Reflectionless Tunneling Through a Double-Barrier NS Junction

The resistance is computed of an ${\rm NI}_{1}{\rm NI}_{2}{\rm S}$ junction, where N = normal metal, S = superconductor, and ${\rm I}_{i}$ = insulator or tunnel barrier (transmission probability per mode $\Gamma_{i}$). The ballistic case is considered, as well as the case that the region between the two barriers contains disorder (mean free path $l$, barrier separation $L$). It is found that the resistance at fixed $\Gamma_{2}$ shows a {\em minimum} as a function of $\Gamma_{1}$, when $\Gamma_{1}\approx\sqrt{2}\Gamma_{2}$, provided $l\gtrsim\Gamma_2 L$. The minimum is explained in terms of the appearance of transmission eigenvalues close to one, analogous to the ``reflectionless tunneling'' through a NIS junction with a disordered normal region. The theory is supported by numerical simulations. ***Submitted to Physica B.***Comment: 10 pages, REVTeX-3.0, 6 postscript figures appended as self-extracting archive, INLO-PUB-940607

Giant Gravitons - with Strings Attached (III)

We develop techniques to compute the one-loop anomalous dimensions of operators in the ${\cal N}=4$ super Yang-Mills theory that are dual to open strings ending on boundstates of sphere giant gravitons. Our results, which are applicable to excitations involving an arbitrary number of open strings, generalize the single string results of hep-th/0701067. The open strings we consider carry angular momentum on an S$^3$ embedded in the S$^5$ of the AdS$_5\times$S$^5$ background. The problem of computing the one loop anomalous dimensions is replaced with the problem of diagonalizing an interacting Cuntz oscillator Hamiltonian. Our Cuntz oscillator dynamics illustrates how the Chan-Paton factors for open strings propagating on multiple branes can arise dynamically.Comment: 66 pages; v2: improved presentatio

Toward Open-Closed String Theoretical Description of Rolling Tachyon

We consider how the time-dependent decay process of an unstable D-brane should be described in the full (quantum) open-closed string theory. It is argued that the system, starting from the unstable D-brane configuration, will evolve in time into the time-independent open string tachyon vacuum configuration which we assume to be finite, with the total energy conserved. As a concrete realization of this idea, we construct a toy model describing the open and closed string tachyons which admits such a time-dependent solution. The structure of our model has some resemblance to that of open-closed string field theory.Comment: 1+10 pages, 6 figures. v2: a reference adde

Non-critical, near extremal AdS_6 background as a holographic laboratory of four dimensional YM theory

We study certain properties of the low energy regime of a theory which resembles four dimensional YM theory in the framework of a non-critical holographic gravity dual. We use for the latter the near extremal $AdS_6$ non-critical SUGRA. We extract the glueball spectra that associates with the fluctuations of the dilaton, one form and the graviton and compare the results to those of the critical near extremal $D4$ model and lattice simulations. We show an area law behavior for the Wilson loop and screening for the 't Hooft loop. The Luscher term is found to be $-{3/24}\frac {\pi}{L}$. We derive the Regge trajectories of glueballs associated with the spinning folded string configurations.Comment: 25 pages, JHEP styl

Relationship between work rate and oxygen uptake in mitochondrial myopathy during ramp-incremental exercise

We determined the response characteristics and functional correlates of the dynamic relationship between the rate (Δ) of oxygen consumption ( O2) and the applied power output (work rate = WR) during ramp-incremental exercise in patients with mitochondrial myopathy (MM). Fourteen patients (7 males, age 35.4 ± 10.8 years) with biopsy-proven MM and 10 sedentary controls (6 males, age 29.0 ± 7.8 years) took a ramp-incremental cycle ergometer test for the determination of the O2 on-exercise mean response time (MRT) and the gas exchange threshold (GET). The ΔO2/ΔWR slope was calculated up to GET (S1), above GET (S2) and over the entire linear portion of the response (S T). Knee muscle endurance was measured by isokinetic dynamometry. As expected, peak O2 and muscle performance were lower in patients than controls (P O2/ΔWR than controls, especially the S2 component (6.8 ± 1.5 vs 10.3 ± 0.6 mL·min-1·W-1, respectively; P O2/ΔWR (S T) and muscle endurance, MRT-O2, GET and peak O2 in MM patients (P O2/ΔWR below 8 mL·min-1·W-1 had severely reduced peak O2 values (O2) had lower ΔO2/ΔWR (P O2/ΔWR) is typically reduced in patients with MM, being related to increased functional impairment and higher cardiopulmonary stress

Controlled transport of solitons and bubbles using external perturbations

We investigate generalized soliton-bearing systems in the presence of external perturbations. We show the possibility of the transport of solitons using external waves, provided the waveform and its velocity satisfy certain conditions. We also investigate the stabilization and transport of bubbles using external perturbations in 3D-systems. We also present the results of real experiments with laser-induced vapor bubbles in liquids.Comment: 26 pages, 24 figure

On the statistical significance of the conductance quantization

Recent experiments on atomic-scale metallic contacts have shown that the quantization of the conductance appears clearly only after the average of the experimental results. Motivated by these results we have analyzed a simplified model system in which a narrow neck is randomly coupled to wide ideal leads, both in absence and presence of time reversal invariance. Based on Random Matrix Theory we study analytically the probability distribution for the conductance of such system. As the width of the leads increases the distribution for the conductance becomes sharply peaked close to an integer multiple of the quantum of conductance. Our results suggest a possible statistical origin of conductance quantization in atomic-scale metallic contacts.Comment: 4 pages, Tex and 3 figures. To be published in PR

Rotating Strings with Two Unequal Spins in Lunin-Maldacena Background

We study a string motion in the Lunin-Maldacena background, that is, the \beta-deformed AdS_5 \times \tilde{S}^5 background dual to a \beta-deformation of \mathcal{N} = 4 super Yang-Mills theory. For real \beta we construct a rotating and wound string solution which has two unequal spins in \tilde{S}^5. The string energy is expressed in terms of the spins, the winding numbers and the deformation parameter. In the expansion of \lambda/J^2 with the total spin J and the string tension \sqrt{\lambda} we present ``one-loop" and ``two-loop" energy corrections. The ``one-loop" one agrees with the one-loop anomalous dimension of the corresponding gauge-theory scalar operators obtained in hep-th/0503192 from the \beta-deformed Bethe equation as well as the anisotropic Landau-Lifshitz equation.Comment: 13 pages, LaTeX, no figure