Microscopic origin of the conducting channels in metallic atomic-size contacts

We present a theoretical approach which allows to determine the number and orbital character of the conducting channels in metallic atomic contacts. We show how the conducting channels arise from the atomic orbitals having a significant contribution to the bands around the Fermi level. Our theory predicts that the number of conducting channels with non negligible transmission is 3 for Al and 5 for Nb one-atom contacts, in agreement with recent experiments. These results are shown to be robust with respect to disorder. The experimental values of the channels transmissions lie within the calculated distributions.Comment: 11 pages, 4 ps-figures. Submitted to Phys. Rev. Let

Single-channel transmission in gold one-atom contacts and chains

We induce superconductivity by proximity effect in thin layers of gold and study the number of conduction channels which contribute to the current in one-atom contacts and atomic wires. The atomic contacts and wires are fabricated with a Scanning Tunneling Microscope. The set of transmission probabilities of the conduction channels is obtained from the analysis of the $I(V)$ characteristic curve which is highly non-linear due to multiple Andreev reflections. In agreement with theoretical calculations we find that there is only one channel which is almost completely open.Comment: 4 pages, 2 figures. To be published in Phys. Rev. B, Rapid Communications (2003

Effects of sports drinks on the maintenance of physical performance during 3 tennis matches: A randomized controlled study

Background: Tennis tournaments often involve playing several consecutive matches interspersed with short periods of recovery. Objective: The objective of this study was firstly to assess the impact of several successive tennis matches on the physical performance of competitive players and secondly to evaluate the potential of sports drinks to minimize the fatigue induced by repeated matches. Methods: This was a crossover, randomized controlled study. Eight male regionally-ranked tennis players participated in this study. Players underwent a series of physical tests to assess their strength, speed, power and endurance following the completion of three tennis matches each of two hours duration played over three consecutive half-days (1.5 day period for each condition). In the first condition the players consumed a sports drink before, during and after each match; in the second, they drank an identical volume of placebo water. The results obtained were compared with the third 'rest' condition in which the subjects did not play any tennis. Main outcomes measured were maximal isometric strength and fatigability of knee and elbow extensors, 20-m sprint speed, jumping height, specific repeated sprint ability test and hand grip strength. Results: The physical test results for the lower limbs showed no significant differences between the three conditions. Conversely, on the upper limbs the EMG data showed greater fatigue of the triceps brachii in the placebo condition compared to the rest condition, while the ingestion of sports drinks attenuated this fatigue. Conclusions: This study has demonstrated for the first time that, when tennis players are adequately hydrated and ingest balanced meals between matches, then no large drop in physical performance is observed even during consecutive competitive matches

From favorable atomic configurations to supershell structures: a new interpretation of conductance histograms

Title: From favorable atomic configurations to supershell structures: a new interpretation of conductance histograms Authors: A. Hasmy (IVIC), E. Medina (IVIC), P.A. Serena (CSIC,IVIC) Comments: 7 pages, 3 figures, cond-mat.anwar.10825 Subj-class: Soft Condensed MatterComment: 7 pages, 3 figuresSubject: fput HMS.tex HMS-FIG1.ps HMS-FIG2.ps HMS-FIG3.p

Point-contact spectroscopy on URu2_2Si2_2

Tunnel and point contact experiments have been made in a URu$_2$Si$_2$ single crystal along the c-axis. The experiments were performed changing temperature and contact size in a low temperature scanning tunneling microscope. A resonance develops at the Fermi level at $T\sim 60$ K. This resonance splits and becomes asymmetric when the 17.5 K phase transition is crossed. These results are consistent with the existence of Kondo like bound states of the U$^{4+}$ ionic configurations and the conduction electrons. Below the transition, these configurations are split by the development of quadrupolar ordering. The peak separation can be interpreted as a direct measurement of the order parameter. Measurements on a policrystalline UAu_2Si_2$ sample are also reported, with a comparative study of the behavior of both materials.Comment: 4 pages (Latex) + 2 postscript figure

Connective neck evolution and conductance steps in hot point contacts

Dynamic evolution of the connective neck in Al and Pb mechanically controllable break junctions was studied during continuous approach of electrodes at bias voltages V_b up to a few hundred mV. A high level of power dissipation (10^-4 - 10^-3 W) and high current density (j > 10^10 A/cm^2) in the constriction lead to overheating of the contact area, electromigration and current-enhanced diffusion of atoms out of the "hot spot". At a low electrode approach rate (10 - 50 pm/s) the transverse dimension of the neck and the conductance of the junction depend on V_b and remain nearly constant over the approach distance of 10 - 30 nm. For V_b > 300 mV the connective neck consists of a few atoms only and the quantum nature of conductance manifests itself in abrupt steps and reversible jumps between two or more levels. These features are related to an ever changing number of individual conductance channels due to the continuous rearrangement in atomic configuration of the neck, the recurring motion of atoms between metastable states, the formation and breaking of isolated one-atom contacts and the switching between energetically preferable neck geometries.Comment: 21 pages 10 figure

Pull-in control in microswitches using acoustic Casimir forces

In this paper we present a theoretical calculation of the acoustic Casimir pressure in a model micro system. Unlike the quantum case, the acoustic Casimir pressure can be made attractive or repulsive depending on the frequency bandwidth of the acoustic noise. As a case study, a one degree of freedom simple-lumped system in an acoustic resonant cavity is considered. We show that the frequency bandwidth of the acoustic field can be tuned to increase the stability in existing microswitch systems by selecting the sign of the force. The acoustic intensity and frequency bandwidth are introduced as two additional control parameters of the microswitch

Canonical quantization of electromagnetism in spatially dispersive media

Copyright © 2014 IOP PublishingOpen Access JournalWe find the action that describes the electromagnetic field in a spatially dispersive, homogeneous medium. This theory is quantized and the Hamiltonian is diagonalized in terms of a continuum of normal modes. It is found that the introduction of nonlocal response in the medium automatically regulates some previously divergent results, and we calculate a finite value for the intensity of the electromagnetic field at a fixed frequency within a homogeneous medium. To conclude we discuss the potential importance of spatial dispersion in taming the divergences that arise in calculations of Casimir-type effects.EPSR

Recuperación y conservación de cultivares tradicionales de melón castellano-manchego

Los trabajos realizados han sido financiados por el proyecto INIARF2008-00003-C02.Ribas, F.; Cabello, M.; Castellanos, MT.; Fita, A.; Roig Montaner, MC.; Nuez Viñals, F.; Picó Sirvent, MB. (2011). Recuperación y conservación de cultivares tradicionales de melón castellano-manchego. Agrícola Vergel. 347:206-213. http://hdl.handle.net/10251/49390S20621334

Long-term benefits of nevirapine-containing regimens: multicenter study with 506 patients, followed-up a median of 9 years

[Abstract] OBJECTIVE: To evaluate long-term outcomes in patients maintaining a nevirapine (NVP)-based regimen. METHODS: Retrospective, multicenter, cohort study including patients currently receiving an NVP regimen that had been started at least 5 years previously. Demographic, clinical, and analytical variables were recorded. RESULTS: Median follow-up was 8.9 (5.7-11.3) years. Baseline characteristics: 74% men, 47 years old, 36% drug users, 40% AIDS, 40% HCV+, 51.4% detectable HIV-1 viral load, CD4 count 395 (4-1,421)/μL, 19% CD4 3.37 mmol/L significantly decreased in a subsample with available values. A significant decrease in transaminases, alkaline phosphatase, and Fib4 score was observed, mainly in HCV+ and ARV-naive patients. CONCLUSIONS: In patients who tolerate NVP therapy, (even those with HCV coinfection), long term benefits may be significant in terms of a progressive improvement in general health status markers and CD4 response, a favorable lipid profile, and good liver tolerability