Two-dimensional Intensity Distribution Research Articles

Small-angle neutron scattering investigation of correlations in charged macromolecular and supramolecular solutions

An overview of an important aspect of SANS research on charged colloidal suspensions is presented. These systems are characterized by pronounced interparticle correlations resulting from a strong and long-range double-layer interaction between macroions (i.e. the charged colloidal particles). Emphasis is laid on the use of simple statistical mechanical models, which are applicable in treating SANS data, that take into account the double-layer interaction. Examples are taken from work on dense protein solutions, ionic micellar solutions and protein-detergent complexes in aqueous solutions. Spherical and rod-like particles are considered. Polydispersity effects are taken into account whenever possible. In the case of rod-like systems, alignment by a shear gradient and the consequent analysis of two-dimensional SANS intensity distributions are briefly discussed.

Triple-crystal diffraction studies on ion-implanted and other silicon crystals using a synchrotron source

Triple-crystal diffraction studies are capable of cleanly separating the various experimental components of the scattering in the vicinity of a Brags peak. The two-dimensional intensity distributions obtained in such an experiment consist of various components which extend in distinct directions in (Atos, A2Os) space, where Atos and A20s are the offset angles of the sample and analyzer/detector from the Bragg condition. One-dimensional 'slice' scans can be used in studying specific details, given a known disposition of the components, be they dynamical, kinematical or aspects of the instrumental arrangement. In this paper triple-crystal diffraction results obtained for given ion-implanted and other Si crystals using both a conventional X-ray tube and a synchrotron source are presented and compared.

Diffuse scattering and long-range order in the octahedral CDW/PLD-bearing transition-metal dichalcogenides

It has long been recognised that the very characteristic, two-dimensional diffuse intensity distributions observed at 'high' temperatures in the octahedral CDW/PLD-bearing transition-metal dichalcogenides must be closely related to the subsequent development of longer-range order at lower temperatures. An interpretation of the 'high-temperature' diffuse intensity distributions in terms of thermally excited nearly soft phonon modes is found to provide a very useful means of interpreting the experimentally observed behavior in the lower-temperature, longer-range-ordered CDW/PLD states.

Computer simulation of two-dimensional intensity distributions obtained with crystal-monochromated X-radiation and a small specimen crystal

Computer simulation of two-dimensional intensity distributions obtained with crystal-monochromated X-radiation and a small specimen crystal

Maximum Entropy Image Restoration in Astronomy

Imaging the two-dimensional intensity distribution of the sky has always been an important part of astronomy. This is particularly true at present, a time when aperture synthesis mapping is firmly established in radio astronomy, charge-coupled devices are revolutionizing optical imaging, and X-ray-imaging cameras are being flown in space. Atmospheric irregularities, instrument aberrations, detector noise, and the diffraction limit all cause the observed image to deviate from the ideal one. Image restoration techniques have therefore had a long history. The field owes much to the classic papers of Bracewell & Roberts ( 12) and Fellgett & Linfoot (35), which focused attention on the amount and nature of information about the image present in the measurements. These ideas have become increasingly relevant with the growth of interferometry, where the data correspond to the Fourier transform of the image. The Michelson stellar interferometer (82) was an early application in optical astronomy. However, it is at radio frequencies where interferometry has proved most fruitful and where astronomers have had to face the problem

An examination of the relationship of the Δω,Δ2Θ intensity distribution to crystal substructure (mosaic distribution) and shape

The basic Δω, Δ2θ technique for examining single-crystal Bragg reflections [Mathieson (1982). Acta Cryst. A38, 378-387] has recently been improved [Mathieson & Stevenson (1984). Aust. J. Phys. 37; 657-665], by using a simple experimental modification which reduces the source component to a minor (angular) role, thereby making the extraction (deconvolution) of the remaining components more accurate. The application of this new technique in the determination of reflectivity (rocking) curves for imperfect crystals has been demonstrated [Mathieson & Stevenson (1985). Acta Cryst. A41, 290-296]. In the present case, the examination of individual reflections from a small single crystal of CuInSe2 reveals that the improved technique is capable (i) of identifying, by its locus extension in Δω, Δ2θ space, diffraction from one side of the specimen crystal to the other (in the diffraction plane), even for a crystal of average dimension ~0.06 mm, and (ii) of estimating the reflectivity curve for different parts of the crystal. A series of model eases is discussed, to clarify the interpretation of observed two-dimensional intensity distributions. While considered here in relation to a small crystal, this technique is applicable to extended-plate crystals (in transmission mode) by a selected-area procedure.

Position and shape of sputtering emission spots measured with hemispherical collectors and electron backscattering

Two-dimensional intensity distributions and angular positions of the emission spots occurring in sputtering experiments with single crystals have been determined for gold and silver targets of different surface orientations under bombardment with argon and oxygen ions. The differential sputtering yield was measured in the whole angular range between 3° and 80° to the target normal using the collector method: after condensation of the sputtered target material on cooled hemispherical collectors the thickness distributions of the sputtered films were measured in a microprocessor controlled electron backscattering device with an angular resolution of 0.2° and a thickness resolution of about 1% of the thickness measuring range. Digital acquisition of the measured data and an image storage unit allow several representation and evaluation methods as e.g., diagrams of constant thickness lines or grey level representations of the emission distributions. Half widths of emission spots have been evaluated in different measuring planes and a strong variation of the maximum spot intensity with the polar emission angle was found.

Small angle light scattering as a probe of flow-induced particle orientation

A new optical technique which digitally records the evolution of the two-dimensional intensity distribution of the small angle light scattering of suspended particles subjected to transient shear flows is described. For dilute suspensions of absorbing particles which are larger than the wavelength of the incident light, scalar diffraction theory is applied to relate the moments of the measured pattern to the degree of alignment and average orientation angle of the particles. The diffraction pattern for non-Brownian, near-sphere particles in Stokes flow is solved and shows an oscillation between isotropic contours, when the particles are randomly oriented, and elliptical contours oriented perpendicular to the average orientation of the particles. Experimental results for the inception and reversal of simple shear flow of a dilute suspension of prolate ellipsoids in a parallel plate device are presented and exhibit this behavior. These data agree well with previous theoretical and experimental findings but bring with them new information that will prove valuable in future rheological studies.

Direct measurement of lateral transport in membranes by using time-resolved spatial photometry.

Spatially resolving light detectors allow, with proper calibration, quantitative analysis of the variations in two-dimensional intensity distributions over time. An ultrasensitive microfluorometer was assembled by using as a detector a microchannel plate-intensified video camera. The camera was interfaced with a software-based digital video analysis system to digitize, average, and process images and to directly control the timing of the experiments to minimize exposure of the specimen to light. The detector system has been characterized to allow its use as a photometer. A major application has been to perform fluorescence recovery after photobleaching measurements by using the camera in place of a photomultiplier tube (video-FRAP) with the goal of detecting possible anisotropic diffusion or convective flow. Analysis of the data on macromolecular diffusion in homogenous aqueous glycol solutions yielded diffusion constants in agreement with previous measurements. Results on lipid probe diffusion in dimyristoylphosphatidylcholine multibilayers indicated that at temperatures above the gel-to-liquid crystalline phase transition diffusion is isotropic, and analysis of video-FRAP data yielded diffusion coefficients consistent with those measured previously by using spot photobleaching. However, lipid probes in these multibilayers held just below the main phase transition temperature exhibited markedly anisotropic diffusive fluxes when the bleaching beam was positioned proximate to domain boundaries in the P beta' phase. Lipid probes and lectin receptor complexes diffused isotropically in fibroblast surface membranes with little evidence for diffusion channeled parallel to stress fibers. A second application was to trace the time evolution of cell surface reactions such as patching. The feasibility of following, on the optical scale, the growth of individual receptor clusters induced by the ligand wheat germ agglutinin was demonstrated.

Solution of the two-dimensional phase-retrieval problem

A new method for solving the phase problem in two dimensions is presented. The solution is noniterative and is based on locating the zeros of one-dimensional strips of a single two-dimensional intensity distribution. A numerical example is included.

A two-dimensional data-acquisition system for a display-type electron energy analyser

A parallel-detection digital data-acquisition system for an ellipsoidal-mirror display-type analyser (EMDA) is described. The operation characteristics for its use in photoelectron spectroscopy are presented. The system is based on an optical readout of the two-dimensional angular intensity distribution of photoelectrons with a phosphor screen of a microchannel plate and a precision SIT video camera. A real-time image-processing system is used for digital video-data processing. Angular distribution patterns of photoelectrons can be obtained in a time of 4-10 s. Energy distribution spectra are recorded in a parallel-detection mode within the whole acceptance cone (88 degrees ) of the EMDA more than two orders of magnitude faster than with a conventional zero-dimensional electrostatic electron energy analyser. The different modes of operation of the EMDA and their realisation with the data-acquisition system are described.

Multichannel semiconductor detectors for high energy X-ray and electron beams

Multichannel semiconductor detectors for high energy X-ray (10 MV) and electron beams (10–15 MeV) have been developed using surface-barrier diodes fabricated from high purity n-type silicon. The experimentally obtained linearity of the detector output current is excellent for a range up to 1000 R/min for 10–15 MeV electron beams and up to 500 R/min for 10 MV X-rays. As the detector operational mode is non-biasing without cooling, there are many useful applications, such as monitoring the two-dimensional radiation intensity distribution of a medical linear accelerator. In addition to the application for high energy radiations, other applications (X-ray computed tomography, automatic X-ray exposure control systems) are discussed briefly.

Neutron diffraction study of the domain structure rearrangement of KD2PO2 in the electric field

There is investigated the rearrangement of the domain structure of KD2PO4 in the external electric field with the time-of-flight diffractometer installed at a pulsed neutron source. Two-dimensional (x*, y*) cross sections of the spots of reciprocal lattice are measured in order to obtain the dependence of packing and relative volume of different types of domains on field strength. The results of measurements of two-dimensional intensity distribution around the reciprocal lattice points in the [hOO] and [hhO] directions in the field Ez increasing from 0 to Ez > Ezc are reported. Possible domain rearrangements within which one may explain the observed changes of the diffraction pattern are proposed.

Radio picture of the sun at 3.2-cm wavelength

In 1957 July the two-dimensional intensity distribution of radio emission over the solar disk was determined at 3.2- and 10-cm wavelengths. The observations were carried out on the radio telescope 31 m in diameter at the Crimean Radio Astronomical Station of the Physical Institute of the Academy of Sciences of the U.S.S.R. The radio telescope was an immovable parabolic reflector with the axis set in the meridian plane on 22-degrees declination [1]. Scanning the pattern of the radio telescope in the declination range ±32 minutes of arc to obtain the intensity distribution was done by setting the feed and preamplifier on a movable carriage reciprocating near the focal plane. In combination with the sun's daily movement it provided the two-dimensional solar distribution along a zigzag line. These sections gave the radio picture.