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As part of a work programme looking into the integration of structured and formal methods for the development of software-based systems, five structured methods were considered, namely SSADM, JSD, Yourdon, CORE and Soft Systems. This memorandum provides concise descriptions of these methods. Great Britain. (rrh)

An approach to modelling upper atmospheric winds is suggested in which the input data is obtained automatically from aircraft via a digital data link. A statistical method is used to combine the observational data, and the realization of a simple, one-dimensional implementation of such a model is described. Finally, the results of operating this model in real time are presented, where the input data were obtained during ascents and descents of BAC 1-11 operated by RAE Bedford. Great Britain. (rrh)

This paper describes an application of the Inside-Outside algorithm to learning rules for the spelling of English words. The initial experiments examine the effect of using prior knowledge and further experiments compare stochastic regular grammars with stochastic context-free grammars. The problems of using the Inside-Outside algorithm are discussed and an implementation on an Array Processor is described. Keywords: Great Britain. (fr)

The requirement for low-cost infrared sensors for a range of applications has led to the development of linear pyroelectric detector arrays of up to 64 elements, integrated with MOSFET readout electronics and low-microphony packaging to give compact and easy-to-use infrared detectors operating at ambient temperatures in the 8-14 micron waveband. Along with these detectors, the necessary signal conditioning techniques have been developed, in order that the best system performance can be obtained whilst maintaining the aims of low cost, low power, and small size. The sensor system described here uses the VX 8-647 detector, developed under DCVD contract at Philips components Ltd. This detector is a 64 element ceramic pyroelectric array, with fully reticulated elements and with thermal and vibration isolation by means of a membrane structure. A custom MOSFET readout chip and standard hybrid components within the detector package make interfacing to the detector array very straightforward. The signal conditioning electronics is designed to be low power at low cost, making maximum use of analogue and digital CMOS components. The sensor is configured to be battery powered and transmit data by means of a serial data link. A measured NEDT of 0.25K at 50 Hz line rate is achieved, which accords well with the theoretical predictions. keywords: Great Britain. (fr)

On 10th and 11th January 1989, dedicated flights of the RAE BAC 1-11 were scheduled to assess the coverage of the aircraft's Mode S aerials. The intention was to fly carefully controlled patterns using different aerial connections during different sections of the flights. It was realized that this trial also afforded an ideal first opportunity to test many aspects of the Mode S data link, following the brief initial test of the GICB protocol during a flight of opportunity on 23rd Sep 1988. The VHF emulation, which had already been tested on several occasions since April 1987, would also be used to down- link aircraft derived data. This report is concerned only with data link aspects of the trials; the surveillance results will be reported elsewhere. Keywords: Great Britain. (fr)

We derive an estimate-maximize (EM) formulation of a Bayesian super-resolution algorithm for reconstructing scattering cross sections from coherent images-this renders obsolete all past attempts to derive such a scheme. We extend the analysis to the case of simultaneous super-resolution and autofocussing, which corrects the damage caused by an uncertain point spread function. Finally, we demonstrate our method by presenting the results of some simple numerical experiments. Keywords: Great Britain; Synthetic aperture radar.(KR)

NODEN is a suite of programs designed to perform hardware analysis on moderately complex blocks of logic, to prove the correspondence between the specification and implementation of a circuit. It is intended that circuits to be analysed should be described in the NODEN Hardware Description Language, NODEN HDL (either directly or by translation from other hardware description languages such as ELLA, HILO etc.). The following paper describes the syntax and semantics of NODEN HDL. Great Britain. (rrh)

The collision avoidance of a pair of uniformly moving bodies is considered in three dimensions. The relative motion of the bodies yields an expression relating the time to closet approach, the minimum range, the current range and its rate of change, other variables being unobservable. A Boolean relation is then proposed that is satisfied whenever the minimum range and time to closet approach simultaneously fall below given thresholds. The relation is further studied, in particular with regard to the issue of false and premature alarms. An airborne collision avoidance system is a possible application.

We describe in this memo the results of a preliminary calculation which shows how the intersubband optical transition in III-V quantum wells may be used as the basis for research into a family of infrared devices. In particular, we show that resonating the transition with a surface plasmon or with a guided mode in a semiconductor-quantum well- metal structure can enhance its optical effects by roughly a factor of 50. This allows only 4x10 to the 12th power carriers per sq. cm to effect total absorption of the incoming radiation. Such a density can be controlled electrostatically and so the transition may be switched by applying a bias to the (Shottky) metal; thus we have an efficient electronic modulator for the 10 micron band. Intersubband absorption should, in addition, show significant photoconductivity and so the device might prove a reasonable infrared detector. Finally, an important consideration of this device is that it is built epitaxially using wide band gap semiconductors. The possibilities, therefore, of substantial monolithic integration are considerable and we allow ourselves some speculation on the types of device which may be possible.

The multi-layer perceptron is investigated as a new approach to the automatic recognition of spoken isolated digits. The choice of the parameters for the multi-layer perceptron is discussed and experimental results are reported. A comparison is made with established techniques such as dynamic time-warping and hidden Markov modelling applied to the same data. The results, for this particular task, show that the recognition accuracy obtained using the multi-layer perceptron is comparable with that from using hidden Markov modelling.

A method is proposed for the production of large software systems via hierarchies of descriptive levels. The method is based upon the simultaneous refinement of data and code adn guarantees conformity between different levels. It is illustrated using the MALPAS Intermediate Language.

The work presented in this Memorandum is the first stage in a programme of work designed to study the scattering of radiation from simple phase objects that have dimensions smaller than the wavelength of the probing laser radiation. This initial work establishes the theory and supporting experimental evidence when the structure is somewhat larger than the probing wavelength.

A computer controlled Auto Prober System has been designed and constructed to allow detailed information to be obtained from the large number of Gallium Arsenide (GaAs) devices fabricated in the Microwave Devices Division (DP2). GaAs substrates up to 2 inch diameter can be processed in the DP2 clean room and typical substrates may contain several thousand devices and test patterns. The prober system consists of two separate facilities, one to carry out the DC measurements and the other to allow the data obtained to be analyzed and correlated. This memo describes the measurement facility and gives details of the DC conditions under which the measurements are carried out. A full description of the software is included in this memo and a listing of the software is given in a separate appendix. The data analysis facility is described in RSRE Memo 4066. Both facilities have been designed as an integrated system and offer a range of on wafer measurements which include characterization of active devices such as GaAs MESFETs (MEtal-Semiconductor Field Effect Transistors) and Schottky diodes as well as measurement routines for use on various test patterns for addressing ohmic contacts and investigating doping profiles of device layers. Passive components such as on wafer capacitors and resistors can be measured., Original contains color plates: All DTIC and NTIS reproductions will be in black and white.

The purpose of this report is to review in detail the type checking and scope rules for the specification language Z. At present no definitive description of the language exists, although it is sufficiently well defined for the informal use which is currently made of it. The production of tools to process the language requires a complete definition during the production of which a number of decisions are made concerning various compromises between mathematical elegance and efficiency of implementation. It is the purpose of this report to review these in detail, using as a basis the syntax developed by King et al (1987, see also Sufrin 1986). This will be referred to as the standard syntax. Rather than following this language definition mechanically some changes have been made. This report is concerned particularly with tool implementation, so a version of the syntax has been produced enabling syntax and type checking to be completed in one pass. Changes introduced under this heading do not affect the appearance of the language, but in some cases a syntactic check is replaced by a semantic check. In some cases variations have been introduced which are a matter of personal preference. The production of variant languages in this way is actually a necessary step towards the goal of the production of a robust and usable language standard. Keywords: Great Britain.

This report presents a review of security models and gives a detailed mathematical description of the property of separability, that is the property that certain software can be treated as though it were being obeyed in isolated computers. The description uses the specification language Z, and the proofs required are given in detail.

The technique of holographic phase correction is described. This scheme offers advantages over more traditional methods, and is applicable to a wide range of problems. The merits and limitations of the technique are investigated by a detailed theoretical analysis, supported by experimental results. Practical problems of implementation are addressed, and it is shown how these limit the accuracy of phase correction.

Over 30 hours of airborne measurement of the atmospheric backscatter coefficient Beta at 10.6 um are reported, for four different regions of the Northern Hemisphere outside the UK, at altitudes up to 13 km. The results exhibit great diversity. In several recordings Beta remains constant within a factor of three over large distances and height intervals; in others over four orders of magnitude change is observed. The value of Beta rarely falls below the sensitivity limit of the equipment of approx. 2.2 X 10 to the minus 11th power per m per sr. If such findings are typical of the atmosphere as a whole they strongly support the conclusion that 1) airborne laser radars for the measurement of true airspeed, and wind shear detection and warning at low levels, would have good reliability and 2) a Laser Atmospheric Wind Sounder (LAWS) for global wind field measurement would provide reliable information for a very large fraction of the time., Original contains color plates: All DTIC and NTIS reproductions will be in black and white.

System-wide types, capabilities and procedure values can be used in computer networks to improve control of access and flexibility. This paper describes a network system based on these ideas. They provide a standard, uniform way of referring to data and using procedures in remote computers, with control over access and system type-checking. A working experimental version of the system exists, implemented on Flex computers, which provide microcoded support of capabilities. The mechanisms are such that normal programs written in terms of procedures, even those using procedure parameters, can be converted into network services without change. A possible way of implementing a similar scheme on conventional hardware is discussed.

The use of biological materials as active components in electronic systems is examined. It is concluded that signal processing is not possible unless their inherently slow switching speed is compensated for by a massive increase in number of elements, which could only be achieved in a cost effective manner if the systems were self organising. However, as components in sensors they are certainly viable and may also be of use for data storage at very high densities. They may also be of use in the fabrication of conventional integrated circuits through exploitation of their capability to self-organise through highly selective biochemical reactions.

We describe the results obtained using three different techniques for thinning silicon chips. We have found that 3 in. diameter silicon wafers can be reliably thinned to thicknesses of under 20 microns by means of a non-selective etch. This technique is also suitable for chemically polishing silicon wafers. Selective anodisation appears to be capable of thinning chips incorporating an epitaxial layer to five microns or less, but this is more complicated since electrical contact must be made with the sample. A selective HNA etch has been investigated which is supposed to selectively dissolve heavily doped silicon, but the results have not been consistent. Methods for handling thin silicon layers and a technique for encapsulating silicon samples for electrochemical measurements and etching are also described. (Great Britain), Original contains color plates: All DTIC and NTIS reproductions will be in black and white.

A calibration scheme is described for a coherent scattering matrix radar to correct for non-ideal antenna polarisation characteristics and amplitude and phase inbalance between the receiver and transmitter channels. Calibration is achieved by measuring the receiver voltages corresponding to scattering the transmitted states from trihedral and dihedral reflectors. Neither the absolute nor relative phase of the calibration targets need to be known. (Great Britain)

An addition to the ELLA system is described, which takes the information stored by the simulator in a history file and outputs it in tabular form. Monitors are displayed horizontally and their values are tabulated against time, which runs vertically. (Great Britain)

This report describes the SCP3 compiler-compiler project. This will be used to generate micro-program assemblers and other small compilers from an attribute grammar description of the language. It runs on a Flex computer system. (Great Britain)

The problem of reducing the carrier centre frequency ambiguity in low data rate satellite communications is well known. Prior solutions to this problem have been slow, bulky or expensive. Our proposed solution does not have these drawbacks, and it is easily implemented in readily available digital hardware. This is achieved by using a 1 bit digital emulation of a bank of forced LCR oscillators to achieve an approximate Fourier decomposition. (Great Britain)

This memorandum is concerned with the operation of a class of multi-layer associative networks commonly known as the multi-layer perceptron (MLP), Rumelhart network or back-propagation network. We describe the operation of the MLP as a pattern recognition device in terms of a feature-space representation. This allows an understanding of how structure in the training data is represented internally in the machine.

Reduction in device dimensions to increase speed and packing density has led to the requirements of very controlled thermal processing of semiconductor wafers. Conventional furnaces are used as standard in IC processing however alternate rapid isothermal processing technologies are gaining prominence., Original contains color plates: All DTIC/NTIS reproductions will be in black and white.

Ten15 is a strongly typed, algebraic abstract machine. It is in use as the target machine of several compilers. The method of definition makes it possible to use formal techniques of algebra as a basis for tools. This memorandum contains an informal description of the machine and its programs. (Great Britain)

We present the conclusions of the RSRE programme on the application of focused ion beams in microelectronics and review the literature published in this field. We discuss the design and performance of focused beam implanters and the viability of their application to semiconductor device fabrication. Applications in the areas of lithography, direct implantation and micromachining are discussed in detail. Comparisons are made between the use of focused ion beams and existing techniques for these fabrication processes with a strong emphasis placed on the relative throughputs. We present results on a novel spot size measurement technique and the effect of beam heating on resist. We also present the results of studies into implantation passivation of resist to oxygen plasma attack as basis for a dry development lithography scheme. A novel lithography system employing flood electron exposure from a photocathode which is patterned by a focused ion beam which can also be used to repair mask defects. (Great Britain)

THIS Report considers the methods which are used to deal with airway junctions at present and reviews how new technology could impact on this process in future.

Simulation results for phased array signal processing using the MUSIC algorithm are presented. The model used is more realistic than previous ones and it gives an indication as to how the algorithm would perform for the case of low signal/noise ratio. Strengths and shortcomings of the method are discussed. (Author)

This memo presents a set of design rules for the thickness and doping levels of the various layers of a modulation doped heterojunction. It is shown how to optimise the heterostructure so that there is no parasitic parallel conduction and for the maximum low temperature mobility. (Author)

The purpose of this Introduction is to present, in a straightforward way, the electromagnetic principles of Radar Absorbent Materials (RAM) for the benefit of the non-electromagnetic-specialist who finds himself involved in this field. The fundamental theory of electromagnetic wave propagation in media and at the interfaces between different media is reviewed and the various approaches to absorber design are described in the light of this. The types of materials required and the techniques for measuring both their electromagnetic properties and the performance of the finished absorber are outlined. Finally, a means of designing absorbers from a knowledge of the properties of its constituent materials is described.

This report describes the firmware architecture of the Flex computing system as implemented on the ICL Perq. This implementation is very similar to that described in RSRE Report 81009, (Flex Firmware by Currie, Edwards and Foster) generally referred to as the Logica implementation. This is rather a misnomer, since although Logica built the hardware (to an RSRE design) on which it was implemented, Logica had nothing to do with the micro-coding or software construction of the Flex architecture. The differences between the Perq and Logica implementation arise mainly from the properties of the underlying hardware. In the Logica Flex, for example, each byte in main-store was in fact nine bits long rather than eight; the extra bits (the tag bits) were used to distinguish between pointers and non-pointers ie between capabilities and scalar data. On Perq, however, there are no bits to spare like this. In order to distinguish between pointers and non-pointers in Perq, it was necessary to steel a bit from each 32-bit word to act as a tag bit. (Great Britain).

The procedure for designing a detour phase computer generated holograms is described with particular reference to a scale and rotation invariant transformation filter known as a Mellin transform filter. Experimental results are presented which demonstrate the main features of the devices. (Great Britain)

Procedure values, as provided in the Flex programming support environment (PSE) developed at RSRE, Malvern, are discussed. A distinction is made between a context independent procedure value and a context dependent procedure. The context independent procedure is shown to provide some useful facilities to the programmer and to the developer of a PSE. (Author)

It is well known that the performance of current automatic speech recognisers varies significantly between talkers. Hence it is essential for anyone involved in the evaluation of speech recognition system, or the assessment of the acceptability of such systems in a particular application, to be able to 'calibrate' potential talkers. The purpose of this memorandum is to provide measurements of the expected performance of a typical speech recoginser on a group of forty subjects who have provided recordings for speech recognister evaluation. The group includes all but one of the speakers from the RSRE speech database, all of the speakers who contributed towards the UK part of the NATO RSG10 spoken digit database, and a group of pilots involved in the assessment of automatic speech recognition in avionics applications at the royal aircraft establishment of Bedford and Farnborough. A method ranking of the subjects based on simpler measurements was also considered. This method potentially requires much less computation and was found to correlate well (rank correlation 0.687) with the ranking by expected error-rate.

A brief theoretical review of adaptive null steering is presented. The basic theory is first outlined in the context of sidelobe cancellation systems as well as general antenna arrays. Various approaches to the practical implementation of adaptive null steering are then discussed. These fall into the two main categories of closed loop methods and direct solution methods. The closed loop methods are very cost-effective and suitable in principle, for either analogue or digital processing. However, their rate of convergence is fundamentally limited and too slow for some applications. The direct solution methods do not suffer from this problem but tend to be suitable only for digital processing and are more expensive from the computational point of view. However they are well suited to parallel processing and now provide a very practical alternative due to recent advances in VLSI circuit technology. A brief discussion on the effects of multi-path propagation on adaptive null steering systems concludes this review.

Three new approaches to combinatorial optimisation have been described recently. They are based on analogies with physical and biological systems. The first, Kirkpatrick's Optimisation by Simulated Annealing method, has already proved useful in engineering optimisation problems such as layout and routing in VLSI chip design. At present, this probably the most powerful general optimization method for use on conventional serial computers. Although the second, Brady's evolution-based approach, has yet to receive a thorough numerical study, it seems likely to provide powerful optimisation methods for parallel SIMD computer architectures of which the most widely distributed example in the UK is the ICL DAP. The third method, Hopfield and Tank's Optimisation via networks of amplifiers, is the most revolutionary and may lead to a new generation of chips with mixed analog/digital functions for rapid optimisation.

This Memorandum describes how Fisher's Linear Discriminant can be combined with the Fukunaga-Koontz transform to give a useful technique for reduction f feature space from many to two or three dimensions. Performance is seen to be superior in general to the Foley-Sammon extension to fisher's method. The technique is then extended to show how a new radius vector (or pair of radius vectors) can be combined with fisher's vector to produce a classifier with even more power of discrimination. Illustrations of the technique show that good discrimination can be obtained even if there is considerable overlap of classes in any single projection. Keywords include: Index Terms; Dimensionality reduction, Discriminant vectors, Feature selection, Fisher criterion, Linear transformations, Separability. (Great Britain)

A system is described for capturing activity at the Human-Computer Interface in complex systems. This system, implemented in a Simulated Air Traffic Control Environment, allows for the subsequent replay of all task related, audio and visual inputs to the controller, synchronised with a record of his own manual and spoken system inputs. Potential applications for such a facility are discussed and three pilot studies considering the tool's usefulness in examining operator workload and assisting in system development are reported. A revised version of the facility, for use in an enhanced simulation environment is also described. (Great Britain)

This Memorandum describes a development of the SPUDT (Single Phase Undirectional Transducer) concept. The fabrication of such devices requires a single stage of photolithography. Prototype devices have shown very encouraging passband characteristics with an insertion loss of less than 3 dB on LiNb03 at 100 MHz, and less than 6 dB on quartz at 400 MHz. In each case the amplitude response is essentially ripple-free, and the phase characteristic agreeable linear. (Great Britain)

The Flex-Pascal compiler runs on the RSRE Flex computer architecture, which is currently available on the ICL Perq 2 workstation. Flex-Pascal conforms to the ISO 7185 (BS 6192) standard for Pascal and provides (as one extension) a separate-compilation facility. This paper discusses the use of ISO 7185 and the BSI Pascal Validation Suite, and criticises areas of Pascal, which, by their nature, have proved particularly difficult to implement.

This paper discusses the effect on the user of a Programming Support Environment (PSE) in which it is unnecessary to give names to objects in order to keep them or use them. The PSE is a highly interactive environment called Flex, that is perceptibly different from other PSEs. It is built on the Flex capability object oriented computer architecture developed at RSRE, Malvern. Names on Flex do not have the importance that they assume on most other PSEs because values need not be named before they can be held on filestore, used and located. Values can be accessed by scanning a structured filestore without the need to use names to identify them. The ability to use values without naming them is shown to be not only possible but also beneficial. Flex is a multi-language Programming Support Environment (PSE) designed to simplify the development and maintenance of complex software, with a high regard for system integrity and reliability. The PSE development since the first Flex architecture came into use in 1978 has been mainly a response to requests from programmers using the system. The large software base includes all normal operating system facilities and many other procedures including compilers for Algo168 and Pascal. An Ada (*) compiler is near completion and an ML compiler is under development.

A comparative study has been made of silicon wafers cleaned using different immersion methods in SPEL. The surfaces so produced have been assessed by various methods. The results obtained after using these cleans are reported and shown to be consistent with those described in the literature. The optimum clean has been found to be that described by RCA. This was adopted in SPEL as a standard procedure in August 1984 and results have been encouraging.

Non-linear optical phase conjugation can be directly applied to real time spatial and/or temporal information processing of electromagnetic waves. In photorefractive materials the process may be described in terms of dynamic holography. The speed at which grating formation takes place is limited by the physical properties of the crystal and the intensities of the optical beams used to write the grating. The speed at which diffraction may occur from this grating does not, however, suffer such limitations and in this memorandum we demonstrate the use of degenerate four wave mixing in BSO to direct the flow of data whose information bandwidth exceeds 1MHz. (Netherlands).

This document proposes that Markov random field models (MRFs) be used as a framework within which to construct models of synthetic aperture radar (SAR) images. Its author clarifies the relationship between this class of models and the Boltzmann machine (BM) of artificial intelligence. He then generalizes the BM training procedure and use it to train MRF models. Using this techniques he investigate the ability of a simple MRF texture model to learn a texture by maximizing a relative entropy objective function. It is found that the marriage of MRF models with the BM training procedure is fruitful. (Author)

This report describes methods of powering devices to which only a/c contact can be made and receiving data transmitted back from them. Examples of such devices include medical implants which communicate with the external environment via ultrasound or rf links. Two breadboard systems have been built to demonstrate the techniques. In both the device is powered by picking up an ac inpt and rectifying it. A signal voltage detected by the device is encoded as a frequency, transmitted and decoded. In one case this is performed on a separate channel from that used to power the device. In the other only one channel is used for both signals, and data is transmitted and decoded. In one case this is performed on a separate channel from that used to power the device. In the other only one channel is used for both signals, and data is transmitted by modulating the impedance presented by the device. The resulting modulation of the input signal was picked up by the external circuit and decoded.

This document suggests improvements to a proposed method of phrase coding for the Mode S Data Link and describes some testing of the phrase programming language. Keywords: Great Britain; Mode-S Secondary Surveillance radar. (Author)

This paper describes the implementation of Pascal files in an object-oriented manner using procedure values. A Pascal compiler has been written to the ISO standard for the Flex computer using these methods. Each file is represented by a package of procedures and every basic operation on the file is a call of one of these procedures. Such an implementation is only possible on a machine which supports true procedure values. Furthermore these procedure values must be able to exist in the filestore as well as in the mainstore of the machine. Keywords: Great Britain. (Author)

A method is described for writing the formal specifications for a digital system, a high level of design which satisfies this requirement and then a gate level realisation, using the languages LCF -LSM and ELLA. Given these formal descriptions, this papers shows how to carry out mathematical proofs to establish that the high level design respects the specification and the gate level design agrees with precisely with the high level design. By this means, a chain of correspondence proof is created from the specification to the ultimate realisation, as required during the development of safety critical and security critical hardware. There methods have been used to develop formal proofs for the VIPER microprocessor and this paper forms an essential tutorial for those studying the validation of this new 32 - bit processor. (Great Britain)