Macroscopic Quantum Phase Interference in Antiferromagnetic Particles

The tunnel splitting in biaxial antiferromagnetic particles is studied with a magnetic field applied along the hard anisotropy axis. We observe the oscillation of tunnel splitting as a function of the magnetic field due to the quantum phase interference of two tunneling paths of opposite windings. The oscillation is similar to the recent experimental result with Fe}$_8$\textrm{\ molecular clusters.}Comment: 8 pages, 2 postscript figures, to appear in J. Phys.: Condes. Matte

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

Dynamics of a Quantum Particle in Asymmetric Bistable Potential with Environmental Noise

In this work we analyze the dynamics of a quantum particle subject to an asymmetric bistable potential and interacting with a thermal reservoir. We obtain the time evolution of the population distributions in both energy and position eigenstates of the particle, for different values of the coupling strength with the thermal bath. The calculation is carried out using the Feynman- Vernon functional under the discrete variable representation

Suppression of decoherence by bath ordering

The dynamics of two coupled spins-1/2 coupled to a spin-bath is studied as an extended model of the Tessieri-Wilkie Hamiltonian \cite{TWmodel}. The pair of spins served as an open subsystem were prepared in one of the Bell states and the bath consisted of some spins-1/2 is in a thermal equilibrium state from the very beginning. It is found that with the increasing the coupling strength of the bath spins, the bath forms a resonant antiferromagnetic order. The polarization correlation between the two spins of the subsystem and the concurrence are recovered in some extent to the isolated subsystem. This suppression of the subsystem decoherence may be used to control the quantum devices in practical applications.Comment: 32 pages, Chinese Physics (accepted

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

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

Study of Spin and Decay-Plane Correlations of W Bosons in the e+e- -> W+W- Process at LEP

Data collected at LEP at centre-of-mass energies \sqrt(s) = 189 - 209 GeV are used to study correlations of the spin of W bosons using e+e- -> W+W- -> lnqq~ events. Spin correlations are favoured by data, and found to agree with the Standard Model predictions. In addition, correlations between the W-boson decay planes are studied in e+e- -> W+W- -> lnqq~ and e+e- -> W+W- -> qq~qq~ events. Decay-plane correlations, consistent with zero and with the Standard Model predictions, are measured

Ultrarelativistic sources in nonlinear electrodynamics

The fields of rapidly moving sources are studied within nonlinear electrodynamics by boosting the fields of sources at rest. As a consequence of the ultrarelativistic limit the delta-like electromagnetic shock waves are found. The character of the field within the shock depends on the theory of nonlinear electrodynamics considered. In particular, we obtain the field of an ultrarelativistic charge in the Born-Infeld theory.Comment: 10 pages, 3 figure

Measurement of the Cross Section for Open-Beauty Production in Photon-Photon Collisions at LEP

The cross section for open-beauty production in photon-photon collisions is measured using the whole high-energy and high-luminosity data sample collected by the L3 detector at LEP. This corresponds to 627/pb of integrated luminosity for electron-positron centre-of-mass energies from 189GeV to 209GeV. Events containing b quarks are identified through their semi-leptonic decay into electrons or muons. The e+e- -> e+e-b b~X cross section is measured within our fiducial volume and then extrapolated to the full phase space. These results are found to be in significant excess with respect to Monte Carlo predictions and next-to-leading order QCD calculations

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