Heat flux operator, current conservation and the formal Fourier's law

By revisiting previous definitions of the heat current operator, we show that one can define a heat current operator that satisfies the continuity equation for a general Hamiltonian in one dimension. This expression is useful for studying electronic, phononic and photonic energy flow in linear systems and in hybrid structures. The definition allows us to deduce the necessary conditions that result in current conservation for general-statistics systems. The discrete form of the Fourier's Law of heat conduction naturally emerges in the present definition

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

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

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

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

ВЛИЯНИЕ БАЗОВОГО СОСТАВА И МИКРОСТРУКТУРЫ НИКЕЛЬ–ЦИНКОВЫХ ФЕРРИТОВ НА УРОВЕНЬ ПОГЛОЩЕНИЯ ЭЛЕКТРОМАГНИТНОГО ИЗЛУЧЕНИЯ

Promising absorbing materials include Ni—Zn−ferrites, as they quite intensively absorb electromagnetic waves in the 50 MHz to 1000 MHz frequency range. In this paper we have studied the electromagnetic properties of Ni—Zn ferrite absorbing materials obtained in different technological modes. We propose a model that allows one to evaluate the dielectric constant of the ferrite material depending on the parameters of the microstructure and electrical properties of grain boundaries. Influence of base composition and microstructure on the level of absorption of electromagnetic radiation by Ni—Zn ferrite absorbing materials has been found. An increase in Fe₂O₃ excess to 51 % has been found to shift the frequency interval of electromagnetic radiation absorption towards lower frequencies, and this effect can be explained by an increase in the dielectric and magnetic constants of ferrite. Introduction of excess Fe₂O₃ in step 2 of grinding proved to be more efficient. An increase in the sintering temperature to 1350 °C also provides for a shift of electromagnetic radiation absorption frequency interval towards lower frequencies, which can be explained by an increase of the dielectric and magnetic constants of ferrite and resonance frequency shift of domain walls due to the formation of a coarse−grained structure.Никель−цинковые ферриты относятся к перспективным радиопоглощающим материалам, так как они интенсивно поглощают электромагнитные волны в интервале частот от 50 до 1000 МГц. Проведены исследования электромагнитных свойств Ni—Zn−ферритовых радиопоглощающих материалов, полученных по различным технологическим режимам. Предложена модель, позволяющая оценить диэлектрическую проницаемость ферритового материала в зависимости от параметров микроструктуры и электрофизических свойств границ зерен. Установлено влияние базового состава и микроструктуры на уровень поглощения электромагнитного излучения Ni—Zn− ферритовыми радиопоглощающими материалами. Установлено, что увеличение содержания избытка Fe2O3 до 51 % (мол.) приводит к смещению частотного интервала поглощения электромагнитного излучения в сторону низких частот. Это можно объяснить увеличением магнитной и диэлектрической проницаемостей феррита. Показано, что более эффективно введение избытка Fe2O3 на стадии измельчения синтезированной шихты. Обнаружено, что увеличение температуры спекания до 1350 °С  также обеспечивает смещение частотного интервала поглощения электромагнитного излучения в сторону низких частот. Вероятно, это обусловлено увеличением магнитной и диэлектрической проницаемостей феррита и смещением частоты резонанса доменных стенок в результате формирования крупнозернистой структуры

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

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