Bright and dark breathers in Fermi-Pasta-Ulam lattices

In this paper we study the existence and linear stability of bright and dark breathers in one-dimensional FPU lattices. On the one hand, we test the range of validity of a recent breathers existence proof [G. James, {\em C. R. Acad. Sci. Paris}, 332, Ser. 1, pp. 581 (2001)] using numerical computations. Approximate analytical expressions for small amplitude bright and dark breathers are found to fit very well exact numerical solutions even far from the top of the phonon band. On the other hand, we study numerically large amplitude breathers non predicted in the above cited reference. In particular, for a class of asymmetric FPU potentials we find an energy threshold for the existence of exact discrete breathers, which is a relatively unexplored phenomenon in one-dimensional lattices. Bright and dark breathers superposed on a uniformly stressed static configuration are also investigated.Comment: 11 pages, 16 figure

Breathers in FPU systems, near and far from the phonon band

There exists a recent mathematical proof on the existence of small amplitude breathers in FPU systems near the phonon band, which includes a prediction of their amplitude and width. In this work we obtain numerically these breathers, and calculate the range of validity of the predictions, which extends relatively far from the phonon band. There exist also large amplitude breathers with the same frequency, with the consequence that there is an energy gap for breather creation in these systems.Comment: 3 pages, 2 figures, proceeding of the conference on Localization and to and Energy Transfer in Nonlinear Systems, June 17-21, 2002, San Lorenzo de El Escorial, Madrid, Spain. To be published by World Scientifi

Numerical Simulation of III-V Solar Cells Using D-AMPS

Numerical simulation of devices plays a crucial role in their design, performance prediction, and comprehension of the fundamental phenomena ruling their operation. Here, we present results obtained using the code D-AMPS-1D, that was conveniently modified to consider the particularities of III-V solar cell devices. This work, that is a continuation of a previous paper regarding solar cells for space applications, is focused on solar cells structures than find application for terrestrial use under concentrated solar illumination. The devices were fabricated at the Solar Energy Institute of the Technical University of Madrid (UPM). The first simulations results on InGaP cells are presented. The influence of band offsets and band bending at the window-emitter interface on the quantum efficiency was studied. A remarkable match of the experimental quantum efficiency was obtained. Finally, numerical simulation of single junction n-p InGaP-Ge solar cells was performed

Phase transitions, entanglement and quantum noise interferometry in cold atoms

We show that entanglement monotones can characterize the pronounced enhancement of entanglement at a quantum phase transition if they are sensitive to long-range high order correlations. These monotones are found to develop a sharp peak at the critical point and to exhibit universal scaling. We demonstrate that similar features are shared by noise correlations and verify that these experimentally accessible quantities indeed encode entanglement information and probe separability.Comment: 4 pages 4 figure

Comment on "High Field Studies of Superconducting Fluctuations in High-Tc Cuprates. Evidence for a Small Gap distinct from the Large Pseudogap"

By using high magnetic field data to estimate the background conductivity, Rullier-Albenque and coworkers have recently published [Phys.Rev.B 84, 014522 (2011)] experimental evidence that the in-plane paraconductivity in cuprates is almost independent of doping. In this Comment we also show that, in contrast with their claims, these useful data may be explained at a quantitative level in terms of the Gaussian-Ginzburg-Landau approach for layered superconductors, extended by Carballeira and coworkers to high reduced-temperatures by introducing a total-energy cutoff [Phys.Rev.B 63, 144515 (2001)]. When combined, these two conclusions further suggest that the paraconductivity in cuprates is conventional, i.e., associated with fluctuating superconducting pairs above the mean-field critical temperature.Comment: 9 pages, 1 figur

Topology of the Universe: background and recent observational approaches

Is the Universe (a spatial section thereof) finite or infinite? Knowing the global geometry of a Friedmann-Lema\^{\i}tre (FL) universe requires knowing both its curvature and its topology. A flat or hyperbolic (``open'') FL universe is {\em not} necessarily infinite in volume. Multiply connected flat and hyperbolic models are, in general, as consistent with present observations on scales of 1-20{\hGpc} as are the corresponding simply connected flat and hyperbolic models. The methods of detecting multiply connected models (MCM's) are presently in their pioneering phase of development and the optimal observationally realistic strategy is probably yet to be calculated. Constraints against MCM's on ~1-4 h^{-1} Gpc scales have been claimed, but relate more to inconsistent assumptions on perturbation statistics rather than just to topology. Candidate 3-manifolds based on hypothesised multiply imaged objects are being offered for observational refutation. The theoretical and observational sides of this rapidly developing subject have yet to make any serious contact, but the prospects of a significant detection in the coming decade may well propel the two together.Comment: 5 pages, proceedings of the Workshop ``Cosmology: Observations Confront Theories,'' 11-17 Jan 1999, IIT Kharagpur, West Bengal, to appear in Pramana - Journal of Physic

Water Buffalo (Bubalus bubalis) and their Technological Advantages for the Design in Healthy Meat Product

Current trends in the formulation for new food shows that healthy or “functional†products are graduallyincreasing their participation in the preference of the consumers (Catalá Ramón). Nowadays, the participation of meatproducts in this behavior of the marketing is not growing at the same rate, because their ingredients and nutritionalcompounds, like saturated fats, which are rejected by consumers. But, a group of investigators from La Salle University(Universidad De La Salle, Bogotá, Colombia), have been working hard, in order to obtain healthier meat products, usingBufalo as the main raw material, because its important properties like 15 to 35% of protein, 40% more water holdingcapacity (CRA, in Spanish) and 30% more emulsifying capacity (CE in Spanish). Previous values are compared with rawbeef. The group, who has developed a functional buffalo meat product, added vegetal oil from soybeans and dehydratedhemoglobin to its formulation and obtained a food with 70% less of saturated fat and a significantly increase of iron,without affecting the non-saturated fat compound of the food. Now, a functional product packed in a "smart packaging" has been studied, in order to increase its shelf life, supported on positive migration process

Design of an RSFQ Control Circuit to Observe MQC on an rf-SQUID

We believe that the best chance to observe macroscopic quantum coherence (MQC) in a rf-SQUID qubit is to use on-chip RSFQ digital circuits for preparing, evolving and reading out the qubit's quantum state. This approach allows experiments to be conducted on a very short time scale (sub-nanosecond) without the use of large bandwidth control lines that would couple environmental degrees of freedom to the qubit thus contributing to its decoherence. In this paper we present our design of a RSFQ digital control circuit for demonstrating MQC in a rf-SQUID. We assess some of the key practical issues in the circuit design including the achievement of the necessary flux bias stability. We present an "active" isolation structure to be used to increase coherence times. The structure decouples the SQUID from external degrees of freedom, and then couples it to the output measurement circuitry when required, all under the active control of RSFQ circuits. Research supported in part by ARO grant # DAAG55-98-1-0367.Comment: 4 pages. More information and publications at http://www.ece.rochester.edu:8080/users/sde/research/publications/index.htm