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排序方式: 共有80条查询结果,搜索用时 109 毫秒
1.
Petrus Zwart John Taylor Simon Morton Randall Cayford Gerald Fontenay Marc Allaire 《Synchrotron Radiation News》2015,28(2):22-27
The Berkeley Center for Structural Biology (BCSB) operates and develops a suite of protein crystallography beamlines at the Advanced Light Source (ALS) located at Lawrence Berkeley National Laboratory (LBNL). Although the ALS was conceived as a low-energy (1.9-GeV), third-generation synchrotron source of vacuum ultraviolet (VUV) and soft X-ray radiation, it was realized during the development of the facility in the mid-1990s that a multipole wiggler coupled with brightness-preserving optics would result in a beamline whose performance in the energy range of 5 to 15 keV would be sufficient for most protein crystallographic experiments. Later, the hard X-ray capabilities of the ALS were expanded by the addition of three superconducting bending magnets, resulting in additional protein crystallography facilities at the ALS [1]. 相似文献
2.
Parity-violating electron deuteron scattering and the proton's neutral weak axial vector form factor
Ito TM Averett T Barkhuff D Batigne G Beck DH Beise EJ Blake A Breuer H Carr R Clasie B Covrig S Danagoulian A Dodson G Dow K Dutta D Farkhondeh M Filippone BW Franklin W Furget C Gao H Gao J Gustafsson K Hannelius L Hasty R Hawthorne-Allen AM Herda MC Jones CE King P Korsch W Kowalski S Kox S Kramer K Lee P Liu J Martin JW McKeown RD Mueller B Pitt ML Plaster B Quéméner G Réal JS Ritter J Roche J Savu V Schiavilla R Seely J Spayde D Suleiman R Taylor S Tieulent R Tipton B Tsentalovich E 《Physical review letters》2004,92(10):102003
We report on a new measurement of the parity-violating asymmetry in quasielastic electron scattering from the deuteron at backward angles at Q2=0.038 (GeV/c)2. This quantity provides a determination of the neutral weak axial vector form factor of the nucleon, which can potentially receive large electroweak corrections. The measured asymmetry A=-3.51+/-0.57 (stat)+/-0.58 (syst) ppm is consistent with theoretical predictions. We also report on updated results of the previous experiment at Q2=0.091 (GeV/c)2, which are also consistent with theoretical predictions. 相似文献
3.
We investigate the tail behavior of the sojourn-time distribution for a request of a given length in an M/G/1 Processor-Sharing
(PS) queue. An exponential asymptote is proven for general service times in two special cases: when the traffic load is sufficiently
high and when the request length is sufficiently small. Furthermore, using the branching process technique we derive exact
asymptotics of exponential type for the sojourn time in the M/M/1 queue. We obtain an equation for the asymptotic decay rate
and an exact expression for the asymptotic constant. The decay rate is studied in detail and is compared to other service
disciplines. Finally, using numerical methods, we investigate the accuracy of the exponential asymptote.
AMS 2000 Subject Classifications Primary:60K25,Secondary: 60F10,68M20,90B22 相似文献
4.
This paper presents a large deviation analysis of the steady-state sojourn time distribution in the GI/G/1 PS queue. Logarithmic estimates are obtained under the assumption of the service time distribution having a light tail,
thus supplementing recent results for the heavy-tailed setting. Our proof gives insight into the way a large sojourn time
occurs, enabling the construction of an (asymptotically efficient) importance sampling algorithm. Finally our results for
PS are compared to a number of other service disciplines, such as FCFS, LCFS, and SRPT.
2000 mathematics subject classification: 60K25. 相似文献
5.
P. Zwart 《Journal of Optimization Theory and Applications》1970,6(2):150-160
In some constrained nonlinear programming problems possessing several local optima, a local optimum can be recognized as the global optimum by looking closely at the Lagrangian, the augmented function. Similarly, classes of constrained optimization problems, such as geometric programming problems, can be recognized as possessing at most a single local optimum.This research was supported in part by the Atomic Energy Commission under Research Contract No. A(11-1)-1493 and by the Department of Defense under Themis Grant No. F44620-69-C-0116. 相似文献
6.
7.
Jeroen Bédorf Evghenii Gaburov Simon Portegies Zwart 《Journal of computational physics》2012,231(7):2825-2839
We present the implementation and performance of a new gravitational N-body tree-code that is specifically designed for the graphics processing unit (GPU).1 All parts of the tree-code algorithm are executed on the GPU. We present algorithms for parallel construction and traversing of sparse octrees. These algorithms are implemented in CUDA and tested on NVIDIA GPUs, but they are portable to OpenCL and can easily be used on many-core devices from other manufacturers. This portability is achieved by using general parallel-scan and sort methods. The gravitational tree-code outperforms tuned CPU code during the tree-construction and shows a performance improvement of more than a factor 20 overall, resulting in a processing rate of more than 2.8 million particles per second. 相似文献
8.
We show for the M/G/1 processor sharing queue that the service time distribution is regularly varying of index -ν, ν non-integer,
iff the sojourn time distribution is regularly varying of index -ν. This result is derived from a new expression for the Laplace–Stieltjes
transform of the sojourn time distribution. That expression also leads to other new properties for the sojourn time distribution.
We show how the moments of the sojourn time can be calculated recursively and prove that the kth moment of the sojourn time is finite iff the kth moment of the service time is finite. In addition, we give a short proof of a heavy traffic theorem for the sojourn time
distribution, prove a heavy traffic theorem for the moments of the sojourn time, and study the properties of the heavy traffic
limiting sojourn time distribution when the service time distribution is regularly varying. Explicit formulas and multiterm
expansions are provided for the case that the service time has a Pareto distribution.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
9.
Hans Zwart 《Semigroup Forum》2001,63(2):153-160
A well-known necessary and sufficient condition for the operator A to be the infinitesimal generator of a strongly continuous (C
0
-) group is that both A and -A generate a C
0
-semigroup. This seems to imply that one has to check the conditions in the Hille-Yosida Theorem for both A and -A . In this paper we show that this is not necessary. Given that A generates a C
0
-semigroup we prove that a (weak) growth bound on the resolvent on a left half plane is sufficient to guarantee that A generates a group. This extends the recent result found by Liu, see [6]. Furthermore, we study when a generator of a bounded
C
0
-semigroup is the generator of a bounded group. The condition that we obtain is the same as found by Van Casteren in [2,
3], but we present a direct proof. 相似文献
10.
We investigate steady state properties of limited processor sharing queues in heavy traffic. Our analysis builds on previously obtained process limit theorems, and requires the interchange of steady state and heavy traffic limits, which are established by a coupling argument. The limit theorems yield explicit approximations of the steady state queue length and response time distribution in heavy traffic, of which the quality is supported by simulation experiments. 相似文献