Exact solution of entanglement of the double Jaynes—Cummings model without rotating wave approximation

This paper investigates the influences of atom--field coupling and dipole--dipole coupling for atoms on the entanglement between two atoms by means of concurrence. The results show that the sudden death occurs when the atom--field coupling is strong enough, and the collapse and the revival appear when the dipole--dipole interaction is strong enough.     

The ground-state entanglement in the spin-XX chain with a magnetization current

The ground-state entanglement in a transverse spin-1/2 XX chain with a magnetization current is studied. By introducing a magnetization current to the system, a quantum phase transition to current-carrying phase may be presented with the variation of the driving field λ for the magnetic field h>1; and the ground-state entanglement arises simultaneously at the critical point of quantum phase transition. In our model, the introduction of magnetization current may result in more entanglement between any two nearest-neighbour spins.     

Assessment of ski condition reliability in the Spanish and Andorran Pyrenees for the second half of the 20th century

In this study temporal trends of 14 climate and snow parameters related to ski conditions were analyzed for 11 ski stations located in the central Pyrenees (Spain and Andorra). We also investigated whether there was a temporal association for the analyzed parameters, such that the occurrence in a particular year of good (or bad) climate or snow conditions as represented by one parameter was similarly reflected by the other parameters. The lack of reliable climate and snow measurements was overcome by the use of simulated climate data retrieved from a high resolution hindcast simulation available for the period 1960–2006. These data were also used as inputs for an energy and mass snow energy model to obtain snow series. The results showed trends in ski reliability parameters for the 1960–2006 period. The number of days having a snowpack deeper than 30 cm and 100 cm showed declines at low and mid altitudes. The start of the ski season appears progressively delayed for all stations, and the ski season shortened. The frequency of rainy days increased at 3 stations and decreased at 8, while the frequency of days having heavy snowfall increased at 8 stations and declined at 3. Days having potential for snowmaking declined at all stations. The number of days having a wind-chill < −20 °C also decreased markedly, as overall did the number of days having a wind speed greater than 80th percentile. The main findings from the assessment of temporal associations between climate and snow parameters were positive correlations between snow depth and windy conditions. Seasons having a higher frequency of very cold days had a lower frequency of heavy snowfall and rainy days. Thus, the adverse effects on the ski industry of lesser snow availability may have been partially negated by the occurrence of fewer days of closure because of high winds, or other adverse meteorological factors.     

空间数据库的WFS长事务管理方案研究

在研究网络要素服务WFS-T对长事务管理的需求以及Geoserver等WFS服务器实现技术的基础上,针对目前进程内锁、行锁长事务管理方案未完全保证强事务性和事务持久性的问题,设计了一种包括长事务锁定表、授权校验规则和相应的SQL函数接口的空间数据库长事务管理方案;并在国产地理空间数据库管理系统BeyonDB上进行了验证.     

Thermal entanglement in molecular spin rings

The thermal entanglement in the triangular molecular spin ring with Dzyaloshinskii--Moriya interaction is studied. The concurrences of arbitrary two spins of the triangular molecular spin ring for various cases are evaluated. The tendency of the concurrence with Dzyaloshinskii--Moriya interaction and temperature is analysed and discussed. We note that the concurrence arrives at its maximum in the regime with the large Dzyaloshinskii--Moriya interaction and low temperature, and gradually decreases to zero with the increase of temperature. The concurrence has different features for the ferromagnetic and antiferromagnetic cases. For completeness, we also numerically calculate the concurrence of spin rings with N>3 spins and analyse their behaviours.     

Concurrence, tangle and fully entangled fraction

We show that although we cannot distil a singlet from many pairs of bound entangled states, the concurrence and the tangle of two entangled quantum states are always strictly larger than those of one of them, even both entangled quantum states are bound entangled. We present a relation between the concurrence and the fidelity of optimal teleportation. We also give new upper and lower bounds for concurrence and tangle.     

Linux下一种多核网络服务器模型设计与实现

传统的基于Linux操作系统的网络服务器程序在高负载情况下不能充分利用多核服务器硬件资源,其原因主要在于没有找到一种高效的服务器编程解决方案.为了解决这一问题,在分析了线程池技术和linux 2.6内核下的I/O多路复用技术各自的优缺点的基础上,设计并实现了一种在多核服务器平台上结合线程池和I/O多路复用的高性能网络服务器编程模型.通过实验表明,新的编程模型相对于线程池模型和单纯的I/O多路复用模型,其任务平均响应时间只占其它两种模型的8%和29%,而其平均吞吐量则达到了其它两种模型的8.4倍和1.9倍.