141 research outputs found
An alternate model for magnetization plateaus in the molecular magnet V_15
Starting from an antiferromagnetic Heisenberg Hamiltonian for the fifteen
spin-1/2 ions in V_15, we construct an effective spin Hamiltonian involving
eight low-lying states (spin-1/2 and spin-3/2) coupled to a phonon bath. We
numerically solve the time-dependent Schrodinger equation of this system, and
obtain the magnetization as a function of temperature in a time-dependent
magnetic field. The magnetization exhibits unusual patterns of hysteresis and
plateaus as the field sweep rate and temperature are varied. The observed
plateaus are not due to quantum tunneling but are a result of thermal
averaging. Our results are in good agreement with recent experimental
observations.Comment: Revtex, 4 pages, 5 eps figure
Linewidth of single photon transitions in Mn-acetate
We use time-domain terahertz spectroscopy to measure the position and
linewidth of single photon transitions in Mn-acetate. This linewidth is
compared to the linewidth measured in tunneling experiments. We conclude that
local magnetic fields (due to dipole or hyperfine interactions) cannot be
responsible for the observed linewidth, and suggest that the linewidth is due
to variations in the anisotropy constants for different clusters. We also
calculate a lower limit on the dipole field distribution that would be expected
due to random orientations of clusters and find that collective effects must
narrow this distribution in tunneling measurements.Comment: 5 pages, accepted to Physical Review
Thermal compression of atomic hydrogen on helium surface
We describe experiments with spin-polarized atomic hydrogen gas adsorbed on
liquid He surface. The surface gas density is increased locally by
thermal compression up to cm at 110 mK. This
corresponds to the onset of quantum degeneracy with the thermal de-Broglie
wavelength being 1.5 times larger than the mean interatomic spacing. The atoms
were detected directly with a 129 GHz electron-spin resonance spectrometer
probing both the surface and the bulk gas. This, and the simultaneous
measurement of the recombination power, allowed us to make accurate studies of
the adsorption isotherm and the heat removal from the adsorbed hydrogen gas.
From the data, we estimate the thermal contact between 2D hydrogen gas and
phonons of the helium film. We analyze the limitations of the thermal
compression method and the possibility to reach the superfluid transition in 2D
hydrogen gas.Comment: 20 pages, 11 figure
Asymmetric Lineshape due to Inhomogeneous Broadening of the Crystal-Field Transitions in Mn12ac Single Crystals
The lineshape of crystal-field transitions in single crystals of Mn12ac
molecular magnets is determined by the magnetic history. The absorption lines
are symmetric and Gaussian for the non-magnetized state obtained by zero-field
cooling (zfc). In the magnetized state which is reached when the sample is
cooled in a magnetic field (fc), however, they are asymmetric even in the
absence of an external magnetic field. These observations are quantitatively
explained by inhomogeneous symmetrical (Gaussian) broadening of the
crystal-field transitions combined with a contribution of off-diagonal
components of the magnetic susceptibility to the effective magnetic
permeability.Comment: 4 pages, 3 figure
Features of matrix metalloproteinases MMP2, MMP3, MMP9 genes regulatory region polymorphism in patients with uterine fbroids
Violation of the extracellular matrix components synthesis regulation contributes to the formation and growth of uterine fbroids (MM). Changes of collagen metabolism in connective tissue may be associated with polymorphism of matrix metalloproteinase (MMP) genes. Aim of the study was to analyze of the association of regulatory regions of matrix metalloproteinase genes MMP2 (rs243865), MMP3 (rs3025058), MMP9 (rs3918242) with the development of uterine myoma, its histological form, several concomitant gynecological diseases. Material and methods. The clinical study of 69 patients (23–54 years old) with uterine myoma was conducted. According to the anamnesis, 57.9 % of patients had childbirth, 46.4 % of women had an artifcial termination of pregnancy, and 15.9 % of women had endometriosis. In histological examination, in 48.14 % the nodes corresponded to the phenotype of simple fbroids with a large proportion of fbrous tissue, 51.6 % with the phenotype of proliferating fbroids. The comparison group is represented by a random population sample of women from Western Siberia. 183 women without pronounced gynecological pathologies were examined. MMP2-1306 C/T polymorphism was analyzed by TaqMan, MMP3-1171 5A/6A, MMP9-1562 C/T by restriction fragment length polymorphism method. Results. The genotype frequencies of the analyzed genes did not signifcantly differ between the groups. The complex genotype MMP2-1306CC:MMP3-11715A6A:MMP9-1562CT was decreased in women with uterine myoma relative to the persons of the comparison group. In endometriosis patients MMP9-1562CC genotype was reduced and heterozygosity was increased relative to patients without endometriosis. The frequency of MMP2-1306CC:MMP9-1562CT complex genotype is signifcantly higher in women who gave birth than in women who did not give birth. Complex genotypes differences between histological variants of uterine myoma were revealed. Conclusions. The results of the study show the signifcance of polymorphism effect of the regulatory regions of the MMP genes in the development and nature of the course of uterine myoma
Non-Fermi liquid behavior and Griffiths phase in {\it f}-electron compounds
We study the interplay among disorder, RKKY and Kondo interactions in {\it
f}-electron alloys. We argue that the non-Fermi liquid behavior observed in
these systems is due to the existence of a Griffiths phase close to a quantum
critical point. The existence of this phase provides a unified picture of a
large class of materials. We also propose new experiments that can test these
ideas.Comment: 4 pages, 1 Figure. NEW version of the original manuscript. A single
framework for NFL behavior in different kinds of alloys is presented. Final
version finally allowed to appear on the glorious Physical Review Letter
Cold bosonic atoms in optical lattices
The dynamics of an ultracold dilute gas of bosonic atoms in an optical
lattice can be described by a Bose-Hubbard model where the system parameters
are controlled by laser light. We study the continuous (zero temperature)
quantum phase transition from the superfluid to the Mott insulator phase
induced by varying the depth of the optical potential, where the Mott insulator
phase corresponds to a commensurate filling of the lattice (``optical
crystal''). Examples for formation of Mott structures in optical lattices with
a superimposed harmonic trap, and in optical superlattices are presented.Comment: 4 pages 4 figures New: added references; Postscript version available
at:
http://th-physics.uibk.ac.at/zoller/Publications/PZListOfPublications.htm
Risk Factors of Portal Vein Thrombosis in Patients with Different Child-Pugh Classes Liver Cirrhosis
Aim: to evaluate the frequency of portal vein thrombosis (PVT) and build predictive models of the development of PVT for patients with liver cirrhosis (LC) of A and B/C classes by Child-Pugh.Materials and methods. Research design is a case-control. The Case group included 130 patients with newly diagnosed PVT not caused by invasive hepatocellular carcinoma (HCC); 29 patients were assigned to class A, 101 patients were assigned to class B/C. From the database of cirrhotic patients without PVT 60 Controls for class A and 205 for B/C were selected using sratified randomization by sex, age and etiology of cirrhosis. The Mann-Whitney U-test and Pearson's chi-squared test were used to compare the groups. Odds ratios (OR) and 95 % confidence intervals (95 % CI) were calculated. Logistic regression models are constructed with the separation of the sample into training and test (0.7; 0.3). The operational characteristics of the models were calculated on the test sample; ROC analysis was carried out, the area under the ROC curve (AUC) was calculated.Results. The overall frequency of PVT was 4.1 % (95 % CI 2.7-5.8 %) in class A and 10.4 % (95 % CI 8.5-12.5 %) class B/C. Patients with class A and B/C PVT differed from the corresponding controls by more severe portal hypertension: the frequency of bleeding / number of interventions on varices compared with the control were 41/45 % vs. 7/8 % (p < 0.001) for class A and 25.7/30.7 % vs. 16.1/16.1 % (p < 0.05) for class B/C, ascites frequency was 24 % vs. 8 % (p < 0.05) for class A and 89.1 % vs. 68.3 % (p < 0.001) for class B/C. The cutoff by the portal vein diameter was the same for both classes — 13.4 mm; the spleen length was similar and amounted 17.5 mm for class A, 17.1 mm for class B/C. Patients with PVT differed from the corresponding controls by neutrophil-to-lymphocyte ratio: class A 2.33 (1.82; 3.61) vs. 1.76 (1.37; 2.20), p < 0.01, class B/C 2.49 (1.93; 3.34) vs. 2.15 (1.49; 3.26), p < 0.05. Patients of class B/C had a higher incidence of newly diagnosed malignant tumors - 23.8% (primarily HCC that does not invade the portal vein), compared with control and cases of class A - 6.3 % and 3 % (p < 0.05), respectively. The best model for class A included variceal bleeding, ascites, portal vein diameter, absolute number of neutrophils, for class B — ascites, spleen length, portal vein diameter, malignant tumors / local factors; sensitivity, specificity, accuracy and AUC were 79.3 %, 90 %, 86.5 %, 0.897 and 73.3 %, 68.3 %, 69.9 %, 0.789, respectively.Conclusion. Independently of the Child-Pugh class of LC, the main risk factor for PVT is severe portal hypertension
Search for Charginos with a Small Mass Difference with the Lightest Supersymmetric Particle at \sqrt{s} = 189 GeV
A search for charginos nearly mass-degenerate with the lightest
supersymmetric particle is performed using the 176 pb^-1 of data collected at
189 GeV in 1998 with the L3 detector. Mass differences between the chargino and
the lightest supersymmetric particle below 4 GeV are considered. The presence
of a high transverse momentum photon is required to single out the signal from
the photon-photon interaction background. No evidence for charginos is found
and upper limits on the cross section for chargino pair production are set. For
the first time, in the case of heavy scalar leptons, chargino mass limits are
obtained for any \tilde{\chi}^{+-}_1 - \tilde{\chi}^0_1 mass difference
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