Improved bounds on the set A(A+1)

For a subset A of a field F, write A(A + 1) for the set {a(b + 1):a,b\in A}. We establish new estimates on the size of A(A+1) in the case where F is either a finite field of prime order, or the real line. In the finite field case we show that A(A+1) is of cardinality at least C|A|^{57/56-o(1)} for some absolute constant C, so long as |A| < p^{1/2}. In the real case we show that the cardinality is at least C|A|^{24/19-o(1)}. These improve on the previously best-known exponents of 106/105-o(1) and 5/4 respectively

Stellar Populations in Ten Clump-Cluster Galaxies of the Ultra Deep Field

Color-color diagrams for the clump and interclump emission in 10 clump-cluster galaxies of the Ultra Deep Field are made from B,V,i, and z images and compared with models to determine redshifts, star formation histories, and galaxy masses. The clump colors suggest declining star formation over the last ~0.3 Gy, while the interclump emission is older. The clump luminous masses are typically 6x10^8 Msun and their diameters average 1.8 kpc. Total galaxy luminous masses average 6.5x10^10 Msun. The distribution of axial ratios is consistent with a thick disk geometry. The ages of the clumps are longer than their internal dynamical times by a factor of ~8, so they are stable clusters, but the clump densities are only ~10 times the limiting tidal densities, so they could be deformed by tidal forces. This is consistent with the observation that some clumps have tails. The clumps could form by gravitational instabilities in accreting disk gas, or they could be captured as gas-rich dwarf galaxies. Support for this second possibility comes from the high abundance of nearly identical bare clumps in the UDF field. Several clump-clusters have disk densities that are much larger than in local disks, suggesting they do not survive but get converted into ellipticals by collisions.Comment: 34 pgs, including 12 figures, accepted by Astrophysical Journal for 20 July 2005 v.62

Near-infrared and Millimeter Constraints on the Nuclear Energy Source of the Infrared Luminous Galaxy NGC 4418

We present near-infrared and millimeter investigations of the nucleus of the infrared luminous galaxy NGC 4418, which previous observations suggest possesses a powerful buried AGN. We found the following main results: (1) The infrared K-band spectrum shows CO absorption features at 2.3-2.4 micron owing to stars and very strong H2 emission lines. The luminosity ratios of H2 emission lines are suggestive of a thermal origin, and the equivalent width of the H2 1-0 S(1) line is the second largest observed to date in an external galaxy, after the well-studied strong H2-emitting galaxy NGC 6240. (2) The infrared L-band spectrum shows a clear polycyclic aromatic hydrocarbon (PAH) emission feature at 3.3 micron, which is usually found in star-forming galaxies. The estimated star-formation luminosity from the observed PAH emission can account for only a small fraction of the infrared luminosity. (3) Millimeter interferometric observations of the nucleus reveal a high HCN (1-0) to HCO+ (1-0) luminosity ratio of 1.8, as has been previously found in pure AGNs. (4) The measurements of HCN (1-0) luminosity using a single-dish millimeter telescope show that the HCN (1-0) to infrared luminosity ratio is slightly larger than the average, but within the scattered range, for other infrared luminous galaxies. All of these results can be explained by the scenario in which, in addition to energetically-insignificant, weakly-obscured star-formation at the surface of the nucleus, a powerful X-ray emitting AGN deeply buried in dust and high density molecular gas is present.Comment: 31 pages, 9 figures, Accepted for publication in Astronomical Journal (2004 November issue

Mechanically-Induced Transport Switching Effect in Graphene-based Nanojunctions

We report a theoretical study suggesting a novel type of electronic switching effect, driven by the geometrical reconstruction of nanoscale graphene-based junctions. We considered junction struc- tures which have alternative metastable configurations transformed by rotations of local carbon dimers. The use of external mechanical strain allows a control of the energy barrier heights of the potential profiles and also changes the reaction character from endothermic to exothermic or vice-versa. The reshaping of the atomic details of the junction encode binary electronic ON or OFF states, with ON/OFF transmission ratio that can reach up to 10^4-10^5. Our results suggest the possibility to design modern logical switching devices or mechanophore sensors, monitored by mechanical strain and structural rearrangements.Comment: 10 pages, 4 figure

Ponts roulants du LHC: Lot 3

Cette présentation traitera du lot 3 des ponts roulants "lourds" du LHC, qui est constitué de sept appareils (plus un en option). Ils doivent équiper les zones d'expériences ATLAS, ALICE et la tête de puits du PMI2. La mise en place de ces ponts roulants est prévue pour les années 2002 et 2003. Cinq ponts sont destinés à l'expérience ATLAS, un portique pour l'expérience ALICE et le dernier pont pour la tête de puits du PMI 2 avec un pont en option ne devant servir que dans le hall de montage. La capacité de ces ponts s'étend sur une gamme de 16t à 2x140t et des hauteurs de levage de 6,5 m à 102 m. Les points forts de ces ponts seront la descente des bobines pour l'expérience ATLAS (deux ponts - trois chariots synchronisés) et la descente de 1200 cryodipoles et tous les aimants du LHC dans PMI2

Heat pipe dynamic behavior

The vapor flow in a heat pipe was mathematically modeled and the equations governing the transient behavior of the core were solved numerically. The modeled vapor flow is transient, axisymmetric (or two-dimensional) compressible viscous flow in a closed chamber. The two methods of solution are described. The more promising method failed (a mixed Galerkin finite difference method) whereas a more common finite difference method was successful. Preliminary results are presented showing that multi-dimensional flows need to be treated. A model of the liquid phase of a high temperature heat pipe was developed. The model is intended to be coupled to a vapor phase model for the complete solution of the heat pipe problem. The mathematical equations are formulated consistent with physical processes while allowing a computationally efficient solution. The model simulates time dependent characteristics of concern to the liquid phase including input phase change, output heat fluxes, liquid temperatures, container temperatures, liquid velocities, and liquid pressure. Preliminary results were obtained for two heat pipe startup cases. The heat pipe studied used lithium as the working fluid and an annular wick configuration. Recommendations for implementation based on the results obtained are presented. Experimental studies were initiated using a rectangular heat pipe. Both twin beam laser holography and laser Doppler anemometry were investigated. Preliminary experiments were completed and results are reported

Noise dephasing in the edge states of the Integer Quantum Hall regime

An electronic Mach Zehnder interferometer is used in the integer quantum hall regime at filling factor 2, to study the dephasing of the interferences. This is found to be induced by the electrical noise existing in the edge states capacitively coupled to each others. Electrical shot noise created in one channel leads to phase randomization in the other, which destroys the interference pattern. These findings are extended to the dephasing induced by thermal noise instead of shot noise: it explains the underlying mechanism responsible for the finite temperature coherence time $\tau_\phi(T)$ of the edge states at filling factor 2, measured in a recent experiment. Finally, we present here a theory of the dephasing based on Gaussian noise, which is found in excellent agreement with our experimental results.Comment: ~4 pages, 4 figure