Showing papers by "Philips published in 1988"

Quantized conductance of point contacts in a two-dimensional electron gas.

Abstract: As a result of the high mobihty attamable in the twodimensional electron gas (2DEG) in GaAs-AlGaAs heterostructures it is now becoming feasible to study ballistic transport in small devices '"6 In metals ideal tools for such studies are constnctions havng a width W and length L much smaller than the mean free path le These are known as Sharvin pomt contacts 7 Because of the ballistic transport through these constnctions, the resistance is determmed by the pomt-contact geometry only Point contacts have been used extensively for the study of elastic and melastic electron scattermg With use of biased pomt contacts, electrons can be mjected mto metals at energies above the Fermi level This allows the study of the energy dependence of the scattermg mechamsms 8 With the use of a geometry containmg two pomt contacts, with Separation smaller than le, electrons mjected by a pomt contact can be focused mto the other contact, by the application of a magnetic field This technique (transverse electron focusmg) has been applied to the detailed study of Fermi surfaces 9 In this Letter we report the first expenmental study of the resistance of ballistic pomt contacts m the 2DEG of high-mobihty GaAs-AlGaAs heterostructures The smgle-pomt contacts discussed m this paper are part of a double-pomt-contact device The results of transverse electron focusmg m these devices will be published elsewhere '° The pomt contacts are dehned by electrostatic depletion of the 2DEG underneath a gate This method, which has been used by several authors for the study of l D conduction,'1 offers the possibility to control the width of the pomt contact by the gate voltage Control of the width is not feasible in metal pomt contacts

Analysis and realization of a pulsewidth modulator based on voltage space vectors

Abstract: A space vector concept for deriving the switching times for pulsewidth-modulated voltage source inverters is compared with the conventional sinusoidal concept. The switching times are deducted from assumptions for minimum current distortion, the resulting mean voltage values are shown, and the differences between these and the established sinusoidal PWM (pulse-width modulator) are elaborated. Based on an analytical calculation the current distortions and torque ripples are evaluated and compared with the values obtained with the conventional method. The space vector representation results in lower current harmonics and possibly a higher modulation index. A modulator based on an 8086 microprocessor has been implemented, and its performance is reported. >

Auto-association by multilayer perceptrons and singular value decomposition

Abstract: The multilayer perceptron, when working in auto-association mode, is sometimes considered as an interesting candidate to perform data compression or dimensionality reduction of the feature space in information processing applications. The present paper shows that, for auto-association, the nonlinearities of the hidden units are useless and that the optimal parameter values can be derived directly by purely linear techniques relying on singular value decomposition and low rank matrix approximation, similar in spirit to the well-known Karhunen-Loeve transform. This approach appears thus as an efficient alternative to the general error back-propagation algorithm commonly used for training multilayer perceptrons. Moreover, it also gives a clear interpretation of the role of the different parameters.

A practical zero-knowledge protocol fitted to security microprocessor minimizing both transmission and memory

Abstract: Zero-knowledge interactive proofs are very promising for the problems related to the verification of identity. After their (mainly theoretical) introduction by S. Goldwasser, S. Micali and C. Rackoff (1985), A. Fiat and A. Shamir (1986) proposed a first practical solution: the scheme of Fiat-Shamir is a trade-off between the number of authentication numbers stored in each security microprocessor and the number of witness numbers to be checked at each verification.This paper proposes a new scheme which requires the storage of only one authentication number in each security microprocessor and the check of only one witness number. The needed computations are only 2 or 3 more than for the scheme of Fiat-Shamir.

A Paradoxical Indentity-Based Signature Scheme Resulting from Zero-Knowledge

Abstract: At EUROCRYPT'88, we introduced an interactive zero-knowledge protocol (Guillou and Quisquater [13]) fitted to the authentication of tamper-resistant devices (e.g. smart cards, Guillou and Ugon [14]).Each security device stores its secret authentication number, an RSA-like signature computed by an authority from the device identity. Any transaction between a tamper-resistant security device and a verifier is limited to a unique interaction: the device sends its identity and a random test number, then the verifier tells a random large question; and finally the device answers by a witness number. The transaction is successful when the test number is reconstructed from the witness number, the question and the identity according to numbers published by the authority and rules of redundancy possibly standardized.This protocol allows a cooperation between users in such a way that a group of cooperative users looks like a new entity, having a shadowed identity the product of the individual shadowed identities, while each member reveals nothing about its secret.In another scenario, the secret is partitioned between distinct devices sharing the same identity. A group of cooperative users looks like a unique user having a larger public exponent which is the greater common multiple of each individual exponent.In this paper, additional features are introduced in order to provide: firstly, a mutual interactive authentication of both communicating entities and previously exchanged messages, and, secondly, a digital signature of messages, with a non-interactive zero-knowledge protocol. The problem of multiple signature is solved here in a very smart way due to the possibilities of cooperation between users.The only secret key is the factors of the composite number chosen by the authority delivering one authentication number to each smart card. This key is not known by the user. At the user level, such a scheme may be considered as a keyless identity-based integrity scheme. This integrity has anew and important property: it cannot be misused, i.e. derived into a confidentiality scheme.

Structure of GaAs(001) ( 2 × 4 ) − c ( 2 × 8 ) Determined by Scanning Tunneling Microscopy

Abstract: The scanning tunneling microscope (STM) has been used to study the $(2\ifmmode\times\else\texttimes\fi{}4)\ensuremath{-}c(2\ifmmode\times\else\texttimes\fi{}8)$ reconstruction on the arsenic-rich surface of GaAs(001). The STM images show that the 4\ifmmode\times\else\texttimes\fi{} periodicity is due to a regular array of missing arsenic dimers. The (2\ifmmode\times\else\texttimes\fi{}4) units are arranged so as to give small domains of either (2\ifmmode\times\else\texttimes\fi{}4) or $c(2\ifmmode\times\else\texttimes\fi{}8)$ reconstructions. These images are the first high-resolution STM images obtained from a surface grown by molecular-beam epitaxy. Features are seen which may be important in the mechanism of growth.

Global optimization and simulated annealing

Abstract: In this paper we are concerned with global optimization, which can be defined as the problem of finding points on a bounded subset of Rn in which some real valued functionf assumes its optimal (i.e. maximal or minimal) value. We present a stochastic approach which is based on the simulated annealing algorithm. The approach closely follows the formulation of the simulated annealing algorithm as originally given for discrete optimization problems. The mathematic formulation is extended to continuous optimization problems and we prove asymptotic convergence to the set of global optima. Furthermore, we discuss an implementation of the algorithm and compare its performance with other well known algorithms. The performance evaluation is carried out for a standard set of test functions from the literature. Keywords: global optimization, continuous variables, simulated annealing.

Accurate quantification of in vivo 31P NMR signals using the variable projection method and prior knowledge.

Abstract: Free induction decay signals are analyzed by fitting a model function directly in the time domain. No starting values are needed for linear model parameters, and omission of corrupted data points poses no problems. A significant gain of accuracy is achieved by imposing prior knowledge about the model parameters. © 1988 Academic Press, Inc.

Perpendicular magnetic anisotropy of Co-Au multilayers induced by interface sharpening.

Abstract: Co-Au multilayers with Co layer thicknesses between 22 and 5 \AA{}A, prepared by ion-beam sputtering, have an easy-plane magnetic anisotropy Their saturation magnetization indicates the presence of diffuse interfaces, caused by ion-beam mixing Annealing of the multilayers at 250-300\ifmmode^\circ\else\textdegree\fi{}C leads to a perpendicular anisotropy for Co thicknesses below about 14 \AA{}A This effect is attributed to a stronlgy enhanced interface anisotropy, which is due to sharpening of the interfaces as revealed by x-ray diffraction

Video cassette recorder programming via teletext transmissions

Abstract: A system for video recorder programming using existing television broadcast teletext transmissions. The programs required are chosen from schedules displayed on teletext pages, the necessary control information is loaded automatically into a video recorder, and program labels are transmitted to ensure that the correct programs will be recorded even if program timings are altered. All the control information for achieving the above are fitted into the coding structure of a teletext transmission using extension packets additional to data packets containg display data. The invention also extends to a video recorder with its own teletext decoder for processing the control information.

Some novel ternary ThMn12-type compounds

Abstract: Ternary compounds based on the tetragonal ThMn 12 structure are formed when rare earth. elements (R) are combined with iron and elements M (M ≡ Si, Ti, V, Cr, Mo or W). A structure determination was made for NdFe 10 Mo 2 , showing that the molybdenum atoms occupy only one of the three available crystallographic sites in this structure type. Detailed investigations of the systems YFe 12 − x V x showed that there is a substantial range of solid solubility extending approximately from x = 1.5 to x = 3. Curie temperatures were determined for the two series YFe 10 M 2 and GdFez 10 M 2 and were found to depend strongly on the component M.

Representation and Hidden Bias: Gray vs. Binary Coding for Genetic Algorithms

Abstract: Experimental results are presented that indicate Gray coding is generally superior to binary coding for function optimization using the genetic algorithm. Analysis suggests that Gray coding eliminates the “Hamming cliff” problem that makes some transitions difficult when using a binary representation. We argue that the “Hamming cliff” is but one instance of hidden bias emerging from an interaction between search control heuristics and the knowledge representation.

Formation and magnetic properties of the compounds R2Fe14C

Abstract: It was shown by X-ray diffraction that rare earth compounds of the type R2Fe17 can dissolve appreciable amounts of carbon up to x = 0.6 in R2Fe17Cx at 900 °C. The increase in the lattice constants is accompanied by a strong increase in Curie temperature. From a structure determination (R = 7%) it was found that the carbon atoms dissolve interstitially and occupy the 9e position in the Th2Zn17 structure type (R3m). This ternary carbide is present as the main phase when compounds of the type R2Fe14C are heated above their decomposition temperatures. The decomposition proceeds by means of a solid state transformation and the corresponding transformation temperatures Tt vary strongly with the R component. In several of the light rare earth systems Tt becomes rather low and makes an annealing treatment ineffective with regard to the formation of R2Fe14C phases. The magnetic properties of the R2Fe14C phases are compared with those of R2Fe14B. It is shown that the former follow the magnetic behaviour of the latter almost completely.

Compounds and phase compatibilities in the system Y2O3-BaO-CuO at 950°C

Abstract: The subsolidus phase diagram of the system Y2O3-BaO-CuO at 950° C in air has been investigated. In the binary system BaO-CuO the compound Ba2CuO3+δ has been isolated and a new compound with composition in the vicinity of Ba3Cu5O8+δ has been found. In the binary system BaO-Y2O3 it is shown in that the compounds “Ba4Y2O7” and “Ba2Y2O5” are oxycarbonates with composition Ba4Y2O7·CO2 and Ba2Y2O5·2CO2. New compounds that have been identified in the ternary system Y2O3-BaO-CuO are YBa4Cu3O8.5+δ, Y3Ba8Cu5O17.5+δ and a compound with composition close to YBa5Cu Cu2O8.5+δ. The oxygen content and the oxidizing power of these compounds has been measured. The oxygen content depends on the preparation method. Lists of interplanar spacings, relative intensities and h k l indices of these oxygen deficient perovskites as determined from X-ray powder diffraction measurements are presented and possible structures of the unit cells are described. Phase equilibrium relations have been investigated and tie lines in the phase diagram are presented.

Fault modeling and test algorithm development for static random access memories

Abstract: A fault model for SRAMs (static random-access memories) is presented based on physical spot defects, which are modeled as local disturbances in the layout of an SRAM. Two linear test algorithms (length 9N and 13N respectively, where N is the number of addresses) plus a data retention test are proposed that cover 100% of the faults under the fault model. The 13N test algorithm is generally applicable while the 9N algorithm can only be used in SRAMs with combinational R/W logic. A general solution is given for testing word-oriented SRAMs. The practical validity of the fault model and the two test algorithms is verified by a large number of actual wafer tests and device failure analysis. >

Variation of geometrics based on a geometric-reasoning method

Abstract: A method is described for processing generic geometric models on the basis of symbol manipulation and inferencing. A two-dimensional model is represented as a set of geometric elements and a set of atomic formulas that define the constraining scheme. Processing of a model is performed by a rule-based system, whose rules embody the general knowledge for the propagation of constraining information in geometric structures. Forward inferencing is used as an example of a possible control strategy. The system detects whether or not a model description is consistent and derives a plan for the construction of variants. Given a numerical value for each parametric constraint of a model, a variant is rapidly generated through automatic plan execution.

Method for connected word recognition

Abstract: In the recognition of words from a large vocabulary the comparison of the spoken signal in each case in parallel with all the words requires an excessively large expenditure of time and the recognition reliability is low. In addition, in the case of words spoken in connected fashion the word boundaries cannot always be readily determined. In the present invention the natural grammar is taken into account to a certain extent and is given in the form of a list which contains the assignment in each case of a syntactic category to a plurality of other categories and/or words. As a result, the number of words which, during the recognition process, have to be handled in each case simultaneously and which are stored in a second list can be considerably reduced in each case. In addition, a third list with information relating to hypotheses for the sentence to be recognised is built up from the first list, the hypotheses being partially verified and further possible hypotheses for the voice signal to follow being newly constructed as the comparison of the voice signal with the current words and the result thereof progresses. … …

Enthalpies of formation of liquid and solid binary alloys based on 3d metals: IV. Alloys of cobalt

Abstract: Continuing the papers on alloys of Sc, Ti, V, Cr, Mn and Fe we review in the present paper, on the basis of the model developed by Miedema and co-workers, experimental and predicted enthalpies of formation of ordered binary intermetallic compounds of Co with arbitrary metal partners. The enthalpy effects are also reviewed for liquid Co alloys. The predicted values agree quite satisfactorily with the available experimental data for binary systems of Co with a transition metal. In the binary systems where Co is alloyed with a non-transition metal larger differences are sometimes observed. Since Co with other transition metals may often form solid solutions the enthalpy of forming solid solutions is dealt with in a concise way distinguishing between magnetic and non-magnetic matrix metals.

Quantized conductance of magnetoelectric subbands in ballistic point contacts

Abstract: The two-terminal conductance of ballistic point contacts in the two-dimensional electron gas of a high-mobility $\frac{\mathrm{GaAs}}{{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}}$ heterostructure has been studied in quantizing electric and magnetic fields. The conductance is found to be quantized at multiples of $\frac{{e}^{2}}{h}$, exclusively determined by the number of occupied magnetoelectric subbands in the constriction. The experiment provides the first direct demonstration of magnetic and electric depopulation of one-dimensional subbands in a single wire.

Device for receiving and processing road information

Abstract: Device for receiving and processing road information messages transmitted in digital form, each message including at least a first section for indicating the zone of the road network to which the message refers, which device includes for the control of the data processing a data processing unit which is connected to a bus for the transfer of data, to which bus are also connected a reception memory for temporarily storing the received messages, a selection unit enabling the selection from among the stored messages of those concerning a zone to be designated and a presentation unit for presenting the selected messages. The device also includes a message analysis unit which includes a zones table memory, which analysis unit is provided for recognizing the zone in question each time a message is received on the basis of the said first section of the received message and for storing in the zones table, by means of at least one indicator for each message, the received messages according to the zone to which they belong, which selection unit is provided for accessing the zones table and for carrying out the said selection by fetching messages for the designated zone in the zones table.

Second-order nonlinear effects in asymmetric quantum-well structures.

Abstract: The expression for second-order optical susceptibility based on band-to-band and intraband transitions in various asymmetric multiple-quantum-well structures is derived. The analogy with organic nonlinear materials is shown. The dependence of the second-harmonic coefficient and Pockels coefficient on well geometry, band offsets, and other material parameters is studied. The nonlinear and electro-optic coefficients of GaAs-${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As asymmetric quantum-well systems are estimated to be in the range of most conventional nonlinear materials, while for proposed ZnSe-GaAs heterostructures these coefficients are found to be substantially larger than in conventional materials. Some practical applications of asymmetric quantum-well systems are discussed, including novel methods of phase matching. The case for engineering of novel nonlinear materials is made.

Method of metallizing silica-containing gel and solid state light modulator incorporating the metallized gel

Abstract: A solid state light modulator structure useful in a video display system includes a deformable silica containing gel layer on an array of charge storage elements, and an adherent, highly light reflective metal (e.g., Ag) electrode layer formed directly on the surface of the gel layer by sputtering in a non-reactive atmosphere.

System for subband coding of a digital audio signal

Abstract: A system for subband coding of a digital audio signal x(k) includes in the coder (1) a filter bank (3) for splitting the audio signal band, with sampling rate reduction, into subbands (p = 1, ....P) of approximately critical bandwidth and in the decoder (2) a filter bank (5) for merging these subbands, with sampling rate increase. For each subband (p) the coder (1) comprises a detector (7(p)) for determining a parameter G(p;m) representative of the signal level in a block (p;m) of M samples of the subband signal xp(k) as well as a quantizer (8(p)) for adaptively block quantizing this subband signal in response to parameter G(p;m), and the decoder (2) comprises a dequantizer (9(p)) for adaptively block dequantizing the quantized subband signal sp(k)in response to parameter G(p;m). The quantizing characteristics are related to the noise-masking curve of the human auditory system, owing to which a high-quality of the replica x/ (k) of audio signal x(k) is attained with an average number of approximately 2.5 bits per sample for representing the output signals of the coder (1). The occasional audibility of quantizing noise in this replica x/ (k) is reduced effectively in that the coder (1) and decoder (2) contain identical bit allocation means (23, 24) responsive to a set of parameters G(p;m) for the higher group of subbands (pim

Analytical analysis of the harmonic effects of a PWM AC drive

Abstract: A novel analysis is presented of the harmonic content of current, torque pulsations, and harmonic copper losses of a three-phase induction machine fed by a two-phase pulsewidth modulation (PWM) inverter. The purely analytical results are based on the assumption that the switching frequency is high compared with the fundamental frequency. It is shown that the results hold accurately for frequency ratios f/sub s//f/sub 1/>9. >

Exciton mixing in quantum wells

Abstract: An effective-mass theory of the properties of excitons in isolated GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As quantum wells is presented. The phenomenon of exciton mixing induced by the complicated valence-band structure is emphasized. The effects of external perturbations such as electric and magnetic fields and uniaxial pressure normal to quantum wells grown in different crystal directions are calculated. Exciton mixing is found to cause many observable effects on transition energies and oscillator strengths.