Power-law Behavior of High Energy String Scatterings in Compact Spaces

We calculate high energy massive scattering amplitudes of closed bosonic string compactified on the torus. We obtain infinite linear relations among high energy scattering amplitudes. For some kinematic regimes, we discover that some linear relations break down and, simultaneously, the amplitudes enhance to power-law behavior due to the space-time T-duality symmetry in the compact direction. This result is consistent with the coexistence of the linear relations and the softer exponential fall-off behavior of high energy string scattering amplitudes as we pointed out prevously. It is also reminiscent of hard (power-law) string scatterings in warped spacetime proposed by Polchinski and Strassler.Comment: 6 pages, no figure. Talk presented by Jen-Chi Lee at Europhysics Conference (EPS2007), Manchester, England, July 19-25, 2007. To be published by Journal of Physics: Conference Series

350 Micron Observations of Ultraluminous Infrared Galaxies at Intermediate Redshifts

We present 350micron observations of 36 ultraluminous infrared galaxies (ULIRGs) at intermediate redshifts (0.089 <= z <= 0.926) using the Submillimeter High Angular Resolution Camera II (SHARC-II) on the Caltech Submillimeter Observatory (CSO). In total, 28 sources are detected at S/N >= 3, providing the first flux measurements longward of 100micron for a statistically significant sample of ULIRGs in the redshift range of 0.1 < z < 1.0. Combining our 350micron flux measurements with the existing IRAS 60 and 100micron data, we fit a single-temperature model to the spectral energy distribution (SED), and thereby estimate dust temperatures and far-IR luminosities. Assuming an emissivity index of beta = 1.5, we find a median dust temperature and far-IR luminosity of Td = 42.8+-7.1K and log(Lfir/Lsolar) = 12.2+-0.5, respectively. The far-IR/radio correlation observed in local star-forming galaxies is found to hold for ULIRGs in the redshift range 0.1 < z < 0.5, suggesting that the dust in these sources is predominantly heated by starbursts. We compare the far-IR luminosities and dust temperatures derived for dusty galaxy samples at low and high redshifts with our sample of ULIRGs at intermediate redshift. A general Lfir-Td relation is observed, albeit with significant scatter, due to differing selection effects and variations in dust mass and grain properties. The relatively high dust temperatures observed for our sample compared to that of high-z submillimeter-selected starbursts with similar far-IR luminosities suggest that the dominant star formation in ULIRGs at moderate redshifts takes place on smaller spatial scales than at higher redshifts.Comment: (24 pages in preprint format, 1 table, 7 figures, accepted for publication in ApJ

Contact law and impact responses of laminated composites

Static identation tests were performed to determine the law of contact between a steel ball and glass/epoxy and graphite/epoxy laminated composites. For both composites the power law with an index of 1.5 was found to be adequate for the loading curve. Substantial permanent deformations were noted after the unloading. A high order beam finite element was used to compute the dynamic contact force and response of the laminated composite subjected to the impact of an elastic sphere. This program can be used with either the classical Hertzian contact law or the measured contact law. A simple method is introduced for estimating the contact force and contact duration in elastic impacts

Cooperative emission of a pulse train in an optically thick scattering medium

An optically thick cold atomic cloud emits a coherent flash of light in the forward direction when the phase of an incident probe field is abruptly changed. Because of cooperativity, the duration of this phenomena can be much shorter than the excited lifetime of a single atom. Repeating periodically the abrupt phase jump, we generate a train of pulses with short repetition time, high intensity contrast and high efficiency. In this regime, the emission is fully governed by cooperativity even if the cloud is dilute.Comment: 5 pages, 3 figure

Theory of fishnet negative-index optical metamaterials

We theoretically study fishnet metamaterials at optical frequencies. In contrast to earlier works, we provide a microscopic description by tracking the transversal and longitudinal flows of energy through the fishnet mesh composed of intersecting subwavelength plasmonic waveguides. The analysis is supported by a semi-analytical model based on surface-plasmon coupled-mode equations, which provides accurate formulas for the fishnet refractive index, including the real-negative and imaginary parts. The model simply explains how the surface plasmons couple at the waveguide intersections and it shines new light on the fishnet negative-index paradigm at optical frequencies. Extension of the theory for loss-compensated metamaterials with gain media is also presented.Comment: 4 figure

The infrared conductivity of Nax_xCoO2_2: evidence of gapped states

We present infrared ab-plane conductivity data for the layered cobaltate Na$_x$CoO$_2$ at three different doping levels ($x=0.25, 0.50$, and 0.75). The Drude weight increases monotonically with hole doping, $1-x$. At the lowest hole doping level $x$=0.75 the system resembles the normal state of underdoped cuprate superconductors with a scattering rate that varies linearly with frequency and temperature and there is an onset of scattering by a bosonic mode at 600 \cm. Two higher hole doped samples ($x=0.50$ and 0.25) show two different-size gaps (110 \cm and 200 \cm, respectively) in the optical conductivities at low temperatures and become insulators. The spectral weights lost in the gap region of 0.50 and 0.25 samples are shifted to prominent peaks at 200 \cm and 800 \cm, respectively. We propose that the two gapped states of the two higher hole doped samples ($x$=0.50 and 0.25) are pinned charge ordered states.Comment: 4 pages, 3 figure