Holographic Shear Viscosity in Hyperscaling Violating Theories without Translational Invariance

In this paper we investigate the ratio of shear viscosity to entropy density, $\eta/s$, in hyperscaling violating geometry with lattice structure. We show that the scaling relation with hyperscaling violation gives a strong constraint to the mass of graviton and usually leads to a power law of temperature, $\eta/s\sim T^\kappa$. We find the exponent $\kappa$ can be greater than two such that the new bound for viscosity raised in arXiv:1601.02757 is violated. Our above observation is testified by constructing specific solutions with UV completion in various holographic models. Finally, we compare the boundedness of $\kappa$ with the behavior of entanglement entropy and conjecture a relation between them.Comment: 38 pages, 8 figures: 1 appendix added, 2 figures added, 1 references adde

Distributions of Upper PAPR and Lower PAPR of OFDM Signals in Visible Light Communications

Orthogonal frequency-division multiplexing (OFDM) in visible light communications (VLC) inherits the disadvantage of high peak-to-average power ratio (PAPR) from OFDM in radio frequency (RF) communications. The upper peak power and lower peak power of real-valued VLC-OFDM signals are both limited by the dynamic constraints of light emitting diodes (LEDs). The efficiency and transmitted electrical power are directly related with the upper PAPR (UPAPR) and lower PAPR (LPAPR) of VLC-OFDM. In this paper, we will derive the complementary cumulative distribution function (CCDF) of UPAPR and LPAPR, and investigate the joint distribution of UPAPR and LPAPR.Comment: acceptted by IEEE ICASSP 2014. arXiv admin note: text overlap with arXiv:1304.019

Holographic Metal-Insulator Transition in Higher Derivative Gravity

We introduce a Weyl term into the Einstein-Maxwell-Axion theory in four dimensional spacetime. Up to the first order of the Weyl coupling parameter $\gamma$, we construct charged black brane solutions without translational invariance in a perturbative manner. Among all the holographic frameworks involving higher derivative gravity, we are the first to obtain metal-insulator transitions (MIT) when varying the system parameters at zero temperature. Furthermore, we study the holographic entanglement entropy (HEE) of strip geometry in this model and find that the second order derivative of HEE with respect to the axion parameter exhibits maximization behavior near quantum critical points (QCPs) of MIT. It testifies the conjecture in 1502.03661 and 1604.04857 that HEE itself or its derivatives can be used to diagnose quantum phase transition (QPT).Comment: 20 pages, 4 figures; typo corrected, added 3 references; minor revisio

Apparatus for Seebeck coefficient and electrical resistivity measurements of bulk thermoelectric materials at high temperature

A high temperature Seebeck coefficient and electrical resistivity measurement apparatus has been designed and built for measuring advanced thermoelectric materials. The apparatus covers the range of temperatures from 300 to 1300 K300to1300K. Different sources of errors involved in the two measurements are discussed. The accuracy of the electrical resistivity measurement is estimated to be better than ±1%±1% by measuring standard graphite sample from NIST.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87891/2/023901_1.pd

Stability of Time-inconsistent Stopping for One-dimensional Diffusion -- A Longer Version

We investigate the stability of the equilibrium-induced optimal value in one-dimensional diffusion setting for a time-inconsistent stopping problem under non-exponential discounting. We show that the optimal value is semi-continuous with respect to the drift, volatility, and reward function. An example is provided showing that the exact continuity may fail. With equilibria extended to $\varepsilon$-equilibria, we establish the relaxed continuity of the optimal value