摘要:

Procedures for an independent characterization of lyotropic nematics by X‐ray diffraction (XD) are presented.Nc(cylindrical micelles) andNd(discotic micelles) can be distinguished on the basis of surface orientation alone by a method of sample scanning through the X‐ray beam. The sign of the diamagnetic anisotropy susceptibility can also be independently obtained. The differences between optical and XD information for such a characterization are discus

ISSN:1600-5767    

DOI:10.1107/S0021889889005273

出版商:International Union of Crystallography    

年代:1989

数据来源: WILEY

摘要:

A system has been constructed which uses a primary‐beam focusing monochromator Debye–Scherrer X‐ray method to perform simultaneouslyin situX‐ray diffraction and resistivity measurements at temperatures of 100 to 1000 K. The Inel curved linear detector, which is capable of recording 120° of 20 angle without moving the detector, makes the Debye–Scherrer geometry possible for high‐speed dynamic studies. The angular resolution of this system is sufficient to observe the separation of a mixture of tungsten and molybdenum powders. The sensitivity of the system makes it possible to record the diffraction pattern from a 100 Å gold film. The sheet resistivity of the sample can be recorded simultaneously to provide a structure‐property correlation. Comparisons with other X‐ray diffraction methods using thin

ISSN:1600-5767    

DOI:10.1107/S0021889889006412

出版商:International Union of Crystallography    

年代:1989

数据来源: WILEY

摘要:

Grazing‐incidence small‐angle X‐ray scattering (GISAXS) is introduced as a method of studying discontinuous thin films. In this method, the incident beam is totally externally reflected from the substrate followed by small‐angle scattering of the refracted beam by the thin film. The experiment described establishes the ability of GISAXS to provide size information for islands formed in the initial stages of thin film growth. The data presented are for gold films of 7 and 15 Å average thicknesses on Corning 7059 glass substrates. The advantages of this technique are that it is non‐destructive, can be donein situ, provides excellent sampling statistics, does not necessarily require a synchrotron source, and is not limited to thin or conductin

ISSN:1600-5767    

DOI:10.1107/S002188988900717X

出版商:International Union of Crystallography    

年代:1989

数据来源: WILEY

摘要:

A method is proposed for measuring textures on the surfaces of thin wires. The method is based on a numerical absorption correction analysis of the sample. Analytical formulas are given for thicker or more strongly absorbing specimens. Experimental work is presented to illustrate the use of the method.

ISSN:1600-5767    

DOI:10.1107/S002188988900748X

出版商:International Union of Crystallography    

年代:1989

数据来源: WILEY

摘要:

Multiple small‐angle neutron scattering was used to characterize the microstructure evolution of porous silica as a function of thermal processing. This new technique offers a statistically significant determination of microstructure morphology in the 0.08–10 μm range, which was previously inaccessible without increasing the resolution of the currently available scattering spectroscopy beamlines. All of the scatterers, which in the present work are pores within ceramic bodies, are measured whether they are open or closed. Earlier mercury porosimetry and nitrogen desorption measurements of the microporous silica system indicated that there are two major populations of pores in this material, differing in pore size by approximately an order of magnitude. In this work, it was found that densification during the intermediate stages of sintering is accompanied by coarsening to radii>0.22 μm within the population of large pores in microporous silica. In the late stages of sintering, there are no detectable pores with radii>0.08 μm, and radii of gyration equal to 33 and 28 nm were measured. Finally, Monte Carlo simulations were carried out to complement the neutron‐scattering measurements, to predict the influence on the results of the bimodal distribution, and to explore the sensitivity of the multiple

ISSN:1600-5767    

DOI:10.1107/S0021889889007119

出版商:International Union of Crystallography    

年代:1989

数据来源: WILEY

摘要:

Small‐angle neutron scattering was used to study the structure of the dense cores of intact neurosecretory vesicles (NSV). Contrast‐variation techniques were used to minimize the scattering due to vesicle membranes and emphasize that due to the cores. By examination of a suspension of NSV membranes along with the intact NSV, residual membrane scattering was suppressed. The resultant scattering is inconsistent with model calculations which assume that the dense state of the vesicle cores is achieved by random dense packing or crystallization of small globular particles. Rather, the data suggest that the core constituents exist in a disordered state, forming aggregates with radii of gyration significantly larger than 10

ISSN:1600-5767    

DOI:10.1107/S0021889889007491

出版商:International Union of Crystallography    

年代:1989

数据来源: WILEY

摘要:

There is a simple way to apply non‐crystallographic symmetry during the course of crystallographic coordinate refinement or structure determination by molecular replacement. A phase set is generated from the molecular coordinates which is invariant with respect to the non‐crystallographic symme

ISSN:1600-5767    

DOI:10.1107/S0021889889007570

出版商:International Union of Crystallography    

年代:1989

数据来源: WILEY

摘要:

Series‐expansion coefficients for an orientation distribution function (ODF) of cold‐rolled aluminium sheet were calculated from the intensity of Debye–Scherrer rings obtained in an experiment using synchrotron radiation. Calculated and observed pole figures demonstrate that a sufficiently good approximation to the ODF is obtained from coefficients calculated t

ISSN:1600-5767    

DOI:10.1107/S0021889889007673

出版商:International Union of Crystallography    

年代:1989

数据来源: WILEY

摘要:

A small position‐sensitive3He gas detector has been developed for diffraction studies using short‐wavelength neutrons. It covers 32 × 32 pixels with a 2 mm resolution, which in the present set up corresponds to 0.25°, and the efficiency is 75% at a wavelength of 0.8 Å. The detector has been used for standard data collection, as well as for studies of twinned crystals and measurements involving parasitic reflections. In all cases it has improved the mode and speed of the measurement, with gain factors compared with single detectors which range from more than two in standard measurements to several hundred for the study of details of the Bragg peak(s). The computation time in data analysis and the storage of the data are no major limitations, partly due to the smallness of the data array, and partly due to efficient packin

ISSN:1600-5767    

DOI:10.1107/S0021889889007752

出版商:International Union of Crystallography    

年代:1989

数据来源: WILEY

摘要:

Simplified representations of components of nucleic acids have been designed and implemented as programs integrated with other software that draws schematic diagrams of proteins. Examples illustrating the structures of oligonucleotides, tRNA and a protein–nucleic acid complex indicate the utility of these representations for making intelligible illustrations of complex structures containing nucleic acid

ISSN:1600-5767    

DOI:10.1107/S0021889889008265

出版商:International Union of Crystallography    

年代:1989

数据来源: WILEY