Showing papers by "Chalmers University of Technology published in 1973"

Discharge of MNOS structures

Abstract: The discharge of MNOS memory devices at zero or low gate voltages is studied theoretically and experimentally. A theory based on direct tunneling of charge carriers from traps in the silicon nitride layer into the silicon describes the experiments quite well. The discharge process is found to be logarithmic in time, starting at a certain time, ift d , which is exponentially dependent on the oxide thickness, and ending at another time, extrapolated to much larger than 10 years. Some implications of the discharge model are discussed.

Radio Detection of Interstellar CH

Abstract: As recently as 1968 the only molecules known to exist in interstellar space were CH, CH+ and CN, identified by means of their absorption spectra superimposed on the optical spectra of bright stars, and OH which in its ground state emits at a radio wavelength of 18 cm. Since then there has been a remarkable series of discoveries of about twenty additional molecules emitting in the radio spectrum, some of them quite complex (CH3OH for example). But of the originally discovered ‘optical’ radicals, only CN, emitting at about 2.6 mm, has been detected at radio frequencies—in the Orion Nebula, in the HII region W51, and in the infrared object IRC+10216. The other radical, CH, has not been found, mainly because the radio frequencies of its ground state lambda doublet have not been found in the laboratory, and it has not been possible to compute them theoretically with sufficient accuracy. The first estimate of the (main line) frequency seems to have been made by Shklovsky1: 3,180±10 MHz.

The piezoelectric capillary injector—A new hydrodynamic method for dot pattern generation

Abstract: When liquid is driven in pulses through two small apertures with liquid between them, there is a hydrodynamic pumping phenomena in the liquid flow. The pulsation can be produced by volume variations obtained from a piezoelectric crystal. The device works as an impulse pump, which can be controlled by modulated electric pulses. When the liquid is ink, the device can be used to generate a dot pattern on paper. Using this technique, two types of printing devices have been developed: one for printing alphanumeric characters in a 7 × 5 matrix, where speeds of more than 1000 characters/s are obtained, and another for copying pictures by a scanning method.

On the thermal degradation of poly(vinyl chloride). I. An apparatus for investigation of early stages of thermal degradation

Abstract: A dehydrochlorination apparatus is described for studies of the early stages of the thermal degradation of poly(vinyl chloride) (PVC), combining good reproducibility, high accuracy, and a low detection limit. The evolved hydrogen chloride is absorbed in water and the electrical conductivity is continuously recorded. Measurements of the rate of dehydrochlorination repeated over an extended period of time showed a standard deviation of 2% of the mean value. The activation energies for the dehydrochlorination in nitrogen for two commercial suspension-polymerized samples were found to be 27.9 ± 1.5 and 26.2 ± 0.6 kcal/mole.

The increase in efficiency with size of research teams

Abstract: The result of an earlier investigation, that the efficiency of research teams increases with team size, has been verified by extending the investigation to further samples. The increase is exponential with team size and amounts to about a threefold increase in productivity per team member as the team is increased from 1 to 50 members. No optimum team size was found. Of two possible reasons for the increased efficiency of large teams, improved research environment (better service, better equipment, improved contacts with team members) and personal factors (improved selection of productive members) both have about equal weight. A preliminary study suggests that very productive team members' influence on other members is the dominating factor in the research environment; that is, that research effectiveness is induced by productive team leaders.

On the thermal degradation of poly(vinyl chloride). II. The effect of atmosphere

Abstract: The early stages of the thermal degradation of PVC were studied. Two commercial, suspension-polymerized resins were thermally treated at different temperatures and oxygen contents. Dehydrochlorination kinetics were followed by conductometric measurements and the formation of polyene sequences by ultraviolet-visible spectroscopy. Crosslinking and chain scission were followed by gel chromatography (GPC) and viscometry. No chain scission was observed in nitrogen atmosphere and no crosslinking in oxygen. Degradation in air proceeded by both reactions. The rate of dehydrochlorination for one of the investigated polymers increased linearly with the logarithm of the oxygen pressure. In nitrogen, an increasing degradation temperature was found to give both an increasing crosslinking and less discoloration. In oxygen, chain scission reactions showed a slight temperature dependence. The temperature effect on the discolorations was similar to that in nitrogen. The main difference between the investigated resins was the amount of internal doubled bonds in the original polymers, the ratio being 2:1. The higher amount resulted in a higher rate of dehydrochlorination, a larger extent of chain scission in oxygen, and a lower extent of crosslinking in nitrogen. Both in oxygen and nitrogen, the obtained results are consistent with allylic mechanisms. In nitrogen, the polyene formation supposedly proceeds by a unimolecular reaction and crosslinking by an intermolecular nonradical dehydrochlorination. In oxygen, radical reactions are superposed and may lead to chain rupture via β-scissions of alkoxy radicals.

The Effect of Fluoride on the Spectral and Catalytic Properties of Three Copper‐Containing Oxidases

Abstract: 1 The optical spectra of fungal laccase, lacquer tree laccase and ceruloplasmin are changed in a similar way when F– is added to the proteins at pH 5.5. 2 A change around 320 nm is associated with the binding of F– to type 2 Cu2+ of the proteins as seen from a correlation with electron paramagnetic resonance spectra. 3 The rate of binding of F– to fungal laccase is first order with respect to uncomplexed enzyme and independent of the F– concentration, indicating that an intramolecular process is rate limiting. The stability constant of the enzyme · F– complex is greater than 10 μM-1. 4 Fungal laccase is almost completely inhibited when 1 equivalent of F– is bound to the type 2 Cu2+. Presence of substrate gradually decreases the inhibition, due to the release of F– from a reduced form of the enzyme.

Ostwald Ripening — A Survey

Abstract: Provided there is enough atomic mobility, a dispersion of particles in a solid or liquid matrix will coarsen by transfer of matter from small to larger particles, reducing the free energy associated with the particle/matrix interface area In 1900, Ostwald1 reported the first systematic study of the increased solubility of small particles which results from the tendency to reduce the total particle surface, and the phenomenon has come to bear his name The basic theory of particle coarsening was developed by Greenwood2, Lifshitz and Slyozov3,4, and Wagner5 For brevity we shall refer to it as the LSW theory Reviews on Ostwald Ripening have been published e g by Greenwood6, by Che-Yu Li and Oriani7, and by Ardell8

The kinetics of the anaerobic reduction of fungal laccase B.

Abstract: 1 A stopped-flow technique was used to study the anaerobic reduction of fungal laccase B by hydroquinone, ascorbate and Fe(CN)64-. The reactions were followed by measurements of the intensity of absorption bands at 610 and 330 nm, related to a one- and a two-electron acceptor, respectively. 2 The experiments confirmed earlier results indicating a second-order reduction of the 610-nm chromophore. The reduction of the 330-nm chromophore was found to be consistent with the concept that the rate is limited by an intramolecular step. A model for the anaerobic reduction of laccase was formulated. 3 The effect of F− on the anaerobic kinetics implies that this inhibitory anion changes the rate constant of the rate-limiting step. 4 The reduction of the 330-nm chromophore, as it appears under anaerobic conditions, cannot be part of the normal catalytic mechanism.

LEED intensity measurements and surface structures: The dynamical approach (Illustrated by Ni/chemisorbed Na system)

Abstract: The authors are concerned with extraction of structural information from LEED intensity measurements by comparison with dynamical calculations for trial structures. The technique is illustrated by the system of sodium on a nickel (100) surface. Experiments are described; resolution is investigated and found to be about +or-0.1 AA. The top layer of a clean nickel (100) surface is shown to be dilated by not more than 0.15 AA and the determination of the sodium nickel distance of 2.9 AA reported earlier by Andersson and Pendry is described in greater detail.

A neuron model with learning capability and its relation to mechanisms of association.

Abstract: A neuron model with the ability of learning has been examined by means of mathematical and statistical methods. By use of the established anatomical concepts the main features of the model can be described as follows. The synapses are randomly distributed on the dendrites in a way that can be described by poisson processes. The afferent connections to the synapses are also random. The input signals are divided into excitatory, inhibitory and unspecified signals. The latter, whose detailed action is not specified, may involve excitatory as well as inhibitory action on the cell. Signals are described in terms of impulse frequencies. Learning takes place through facilitation of excitatory synapses. The condition for facilitation is the occurrence of simultaneous presynaptic and postsynaptic activity. The synaptical changes occurring during repeated learning are superimposed. Inhibitory synapses are capable of influencing learning by blocking the dendritic transmission. It is shown that, under certain conditions, a collection of model cells is able to work as an associative memory. This means that a pattern of output signals that once occurred through the combined action of the excitatory, the inhibitory, and the unspecified signals may later be recalled by applying just the two former signal patterns. It is shown that excitatory and inhibitory signals are similar in their ability to evoke associations. However there is also a difference between excitation and inhibition due to the fact that the pattern of inhibitory signals is subject to a non-linear transformation. This implies that great similarity is required between the inhibitory pattern once present during learning and the inhibitory pattern that is fed in later in order to obtain an associative recall. This phenomenon is called pattern separation and is supposed to be of importance when discriminating between patterns.

Experiments on the Nature of Steric Isotope Effects

Abstract: Publisher Summary This chapter presents the results of the experiments undertaken on the nature of steric isotope effects, which are ascribed to differences in “effective size” of isotopic atoms. The experimental outcome has been entirely in agreement with expectations based on the ordinary transition-state model. The chapter presents an exposition of Bartell's theory of steric isotope effects and proposes an alternative model based on somewhat different assumptions about the timing in the transition state, leading to predictions at variance with the experimental results. Special reference is made to the work of Melander and Carter. A selective non-comprehensive review of other experimental work in this field is presented. The chapter demonstrates the use of first-order perturbation theory in finding the isotopic difference in non-bonded interaction energy for hydrogen/deuterium (bonded to carbon) in contact with another atom.

Stabilization of explosive instabilities by nonlinear frequency shifts.

Abstract: It is found that nonlinear frequency shifts proportional to the square of the amplitudes of the waves may lead to a soliton-type solution in time for stabilized explosive instabilities.

Ground State Properties of Deformed Rare-earth Nuclei

Abstract: Nuclear spins and moments as determined by the atomic-beam magnetic resonance (ABMR) method on isotopes of the heavier rare-earths are compared with results from Nilsson model calculations. Special emphasis is aid on isotopes of the elements dysprosium, holmium, erbium and thulium on which in recent years the experimental body has increased considerably. From systematic trends, nuclear spins and moments are also theoretically predicted in several cases where experimental data are lacking.

Optical Absorption in Vapor-Quenched Aluminum

Abstract: An aluminum film formed by evaporation at 25 K onto a similar film previously deposited at room temperature displayed a featureless optical spectrum in the range 0.6-3.5 eV, the characteristic (200) peak being completely absent. A closer analysis showed the absorption to consist of a Drude term ($\ensuremath{\hbar}{\ensuremath{\omega}}_{p}=7.45$ eV; $\ensuremath{\tau}=3.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ sec) and what is believed to be interband absorption, possibly associated with a residual (111) absorption band.

Depletion layer characteristics at the surface of beveled high-voltage P-N junctions

Abstract: The design of high-voltage p-n-junction devices used today is usually based on beveling of the p-n junctions in order to reduce the tangential surface field far enough below the bulk field and to secure thus that breakdown occurs in the bulk of the device rather than at the surface. Using relaxation methods, solutions of Poisson's equation in two dimensions have been found which reveal that for commonly used bevelings of the forward-blocking junction in a thyristor structure, the electric field in the region below the surface is larger than in the bulk and at the surface. This field is strongly dependent on surface charges. It is shown that bevelings avoid the surface breakdown but the body breakdown obtained is not the true bulk breakdown as expected but rather occurs in the immediate neighborhood to the surface. The calculations make it possible to obtain the breakdown voltage for beveled structures. Measurements of the tangential surface field obtained by probing the junctions, light-spot measurements of the space-charge-region width on the surface and capacitance measurements of the surface charge as well as breakdown measurements are in good agreement with the calculations. This approach has led to the design of high-voltage thyristor structures that exhibit true bulk breakdown and, at the same time, loss of semiconducting material due to beveling is reduced.

Thin, quench-condensed lead-based alloy films investigated by resistivity and superconducting tunneling measurements

Abstract: Quench-condensed lead-based alloy films were investigated by the superconductive tunneling method to study how structural order affects the phonon distribution, and in particular the appearance of localized impurity modes, As solute, 10 at. % of either Na, Mg, Zn, Ga, Ge, Ag, Cd, In, Sn, Sb, or Te was used. The films were condensed upon a substrate at 0.4 K and studied as deposited and after anneals to 30, 100, and 300 K. It was found that the shape of the phonon-induced tunneling structure could be used as a means to classify the state of structural order in the films. Temperatures of transformations from one state to another could be identified with those where steps occurred in curves of film resistance vs. annealing temperature. The most notable transformation was the one that took the film from an amorphous to a finely grained crystalline state. The transformation temperature scales with the melting point of the pure impurity element of the binary alloy. As the annealing temperature was increased further another temperature region was reached where the crystallites grew in size, causing notable changes in the phonon spectra. A third transformation occurred at low temperatures within the amorphous state for a few of the alloys.

Superconducting energy gaps and transition temperatures of quench-condensed cadmium and zinc films

Abstract: The superconducting transition temperatures of Cd and Zn films deposited upon a liquid3He-cooled substrate increase compared to the bulk values. In disordered Cd, values of around 0.9 K are obtained, while correspondingT c for Zn is about 1.4 K. These values agree well with theoretically predicted ones. For a Cd0.9Ge0.1, probably amorphous, film,T c is further increased to about 1.6 K in approximate agreement with theory. The ratio between the energy gap andT c , 2Δ(0)/k B T c , remains considerably lower than 3.53 in all the disordered films. This, as well as fairly broad transition ranges and the shape of the fluctuation pairing contribution to the conductance, is taken as an indication of structural inhomogeneities of the films. In pure, quenchcondensed Mg films, no superconductivity is detected above 0.35 K.

On the Stabilization of Explosive Instabilities by Nonlinear Frequency Shifts

Abstract: This paper presents an analytic solution to the problem of explosive instabilities, including the effects of nonlinear frequency shifts proportional to the squares of the amplitudes. It is found that such frequency shifts may introduce stabilization of the explosive instabilities and may lead to soliton-like solutions in time or to solutions which are periodic in time.