515 research outputs found
Bistable behavior of a two-mode Bose-Einstein condensate in an optical cavity
We consider a two-component Bose-Einstein condensate in a one-dimensional
optical cavity. Specifically, the condensate atoms are taken to be in two
degenerate modes due to their internal hyperfine spin degrees of freedom and
they are coupled to the cavity field and an external transverse laser field in
a Raman scheme. A parallel laser is also exciting the cavity mode. When the
pump laser is far detuned from its resonance atomic transition frequency, an
effective nonlinear optical model of the cavity-condensate system is developed
under Discrete Mode Approximation (DMA), while matter-field coupling has been
considered beyond the Rotating Wave Approximation. By analytical and numerical
solutions of the nonlinear dynamical equations, we examine the mean cavity
field and population difference (magnetization) of the condensate modes. The
stationary solutions of both the mean cavity field and normalized magnetization
demonstrate bistable behavior under certain conditions for the laser pump
intensity and matter-field coupling strength.Comment: Proceeding of Laser Physics 201
Error exponent of amplify and forward relay networks in presence of I.I.D. interferers
© 2014 IEEE. In this paper, we derive the random coding error exponent of amplify-and-forward (AF) relay networks in presence of arbitrary number of independent and identically distributed (i.i.d.) interferers both at the relay and the destination. Multiuser networks are common examples of interference limited networks. We derive the ergodic capacity of the network and present simulation results on the performance of the network where we compare the capacity and error exponent performance of interference limited networks with noise limited networks. Numerical results show that noise limited networks outperform interference limited networks even when only a very few interferers exist in the network
Text Summarization Techniques: A Brief Survey
In recent years, there has been a explosion in the amount of text data from a
variety of sources. This volume of text is an invaluable source of information
and knowledge which needs to be effectively summarized to be useful. In this
review, the main approaches to automatic text summarization are described. We
review the different processes for summarization and describe the effectiveness
and shortcomings of the different methods.Comment: Some of references format have update
An Efficient Opportunistic Cooperative Diversity Protocol for IEEE 802.11 Networks
Opportunistic cooperation promises to enhance the user experience when streaming media over wireless devices by improving wireless network reliability at the link level. This paper presents DAFMAC, an efficient cooperative diversity partner selection algorithm for IEEE 802.11 devices. Simulation results show DAFMAC provides a significantly higher transmission reliability in poor channel conditions than traditional ARQ techniques without modifying the device hardware. Further analysis shows the low overhead of DAFMAC makes it highly competitive with other proposed cooperative retransmission mechanisms in an ad-hoc network
Spinodal decomposition driven formation of Pt-nanowires on Ge(001)
Using low energy electron microscopy, we have found that the deposition of Pt on Ge(001) leads to the formation of a surface confined eutectic liquid when the system is heated above 980 K. From the bulk phase diagram we derive the composition of the eutectic phase: GePt. Upon solidification and further cooling down, two distinct types of terrace emerge, the so-called α and β terraces, which have been assigned previously as relatively Pt-poor and Pt-rich, respectively. Immediately after solidification β terraces fully cover the surface, while further cooling leads to their partial transformation into α terraces. Subsequently, Pt nanowire domains nucleate and grow exclusively on β terraces at about 600 K. The results are discussed using spinodal decomposition concepts and reveal a new pathway for nanowire formation
Nonlinear Vibrational Analysis of Nanobeams Embedded in an Elastic Medium including Surface Stress Effects
Due to size-dependent behavior of nanostructures, the classical continuum models are not applicable for the analyses at this submicron size. Surface stress effect is one of the most important matters which make the nanoscale structures have different properties compared to the conventional structures due to high surface to volume ratio. In the present study, nonlinear free vibrational characteristics of embedded nanobeams are investigated including surface stress effects. To this end, a thin surface layer is assumed on the upper and lower surfaces of the cross section to separate the surface and bulk of nanobeams with their own different material properties. Based on harmonic balance method, closed-form analytical solution is conducted for nonlinear vibrations to obtain natural frequencies of embedded nanobeams with and without considerations of surface elasticity and residual surface tension effects corresponding to the various values of nondimensional amplitude, elastic foundation modulus, and geometrical variables of the system. Selected numerical results are given to indicate the influence of each one in detail
Outage Probability Analysis of Dual Hop Relay Networks in Presence of Interference
Cooperative relaying improves the performance of wireless networks by forming a network of multiple independent virtual sources transmitting the same information as the source node. However, interference induced in the network reduces the performance of cooperative communications. In this work the statistical properties, the cumulative distribution function (CDF) and the probability density function (PDF) for a basic dual hop cooperative relay network with an arbitrary number of interferers over Rayleigh fading channels are derived. Two system models are considered: in the first system model, the interferers are only at the relay node; and in the second system model, interferers are both at the relay and the destination. This work is further extended to Nakagami-m faded interfering channels. Simulation results are presented on outage probability performance to verify the theoretical analysis
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