walking speed was associated with both step length (r=0.54,P=0.002) and cadence (r=0.58,P=0.001). While placing the foot further ahead of the body at heel strike was associated with greater step lengths (r=0.45,P=0.013), it was also negatively associated with cadence (r= -0.62,P<0.001). In the World Cup, knee angles ranged between 175 and 186° at initial contact and between 180 and 195° at midstance. During the European Cup, walking speed decreased significantly (F=9.35,P=0.002), mostly due to a decrease in step length between 38.5 and 48.5 km (t=8.59,P=0.014). From this study, it would appear that the key areas a 50 km race walker must develop and coordinate are step length and cadence, although it is also important to ensure legal walking technique is maintained with the onset of fatigue
A reanalysis of the luminosities of clusters of galaxies in the EMSS sample with 0.3 < z < 0.6
The X-ray luminosities of the Einstein Extended Medium Sensitivity Survey
(EMSS) clusters of galaxies with redshifts 0.3<z<0.6 are remeasured using ROSAT
PSPC data. It is found that the new luminosities are on average 1.18 +/- 0.08
times higher than previously measured but that this ratio depends strongly on
the X-ray core radii we measure. For the clusters with small core radii, in
general we confirm the EMSS luminosities, but for clusters with core radii >250
kpc (the constant value assumed in the EMSS), the new luminosities are 2.2 +/-
0.15 times the previous measurements. The X-ray luminosity function (XLF) at
0.3<z<0.6 is recalculated and is found to be consistent with the local XLF. The
constraints on the updated properties of the 0.3<z<0.6 EMSS sample, including a
comparison with the number of clusters predicted from local XLFs, indicate that
the space density of luminous, massive clusters has either not evolved or has
increased by a small factor ~2 since z=0.4. The implications of this result are
discussed in terms of constraints on the cosmological parameter Omega_0.Comment: 12 pages, 7 figures. Accepted for publication in MNRA
From antiferromagnetism to d-wave superconductivity in the 2D t-J model
We have found that the two dimensional t-J model, for the physical parameter
range J/t = 0.4 reproduces the main experimental qualitative features of
High-Tc copper oxide superconductors: d-wave superconducting correlations are
strongly enhanced upon small doping and clear evidence of off diagonal long
range order is found at the optimal doping \delta ~ 0.15. On the other hand
antiferromagnetic long range order, clearly present at zero hole doping, is
suppressed at small hole density with clear absence of antiferromagnetism at
\delta >~ 0.1.Comment: 4 pages, 5 figure
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