Showing papers by "University of Chicago published in 1970"
TL;DR: In this article, the free volume model for molecular transport in dense fluids is improved by taking account of the variable magnitude of the diffusive displacement, which may display more clearly the relation between the freevolume model and the Enskog theory.
Abstract: We have improved the free‐volume model for molecular transport in dense fluids, as developed in earlier papers, by taking account of the variable magnitude of the diffusive displacement. The development is carried through in a way which may display more clearly the relation between the free‐volume model and the Enskog theory. Implicit in the free‐volume development is the association, on the average, of a correlation factor f(a) with each magnitude, a, of the displacement. It is assumed that f(a) is a step function which is zero, because of the predominance of back scattering, for a a.* This corresponds to dividing the displacements sharply into two categories, one “gaslike” and the other “solidlike.” Molecular dynamics computations have shown that the self‐diffusion coefficient in the hard‐sphere fluid at the highest densities is falling precipitously, with increasing density, away from the Enskog values. It appears that this density trend, which was attributed to back scattering, ...
688 citations
TL;DR: Theoretical and experimental studies indicate that, with a high-resolution scanning electron microscope, it is now possible to obtain pictures of a single heavy atom resting on a thin carbon substrate.
Abstract: Theoretical and experimental studies indicate that, with a high-resolution scanning electron microscope, it is now possible to obtain pictures of a single heavy atom resting on a thin carbon substrate.
664 citations
TL;DR: In this article, a method of estimating the parameters of the normal ogive model for dichotomously scored item-responses by maximum likelihood is demonstrated, which requires numerical integration in order to evaluate the likelihood equations, but is shown to be straightforward in other respects.
Abstract: A method of estimating the parameters of the normal ogive model for dichotomously scored item-responses by maximum likelihood is demonstrated. Although the procedure requires numerical integration in order to evaluate the likelihood equations, a computer implemented Newton-Raphson solution is shown to be straightforward in other respects. Empirical tests of the procedure show that the resulting estimates are very similar to those based on a conventional analysis of item “difficulties” and first factor loadings obtained from the matrix of tetrachoric correlation coefficients. Problems of testing the fit of the model, and of obtaining invariant parameters are discussed.
619 citations
TL;DR: In this paper, the problem of the band structure of semiconductor alloy systems is treated by both the dielectric two-band method and by the use of an empirical (local) pseudopotential.
Abstract: The problem of the band structure of semiconductor alloy systems is treated by both the dielectric two-band method and by the use of an empirical (local) pseudopotential. With both methods, calculations are made in the virtual-crystal approximation assuming linear dependence on alloy concentration of the lattice constant and the parameters of the two methods. Contrary to some previous assertions, both methods predict, in general, a nonlinear dependence of the interband gaps on concentration. An estimate is also made of the effects of second-order perturbations to the virtual-crystal approximation, i.e., the effect of disorder. Of particular interest are the lowest direct and indirect energy gaps and the deviations of these from linearity. The treatment is confined to alloys of compounds having the formula ${A}^{N}{B}^{8\ensuremath{-}N}$, but quaternary and more complicated alloys may be treated as easily as the ternary alloys to which most previous experimental work has been confined. Results are compared to experiment and to the empirical formula of Thompson and Woolley. We find that, with one free parameter, the dielectric method gives good agreement with experiment, but that the local-pseudopotential method apparently does not yield satisfactory results for this problem.
548 citations
TL;DR: These models, called conjunctive and disjunctive, are approximated here by suitable nonlinear functions of utility and are shown to give a better fit to certain decision data than the linear model.
Abstract: An important problem in decision making concerns finding the utility of a multidimensional stimulus. This has traditionally been done by assuming that total utility is a linear function of the attributes of the stimulus. In clinical decision making, the linear regression model has been used to predict and diagnose on the basis of multidimensio nal information as well as to approximate the clinician's own judgment. Other nonlinear, noncompensatory models are available for combining information. These models, called conjunctive and disjunctive, are approximated here by suitable nonlinear functions of utility. They are then shown to give a better fit to certain decision data than the linear model. The factors affecting the use of these models and their implications are discussed.
547 citations
TL;DR: In this article, the Born-von Karman force constants in an arbitrary solid, crystalline or amorphous, are derived in terms of the complete inverse dielectric function of the electrons.
Abstract: The microscopic quantum-mechanical expressions for the Born-von Karman force constants in an arbitrary solid, crystalline or amorphous, are derived in terms of the complete inverse dielectric function ${\ensuremath{\epsilon}}^{\ensuremath{-}1}(\mathrm{r}, {\mathrm{r}}^{\ensuremath{'}})$ of the electrons The many-body nature of the electrons is treated exactly; only the Born-Oppenheimer approximation is made. Born's translation and rotation invariance conditions are shown to be satisfied by the microscopic force constants. In the case of a perfect crystal, it is shown for the first time that the microscopic formulas recapture completely the phenomenological form of the dynamical matrix; in particular, the microscopic expression for the effective charge in an insulator is found. We prove that the charge neutrality of the system implies the "effective charge neutrality" condition and that, consequently, all acoustic-mode frequencies vanish at long wavelength. This condition may be stated as a useful property of ${\ensuremath{\epsilon}}^{\ensuremath{-}1}$ which we term the acoustic sum rule. Many results of the phenomenological theory, e.g., the generalized Lyddane-Sachs-Teller relation, carry over exactly to the microscopic theory.
508 citations
TL;DR: Membranes prepared from HEp-2 cells infected with herpes simplex virus and free from soluble proteins, virus, ribosomes, and other cellular constituents were solubilized and subjected to electrophoresis on acrylamide gels to show the synthesis of host proteins and glycoproteins ceases after infection.
Abstract: Membranes prepared from HEp-2 cells infected with herpes simplex virus and free from soluble proteins, virus, ribosomes, and other cellular constituents were solubilized and subjected to electrophoresis on acrylamide gels. The electropherograms showed the following. (i) The synthesis of host proteins and glycoproteins ceases after infection. However, the spectrum of host proteins in membranes remains unaltered. (ii) Between 4 and 22 hr postinfection, at least four glycoproteins are synthesized and bound to the smooth cytoplasmic membranes. On electrophoresis, these glycoproteins form two major and two minor bands in the gel and migrate with proteins ranging from 50,000 to 100,000 daltons in molecular weight. (iii) The same glycoproteins are present in all membranes fractionated by density and in partially purified virus. The implications of the data are discussed.
501 citations
TL;DR: In this paper, the details of the high-resolution photoabsorption spectrum of the H 2 near threshold observed by Herzberg were derived. Butler et al. applied Seaton's multichannel quantum defect method under schematic conditions, and might serve as a basis for further developments.
Abstract: Formulas are developed which account for the details of the high-resolution photoabsorption spectrum of ${\mathrm{H}}_{2}$ near threshold observed by Herzberg. The treatment illustrates the application of Seaton's multichannel quantum defect method under schematic conditions, and might serve as a basis for further developments.
435 citations
TL;DR: Carbonaceous chondrites noble gases measurement by mass spectroscopy, discussing compositional trends and origins as mentioned in this paper, discussed compositional trend and origins of chondrite noble gases.
380 citations
TL;DR: In this article, the problem of light collection is examined from first principles within the framework of geometrical optics, and a generalization of the Abbe sine law appropriate to non-imaging systems is presented.
Abstract: The problem of light collection is examined from first principles within the framework of geometrical optics. From the outset, we distinguish between light collection and the usual theory of image formation. From phase-space considerations, we derive the sine inequality, a generalization of the Abbe sine law appropriate to nonimaging systems. We construct two- and three-dimensional nonimaging systems that reduce the f number to the least allowed by the sine inequality. Such systems give substantially improved light collection as compared with conventional systems.
372 citations
TL;DR: In this paper, the authors considered the evolution of an elongated rotating configuration by gravitational radiation and the possibility of a secular instability being induced by it, in the context of the classical homogeneous figures of Maclaurin and Jacobi.
Abstract: The evolution of an elongated rotating configuration by gravitational radiation and the possibility of a secular instability being induced by it are considered in the context of the classical homogeneous figures of Maclaurin and Jacobi. The triaxial Jacobian ellipsoid evolves in the direction of increasing angular velocity and approaches (exponentially) the point of bifurcation where it ceases to radiate. Further, radiation reaction does not make the Maclaurin spheroid secularly unstable past the point of bifurcation.
TL;DR: In this paper, a class of models analogous to those used in the analysis of variance is discussed, and a method for computing the expected cell counts for the different models is presented.
Abstract: Ecological data often come in the form of multidimensional tables of counts, referred to as contingency tables. During the last decade several new methods of analyzing such tables have been proposed. Here, a class of models analogous to those used in the analysis of variance is discussed, and a method for computing the expected cell counts for the different models is presented. Two differenet tests for checking the goodness—of—fit of a particular model are then examined. The first is the simple generalization of the Pearson chi—square test statistic, while the second is referred to as the likelihood—ratio chi—square test statistic. Both have the same asympototic g2 distribution. The likelihood—ratio statistic can be used in the selection of a suitable model, via the technique of partitioning. All of the methods presented are illustrated using data collected by Schoener on lizards from the West Indies. See full-text article at JSTOR
TL;DR: In this article, the authors analyzed available snow particle-size distribution data and concluded that the equation, ND = N0 exp (−ΛD), describes the size distribution data for snow adequately.
Abstract: Some general properties of exponential particle-size distributions are discussed. Especially significant are the corrections to calculated liquid water content, precipitation rate, radar reflectivity, and median volume diameter resulting from truncations of the exponential size spectrum at maximum diameters less than infinity. These properties are used to analyze available snow particle-size distribution data. It is concluded that the equation, ND = N0 exp (−ΛD), describes the size distribution data for snow adequately. In the equation NDΔD is the concentration of snow particles of melted diameter D to D + ΛD, N0 = 2.50 × 103 R−0.94 [mm−1 m−3], and Λ = 22.9 R−0.45 [cm−1], where R is the precipitation rate in mm hr−1. These expressions for N0 and Λ differ from those given by Gunn and Marshall, and have the advantage that analytical manipulation of the size distribution equation yields consistent results. The following equations have been found for the precipitation content W, the median volume dia...
TL;DR: This report extends and systematizes the observations on the phase resetting of the circadian rhythm of pupal eclosion in populations of the fruitfly, Drosophila pseudoobscura, in response to a single discrete perturbation.
TL;DR: In this paper, the major constituents of chondritic matter are fractionated among the several chondrite classes in the solar nebula, starting from material of carbonaceous chondrites composition.
TL;DR: These data are interpreted as an unequivocal demonstration of the inductive role of the dental mesenchyme and the nature of epithelio-mesenchymal interactions in the developing mouse integument.
Abstract: The response of embryonic mouse dental epithelium and mesoderm to tissues of ectopic origin was examined. Isolated molar or incisor mesoderm was confronted with epithelium isolated from the plantar surface of the embryonic mouse foot plate or from the snout. Harmoniously structured teeth were formed from the foot epithelium and incisor or molar mesoderm. These data are interpreted as an unequivocal demonstration of the inductive role of the dental mesenchyme. Teeth were absent in confrontations of dental mesenchyme and snout epithelium. The presence of hair follicles in these explants is described and discussed with reference to other integumental epithelio-mesenchymal interactions. Dental epithelium forms keratinizing surface-like epithelium and invading bands of epithelium in association with foot mesoderm; definitive structures are not formed. On the other hand, when incisor or molar epithelium is associated with snout mesoderm, hair follicles are seen in addition to keratinizing surface-like epithelial configurations. The roles of the epithelial and mesenchymal tissues and the nature of epithelio-mesenchymal interactions in the developing mouse integument are discussed.
TL;DR: In this article, a theory for the finite-amplitude behavior of unstable baroclinic waves in a quasi-geostrophic two-layer model is presented, and it is shown that in the absence of dissipation, the equilibrated finite amplitude state exhibits an oscillation.
Abstract: A theory is presented for the finite-amplitude behavior of unstable baroclinic waves in a quasi-geostrophic two-layer model. It is shown that in the absence of dissipation the equilibrated finite-amplitude state exhibits an oscillation, both of the mean flow and the baroclinic wave. On the other hand, if sufficient dissipation is present, the final state is a wave whose amplitude is steady and the approach to that state is non-oscillatory.
TL;DR: The Hartree approximation of the dielectric response of an idealized metal with two plane parallel surfaces is calculated in this article, with special emphasis on the limit of infinite thickness.
Abstract: The dielectric response at frequency $\ensuremath{\omega}$ (neglecting retardation) of an idealized metal with two plane parallel surfaces is calculated in the Hartree approximation, with special emphasis on the limit of infinite thickness. It is assumed that the unperturbed system may be regarded as consisting of free particles confined between plane parallel boundaries. The validity of this approximation is discussed. The response is expressed in terms of the perturbing source potential in Fourier representation, and involves the inverse of an infinite matrix E; E is calculated in the limit of infinite interfacial separation at $\ensuremath{\omega}=0$ and at $\ensuremath{\omega}\ensuremath{
e}0$ for one-dimensional potentials. A dielectric function ${\ensuremath{\epsilon}}_{\mathrm{Q}}(\ensuremath{\omega})$, where Q is a wave vector parallel to the surface, is introduced, which is inversely proportional to the sum of all elements in ${\mathbf{E}}^{\ensuremath{-}1}$. The surface-plasmon dispersion relation is given implicitly by ${\ensuremath{\epsilon}}_{\mathrm{Q}}(\ensuremath{\omega})+1=0$. The classical image theorem for a semi-infinite dielectric medium is obeyed at a given Q and $\ensuremath{\omega}$ if ${\ensuremath{\epsilon}}_{\mathrm{Q}}(\ensuremath{\omega})$ replaces the classical dielectric constant. The Fermi-Thomas approximation, the lowest-order correction to it, and the classical (high-frequency) approximation are derived. In agreement with earlier work, the corrections to the classical approximation, which relate to the damping and dispersion of surface plasmons, are found to be linear in the wave vector. Numerical results are obtained for a uniform static electric field normal to the surface. The calculated screening length $d$ is well approximated by $d\ensuremath{\simeq}{\ensuremath{\lambda}}^{\ensuremath{-}1}+\frac{1}{8}{\ensuremath{\lambda}}_{F}$, where ${\ensuremath{\lambda}}^{\ensuremath{-}1}$ is the Fermi-Thomas screening length and ${\ensuremath{\lambda}}_{F}$ the Fermi wavelength, the second term representing the lowest quantum correction; this result is 2-3 times ${\ensuremath{\lambda}}^{\ensuremath{-}1}$ in the metallic density range, owing almost entirely to the low electron density in the surface region. The results are compared with experiment. The long-range Friedel oscillations are discussed in an appendix.
TL;DR: In this article, simple models of the electronic structure of disordered materials are reviewed and the universal features of these models and their consequences for amorphous semiconductors are discussed.
Abstract: The existing simple models of the electronic structure of disordered materials are reviewed. The focus is on the universal features of these models and their consequences for amorphous semiconductors. Simple plausibility arguments are given showing that continuous bands of extended states with tails of localized states associated with fluctuations within the disordered material can always be expected. Models for the mobility in which shoulders occur at the energies of transition from localized to extended states are reviewed. It is a mobility gap rather than a gap in the density of states which is responsible for the activated temperature dependence of the conductivity in amorphous semiconductors. Hopping conduction and the nature of the electronic motion in extended states near the mobility edges is discussed. The latter is likened to Brownian motion within certain limitations. Finally, the Anderson transition is discussed within the present models.
TL;DR: Of the 10 experimental animals, each, without exception, showed full maternal behavior at between 35 and 40 hr, which represents a significant reduction in latency from the average of 6–7 days characteristic of untreated nulliparae, but represents as well a uniformity in time of onset closely approaching that exhibited by the puerperal female.
TL;DR: The authors make oversimplified assumptions about the structure of husband-wife roles in consumer decisions and the sufficiency of responses from one spouse, and make assumptions about how well one spouse responds to questions about the dimensionalit...
Abstract: Researchers often make oversimplified assumptions about the structure of husband-wife roles in consumer decisions and the sufficiency of responses from one spouse. Questions about the dimensionalit...
TL;DR: This chapter discusses receptor-proteins for androgens and the mode of action of androgens on gene transcription in ventral prostate and the search for the trigger mechanisms of hormones relies on the trial addition of hormones to an in vitro system.
Abstract: Publisher Summary This chapter discusses receptor-proteins for androgens and the mode of action of androgens on gene transcription in ventral prostate. The primary molecular processes by which hormones elicit their remarkable effects are still unclear. Historically, the study of the mechanism of action of hormones has followed very closely the advance in knowledge of the basic molecular processes operating in living organisms. It is quite natural that one of the most widely used approaches has been to study the effect of hormones on isolated enzymes. With few exceptions, the results have been rather disappointing. Generally, the effects were observable only under conditions unlikely to be physiological, or they could not be correlated with in vivo situations. In the search for the trigger mechanisms of hormones, one generally relies on the trial addition of hormones to an in vitro system believed to be the earliest event in a sequence of hormone effects in vivo. However, the in vivo time sequences for visible hormone effects may depend more on the relative time required to magnify each of the sequential events than on the true order in the initial chain of processes.
TL;DR: The upper lateral incisor was most frequently missing and was the tooth most often involved in the different combinations of congenitally missing teeth.
Abstract: Among 14,940 Evanston and Oak Park, Illinois, white and Negro students 11 to 15 years of age, there were 521 children in whom permanent teeth were congenitally missing. The incidence, frequency, and combinations of congenitally missing teeth were studied. An overall incidence of 3.49 was found. The upper lateral incisor was most frequently missing and was the tooth most often involved in the different combinations of congenitally missing teeth.
TL;DR: The data suggest that the membrane may exist in two physical states, one above and the other below a transition point determined by the composition of the lipid phase.
TL;DR: In this paper, a method of analysis of all level positions in multiple strongly perturbed series of levels is presented and illustrated by examples from the rare gas and Ba spectra, which emphasizes the dependence of a perturbation on the periodicity of the perturbing series and aims at extracting significant information from experimental data in compact form.
Abstract: A method of analysis of all level positions in multiple strongly perturbed series of levels is presented and illustrated by examples from the rare gas and Ba spectra. The method is suggested by Seaton's multichannel quantum defect theory but is presented here as an empirical approach. It emphasizes the dependence of a perturbation on the periodicity of the perturbing series and aims at extracting significant information from experimental data in compact form; this goal will be pursued in later works.
TL;DR: Structural changes in endosperm cells of germinating castor beans were examined and complemented with a cytochemical analysis of staining with diaminobenzidine (DAB), which revealed an increase in microbodies, mitochondria, plastids with an elaborate tubular network, and the formation of a new protein body referred to as a dilated cisterna.
Abstract: Structural changes in endosperm cells of germinating castor beans were examined and complemented with a cytochemical analysis of staining with diaminobenzidine (DAB). Deposition of oxidized DAB occurred only in microbodies due to the presence of catalase, and in cell walls associated with peroxidase activity. Seedling development paralleled the disappearance of spherosomes (lipid bodies) and matrix of aleurone grains in endosperm cells. 6 to 7 days after germination, a cross-section through the endosperm contained cells in all stages of development and senescence beginning at the seed coat and progressing inward to the cotyledons. Part of this aging process involved vacuole formation by fusion of aleurone grain membranes. This coincided with an increase in microbodies (glyoxsomes), mitochondria, plastids with an elaborate tubular network, and the formation of a new protein body referred to as a dilated cisterna, which is structurally and biochemically distinct from microbodies although both apparently develop from rough endoplasmic reticulum (ER). In vacuolate cells microbodies are the most numerous organelle and are intimately associated with spherosomes and dilated cisternae. This phenomenon is discussed in relation to the biochemical activities of these organelles. Turnover of microbodies involves sequestration into autophagic vacuoles as intact organelles which still retain catalase activity. Crystalloids present in microbodies develop by condensation of matrix protein and are the principal site of catalase formerly in the matrix.
TL;DR: Cardiac microsomes represent a heterogeneous fraction which contains mitochondrial, plasma membrane and lysosomal enzymes in addition to markers believed to originate in the sarcoplasmic reticulum in that prolonged homogenization of ventricular myocardium increases both the yield of microsomal protein and the proportion of the mitochondrial contaminant.
TL;DR: To compare degrees of protein polymorphism and underlying genic heterozygosity in a classic phylogenetic "relic," the horseshoe or king crab (Limulus polyphemus), and in several representatives of horotelic lines (those evolving at standard rates) for which data are already available, a test of the mutationists' thesis is allowed.
Abstract: To many early evolutionists, particularly those of the mutationist school, the existence of evolutionarily stable forms ("living fossils" or phylogenetic "relics") posed a difficult problem, and, even among contemporary biologists, the feeling that "a long-standing stability of organization seems antithetical to the concept of evolution" may persist (Volpe, 1967:140). In the early part of this century, it was popularly believed that stable or slowly evolving (bradytelic) lines lacked the genetic variation necessary for more rapid evolution as a result of having abnormally low mutation rates; as Mayr (1963) puts it, a lack of variation in time and space was interpreted as a reflection of genotypic stability. Largely because of the influence of Simpson (1944), Stebbins (1944), Schmalhausen (1949), and Dobzhansky (1951), the mutationists' interpretation of bradytely has now been all but abandoned by evolutionists in favor of the view that the principal factors controlling rates of evolution are to be found in the organism-environment relationship. Additionally, Mayr (1963 :304) has suggested that phenotypic "uniformity in space and time is due to a highly perfected 'buffering system,' in other words, to genetic homeostasis." The ecological hypothesis is well expressed in Simpson's (1944:141) conclusions that "the final and probably the most fundamental factor in the relationship is that bradytelic groups are so well adapted to a particular, continuously available environment that almost any mutation occurring in them must be disadvantageous" and that "bradytely results from the equilibrium of large breeding populations of animals specifically adapted to a continuously available environment that is relatively invariable . . . ." Yet, as Mayr (1963) notes, there is no evidence to refute (or to support) the hypothesis that bradytely results from loss of mutability. The recent development of electrophoretic techniques for demonstrating allelic variation at loci controlling enzymes and other proteins in natural populations (Hubby and Lewontin, 1966; Lewontin and Hubby, 1966) permits a test of the mutationists' thesis. The purpose of this study is to compare degrees of protein polymorphism and underlying genic heterozygosity in a classic phylogenetic "relic," the horseshoe or king crab (Limulus polyphemus), and in several representatives of horotelic lines (those evolving at standard rates) for which data are already available. Evidence of a level of genetic variation in Limulus similar to that in horotelic forms will support the modern ecological and homeostatic interpretations of bradytely. But if the mutationists' thesis is valid, Limulus should show an unusually low degree of polymorphism at its genetic loci. Limulus polyphemus is one of five living species of the Subclass Xiphosura, a group of marine arthropods usually placed with the Subclass Eurypterida (extinct giant water scorpions) in the Class Merostomata of the Subphylum Chelicerata. Following a period of adaptive radiation in the early and middle Paleozoic, the Merostomata became much less prominent after the Permian. Several Mesozoic forms are known in the Family Mesolimulidae, but by the Tertiary the fossil record is all but absent. There are presently three living genera, all belonging to the Family Limulidae, only one of which, Tachypleus, is known from the fossil record (Stormer,
TL;DR: Carbon dioxide and organic compounds made by a Fischer-Tropsch reaction at 400�K show a kinetic isotope fractionation of 50 to 100 per mil, similar to that observed in carbonaceous chondrites, which supports the view that organic compounds in meteorites were produced by catalytic reactions between carbon monoxide and hydrogen in the solar nebula.
Abstract: Carbon dioxide and organic compounds made by a Fischer-Tropsch reaction at 400 degrees K show a kinetic isotope fractionation of 50 to 100 per mil, similar to that observed in carbonaceous chondrites. This result supports the view that organic compounds in meteorites were produced by catalytic reactions between carbon monoxide and hydrogen in the solar nebula.