Showing papers by "Philips published in 1983"

New Class of Materials: Half-Metallic Ferromagnets

Abstract: The band structure of Mn-based Heusler alloys of the $C{1}_{b}$ crystal structure (MgAgAs type) has been calculated with the augmented-spherical-wave method. Some of these magnetic compounds show unusual electronic properties. The majority-spin electrons are metallic, whereas the minority-spin electrons are semiconducting.

Dynamics of film growth of GaAs by MBE from Rheed observations

Abstract: Detailed observations have been made of the intensity oscillations in the specularly reflected and various diffracted beams in the RHEED pattern during MBE growth of GaAs, Ga x Al1−x As and Ge. The results indicate that growth occurs predominantly in a two-dimensional layer-by-layer mode, but there is some roughening, which is enhanced by deviations from stoichiometry and the presence of impurities. In the case of the GaAs (001) −2×4 reconstructed surface a combination of dynamic and static RHEED measurements has provided firm evidence for the presence of one-dimensional disorder features as well as surface steps.

Dynamic Frame Length ALOHA

Abstract: Adding frame structure to slotted ALOHA makes it very convenient to control the ALOHA channel and eliminate instability. The frame length is adjusted dynamically according to the number of garbled, successful, and empty timeslots in the past. Each terminal that has a packet to transmit selects at random one of the n timeslots of a frame. Dynamic frame length ALOHA achieves a throughput (expected number of successful packets per timeslot) of 0.426 which compares favorably with the 1/e (\approx0.368) upper bound of ordinary slotted ALOHA.

Magnetic and magneto-optic properties of lead- and bismuth-substituted yttrium iron garnet films

Abstract: The saturation magnetization ${M}_{s}$, the uniaxial anisotropy ${K}_{u}$, the optical absorption $\ensuremath{\alpha}$, the Faraday rotation ${\ensuremath{\theta}}_{F}$, and the Faraday ellipticity ${\ensuremath{\psi}}_{F}$ of epitaxial garent films of composition ${\mathrm{Y}}_{3\ensuremath{-}x}{\mathrm{Bi}}_{x}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ and ${\mathrm{Y}}_{3\ensuremath{-}y}{\mathrm{Pb}}_{y}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ have been investigated for $x\ensuremath{\le}1.7$ and $y\ensuremath{\le}0.25$. The magnetostriction constants ${\ensuremath{\lambda}}_{100}$,${\ensuremath{\lambda}}_{111}$ and the cubic anisotropy ${K}_{1}$ were studied on flux-grown crystals for $x\ensuremath{\le}1$. The temperature dependence of ${M}_{s}$, ${K}_{1}$, ${K}_{u}$, ${\ensuremath{\lambda}}_{100}$, ${\ensuremath{\lambda}}_{111}$, and ${\ensuremath{\theta}}_{F}$, ${\ensuremath{\psi}}_{F}$ at 633 nm has been measured in the range $4.2 \mathrm{K}\ensuremath{\le}T\ensuremath{\le}{T}_{c}$. The concentration dependence of these properties is linear. In particular, the contribution of the bismuth and lead to the Faraday rotation $\frac{\ensuremath{\Delta}{\ensuremath{\theta}}_{F}}{x}$ and $\frac{\ensuremath{\Delta}{\ensuremath{\theta}}_{F}}{y}$ at $\ensuremath{\lambda}=633$ nm turned out to be -25 400 and -18 500 deg ${\mathrm{cm}}^{\ensuremath{-}1}$ at $T=4.2$ K and -20 600 and -18 400 deg ${\mathrm{cm}}^{\ensuremath{-}1}$ at $T=295$ K, respectively. The temperature dependence of ${\ensuremath{\theta}}_{F}$ and ${\ensuremath{\psi}}_{F}$ can be described in terms of the sublattice magnetizations inferred from the fit of the molecular-field theory to the measured saturation magnetization. The extracted magneto-optical coefficients reveal a nonlinear concentration dependence. The magnitude of the growth-induced anisotropy is essentially controlled by the supercooling of the melt for both the lead- and bismuth-substituted films. The temperature dependence of ${K}_{u}^{g}$ is discussed in terms of the single-ion theory.

Combined position sensor and magnetic motor or bearing

Abstract: A combined magnetic sensor and actuator device for applying a magnetic force to a magnetizable body and for sensing the distance between the device and the magnetizable body. The device includes a magnetizable pole piece separated from the magnetizable body by gaps. The pole piece, gaps, and magnetizable body form a magnetic circuit with the gaps preferably being the major reluctance of the circuit. Separate means are provided for generating a relatively large time-varying magnetic actuating flux in the magnetic circuit and for generating a relatively small time-varying magnetic sensing flux in the magnetic circuit. Each magnetic flux follows a flux path, such that the two flux paths have at least a portion in common. Detection means measure the relatively small magnetic flux in the magnetic circuit, and thereby measure the distance between the device and the magnetizable body.

Tunable waveguide oscillator

Abstract: An oscillator formed in rectangular waveguide (1) with both mechanical and electronic tuning comprises an oscillator device (4) spaced from a movable short-circuit termination (2) with a varactor diode (5) therebetween, the effective electrical spacing between the oscillator device (4) and the varactor (5) being approximately an integral number of halv-wavelengths at the operating frequency. The varactor (5) extends into the waveguide (1) from one broad wall thereof and engages a transverse member (10) extending between the narrow walls so that only part of the heigth of the waveguide (1) at that region is obscured. This enables the operating frequency and hence the extent of coupling of the varactor (5) to the oscillator cavity, and thus the electronic tuning range, to be varied by adjusting the position of the short-circuit (2). To enable the operating frequency to be mechanically adjusted without greatly influencing the electronic tuning range, an E-plane stub (11) with a movable short-circuit termination (12) may be branched from the waveguide (1) at the same region as the varactor (5).

GaAs ( 001 ) − c ( 4 × 4 ) : A chemisorbed structure

Abstract: We have carried out an experimental study of the As-stable $\mathrm{GaAs}(001)\ensuremath{-}c(4\ifmmode\times\else\texttimes\fi{}4)$ reconstruction using a combination of molecular-beam epitaxy with reflection electron diffraction, angle-resolved photoemission, and surface-sensitive core-level photoemission. (The measurements were performed at Laboratoire pour l'Utilisation du Rayonnement Electromagn\'etique, Universit\'e Paris---Sud, F-91405 Orsay, France.) Apart from the surface symmetry, the electron-diffraction data show one-dimensional disorder along the [110] direction, probably corresponding to a corrugated-sheet structure in reciprocal space. Photoemission from surface states having dangling-bond character shows a onefold periodicity and an energy dispersion of 0.65 eV along [110], while along [$\overline{1}10$] the dispersion is much smaller, but there is a doubling of the periodicity. Observations of the $\mathrm{As}3d$ and $\mathrm{Ga}3d$ core levels show a surface $\mathrm{As}3d$ component at 0.62 eV higher binding energy than the bulk component, indicative of As---As bonding. The $\mathrm{Ga}3d$ surface core-level shift is very small and the line shape is similar to that from the (2 \ifmmode\times\else\texttimes\fi{} 4) surface. The experimental results can be understood on the basis of an As overlayer structure, for which we propose specific models derived from trigonally bonded chemisorbed As.

Arrangement for the programmable control of a radio and/or television receiver

Abstract: When programming a radio and/or television receiver for future transmissions, problems may occur due to overlapping of the programmed transmissions. For this purpose the individually programmed transmissions are provided with priority data which control the sequence in the event of overlapping transmissions. In the same way given transmissions can also be provided with blocking data which block the reception or reproduction, respectively, thereof. The use of the priority data is particularly efficient when the transmissions are controlled in addition or exclusively by transmitted identification numbers and consequently are only received during the actual transmission time, as then shifts with respect to the planned transmission times cannot be foreseen. Additional possibilities are derived from the storage of data characterizing the type of the transmission, when these data are transmitted simultaneously with the relevant transmission.

Linear time-variable systems: Balancing and model reduction

Abstract: A "uniformly balanced" realization for linear time-variable systems is defined. This representation is characterized by the fact that its controllability, and observability Gramians are equal and diagonal. Existence and uniqueness of the uniformly balanced realization is studied. Such a framework has many remarkable properties and leads to a novel method for approximating time-variable systems, where the subsystems of the balanced realization can be taken as a reduced model. The reduced model is examined from the point of view of stability, controllability, and observability.

Exercise bicycle apparatus particularly adapted for controlling video games

Abstract: An exercise bicycle is associated with controllable apparatus such as potentiometers which provide an electrical signal based on the motion of the handlebars as well as signals proportional to the speed at which the bicycle is being operated at. These signals are interfaced with a typical microcomputer or video game machine which can utilize these signals to control the motions necessary to operate a video game. In this manner the apparatus generates five separate control signals one of which is indicative of the speed that the bicycle is being pedaled, the left to right movement of the handlebars as well as the forward to backward or up and down movement of the handlebars. There are associated with the handlebars two separate switches which can further be activated by the operator. In this manner the exercise bicycle is used to control and fully operate the video game thereby allowing a user to receive healthful exercise while participating in the skills necessary to play the video game.

The Enthalpy Effect on Forming Diluted Solid Solutions of Two 4d and 5d Transition Metals

Abstract: Predictions of the enthalpies of solution in the solid state will be presented for arbitrary combinations of 4d and 5d transition metals. The approach is similar to the one used in a previous paper on combinations of two 4d metals. In addition to the contribution stemming from the chemical interaction, which is equal to the enthalpy of solution in the liquid state, the enthalpy of solution in the solid state contains two other terms. The first of these accounts for the elastic energy arising from the atomic size mismatch, where this size mismatch has been corrected for volume changes that accompany the alloy formation. The second term takes into account the variation of the structure dependent energy in relation to the number of d-electrons per atom. – The predictions are generally in good agreement with the solubilities found in the respective phase diagrams. For two systems, Zr in Pt and Pt in Nb, that on first sight present exceptions, preliminary experiments indicate that parts of the respective phase diagrams have to be revised. The structure-dependent contribution manifests itself not only in the limiting solubilities in the main crystal structures of the pure metals, but also in the existence of disordered intermediate phases and may also be responsible for the anomalously large entropy of fusion recently observed for some transition metals.

On automatic recognition of 3D structures from 2D representations

Abstract: One possible way of specifying the geometry of mechanical parts in CAD follows a two-step procedure: input of a graphics-oriented 2D representation corresponding to views and cuts; and interpretation of this data to give the explicit 3D description. This paper is concerned with the problem of automating the interpretation step. The method of solution presented is based on viewing a part as consisting of several elementary objects and on recognizing these from their specific patterns in the 2D representation. A detailed algorithm is given for the case of three-view representations of parts whose constituent elementary objects are of the uniform-thickness type.

Variable frequency current control device for discharge lamps

Abstract: A control circuit for starting and operating a gas discharge lamp comprising a variable frequency waveform generator coupled to the discharge lamp via a non-resonant coupling network that includes a reactance type ballast impedance. The lamp current is monitored to automatically vary the frequency of the variable frequency generator as a function of the lamp current so as to vary the reactance of the ballast impedance in a sense to regulate or limit the lamp current.

The aliasing problem in discrete-time Wigner distributions

Abstract: There is no straightforward way to proceed from the continuous-time Wigner distribution to a discrete-time version of this time-frequency signal representation. A previously given definition of such a function turned out to yield a distribution that was periodic with period π instead of 2π and this caused aliasing to occur. Various alternative definitions are considered and compared with respect to aliasing and computational complexity. From this comparison it appears that no definition leads to a function that is optimum in all respects. This is illustrated by an example.

The Quality of Die-Attachment and Its Relationship to Stresses and Vertical Die-Cracking

Abstract: The residual stresses after die-attachment have been studied experimentally using a test chip with diffused resistor strain gauges. Extensive measurements are reported for the following dieattachment/leadframe combinations: Au-Si/Alloy 42, epoxy adhesive/ Copper 194, and polyimide adhesive/Copper 194. Two-dimensional distributions of the stresses in the device surface are shown, and additional thickness measurements of the adhesive layer are used to assess the amount of stress relaxation occuring in adhesive die-attachment. Large variations in the measured stresses were found for die-attachment with polyimide adhesive. Thickness measurements and radiography showed that the stress variations are caused by large voids formed during the drying cycle of the adhesive. The effect of voids on die-attachment stresses is analyzed, and its potential as a cause of vertical die-cracking is discussed.

Premodulation filter for generating a generalized tamed frequency modulated signal

Abstract: A transmitter for transmitting a carrier whose frequency is modulated by pseudo five-level signals. In order to obtain a simple receiver and an improved signal-to-noise ratio, a substantially three-level signal is generated in the transmitter at the detection instants t=(2m-1)T/2 by means of a pre-modulation filter.

The enthalpy of solution for solid binary alloys of two 4d-transition metals

Abstract: A demonstration is given how to derive the enthalpy of solid solution of alloys of two 4d transition metals for the three main crystallographic structures, fcc, hcp and bcc. Because of two additional terms the enthalpy of solution for solid phases differs from that in the corresponding liquid alloys. The first of these, accounting for elastic mismatch, can be estimated from Eshelby/Friedel-type elastic continuum theory. In our case we correct the atomic size mismatch for volume changes that accompany the formation of alloys. The second term accounts for the variation of structure dependent energies (i.e. the preference for either the fcc, bcc or hcp type of crystal structure) with the average number of electrons per atom. We derive an empirical curve for these structure dependent enthalpy terms, which is essentially based on theoretical results and gives a fair account of binary phase diagram characteristics.

A method for preventing collision for two mutually movable bodies and an apparatus including an arrangement for preventing collision

Abstract: The invention relates to a method and a device for prevention of collision between two mutually and independently movable bodies (A, B) In the method the outer contour of each body is approximated by a number of virtual subvolumes, preferably spheres (SA 1 , SA 2 ), whereafter the position of the centrum point (c 1 , c 2 ) of each such sphere, when the respective body assumes a zero or reference position, is stored in a fixed memory together with the radius (r 1 , r 2 ) of each sphere Repeatedly during a motion the new position of each sphere (SA 1 , SA 2 ) is determined by means of the stored positions and the output signals from position transducers associated to the bodies (A, B) and finally the distance between each sphere of one body (A) and each sphere of the second body (B) is calculated These calculated distances indicate the risk for collision and must exceed a given threshold value In an anti-collision system said calculated distances may be used to generate signals, which automatically brake or stop the motion of the bodies

Signal distribution system

Abstract: A head-end for a signal distribution system with selection facility, includes a matrix (8) and a multiplexer (12) connected thereto for forming a multiplex signal. The head-end further comprises A/D converters (4-1 to Δ-N) for converting the wide-band input signals into digital signals prior to supply to the matrix. The multiplexer comprises two amplitude modulators (13, 14) for the mutual quadrature amplitude modulation of a carrier (17) by two digital signals, and a summing means (18) for adding a digital signal in the base band to the modulated signal. A signal receiver for one of the modulated signals comprises a synchronous amplitude demodulator (21) connected to a synchronized carrier source (20) and also comprises means for digital-to-analog conversion (24).

Compact fluorescent lamp unit having segregated air-cooling means

Abstract: Convection air-cooling of a compact electric discharge lamp unit that is adapted for use as a screw-in energy-converv- ing substitute for an incandescent-type lamp bulb is enhanced by partitioning the lamp housing into two separate compartments and providing vents and connecting air passageways that direct ambient air through the respective housing compartments along two different paths thereby cooling the compartments independently of one another. A light source (such as a convolute low-pressure discharge tube) is located within one of the compartments and an electrical circuit for energizing the lamp is located in the other compartment. The "segregated air-flow" mode of cooling prevents heat that is generated by the lamp from being introduced into the compartment that contains the electrical circuit and thus prevents the circuit components from becoming overheated and possibly damaged.

Method and device for moulding a transparent object

Abstract: A method of and a device for high-precision moulding of transparent objects is described. Before the object assumes its final shape, a radiation beam is passed through the moulds of a moulding device and the material contained therein, and the intensity distribution of the radiation spot formed by the beam is compared with a reference, thereby enabling the moulds to be aligned very accurately, so that high-quality products can be manufactured.

Loudspeaker arrangement comprising one or more flat diaphragms

Abstract: A modular loudspeaker comprises a first module including a first loudspeaker unit (1) for reproducing a low-frequency audio signal and provided with at least two flat diaphragms (4, 5) and a second module including a second loudspeaker unit (2) for reproducing a high-frequency audio signal by means of a loudspeaker (8). The first and second loudspeaker units are constructed either to be mechanically detached from one another or to have connecting means whereby they can be rigidly mechanically connected to one another in a manner that will permit relatively easy mechanical detachment of the units from one another. Connecting means (10 or 11) allows the loudspeaker units to be electrically connected to one another and comprise interengageable parts that can be disengaged to disconnect the units. Another loudspeaker arrangement, which need not be of a modular construction, comprises a first loudspeaker unit (60) having at least one flat-diaphragm loudspeaker (61) and a second loudspeaker unit (62) which is pivotable about two orthogonal axes (65, 66).

Optical constants of absorbing thin solid films on a substrate.

Abstract: The optical constants nf and kf of an absorbing thin solid film, deposited on a transparent or a slightly absorbing substrate, depend in a complex way on measurable quantities such as the transmittance T and the air-incident and substrate-incident reflectances R and R′. Simple analytical formulas, which minimize propagation of experimental errors, are derived for determining ks of the substrate and kf and nf of the film. The formulas are applied to Te alloy films of varying thickness deposited on glass substrates.