The Selberg zeta function for convex co-compact Schottky groups

We give a new upper bound on the Selberg zeta function for a convex co-compact Schottky group acting on ${\mathbb H}^{n+1}$: in strips parallel to the imaginary axis the zeta function is bounded by $\exp (C |s|^\delta)$ where $\delta$ is the dimension of the limit set of the group. This bound is more precise than the optimal global bound $\exp (C |s|^{n+1})$, and it gives new bounds on the number of resonances (scattering poles) of $\Gamma \backslash {\mathbb H}^{n+1}$. The proof of this result is based on the application of holomorphic $L^2$-techniques to the study of the determinants of the Ruelle transfer operators and on the quasi-self-similarity of limit sets. We also study this problem numerically and provide evidence that the bound may be optimal. Our motivation comes from molecular dynamics and we consider $\Gamma \backslash {\mathbb H}^{n+1}$ as the simplest model of quantum chaotic scattering. The proof of this result is based on the application of holomorphic $L^2$-techniques to the study of the determinants of the Ruelle transfer operators and on the quasi-self-similarity of limit sets

A Bose-Einstein Condensate in a Uniform Light-induced Vector Potential

We use a two-photon dressing field to create an effective vector gauge potential for Bose-condensed Rb atoms in the F=1 hyperfine ground state. The dressed states in this Raman field are spin and momentum superpositions, and we adiabatically load the atoms into the lowest energy dressed state. The effective Hamiltonian of these neutral atoms is like that of charged particles in a uniform magnetic vector potential, whose magnitude is set by the strength and detuning of Raman coupling. The spin and momentum decomposition of the dressed states reveals the strength of the effective vector potential, and our measurements agree quantitatively with a simple single-particle model. While the uniform effective vector potential described here corresponds to zero magnetic field, our technique can be extended to non-uniform vector potentials, giving non-zero effective magnetic fields.Comment: 5 pages, submitted to Physical Review Letter

Regulation of Membrane Targeting of the G Protein-coupled Receptor Kinase 2 by Protein Kinase A and Its Anchoring Protein AKAP79

The beta 2 adrenergic receptor (beta 2AR) undergoes desensitization by a process involving its phosphorylation by both protein kinase A (PKA) and G protein-coupled receptor kinases (GRKs). The protein kinase A-anchoring protein AKAP79 influences beta 2AR phosphorylation by complexing PKA with the receptor at the membrane. Here we show that AKAP79 also regulates the ability of GRK2 to phosphorylate agonist-occupied receptors. In human embryonic kidney 293 cells, overexpression of AKAP79 enhances agonist-induced phosphorylation of both the beta 2AR and a mutant of the receptor that cannot be phosphorylated by PKA (beta 2AR/PKA-). Mutants of AKAP79 that do not bind PKA or target to the beta 2AR markedly inhibit phosphorylation of beta 2AR/PKA-. We show that PKA directly phosphorylates GRK2 on serine 685. This modification increases Gbeta gamma subunit binding to GRK2 and thus enhances the ability of the kinase to translocate to the membrane and phosphorylate the receptor. Abrogation of the phosphorylation of serine 685 on GRK2 by mutagenesis (S685A) or by expression of a dominant negative AKAP79 mutant reduces GRK2-mediated translocation to beta 2AR and phosphorylation of agonist-occupied beta 2AR, thus reducing subsequent receptor internalization. Agonist-stimulated PKA-mediated phosphorylation of GRK2 may represent a mechanism for enhancing receptor phosphorylation and desensitization

The Human Pregnancy-Specific Glycoprotein Genes are Tightly Linked on the Long Arm of Chromosome 19 and are Coordinately Expressed

The pregnancy-specific glycoprotein (PSG) genes encode a group of proteins which are found in large amounts in placenta and maternal serum. In situ hybridization analyses of metaphase chromosomes reveal that all the human pregnancy-specific glycoprotein (PSG) genes are located on the long arm of chromosome 19 (19q13.2–13.3), overlapping the region containing the closely-related carcinoembryonic antigen (CEA) gene subgroup. Higher resolution analyses indicate that the PSG genes are closely linked within an 800kb SacII restriction endonuclease fragment. This has been confirmed through restriction endonuclease mapping and DNA sequence analyses of isolated genomic clones, which show that at least some of these genes are located in very close proximity. Further, these studies have helped to identify a new member of the PSG gene sub-family (PSG7). DNA/RNA hybridization analyses, using gene-specific oligonucleotide probes based on published sequences, showed that five from six PSG genes tested are coordinately transcribed in the placenta. Due to the close proximity of these genes and their coordinated expression pattern, common transcriptional regulatory elements may exist

Characterizing the Hofstadter butterfly's outline with Chern numbers

In this work, we report original properties inherent to independent particles subjected to a magnetic field by emphasizing the existence of regular structures in the energy spectrum's outline. We show that this fractal curve, the well-known Hofstadter butterfly's outline, is associated to a specific sequence of Chern numbers that correspond to the quantized transverse conductivity. Indeed the topological invariant that characterizes the fundamental energy band depicts successive stairways as the magnetic flux varies. Moreover each stairway is shown to be labeled by another Chern number which measures the charge transported under displacement of the periodic potential. We put forward the universal character of these properties by comparing the results obtained for the square and the honeycomb geometries.Comment: Accepted for publication in J. Phys. B (Jan 2009

Electro-optical generation and distribution of ultrawideband signals based on the gain switching technique

We demonstrate and compare the generation and distribution of pulse position modulation (PPM) ultrawideband (UWB) signals, based on two different techniques using a gain-switched laser (GSL). One uses a GSL followed by two external modulators, while the second technique employs two laser diodes gain switched (GS) using a combined signal from a pattern generator and an RF signal generator. Bit-error-rate (BER) measurements and eye diagrams for UWB signals have been measured experimentally by using the different GS transmitter configurations and various fiber transmission distances. The simulation of both systems also has been carried out to verify our obtained results, which show the suitability of employing gain switching in a UWB over fiber (UWBoF) system to develop a reliable, simple, and low-cost technique for distributing the impulse-radio UWB (IR-UWB) pulses to the receiver destination

Accelerating universe emergent from the landscape

We propose that the existence of the string landscape suggests the universe can be in a quantum glass state, where an extremely large viscosity is generated, and long distance dynamics slows down. At the same time, the short distance dynamics is not altered due to the separation of time scales. This scenario can help to understand some controversies in cosmology, for example the natural existence of slow roll inflation and dark energy in the landscape, the apparent smallness of the cosmological constant. We see also that moduli stabilization is no longer necessary. We further identify the glass transition point, where the viscosity diverges, as the location of the cosmic horizon. We try to reconstruct the geometry of the accelerating universe from the structure of the landscape, and find that the metric should have an infinite jump when crossing the horizon. We predict that the static coordinate metric for dS space breaks down outside the horizon.Comment: 20 pages, no figures, harvma