We employ a first-principles plane wave method with the
relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter
(HGH) scheme in the frame of DFT to calculate
the equilibrium lattice parameters and the thermodynamic properties of
AlB2 compound with hcp structure. The obtained lattice parameters are in
good agreement with the available experimental data and those calculated by
others. Through the quasi-harmonic Debye model, obtained successfully are
the dependences of the
normalized lattice parameters a/a0 and c/c0 on pressure P, the normalized
primitive cell volume V/V0 on pressure P, the variation of the thermal
expansion α with pressure P and temperature T, as well as the Debye
temperature \ThetaD and the heat capacity CV on pressure P and
temperature T. 相似文献
The solar wind almost disappeared on May 11, 1999: the solar wind plasma density and dynamic pressure were less than 1cm−3 and 0.1 nPa respectively, while the interplanetary magnetic field was northward. The polar ionospheric data observed by the multi-instruments at Zhongshan Station in Antarctica on such special event day was compared with those of the control day (May 14). It was shown that geomagnetic activity was very quiet on May 11 at Zhongshan. The magnetic pulsation, which usually occurred at about magnetic noon, did not appear. The ionosphere was steady and stratified, and the F2 layer spread very little. The critical frequency of day-side F2 layer, f0F2, was larger than that of control day, and the peak of f0F2 appeared 2 hours earlier. The ionospheric drift velocity was less than usual. There were intensive auroral Es appearing at magnetic noon. All this indicates that the polar ionosphere was extremely quiet and geomagnetic field was much more dipolar on May 11. There were some signatures of auroral substorm before midnight, such as the negative deviation of the geomagnetic H component, accompanied with auroral Es and weak Pc3 pulsation.
In this paper, the author studies the Laplace operator on the quaternionic Heisenberg group, construct a fundamental solution for it and use this solution to prove the Lp-boundedness and the weak (1-1) boundedness of certain singular convolution operators on the quaternionic Heisenberg group. 相似文献
It is widely accepted that next-generation networks will provide guaranteed services, in contrast to the “best effort” approach today. We study and analyze queueing policies for network switches that support the QoS (Quality of Service) feature. One realization of the QoS feature is that packets are not necessarily all equal, with some having higher priorities than the others. We model this situation by assigning an intrinsic value to each packet. In this paper we are concerned with three different queueing policies: the nonpreemptive model, the FIFO preemptive model, and the bounded delay model. We concentrate on the situation where the incoming traffic overloads the queue, resulting in packet loss. The objective is to maximize the total value of packets transmitted by the queueing policy. The difficulty lies in the unpredictable nature of the future packet arrivals. We analyze the performance of the online queueing policies via competitive analysis, providing upper and lower bounds for the competitive ratios. We develop practical yet sophisticated online algorithms (queueing policies) for the three queueing models. The algorithms in many cases have provably optimal worst-case bounds. For the nonpreemptive model, we devise an optimal online algorithm for the common 2-value model. We provide a tight logarithmic bound for the general nonpreemptive model. For the FIFO preemptive model, we improve the general lower bound to 1.414, while showing a tight bound of 1.434 for the special case of queue size 2. We prove that the bounded delay model with uniform delay 2 is equivalent to a modified FIFO preemptive model with queue size 2. We then give improved upper and lower bounds on the 2-uniform bounded delay model. We also show an improved lower bound of 1.618 for the 2-variable bounded delay model, matching the previously known upper bound. 相似文献