消息与动态

<正> 台式扭摆转动惯量测试仪台式扭摆转动惯量测试仪由空心转轴台式扭摆和电子测试仪两部分组成.空心转轴台式扭摆作为物理量变换器与电子测试仪连接.空心转轴台式扭摆主要包括空心转轴、可拆卸平台,平面螺旋弹簧、通孔光照式电传感器、定位机构及可调节 V 型架等.可调节 V 型架固定在可拆平台上,可拆卸平台可以放     

线性特性与卡氏定理

<正> 力学中的卡氏(Castigliano)定理是说,变形能“对任一外力 P.的偏导数,等于 P.作用点沿 P.方向上的位移δ,用公式表示这一公式在教科书中是从变形能出发得到的,并且在推导过程中假定所求的位移点及方向上有力作用.但在实际应用中,往往在所要求的点及位移方向上没有力作用.这时教科书告诉我们是用附加力的办     

Application of colloidal palladium nanoparticles for labeling in electron microscopy

The application of palladium nanoparticles as electron-dense markers for labeling in both transmission and scanning electron microscopy requires their conjugation to a specific protein. The conjugation protocol described here includes the dihydrolipoic acid (DHLA) capping of Pd nanoparticles (8 nm equivalent diameter) and their subsequent covalent attachment to functional protein molecules such as streptavidin, protein A, or avidin. The single-step reaction was mediated using the cross-linking agent ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). The final Pd conjugates were fully functional, as demonstrated by labeling of ultrathin resin sections of either bovine serum albumin or secretory granules of the salivary gland isolated from the partially fed female Ixodes ricinus tick. The results of bovine serum labeling were quantified, statistically evaluated, and compared with results obtained using commercially available gold particle conjugates (10 nm diameter). The highest values of labeling density were achieved using both streptavidin-Pd (106 ± 7 particles/μm2) and protein A-Au conjugates (130 ± 18 particles/μm2) compared to a commercial streptavidin-Au (66 ± 16 particles/μm2) and protein A-Pd conjugates (70 ± 11 particles/μm2). The concentrations of both DHLA and EDC, pH during conjugation, and finally thorough washing away of unbound proteins crucially influenced conjugation.     

Electron image series reconstruction of twin interfaces in InP superlattice nanowires

The twin interface structure in twinning superlattice InP nanowires with zincblende structure has been investigated using electron exit wavefunction restoration from focal series images recorded on an aberration-corrected transmission electron microscope. By comparing the exit wavefunction phase with simulations from model structures, it was possible to determine the twin structure to be the ortho type with preserved In-P bonding order across the interface. The bending of the thin nanowires away from the intended 110 axis could be estimated locally from the calculated diffraction pattern, and this parameter was successfully taken into account in the simulations.     

Simulation of photoelectron spectra using the reflection principle in combination with unrestricted excitation ADC2 to assess the accuracy of excited-state calculations

The gas-phase photoelectron spectra of ethene, formaldehyde, formic acid and difluoromethane are simulated using the reflection principle and the unrestricted second-order algebraic diagrammatic construction [UADC(2)] scheme of the polarization propagator for the computation of the vertical-excited states of the cations at the equilibrium geometry of the parent neutral molecule. Comparison is made with experimental spectra and the established highly accurate ionization IP-ADC(3) theory to gain insight into the accuracy and applicability of recently developed excitation UADC schemes. Within UADC(2), we distinguish between the strict and extended schemes UADC(2)-s and UADC(2)-x. While the latter approach is found to slightly underestimate the experimental photoelectron spectra by 0.3 eV and can thus be regarded as a reliable scheme within the limits of the applied reflection principle and the underlying approximations, the UADC(2)-s scheme tends to overestimate the excitation energies by about 0.5 eV. Time-dependent density functional theory is also applied in combination with the standard B3LYP xc functional and turns out to be a useful computational tool for the simulation of the photoelectron spectra of the studied species.     

Novel covalent bond in proteins: calculations on model systems question the bond stability

We have investigated the sulfilimine covalent link between methionine (Met) and lysine (Lys), recently identified in collagen IV (R. Vanacore, A.-J. L. Ham, M. Voehler, C. R. Sanders, T. P. Conrads, T. D. Veenstra, K. B. Sharpless, P. E. Dawson, B. G. Hudson, Science 2009, 325, 1230), and have explored its stability with respect to both the redox processes and UV radiation by means of advanced computational methods. We have concluded that the bond should be present in a protonated state, (-NH=S-)(+). The bond is characterized by a relatively high standard reduction potential, that is, the bond should not be stable in a typical cell environment; if the sulfilimine bond exists (as suggested by the experiment) then the bond has to be supported by the protein environment. The sulfilimine bond then destabilizes the protein structure with respect to the alternative tertiary structure. We discuss conditions under which the bond could be formed as well as other possible structural arrangements consistent with the Met-Lys stoichiometry; some of the alternative bond motifs are more thermodynamically stable than the sulfilimine bond. We suggest that the character of the Met-Lys contact could be approached via NEXAFS spectroscopy. Finally, we show that the protonation brings photostability to the sulfilimine bond.     

幂硬化材料平面应变条件下的复应力函数解

本文导出应力函数的几个特解，以便增加对幂硬化材料平面应变问题的认识     

The First Total Synthesis of Triprenylquinone and Hydroquinones

Marine natural products have received much attention for their attractive structural features and biological activities1. Since the isolation of the moritoside, about 10 related triprenylquinones and hydroquinones were isolated. Some of these natural products exhibit interesting biological effects including inhibit cell division of fertilized starfish eggs2 and anti-HIV3. Triprenylquinone and hydroquinones 1, 2 and 3 were recently isolated from endemic nudibranch Leminda millecra collected i…     

POSITRON ANNIHILATION WITH VACANCIES IN THIN SURFACE LAYER OF As HEAVILY DOPED Si

The lifetime spectroscopy of slow positron accelerated with linear accelerator and pulse punch system was first used to analyze the vacancies in the thin surface layer of silicon heavily doped with arsenic. The results demonstrated that no mono-vacancy was detected to support the arsenic-vacancy complex models for explaining the electrical deactivation mechanism of arsenic-heavily-doped silicon.     

心脏内部血流实时动态径迹的非侵入性显示方法——超声微泡血流图

前言人体心内血液流动是生命存在的象征.显示人体心内血液流场对研究心脏力学及其病理改变有着重要意义.虽然流体力学中显示流场动态的方法有多种形式,但要显示人体心内血液流场,又要做到...