An electron jet pump: The Venturi effect of a Fermi liquid

A three-terminal device based on a two-dimensional electron system is investigated in the regime of non-equilibrium transport. Excited electrons scatter with the cold Fermi sea and transfer energy and momentum to other electrons. A geometry analogous to a water jet pump is used to create a jet pump for electrons. Because of its phenomenological similarity we name the observed behavior "electronic Venturi effect".Comment: Journal of Applied Physics Special Topic: Plenary and Invited Papers from the 30th International Conference on the Physics of Semiconductors, Seoul, Korea, 2010; http://link.aip.org/link/?JAP/109/10241

Relaxation of hot electrons in a degenerate two-dimensional electron system: transition to one-dimensional scattering

The energy relaxation channels of hot electrons far from thermal equilibrium in a degenerate two-dimensional electron system are investigated in transport experiments in a mesoscopic three-terminal device. We observe a transition from two dimensions at zero magnetic field to quasi--one-dimensional scattering of the hot electrons in a strong magnetic field. In the two-dimensional case electron-electron scattering is the dominant relaxation mechanism, while the emission of optical phonons becomes more and more important as the magnetic field is increased. The observation of up to 11 optical phonons emitted per hot electron allows us to determine the onset energy of LO phonons in GaAs at cryogenic temperatures with a high precision, \eph=36.0\pm0.1\,meV. Numerical calculations of electron-electron scattering and the emission of optical phonons underline our interpretation in terms of a transition to one-dimensional dynamics.Comment: 15 pages, 9 figure

Gravitating defects of codimension-two

Thin gravitating defects with conical singularities in higher codimensions and with generalized Israel matching conditions are known to be inconsistent for generic energy-momentum. A way to remove this inconsistency is proposed and is realized for an axially symmetric gravitating codimension-two defect in six dimensional Einstein gravity. By varying with respect to the brane embedding fields, alternative matching conditions are derived, which are generalizations of the Nambu-Goto equations of motion of the defect, consistent with bulk gravity. For a maximally symmetric defect the standard picture is recovered. The four-dimensional perfect fluid cosmology coincides with conventional FRW in the case of radiation, but for dust it has rho^{4/3} instead of rho. A four-dimensional black hole solution is presented having the Schwarzschild form with a short-distance correction r^{-2}.Comment: Minor changes, to appear in Classical and Quantum Gravit

Molecular Investigations of PenA-mediated β-lactam Resistance in Burkholderia pseudomallei

Burkholderia pseudomallei is the etiological agent of melioidosis. Because of the bacterium’s intrinsic resistance and propensity to establish latent infections, melioidosis therapy is complicated and prolonged. Newer generation β-lactams, specifically ceftazidime, are used for acute phase therapy, but resistance to this cephalosporin has been observed. The chromosomally encoded penA gene encodes a putative twin arginine translocase (TAT)-secreted β-lactamase, and penA mutations have been implicated in ceftazidime resistance in clinical isolates. However, the role of PenA in resistance has not yet been systematically studied in isogenetic B. pseudomallei mutant backgrounds. We investigated the effects of penA deletion, point mutations, and up-regulation, as well as tat operon deletion and PenA TAT-signal sequence mutations. These experiments were made possible by employing a B. pseudomallei strain that is excluded from Select Agent regulations. Deletion of penA significantly (>4-fold) reduced the susceptibility to six of the nine β-lactams tested and ≥16-fold for ampicillin, amoxicillin, and carbenicillin. Overexpression of penA by single-copy, chromosomal expression of the gene under control of the inducible Ptac promoter, increased resistance levels for all β-lactams tested 2- to 10-fold. Recreation of the C69Y and P167S PenA amino acid substitutions previously observed in resistant clinical isolates increased resistance to ceftazidime by ≥85- and 5- to 8-fold, respectively. Similarly, a S72F substitution resulted in a 4-fold increase in resistance to amoxicillin and clavulanic acid. Susceptibility assays with PenA TAT-signal sequence and ΔtatABC mutants, as well as Western blot analysis, confirmed that PenA is a TAT secreted enzyme and not periplasmic but associated with the spheroplastic cell fraction. Lastly, we determined that two LysR-family regulators encoded by genes adjacent to penA do not play a role in transcriptional regulation of penA expression

On the Need for Phenomenological Theory of P-Vortices or Does Spaghetti Confinement Pattern Admit Condensed-Matter Analogies?

Usually the intuition from condensed-matter physics is used to provide ideas for possible confinement mechanisms in gauge theories. Today, with a clear but puzzling ``spaghetti'' confinement pattern, arising after a decade of lattice computer experiments, which implies formation of a fluctuating net of peculiar magnetic vortices rather than condensation of the homogeneously distributed magnetic monopoles, the time is coming to reverse the logic and search for similar patterns in condensed matter systems. The main thing to look for in a condensed matter setup is the simultaneous existence of narrow tubes ($P$-vortices or 1-branes) of direction-changing electric field and broader tubes (Abrikosov lines) of magnetic field, a pattern dual to the one, presumably underlying confinement in gluodynamics. As a possible place for this search we suggest systems with coexisting charge-density waves and superconductivity.Comment: 20 pages, 7 figures; to be published in ZhET

Non-local SFT Tachyon and Cosmology

Cosmological scenarios built upon the generalized non-local String Field Theory and $p$-adic tachyons are examined. A general kinetic operator involving an infinite number of derivatives is studied as well as arbitrary parameter $p$. The late time dynamics of just the tachyon around the non-perturbative vacuum is shown to leave the cosmology trivial. A late time behavior of the tachyon and the scale factor of the FRW metric in the presence of the cosmological constant or a perfect fluid with $w>-1$ is constructed explicitly and a possibility of non-vanishing oscillations of the total effective state parameter around the phantom divide is proven.Comment: 17 pages, LaTeX; v2: JHEP3 class is used, references adde

Supergrassmannian and large N limit of quantum field theory with bosons and fermions

We study a large N_{c} limit of a two-dimensional Yang-Mills theory coupled to bosons and fermions in the fundamental representation. Extending an approach due to Rajeev we show that the limiting theory can be described as a classical Hamiltonian system whose phase space is an infinite-dimensional supergrassmannian. The linear approximation to the equations of motion and the constraint yields the 't Hooft equations for the mesonic spectrum. Two other approximation schemes to the exact equations are discussed.Comment: 24 pages, Latex; v.3 appendix added, typos corrected, to appear in JM

Back-Reaction In Lightcone QED

We consider the back-reaction of quantum electrodynamics upon an electric field E(x_+) = - A'_-(x_+) which is parallel to x^3 and depends only on the lightcone coordinate x_+ = (x^0 + x^3)/\sqrt{2}. Novel features are that the mode functions have simple expressions for arbitrary A_-(x_+), and that one cannot ignore the usual lightcone ambiguity at zero + momentum. Each mode of definite canonical momenta k_+ experiences pair creation at the instant when its kinetic momentum p_+=k_+ - e A_-(x_+) vanishes, at which point operators from the surface at x_- =-\infty play a crucial role. Our formalism permits a more explicit and complete derivation of the rate of particle production than is usually given. We show that the system can be understood as the infinite boost limit of the analogous problem of an electric field which is homogeneous on surfaces of constant x^0.Comment: 37 pages, 2 figures, LaTeX 2 epsilo

Brane-bulk energy exchange : a model with the present universe as a global attractor

The role of brane-bulk energy exchange and of an induced gravity term on a single braneworld of negative tension and vanishing effective cosmological constant is studied. It is shown that for the physically interesting cases of dust and radiation a unique global attractor which can realize our present universe (accelerating and 0<Omega_{m0}<1) exists for a wide range of the parameters of the model. For Omega_{m0}=0.3, independently of the other parameters, the model predicts that the equation of state for the dark energy today is w_{DE,0}=-1.4, while Omega_{m0}=0.03 leads to w_{DE,0}=-1.03. In addition, during its evolution, w_{DE} crosses the w_{DE}=-1 line to smaller values.Comment: 8 pages, 2 figures, RevTex; references added, to appear in JHE