Spatial devices

The evolution of detection systems suitable for multielement determinations has proceeded along two basic lines of development as indicated in Figure 1. One line of development is based upon dispersive systems. Dispersive systems are all multichannel devices which may be further classified as temporal or spatial devices. In the temporal approach, the measurement of intensities in different resolution elements is separated in time. The spatial approach uses detectors which are separated in space. 

Spatial Devices. Spatial devices use detection elements which are separated from each other in space. Although the photographic plate may be considered the original spatial detector, this discussion will be limited to electronically-based detection systems. Such systems include the direct-reading spectrometer and various solid-state array detector spectrometers. 

Visual and spatial devices used to convey categorical and nominal relations... 

Now to ways of indicating order, first using space. Many of the devices used to indicate groupings can be adapted to indicate order. Writing is ordered, so one of the simplest spatial devices to indicate rank on some property is to write items according to the order on the property, for example, writing countries in order of GNP, or people in order of age. Empty space is used to convey order, as in indentation in outlines, where successively subordinate items are successively indented relative to superordinate items. 

Visual devices are also useful for indicating order. Primary among them are lines. Lines form the skeletons of trees and graphs, both of which are commonly used to display ordered concepts, to indicate asymmetry on a variety of relations, including kind of, part of, reports to, and derived from. Examples include hierarchical displays, as in linguistic trees, evolutionary trees, and organizational charts. Other visual and spatial devices used to display order rest on the metaphor of salience. More salient features have more of the relevant property. Such features include size, color,... 

Thermogravimetric Analysis - Empty UF microcapsule shows - Figure 8, a weight loss (around 10 %) until 110 °C corresponding to the evaporation of free water in microcapsules, and an important decreasing in weight (around 80 %) starting from 180 °C due to the decomposition of urea-formaldehyde microparticles. Therefore the urea formaldehyde could not be used to self-heal spatial device composites because of polymer decomposition below 300 °C (maximum temperature in space). 

Recently commercially available X-ray systems for laminography have a spatial resolution limited to hundred microns, which is not enough for modem multilayer electronic devices and assembles. Modem PCBs, flip-chips, BGA-connections etc. can contain contacts and soldering points of 10 to 20 microns. The classical approach for industrial laminography in electronic applications is shown in Fig.2. 

One of the more recent advances in XPS is the development of photoelectron microscopy [ ]. By either focusing the incident x-ray beam, or by using electrostatic lenses to image a small spot on the sample, spatially-resolved XPS has become feasible. The limits to the spatial resolution are currently of the order of 1 pm, but are expected to improve. This teclmique has many teclmological applications. For example, the chemical makeup of micromechanical and microelectronic devices can be monitored on the scale of the device dimensions. 

Sihcon charge coupled devices (CCDs), commonly used in soHd-state video cameras and in research appHcations, are being appHed to low light level spectroscopy appHcations. The main advantage of area array CCDs over linear photodiode detectors is the two-dimensional format, which provides simultaneous measurements of spatial and spectral data. 

Cathodoluminescence microscopy and spectroscopy techniques are powerful tools for analyzing the spatial uniformity of stresses in mismatched heterostructures, such as GaAs/Si and GaAs/InP. The stresses in such systems are due to the difference in thermal expansion coefficients between the epitaxial layer and the substrate. The presence of stress in the epitaxial layer leads to the modification of the band structure, and thus affects its electronic properties it also can cause the migration of dislocations, which may lead to the degradation of optoelectronic devices based on such mismatched heterostructures. This application employs low-temperature (preferably liquid-helium) CL microscopy and spectroscopy in conjunction with the known behavior of the optical transitions in the presence of stress to analyze the spatial uniformity of stress in GaAs epitaxial layers. This analysis can reveal,... 

In certain cases, the optical probe can be used at a large distance from the experimental equipment. Hence, spatial zones can be probed that are normally accessible with difficulty or inaccessible for traditional measurement devices. This arrangement provides a means for remote measurements. 

Theoretical representation of the behaviour of a hydrocyclone requires adequate analysis of three distinct physical phenomenon taking place in these devices, viz. the understanding of fluid flow, its interactions with the dispersed solid phase and the quantification of shear induced attrition of crystals. Simplified analytical solutions to conservation of mass and momentum equations derived from the Navier-Stokes equation can be used to quantify fluid flow in the hydrocyclone. For dilute slurries, once bulk flow has been quantified in terms of spatial components of velocity, crystal motion can then be traced by balancing forces on the crystals themselves to map out their trajectories. The trajectories for different sizes can then be used to develop a separation efficiency curve, which quantifies performance of the vessel (Bloor and Ingham, 1987). In principle, population balances can be included for crystal attrition in the above description for developing a thorough mathematical model. 

Figure 13-14. Spatial profiles of the carrier densities and the recombination for devices of width 100 nrn (dotted lilies) and 10 pm (solid lilies), for equal electron and hole mobilities. Reproduced with permission from I05J. Copyright I99K by the American Physical Society.

The promise of 3-D detectors The ideal detector would be able to measure the wavelength dimension of each photon in addition to the two spatial dimensions - a 3-D detector . There is progress being made on 3-D detectors - for example, the superconducting tunneling junction (STJ). However, at present, 3-D detectors are experimental and have only achieved limited wavelength resolution ( /5 < 25) with relatively slow count rates (few kHz per pixel) on a small number of pixels 100 j. Since these devices are experimental and are not being used... 

Obviously, the analysis of the correlation between the two fields emerging from the telescope and related devices makes necessary to avoid dissymmetry between the interferometric arms. Otherwise, it may result in confusion between a low correlation due to a low spatial coherence of the source and a degradation of the fringe contrast due to defects of the interferometer. The following paragraphs summarize the parameters to be controlled in order to get calibrated data. 

This first step makes necessary a correction of the atmosphere aberrations by means of an adaptive optics or at the minimum a tip tilt device. If the turbulence induces high aberrations the coupling efficiency is decreased by a factor VN where N is the number of spatial modes of the input beam. Note that tilt correction is also mandatory in a space mission as long as instabilities of the mission platform may induce pointing errors. Figure 10 (left) illustrates the spatial filtering operation. This function allows a very good calibration of... 

Figure 18. ISTROG Interferometer. The high improvement on the accuracy of contrast measurements with such devices mainly results from the efficient spatial filtering and the spatial stability of the recombining assembly.

Equation (8.4) defines the average concentration, Ugut, of material flowing from the reactor. Omit the V ir) term inside the integral and normalize by the cross-sectional area, Ac = ttR, rather than the volumetric flow rate, Q. The result is the spatial average concentration a patiai, and is what you would measure if the contents of the tube were frozen and a small disk of the material was cut out and analyzed. In-line devices for measuring concentration may measure a panai rather than Uout- Is the difference important ... 

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