Number Of Diffraction Patterns Research Articles

Common architectures in cyanobacteria Prochlorococcus cells visualized by X-ray diffraction imaging using X-ray free electron laser

Visualization of intracellular structures and their spatial organization inside cells without any modification is essential to understand the mechanisms underlying the biological functions of cells. Here, we investigated the intracellular structure of cyanobacteria Prochlorococcus in the interphase by X-ray diffraction imaging using X-ray free-electron laser. A number of diffraction patterns from single cells smaller than 1 µm in size were collected with high signal-to-noise ratio with a resolution of up to 30 nm. From diffraction patterns, a set of electron density maps projected along the direction of the incident X-ray were retrieved with high reliability. The most characteristic structure found to be common among the cells was a C-shaped arrangement of 100-nm sized high-density spots, which surrounded a low-density area of 100 nm. Furthermore, a three-dimensional map reconstructed from the projection maps of individual cells was non-uniform, indicating the presence of common structures among cyanobacteria cells in the interphase. By referring to the fluorescent images for distributions of thylakoid membranes, nucleoids, and carboxysomes, we inferred and represented their spatial arrangements in the three-dimensional map. The arrangement allowed us to discuss the relevance of the intracellular organization to the biological functions of cyanobacteria.

Reconstruction of 3D structure for nanoscale biological objects from experiments data on super-bright X-ray free electron lasers (XFELs): dependence of the 3D resolution on the experiment parameters

The ability to investigate 3D structure of biomolecules, such as proteins and viruses, is essential in biology and medicine. With the invention of super-bright X-ray free electron lasers (e.g. European XFEL and Linac Coherent Light Source (LCLS)) the Single Particle Imaging (SPI) approach allows to reconstruct 3D structures from many 2D diffraction images produced in the experiment by X-rays scattered on the biomolecule exposed in different orientations. In the same time, there are still many challenging problems in experiment setup, sample preparation and injection, which limit number and quality of obtained diffraction patterns and, consequently, limit achievable resolution of recovered 3D structure. However even with the current experimental limitations it is possible to reconstruct 3D structures of some large biomolecules. An important question arises: what range of 3D resolution is possible to achieve under experimental conditions available now. We investigated how the number and quality of diffraction images affect the 3D resolution. First the SPI experiment was simulated and reconstructed with the Dragonfly software. Then we analyzed how the number of diffraction images and the beam intensity affect the final 3D resolution. We come to the following conclusions:1) starting from the beam intensity value (fluence) equal to 3×1012photons/μm2 the resolution becomes to be almost constant;2) the resolution strongly depends on the number of diffraction patterns. More than 10 000 diffraction images are required to get 4 nm resolution.

Single-beam phase retrieval with partially coherent light illumination

A single-beam phase retrieval method with partially coherent illumination is proposed. By using an obverse and reverse iterative (ORI) algorithm, objects can be reconstructed within less time by recording a sequence of diffraction patterns at different axial planes under partially coherent light illumination. Partially coherent light illumination reduces coherent noise and the number of diffraction patterns needed for reconstruction. Thus, the whole process is fast and has high immunity to external perturbation due to the reference-less configuration. Both simulation and experimental results are presented to demonstrate the feasibility of the proposed approach.

Characterization of gamma irradiated polyethylene films by DSC and X-ray diffraction techniques

The effect of gamma radiation on the thermal behavior and crystalline structure of low density polyethylene (LDPE) has been investigated using differential scanning calorimetry (DSC) and X-ray diffraction techniques (XRD). Gamma irradiation was carried out in atmospheric air to a maximum dose of 883 kGy. DSC results of the heating run from room temperature up to 150 °C showed that the melting temperature (Tm), and onset temperature of LDPE film decrease linearly with increasing irradiation dose. However, upon cooling LDPE film from 150 °C to room temperature, the crystallization temperature (Tc) and onset temperature were found to decrease non-linearly with increasing irradiation dose up to 500 kGy and then tended to level off. The change in heat of fusion (ΔHf) with irradiation dose was found to proceed with different behaviour, two stages, with a kink at irradiation dose of about 500 kGy, being observed. This suggests the occurrence of degradation and crosslinking at low and high doses, respectively. However, parameters of the X-ray diffraction pattern such as number of diffraction patterns, peak position (2θ) and width of the diffraction pattern, support the results of DSC measurements. © 2000 Society of Chemical Industry

Quantitative assessment of radiation damage in protein crystal

Radiation damage is a well known phenomenon in the electron microscopic study of thin crystals of macromolecules. A quantitative description of radiation damage is essential for at least 3 reasons: (i) it can provide numerical parameters for evaluating the extent of specimen damage at various experimental conditions, (ii) it can provide an indicator as to the maximum number of diffraction patterns and images obtainable from a single crystal before the specimen is significantly altered, and (iii) since the specimen is being altered after the initial hit by the electrons, schemes are needed to make correction of the data prior to its use for structural calculation. This paper primarily deals with the methodology used to evaluate the quantitative aspects of radiation damage of thin protein crystals. The example of crystal used in this study was crotoxin complex embedded in glucose.A standard set of data recorded in a radiation damage study is a series of electron diffraction patterns from a single crystal. The important experimental variables include the exposure rate, the exposure time and the accumulating exposure between successive patterns.

A low energy electron diffraction study of the PH 3 adsorption on the Si (111) surface

The reaction of PH 3 with a clean silicon (111) surface was studied by low energy electron diffraction (LEED). A number of diffraction patterns were observed in the temperature range of 25–1000°C using PH 3 pressures of 5 × 10 −8 to 10 −5 Torr. The LEED pattern of one of them, the P-6 √3 structure, could be interpreted by multiple diffraction. The structure appears to be a densely packed phosphorus layer on top of the surface. The activation energy for desorption of the layer was calculated. For the other patterns no structure models could be proposed with certainty. The correlation with adsorption measurements on powders is discussed and the LEED results of reactions of other hydrides with silicon and germanium (111) surfaces are mentioned.

銅・スズ合金電気メッキについて

Experiments on electroplating of Cu-Sn alloys under various conditions were carried out in the plating solution composing mainly of copper cyanide and sodium stanate, of which five kinds were used varying the ratio of Cu/Sn from 7/10 to 16/1.The results of X-ray diffraction examination are as follows:1. Sn content in the electrodeposited Cu-Sn alloys varies from 10 to 78%. Phases in the alloys are classified into four groups, namely, (a) α only, (b) α+η, (c) η only, and (d) θ+ξ.2. In the electrodeposited alloys, the phase of (η+ζ), which exists in the equilibrium phase diagram of Cu-Sn alloy, can not be seen, and the region of this phase is displaced by η and (θ+ξ) phases.3. β, δ, and ε phases, which exist in the phase diagram at high temperature, also can not be seen in the deposited alloy.4. In the electroplated alloy of speculum plating, only (α+η) or η phase is crystallized and the number of diffraction patterns in this case is significantly small as compared with that in the other cases.5. The composition of the deposited alloy is decided mostly depending upon the composition of plating solution, but not mach upon other plating conditions such as current density, stirring, etc.

Operational Features of a New Electron Diffraction Unit

A new electron diffraction unit having a three-lens optical system and a maximum effective specimen-to-plate distance of 200 cm is described. The applications of such a system to the study of long interatomic spacings is discussed. Wide variations in the area of specimen irradiated are obtainable. An explanation is given of the design considerations in such an optical system, with special reference to the functioning of the post-specimen lens as both focusing and magnifying lens. The use of the unit as a shadow microscope is explained, and the advantages are given of this instrument over other shadow microscopes with respect to increased size of image, increased size of specimen field available for observation, and greater specimen protection from damage by the concentrated electron beam. The resolution attainable with the instrument is calculated and a ``resolution index'' is defined which makes possible intercomparisons of resolution under various operating conditions. Factors which limit accuracy, as opposed to resolution, are discussed critically and the accuracy of data obtainable with the instrument is estimated. A number of diffraction patterns are shown to illustrate the results obtained under various operating conditions as diffraction camera and shadow microscope, and also to illustrate the techniques of charge neutralization, spot diameter measurement, and internal calibration of plates using a known specimen.