6,861 research outputs found
Initial static susceptibilities of nonuniform and random Ising chains
Within the conventional framework of standard linear response theory we have
derived exact results for the initial static susceptibilities of nonuniform
spin-1/2 Ising chains. The results obtained permit one to study regularly
alternating-bond and random-bond Ising chains. The influence of several types
of nonuniformity and disorder on the temperature dependence of the initial
longitudinal and transverse static susceptibilities is discussed.Comment: LaTeX, 7 figure
Most robust and fragile two-qubit entangled states under depolarizing channels
For a two-qubit system under local depolarizing channels, the most robust and
most fragile states are derived for a given concurrence or negativity. For the
one-sided channel, the pure states are proved to be the most robust ones, with
the aid of the evolution equation for entanglement given by Konrad et al. [Nat.
Phys. 4, 99 (2008)]. Based on a generalization of the evolution equation for
entanglement, we classify the ansatz states in our investigation by the amount
of robustness, and consequently derive the most fragile states. For the
two-sided channel, the pure states are the most robust for a fixed concurrence.
Under the uniform channel, the most fragile states have the minimal negativity
when the concurrence is given in the region [1/2,1]. For a given negativity,
the most robust states are the ones with the maximal concurrence, and the most
fragile ones are the pure states with minimum of concurrence. When the
entanglement approaches zero, the most fragile states under general nonuniform
channels tend to the ones in the uniform channel. Influences on robustness by
entanglement, degree of mixture, and asymmetry between the two qubits are
discussed through numerical calculations. It turns out that the concurrence and
negativity are major factors for the robustness. When they are fixed, the
impact of the mixedness becomes obvious. In the nonuniform channels, the most
fragile states are closely correlated with the asymmetry, while the most robust
ones with the degree of mixture.Comment: 10 pages, 9 figs. to appear in Quantum Information & Computation
(QIC
Theoretical models for duct acoustic propagation and radiation
The development of computational methods in acoustics has led to the introduction of analysis and design procedures which model the turbofan inlet as a coupled system, simultaneously modeling propagation and radiation in the presence of realistic internal and external flows. Such models are generally large, require substantial computer speed and capacity, and can be expected to be used in the final design stages, with the simpler models being used in the early design iterations. Emphasis is given to practical modeling methods that have been applied to the acoustical design problem in turbofan engines. The mathematical model is established and the simplest case of propagation in a duct with hard walls is solved to introduce concepts and terminologies. An extensive overview is given of methods for the calculation of attenuation in uniform ducts with uniform flow and with shear flow. Subsequent sections deal with numerical techniques which provide an integrated representation of duct propagation and near- and far-field radiation for realistic geometries and flight conditions
Analysis of crosstalk and field coupling to lossy MTL's in a SPICE environment
This paper proposes a circuit model for lossy multiconductor transmission lines (MTLs) suitable for implementation in modern SPICE simulators, as well as in any simulator supporting differential operators. The model includes the effects of a uniform or nonuniform disturbing field illuminating the line and is especially devised for the transient simulation of electrically long wideband interconnects with frequency dependent per-unit-length parameters. The MTL is characterized by its transient matched scattering responses, which are computed including both dc and skin losses by means of a specific algorithm for the inversion of the Laplace transform. The line characteristics are then represented in terms of differential operators and ideal delays to improve the numerical efficiency and to simplify the coding of the model in existing simulators. The model can be successfully applied to many kinds of interconnects ranging from micrometric high-resistivity metallizations to low-loss PCBs and cables, and can be considered a practical extension of the widely appreciated lossless MTL SPICE model, which maintains the simplicity and efficienc
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