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排序方式: 共有97条查询结果,搜索用时 15 毫秒
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33.
《Discrete Mathematics》2019,342(7):1966-1978
We study methods for computing the bridge number of a knot from a knot diagram. We prove equivalence between a geometric and a combinatorial definition of the bridge number of a knot diagram. For each notion of diagrammatic bridge number considered, we find crossing number minimizing knot diagrams which fail to minimize bridge number. Furthermore, we construct a family of minimal crossing diagrams for which the difference between diagrammatic bridge number and the actual bridge number of the knot grows to infinity. 相似文献
34.
Kippi M. Dyer John S. Perkyns B. Montgomery Pettitt 《Theoretical chemistry accounts》2001,105(3):244-251
The fourth-order virial coefficients have been calculated exactly to five decimal places for pure fluids of the Lennard-Jones
potential at many points in the phase diagram. The calculations were performed through direct evaluation of the integrals,
or diagrams, which make up the density expansion of the radial distribution function: included were the standard fast Fourier
transform method of evaluating the simply connected diagrams and the evaluation of the bridge diagram for the fourth order
in density by expansion in Legendre polynomials. The polynomial-order dependence of the bridge diagram calculation and the
range dependence of the simply connected diagrams of the fourth order are found to have more significance than was thought
from previous studies, especially in the low-temperature range. This result was confirmed by direct evaluation of the diagrams
which construct the virial coefficients, as given by Rowlinson, Barker, and coworkers. This calculation confirmed that numerical
convergence has not been achieved at the precision levels previously reported in the literature. These differences, though
minor at higher temperatures, can be seen to be more significant at the lower temperature ranges.
Received: 31 July 2000 / Accepted: 18 September 2000 / Published online: 21 December 2000 相似文献
35.
Spectral assessment of mesh adaptations for the analysis of the dynamical longitudinal behavior of railway bridges 总被引:2,自引:0,他引:2
Summary Extensive studies, [1], concerning the longitudinal behavior of long railway bridges due to braking forces have been done
by measurements in situ, [2], and by statical, [3, 4], as well as dynamical simulations. Thereby, the only consistent numerical
realization with respect to the measured data was the dynamical one. However, the consecutive discretizations in space and
time with time-dependent system matrices are extremely time consuming due to the moving loads and varying stiffness of the
ballast under, and in front of, the moving train. Therefore, every effort should be made to optimize the discretization in
the space domain. This paper presents a strategy for assessing the quality of finite elements in space and for applying an
adaptive mesh-refinement for this special engineering problem. The method is characterized by a spectral assessment, comparing
a certain set of eigenvalues of the actual discretization with those of a very fine and rather exact numerical model. The
error estimator introduced in this paper controls a whole set of global eigenvalues with corresponding natural vibration modes
in order to assess certain types of shape functions. Thus, the procedure estimates local modifications on the one hand and
p-properties on the other by means of global indication.
Received 30 August 1999; accepted for publication 26 September 2000 相似文献
36.
《Analytical letters》2012,45(7-8):825-835
Abstract The flow injection technique is shown to provide fast, reliable and sensitive determination of solubility product constants of silver acetate, silver sulfate, silver oxide, silver bromate and silver chloride in microliter volume samples. Potentiometric detection using electrodes of the first kind and second kind was used for measuring silver ions and chloride ions, respectively. The solubilities were determined from measurement of the silver ion concentration in the saturated solutions. In the case of silver chloride, the solubility product constant was calculated from the concentrations corresponding to the intersection of the silver ion calibration curve and the chloride ion calibration curve, i.e., where the potentials of the two electrodes are equal. Tenth-molar sodium nitrate was used for all solutions to maintain constant ionic strength. At a concentration range of 1.00 × 10?2 ? 1.00 × 10?5 M silver, and 1.00 × 10?2 ? 1.00 × 10?4 M chloride, a Nernstian response of 60 m V per decade was obtained. At a sampling rate of 50–70 samples per hour, with 50 μl sample injections, high reproducibility of measurements was achieved, with a -pL 2% relative standard deviation in measured concentrations. The scope and applications of this system are discussed. 相似文献
37.
采用数值计算的方法分析了赵州桥上的两对伏拱对桥身拱轴线形状及拱券应力分布的影响,一方面阐明了伏拱的存在使桥体的圆弧形拱轴线与符合力学原理的恒载压力线十分接近,另一方面,说明伏拱的存在明显消除了桥体拱券中的拉应力,加强了桥体的安全性,从而对这座千年古桥的卓越力学性能有了进一步的认识。 相似文献
38.
中心螺管是超导托卡马克装置磁体系统的重要组成部分 ,在 HT- 7U中 ,中心螺管采用管装超导电缆绕制 ,线圈以脉冲方式运行。文中介绍了 HT- 7U中心螺管模型线圈实验中 ,失超信号检测系统的工作原理及失超信号特点。当磁体以脉冲方式运行时 ,失超信号检测系统为装置提供可靠的失超保护动作信号 ;还给出了有关的实验数据和检测系统记录的失超信号变化曲线。 相似文献
39.
40.
Falko Wachholz Jan Gimsa Heiko Duwensee Harald Grabow Peter Gründler Gerd‐Uwe Flechsig 《Electroanalysis》2007,19(5):535-540
We describe a novel instrument and electrical circuit for sensitive electrochemical measurements at simultaneous direct electrode heating. The new measuring principle can be applied to working electrodes of various designs featuring two end contacts. In our experiments, the contacts were connected to a 100 kHz AC heating power supply and the potentiostat via the new inductor bridge circuit. A compact heating‐generator housing contains all components necessary for sine wave generation as well as amplification and transformation of the heating power. The new arrangement yields high temperature cyclovoltammetric signals for the [Fe(CN)6]3?/4? redox system with a noise level superior to the earlier symmetrically branched wire electrode designs. Noise and disturbances are dramatically suppressed especially for high resistance electrodes such as glassy carbon electrodes. Without a center contact, the working electrode design is greatly simplified. This opens new opportunities for the design of a great variety of heated electrodes that may be arranged in arrays or consist of materials with relatively high resistivity such as carbon and conducting polymers. 相似文献