Showing papers by "Brown University published in 1975"
TL;DR: In this paper, the authors investigated the hypothesis that localization of deformation into a shear band may be considered a result of an instability in the constitutive description of homogeneous deformation.
Abstract: T his paper investigates the hypothesis that localization of deformation into a shear band may be considered a result of an instability in the constitutive description of homogeneous deformation. General conditions for a bifurcation, corresponding to the localization of deformation into a planar band, are derived. Although the analysis is general and applications to other localization phenomena are noted, the constitutive relations which are examined in application of the criterion for localization are intended to model the behavior of brittle rock masses under compressive principal stresses. These relations are strongly pressure-sensitive since inelasticity results from frictional sliding on an array of fissures; the resulting inelastic response is dilatant, owing to uplift in sliding at asperities and to local tensile cracking from fissure tips. The appropriate constitutive descriptions involve non-normality of plastic strain increments to the yield hyper-surface. Also, it is argued that the subsequent yield surfaces will develop a vertex-like structure. Both of these features are shown to be destabilizing and to strongly influence the resulting predictions for localization by comparison to predictions based on classical plasticity idealizations, involving normality and smooth yield surfaces. These results seem widely applicable to discussions of the inception of rupture as a constitutive instability.
2,411 citations
TL;DR: Using a simplified constitutive model of a pointed vertex on subsequent yield loci, the onset of localized necking under biaxial stretching has been predicted and this result supports the hypothesis of vertex-formation on the yield locus under continued plastic flow.
Abstract: B y using a simplified constitutive model of a pointed vertex on subsequent yield loci, namely, such that the equations of deformation-theory of rigid-plastic solids apply for fully-active stress increments, the onset of localized necking under biaxial stretching has been predicted. The predictions agree reasonably well with reported experimental observations. Since localized necking under biaxial stretching of a uniform and homogeneous sheet is impossible when flow theories of plasticity with smooth yield-loci are used, this result supports the hypothesis of vertex-formation on the yield locus under continued plastic flow. The implications of this conclusion with respect to the study of the inception of ductile fracture in solids, viewed as a material instability, may be far-reaching. Still, explanations based on a smooth yield-locus but small initial inhomogeneities cannot be ruled out, and both initial imperfections and yield-vertex effects may contribute in general to localization instabilities.
816 citations
TL;DR: In this article, an Eulerian finite element formulation for large elastic-plastic flow is presented, based on Hill's variational principle for incremental deformations, and is suited to isotropically hardening Prandtl-Reuss materials.
724 citations
TL;DR: The relationships between 50 per cent inhibitory concentration and dissociation constants of the complex are shown for various mechanisms of inhibition, and several methods for the estimation of very low Ki, values are presented.
483 citations
TL;DR: In this paper, a nearly free-electron model for explaining the relative stability of some metallic alloys against crystallization is proposed, and the maximum stability corresponds to the composition for which the Fermi level lies at a minimum of the density of states.
Abstract: A nearly-free-electron model for explaining the relative stability of some metallic alloys against crystallization is proposed. Arguments are presented which show that in an alloy the maximum stability corresponds to the composition for which the Fermi level lies at a minimum of the density of states. In this case any small enough perturbation around this configuration will increase the total electron energy. This approach predicts the correct composition range of metal glasses.
452 citations
TL;DR: In this paper, the Weber's law model was used to predict the initial drop in the Weber fraction for very short durations and the observed constancy of the Weber fractions for durations up to 2 sec.
Abstract: Duration-discrimination data from an experiment using empty auditory intervals in a two-alternative forced-choice paradigm are presented The observed functional relationship between standard deviation of the psychometric density function and stimulus duration is shown to be fit significantly better by a Weber’s law model of duration discrimination than by Creelman’s counter model Both models fail to predict the rapid rise in the Weber fraction observed for durations longer than about 2 sec However, the Weber’s law model, based on a generalization of Weber’s law, accurately predicts the initial drop in the Weber fraction for very short durations and the observed constancy of the Weber fraction for durations up to 2 sec
301 citations
TL;DR: The basic tool for a general Riemann-Roch theorem is MacPherson's graph construction, applied to a complex E of vector bundles on a scheme Y, exact off a closed subset X as discussed by the authors.
Abstract: The basic tool for a general Riemann-Roch theorem is MacPherson’s graph construction, applied to a complex E. of vector bundles on a scheme Y, exact off a closed subset X. This produces a localized Chern character1 ch x y (E.) which lives in the bivariant group \( A{\left( {X \to Y} \right)_\mathbb{Q}} \) For each class α∈A * Y, this gives a class
$$ ch_X^Y\left( {E.} \right) \cap \alpha \in {A_ * }{X_\mathbb{Q}} $$
whose image in \( {A_ * }{Y_\mathbb{Q}} \) is \( {\sum {\left( { - 1} \right)} ^i}ch\left( {{E_i}} \right) \cap \alpha \) The properties needed for Riemann-Roch, in particular the invariance under rational deformation, follow from the bivariant nature of ch x y E.
291 citations
TL;DR: This paper found that infants, 2 and 3 months of age, were able to discriminate stimuli along the acoustic continuum underlying the phonetic contrast [r] vs. [l] in a nearly categorical manner.
Abstract: Infants, 2 and 3 months of age, were found to discriminte stimuli along the acoustic continuum underlying the phonetic contrast [r] vs. [l] in a nearly categorical manner. For an approximately equal acoustic difference, discrimination, as measured by recovery from satiation or familiarization, was reliably better when the two stimuli were exemplars of different phonetic categories than when they were acoustic variations of the same phonetic category. Discrimination of the same acoustic information presented in a nonspeech mode was found to be continuous, that is, determined by acoustic rather than phonetic characteristics of the stimuli. The findings were discussed with reference to the nature of the mechanisms that may determine the processing of complex acoustic signals in young infants and with reference to the role of linguistic experience on the development of speech perception at the phonetic level.
284 citations
TL;DR: A modified thiocarbohydrazide (TCH) technique to cross-link osmium layers has resulted in a reliable method for preparing a wide variety of soft biological tissues for scanning electron microscopy without the use of evaported metal.
Abstract: A modified thiocarbohydrazide (TCH) technique to cross-link osmium layers has resulted in a reliable method for preparing a wide variety of soft biological tissues for scanning electron microscopy without the use of evaporated metal. The technique works equally well on tissues with smooth surfaces and those with abrupt changes in contour or cut surfaces, as in biopsy or autopsied material or pathologically altered tissues, and thus has wide applicability. Small surface structures and functional areas between cells are distinct. In addition, thin cells such as alveolar endothelium in the lung exhibit a transparent property, allowing the visualization of cells within the capillary lumen while retaining adequate contrast for study of the capillary wall itself. Absence of an evaporated metal coat makes the removal of tissue from the scanning electron microscope specimen easy for embedding and examination of the same material with the transmission electron microscope.
263 citations
232 citations
TL;DR: In this article, the first rigorous kinetic theory of ion mobility in neutral gases, valid for electric fields of arbitrary strength without restriction on the ion-neutral mass ratio or interaction potential, is presented.
TL;DR: In this paper, the authors considered a model with two types of genes (alleles) A1 A2 and A2 A2, and considered the effects of population dispersal within R and selective advantages among the three possible genotypes A 1A1, A1A2, A2A2.
Abstract: We consider a model with two types of genes (alleles) A1 A2. The population lives in a bounded habitat R, contained in r-dimensional space (r= 1, 2, 3). Let u (t, x) denote the frequency of A1 at time t and place x ɛ R. Then u (t, x) is assumed to obey a nonlinear parabolic partial differential equation, describing the effects of population dispersal within R and selective advantages among the three possible genotypes A1A1, A1A2, A2A2. It is assumed that the selection coefficients vary over R, so that a selective advantage at some points x becomes a disadvantage at others. The results concern the existence, stability properties, and bifurcation phenomena for equilibrium solutions.
TL;DR: Adenosine deaminase (adenosine aminohydrolase, EC 3.5.4) has been purified about 3000-fold from human erythrocytes and Tubercidin (7-deaza- adenosine) and toyocamycin were devoid both of substrate and inhibitor activity.
TL;DR: After humans were treated at therapeutic doses with the trichomonacide metronidazole (Flagyl) and the antischistosomal agent niridazoles mutagenic activity was demonstrable in their urines when tested with the histidine auxotroph of Salmonella typhimurium.
Abstract: After humans were treated at therapeutic doses with the trichomonacide metronidazole (Flagyl) and the antischistosomal agent niridazole mutagenic activity was demonstrable in their urines when tested with the histidine auxotroph of Salmonella typhimurium. Both compounds were active in the host-mediated assay in mice, and evidence of activity was found in the blood and urine of mice treated with niridazole but not with metronidazole.
TL;DR: The biphasic nature of the dissociation of the deaminase-coformycin complex (EI complex) indicates that the EI complex undergoes a slow conformational change, which is consistent with the known mechanisms of inhibitions by these inhibitors.
TL;DR: By mapping and summarizing 478 pollen counts from surface samples at 406 locations in eastern North America, the authors documents the relationships between the distributions of pollen and vegetation on a continental scale.
TL;DR: In this article, the scaling transformation is used in numerical calculations of the properties of the two-dimensional Ising model near its critical point, and the best approximation is seen to lead to 1 part in ${10}^{4}$ accuracy for the two largest scaling indices.
Abstract: Scaling transformations are used in numerical calculations of the properties of the two-dimensional Ising model near its critical point. When compared with the exact Onsager solution, the best approximation is seen to lead to 1 part in ${10}^{4}$ accuracy for the two largest scaling indices. This rather accurate calculation is obtained by utilizing a scaling transformation which depends upon a parameter. The parameter is set by demanding that two different evaluations of the magnetic eigenvalue agree with one another. One evaluation is found via the standard eigenvalue method; the other comes from a consistency condition for the spin-spin correlation function. This condition may also be used to distinguish scaling eigenvalues from other eigenvalues.
TL;DR: In this article, the authors used the Keylis-Borok relationship to evaluate the fracture energy of a semi-infinite longitudinal shear crack and found that fresh fracture was associated with 10'-lQ9 erg cm-2 while frictional rupture with 103-107 erg cm -2.
Abstract: Summary The arrest of a semi-infinite longitudinal shear crack is caused by either (1) the finiteness of available strain energy, or (2) an increase in fracture energy along the trajectory of the running crack. In the former case the following relationship may be used to evaluate the fracture energy: yo = RAa2/2ptn where yo is the fracture energy per unit length along the crack edge per unit extension of the cracktip (erg cm-2), R is the characteristic radius of the fault (cm), ACJ is the stress drop (dyne cm-2) and p is the rigidity (dyne cm-2). This leads to the following relationship: log Aa = -3 log R +f log (2ptny0) or from the Keylis-Borok relationship (1959): log Mo = 5/2 log R +* log (2ptny0)+0*64 where M, is the seismic moment in dyne cm-'. These two relationships are statistically acceptable for Southern California faults and the TongaKermadec Arc earthquakes. The fracture energy is found to vary from lo3 to lo9 erg cm-' with fresh fracture being associated with 10'-lQ9 erg cm-2 while frictional rupture with 103-107 erg cm-2. These values are in good agreement with other independent estimates.
TL;DR: In this article, the direction of spin alignment in the A, phase is opposite to that which is predicted using weakcoupling theory, and the magnitude of the linear splitting calculated using spin-fluctuation theory with 1 −IN(eF) =~, (ug =eF/20, and N(eV)V = 4.0) is about 4 times larger than that measured experimentally.
Abstract: the direction of spin alignment in the A, phase is opposite to that which is predicted using weakcoupling theory. The magnitude of the linear splitting calculated using spin-fluctuation theory with 1 —IN(eF) =~, (ug =eF/20, and N(eF)V = 4.0— (and the RPA approximation for p, '") is about 4 times larger than that measured experimentally; in weak-coupling theory, the calculated splitting diff ers from the experimental one by a factor of more than 25. While there are, at present, no measurements which can verify this prediction, it should shortly be possible" to ascertain the direction of the spin pairs in the A, state. Useful conversations with D. L. Mills and K. Maki are gratefully acknowledged.
TL;DR: The data suggest that, under certain conditions, large increases in the intra-cellular concentration of cyclic AMP may not be necessary for stimulation ofalpha-amylase release by adrenergic agonists, and demonstrate the need for caution in interpreting evidence obtained using alpha-adrenergic blocking agents as tools for investigation of alpha- and beta- adrenergic antagonism.
TL;DR: In this article, it is shown that the strain rate history effects play a very important role in the plastic behavior of polycrystaline f.c. metals. But the results of these experiments are limited to a range of shear prestrainings of up to 0.15 for aluminum and 0.25 for copper.
TL;DR: Passive modification of the strength of synaptic junctions that results in the construction of internal mappings with some of the properties of memory is shown to lead to the development of Hubel-Wiesel type feature detectors in visual cortex.
Abstract: Passive modification of the strength of synaptic junctions that results in the construction of internal mappings with some of the properties of memory is shown to lead to the development of Hubel-Wiesel type feature detectors in visual cortex. With such synaptic modification a cortical cell can become committed to an arbitrary but repeated external pattern, and thus fire every time the pattern is presented even if that cell has no genetic pre-disposition to respond to the particular pattern. The additional assumption of lateral inhibition between cortical cells severely limits the number of cells which respond to one pattern as well as the number of patterns that are picked up by a cell. The introduction of a simple neural mapping from the visual field to the lateral geniculate leads to an interaction between patterns which, combined with our assumptions above, seems to lead to a progression of patterns from column to column of the type observed by Hubel and Wiesel in monkey.
01 Jan 1975
TL;DR: The form is one of a linear combination of beta densities with random coefficients, and the order of convergence of the Bernstein polynomial estimate is comparable to that of other methods.
Abstract: Publisher Summary This chapter presents a Bernstein polynomial approach to density function estimation and describes the Bernstein polynomial estimate of f(x). The form is one of a linear combination of beta densities with random coefficients. The order of convergence of the Bernstein polynomial estimate is comparable to that of other methods. The estimate chapter has a significant practical advantage as it is well adapted to computation.
TL;DR: Evidence has been presented supporting the hypothesis that at least 2 different types of mechanisms may be involved in aspirin intolerance, one resulting in bronchospasm and the other producing urticaria/angioedema.
Abstract: Evidence has been presented supporting the hypothesis that at least 2 different types of mechanisms may be involved in aspirin intolerance, one resulting in bronchospasm and the other producing urticaria/angioedema. Bronchospasm is the predominant symptom of aspirin intolerance in patients who have asthma. In contrast, the predominant symptom of aspirin intolerance in patients who have rhinitis is urticaria/angioedema. In the bronchospastic type of aspirin intolerance, there is a significant correlation with an increased frequency of nasal polyposis, and with a similar ageonset of asthma and aspirin intolerance. These correlations were not present in the urticari/angioedema type. Additional evidence for familial occurrence of aspirin intolerance is presented, and its relationship with subtypes of aaspirin intolerance is discussed. In a double-blind, crossover study with normal control subjects matched by age and sex 15% (6/40) of aspirin-intolerant individuals had significant adverse reactions to tartrazine challenge and not to the placebo. None of the 40 normal control subjects had any adverse reactions.
TL;DR: In this article, the authors present conditions générales d'utilisation (http://www.numdam.org/conditions), i.e., Toute copie ou impression de ce fichier doit contenir la présente mention de copyright.
Abstract: © Publications mathématiques de l’I.H.É.S., 1975, tous droits réservés. L’accès aux archives de la revue « Publications mathématiques de l’I.H.É.S. » (http:// www.ihes.fr/IHES/Publications/Publications.html) implique l’accord avec les conditions générales d’utilisation (http://www.numdam.org/conditions). Toute utilisation commerciale ou impression systématique est constitutive d’une infraction pénale. Toute copie ou impression de ce fichier doit contenir la présente mention de copyright.
01 Apr 1975
TL;DR: Having been delegated the authority to make the key decisions, effective corporate power is conventionally defined, following A. A. Berle, Jr. and Gardiner Means as the ability to choose the membership of the board.
Abstract: Dans l'introduction, l'auteur presente le probleme de l'etude des conseils de direction des grandes compagnies americaines par l'analyse des reseaux. En effet, l'emploi le plus courant d'un membre d'un conseil de direction d'une compagnie est celui de directeur du conseil d'une autre compagnie. L'etude de cette question s'est limitee jusqu'ici a des sous-ensembles prealablement choisis de la population des grandes compagnies. Ce type d'etude, en outre, s'est presque toujours base sur une orientation theorique definie d'avance.Dans la deuxieme partie de cet article, l'auteur decrit les quatre orientations theoriques principales : controle directorial ; controle de l'environnement et reciprocite ; controle financier ; controle par hegenomie de classe. Les resultats prevus par chacune de ces orientations sont aussi clairement decrits.Dans la troisieme partie, l'auteur presente la methode de recherche des "cliques" a l'interieur d'un reseau dense de liens entre des points. Comme l'auteur s'est donne comme but...
TL;DR: In this article, the interface excitations associated with the inversion layer of a metal-insulator-semiconductor structure are investigated, and the dependence of the coupled modes on the insulator thickness and the gate-electrode plasma frequency are studied.
Abstract: The interface excitations associated with the inversion layer of a metal-insulator-semiconductor structure are investigated. These excitations can be regarded as coupled modes whose components are the two-dimensional-electron-gas plasmon and the surface plasmon of the metal-insulator interface. The dependence of the coupled modes on the insulator thickness and the gate-electrode plasma frequency are studied.