Showing papers by "Chalmers University of Technology published in 1978"
TL;DR: In this article, the attenuating properties of the atmosphere are presented in a form that permits the calculation of direct, diffuse and global spectral solar irradiance at ground level, using the extraterrestrial irradiance values of Thekaekara.
542 citations
TL;DR: A class of first order factorization methods for the solution of large, symmetric, sparse systems of equations is introduced and results from numerical experiments are presented and comparisons with other iterative and direct methods are carried out.
Abstract: A class of first order factorization methods for the solution of large, symmetric, sparse systems of equations is introduced. Asymptotic results for the computational complexity are developed, results from numerical experiments are presented and comparisons with other iterative and direct methods are carried out.
465 citations
TL;DR: Findings in patients with double primary curvatures, and the results of the study of brace effects, indirectly indicate the possibility of a postural disequilibrium as a contributory causative factor in adolescent idiopathic scoliosis.
Abstract: Postural equilibrium has been quantified by stabilometry in 57 patients with adolescent idiopathic scoliosis aged 10-16 years. Treatment was required in 39 cases whereof 18 were placed under observation only. The control group comprised 32 healthy children of the same age. An experimental design was made to vary the degree of difficulty of upright standing in four different test situations. The postural sway was analysed in the sagittal and lateral direction as well as in the area of total sway. The scoliotic patients had a significantly poorer postural control compared with the healthy children in all the tests. The difference was most pronounced in tests in which the proprioceptive functions were most important for maintaining the postural equilibrium. The left convex patients had quantitatively more pronounced reactions than the right convex patients. Patients with small curvatures, i.e., patients placed under observation only, had significantly increased postural sway compared with patients with more severe deformity. This fact, together with findings in patients with double primary curvatures, and the results of the study of brace effects, indirectly indicate the possibility of a postural disequilibrium as a contributory causative factor in adolescent idiopathic scoliosis.
190 citations
TL;DR: In this article, the authors considered some equilibrium finite element methods for two-dimensional elasticity problems and established L 2-estimates of orderO(h 2 ) for both stresses and displacements.
Abstract: We consider some equilibrium finite element methods for two-dimensional elasticity problems. The stresses and the displacements are approximated by using piecewise linear functions. We establishL 2-estimates of orderO(h 2) for both stresses and displacements.
188 citations
TL;DR: In this paper, two-dimensional finite-element models were formulated to satisfactorily represent the transient thermal and mechanical stress patterns occurring during the cooling of a butt weld produced by the submerged-arc welding of a heat-treated HT-36 steel alloy.
Abstract: Chalmers University of Technology, Sweden, has formulated two-dimensional finite-element models that satisfactorily represent the transient thermal and mechanical stress patterns occurring during the cooling of a butt weld produced by the submerged-arc welding of a heat-treated HT-36 steel alloy. The models offer a means of understanding the thermo-mechanical response caused by welding under various conditions without requiring the use of complex three-dimensional calculations.
166 citations
TL;DR: In this article, the authors made an analysis of the relationship between load and crack extension in the Hertzian indentation of a solid surface with a spherical indentor and proposed that the minimum load for ring-crack formation becomes independent of the flaws in the solid if these have a size above a certain threshold value.
137 citations
TL;DR: In this article, the effective medium theory was extended by incorporating dipole-dipole interactions to account for local field effects, represented approximately by use of effective depolarization factors.
Abstract: We extend the old effective-medium theory, originally due to Bruggeman, by incorporating dipole-dipole interactions to account for local-field effects. The interactions are represented approximately by use of effective depolarization factors. For close-packed clusters of conducting regions, a description which is appropriate at the percolation threshold, we predict an onset of percolation processes when 15.6 vol% is conducting. This is in very good agreement with numerical simulations as well as with experimental data for the metal-insulator transitions in metal-ammonia solutions and in alkali-tungsten bronzes.
129 citations
TL;DR: In this paper, high-resolution electron energy loss spectra of H2, D2 and HD chemisorbed at 200 K on the clean Ni(100) surface reveal vibrational excitations significant for dissociative chemistry.
116 citations
TL;DR: In this paper, the authors measured loss spectra for CO on Ni (100) and OH on NiO (111) as a function of primary electron energy and found that the dipole interaction describes the data for the CO system but fails completely for the OH system.
97 citations
TL;DR: In this article, the c(2 × 2) configuration of CO chemisorbed on Ni(100) has been examined by the dynamical LEED method of surface structure analysis.
93 citations
TL;DR: In this article, the structural changes have been studied with gel chromatography, viscometry, infrared spectroscopy, differential scanning calorimetry, and gravimetric measurements.
Abstract: Samples of low-density polyethylene (LDPE), high-density polyethylene (HDPE), and tetratetracontane (n-C44H90) free from additives were heated in air at temperatures between 120 and 180°C. As a comparison, “as received” HDPE containing unspecified additives has also been included.
The structural changes have been studied with gel chromatography, viscometry, infrared spectroscopy, differential scanning calorimetry, and gravimetric measurements.
LDPE, HDPE, and n-C44H90 follow the same course of thermooxidative degradation when they are free from additives and present in the molten state. Both molecular-diminishing and enlargement reactions occur. At temperatures below 150°C molecular enlargement is not observed until after rather long exposure times, whereas at higher temperatures enlargement occurs immediately. The difference is because “peroxide curing” becomes increasingly important above 150°C, whereas ester formation is operating at all temperature levels. Degradation below Tm is restricted to the amorphous phase that results in a different degradation pattern.
In accelerated testing work extrapolations of the Arrhenius type in the prediction of structural change are thus not justified, even within the actual narrow temperature range. Neither are changes in commonly used standards like carbonyl content justified as a measure of the changes; for example, in mechanical properties.
The stabilizer in the unpurified HDPE not only influences the induction period but also the course of the thermooxidative degradation.
TL;DR: In this paper, the Rat-incisor phosphoprotein (RIP) was subjected to isoelectric focusing at 4 degrees in an Ampholine pH gradient of 2.5-4 and an acid pH gradient created by electrolysis of a system of acids and acidic ampholytes.
TL;DR: In this article, an electronic surface band of Cu(111) was found to shift to lower energy upon adsorption of Cs, and at Cs coverages corresponding to more than approximately half of a full monolayer the Cs valence electrons produced an emission peak close below the Fermi edge.
TL;DR: In this article, the numerical solution of the Navier equations discretized by finite elements is studied by various forms of pre-conditioned conjugate gradient methods, and the dependence of the number of iterations is examined as a function of Poisson's ratio.
TL;DR: In this article, a full monolayer of Cs on Cu(111) forms a p(2 × 2) structure and the atoms become disordered but are still distributed uniformly over the surface.
TL;DR: In this article, transmission electron microscopy of an air-cooled medium carbon (0.5 wt pct) steel containing 0.1 wt 1 pct vanadium has shown that VC precipitates by the interphase mecha-nism during transformation to both proeutectoid and pearlitic ferrite.
Abstract: Transmission electron microscopy of an air-cooled medium carbon (0.5 wt pct) steel containing 0.1 wt pct vanadium has shown that VC precipitates by the interphase mecha-nism during transformation to both proeutectoid and pearlitic ferrite. Depending upon the rate of transformation, a considerable proportion of the available vanadium may remain in supersaturated solid solution and can be precipitated as VC upon subsequent aging at 700°C. It was found that the proportion of proeutectoid ferrite, the interlamellae pearlite spac-ings and the VC precipitate dispersion parameters all decreased with increasing cooling rate in as-transformed material.
TL;DR: In this article, a general three-dimensional formalism for scattering in two half spaces, one of which contains a bounded inhomogeneity, is presented, and the basic equations are given also for the case when the source and the inhomogeneous lie in the same half space.
Abstract: In the present article we give a general three‐dimensional formalism for scattering in two half spaces, one of which contains a bounded inhomogeneity. Our formalism consists of an extension of the transition matrix method which has been given by Waterman, a method which applies equally well to acoustic, electromagnetic, and elastic scattering. The formalism is here developed in detail for the case when the source and inhomogeneity are situated in different half‐spaces. However, the same method works for other source positions as well, and the basic equations are given also for the case when the source and the inhomogeneity lie in the same half space. In the final expression for the total scattered field, that part (the so‐called anomalous scattered field) which depends on the presence of the inhomogeneity, can be separated, and the physical meaning of the various quantities which determine this anomalous scattered field can be identified. The inhomogeneity enters through its T matrix, and previous results...
TL;DR: The nuclear spins and magnetic moments of some neutron-deficient rubidium isotopes have been measured by atomic-beam magnetic resonance techniques at the ISOLDE facility, CERN.
TL;DR: In this article, the adsorption of O 2 and CO on Ti films with thicknesses in the range 0-200 A was investigated by quartz crystal microbalance (QCM) measurements.
TL;DR: Using on-line mass separation, eight α-emitters (given with their α-decay energies in keV) in the trans-tin region were investigated in this article.
TL;DR: In this article, the thermal degradation of PVC was studied at 190°C in pure nitrogen and nitrogen containing 10, 20, and 40% HCl (by volume) and the rate of dehydrochlorination was determined by gravimetry.
Abstract: The thermal degradation of PVC was studied at 190°C in pure nitrogen and nitrogen containing 10, 20, and 40% HCl (by volume). The rate of dehydrochlorination was determined by gravimetry. Degradations in nitrogen were followed with conductometry in addition. Changes in molecular weight distribution and degree of long-chain branching (LCB) were determined by gel permeation chromatography–viscometry and polyene sequence distribution by UV spectroscopy. The rate of dehydrochlorination increases with the HCI content of the atmosphere. The rate of molecular enlargement also increases but only as a result of the increased dehydrochlorination rate. The increase in Mw and LCB are thus related to the extent of conversion only. Changes in the UV spectra indicate that the increase in rate of dehydrochlorination is mainly due to increased propagation rate in atmospheres containing less than 10% HCI. At higher HCI contents an increase in initiation rate is noted. It is suggested that this, at least in part, is due to the fact that HCI, by forming a cyclic transition state, catalyzes the random elimination of HCI. This process, in turn, is promoted by the presence of polyene sequences.
TL;DR: In this article, the authors compute the optical absorption of a glass containing a small fraction of silver particles with dielectric cores based on the Maxwell Garnett formalism, and they argue that their observed absorption maxima can be explained without invoking any quantum effects.
Abstract: We compute the optical absorption of a glass containing a small fraction of silver particles with dielectric cores. The results are based on the Maxwell Garnett formalism. The dielectric permeability of the metallic shells is obtained by modifying experimental data for bulk silver to account for size dependent scattering of the conduction electrons. We find an absorption maximum in the visible range at a wavelength which, for sufficiently minute particles, depends rather strongly on the size of the cores and on their dielectric constant. The relevance of these results to recent experimental data by Smithard and by Genzel et al. is pointed out. We argue that their observed absorption maxima can be explained without invoking any quantum effects.
TL;DR: In this article, the morphology development and overall crystallization rate between 900° and 990°C of MgO-Al2O3−SiO2 glasses with added ZrO, TiO2, CaF2, or CeO2 were studied.
Abstract: Quantitative X-ray diffraction and microscopy were used to study the morphology development and overall crystallization rate between 900° and 990°C of MgO-Al2O3−SiO2 glasses with added ZrO, TiO2, CaF2, or CeO2. Three basic stages of micro-structural development were distinguishable: I, an induction period, II, a spherulitic crystallization stage, and III, a final crystallization stage. The duration of the induction period, the crystallization rate of the high-quartz solid solution, and the microstructures varied markedly with prior nucleation treatment and the type of modifier present in a glass of nearly equal silica content. The roles of major (high-quartz ss, high cordierite) and of minor crystalline and liquid phases in textural development are discussed, and it is postulated that nucleants (ZrO2, TiO2) act also as growth-modifying “impurities” in crystal growth.
01 Sep 1978
TL;DR: In this article, a survey of a kinetic theory for micelle formation and disintegration at small deviations from equilibrium guided by a concept of a diffusion-like flow along an aggregation number axis is given.
Abstract: A survey is given of a kinetic theory for micelle formation and disintegration at small deviations from equilibrium guided by a concept of a diffusionlike flow along an aggregation number axis. Two well separated relaxation times for the monomer concentration are predicted, the short one pertaining to the rearrangement of the micellar distribution at a constant number of micelles and the long one pertaining to the change in the number of micelles with a concomitant shift in the position of the mean aggregation number of the micelles. – A “reverse” case is shown to give a relaxation time distribution at complete variance with experimental results, general conditions are given for the occurrence of only one relaxation time in the rearrangement process, and the movements of the micellar distribution at moderate and large dilutions are described. – Finally a theoretical calculation of the disintegration rate constants is presented, its extension to the dynamics of partial exits of the amphiphilic molecules is sketched, and its inferences for monolayer and bilayer structures are pointed out.
01 Jan 1978
TL;DR: In this paper, the authors formulate an unifying model describing the properties of Si-SiO 2 interface defects, including fixed surface charge, interface traps and radiation induced charge, and show that the model makes it possible to understand most known properties of the interface defects.
Abstract: The present paper is an attempt to formulate an unifying model describing the properties of the Si-SiO 2 interface defects. We concentrate on the “classical” defects, fixed surface charge, interface traps and radiation induced charge. We postulate the existence of three different forms of trivalent silicon and electrical and chemical properties of these. We show that the model makes it possible to understand most known properties of the interface defects. We can for example understand why fixed charge and interface trap densities follow each other after oxidation but not after hydrogen anneal. We can also understand how holes, trapped in the oxide, can give rise to new interface traps.
TL;DR: The nuclear ground state spins of some francium isotopes have been measured using on-line atomic-beam magnetic resonance techniques as mentioned in this paper, and the spin values are discussed briefly in terms of current nuclear models.
Abstract: The nuclear ground state spins of some francium isotopes have been measured using on-line atomic-beam magnetic resonance techniques. The following results have been obtained: 208Fr I = 7, 209Fr I = 9/2, 210Fr I = 6, 211Fr I = 9/2, 212Fr I = 5, 213Fr I = 9/2, 220Fr I = 1, 221Fr I = 5/2 and 222Fr I = 2. The spin values are discussed briefly in terms of current nuclear models.
TL;DR: The influence of sodium chloride on the atmospheric corrosion of mild steel has been studied in this paper, where samples covered with sodium chloride crystals (8 mg NaCl · cm−2) have been exposed to an SO2-free atmosphere at different relative humidity.
Abstract: The influence of sodium chloride on the atmospheric corrosion of mild steel has been studied. Samples covered with sodium chloride crystals (8 mg NaCl · cm−2) have been exposed to an SO2-free atmosphere at different relative humidities. The combined effect of sodium chloride crystals on a steel surface and sulphur dioxide in the atmosphere has been investigated at an SO2-supply of 1 mg SO2 · cm–2 · h–1 (1 ppm SO2). The corrosion attack was followed by periodic weighings. The corrosion products formed have been studied using the SEM-technique. On exposure of samples with sodium chloride in an SO2-free atmosphere the extent of corrosion increased with increasing relative humidity from 58% to 90%, interrupted by a sharp minimum at about 87% relative humidity. The SEM-studies showed that tower shaped corrosion products were formed at a high relative humidity while filiform corrosion appeared when the relative humidity was lowered. At 90% relative humidity more corrosion was observed with clean steel samples and an SO2-supply of 1 mg ·cm–2 ·h–1 than with sodium chloride crystals on the surfaces (8 mg NaCl ·cm–2) in the absence of SO2. In the combined influence of sodium chloride on the steel surfaces and sulphur dioxide in the atmosphere a synergic effect was noticed at 90% relative humidity. At 70% relative humidity no influence of an SO2-supply of 1 mg SO2 ·cm–2 ·h–1 on the corrosion of steel samples with sodium chloride crystals on their surfaces could be observed.
TL;DR: In this article, a study has been made of the elevated temperature degradation of a number of carbon fibre types coated with nickel by a variety of methods (electroless, electrolytic, carbonyl and physical vapour deposition).
Abstract: A study has been made of the elevated temperature degradation of a number of carbon fibre types coated with nickel by a variety of methods (electroless, electrolytic, carbonyl and physical vapour deposition). At high temperatures, Ni-coated fibres undergo a transformation of structure to crystalline graphite with a consequent loss of strength and elastic modulus. Resistance to this recrystallization is related to the fibre type and structure and increases in the order HTS PAN-based, HM PAN-based, HM rayon-based. For PAN-based fibres the resistance increases with the degree of structural order and orientation. The recrystallization of HTS fibres is consistent with a simple model of dissolution and reprecipitation controlled by diffusion of carbon in nickel. To explain the higher stability of HM fibres an additional factor must be introduced. For example, their behaviour can be explained in terms of a highly stable surface layer between about 0.1 and 0.5μm thick. Rapid recrystallization occurs when the nickel breaks through this layer e.g. by dissolution. The recrystallization was not greatly affected by the type of nickel coating but the recrystallization temperature of HM fibres was considerably reduced by a small proportion of air in the heat-treatment atmosphere. HTS fibres were not affected in this way but the fibres were severely weakened through surface attack by both air and hydrogen at temperatures well below the recrystallization temperature.