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Journal of Computational Mathematics 2018年第5期36卷 739-760页

作者： Yunfeng Cai Zhaojun Bai John e. Pask n. Sukumar LMAM & School of Mathematical Sciences Peking University Beijing 100871 China Department of Computer Science and Department of Mathematics University of California Davis CA 95616 USA Physics Division Lawrence Livermore National Laboratory Livermore CA 94550 USA Department of Civil and environmental engineering University of California Davis CA 95616 USA

By extending the classical analysis techniques due to Samokish, Faddeev and Faddee- va, and Longsine and McCormick among others, we prove the convergence of the precon- ditioned steepest descent with implicit deflation （PSD-id） method for solving Hermitian- definite generalized eigenvalue problems. Furthermore, we derive a nonasymptotie estimate of the rate of convergence of the PSD-id method. We show that with a proper choice of the shift, the indefinite shift-and-invert preconditioner is a locally accelerated preconditioner, and is asymptotically optimal which leads to superlinear convergence numerical examples are presented to verify the theoretical results on the convergence behavior of the PSD- id method for solving ill-conditioned Hermitian-definite generalized eigenvalue problems arising from electronic structure calculations. While rigorous and full-scale convergence proofs of preconditioned block steepest descent methods in practical use still largely eludes us, we believe the theoretical results presented in this paper shed light on an improved understanding of the convergence behavior of these block methods.

关键词： eigenvalue problem Steepest descent method Preconditioning Superlinear convergence.

Impact of mechanical bowel preparation in elective colorectal surgery:A meta-analysis

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World Journal of Gastroenterology 2018年第4期24卷 519-536页

作者： Katie e Rollins Hannah Javanmard-emamghissi Dileep n Lobo Gastrointestinal Surgery Nottingham Digestive Diseases Centre National Institute of Health Research (NIHR) Nottingham Biomedical Research Centre Nottingham University Hospitals NHS Trust and University of Nottingham Queen’s Medical Centre

AIM To analyse the effect of mechanical bowel preparation vs no mechanical bowel preparation on outcome in patients undergoing elective colorectal *** Meta-analysis of randomised controlled trials and observational studies comparing adult patients receiving mechanical bowel preparation with those receiving no mechanical bowel preparation, subdivided into those receiving a single rectal enema and those who received no preparation at all prior to elective colorectal surgery. ReSULTS A total of 36 studies(23 randomised controlled trials and 13 observational studies) including 21568 patients undergoing elective colorectal surgery were included. When all studies were considered, mechanical bowel preparation was not associated with any significant difference in anastomotic leak rates(OR = 0.90, 95%CI: 0.74 to 1.10, P = 0.32), surgical site infection(OR = 0.99, 95%CI: 0.80 to 1.24, P = 0.96), intraabdominal collection(OR = 0.86, 95%CI: 0.63 to 1.17, P = 0.34), mortality(OR = 0.85, 95%CI: 0.57 to 1.27, P = 0.43), reoperation(OR = 0.91, 95%CI: 0.75 to 1.12, P = 0.38) or hospital length of stay(overall mean difference 0.11 d, 95%CI:-0.51 to 0.73, P = 0.72), when compared with no mechanical bowel preparation, nor when evidence from just randomized controlledtrials was analysed. A sub-analysis of mechanical bowel preparation vs absolutely no preparation or a single rectal enema similarly revealed no differences in clinical outcome measures. COnCLUSIOn In the most comprehensive meta-analysis of mechanical bowel preparation in elective colorectal surgery to date, this study has suggested that the use of mechanical bowel preparation does not affect the incidence of postoperative complications when compared with no preparation. Hence, mechanical bowel preparation should not be administered routinely prior to elective colorectal surgery.

关键词： bowel preparation Mechanical antibiotics morbidity mortality surgery outcome complications meta-analysis

Phase analysis of AlFe2B2 by synchrotron X-ray diffraction,magnetic and M?ssbauer studies

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Progress in natural Science:Materials International 2017年第2期27卷 251-256页

作者： Tahir Ali M.n.Khan e.Ahmed Asad Ali Physics Division Pakistan Institute of Nuclear Science and technology Department of Physics Abdul Wali Khan University PInSAT Preston University

The structural and magnetic properties of essentially phase pure AlFe2B2prepared by arc melting were compared with a sample containing impurities. Analysis was carried out by means of synchrotron X-ray diffraction, magnetic measurements and M?ssbauer spectroscopy. The analysis of synchrotron X-ray diffraction data confirmed the orthorhombic structure of space group Cmmm for AlFe2B2with Al13Fe4as main impurity phase. The magnetic measurements revealed an unsaturated ferromagnetic state in AlFe2B2with a transition temperature（Tc） of 286 K. Isothermal magnetization measurment at 5 K gave a saturation magnetization of 0.7 μB per Fe atom while Arrott plots establish the second order nature of ferromagnetic transition. The thermal evolution of M?ssbauer spectra confirmed the ferromagnetic nature of this material revealing an hyperfine field of 73 kOe and an isomer shift of 0.46 mm/s at 100 K. The M?ssbauer spectra of a phase pure sample was compared with the one containing impurity phases. It is suggested that the low temperature paramagnetic contribution in M?ssbauer spectra of phase pure material may have its origin in some intrinsic phenomena arising from defects or inhomogeneities in crystal structure.

关键词： AlFe2B2 Synchrotron X-ray diffraction Ferromagnetism Mossbauer effect spectroscopy

Solvent extraction and recovery of Y(Ⅲ) and Yb(Ⅲ) from fluorspar mineral

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International Journal of Minerals,Metallurgy and Materials 2013年第8期20卷 713-719页

作者： Y.A.el-nadi n.e.el-Hefny H.F.Aly Hot Laboratories Centre Atomic Energy Authority13759Egypt Faculty of Science Jazan UniversityJazan 2097Saudi Arabia

Yttrium and ytterbium were extracted from sulfuric acid medium using triphenylarsine （TPAs） dissolved in kerosene. The influence of different factors, such as shaking time, extractants, metal ions, sulfate ion concentrations, as well as temperature, was studied in detail. From the slope analysis method and IR measurements, the structure of the extracted species was suggested as MSO4（HSO4）.TPAs, where M refers to Y（III） or Yb（III）. The equilibrium constants （Kex） and thermodynamic parameters, such as the change in enthalpy （△H）, free energy （△G）, and entropy （△S）, were calculated. The method of extraction and stripping was applied to obtain the aforementioned metals from a sample of fluorspar mineral giving a recovery yield of 88.2% and 83.5% for yttrium and ytterbium, respectively.

关键词： yttrium ytterbium extraction fluorspar triphenylarsine

LTT switch unit for capacitive energy storages

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Defence Technology（防务技术） 2018年第5期14卷 616-621页

作者： n.e.nechaev B.e.Fridman A.A.Khapugin V.A.Martynenko R.A.Serebrov D.V.efremov Scientific Research Institute of electrophysical Apparatus Saint Petersburg196641Russia electrovipryamitel Saransk430001Russia

When the capacitor cell is discharged in the short-circuit mode, the current pulse amplitude and duration are maximal. Therefore, this mode is the most severe for discharge switches of capacitive energy storage. The characteristics of the transient process of the discharge capacitive energy storage and the current loads acting in the facility discharge circuit have been defined for this mode. The test bench for definition of the LTT(Light Triggered Thyristors) loading capacity is described. The limiting characteristics have been experimentally obtained for LTT, at which there emerges the thermo-generation *** process of OFF-On switching of LTTs has been investigated, the necessity is shown to use the speedup R-C circuits to ensure fast and stable transition of LTT into the conducting state. The design of the switch unit for the capacitive energy storage comprising LTTs and crowbar diodes is described, and the transient processes of current switching in crowbar diodes are considered. The tests carried out during switching of pul se current up to 100 kA at a voltage of 6 kV have confirmed the workability of the switch unit.

关键词： energy storage Power semiconductor switches Photothyristors Pulse power systems

Simulink Behavioral Modeling of a 10-bit Pipelined ADC

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International Journal of Automation and computing 2013年第2期10卷 134-142页

作者： Samir Barra Souhil Kouda Abdelghani Dendouga n. e. Bouguechal Advanced electronics Laboratory Department of Electronics University of Batna Avenue Chahid Boukhlouf Mohamed El Hadi05000Batna Algeria Department of electronics University of M'sila M'silaAlgeria Center for Development of Advanced Technologies Microelectronics and Nanotechnology DivisionAugust 20 1956 City BP 17 BabaHassen Algiers Algeria

The increasing architecture complexity of data converters makes it necessary to use behavioral models to simulate their electrical performance and to determine their relevant data features. For this purpose, a specific data converter simulation environment has been developed which allows designers to perform time-domain behavioral simulations of pipelined analog to digital converters （ADCs）. All the necessary blocks of this specific simulation environment have been implemented using the popular Matlab simulink environment. The purpose of this paper is to present the behavioral models of these blocks taking into account most of the pipelined ADC non-idealities, such as sampling jitter, noise, and operational amplifier parameters （white noise, finite DC gain, finite bandwidth, slew rate, and saturation voltages）. Simulations, using a 10-bit pipelined ADC as a design example, show that in addition to the limits analysis and the electrical features extraction, designers can determine the specifications of the basic blocks in order to meet the given data converter requirements.

关键词： Behavioral modeling analog to digital converters (ADCs) pipelined ADC multiple digital to analog converter (MDAC) sample and hold (S/H)

Geochemical evidence for the characteristic of the 1908 Tunguska explosion body in Siberia,Russia

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Science China earth Sciences 2001年第11期44卷 1029-1037页

作者：谢烈文侯泉林 e.M.Kolesnikov n.V.Kolesnikova 1. Laboratory of Lithosphere Tectonic evolution Institute of Geology and Geophysics Chinese Academy of Sciences 100029 Beijing China 2. Geological Faculty of Moscow State University 119899 Moscow Russia

Twenty-two peat samples collected at different depths of a core including the layer affected by the 1908 explosion in Tunguska area of Central Siberia, Russia, and three basalt samples collected near the site, are analyzed by ICP-MS. The concentrations of Pd, ni, Co, ΣRee, Ti and Sr in the event layers are 4–35 times higher than the background values in the normal layers. The variation of Pd is closely related to ni, Co and ΣRee in the event layers, but not to these elements in the normal layers. It indicates that these excess elements came from the same source, i.e. the Tunguska explosion body. In addition, the patterns of Cl-chondrite-normalized Ree in the event layers ((La/Yb)n ≈2–3) are much flatter than those in the normal layers ((La/Yb)n ≈7–143), and differ from those in the three basalt samples. The concentrations of Ree in the three basalt samples are tens times higher than those in the event layers. It may be inferred that these excess elements could not be produced by the contamination of the terrestrial material, but probably by the Tunguska explosion body. Additionally, the ratios of Ti/ni and Sr/Co in the event layers are close to those in comet. It implies that the solid part of the explosion body was compositionally similar to carbonaceous chondrites (Cl) and more probably a small comet. In terms of the Pd excess fluxes in the explosion area, it can be estimated that the celestial body that exploded over Tunguska in 1908 weighed more than 107 tons, corresponding to a radius of > 126 m.

关键词： Tunguska explosion trace elements geochemistry

Unique Outcomes of Internal Heat Generation and Thermal Deposition on Viscous Dissipative Transport of Viscoplastic Fluid over a Riga-Plate

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Communications in Theoretical Physics 2018年第1期69卷 68-76页

作者： Z.Iqbal ehtsham Azhar Zaffar Mehmood e.n.Maraj Department of Mathematics Faculty of Sciences HITEC University

Boundary layer stagnation point flow of Casson fluid over a Riga plate of variable thickness is investigated in present article. Riga plate is an electromagnetic actuator consists of enduring magnets and gyrated aligned array of alternating electrodes mounted on a plane surface. Physical problem is modeled and simplified under appropriate transformations. effects of thermal radiation and viscous dissipation are incorporated. These differential equations are solved by Keller Box Scheme using MATLAB. Comparison is given with shooting techniques along with RangeKutta Fehlberg method of order 5. Graphical and tabulated analysis is drawn. The results reveal that eckert number,radiation and fluid parameters enhance temperature whereas they contribute in lowering rate of heat transfer. The numerical outcomes of present analysis depicts that Keller Box Method is capable and consistent to solve proposed nonlinear problem with high accuracy.

关键词： Riga-plate Keller Box method Casson fluid variable thickness stagnation point flow internal heat generation

Hopf-flip bifurcation of high dimensional maps and application to vibro-impact systems

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Acta Mechanica Sinica 2005年第4期21卷 402-410页

作者： Jianhua Xie Wangcai Ding e.H. Dowell L. n. Virgin Department of Applied Mechanics and engineering Southwest Jiaotong University Chengdu 610031 China School of Mechanical engineering Lanzhou Jiaotong UniversityLanzhou 730070 China School of engineering.Duke University. Durham NC27708-0300USA

This paper addresses the problem of Hopf-flip bifurcation of high dimensional maps. Using the center manifold theorem, we obtain a three dimensional reduced map through the projection technique. The reduced map is further transformed into its normal form whose coefficients are determined by that of the original system. The dynamics of the map near the Hopf-flip bifurcation point is approximated by a so called “time-2τ^2 map” of a planar autonomous differential equation. It is shown that high dimensional maps may result in cycles of period two, tori T^1 （Hopf invariant circles）, tori 2T^1 and tori 2T^2 depending both on how the critical eigenvalues pass the unit circle and on the signs of resonant terms＇ coefficients. A two-degree-of-freedom vibro-impact system is given as an example to show how the procedure of this paper works. It reveals that through Hopf-flip bifurcations, periodic motions may lead directly to different types of motion, such as subharmonic motions, quasi-periodic motions, motions on high dimensional tori and even to chaotic motions depending both on change in direction of the parameter vector and on the nonlinear terms of the first three orders.

关键词： Maps Vibro-impact dynamics Hopf-flip bifurcation Torus Chaos

Characterization of a new shielding rubber for use in neutron–gamma mixed fields

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nuclear Science and Techniques 2018年第3期29卷 78-85页

作者： M.Salimi n.Ghal-eh e.Asadi Amirabadi School of Physics Damghan UniversityP.O.Box 36716-41167DamghanIran Department of Physics School of SciencesFerdowsi University of MashhadP.O.Box 91775-1436MashhadIran Laser-Plasma Research Institute Shahid Beheshti UniversityP.O.Box 19839-63113TehranIran

A variety of formulations was investigated for the fabrication of an appropriate shielding rubber to be used in neutron–gamma mixed fields. Having considered the required mechanical properties together with tungsten as the gamma-ray absorbing element, calculations with MCnPX 2.6 code confirmed that the incorporation of 5 weight percentage(wt%) of boron carbide exhibited the best performance as a thermal neutron absorber. A series of both experimental and simulation results are provided for comparison.

关键词： Shielding Rubber neutron Gamma MCnPX