Showing papers by "Technical University of Denmark published in 1981"
TL;DR: In this paper, the effect of microscopic voids on the failure mechanism of a ductile material is investigated by considering an elastic-plastic medium containing a boubly periodic array of circular cylindrical voids.
Abstract: The effect of microscopic voids on the failure mechanism of a ductile material is investigated by considering an elastic-plastic medium containing a boubly periodic array of circular cylindrical voids. For this voided material under uniaxial or biaxial plane strain tension the state of stresses and deformations is determined numerically. Bifurcation away from the fundamental state of deformation is analysed with special interest in a repetitive pattern that represents the state of deformation inside a shear band. Both in the fundamental state and in the bifurcation analysis the interaction between voids and the details of the stress distribution around voids are fully accounted for. Comparison is made with the shear band instabilities predicted by a continuum model of a ductile porous medium. Based on the numerical results an adjustment is suggested for the approximate yield condition in this model of dilatant, pressure sensitive plastic behaviour.
2,021 citations
TL;DR: In this paper, a general representation for the macroscopic stresses in terms of the volume average of the (tensorial) product of the contact forces and the vectors which connect the centroids of adjacent contacting granules is established.
Abstract: Considered is a sample of cohesionless granular material, in which the individual granules are regarded rigid, and which is subjected to overall macroscopic average stresses. On the basis of the principle of virtual work, and by an examination of the manner by which adjacent granules transmit forces through their contacts, a general representation is established for the macroscopic stresses in terms of the volume average of the (tensorial) product of the contact forces and the vectors which connect the centroids of adjacent contacting granules. Then the corresponding kinematics is examined and the overall macroscopic deformation rate and spin tensors are developed in terms of the volume average of relevant microscopic kinematical variables. As an illustration of the application of the general expressions developed, two explicit macroscopic results are deduced: (1) a dilatancy equation which both qualitatively and quantitatively seems to be in accord with experimental observation, and (2) a noncoaxiality equation which seems to support the vertex plasticity model. Since the development is based on a microstructural consideration, all material coefficients entering the results have well-defined physical interpretations.
760 citations
700 citations
TL;DR: In this paper, the structure and type of phases present in sulfided alumina-supported, as well as unsupported, Co-Mo catalysts is obtained from in situ Mossbauer emission spectroscopy (MES) studies.
563 citations
TL;DR: In this article, the problem of maximizing the integral stiffness of solid elastic plates described by thin plate theory is considered and an efficient and quite general numerical algorithm by means of which a number of stationary solutions for rectangular and axisymmetric annular plates with various boundary conditions are obtained.
389 citations
TL;DR: In this article, a series of sulfided Co-Mo Al 2 O 3 catalysts with different Co Mo ratios but with constant molybdenum content was investigated, and it was shown that the relative amounts of the three phases depend strongly on the Co Mo ratio.
354 citations
TL;DR: In this paper, the basic fatigue damage mechanisms in composite laminates are reviewed and a pattern in the fatigue-life diagrams is proposed based on these mechanisms, and several experimental data are shown to agree with this basic pattern.
Abstract: The basic fatigue damage mechanisms in composite laminates are reviewed. Based on these mechanisms a pattern in the fatigue-life diagrams is proposed. Several experimental data are shown to agree with this basic pattern. Fatigue ratio is defined in terms of strains, and fatigue limit is shown to exist for unidirectional, cross-plied and angle-plied laminates. The limitations to the fatigue performance of composite laminates are pointed out and suggestions for improving the fatigue resistance are made.
330 citations
TL;DR: In this paper, a superconductivity in the organic conductor di-(tetramethyltetraselenafulvalenium)-perchlorate [(TMTSF)2C104] has been found by resistance measurements in the absence of applied pressure.
Abstract: Evidence for superconductivity in the organic conductor di-(tetramethyltetraselenafulvalenium)-perchlorate [(TMTSF)2C104] has been found by resistance measurements in the absence of applied pressure. For different crystals the transitions are approximately 0. 3 K wide and are centered around temperatures between 1. 2 and 1. 4 K. At 0. 9 K, a perpendicular magnetic field of 25 mT nearly restores normal resistance. Below 0. 1 K, this critical field exceeds 50 mT.
322 citations
289 citations
TL;DR: In this article, the growth of a single shear band in an infinite block of an incompressible solid undergoing plane strain tension or compression is studied for three material models, including nonlinear elasticity, kinematic hardening plasticity and a plasticity theory based on yield surface corner development.
189 citations
TL;DR: The taxonomy of the asymmetric (predominantly terverticillate) penicillia is based on morphological differences that leave identification difficult, and the application of physiological criteria facilitated the identification of the common asymmetric penicllia investigated.
Abstract: The taxonomy of the asymmetric (predominantly terverticillate) penicillia is based on morphological differences that leave identification difficult. The application of physiological criteria facilitated the identification of the common asymmetric penicillia investigated. Changes in the placement of some strains of these penicillia made the connection to mycotoxin-producing ability clearer. The classical criterion of conidium color was deemphasized and replaced by the following criteria: (i) growth on nitrite-sucrose agar and (ii) growth and acid (and subsequent base) production on creatine-sucrose agar (containing bromocresol purple). Other criteria used or developed were: (iii) growth on sorbic acid plus benzoic acid agar (50 + 50 ppm, pH 3.8), (iv) growth on an agar containing 1,000 ppm propionic acid (pH 3.8), (v) growth on an agar containing 0.5% acetic acid, (vi) growth at 37°C, (vii) growth rate on an agar containing 0.1% pentachloronitrobenzene, (viii) production of extracellular tricaproinase, and (ix) fasciculation on a medium containing 10 ppm botran (2,6-dichloro-4-nitroanilin). The pattern of extracellular metabolites after thin-layer chromatography was used as a chemotaxonomic criterion. The species investigated, the number of isolates investigated, and the toxins which some of these isolates produce were: Penicillium roqueforti (18) (patulin), P. citrinum (11) (citrinin), P. patulum (9) (patulin and griseofulvin), P. expansum (patulin and citrinin), P. hirsutum (13), P. brevicompactum (19), and P. chrysogenum (12). Widespread species of the P. cyclopium, P. viridicatum, and P. expansum series of Raper and Thom (A Manual of the Penicillia, 1949) were subdivided into four new groups: “P. crustosum pA” (29) (penitrem A), “P. melanochlorum” (29), “P. cyclopium p” (119) (penicillic acid and infrequently penitrem A), and “P. viridicatum o-c” (43) (ochratoxin A and citrinin). “P. viridicatum o-c” was separated from “P. cyclopium p” due to its ability to grow on nitrite as sole nitrogen source. The species and groups investigated were related to the new taxonomic classification of the genus Penicillium according to Pitt.
TL;DR: In this article, the chemical shift for C-9 in a range of substituted compounds is shown to be numerically related to the stereochemistry at C-8, which allows the determination of the configuration at this centre for most types of substitution patterns by calculation of the C- 9 shift using increments for each substituent.
TL;DR: In this article, experimental results for deep surge in a small single-stage centrifugal compressor are compared to predictions based on the lumped parameter Greitzer model developed for axial compressors.
Abstract: Experimental results for deep surge in a small single-stage centrifugal compressor are compared to predictions based on the lumped parameter Greitzer model developed for axial compressors. Both negative and positive flow branches of the steady characteristic, being essential for the model, were measured. Predictions are in fair agreement with data when using a relaxation time smaller than the one proposed for axial compressors. The stability limit of the model equations have been studied for finite amplitude disturbances.
TL;DR: In this article, the advantages of using piezoelectric polymer (plastic) materials as the sensitive element in miniature ultrasonic hydrophone probes are described, and proposed designs are critically reviewed.
TL;DR: In this article, the authors considered the temperature dependence of the threshold current of GaInAsP/InP lasers in terms of linear gain, loss, and carder lifetime, taking into account electronic intraband relaxation effects.
Abstract: The temperature dependence of the threshold current of GaInAsP/InP lasers was considered in terms of linear gain, loss, and carder lifetime. The linear gain was calculated taking into account electronic intraband relaxation effects. The carrier lifetime, intraband relaxation time, loss in the active region, and dipole moment, all of which determine the threshold condition, were estimated from the experiments. The main loss mechanism which determines the temperature dependence of the differential quantum efficiency appears to be the absorption due to transitions between the split-off and heavy-hole valence bands. The temperature dependence of the theoretical threshold current I th calculated in terms of these parameters was compared with the measured results and reasonable agreement was obtained.
TL;DR: In this article, the authors reported polarized reflectance measurements from the far infrared to the visible for the TTSF (TMTSF) and F F (F F 6 ).
Abstract: Polarized reflectance measurements from the far infrared to the visible are reported for ${(\mathrm{TMTSF})}_{2}$P${\mathrm{F}}_{6}$. At low temperatures, both parallel and perpendicular polarizations show plasma edges in the infrared with metallic reflection below these edges, indicating two- or three-dimensional behavior. The transverse plasma frequency is $\ensuremath{\sim}\frac{1}{5}$ of the parallel plasma frequency. At higher temperatures, the plasmon in the perpendicular polarization becomes highly overdamped, indicating a crossover to one-dimensional behavior.
TL;DR: It is suggested, however, that the a-subunit (atpB) contains only 201 amino acids, in accordance with its known size, starting from a translation initiation site within the larger coding sequence.
Abstract: The nucleotide sequence has been determined of a 2.500 base pair segment of the E. coli chromosome located between 3.75 and 6.25 kb counterclockwise of the origin of replication at 83.5 min. The sequence contains the atp genes coding for subunits a-, b-, c-, δ- and part of the α-subunit of the membrane bound ATP synthase. The precise start positions of the atpE (c), atpF (b), atpH (δ) and atpA (α) genes have been defined by comparison of the potential coding sequences with the known amino acid sequence of the c-subunit and the determined N-terminal amino acid sequences of the respective subunits. The genes are expressed in the counterclockwise direction. Their order (counterclockwise) is: atpB (a), atpE (c), atpF (b), atpH (δ) and atpA (α). The coding sequences for subunits b and δ yield polypeptides of 156 and 177 amino acids, respectively, in accordance with the established sizes of these subunits; the one for the c-subunit, the DCCD binding protein, fits perfectly with its known sequence of 79 amino acids. The a-subunit is comprised within a coding sequence yielding a polypeptide of 271 amino acids. It is suggested, however, that the a-subunit (atpB) contains only 201 amino acids, in accordance with its known size, starting from a translation initiation site within the larger coding sequence. The stoichiometry of the F0 sector subunits is discussed and a model is proposed for the functioning of the highly charged b-subunit of the F0 sector as the actual proton conductor.
TL;DR: Haematococcus pluvialis cultivated in a N-deficient medium produced astaxanthin (1 % of total carotenoids), the monoester (76 %) and diester (7 %) of astaxantin, β,β-carotene (1%)), an adonirubin ester (3 %), (3R,3′R,6′R)-lutein (7%), violaxanthins (2%), and neoxanthin(1%) as mentioned in this paper.
TL;DR: In this article, the dynamics of sine-Gordon solitons in two spatial dimensions are studied and new results like 4π-break up, solon-on-soliton effect, and scattering at a circular inhomogeneity are reported.
TL;DR: In this article, the Working Group of the IAHR Section on Ice Problems proposes its recommendation for "Standardized Testing Methods for Measuring Mechanical Properties of Ice" (SATML).
TL;DR: It is shown that every k-connected graph with no 3-cycle contains an edge whose contraction results in a k- Connected graph and this is used to prove that every (k + 3)-connected graph contains a cycle whose deletion results in an k- connected graph.
Abstract: We show that every k-connected graph with no 3-cycle contains an edge whose contraction results in a k-connected graph and use this to prove that every (k + 3)-connected graph contains a cycle whose deletion results in a k-connected graph. This settles a problem of L. Lovasz.
TL;DR: In this article, it is demonstrated how the computer, used in a heuristic mode, has greatly augmented our understanding of the mathematics of nonlinear dynamical process, and the role of good graphics in enhancing the discovery and retention of new mathematical properties of equations is illustrated.
TL;DR: The late averaged magnetic field evoked by contra- and ipsilateral auditory stimulation is recorded by means of a SQUID magnetometer from both hemispheres in four normally hearing, right-handed male adults.
Abstract: The late averaged magnetic field evoked by contra- and ipsilateral auditory stimulation is recorded by means of a SQUID magnetometer from both hemispheres in four normally hearing, right-handed male adults. The stimuli consist of 1 kHz, 500 ms tone pulses with intensities from 5 to 85 dB HL and averaging is based on 60 sweeps. Stimulating the right ear the averaged magnetic field from the left hemisphere is approx. twice as great as that from the right hemisphere, whereas stimulating the left ear no difference in magnitude is found. The amplitude input-output functions are steeply rising near threshold and more shallow at high intensities. The responses from contralateral stimulation are approx. 9 ms earlier than those from ipsilateral stimulation with no interhemispheric difference.
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TL;DR: Three short proofs of Kuratowski's theorem on planarity of graphs are presented and applications, extensions, and some related problems are discussed.
Abstract: We present three short proofs of Kuratowski's theorem on planarity of graphs and discuss applications, extensions, and some related problems.
TL;DR: In this paper, a modification of the Heidemann-Khalil method for calculating the critical temperatures and pressures for general phase-equilibrium problems greatly reduced the computing time for simple two-constant cubic equations of state.
Abstract: A computational modification of the Heidemann-Khalil method for calculating the critical temperatures and pressures for general phase-equilibrium problems greatly reduced the computing time for simple two-constant cubic equations of state. For systems where the unlike binary interaction parameters can be derived from the pure-component parameters using the geometric mean values, a further simplification lowers the computing times to a few milliseconds, regardless of the number of components.
TL;DR: In this paper, the authors exploit the reproducible concentration gradients formed between an injected sample zone and the carrier stream in flow injection analysis for titrations based on measuring the time span between points of identical gradient dispersion.
TL;DR: An algorithm for minimax optimization that combines LP methods and quasi-Newton methods is presented and it is proved that the algorithm can converge only to a stationary point and that normally the final rate of convergence will be either quadratic or superlinear.
Abstract: We present an algorithm for minimax optimization that combines LP methods and quasi-Newton methods. The quasi-Newton algorithm is used only if an irregular solution is detected, in which case second-order derivative information is needed in order to obtain a fast final rate of convergence. We prove that the algorithm can converge only to a stationary point and that normally the final rate of convergence will be either quadratic or superlinear. The performance is illustrated through some numerical examples.
TL;DR: In this paper, the microwave emission from long Josephson tunnel junctions dc-current biased on zero-field and Fiske steps has been measured and the frequency and power variation on all steps of the narrow-linewidth radiation near the fundamental cavity-mode frequency and the observed transitions between different modes on a given step may be understood in a picture of multifluxon excitations with propagation of different bunched fluxon configurations depending on the current and magnetic field bias.
Abstract: The microwave emission from long Josephson tunnel junctions dc-current biased on zero-field and Fiske steps has been measured. The frequency and power variation on all steps of the narrow-linewidth radiation near the fundamental cavity-mode frequency and the observed transitions between different modes on a given step may be understood in a picture of multifluxon excitations with propagation of different bunched fluxon configurations depending on the current and magnetic field bias.
TL;DR: In this paper, the optimal design of axisymmetric plates performing free, transverse vibrations has been studied, where the plate thickness distribution is determined from the condition that the plate volume is minimized for a given value of the fundamental natural frequency, or for a higher order natural frequency that corresponds to a vibration mode with a prescribed number of nodal diameters.