By finding measurements that optimally resolve neighboring quantum states, we use statistical distinguishability to define a natural Riemannian metric on the space of quantum-mechanical density ...operators and to formulate uncertainty principles that are more general and more stringent than standard uncertainty principles.
A theoretical description of vortex dynamics in thin flat samples is derived and is found to compare favorably with experimental results. In perpendicular applied magnetic field the vortex ...penetration is delayed significantly due to the presence of a potential barrier of geometrical origin. This novel geometrical barrier effect results in hysteretic magnetization and in the existence of an irreversibility line in the ital absence of bulk pinning. Among the unique characteristics of the barrier are a vortex concentration in the center of the sample and a zero-field peak in the magnetization loops.
The nucleon-nucleon potential obtained from the most general effective chiral Lagrangian involving low momentum pions, nonrelativistic nucleons, and Delta isobars was considered to third order in the ...chiral expansion. The parameters of the potential were adjusted to reproduce the low energy nucleon-nucleon scattering phase shifts as well as the properties of the deuteron. Reasonable fits are obtained in this first application of a nucleon-nucleon potential based on chiral symemtry.
Theoretical ideas and experimental results concerning high-temperature superconductors are reviewed. Special emphasis is given to calculations performed with the help of computers applied to models ...of strongly correlated electrons proposed to describe the two-dimensional CuOsub 2 planes. The review also includes results using several analytical techniques. The one- and three-band Hubbard models and the ital t-ital J model are discussed, and their behavior compared against experiments when available. The author found, among the conclusions of the review, that some experimentally observed unusual properties of the cuprates have a natural explanation through Hubbard-like models. In particular, abnormal features like the mid-infrared band of the optical conductivity sigma(omega), the new states observed in the gap in photoemission experiments, the behavior of the spin correlations with doping, and the presence of phase separation in the copper oxide superconductors may be explained, at least in part, by these models. Finally, the existence of superconductivity in Hubbard-like models is analyzed. Some aspects of the recently proposed ideas to describe the cuprates as having a ital dsub ital xsup 2-ital ysup 2 superconducting condensate at low temperatures are discussed. Numerical results favor this scenario over others. It is concluded that computational techniques provide a useful, unbiased tool for studying the difficult regime where electrons are strongly interacting, and that considerable progress can be achieved by comparing numerical results against analytical predictions for the properties of these models. Future directions of the active field of computational studies of correlated electrons are briefly discussed.
We introduce a class of stochastic process, the ital truncated Levy flight (TLF), in which the arbitrarily large steps of a Levy flight are eliminated. We find that the convergence of the sum of ital ...n independent TLFs to a Gaussian process can require a remarkably large value of ital n---typically ital napprox10sup 4 in contrast to ital napprox10 for common distributions. We find a well-defined crossover between a Levy and a Gaussian regime, and that the crossover carries information about the relevant parameters of the underlying stochastic process.
The critical micellization temperature (cmt) and critical micellization concentration (cmc) values of 12 Pluronic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block ...copolymers, covering a wide range of molecular weights (2,900--14,600) and PPO/PEO ratios (0.19--1.79), were determined employing a dye solubilization method. A closed association model was found to describe adequately the copolymer micellization process for the majority of the Pluronics and used to obtain the standard free energies (DeltaGdegree), enthalpies (DeltaHdegree), and entropies (DeltaSdegree) of micellization. It was determined that the micellization process is entropy-driven and has an endothermic micellization enthalpy. The hydrophobic part of the Pluronics, PPO, was responsible for the micellization, apparently due to diminishing hydrogen bonding between water and PPO with increasing temperature. The cmc dependence on temperature and size of headgroup (PEO) of Pluronics follows a similar trend with lower molecular weight Csub iEsub j nonionic surfactants, the effect of temperature being more pronounced with the Pluronics. The PEO-PPO-PEO block copolymers were compared to PPO-PEO-PPO block and PEO-PPO random copolymers, in an attempt to probe the effect of molecular architecture in the formation of micelles. No micelles were observed in aqueous PPO-PEO-PPO block copolymer solutions with increasing temperature, up to the cloud point.
Hybridization of the sigmasup * and pisup * states of the graphene network is shown to be as important as band-folding effects in determining the metallicity of small radius carbon nanotubes. Using ...detailed plane-wave ital ab ital initio pseudopotential local density functional (LDA) calculations, we find that the electronic properties of small tubes are significantly altered from those obtained in previous tight-binding calculations. Strongly modified low-lying conduction band states are introduced into the band gap of insulating tubes because of strong sigmasup *-pisup * hybridization. As a result, the LDA gaps of some tubes are lowered by more than 50%, and a tube previously predicted to be semiconducting is shown to be metallic.
The production of Hesup + and Hesup 2+ by a 160 fs, 780 nm laser has been measured over an unprecedented 12 orders of magnitude in counting range. Enhanced double electron emission, called ...nonsequential (NS) ionization, was observed over an intensity range where the single ionization dynamics is evolving from multiphoton to pure tunneling. The NS yield is found to scale with the ac-tunneling rate for the neutral, even when tunneling is not the dominant ionization pathway. A rescattering mechanism fails to predict the observed NS threshold or magnitude.
Optical sum-frequency generation was used to study OH stretch vibrations of water molecules at fused quartz-water interfaces. The results indicate that orientations and bond ordering of interfacial ...water molecules are strongly affected by electrostatic interaction and hydrogen bonding of the molecules with the quartz surface.
Quantum wave function of a chaotic system spreads rapidly over distances on which the potential is significantly nonlinear. As a result, the effective force is no longer just a gradient of the ...potential, and predictions of classical and quantum dynamics begin to differ. We show how the interaction with the environment limits distances over which quantum coherence can persist, and therefore reconciles quantum dynamics with classical Hamiltonian chaos. The entropy production rate for such open chaotic systems exhibits a sharp transition between reversible and dissipative regimes, where it is set by the chaotic dynamics.
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