Showing papers by "Philips published in 1987"

Static-noise margin analysis of MOS SRAM cells

Abstract: The stability of both resistor-load (R-load) and full-CMOS SRAM cells is investigated analytically as well as by simulation. Explicit analytic expressions for the static-noise margin (SNM) as a function of device parameters and supply voltage are derived. The expressions are useful in predicting the effect of parameter changes on the stability as well as in optimizing the design of SRAM cells. An easy-to-use SNM simulation method is presented, the results of which are in good agreement with the results predicted by the analytic SNM expressions. It is further concluded that full-CMOS cells are much more stable than R-local cells at a low supply voltage.

Linewidth dependence of radiative exciton lifetimes in quantum wells

Abstract: The fundamental relationship between radiative lifetime and spectral linewidth of free excitons is demonstrated theoretically and experimentally for quasi 2D excitons in GaAs/AlGaAs quantum wells.

From permanent magnets to rechargeable hydride electrodes

Abstract: A brief historical survey is given of how the study of coercitivity mechanisms in SmCo5 permanent-magnet materials eventually led to the discovery of the favourable hydrogen sorption properties of the compound LaNi5. It is shown how continued research by many investigators dealing with a variety of different physical and chemical properties has resulted in an advanced understanding of some of the principles that govern hydrogen absorption and which are responsible for the changes in physical properties that accompany it. The problems associated with various applications of LaNi5-based hydrogen-storage materials are also briefly discussed. A large part of this paper is devoted to the applicability of LaNi5-type materials in batteries. Research in this area has resulted in the development of a new type of rechargeable battery: the nickel-hydride cell. This battery can be charged and discharged at high rates and is relatively insensitive to overcharging and overdischarging. Special attention is given to the nature of the electrode degradation process and the effect of composition variations in LaNi5-related materials on the lifetime of the corresponding hydride electrodes when subjected to severe electrochemical charge-discharge cycles.

Radiofrequency penetration and absorption in the human body: Limitations to high-field whole-body nuclear magnetic resonance imaging

Abstract: This study presents experimental results about the effective depth of penetration and about the radiofrequency (rf) power absorption in humans as a function of frequency. The frequency range investigated covers 10 up to 220 MHz. For the main part, the results were derived from bench measurements of the quality factor Q, and of the resonance frequency shift due to the loading of the coil. Different types of head-, body-, and surface coils were investigated loaded with volunteers or metallic phantoms. For spin-echo imaging at 2 T (85 MHz), the local specific absorption rate (SAR) was found to be approximately equal to 0.05 W/kg using a pi pulse of 1-ms duration and pulse repetition time TR = 1 s. Measurements of the quality factor Q as a function of frequency show that the SAR depends upon the frequency f according to approximately f2.15. The effective depth of rf penetration as derived drops from 17 cm at 85 MHz to 7 cm at 220 MHz. Head imaging with B1 penetrating from practically all sides into the object should be possible up to 220 MHz (5 T) with SAR values staying within the local limit of 2 W/kg as set by the FDA. Whole-body imaging of large subjects as well as surface coil imaging is depth limited above 100-MHz frequency. Perturbation methods are applied in order to separate the total rf power deposition in the patient into dielectric and magnetic contributions. The observed effects due to interactions of rf magnetic fields with biological tissue contradict predictions based on homogeneous tissue models. A refined tissue model with regions of high electrical conductivity, subdivided by quasi-insulating adipose layers, provides a rationale for a better understanding of the underlying processes. At frequencies below 100 MHz, the rf power deposition in patients is apparently more evenly distributed over the exposed body volume than currently assumed.

X-ray diffraction computed tomography

Abstract: Coherent scattering of x-ray photons leads to the phenomenon of x-ray diffraction, which is widely used for determining atomic structure in materials science. A technique [x-ray diffraction computed tomography (CT)] is described, analogous to conventional CT, in which the x-ray diffraction properties of a stack of two-dimensional object sections may be imaged. The technique has been investigated using a first generation (single pencil beam) CT scanner to measure small angle coherent scatter, in addition to the customary transmitted radiation. Diffraction data from a standard CT performance phantom obtained with this new technique and with an x-ray diffractometer are compared. The agreement is satisfactory bearing in mind the poor momentum resolution of our apparatus. The dose and sensitivity of x-ray diffraction CT are compared with those of conventional transmission CT. Diffraction patterns of some biological tissues and plastics presented in a companion paper indicate the potential of x-ray diffraction CT for tissue discrimination and material characterization. Finally, possibilities for refinement of the technique by improving the momentum resolution are discussed.

Method and apparatus for handing-over a radio connection from one radio cell to another radio cell of a digital radio transmission system

Abstract: Base radio stations are spatially arranged in a radio transmission system in accordance with a cellular system, separating the message transmission channels from adjacent base stations being effected either by using the frequency-division multiplex method or by using the code-division multiplex method or by using a combination of these multiplex methods. In appropriately large spatial distances the same set of channels can be repeated in a further radio cell. If a mobile radio station moves during the conversation from one radio cell into another, then it is necessary to hand-over the then existing radio connection. To avoid the necessity of using additional receivers in each base station and to prevent a repeated hand-over in the event of high co-channel interferences, the measurements used for hand-over decision are effected in the mobile radio station. As part of the method the reception quality of the co-channel message transmission channels of remote base stations are additionally measured in the mobile station during the existence of a radio connection to a near base station.

Giant oscillator strength of free excitons in GaAs

Abstract: The radiative lifetime of free excitons in GaAs is unambiguously determined for the first time using ultrapure material grown by molecular-beam epitaxy. Its value amounts to 3.3\ifmmode\pm\else\textpm\fi{}0.5 ns in the limit of very low temperatures. Consequently, the oscillator strength of free excitons is on the order of unity, in contrast to what commonly is deduced from the total absorption cross section. At excitation densities above 0.5 W/${\mathrm{cm}}^{2}$ we have observed the radiative recombination of excitonic molecules (biexcitons) at 1.5146 eV in accordance with theoretical considerations.

Laser Diffraction Spectrometry: Fraunhofer Diffraction Versus Mie Scattering

Abstract: Laser diffraction spectrometry (LDS) is often claimed to operate on the principle of Fraunhofer diffraction. This is only true, however, if particles are large compared to the wavelength of light or if the ratio of the refractive indices of the disperse and continuous phases, m, is clearly different from unity. In this study it has been established that LDS, as applied to particle and droplet sizing in suspensions and emulsions, is based on Miescattering. Scattering patterns of single particles may be calculated if the refractive indices of both phases are known. Thus, a theoretical basis has been provided for the application of LDS to size-measurement in suspensions and emulsions, and for extension of this method to the lower size ranges and those cases in which the refractive indices of the disperse and continuous phases are similar. Extension of the work presented in this paper will enable the calculation of scattering matrices so that calibration of the apparatus with standard materials may be avoided.

An 8-bit video ADC incorporating folding and interpolation techniques

Abstract: A flash-type analog-to-digital converter that operates without a sample-and-hold circuit and incorporates folding and interpolation techniques is presented. It achieves an excellent performance while dissipating only 300 mW from a single 5-V power supply. The folding and interpolation system and the corresponding block diagram are explained. Implementation of folding and interpolation circuitry and the design of the reference resistor are discussed in detail. Several advantages of the system are investigated. The effective resolution of the converter is given as a function of analog input frequency. An 8-bit resolution bandwidth of 8 MHz is achieved. Up to an analog input frequency of 5 MHz, every distortion component stays below -60 dB. The maximum sample rate is 55 MHz. The circuit occupies 6 mm/SUP 2/ of silicon area, bonding pads included. It is realized in a 2.5-/spl mu/m bipolar process with an f/SUB T/ of 7.5 GHz.

Timing of Skilled Motor Performance: Tests of the Proportional Duration Model.

Abstract: Historically, theories of motor control have been based on either central or peripheral mechanisms. This article examines a current, expfieit, central theory accounting for the observed flexibility in motor performance: the generafized motor program with a multiplicative rate parameter. Reanalysis of data from a variety of motor skills reported in the literature and a detailed study of skilled typewriting show that a generalized motor program with a multiplicative rate parameter generally does not fit observed performance. Instead, the data support a composite model of motor control in which performance is determined by both central and peripheral mechanisms.

Control of Liquid‐Phase‐Enhanced Discontinuous Grain Growth in Barium Titanate

Abstract: Le titanate de baryum presente une croissance de grain discontinue en presence de petites quantites de l'eutectique liquide Ba 6 Ti 17 O 40 −BaTiO 3 a T>1312°C. La croissance de grain exageree en presence de la phase liquide peut s'expliquer en termes d'un processus de segregation de solution. La distribution granulometrique de ceramiques frittees de BaTiO 3 et la dimension moyenne de grain sont fortement modifiees par l'addition de «grains-germes» a la poudre de BaTiO 3 . Ce processus de controle de la croissance de grain discontinue semble applicable en general aux ceramiques

A liquid crystal display illumination system

Abstract: An illumination system is provided for a liquid crystal display panel. The panel 1 is placed to transmit light 2 from a light source 3 to a viewing location, the light source being an extended area source of omnidirectional light of high efficiency, such as a fluorescent tube. A light guide 6 is placed between the source and the panel, the light guide comprising a transparent input face 7 adjacent the source, a transparent output face 10 adjacent the panel, and reflective side walls 11 transverse to the input and output faces. The light guide is tapered, the input face being smaller in area than the output face. The divergence of light from the source is thereby reduced as it passes through the panel. The LCD panel then functions with an improved contrast range.

Imaging performance of a digital storage phosphor system.

Abstract: The imaging performance of a storage phosphor system (SPS) for digital projection radiography is studied in which the x‐ray image is temporarily stored in a light‐stimulable phosphor plate which is subsequently read out by a scanning laser beam. The imaging performance of this system has been analyzed for two types of imaging plates. The spatial resolution is described by the modulation transfer function and the signal‐to‐noise (S/N) ratios of the recorded image data are measured in terms of noise‐equivalent quanta and detectivequantum efficiency. Their dependence on detector entrance dose and space and spatial frequency is discussed. A detailed analysis of the different sources of image noise is given to outline the intrinsic features and limits of the system. Finally, the S/N behavior of the SPS is compared with published data of screen–film systems.

Magnetic properties of a series of novel ternary intermetallics (RFe10V2)

Abstract: We have studied the magnetic properties of a series of novel ternary compounds of the composition RFe 10 V 2 (R ≡ Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y) X-ray diffraction showed that these materials crystallize in the tetragonal ThMn 12 structure The Curie temperature falls into the range 483 to 616 K From high-field magnetic measurements made at 42 K on aligned powders it was derived that the iron sublattice anisotropy is about 4 T, while the rare earth sublattice anisotropy is comparatively low in most of the compounds studied

Device comprising a flat susceptor rotating parallel to a reference surface about a shift perpendicular to this surface

Abstract: A device comprising a flat susceptor rotating parallel to a reference surface about a rotary shaft perpendicular to this surface and comprising means for obtaining the stability of the susceptor held in sustentation and means for obtaining its rotary movement, is characterized in that these means are constituted by the structure of the susceptor, of the rotary shaft and of the reference surface, which cooperate with each other under the action of one or several flow of gas.

Inheritance and Subtyping in a Parallel Object-Oriented Language

Abstract: We have investigated the concepts of inheritance and subtyping in order to integrate them in a parallel object-oriented language In doing so, we have concluded that inheritance and subtyping are two different concepts, which should not be confused in any object-oriented language (be it parallel or sequential) Inheritance takes place on the implementation level of classes, and it is a convenient mechanism for code sharing It can be supported, for example, by introducing inheritance packages into a programming language Subtyping deals with the message interface of objects, and it leads to a conceptual hierarchy based on behavioural specialization Subtyping should take place on the basis of specifications of the external behaviour of objects, and as much as possible of these specifications should be formal Some specific problems with introducing these two concepts into a parallel language are also discussed

RLSQ: T1, T2, and ρ calculations, combining ratios and least squares

Abstract: A method is proposed for calculating images of spin density p and relaxation times T1T2 from MR imaging sequencies with the following characteristics: • it avoids nonlinear iterative techniques and is consequently sufficiently fast to allow calculation ofp, T1 and T2 on a pixel by pixel basis routinely; • it uses all available data simultaneously in an approximately optimal fashion. The method is applied to the combined SE + IR sequence but can be used for other acquisition Schemes as Well. © Academic Press, Inc.

X-ray diffraction measurements of some plastic materials and body tissues

Abstract: X‐ray diffraction allows the investigation of the atomic or molecular structure of materials. The combination of diffractometry with computerized tomography enables spatially resolved imaging of the diffraction properties of extended objects as described in more detail in a companion article [Harding e t a l., Med. Phys. 1 4, 515 (1987)]. We present measured diffraction patterns of some plastics and several biological materials, which allow further optimization of our method and the selection of suitable application areas.

Explicit time correlation in hidden Markov models for speech recognition

Abstract: The Hidden Markov models are generalized by defining a new emission probability which takes the correlation between successive feature vectors into account. Estimation formulas for the iterative learning both along Viterbi and Maximum likelihood criteria are presented.

Mobile radio transmission system

Abstract: A mobile radio tarnsmission system comprises a plurality of base stations (BS) with corresponding service areas (SA) which together cover a geographical area through which mobile stations (M) can roam. Each base station is connected to a central station (CS) by means of a respective two-way communication link (CL). In order that it can be contacted without all the base stations having to put out a call, each mobile station registers in known manner with the base station in whose service area it is situated, and this is recorded by the control station. When it roams into a new service area this process is repeated. However, in order to preclude frequent re-registrations when the mobile station repeatedly crosses the boundary between two service areas, when it registers with a new base station and hence a new service area it retains its registration with at least one service area with which it is already registered, thereby creating its own customized enlarged registration area. Thus the transmission overhead created by the registration procedure is reduced.

Optically readable record carrier for recording information, method and apparatus for manufacturing such a record carrier, apparatus for recording information on such a record carrier, and apparatus for reading information recorded on such a record carrier

Abstract: An optical disc record carrier having a radiation-sensitive surface and a spiral or concentric pattern of information tracks thereon. The radial displacement of each track is modulated to produce a periodic radial wobble, the frequency of such periodic displacement being modulated by a position-information signal identifying the relative positions of the tracks. During recording or reading of information on the tracks the track modulation is read by a scanning beam. A clock signal for controlling scanning velocity is recovered from the track displacement modulation, and an FM demodulator recovers the position-information signal from the frequency modulation of such displacement.

A data-driven organization of the dynamic programming beam search for continuous speech recognition

Abstract: This paper describes a data-driven organization of the dynamic programming beam search for large vocabulary, continuous speech recognition. This organization can be viewed as an extension of the one-pass dynamic programming algorithm for connected word recognition. In continuous speech recognition we are faced with a huge search space, and search hypotheses have to be formed at the 10-ms level. The organization of the search presented has the following characteristics. Its computational cost is proportional only to the number of hypotheses actually generated and is independent of the overall size of the potential search space. There is no limit on the number of word hypotheses, there is only a limit to the overall number of hypotheses due to memory constraints. The implementation of the search has been studied and tested on a continuous speech data base comprising 20672 words.

High speed robot control and obstacle avoidance using dynamic potential functions

Abstract: Time-optimal control of robot motion for dynamically decoupled manipulators is described in terms of potential functions. Avoidance of moving obstacles is incorporated via protective potential functions. An energy interpretation of the potential functions leads to rules for construction of avoidance functions and logical operations among them. Simple expressions for combining obstacle fields with an obstacle-free time-optimal solution result in the minimum safe influence of obstacles. Simulation results are given demonstrating high-speed target interception in the presence of obstacles.