Real-time Representation Research Articles

In-situ X-ray diffraction study of the decomposition of NaAlH4

Abstract Phase transitions and crystal structure modifications were observed during the thermal-desorption decomposition of the alanate NaAlH 4 . This was accomplished through the use of in-situ X-ray powder diffraction. A sequence of θ –2 θ scans were collected while heating the sample under a vacuum. The resulting diffraction patterns were assembled to provide a real-time representation of the decomposition reactions. It was found that upon heating, NaAlH 4 initially experienced a lattice expansion principally in the c -axis direction. This was followed by continuous structural distortions observed as erratic variations in the Bragg intensities. Melting of NaAlH 4 was observed at 180°C followed by the rapid precipitation of a cubic Na 3 AlH X phase. This phase then underwent a slow transformation into a Na-rich cubic phase. The decomposition of NaAlH 4 doped with a double catalyst (Ti+Zr) was also investigated. The uncatalyzed sample showed no decomposition when held under a vacuum at 150°C for several hours. The catalyzed sample, on the other hand, began to decompose readily into the monoclinic (α)-Na 3 AlH 6 phase when heated to 100°C in vacuum. At 150°C the (α)-Na 3 AlH 6 phase decomposed in a second reaction according to α-Na 3 AlH 6 →3 NaH+Al+3/2 H 2 . The two decomposition reactions appear to be interdependent as the second transformation commenced only after the first reaction neared completion. The observed growth of a narrow Al (111) diffraction peak indicates the formation of aluminum crystallites (>100 nm) as a part of the decomposition reactions. This, and the fact that this solid state process is assisted through the interaction of a surface catalyst suggests long-range transport of a metal species. Some mechanisms are proposed to explain the catalytically enhanced kinetics of these materials.

Clinical Evaluation of Multimodality Registration in Frameless Stereotaxy

Computer-assisted frameless neurosurgery bases its accuracy and reliability on registration. The aim of this prospective study was to compare the clinical accuracy of different registration techniques used for computer-assisted frameless neurosurgeryNinety-eight registrations in 44 patients were used to compare the clinical accuracy of self-adhesive marker (MR) and facial landmark (FR) registrations used alone or in conjunction with surface-fit registration (MR/SR and FR/SR, respectively) for cranial neurosurgery. The computer estimated error (CEE) of each registration was compared to the real error (RE). This was obtained by holding the frameless pointer at the center of three different markers and measuring the distance from the real-time representation on the computer three-planar images to the center of the marker on the screenThe most accurate registration was obtained using MR; the RE of MR was 1.6 ± 0.1 mm compared to 3.4 ± 0.4 mm for FR. Although the smallest CEE error was obtained using MR/SR, this was not sustained by the RE. Furthermore, the RE of FR/SR was significantly larger than the CEE (Student t test, p <. 001)This study corroborates previous results showing that, in the clinical setting, self-adhesive marker registration is more accurate than facial landmark registration. Furthermore, although surface-fit registration can be used in conjunction with self-adhesive marker registration, this does not improve the degree of real accuracy for cranial registration.

An electronic spectroscope for classroom displays of visible spectra

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), a section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by an electronic archive, stored on the SAE homepage at http://www.elsevier.nl/locate/sabe. The archive contains program, data and text files. The hardcopy text describes a program that has been developed to accept data from a compact electronic spectrograph and translate the data into a display on a computer screen. The computer display mimics the view seen through a direct vision spectroscope. Atomic spectra appear as vertical lines of the appropriate color dispersed on a black field. A conventional plot of intensity versus wavelength is simultaneously displayed. The update of the display is sufficiently rapid that the image on the screen is essentially a real-time representation of the light entering the spectrograph. The system was designed for use in conjunction with video projection equipment in demonstrations to large groups of students.

Implementation and application of real-time motion analysis based on passive markers.

A method for real-time motion analysis based on passive markers is presented. An opto-electronic automatic motion analyser was used as hardware platform and the real-time operation was based on the interfacing between two levels of the system architecture. True real-time acquisition, processing and representation of two-dimensional and three-dimensional kinematics data were implemented through a newly conceived data acquisition procedure and high speed optimisation of the kinematics data processing. The method allows one to operate the motion analysis system in real-time; even when the data elaboration unit is required to perform other processing functions, the only consequence is a decrease in system sampling rate. The maximum number of processed and plotted markers in three dimensions at the highest system sampling rate (100 Hz) turned out to be suitable for the implementation of analytical and visual kinematics biofeedback. An example of the achievable level of complexity in terms of marker disposition model and graphic representation is reported by describing a demonstration of the real-time representation of human face movements. A clinical application of the method for patient position definition and control at radiotherapy units is presented.

System architecture and implementation of a CEBus/Internet gateway

Class structures and an object-oriented software framework to facilitate Internet access to CEBus networks are described. The Internet/CEBus gateway consists of a server application and dynamic data structures which provide a real-time representation of a CEBus network. The CEBus network traffic is continually monitored and interpreted and these data structures updated accordingly. In addition the creation of virtual CEBus devices is supported. These virtual devices can interact with the real CEBus network. This allows the creation of new device personalities whose behaviour can then be characterised through interaction with a real CEBus network.

Constraint logic programming for structure-based reasoning about dynamic physical systems

The paper describes a constraint logic programming approach for reasoning about dynamic physical systems based on structure. The approach takes a bond graph model of a system and computes a causal graph representation of its causal structure. Causal graphs can be used for causal explanations and for explaining the effect of modeling abstractions on causal structure. The paper shows how causal graphs can be used to compute a simulation model of a system in the form of a set of differential algebraic equations. The topological properties of the causal graph determine whether a simulation model is regular i.e. conforming to the criterion of ‘real-time representation’ or causality. In case the simulation model is not regular, a method is given for identifying all causal problems of a bond graph model.

Neurological Distribution of Processing Resources Underlying Language Comprehension

Using a cross-modal lexical priming technique we provide an on-line examination of the ability of aphasic patients to construct syntactically licensed dependencies in real time. We show a distinct difference between Wernicke's and Broca's aphasic patients with respect to this form of syntactic processing: the Wernicke's patients link the elements of dependency relations in the same manner as do neurologically intact individuals; the Broca's patients show no evidence of such linkage. These findings indicate that the cerebral tissue implicated in Wernicke's aphasia is not crucial for recovering syntactically licensed structural dependencies, while that implicated in Broca's aphasia is. Moreover, additional considerations suggest that the latter region is not the locus of syntactic representations per se, but rather provides the resources that sustain the normal operating characteristics of the lexical processing system-characteristics that are, in turn, necessary for building syntactic representations in real time.

Analog VLSI model of binaural hearing

The stereausis model of biological auditory processing is proposed as a representation that encodes both binaural and spectral information in a unified framework. A working analog VLSI chip that implements this model of early auditory processing in the brain is described. The chip is a 100000-transistor integrated circuit that computes the stereausis representation in real time, using continuous-time analog processing. The chip receives two audio inputs, representing sound entering the two ears, computes the stereausis representation, and generates output signals that can directly drive a color CRT display. Outputs from the chips for a variety of artificial and speech stimuli are shown.

Distributed supercomputing to achieve real-time representation and manipulation of complex scenes

Besides the ray tracing technique, the radiosity method is another major approach for global illumination modeling in the field of computer graphics. Since this method needs a huge amount of storage space (both memory and disk) and a long pre-computation cycle, it is not suitable to implement it on conventional workstations. Supercomputers seem to be necessary for such kind of graphics applications. However, some problems appear with the integration of supercomputers and workstations in a distributed computing environment, especially for graphics application. The major problems are: (i) unavailability of standard higher-level mechanisms for building distributed application; (ii) transparent access to supercomputers without remote login or file transfer sessions; (iii) computation balance to make the best use of the performance of supercomputers and workstations; (iv) data transfer/storage strategy between supercomputers and workstations; and (v) conflict between interaction and response time for graphics applications. In this paper we suggest solutions to the above mentioned problems based on the remote procedure call (RPC) and the client/server model, for the radiosity package implementation. After the introduction of the radiosity method, we concentrate on the integration between supercomputers and high-performance workstations. We also convey some general issues related to distributed computing and present the experience with our implementation, such as the application protocol definition, error recovery, code debugging etc. The radiosity package has been implemented at ZGDV in Darmstadt, F.R.G. in a network environment including a Multiflow TRACE 7/300 supercomputer connected to several VAX, SUN and HP workstations.

Simulation of PVT Experiments

Summary An interactive program (PVTLAB) was written to simulate PVT experiments with a microcomputer. The simulator is a real-time representation of an actual PVT laboratory. Operations typically performed in the laboratory may also be performed with the simulator. The Peng-Robinson equation of state (PR-EOS) is used to calculate phase behavior, and the results of the calculations are displayed in color on the microcomputer monitor. The monitor graphically represents the condition of all the physical components of the PVT laboratory, including pressures, fluid levels in vessels, and the status of valves and pumps. A printed record of every action taken during a run is kept if desired. A simulated experimental error results in an appropriate termination of the run. Program structure and operation are described, and examples of simulated PVT experiments are given.

Computer‐based automation of concentration measurementswith ion‐selective electrodes

An integrated computer system consisting of an expandable ionanalyzer and a PC has been used to automate concentration measurements with ion-selective electrodes (ISEs). The ionanalyzer determines ionic concentrations using a reference electrode coupled with an ISE. The measurements and calibrations are carried out in a thermostated sample changer equipped with a flow cell. The data obtained by the ionanalyzer are sent via a standard RS 232-C interface to a microcomputer. In this paper, we describe the automatic data acquisition system and the subsequent processing of the measurements. One program (Transorion) automatically collects the measurements carried out by the ionanalyzer, giving a real-time graphic representation of the measurement on the computer screen. A second program (Graforion) facilitates the management of the data stored by the first program, and listing and graphics of these can be obtained on the printer/plotter. The method has been used to study continuous concentration changes in an aqueous solution of potassium iodide.

Computer display of vowel quadrilateral with real-time representation of articulation

The classical characterisation of vowel sounds used by phoneticians is the vowel quadrilateral, which originally was assumed to be the locus of the tongue body between its four extreme vowel positions. A method of real-time computer analysis and display which represents the vowel quadrilateral is described. This has application in computer-based speech training aids, but may have wider use in speech research generally.

Simulator provides real-time representation of missile mission

Simulator provides real-time representation of missile mission