Showing papers by "Eindhoven University of Technology published in 1985"
TL;DR: It is found that polaron effects in ideal 2D systems are larger than in 3D systems which agrees with recent results of Das Sarma and Larsen.
Abstract: The influence of the electron-phonon interaction on the Landau levels of two- (2D) and three-dimensional (3D) electrons are studied within second-order perturbation theory. It is found that polaron effects in ideal 2D systems are larger than in 3D systems which agrees with recent results of Das Sarma and Larsen. Analytical and numerical results are presented for the electron-phonon correction to the different Landau levels (n) below the LO-phonon continuum. Special attention is paid to the small and large magnetic-field limit and to the splitting of the Landau levels which occurs at n${\ensuremath{\omega}}_{c}$\ensuremath{\approxeq}${\ensuremath{\omega}}_{0}$ (${\ensuremath{\omega}}_{c}$ is the cyclotron frequency and ${\ensuremath{\omega}}_{0}$ is the LO-phonon frequency). Existing results are rederived and generalized.
120 citations
01 Jan 1985
TL;DR: In this paper, two criteria for choosing between different model-structures are proposed and their derivation is within a natural cross-validatory assessment context and is fairly assumption-free.
Abstract: Two criteria for choosing between different model-structures are proposed. Their derivation is within a natural cross-validatory assessment context and is fairly assumption-free. In particular, the two criteria can be used for discriminating between non-nested model structures and, more importantly, the ‘true’ system is not required to belong to the considered set of models. Should the true system belong to the model set, the two proposed criteria will asymptotically reduce to some well-known structure selection criteria. This is believed to be a desirable feature of our proposals. On the other hand, it provides a nice cross-validation interpretation of some well-known model structure selection rules. Also, the cross-validation interpretation helps one to choose which criteria to use in a given application The paper also has a second purpose, somewhat decoupled from that mentioned above. It contains an extensive survey of the literature that is useful in its own right.
117 citations
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88 citations
TL;DR: Optical properties of blood vessel wall and plaque from human cadaver material are presented for the argon laser, He‐Ne laser, and the Nd‐YAG laser wavelengths.
Abstract: Optical properties of blood vessel wall and plaque from human cadaver material are presented for the argon laser (514.5 nm), He-Ne laser (633 nm), and the Nd-YAG laser (1,060 nm) wavelengths. Measurements were performed with an integrating sphere arrangement and analyzed in terms of Kubelka-Munk absorption and scattering coefficients.
87 citations
TL;DR: In this paper, it was shown that linear temperature programmed retention indices can only be calculated from isothermal retention data if the temperature dependence of both the distribution coefficients and the column dead time are taken into account.
Abstract: Summary Direct conversion of isothermal to temperature programmed indices is not possible. In this work it is shown that linear temperature programmed retention indices can only be calculated from isothermal retention data if the temperature dependence of both the distribution coefficients and the column dead time are taken into account. Procedures are described which allow calculation of retention temperatures and from these, accurate programmed retention indices. Within certain limits the initial oven temperature and programming rate can be chosen freely.The prerequisite forthis calculation
87 citations
TL;DR: In this article, the ground-state energy of a 2D Frabbohlich polaron is calculated to second order in the coupling constant (ensuremath{\alpha}) and gives the surface optical-phonon energy.
Abstract: The ground-state energy of a two-dimensional (2D) Fr\"ohlich polaron is calculated to second order in the coupling constant (\ensuremath{\alpha}) and gives E/\ensuremath{\Elzxh}${\ensuremath{\omega}}_{s}$=-(\ensuremath{\pi}/2)\ensuremath{\alpha}-0.063 97${\ensuremath{\alpha}}^{2}$ with \ensuremath{\Elzxh}${\ensuremath{\omega}}_{s}$ the surface optical-phonon energy. In the strong-coupling limit the adiabatic approximation is used and E/\ensuremath{\Elzxh}${\ensuremath{\omega}}_{s}$=-0.4047${\ensuremath{\alpha}}^{2}$ is found to leading order in \ensuremath{\alpha}. The Feynman path-integral approximation, the Gaussian approximation, and the modified Lee-Low-Pines unitary transformation approximation to the polaron ground-state energy all satisfy the scaling relation ${E}_{2\mathrm{D}}$(\ensuremath{\alpha})=(2/3)${E}_{3\mathrm{D}}$(( 3\ensuremath{\pi}/4)\ensuremath{\alpha}), where ${E}_{2\mathrm{D}}$ (${E}_{3\mathrm{D}}$) is the ground-state energy of the 2D (3D) polaron.
78 citations
TL;DR: In this article, the authors investigated the dispersion of Rh Al 2 O 3 and Rh TiO 2 catalysts with varying metal loadings, and showed that the high dispersion was due to the growth of two different kinds of Rh Rh 2O 3 particles on TiO2.
76 citations
TL;DR: The rotating ring disc electrode (rrde) was used to determine the heterogeneous reaction rate constants for the cathodic reduction of molecular oxygen at a polypyrrole electrode in 0.5 M H2SO4.
74 citations
TL;DR: In this paper, temperature-programmed reduction (TPR) has been applied to characterize the reducibility of Al2O3, SiO2-, and carbon-supported Re2O7 catalysts, over a wide range of transition metal content.
74 citations
01 Jun 1985
TL;DR: In this article, the authors used the theoretical frame work of an ideal undisturbed expansion as a reference to determine a model description of the two characteristic features of a Campargue-type expansion, i.e., the nozzle-skimmer distance zam (po) of maximum intensity at each value of the reservoir pressure po and the skimmer transmission probability Ta(zam-I(O)expt/I(0) in this maximum.
Abstract: The process of beam formation in a supersonic expansion into a high pressure (10−2 -1 Torr) expansion chamber, a so-called Campargue-type beam source, has been investigated, using the theoretical frame work of an ideal undisturbed expansion as a reference. Absolute values of the centre-line intensity I(O)expt have been measured as a function of the reservoir pressure po at three different pumping speeds in the range of 25-230 l/s for the gases He, Ne and Ar. These experimental results have been used to determine a model description of the two characteristic features of a Campargue-type expansion, i-e. the nozzle-skimmer distance zam (po) of maximum intensity at each value of the reservoir pressure po and the skimmer transmission probability Ta(zam-I(O)expt/I(0) in this maximum, using the centre-line intensity I(O) of an ideal undisturbed expansion as a reference. A simple model function Ta (zam = q1 expt-q2Kna− (z am) gives a perfect description, when using an inverse skimmer Knudsen number Kna−1 with a mean free path based on the long-range van der Waals interactions that dominate the collisions at the low temperatures of the flow field at the skimmer orifice. The value of zam can be described by a non-dimensional length c which measures the distance zM - Zam. with zM the position of the Mach disk, in units of the viscosity based mean free path. Using the model functions for zam and T3(zam) as input we present scaling laws that predict the performance of a Campargue type beam source as a function of the gas properties (van der waals constant C6, mass m, viscosity based cross section Qvimc), the reservoir conditions (nozzle radius, reservoir pressure po and temperature To) and the parameters of the experimental arrangement (skimmer radius, temperature of the expansion chamber, pumping speed S). Measured values for He and Ne of the maximum maximorum J(O)exptmmm, i.e, the maximum of I (O)expt as a function of po, are well described by the scaling law presented. Preliminary measurements of the dependency of I(O)exptmm on the reservoir temperature To are also in good agreement with our scaling law which predicts I(O)exptmm Toii/g. Heating the nozzle is an inexpensive way of increasing the centre-line intensity, as compared to the expensive approach of increasing pumping speed with a dependency I(O)exptmm S79. Typical values of I(O)exptmm at room temperature are 1.5x1020 and 33x1019 s−1 sr-−1 for He at S = 230 l s−1 and Ne at S = 180 l s−1, respectively, showing a favourable comparison to conventional low-pressure expansions with oil diffusion pumps in the expansion chamber. Measurements of the virtual source radius, i.e. a mapping of the velocity component perpendicular to the stream lines, provide design rules for the ratio of skimmer radiu s to nozzle radius required for optimum performance. Moreover, they provide qualitative support of our model description of the loss processes at the skimmer orifice.
66 citations
TL;DR: It is hypothesized that the femoral surface cup is more sensitive to local loosening than other prostheses, which would indicate that prosthetic designs should be analysed relative to their potential to provoke failure propagation, rather than only initiation of mechanical failure and loosening.
Abstract: The load transmission and interface stresses in the Wagner resurfaced femoral head were evaluated for the purpose of studying possible failure mechanisms. We found that unnatural stress patterns occur in the head and at the implant-bone interfaces, in addition to regions of stress protection in the bone, possibly enhancing interface failure and bone remodelling. However, these stresses are not higher than those reported for other kinds of prostheses, e.g. acetabular cup, tibial plateau. From these findings, together with clinical observations, it is hypothesized that the femoral surface cup is more sensitive to local loosening than other prostheses. This hypothesis would indicate that prosthetic designs should be analysed relative to their potential to provoke failure propagation, rather than only initiation of mechanical failure and loosening.
TL;DR: In this article, the production of s-sialon and nonoxidic powders by carbothermal reduction of oxides is discussed, with special attention paid to the rate-determining steps in the conversion process performed in a packed-bed reactor.
Abstract: The production of s-sialon (Si3A1303N5) and nonoxidic powders by carbothermal reduction of oxides is discussed. Special attention is paid to the rate-determining steps in the conversion process performed in a packed-bed reactor. It is shown that powders with specific surface area >10 m2/g can be produced by the correct choice of pellet size, gas flow rate, temperature, and raw material.
TL;DR: In this article, a two-dimensional electrostatic analyser for ion scattering spectroscopy is presented. But the analysis is performed using the Laplace equation and the exact shape of the toroidal plates is not computed numerically.
TL;DR: In this article, the shape selective properties of H-ZSM-5 zeolite have been investigated for the formation of propene over Pt and subsequent oligomerization over acid sites of the Zeolite.
TL;DR: In this paper, the authors extend the classical economic batch size model of Camp to situations where a range of products is made to stock and where the products are manufactured in a production shop consisting of a number of work centers of functionally grouped machines.
Abstract: In this paper we extend the classical economic batch size model of Camp to situations where a range of products is made to stock and where the products are manufactured in a production shop consisting of a number of work centers of functionally grouped machines. Assuming that the flow times of the batches along the work centers can be modelled as a queueing process, it is shown that the batch sizes influence the batch waiting times in the shop, and the amount of work in process. The cost function to be minimized consists of ordering costs, final inventory holding costs, and work-in-process carrying costs. We show that the cost function is strictly convex and that the optimal batch sizes can be found by means of well-known numerical methods. We present an outline of an iterative procedure in which the batch size optimization procedure is combined with a shop load optimization procedure to achieve a good overall performance. Using a simplified model that assumes that the products are homogeneous in...
TL;DR: In this article, the authors used the Golay-Giddings and Poiseuille equations to derive equations for the calculation of the maximum plate number and minimum time conditions for given columns at fixed, but selectable, outlet pressures.
Abstract: Summary The Golay-Giddings and Poiseuille equations are used to derive equations for the calculation of the maximum plate number and minimum time conditions for given columns at fixed, but selectable, outlet pressures. In addition, expressions are presented for the determination of minimum analysis times for separation problems requiring given plate numbers. In this instance, the optimum column length can be calculated as a function of outlet pressure. A Basic computer program, incorporating the equations for the various optima, together with the H-l curves, is described. Input variables are either column length or desired plate number, column diameter, film thickness, capacity ratio of the solute, column outlet pressure, separation temperature, and carrier gas. The carrier gas viscosity is automatically calculated in thecaseof hydrogen, helium, or nitrogen. Forthesegases, and if the solute is a n-alkane, the diffusivity of the solute in the mobilephaseiscalculated. In thiscase, thecarbon numberof the solute is needed in the computation.
TL;DR: In this article, the oxidation of hydroquinone and reduction of p-benzoquinone in aqueous solution was studied at polypyrrole electrode and at a poly- N -methylpyrro-role electrode.
TL;DR: In this paper, the effect of the gas void distribution on the ohmic resistance in the electrolysis cell was investigated and two bubble layers can be distinguished using a segmented nickel electrode.
Abstract: Due to the presence of gas bubbles on the electrode surface and in the interelectrode gap during water electrolysis, the ohmic resistance in the cell increases The main aim of this investigation is to obtain insight into the effect of the gas void distribution on the ohmic resistance in the electrolysis cell The gas void distribution perpendicular to the electrode surface has been determined at various current densities, solution flow velocities and heights in the cell, taking high speed motion pictures From these measurements it follows that two bubble layers can be distinguished The current density distribution and the ohmic resistance in the electrolysis cell have been determined using a segmented nickel electrode The current density decreases at increasing height in the cell The effect is more pronounced at low solution flow velocities and high current densities A new model to calculate the ohmic resistance in the cell is proposed
TL;DR: In situ measurements of electrical conductivities were performed on MoO3, Bi2Mo2O9, and Bi 2MoO6 (koechlinite), the latter either as such or doped with small amounts of Mo or Bi.
TL;DR: In this article, NiCo2O4 was investigated as anode material for alkaline water electrolysis and this catalyst was prepared by thermal decomposition of metal salts and this rapid and simple technique gives reproducible results.
Abstract: NiCo2O4 was investigated as anode material for alkaline water electrolysis. This catalyst was prepared by thermal decomposition of metal salts and this rapid and simple technique gives reproducible results. A study of the preparation parameters shows that factors such as decomposition temperature, duration of the heat treatment and catalyst loading, determine the morphology of the oxide layer and so influence the performance of the catalyst. The conductivity of the oxide layer was found to change markedly with the final heat treatment.
TL;DR: In this paper, a wall stabilized argon arc (40-200 A) at atmospheric pressure with diameters of 5 and 8 mm is studied by spectroscopy and interferometry, where the plasma is assumed to be partial local thermal equilibrium and this assumption is verified with the aid of a collisional-radiative model.
Abstract: The parameters and transport properties of a wall stabilized argon arc (40-200 A) at atmospheric pressure with diameters of 5 and 8 mm are studied by spectroscopy and interferometry. The plasma is assumed to be partial local thermal equilibrium and this assumption is verified with the aid of a collisional-radiative model. The departures from Saha-equilibrium of the argon neutral ground state are found to be associated with particle diffusion and the escape of recombination radiation. The measurement of the total excitation rate, from the ground level, including direct ionization, of neutral argon is in reasonable agreement with the literature value
TL;DR: In this paper, the authors calculated the thermodynamic quantities of dilute liquid 3He-4He mixtures, starting from experimental values of the specific heat and the osmotic pressure.
TL;DR: In this article, the 1/f noise in MOS transistors has been investigated and is shown to correlate with charge transfer inefficiency experiments on surface-channel CCDs.
Abstract: The 1/f noise in MOS transistors has been investigated and is shown to correlate with charge transfer inefficiency experiments on surface-channel CCDs. Both independent phenomena can be quantitatively explained by the same interface state model. The oxide trap density turns out to vary by more than a factor 10. The 1/f noise is compared with McWhorter's number fluctuation model and with the mobility fluctuation model. The oxide trap density is calculated from the charge transfer inefficiency in surface CCDs. Both the quantitative agreement between oxide trap density and 1/f noise and the observed dependence of 1/f noise on gate voltage here give strong arguments in favour of the McWhorter model. The investigated MOS transistors fall into a category that cannot be explained by the present mobility fluctuation model.
TL;DR: In this paper, the authors studied the cathodic reduction of molecular oxygen at a polypyrrole electrode in 0.5 M H 2 SO 4 using a rrde and found that the polymeric layer is permeable and that the reduction of oxygen mainly occurs at the interface metal/polypyrpoly.
TL;DR: The heterogeneity of the population of uremic patients, with respect to the UV-absorbing solutes, was estimated and significant differences of solute blood level changes during hemodialysis, hemodiafiltration and hemofiltration, were observed.
TL;DR: In this article, the authors investigated the interaction of sampling site, fresh gas flow rate, expiratory flow rate and sampling flow rate on exporatory capnography and found that sampling near the fresh gas outlet yielded inaccurate results under several of these conditions.
Abstract: The Bain circuit provides continuous fresh gas flow near the airway. The potential mixing of this fresh gas with expired gas may prevent reliable analysis of expired gas. We therefore investigated the interaction of sampling site, fresh gas flow rate, expiratory flow rate, and sampling flow rate on expiratory capnography. Sampling near the fresh gas outlet yielded inaccurate results under several of these conditions. The magnitude of the error was related to the fresh gas and expiratory flow rates. A reliable sampling region near the endotracheal tube was identified.
TL;DR: Based on the stability range of the CuxMn3−x04 solid solution, two different preparation methods for polycrystaline samples are proposed: for the compositions 0.98 ≤ × ≤ 1.10 sintering of mixtures of the oxides is used, while for x > 1.
TL;DR: A first attempt to describe (coronary) laser angioplasty is presented using simplified but standard optical and thermal modeling of tissue in interaction with a laser, showing a relatively fast initial process followed by a very slow one.
Abstract: A first attempt to describe (coronary) laser angioplasty is presented using simplified but standard optical and thermal modeling of tissue in interaction with a laser. Ablation behavior of blood thrombi and plaque has been approximated from numerical computations for various wavelengths representing the Ar, Nd-YAG, and CO2 lasers. The overall results, in terms of calculated depth of ablation versus laser irradiation time, show a relatively fast initial process followed by a very slow one. The analysis suggests that a sequence of laser pulse-catheter tip flushing should substantially increase the overall ablation velocity. The physics of threshold laser power and influence of laser beam diameter is discussed. A comparison between experimental results is made when possible. Suggestions for further test experiments are made.
TL;DR: In this paper, a kinetic study of the autoxidation of 2-mercaptoethanol using cobalt(II) phthalocyanine tetrasodium sulfonate attached to poly(vinylamine) as a catalyst was presented.
TL;DR: In this article, the competition between craze formation and shear band formation at small glass beads embedded in matrices of glassy polymers has been investigated by performing constant strain rate tensile tests over a wide range of strain rates and temperatures, and examining the deformation pattern formed at the beads with a light microscope.
Abstract: The competition between craze formation and shear band formation at small glass beads embedded in matrices of glassy polymers has been investigated. This has been done by performing constant strain rate tensile tests over a wide range of strain rates and temperatures, and examining the deformation pattern formed at the beads with a light microscope. The glassy polymers under investigation were polystyrene, polycarbonate, and two types of styrene—acrylonitrile copolymer. It was found that besides matrix properties, strain rate and temperature, the degree of interfacial adhesion between the glass beads and the matrix also has a profound effect on the competition between craze and shear band formation: at excellently adhering beads craze formation is favoured, whereas at poorly adhering beads shear band formation is favoured. This effect is caused by the difference in local stress situation, craze formation being favoured under a triaxial stress state and shear band formation under a biaxial stress state. The kinetics of crazing and shear deformation have also been studied, using a simple model and Eyring's rate theory of plastic deformation. The results suggest that chain scission may be the rate-determining step in crazing but not in shear deformation.