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961.
Lorraine M. Deck Robert T. Paine Elizabeth R. BrightSabrina Ouizem Diane A. Dickie 《Tetrahedron letters》2014
Simple, aqueous-based syntheses of methylpyridine and methylpyridine N-oxide decorated 3,4-dihydro-2H-naphthoxazine and 2,3-dihydro-1H-naphthoxazine monomers, as well as thermally promoted syntheses of 3,4-dihydro-2H-benzoxazine monomers and bisoxazine methylpyridine derivatives of substituted 1,5-, 2,6-, and 2,7-dihydroxynaphthalenes are described. The crystal structures of two derivatives are presented. 相似文献
962.
Sebastian Send Ali Abboud Wolfram Leitenberger Manfred S. Weiss Robert Hartmann Lothar Strüder Ullrich Pietsch 《Journal of Applied Crystallography》2012,45(3):517-522
A crystal of hen egg‐white lysozyme was analyzed by means of energy‐dispersive X‐ray Laue diffraction with white synchrotron radiation at 2.7 Å resolution using a pnCCD detector. From Laue spots measured in a single exposure of the arbitrarily oriented crystal, the lattice constants of the tetragonal unit cell could be extracted with an accuracy of about 2.5%. Scanning across the sample surface, Laue images with split reflections were recorded at various positions. The corresponding diffraction patterns were generated by two crystalline domains with a tilt of about 1° relative to each other. The obtained results demonstrate the potential of the pnCCD for fast X‐ray screening of crystals of macromolecules or proteins prior to conventional X‐ray structure analysis. The described experiment can be automatized to quantitatively characterize imperfect single crystals or polycrystals. 相似文献
963.
Lukas Lomb Jan Steinbrener Sadia Bari Daniel Beisel Daniel Berndt Christian Kieser Martin Lukat Niklas Neef Robert L. Shoeman 《Journal of Applied Crystallography》2012,45(4):674-678
Serial femtosecond crystallography (SFX) using X‐ray free‐electron laser (FEL) sources has the potential to determine the structures of macromolecules beyond the limitation of radiation damage and without the need for crystals of sufficient size for conventional crystallography. In SFX, a liquid microjet is used to inject randomly oriented crystals suspended in their storage solution into the FEL beam. Settling of crystals in the reservoir prior to the injection has been found to complicate the data collection. This article details the development of an anti‐settling sample delivery instrument based on a rotating syringe pump, capable of producing flow rates and liquid pressures necessary for the operation of the injector. The device has been used successfully with crystals of different proteins, with crystal sizes smaller than 20 µm. Even after hours of continuous operation, no significant impairment of the experiments due to sample settling was observed. This article describes the working principle of the instrument and sets it in context with regard to the experimental conditions used for SFX. Hit rates for longer measuring periods are compared with and without the instrument operating. Two versions of the instrument have been developed, which both deliver sample at a constant flow rate but which differ in their minimum liquid flow rates and maximum pressures. 相似文献
964.
Naji S. Husseini Osama A. Alsaied Robert E. Thorne Viatcheslav Berejnov 《Journal of Applied Crystallography》2006,39(2):244-251
Vitrification of aqueous cryoprotectant mixtures is essential in cryopreservation of proteins and other biological samples. Systematic measurements of critical cryoprotective agent (CPA) concentrations required for vitrification during plunge‐cooling from T = 295 K to T = 77 K in liquid nitrogen are reported. Measurements on fourteen common CPAs, including alcohols (glycerol, methanol, 2‐propanol), sugars (sucrose, xylitol, dextrose, trehalose), polyethylene glycols (ethylene glycol, PEG 200, PEG 2000, PEG 20000), glycols [dimethyl sulfoxide (DMSO), 2‐methyl‐2,4‐pentanediol (MPD)], and salt (NaCl), were performed for volumes ranging over four orders of magnitude from ∼1 nl to 20 µl, and covering the range of interest in protein crystallography. X‐ray diffraction measurements on aqueous glycerol mixtures confirm that the polycrystalline‐to‐vitreous transition occurs within a span of less than 2% w/v in CPA concentration, and that the form of polycrystalline ice (hexagonal or cubic) depends on CPA concentration and cooling rate. For most of the studied cryoprotectants, the critical concentration decreases strongly with volume in the range from ∼5 µl to ∼0.1 µl, typically by a factor of two. By combining measurements of the critical concentration versus volume with cooling time versus volume, the function of greatest intrinsic physical interest is obtained: the critical CPA concentration versus cooling rate during flash‐cooling. These results provide a basis for more rational design of cryoprotective protocols, and should yield insight into the physics of glass formation in aqueous mixtures. 相似文献
965.
H. Haddadi S. Bouvier M. Banu C. Maier C. Teodosiu 《International Journal of Plasticity》2006,22(12):2226-2271
966.
Trushar Gohil Robert H. P. McGregor Dominik Szczerba Kathrin Burckhardt Krishnamurthy Muralidhar Gábor Székely 《国际流体数值方法杂志》2011,66(8):1037-1067
Cardiovascular diseases are one of the major causes of long‐term morbidity and mortality in human beings. The nearly epidemic increase in prevalence of such diseases poses a serious threat to public health and calls for efficient methods of diagnosis and treatment. Non‐invasive diagnostic procedures such as MRI are often used in this context; however, these are limited in terms of spatial and temporal resolution and do not provide information on time‐dependent pressures and wall shear stresses—key quantities considered to be partially responsible for the formation and development of related pathologies. The present study is concerned with the numerical simulation of oscillatory flow through the abdominal aortic bifurcation. Computational fluid dynamics simulation of oscillatory flow in a branched geometry at high Reynolds numbers poses considerable challenges. The present study reports a detailed comparison of simulations performed with a finite volume and a finite element method, two approaches with significant differences in their discretization strategy, treatment of boundary conditions and other numerical aspects. Both solvers were parallelized, using loop parallelization of the BiCGStab linear solver for the finite volume and domain decomposition based on the Schur complement method for the finite element technique. The experience gained with these two approaches for the solution of flow in a bifurcation forms the focus of this study. Although similar results were obtained for both methods, the computation time required for convergence was found to be significantly smaller for the finite element approach. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
967.
This paper comprises an implementation of a fourth‐order Runge–Kutta discontinuous Galerkin (RKDG4) scheme for computing the open‐channel flow equations. The main features of the proposed methodology are simplicity and easiness in the implementation, which may be of possible interest to water resources numerical modellers. A version of the RKDG4 is blended with the Roe Riemann solver, an adaptive high‐order slope limiting procedure, and high‐order source terms approximations. A comparison of the performance of the proposed method with lower‐order RKDG models is performed showing a benefit of considering the RKDG4 model. The scheme is applied to computerize the Saint Venant system by considering benchmark tests that have exact solutions. Finally, numerical results are illustrated discussing the performance of the proposed high‐order model. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
968.
Quentin Araud Pascal Finaud‐Guyot Vincent Guinot Robert Mosé José Vazquez 《国际流体数值方法杂志》2012,70(12):1590-1604
Discontinuous Galerkin (DG) methods have shown promising results for solving the two‐dimensional shallow water equations. In this paper, the classical Runge–Kutta (RK) time discretisation is replaced by the eigenvector‐based reconstruction (EVR) that allows the second‐order time accuracy to be achieved within a single time‐stepping procedure. Moreover, the EVRDG approach yields stable solutions near drying and wetting fronts, whereas the classical RKDG approach yields instabilities. The proposed EVRDG technique is compared with the original RKDG approach on various test cases with analytical solutions. The EVRDG solutions are shown to be as accurate as those obtained with the RKDG scheme. Besides, the EVRDG scheme is 1.6 times faster than the RKDG method. Simulating dambreaks involving dry beds confirms that EVRDG scheme gives correct solutions, whereas the RKDG method yields instabilities. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
969.
Roman Bogacz Robert Konowrocki 《Archive of Applied Mechanics (Ingenieur Archiv)》2012,82(10-11):1313-1323
The paper is devoted to the experimental, theoretical analysis and computer simulation of influence of elastic properties of contact stiffness and wheel-plate stiffness on the forces of vehicle-track interaction. Three types of wheels are considered with different contact stiffness and wheel-plate design. Exemplary simulation of freight car interaction with track which posses one corrugated rail for each type of wheel is presented. 相似文献
970.
A space and time third‐order discontinuous Galerkin method based on a Hermite weighted essentially non‐oscillatory reconstruction is presented for the unsteady compressible Euler and Navier–Stokes equations. At each time step, a lower‐upper symmetric Gauss–Seidel preconditioned generalized minimal residual solver is used to solve the systems of linear equations arising from an explicit first stage, single diagonal coefficient, diagonally implicit Runge–Kutta time integration scheme. The performance of the developed method is assessed through a variety of unsteady flow problems. Numerical results indicate that this method is able to deliver the designed third‐order accuracy of convergence in both space and time, while requiring remarkably less storage than the standard third‐order discontinous Galerkin methods, and less computing time than the lower‐order discontinous Galerkin methods to achieve the same level of temporal accuracy for computing unsteady flow problems. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献