Emergent Gravity from Noncommutative Gauge Theory

We show that the matrix-model action for noncommutative U(n) gauge theory actually describes SU(n) gauge theory coupled to gravity. This is elaborated in the 4-dimensional case. The SU(n) gauge fields as well as additional scalar fields couple to an effective metric G_{ab}, which is determined by a dynamical Poisson structure. The emergent gravity is intimately related to noncommutativity, encoding those degrees of freedom which are usually interpreted as U(1) gauge fields. This leads to a class of metrics which contains the physical degrees of freedom of gravitational waves, and allows to recover e.g. the Newtonian limit with arbitrary mass distribution. It also suggests a consistent picture of UV/IR mixing in terms of an induced gravity action. This should provide a suitable framework for quantizing gravity.Comment: 28 pages + 11 pages appendix. V2: references and discussion added. V3: minor correctio

Greybody Factors of Charged Dilaton Black Holes in 2 + 1 Dimensions

We have studied scalar perturbations of charged dilaton black holes in 2+1 dimensions. The black hole considered here is a solution to the low-energy string theory in 2+1 dimensions. The exact decay rates and the grey body factors for the massless minimally coupled scalar is computed for both the charged and the uncharged dilaton black holes. The charged and the uncharged black hole show similar behavior for grey body factors, reflection coefficients and decay rates.Comment: The equation for the potential and figure:1 are changed. The changes does not effect the result

Anomalous Heat Conduction and Anomalous Diffusion in Low Dimensional Nanoscale Systems

Thermal transport is an important energy transfer process in nature. Phonon is the major energy carrier for heat in semiconductor and dielectric materials. In analogy to Ohm's law for electrical conductivity, Fourier's law is a fundamental rule of heat transfer in solids. It states that the thermal conductivity is independent of sample scale and geometry. Although Fourier's law has received great success in describing macroscopic thermal transport in the past two hundreds years, its validity in low dimensional systems is still an open question. Here we give a brief review of the recent developments in experimental, theoretical and numerical studies of heat transport in low dimensional systems, include lattice models, nanowires, nanotubes and graphenes. We will demonstrate that the phonon transports in low dimensional systems super-diffusively, which leads to a size dependent thermal conductivity. In other words, Fourier's law is breakdown in low dimensional structures

Erbium-doped multi-element fiber amplifiers for space-division multiplexing operations

Erbium-doped multi-element fiber (MEF) amplifiers have been fabricated to simultaneously amplify multiple transmission channels. MEF devices comprise of multiple single-core fibers (elements) combined in a common coating, with each element working as a single fiber in isolation. MEFs containing 3-elements and 7-elements have been fabricated and characterized. Each element of the fabricated MEFs provides nearly 32dB of gain with a noise figure of <5dB for an input signal level of -23dBm at 1530 nm. Different permutations of element pairs within the MEFs were checked for crosstalk and none was detected, confirming the simultaneous multi-channel amplification capabilities of MEFs