50,048 research outputs found
Horizon Entropy in Modified Gravity
We present an observation about the proposal that four-dimensional
modification of general relativity may explain the observed cosmic acceleration
today. Assuming that the thermodynamical nature of gravity theory continues to
hold in modified gravity theories, we derive the modified horizon entropy
formula from the modified Friedmann equation. We argue that our results imply
that there are conceptual problems in some models of four-dimensional
modification of general relativity.Comment: 8 pages. v2: references adde
A general comparison theorem for 1-dimensional anticipated BSDEs
Anticipated backward stochastic differential equation (ABSDE) studied the
first time in 2007 is a new type of stochastic differential equations. In this
paper, we establish a general comparison theorem for 1-dimensional ABSDEs with
the generators depending on the anticipated term of .Comment: 8 page
Angular Momentum of a Brane-world Model
In this paper we discuss the properties of the general covariant angular
momentum of a five-dimensional brane-world model. Through calculating the total
angular momentum of this model, we are able to analyze the properties of the
total angular momentum in the inflationary RS model. We show that the
space-like components of the total angular momentum of are all zero while the
others are non-zero, which agrees with the results from ordinary RS model.Comment: 8 pages; accepted by Chinese Physics
A Simplified Scheme of Estimation and Cancellation of Companding Noise for Companded Multicarrier Transmission Systems
Nonlinear companding transform is an efficient method to reduce the high peak-to-average power ratio (PAPR) of multicarrier transmission systems. However, the introduced companding noise greatly degrades the bit-error-rate (BER) performance of the companded multicarrier systems. In this paper, a simplified but effective scheme of estimation and cancellation of companding noise for the companded multicarrier transmission system is proposed. By expressing the companded signals as the summation of original signals added with a companding noise component, and subtracting this estimated companding noise from the received signals, the BER performance of the overall system can be significantly improved. Simulation results well confirm the great advantages of the proposed scheme over other conventional decompanding or no decompanding schemes under various situations
Multi-GPU Acceleration of the iPIC3D Implicit Particle-in-Cell Code
iPIC3D is a widely used massively parallel Particle-in-Cell code for the
simulation of space plasmas. However, its current implementation does not
support execution on multiple GPUs. In this paper, we describe the porting of
iPIC3D particle mover to GPUs and the optimization steps to increase the
performance and parallel scaling on multiple GPUs. We analyze the strong
scaling of the mover on two GPU clusters and evaluate its performance and
acceleration. The optimized GPU version which uses pinned memory and
asynchronous data prefetching outperform their corresponding CPU versions by
5-10x on two different systems equipped with NVIDIA K80 and V100 GPUs.Comment: Accepted for publication in ICCS 201
Review of morphology dependent charge carrier mobility in MEH-PPV
Charge carrier mobility in poly(2-methoxy,5(2'-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) films were measured as a function of temperature and electric field parallel and perpendicular to the substrate for devices prepared from different solvents and under different processing conditions Bulk structural morphology was characterized by various X-ray diffraction measurements such as wide angle, small angle and X-ray reflection. Surface morphology was characterized using various scanning probe microscopic techniques Mobilities were found to follow Gaussian disorder model (GDM) and to be highly anisotropic not only depending on the solvents used but also on the film preparation method such as spin-coating or drop-casting While no direct correlation was found between charge carrier mobility and photoluminescence, charge transport parameters were correlated with structural morpholog
- …