Macroscopic electrostatic potentials and interactions in self-assembled molecular bilayers: the case of Newton black films

We propose a very simple but 'realistic' model of amphiphilic bilayers,simple enough to be able to include a large number of molecules in the sample, but nevertheless detailed enough to include molecular charge distributions, flexible amphiphilic molecules and a reliable model of water. All these parameters are essential in a nanoscopic scale study of intermolecular and long range electrostatic interactions. We also propose a novel, simple and more accurate macroscopic electrostatic field for model bilayers. This model goes beyond the total dipole moment of the sample, which on a time average is zero for this type of symmetrical samples, i. e., it includes higher order moments of this macroscopic electric field. We show that by representing it with a superposition of gaussians it can be 'analytically' integrated, and therefore its calculation is easily implemented in a MD simulation (even in simulations of non-symmetrical bi- or multi-layers). In this paper we test our model by molecular dynamics simulations of Newton black films

Temporal and diffraction effects in entanglement creation in an optical cavity

A practical scheme for entanglement creation between distant atoms located inside a single-mode optical cavity is discussed. We show that the degree of entanglement and the time it takes for the entanglement to reach its optimum value is a sensitive function the initial conditions and the position of the atoms inside the cavity mode. It is found that the entangled properties of the two atoms can readily be extracted from dynamics of a simple two-level system. Effectively, we engineer two coupled qubits whose the dynamics are analogous to that of a driven single two-level system. It is found that spatial variations of the coupling constants actually help to create transient entanglement which may appear on the time scale much longer than that predicted for the case of equal coupling constants. When the atoms are initially prepared in an entangled state, they may remain entangled for all times. We also find that the entanglement exhibits an interesting phenomenon of diffraction when the the atoms are located between the nodes and antinodes of the cavity mode. The diffraction pattern of the entanglement varies with time and we explain this effect in terms of the quantum property of complementarity, which is manifested as a tradeoff between the knowledge of energy of the exchanged photon versus the evolution time of the system.Comment: Phys. Rev. A75, 042307 (2007

Defining Textual Entailment

Textual entailment is a relationship that obtains between fragments of text when one fragment in some sense implies the other fragment. The automation of textual entailment recognition supports a wide variety of text-based tasks, including information retrieval, information extraction, question answering, text summarization, and machine translation. Much ingenuity has been devoted to developing algorithms for identifying textual entailments, but relatively little to saying what textual entailment actually is. This article is a review of the logical and philosophical issues involved in providing an adequate definition of textual entailment. We show that many natural definitions of textual entailment are refuted by counterexamples, including the most widely cited definition of Dagan et al. We then articulate and defend the following revised definition: T textually entails H = df typically, a human reading T would be justified in inferring the proposition expressed by H from the proposition expressed by T. We also show that textual entailment is context-sensitive, nontransitive, and nonmonotonic

Electrolytes between dielectric charged surfaces: Simulations and theory

We present a simulation method to study electrolyte solutions in a dielectric slab geometry using a modified 3D Ewald summation. The method is fast and easy to implement, allowing us to rapidly resum an infinite series of image charges. In the weak coupling limit, we also develop a mean-field theory which allows us to predict the ionic distribution between the dielectric charged plates. The agreement between both approaches, theoretical and simulational, is very good, validating both methods. Examples of ionic density profiles in the strong electrostatic coupling limit are also presented. Finally, we explore the confinement of charge asymmetric electrolytes between neutral surfaces

Small-q electron-phonon scattering and linear dc resistivity in high-T_c oxides

We examine the effect on the DC resistivity of small-q electron-phonon scattering, in a system with the electronic topology of the high-T_c oxides. Despite the fact that the scattering is dominantly forward, its contribution to the transport can be significant due to ``ondulations'' of the bands in the flat region and to the umpklapp process. When the extended van-Hove singularities are sufficiently close to $E_F$ the acoustic branch of the phonons contribute significantly to the transport. In that case one can obtain linear $T$ dependent resistivity down to temperatures as low as 10 K, even if electrons are scattered also by optical phonons of about 500 K as reported by Raman measurements.Comment: LATEX file and 4 Postscript figure

Gauge Boson Exchange in AdSd+1AdS_{d+1}

We study the amplitude for exchange of massless gauge bosons between pairs of massive scalar fields in Anti-de Sitter space. In the AdS/CFT correspondence this amplitude describes the contribution of conserved flavor symmetry currents to 4-point functions of scalar operators in the boundary conformal theory. A concise, covariant (Y2K-compatible) derivation of the gauge boson propagator in \AdS_{d+1} is given. Techniques are developed to calculate the two bulk integrals over AdS space leading to explicit expressions or convenient, simple integral representations for the amplitude. The amplitude contains leading power and sub-leading logarithmic singularities in the gauge boson channel and leading logarithms in the crossed channel. The new methods of this paper are expected to have other applications in the study of the Maldacena conjecture.Comment: Corrections in (3.17) and (4.23); version to be published in Nuclear Physics B; 22 pages, 1 figure, using Plain TeX and BoxedEPS macros; email to [email protected]

Magnetic field-induced spectroscopy of forbidden optical transitions with application to lattice-based optical atomic clocks

We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method -- a single clock laser combined with a DC magnetic field-- relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10^-17 for the metrologically preferred even isotopes