Showing papers by "Brown University published in 1968"
TL;DR: In this article, the authors developed a general theory of heat conduction for nonlinear materials with memory, a theory which has associated with it finite propagation speeds, i.e., a thermal disturbance at any point in the body is felt instantly at every other point; or in terms more suggestive than precise, the speed of propagation of disturbances is infinite.
Abstract: > 0 is a constant. This equation, which is parabolic, has a very unpleasant feature: a thermal disturbance at any point in the body is felt instantly at every other point; or in terms more suggestive than precise, the speed of propagation of disturbances is infinite. In this paper we develop a general theory of heat conduction for nonlinear materials with memory, a theory which has associated with it finite propagation speeds. In Section 3 we determine the restrictions that thermodynamics places on our constitutive relations. We show that our theory differs f rom other theories of heat conduction in that the heat-flux, like the entropy, is determined by the functional for the free-energy. In Section 6 we study the propagation of certain types of weak discontinuities. We show that in certain circumstances waves travelling in the direction of the heat-flux vector propagate faster than waves travelling in the opposite direction. In Section 7 we deduce the linearized theory appropriate to infinitesimal temperature gradients. We show that the linearized constitutive equation for the heat-flux q has the form: 1
1,064 citations
TL;DR: The kinetics of biopolymerization on nucleic acid templates is discussed and the model introduced allows for the simultaneous synthesis of several chains, of a given type, on a common template, e.g., the polyribosome situation.
Abstract: The kinetics of biopolymerization on nucleic acid templates is discussed. The model introduced allows for the simultaneous synthesis of several chains, of a given type, on a common template, e.g., the polyribosome situation. Each growth center [growing chain end plus enzyme(s)] moves one template site at a time, but blocks L adjacent sites. Solutions are found for the probability nj(t) that a template has a growing center that occupies the sites j — L + 1,…, j at time t. Two special sets of solutions are considered, the uniform-density solutions, for which nj(t) = n, and the more general steady-state solutions, for which dnj(t)/dt = 0. In the uniform-density case, there is an upper bound to the range of rates of polymerization that can occur. Corresponding to this maximum rate, there is one uniform solution. For a polymerization rate less than this maximum, there are two uniform solutions that give the same rate. In the steady-state case, only L = 1 is discussed. For a steady-state polymerization rate less than the maximum uniform-density rate, the steady-state solutions consist of either one or two regions of nearly uniform density, with the density value(s) assumed in the uniform region(s) being either or both of the uniform-density solutions corresponding to that polymerization rate. For a steady-state polymerization rate equal to or slightly larger than the maximum uniform-density rate, the steady-state solutions are nearly uniform to the single uniform-density solution for the maximum rate. The boundary conditions (rate of initiation and rate, of release of completed chains from the template) govern the choice among the possible solutions, i.e., determine the region(s) of uniformity and the value(s) assumed in the uniform region(s).
836 citations
TL;DR: In this article, piezoelectroreflectance in Ge, Si and GaAs was studied for uniaxial stress effects on electronic energy bands in three different energy bands.
Abstract: Piezoelectroreflectance in Ge, Si and GaAs studied for uniaxial stress effects on electronic energy bands
594 citations
TL;DR: In this article, a steady-state technique for measuring heat capacity using ac heating is described, where heat is applied sinusoidally in time to a sample coupled thermally to a reservoir; the resultant equilibrium temperature of the sample contains a term that is both inversely proportional to the heat capacity and measurable with high precision.
Abstract: A steady-state technique for measuring heat capacity using ac heating is described. Heat is applied sinusoidally in time to a sample coupled thermally to a reservoir; the resultant equilibrium temperature of the sample contains a term that is both inversely proportional to the heat capacity and measurable with high precision. The effects of various corrections that must be applied to the data are considered in detail. Measurements of the absolute magnitude of the heat capacity of indium and the field dependence of the heat capacity of beryllium have been made and are used to illustrate the power of the method. The observed quantum oscillations in the heat capacity of beryllium are in agreement with predictions based on other measurements.
573 citations
TL;DR: LaSalle stability theorems refined for ordinary differential equations, discussing classical Liapunov results on system stability were discussed in this article, where they were refined for the case of continuous systems.
546 citations
TL;DR: Data show a parallelism over the last 150,000 years between changes in Earth's climate and changes in the summer insolation predicted from cycles in the tilt and precession of Earth's axis.
Abstract: Barbados provides a possibly unique opportunity for reconstruction of the times and elevations of late-Pleistocene high stands of the sea. The island appears to be rising from the sea at a uniform rate that is fast enough to separate in elevation coral-reef tracts formed at successive high stands of the sea. Unaltered coral found in the lower terraces enables high-precision Th(230): U(234) and Pa(231): U(235) dating. Three distinct high stands of the sea are found about 122,000, 103,000, and 82,000 years ago. New Pa(231) and Th(230) dates from a deep-sea core also indicate that Ericson's W-X cold-to-warm climatic change occurred close to 126,000 years ago. These data show a parallelism over the last 150,000 years between changes in Earth's climate and changes in the summer insolation predicted from cycles in the tilt and precession of Earth's axis.
403 citations
TL;DR: Rate equations are derived by inspecting the reaction pathways without solving simultaneous equations in the conventional way for the reversible single substrate-single modifier system, the partial equilibrium ping-pong bi-bi mechanism, the general mechanism for two- Substrate system, and a complicated three-substrate mechanism.
292 citations
TL;DR: In this article, a n integral series representation for non-linear viscoelastic response to an arbitrary strain (or stress) history is obtained, where the series has the distinctive property that it terminates at the n th term whenever the strain or stress history is an n-step history.
Abstract: A n integral series representation is obtained for non-linear viscoelastic response to an arbitrary strain (or stress) history. The series is arranged so that experimental data can be incorporated directly. Each of the terms has a definite intrinsic meaning that is independent of the choice of strain measure. The first term is a single integral with a non-linear integrand determined completely by single-step creep or relaxation tests. The n th term is obtained directly by the difference, if any is observed, between the experimental results for n -step tests and the prediction based on ( n −1)-step data. The series has the distinctive property that it terminates at the n th term whenever the strain (or stress) history is an n -step history. p]Previously published experimental data on non-linear viscoelastic behaviour are re-interpreted on the basis of this theory; in most cases they agree very closely with the single integral approximation given by the first term alone. p]The generalization to three-dimensional form and the implications of isotropy are also given.
250 citations
TL;DR: Partial inhibition of vision occurs during voluntary saccadic eye movements as discussed by the authors, measured by detection of a target flashed at various times in relation to the saccade. But the time course of partial inhibition is not described.
Abstract: Partial inhibition of vision occurs during voluntary saccadic eye movements. This paper reports its time course, measured by detection of a target flashed at various times in relation to the saccade. One value of stimulus luminance was chosen which was nearly always detected by the fixating eye, but hardly ever by the moving eye. A dot pattern was presented to the fovea in 6-μsec flashes of this luminance under photopic viewing conditions. Photographic records of each saccade made by the subject and each stimulus flash permitted analysis of the precise time of occurrence of the flash in relation to the saccade. Under these conditions, curves from three subjects showed that detection decreases to 50% for a flash occurring about 20 msec before the onset of the saccade and reaches a minimum such that vision of the flash is almost completely absent when it occurs during the saccade. Detection then begins to improve, reaching the 50% point again for a flash occurring about 75 msec after the onset of the eye movement. Results are compared with other studies which employed different viewing conditions, and the use of the data to support a notion of partial central inhibition is evaluated.
246 citations
TL;DR: Antibody was localized by electron microscopy within differentiating and mature plasma cells of the spleens of hyperimmunized rabbits by coupling it with its antigen and revealing the sites of peroxidase activity cytochemically.
Abstract: Antibody was localized by electron microscopy within differentiating and mature plasma cells of the spleens of hyperimmunized rabbits. Horseradish peroxidase was used as antigen. Intracellular antibody to peroxidase was revealed in glutaraldehyde-fixed tissue by coupling it with its antigen and then revealing the sites of peroxidase activity cytochemically. Antibody first appears in the perinuclear space of hemocytoblasts where it persists through differentiation into immature plasma cells, but it disappears from this site in mature plasma cells. Concomitant with the development of the ergastoplasm, antibody accumulates in many but not all of its cisternae. Antibody is present in the lamellar portion of the Golgi apparatus in all phases of plasmacytic differentiation. Mature plasma cells exhibit two types of antibody distribution, a concentration into large spherical intracisternal granules or an overflowing into all parts of the cytoplasm.
234 citations
TL;DR: That this increase in myosin and creatine kinase is strictly a function of the multinuclear cells is demonstrated by experiments in which the mononuclear cell population has been drastically reduced by treatment with 5‐fluorodeoxyuridine shortly after fusion.
Abstract: Cytodifferentiation of skeletal muscle has been studied in cell cultures derived from leg muscle of 12-day chicken embryos. Myogenesis in cell culture closely simulates myogenesis in vivo, but is more highly synchronized. Massive cell fusion occurs in control cultures between the second and third days in vitro, during which time most of the myoblasts are swept into syncytia. On successive days, the syncytia mature into cross-striated muscle fibers, and the cultures are progressively overgrown by fibroblastic cells. Myosin-containing cells can be detected at any time by immunofluorescence, and myosin has been measured by quantitative immunological precipitation as early as 3 days in vitro, a few hours after fusion. Myosin in the cultures increases over the next few days, and this is reflected in the rate of incorporation of labeled amino acids into immunologically precipitable myosin. Creatine kinase, assayed spectrophotometrically by linked dehydrogenase reactions, shows a similar pattern: measurable early but rapidly increasing in activity after fusion. That this increase in myosin and creatine kinase is strictly a function of the multinuclear cells is demonstrated by experiments in which the mononuclear cell population has been drastically reduced by treatment with 5-fluorodeoxyuridine shortly after fusion. Myosin synthesis has not been detectable in cells prevented from fusing by growth in 5-bromo-deoxyuridine, but low levels of creatine kinase have been demonstrated. Newly formed muscle fibers incorporate precursors into RNA at lower rates than do mononuclear cells. The relationship of this change in RNA synthesis to the formation of muscle proteins remains obscure.
TL;DR: In this paper, a Kramers-Kronig analysis of the thermoreflectance spectra of Si, AlSb, GaP, GaAs, GaSb and HgTe is presented.
Abstract: The thermoreflectance spectra of Si, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgSe, and HgTe are reported. Measurements were made on most materials at both room and liquid-nitrogen temperatures. The positions of the peaks observed are compared with previous reflectance and electroreflectance data. Some representative spectra were subjected to a Kramers-Kronig analysis, and the changes in the real and imaginary parts of the dielectric constant, induced by the change in temperature of the sample, were obtained. The resulting line shapes are compared with those derived from elementary theory. In order to achieve reasonable agreement between theory and experiment, it is found necessary to invoke the presence of excitons at all the interband edges. It is demonstrated that, under certain conditions, the type of critical point involved in the transition can be identified.
TL;DR: In this article, the principle of virtual work is employed to derive general relations governing geometrically nonlinear structural behavior and three general finite-element analysis models, namely, potential energy, direct and incremental, are formulated for nonlinear pre-and post-buckling analyses.
Abstract: The principle of virtual work is employed to derive general relations governing geometrically nonlinear structural behavior. From these basic relations, three general finite-element analysis models, namely, potential energy, direct and incremental, are formulated for nonlinear pre- and post-buckling analyses. In addition, a quadratic eigenvalue model is developed for the prediction of critical load levels. The analysis models are expressed in matrix notation within the framework of the finite-element technology and an inter-consistency is observed among the component matrices. These matrices are given geometrical interpretation and a hierarchy of nonlinearity is developed. Specific representative finite elements are considered and alternative computational procedures are associated with the several levels in the hierarchy of nonlinearity. Recommendations are made concerning the conduct of geometrically nonlinear finite-element analysis.
TL;DR: In this paper, the problem of finite-amplitude folding of an isolated, linearly viscous layer under compression and being embedded in a medium of lower viscosity is treated theoretically by using a variational method to derive finite difference.
Abstract: The problem of the finite-amplitude folding of an
isolated, linearly viscous layer under compression and
imbedded in a medium of lower viscosity is treated theoretically
by using a variational method to derive finite difference
equations which are solved on a digital computer. The
problem depends on a single physical parameter, the ratio
of the fold wavelength, L, to the "dominant wavelength" of
the infinitesimal-amplitude treatment, L_d. Therefore, the
natural range of physical parameters is covered by the
computation of three folds, with L/L_d = 0, 1, and 4.6, up
to a maximum dip of 90°. Significant differences in fold shape are found
among the three folds; folds with higher L/L_d have sharper
crests. Folds with L/L_d = 0 and L/L_d = 1 become fan folds
at high amplitude. A description of the shape in terms of
a harmonic analysis of inclination as a function of arc
length shows this systematic variation with L/L_d and is
relatively insensitive to the initial shape of the layer.
This method of shape description is proposed as a convenient
way of measuring the shape of natural folds. The infinitesimal-amplitude treatment does not
predict fold-shape development satisfactorily beyond a
limb-dip of 5°. A proposed extension of the treatment
continues the wavelength-selection mechanism of the
infinitesimal treatment up to a limb-dip of 15°; after
this stage the wavelength-selection mechanism no longer
operates and fold shape is mainly determined by L/L_d and
limb-dip. Strain-rates and finite strains in the medium are
calculated f or all stages of the L/L_d = 1 and L/L_d = 4.6
folds. At limb-dips greater than 45° the planes of
maximum flattening and maximum flattening rat e show the
characteristic orientation and fanning of axial-plane
cleavage.
TL;DR: It is concluded that the four permeases of E. coli K12 show some similarities in the sugars which they transport, and which act as inducers, however, the galactose and methylgalactoside permeases can be distinguished from each other and from the TMG I and TMG II permeases by their substrate and inducer preferences.
TL;DR: The results of alternative substrate studies were consistent with the hypothesis that the enzyme is multivalent with cooperative interaction between the active sites of Purine nucleoside phosphorylase, and it was not possible to detect any separation of these activities.
TL;DR: Linear nonautonomous random system stability, presenting theorem, two corollaries and second order examples as mentioned in this paper, and showing that linear non-autonomous system stability can be maintained.
Abstract: Linear nonautonomous random system stability, presenting theorem, two corollaries and second order examples
TL;DR: Two experiments were conducted in which five-month-old infants' visual fixations on silent, color motion pictures of a woman's face were observed, and no significant differences among kicking rates during the different stimuli were found.
TL;DR: This paper described a multibeam recording technique that produces redundant holograms that yield speckle free images of transparencies and shows that, in order to obtain an acceptably high signal-to-noise ratio, the area of this type hologram must be more than 100 times the area needed to achieve a desired image resolution.
Abstract: Holograms made of diffusely reflecting or diffusely illuminated objects can be scratched, spotted with dirt, and even broken into pieces without serious loss of information. This remarkable property is due to the redundancy introduced by diffuse illumination which, in effect, spreads information all over the hologram. Unfortunately, an unwanted by-product of diffuse illumination is speckle noise. This noise becomes more severe as hologram size is reduced. We show that, in order to obtain an acceptably high signal-to-noise ratio, the area of this type hologram must be more than 100 times the area needed to achieve a desired image resolution, making it prohibitively large for most data storage applications. In this paper we described a multibeam recording technique that produces redundant holograms that yield speckle free images of transparencies. We show that (1) achievable redundancy is equal to the ratio of actual hologram area to that area which just satisfies resolution requirements, (2) a two-dimensional phase grating provides a simple, efficient means for generating multiple beams, an optimized grating producing nine equally intense beams with 81% efficiency, (3) an optimized phase grating having a spatial period just equal to desired image resolution yields fourfold redundancy in holograms that are just large enough to encompass both side bands of the central (or zero order) beam, and (4) holograms having fourfold redundancy give reasonably good immunity to dust and scratches.
TL;DR: The results of the kinetic analysis are consistent with the predominant mechanism being an ordered bi-Bi reaction, with the nucleoside the first substrate to add to, and the purine base the last product to leave, the enzyme surface as mentioned in this paper.
TL;DR: In this article, the authors conjecture that the answer is affirmative in the case where M is irreducible and complete and d i m M ^ 3, where m is a complete hypersurface in a Euclidean space.
Abstract: where the endomorphism R(X, Y) operates on R as a derivation of the tensor algebra at each point of M. Conversely, does this algebraic condition (•*) on the curvature tensor field R imply that M is locally symmetric (i.e. Vi? = 0) ? We conjecture that the answer is affirmative in the case where M is irreducible and complete and d i m M ^ 3 . For partial and related results, see [4], p.ll, [9], Theorem 8, and [6]. The main purpose of the present paper is to give an affirmative answer in the case where M is a complete hypersurface in a Euclidean space. More precisely, we prove
TL;DR: It is known that if an adult deer is castrated in the autumn or winter after the velvet has been shed, its bony antlers are lost within several weeks and replaced by new ones that are retained permanently in velvet.
Abstract: “IF stags be mutilated,” wrote Aristotle1, “when, by reason of their age, they have as yet no horns, they never grow horns at all; if they be mutilated when they have horns, the horns remain unchanged in size, and the animal does not lose them.” What Aristotle already knew, other biologists confirmed centuries later2, and today we know that if an adult deer is castrated in the autumn or winter after the velvet has been shed, its bony antlers are lost within several weeks and replaced by new ones that are retained permanently in velvet. Such “castrate antlers” will continue to undergo annual increments of growth, and may eventually develop into very grotesque headpieces, or “perukes”. Only by administering testosterone or oestrogen can the velvet be induced to peel off and the antlers shed3.
TL;DR: Stability of stochastic processes defined by difference differential equations, noting properties of solution, weak infinitesimal operator, etc. as discussed by the authors, and the properties of the solution of the difference differential equation.
TL;DR: High-resolution proton nuclear magnetic resonance spectra of low- and high-density lipoproteins from human serum closely resemble those of dispersions of lipoprotein lipids in water, consistent with a predominantly micellar structure for the lipoproduins rather than with extensive hydrophobic association of lipid and protein.
Abstract: High-resolution proton nuclear magnetic resonance spectra of low- and high-density lipoproteins from human serum closely resemble those of dispersions of lipoprotein lipids in water. Linewidths of hydrocarbon proton absorptions are not increased in the lipoproteins. In contrast, apolar binding of lysolecithin on serum albumin causes extensive line-broadening and an upfield chemical shift of the hydrocarbon proton resonances of lysolecithin. The results are consistent with a predominantly micellar structure for the lipoproteins rather than with extensive hydrophobic association of lipid and protein.
TL;DR: Mitosis in the slime mold Physarum polycephalum occurs within the nuclear membrane, and the mitotic spindle appears as a small plaque of fibrous material at a short distance from the surface of the disintegrating nucleolus.