Engineered-membranes: A novel concept for clustering of native lipid bilayers

A strategy for clustering of native lipid membranes is presented. It relies on the formation of complexes between hydrophobic chelators embedded within the lipid bilayer and metal cations in the aqueous phase, capable of binding two (or more) chelators simultaneously Fig. 1. We used this approach with purple membranes containing the light driven proton pump protein bacteriorhodopsin (bR) and showed that patches of purple membranes cluster into mm sized aggregates and that these are stable for months when incubated at 19 °C in the dark. The strategy may be general since four different hydrophobic chelators (1,10-phenanthroline, bathophenanthroline, Phen-C10, and 8-hydroxyquinoline) and various divalent cations (Ni²⁺, Zn²⁺, Cd²⁺, Mn²⁺, and Cu²⁺) induced formation of membrane clusters. Moreover, the absolute requirement for a hydrophobic chelator and the appropriate metal cations was demonstrated with light and atomic force microscopy (AFM); the presence of the metal does not appear to affect the functional state of the protein. The potential utility of the approach as an alternative to assembled lipid bilayers is suggested.     

A specific standard for quality in fundamental research

 The specific standard described here constitutes the heart of the quality system set up by the Commissariat à l'Energie Atomique – French Atomic Energy Commission – for its main "Fundamental Research" entity, the Directorate for the Sciences of Matter. It is a coherent standard (set of shared rules and provisions laid out in a clear fashion) designed, in the first instance, to provide those taking part in research, including the hierarchy, with the means to satisfy their requirements in the field of quality. And, secondly, to create the conditions for recognition of this action by third parties, which all research entities must nowadays convince of their trustworthiness (supervisory ministries, research partners, industrial companies, etc.). This standard places particular emphasis on the preponderant roles of initiative and freedom in fundamental research, which are a prerequisite for creativity, innovation and, last but not least, the motivation of personnel.     

X-ray double-crystal rocking curves in GaAlAs/GaAs heterostructures

Summary X-ray double-crystal rocking curves of Ga_1−x Al _x As/GaAs heterostructures have been calculated using a dynamical diffraction model for the general case of Bragg reflection geometry. Different experimental configurations have been considered and the possibility of studying both slightly mismatched and relatively thin layers has been investigated. Experimental rocking curves have been measured using the CuKα ₁ radiation, the 004 symmetric reflection and a perfect crystal as the monochromator. An excellent agreement between calculated and experimental rocking curves has been found and this demonstrates the reliability of both the experimental procedure and the theoretical approach.     

Corrections to the wave function and the hyperfine structure in exotic atoms

We present an analytical evaluation of radiative corrections in exotic atoms induced by the one-loop electronic vacuum polarization. We evaluate corrections to the energy levels, to the wave function (at the origin) and to the hyperfine structure. We treat all corrections analytically within a non-relativistic approximation. Agreement is found with a few available numerical results. The analytical treatment allows to determine the asymptotic forms of the corrections in the limit of a small atomic radius, which for the atomic systems considered corresponds to a large mass of the constituent particle as compared to the electron mass. The asymptotics can be verified using the effective charge approach. Received: 28 January 1998 / Accepted: 13 March 1998     

Statistical theory of force-induced unzipping of DNA

The unzipping transition under the influence of external force of a dsDNA molecule has been studied using the Peyrard-Bishop Hamiltonian. The critical force F_c(T) for unzipping calculated in the constant force ensemble is found to depend on the potential parameter k which measures the stiffness associated with a single strand of DNA and on D, the well depth of the on-site potential representing the strength of hydrogen bonds in a base pair. The dependence on temperature of F_c(T) is found to be (T_D - T)^1/2 (T_D being the thermal denaturation temperature) with F_c(T_D) = 0 and F_c(0) = . We used the constant extension ensemble to calculate the average force F(y) required to stretch a base pair a y distance apart. The value of F(y) needed to stretch a base pair located far away from the ends of a dsDNA molecule is found twice the value of the force needed to stretch a base pair located at one of the ends to the same distance for y 1.0 . The force F(y) in both cases is found to have a very large value for y 0.2 compared to the critical force found from the constant force ensemble to which F(y) approaches for large values of y. It is shown that the value of F(y) at the peak depends on the value of k which measures the energy barrier associated with the reduction in DNA strand rigidity as one passes from dsDNA to ssDNA and on the value of the depth of the on-site potential. The effect of defects on the position and height of the peak in the F(y) curve is investigated by replacing some of the base pairs including the one being stretched by defect base pairs. The formation and behaviour of a loop of Y shape when one of the ends base pair is stretched and a bubble of ssDNA with the shape of an eye when a base pair far from ends is stretched are investigated.     

Relationships between mastication conditions and rheological behavior of a natural rubber

The mastication of natural rubber results in the shortening of the long molecular chains, which affects the viscosity of the material. Mechanical and thermo-oxidative breakdowns are the two major factors that interfere during mastication and processing of natural rubber. In an attempt to characterize the viscous behavior of a such product during processing, rheological properties of unvulcanized rubber are studied with a capillary rheometer and a parallel plate rheometer, in small amplitude oscillatory shear. An investigation is carried out with an internal mixer to determine the effect of mastication and temperature on the rheological properties. The influence of thermomechanical effect is quantified as a function of the specific energy and mastication temperature. Depending on mastication conditions, the variation of viscosity may be important and its decrease is quantified by integrating the specific energy and the mastication temperature in a Carreau-Yasuda model.     

Extraction of the neutron charge form factor G<Superscript>n</Superscript><Subscript>E</Subscript>(Q<Superscript>2</Superscript>) from the charge form factor of deuteron G<Superscript>d</Superscript><Subscript>C</Subscript>(Q<Superscript>2</Superscript>)

We extract the neutron charge form factor G ⁿ _E(Q ²) from the charge form factor of deuteron G ^d _C(Q ²) obtained from T ₂₀(Q ²) data at 0≤Q ²≤ 1.717 (GeV/c)². The extraction is based on the relativistic impulse approximation in the instant form of the relativistic Hamiltonian dynamics. Our results (12 new points) are compatible with existing values of the neutron charge form factor of other authors. We propose a fit for the whole set (36 points) taking into account the data for the slope of the form factor at Q ² = 0. Received: 26 July 2002 / Accepted: 18 September 2002 / Published online: 4 February 2003 RID="a" ID="a"e-mail: krutov@ssu.samara.ru RID="b" ID="b"e-mail: troitsky@theory.sinp.msu.ru Communicated by V.V. Anisovich     

超光滑表面加工方法的新进展

通过回顾超光滑表面加工技术的发展历程,对多种具有代表性的超光滑表面加工方法的原理和应用作了简单阐述,并重点提出和介绍了一种大气等离子体抛光方法。该方法实现了利用常压等离子体激发化学反应来完成超光滑表面的无损伤抛光加工,并首次引入电容耦合式炬型等离子体源,为高质量光学表面的加工提供了一条新的途径。试验结果表明,在针对单晶硅的加工过程中实现了1μm/min的加工速率和Ra 0.6nm的表面粗糙度。     

栅耦合型静电泄放保护结构设计

提出了一种新型栅耦合型静电泄放(ESD)保护器件——压焊块电容栅耦合型保护管.该结构不仅解决了原有栅耦合型结构对特定ESD冲击不能及时响应的问题，而且节省了版图面积，提高了ESD失效电压.0.5 μm标准互补型金属氧化物半导体工艺流片测试结果表明，该结构人体模型ESD失效电压超过8 kV.给出了栅耦合型ESD保护结构中ESD检测结构的设计方法，能够精确计算检测结构中电容和电阻的取值. 关键词： 静电泄放 栅耦合 金属氧化物半导体场效应管 压焊块电容     

Temperature dependence of thermal property for lead nitrate crystal

Thermal property was measured in a lead nitrate crystal, Pb(NO₃)₂, at temperatures from 90 to 340 K by use of ac calorimetry technique. The heat capacity derived from the measurements showed temperature dependence with thermal hysteresis, in the temperature region from 240 to 300 K. The anomaly of the heat capacity was found in the vicinity of 275.22 K. The broad temperature variation in the heat capacity was observed in the region from 235 to 260 K.