11,463 research outputs found
Topological Aspects of Spin and Statistics in Nonlinear Sigma Models
We study the purely topological restrictions on allowed spin and statistics
of topological solitons in nonlinear sigma models. Taking as space the
connected -manifold , and considering nonlinear sigma models with the
connected manifold as target space, topological solitons are given by
elements of . Any topological soliton determines
a quotient \Stat_n(X,\alpha) of the group of framed braids on , such that
choices of allowed statistics for solitons of type are given by
unitary representations of \Stat_n(X,\alpha) when solitons are present.
In particular, when , as in the nonlinear sigma model with Hopf
term, and is a generator, we compute that
\Stat_n(\R^2,\alpha) = \Z, while \Stat_n(S^2,\alpha) = \Z_{2n}. It follows
that phase for interchanging two solitons of type on
must satisfy the constraint , , when such
solitons are present.Comment: 14 page
A solvable model of a random spin-1/2 XY chain
The paper presents exact calculations of thermodynamic quantities for the
spin-1/2 isotropic XY chain with random lorentzian intersite interaction and
transverse field that depends linearly on the surrounding intersite
interactions.Comment: 14 pages (Latex), 2 tables, 13 ps-figures included, (accepted for
publication in Phys.Rev.B
Intrinsic peculiarities of real material realizations of a spin-1/2 kagome lattice
Spin-1/2 magnets with kagome geometry, being for years a generic object of
theoretical investigations, have few real material realizations. Recently, a
DFT-based microscopic model for two such materials, kapellasite Cu3Zn(OH)6Cl2
and haydeeite Cu3Mg(OH)6Cl2, was presented [O. Janson, J. Richter and H.
Rosner, arXiv:0806.1592]. Here, we focus on the intrinsic properties of real
spin-1/2 kagome materials having influence on the magnetic ground state and the
low-temperature excitations. We find that the values of exchange integrals are
strongly dependent on O--H distance inside the hydroxyl groups, present in most
spin-1/2 kagome compounds up to date. Besides the original kagome model,
considering only the nearest neighbour exchange, we emphasize the crucial role
of the exchange along the diagonals of the kagome lattice.Comment: 4 pages, 4 figures. A paper for the proceedings of the HFM 2008
conferenc
Microscopic magnetic modeling for the =1/2 alternating chain compounds NaCuSbO and NaCuTeO
The spin-1/2 alternating Heisenberg chain system NaCuSbO features
two relevant exchange couplings: within the structural CuO
dimers and between the dimers. Motivated by the controversially
discussed nature of , we perform extensive density-functional-theory
(DFT) calculations, including DFT+ and hybrid functionals. Fits to the
experimental magnetic susceptibility using high-temperature series expansions
and quantum Monte Carlo simulations yield the optimal parameters =
217 K and = 174 K with the alternation ratio 1.25. For the closely related system
NaCuTeO, DFT yields substantially enhanced , but weaker
. The comparative analysis renders the buckling of the chains as the
key parameter altering the magnetic coupling regime. Numerical simulation of
the dispersion relations of the alternating chain model clarify why both
antiferromagnetic and ferrromagnetic can reproduce the experimental
magnetic susceptibility data.Comment: published version: 11 pages, 8 figures, 5 tables + Supplemental
materia
Indomethacin decreases viscosity of gallbladder bile in patients with cholesterol gallstone disease
There is experimental evidence that inhibition of cyclooxygenase with nonsteroidal anti-inflammatory drugs may decrease cholesterol gall-stone formation and mitigate biliary pain in gall-stone patients. The mechanisms by which NSAIDs exert these effect are unclear. In a prospective, controlled clinical trial we examined the effects of oral indomethacin on the composition of human gall-bladder bile. The study included 28 patients with symptomatic cholesterol or mixed gallstones. Of these, 8 were treated with 3 × 25 mg indomethacin daily for 7 days prior to elective cholecystectomy while 20 received no treatment and served as controls. Bile and tissue samples from the gallbladder were obtained during cholecystectomy. Indomethacin tissue levels in the gallbladder mucosa, as assessed by HPLC, were 1.05±0.4 ng/mg wet weight, a concentration known to inhibit effectively cyclooxygenase activity. Nevertheless, no differences between the treated and untreated groups were found in the concentrations of biliary mucus glycoprotein (0.94±0.27 versus 0.93±0.32 mg/ml) or total protein (5.8±0.9 versus 6.4±1.3 mg/ml), cholesterol saturation (1.3±0.2 versus 1.5±0.2), or nucleation time (2.0±3.0 versus 1.5±2.0 days). However, biliary viscosity, measured using a low-shear rotation viscosimeter, was significantly lower in patients receiving indomethacin treatment (2.9±0.6 versus 5.6±1.2 mPa.s; P < 0.02). In conclusion, in man oral indomethacin decreases bile viscosity without alteration of bile lithogenicity or biliary mucus glycoprotein content. Since mucus glycoproteins are major determinants of bile viscosity, an alteration in mucin macromolecular composition may conceivably cause the indomethacin-induced decrease in biliary viscosity and explain the beneficial effects of nonsteroidal anti-inflammatory drugs in gallstone disease
Resolution and Efficiency of the ATLAS Muon Drift-Tube Chambers at High Background Rates
The resolution and efficiency of a precision drift-tube chamber for the ATLAS
muon spectrometer with final read-out electronics was tested at the Gamma
Irradiation Facility at CERN in a 100 GeV muon beam and at photon irradiation
rates of up to 990 Hz/square cm which corresponds to twice the highest
background rate expected in ATLAS. A silicon strip detector telescope was used
as external reference in the beam. The pulse-height measurement of the read-out
electronics was used to perform time-slewing corrections which lead to an
improvement of the average drift-tube resolution from 104 microns to 82 microns
without irradiation and from 128 microns to 108 microns at the maximum expected
rate. The measured drift-tube efficiency agrees with the expectation from the
dead time of the read-out electronics up to the maximum expected rate
Completion of Mitosis Requires Neither fzr/rap nor fzr2, a Male Germline-Specific Drosophila Cdh1 Homolog
AbstractProteolysis of mitotic regulators like securins and cyclins requires Fizzy(FZY)/Cdc20 and Fizzy-related(FZR)/Hct1/Cdh1 proteins [1–5]. Budding yeast Cdh1 acts not only during G1, but is also required for B-type cyclin degradation during exit from mitosis when Cdh1 is a target of the mitotic exit network controlling progression through late mitosis and cytokinesis [6, 7]. In contrast, observations in frog and Drosophila embryos have suggested that the orthologous FZR is not involved during exit from mitosis [3, 8]. However, the potential involvement of minor amounts of maternally derived FZR was not excluded in these studies. Similarly, the reported absence of severe mitotic defects in chicken Cdh1−/− cells [9] might be explained by the recent identification of multiple Cdh1 genes [10]. Here, we have carefully analyzed the FZR requirement during exit from mitosis in Drosophila, which, apart from fzr, has only one additional homolog. We find that this fzr2 gene, although expressed in the male germline, is not expressed during mitotic divisions. Moreover, by characterizing fzr alleles, we demonstrate that completion of mitosis including Cyclin B degradation does not require FZR. However, fzr is an essential gene corresponding to the rap locus, and FZR, which accumulates predominantly in the cytoplasm, is clearly required during G1
Universal properties of highly frustrated quantum magnets in strong magnetic fields
The purpose of the present paper is two-fold. On the one hand, we review some
recent studies on the low-temperature strong-field thermodynamic properties of
frustrated quantum spin antiferromagnets which admit the so-called
localized-magnon eigenstates. One the other hand, we provide some complementary
new results. We focus on the linear independence of the localized-magnon
states, the estimation of their degeneracy with the help of auxiliary classical
lattice-gas models and the analysis of the contribution of these states to
thermodynamics.Comment: Paper based on the invited talk given by J. Richter at the
International Conference "Statistical Physics 2006. Condensed Matter: Theory
and Applications" dedicated to the 90th anniversary of Ilya Lifshitz
(Kharkiv, 11-15 September, 2006
Thermodynamic properties of spin-1/2 transverse XY chain with Dzyaloshinskii-Moriya interaction: Exact solution for correlated Lorentzian disorder
We extend the consideration of the spin-1/2 transverse XY chain with
correlated Lorentzian disorder (Phys. Rev. B {\bf 55,} 14298 (1997)) for the
case of additional Dzyaloshinskii-Moriya interspin interaction. It is shown how
the averaged density of states can be calculated exactly. Results are presented
for the density of states and the transverse magnetization.Comment: 2 figure
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