Showing papers by "Eindhoven University of Technology published in 1972"

On the instantaneous measurement of bloodflow by ultrasonic means.

Abstract: Part of the problem of determining the flow through a blood vessel is the measurement of the instantaneous average blood velocity over a cross-section of the vessel. In this paper a new method is described to estimate that velocity from the received signal of a Doppler flowmeter using continuous ultrasound. The method is based on the determination of the frequency shift averaged over the power density spectrum of the received signal. Due to a new type of instrumentation this can be done without carrying through a complete frequency analysis of that signal. This provides a rather accurate determination of the instantaneous value of the blood velocity.

Magnetic Studies of the Canted Ising Linear Chain CsCo Cl 3 ·2 H 2 O

Abstract: Specific-heat, nuclear-magnetic-resonance, magnetic-susceptibility, magnetization, and antiferromagnetic-resonance measurements on the orthorhombic crystal CsCo${\mathrm{Cl}}_{3}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O have led to the following model of the magnetic structure and the exchange interactions: The interaction is Ising-like with very strong exchange along the $\stackrel{\ensuremath{\rightarrow}}{\mathrm{a}}$ axis resulting in canted-antiferromagnetic chains lying in the $\mathrm{ac}$ plane with their moments 10\ifmmode^\circ\else\textdegree\fi{} from the $\stackrel{\ensuremath{\rightarrow}}{\mathrm{c}}$ axis and a net moment in the $\stackrel{\ensuremath{\rightarrow}}{\mathrm{a}}$ direction. At ${T}_{N}=3.38$ K the chains in each $\mathrm{ac}$ plane couple ferromagnetically so that their net moments are all in the same sense, but with the net moments in alternate planes antiparallel. At a critical field of 2.9 kOe at 1.1 K ($\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}$ applied along the $\stackrel{\ensuremath{\rightarrow}}{\mathrm{a}}$ axis) the moments in half of the planes reverse giving rise to an induced ferromagnetic moment parallel to the $\stackrel{\ensuremath{\rightarrow}}{\mathrm{a}}$ axis. At temperatures well above ${T}_{N}$ the strong Ising interaction produces correlations which manifest themselves as a large induced moment at relatively modest fields. The general features of these experimental results have been reproduced using a Hamiltonian which includes Ising and Dzyaloshinsky-Moriya terms for the interaction along the $\stackrel{\ensuremath{\rightarrow}}{\mathrm{a}}$ axis and isotropic terms for the interactions along $\stackrel{\ensuremath{\rightarrow}}{\mathrm{b}}$ and $\stackrel{\ensuremath{\rightarrow}}{\mathrm{c}}$. Applying this Hamiltonian to the critical-field and antiferromagnetic-resonance data, we obtain the following values: ${J}^{a}=\ensuremath{-}13$ K, ${J}^{b}=\ensuremath{-}0.2$ K, ${J}^{c}=+4.5$ K, and $D=+3.6$ K. These numerical values are the result of applying a very simplified model to a very complex system and thus must be considered as qualitative rather than quantitative.

Cyclopentadienic compounds as intermediates in the thermal degradation of phenols. Kinetics of the thermal decomposition of cyclopentadiene

Abstract: The thermal degradation of phenol and some methylphenols was followed by pyrolysis gas chromatography. An important step in the thermolysis turns out to be the decarbonylation of the phenols yielding cyclopentadienic compounds. It was shown that thermal cracking of cyclopentadiene and its methyl derivatives, in fact, yield pyrograms similar to those of the phenolic parent compounds. The kinetics of the thermal degradation of cyclopentadiene in the gas phase were studied in detail by means of a tubular flow reactor with continuous feed of reactant. The decomposition reaction obeys second order reaction kinetics; the activation energy being 20.9 Kcal/mol. A reaction mechanism is proposed including the dimerization of cyclopentadiene to exo-dicyclopentadiene as the first step.

Structures and compounds in the system Ga1−xSex

Abstract: Structural investigations were made on the system Ga1−xSex for 0.48 < x < 0.60 with powder and single crystal X-ray technique. It is checked, which possible structure types, known in the literature, could exist in the different regions of the T−x diagram of Ga–Se. Further is reported that a new compound Ga3Se2 was found.

Rheological properties of boric oxide and alkali borate glasses

Abstract: The rheological behaviour of boric oxide and alkali borate glasses has been studied in the region of high viscosity (1010–1013 poise). The change in viscosity of boric oxide glass with the introduction of alkali oxide is in agreement with what is known about the structure of alkali borate glasses. The rheological behaviour of boric oxide glass appeared to be of the Newtonian type up to a viscosity of 1013 poise, whereas the alkali borate glasses showed a Bingham flow behaviour at viscosities higher than 1011 poise. The experiments have yielded evidence of the correctness of the theory of Stein et al. concerning the rheological behaviour of glasses. A possible correlation between the phenomena of Bingham yield value and phase separation was not observed.

Influence of water on the rheological properties of alkali borate glasses

Abstract: The influence of water on the rheological properties has been investigated for boric oxide glass and two sodium borate glasses. The reducing influence of water on the viscosity appears to be about five times stronger than the increasing influence of sodium oxide. The deviations from Newtonian flow (Bingham yield values) have shown a similar picture. The explanation of the behaviour of water is based on the idea that BOB bonds in the glass are “hydrolysed”, which causes a preferable viscous flow along OH groups.

Growth and habit of GaS single crystals obtained from the vapour phase

Abstract: A comparative study of the sublimation and chemical transport of the compound GaS is reported. The parameters investigated in the closed system are the iodine concentration, the tube geometry, and undercooling. The rate of transport in case of sublimation is diffusion-controlled, in the iodine-assisted transport process at concentrations higher than 1 mg/cm3, convection governs the process, while at lower concentrations the diffusion-controlled sublimation becomes important. In general, the lateral growth is fast when the chemical transport is used; the habit of the crystals is plate-like, the c-axis being normal to the plane of the platelet. A large amount of screw dislocations can be seen on the (0001) faces and the crystals exhibit in general n-type conductivity. If the sublimation technique is used, the crystals are not exclusively plate-like, the majority of the crystals exhibit needle-like and ribbon-like habit. With growth in the length direction, the growth axis is parallel to the c-axis, it takes place around screw dislocations and two crystallization mechanisms are assumed to take place simultaneously. The formation of a large number of two-dimensional nuclei between the arms of the screw dislocation seems to be responsible for a decrease of the mean surface migration distance Xs on the basal plane. Es wird uber eine vergleichende Untersuchung der Sublimation und des chemischen Transports der Verbindung GaS berichtet. Die im abgeschlossenen System untersuchten Parameter waren: Die Jodkonzentration, die Gefasgeometrie und die Unterkuhlung. Im Falle der Sublimation ist die Transportrate diffusionsgesteuert, im Jod-assistierten Transportprozes bei Konzentrationen uber 1 mg/cm3 steuert Konvektion den Prozes, wahrend bei niedrigeren Konzentrationen diffusionsgesteuerte Sublimation bedeutsam wird. Im allgemeinen ist das laterale Wachstum schnell, wenn chemischer Transport benutzt wird; der Habitus des Kristalls ist plattchenformig, wobei die c-Achse normal zur Plattchenebene ist. Ein groser Anteil von Schraubenversetzungen wird auf den (0001)-Ebenen beobachtet und die Kristalle zeigen im allgemeinen n-Leitfahigkeit. Wenn die Sublimationstechnik benutzt wird, sind die Kristalle nicht ausschlieslich plattchenformig, die Mehrzahl der Kristalle zeigen nadelformigen und Streifenhabitus. Bei Wachstum in der Langsrichtung ist die Wachstumsachse parallel zur c-Achse; es findet um eine Schraubenversetzung herum statt und es wird angenommen, das zwei Kristallisationsmechanismen simultan wirken. Die Bildung einer grosen Zahl zweidimensionaler Kerne zwischen den Zweigen der Schraubenversetzung scheint fur den Abfall des mittleren Oberflachenwanderungsabstands Xs auf der Basisebene verantwortlich zu sein.

Temperature and density profiles of electrons in a hollow cathode argon-arc discharge

Abstract: Measurements have been performed of radial radiation profiles of argon I and II lines in a hollow cathode, low-pressure, magnetically confined argon-arc discharge with currents of 15–60 A. The working pressure of the discharge was ∼10 -3 mm of Hg and the electron density was ∼10 19 m -3 . From the radiation profiles, radial temperature and density profiles of the electrons have been calculated. For the calculations, we made use of Corono equilibrium formulae and we discuss how far these formulae give a good description of the excitation phenomena in the plasma. It appears that, in most cases, the decrease of the electron temperature is about 10 per cent per 10 mm or less and that the width at half-maximum value of the electron-density profile for a confined plasma is about 18 mm for an end-anode configuration situated at 1.2 m from the cathode, and 27 mm for a ringshaped anode situated near the cathode. These widths are roughly independent of the magnetic induction value between 3.75 × 10 -2 and 12.5 × 10 -2 T .

Measurements of the thermal conductivity of gases and gas mixtures, methods and results

Abstract: Two methods for measuring the thermal conductivity have been employed: 1. a cylindrical cell type of apparatus for absolute measurements, with an accuracy of 0.5%. 2. a thermistor katharometer bridge for differential measurements, allowing an accuracy of 0.1%. The thermistor bridge is described in some detail and its performance is analysed.

Fatty acid composition of carotenoid esters in soybean and rapeseed oils

Abstract: The amounts of the different carotenoids (lutein, lutein monoesters and diesters) in soybean and rapeseed oil were determined through a combination of column chromatography and UV spectrometry. The lutein diesters in the oils have been isolated by a combination of column and thin layer chromatography. Identification and determination of the amount of the various fatty acids of the lutein diesters have been carried out by means of gas chromatography after transesterification of the fatty acids to their methyl esters. Comparison of the fatty acids of the lutein diesters with those of the triglycerides of the oils revealed a striking difference. First, the fatty acids of the lutein diesters have shorter chains than the triglycerides acids. Secondly, the lutein fatty acids are more saturated than the fatty acids of the triglycerides of the corresponding oils. However the amount of linoleic acid in the case of the fatty acids of the lutein diesters in rapeseed oil is greater than that in the fatty acids of the triglycerides in rapeseed oil.

Excitation mechanisms in the argon-ion spectrum at near laser conditions and temperatures and densities in a hollow cathode argon-arc discharge

Abstract: For a hollow cathode, low-pressure, magnetically-confined argon-arc discharge, an investigation was made of spectral line-intensities of the argon II spectrum to ascertain the excitation mechanisms in this spectrum, especially for the 4p group (excitation energy 19.2–20.0 eV). It appears that, for ne values of 1 × 1019 to 2 × 1019 m -3, stepwise excitation from the ion ground levels through short-lived intermediate levels (16.3–16.8 eV) contributes at least 70% of the 4p argon II group population. Direct excitation from the ion ground levels is dominant for considerably smaller ne values. Cascade radiation plays a minor role in populating the 4p group. The stepwise excitation may lead to laser action in this type of discharge in the same way as it does in the common argon ion laser. The proposed mechanism is not cited in the literature with any certainty as being responsible for laser action. The electron temperature Te was determined from absolute line-intensity measurements of the argon I and II spectra. For argon I, the method is based on cross-section data for the 4p group, for argon II on Corona equilibrium formulae. For a well-confined plasma, Te(0) on the axis was 30 × 103 to 40 × 103 °K at an axial distance of 0·6 m from the cathode. The value of the electron density ne was calculated from phase-shift measurements with microwaves, accounting for the non-linear relation between ne and the refractive index μ. The calculation was performed with the help of a method described in a previous paper. The influence of the slice breadth, interacting with the microwaves and of diffraction are discussed. It appeared that ne(0) on the axis is 1 × 1019 to 2 × 1019 m-3 for a confined plasma. Ion temperatures were determined from Doppler-width measurements of an argon II line with a Fabry-Perot interferometer. The values Ti varied for different discharge conditions from 1 × 103 to 30 × 103 °K. The temperatures of the neutral particles, determined with the help of the width of an argon I line, varied from 500 to 4 × 103 °K for similar conditions. The ionization degree is between 0 and 80 per cent.

A Model for n‐type and p‐type Gallium Sulphide

Abstract: Using the results of the temperature dependence of the specific dark conductivity measured for n- and p-type GaS single crystals, an attempt is made to construct band schemes for these crystals. The band schemes for n-type material contain two donors and one compensating acceptor. The donors are incorporated iodine and sulphur vacancies, the acceptor is believed to be incorporated sodium. For the p-type crystals the band scheme contains two acceptors and one compensating donor. The acceptor role is played by incorporated sodium and gallium vacancies, while sulphur vacancies are assumed to be the donor. Die Temperaturabhangigkeit der Dunkelleitfahigkeit von n- und p-leitenden GaS-Ein-kristallen wird benutzt, um ein Banderschema fur diese Kristalle zu konstruieren. Fur n-leitendes Material enthalt das Modell zwei Donatoren und einen Akzeptor. Die Donatoren sind eingebautes Jod und Schwefellucken, wahrend eingebautes Natrium der Akzeptor ist. Fur p-leitendes Material enthalt das Modell zwei Akzeptoren und einen Donator. Eingebautes Natrium und Galliumlucken sind die Akzeptoren und Schwefellucken spielen die Donatorenrolle.

On plasticity, elastic relaxation phenomena, and a stress-strain relation which characterizes Schofield-Scott Blair media

Abstract: A generalization is given of the author's theory for plasticity phenomena. The theory includes the possibility of both stress and strain relaxation in the preplastic range. Methods of non-equilibrium thermodynamics are used. The plasticity phenomenon is explained by introducing a physical assumption concerning the phenomenological coefficients. A yield function is proposed which includes the Bauschinger effect and strain hardening. If the free energy f has the form f=f(1)+f(2), where f(1) is a function of the temperature and the elastic strains and f(2) is a function of the temperature and the inelastic strains, and if cross effects between the plastic flow and elastic relaxation phenomena may be neglected, the proposed yield function is such that the derivative with respect to time of the deviator of the plastic strain tensor is given by \(\eta \left( {{{\partial \Phi } \mathord{\left/ {\vphantom {{\partial \Phi } {\partial _{\tau \alpha \beta } }}} \right. \kern- ulldelimiterspace} {\partial _{\tau \alpha \beta } }}} \right)\), where Φ is the yield function, ταβ is the mechanical stress tensor, and η is a coefficient which vanishes in the preplastic range. If the equations of state may be linearized the proposed yield function reduces to a function which is analogous to a yield function proposed by Freudenthal. If the plastic flow phenomenon is not associated with changes in the microscopic structure of the medium the proposed yield function reduces to the Von Mises function. It follows from the theory that in a first approximation elastic relaxation phenomena in the preplastic range may be described by the equation for Poynting-Thomson media (standard linear solids). An equation which characterizes Schofield-Scott Blair media is also derived from the developed theory.

Dark conductivity as a function of temperature in GaS single crystals

Abstract: The specific dark conductivity as a function of temperature up to 450 °C is investigated for both n- and p-type single crystals of the platelike compound GaS. The activation energies for both types of samples show a dependence on the purity of the crystals. A difference in the temperature dependence of the electron concentration is observed between n-type crystals which were very slowly cooled after a heat-treatment and those which were rapidly cooled. Furthermore, the conductivity becomes independent of the amount of iodine used during the growth of the n-type crystals, when the concentration of the halogen exceeds a value of 2.5 mg cm−3. Die Dunkelleitung fur n- und p-leitende Einkristalle der Verbindung GaS wird bis 450 °C untersucht. Fur beide Leitungstypen werden Aktivierungsenergien gefunden, die eine Abhangigkeit von der Kristallverunreinigung zeigen. Fur n-leitende Kristalle, die nach einer Behandlung bei hoherer Temperatur sehr langsam bis Zimmertemperatur abgekuhlt wurden, und solche, die sehr schnell abgekuhlt wurden, zeigt sich ein Unterschied in der Temperaturabhangigkeit der Elektronenkonzentration. Die Leitfahigkeit wird unabhangig von der wahrend des Wachstums der n-Typ Kristalle benutzten Jodmenge, wenn die Jodkonzentration mehr als 2,5 mg cm−3 betragt.