2,476 research outputs found
Transport in the XX chain at zero temperature: Emergence of flat magnetization profiles
We study the connection between magnetization transport and magnetization
profiles in zero-temperature XX chains. The time evolution of the transverse
magnetization, m(x,t), is calculated using an inhomogeneous initial state that
is the ground state at fixed magnetization but with m reversed from -m_0 for
x0. In the long-time limit, the magnetization evolves into a
scaling form m(x,t)=P(x/t) and the profile develops a flat part (m=P=0) in the
|x/t|1/2 while it
expands with the maximum velocity, c_0=1, for m_0->0. The states emerging in
the scaling limit are compared to those of a homogeneous system where the same
magnetization current is driven by a bulk field, and we find that the
expectation values of various quantities (energy, occupation number in the
fermionic representation) agree in the two systems.Comment: RevTex, 8 pages, 3 ps figure
From "Sirups" to Biocarbons: A 30 Year Research Cooperation for Better Biomass Utilization with Michael J. Antal, Jr
The results of a 30 year U.S.-Hungarian research cooperation are surveyed. The head of the cooperating U.S. laboratory, Michael J. Antal, Jr., died on Oct 21, 2015. He was a leading person in biomass research. The collaboration started with pyrolysis studies. In this phase of the work, the aim was to clarify the factors that enhance the formation of the valuable volatile products ("sirups"). For this purpose, the kinetics and mechanism of the biomass pyrolysis were studied with a particular emphasis on the behavior of the cellulose component. Later, the interest of the cooperation gradually shifted to the solid products of the pyrolysis: chars, charcoals, and biocarbons. Hence, the formation, properties, and uses of these products were studied. The present paper illustrates the 3 decades of the common work by selected results. Such examples are shown that (i) are thought to be useful in the planning of future studies on pyrolysis and combustion of biomass materials (ii) and/or may help in the interpretation of the existing literature data. The presented results include the choice of the proper experimental conditions, the evaluation of experiments with linear and nonlinear temperature programs by the method of least squares, the assessment of complex mechanism schemes by a suitable series of experiments, and the kinetic modeling of the combustion of inhomogeneous chars in the kinetic regime
Optical properties of the iron-pnictide analog BaMn2As2
We have investigated the infrared and Raman optical properties of BaMn2As2 in
the ab-plane and along the c-axis. The most prominent features in the infrared
spectra are the Eu and A2u phonon modes which show clear TO-LO splitting from
the energy loss function analysis. All the phonon features we observed in
infrared and Raman spectra are consistent with the calculated values. Compared
to the iron-pnictide analog AFe2As2, this compound is much more two-dimensional
in its electronic properties. For E || c-axis, the overall infrared
reflectivity is insulating like. Within the ab-plane the material exhibits a
semiconducting behavior. An energy gap 2{\Delta}=48 meV can be clearly
identified below room temperature.Comment: 5 pages, 7 figure
Probability distribution of magnetization in the one-dimensional Ising model: Effects of boundary conditions
Finite-size scaling functions are investigated both for the mean-square
magnetization fluctuations and for the probability distribution of the
magnetization in the one-dimensional Ising model. The scaling functions are
evaluated in the limit of the temperature going to zero (T -> 0), the size of
the system going to infinity (N -> oo) while N[1-tanh(J/k_BT)] is kept finite
(J being the nearest neighbor coupling). Exact calculations using various
boundary conditions (periodic, antiperiodic, free, block) demonstrate
explicitly how the scaling functions depend on the boundary conditions. We also
show that the block (small part of a large system) magnetization distribution
results are identical to those obtained for free boundary conditions.Comment: 8 pages, 5 figure
Magnetization distribution in the transverse Ising chain with energy flux
The zero-temperature transverse Ising chain carrying an energy flux j_E is
studied with the aim of determining the nonequilibrium distribution functions,
P(M_z) and P(M_x), of its transverse and longitudinal magnetizations,
respectively. An exact calculation reveals that P(M_z) is a Gaussian both at
j_E=0 and j_E not equal 0, and the width of the distribution decreases with
increasing energy flux. The distribution of the order-parameter fluctuations,
P(M_x), is evaluated numerically for spin-chains of up to 20 spins. For the
equilibrium case (j_E=0), we find the expected Gaussian fluctuations away from
the critical point while the critical order-parameter fluctuations are shown to
be non-gaussian with a scaling function Phi(x)=Phi(M_x/)=P(M_x)
strongly dependent on the boundary conditions. When j_E not equal 0, the system
displays long-range, oscillating correlations but P(M_x) is a Gaussian
nevertheless, and the width of the Gaussian decreases with increasing j_E. In
particular, we find that, at critical transverse field, the width has a
j_E^(-3/8) asymptotic in the j_E -> 0 limit.Comment: 8 pages, 5 ps figure
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