Showing papers by "Rensselaer Polytechnic Institute published in 1972"
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01 Jan 19722,790 citations
TL;DR: This study suggests that diffusive instabilities should also be sought in ecological interactions by presenting an example of their occurrence when cooperating prey interact with predators.
622 citations
TL;DR: In this paper, the transport processes occurring in an evaporating two-dimensional meniscus and adsorbed thin film formed on a superheated flat glass plate (0.272°C superheat) immersed in a pool of saturated carbon tetrachloride are modeled and analyzed.
415 citations
TL;DR: In this article, the authors derived the third-order and chromatic aberrations of the zone plate and showed that the image may be diffraction limited only if the illumination is relatively monochromatic.
Abstract: The zone plate is an optical device that depends on interference, not reflection or refraction, for its image-forming properties. Although the irradiance at the focus is only 110 that of a lens with the same aperture, a zone plate with 100 or more zones is capable of resolution equal to that of the lens. Zone plates can be used in spectral regions where conventional optics are unavailable and for special applications in the visible spectrum. This paper derives the third-order and chromatic aberrations of the zone plate. The image may be diffraction limited only if the illumination is relatively monochromatic. Like the pinhole camera, the zone plate turns out not to suffer from linear distortion, even at very wide fields.
179 citations
TL;DR: It is shown that with a careful choice of conditions and in the presence of catalase a very substantial protective effect of externally added superoxide dismutase can be observed.
164 citations
TL;DR: The results show that there are at least four anion binding sites on the protein, and these are divided equally into two classes, with zinc and copper appearing to bind only to the Zn2+, having no effect on the NMRD and minor effects on the optical spectrum.
127 citations
126 citations
TL;DR: It is concluded that there is at least one rapidly exchanging water molecule (exchange time τM in the range 4·10−6 to 10−8 s) on each of the two Cu2+ per protein molecule, and speculate that the water binding sites on the Cu2+, are similarly accessible to the superoxide anion and are the loci for the catalytic activity of the enzyme.
112 citations
TL;DR: In this article, the authors present a general summary and attempt to organize the nomenclature of mechanism dynamics, and indicate the current trend in the literature of kineto-elastodynamics and points the way to a possible unification of all dynamic effects.
110 citations
TL;DR: The pressure dependence of the elastic constants of various halides, hard tissues and synthetic apatites have been examined using a solid media, pressure apparatus coupled with an ultrasonic interferometer to assess the effects of porosity in aggregate samples and to make measurements on specimens of ideal density.
Abstract: The pressure dependence of the elastic constants of various halides, hard tissues and synthetic apatites have been examined in the 0- to 50-kilobar range using a solid media, pressure apparatus coupled with an ultrasonic interferometer. The samples includ: hydroxy-, fluor-, and chlor-apatite, NaCl, CaF2, mollusc shell (aragonite), ivory, dentin and enamel, and fish, bovine, and human bones. High pressures were used in order to assess the effects of porosity in aggregate samples and to make measurements on specimens of ideal density. Computer analysis of the measured longitudinal and shear ultrasonic velocities yields the pressure dependence of the bulk, shear, and Young's moduli and Poisson's ratio. Atmospheric pressure values at ideal density are obtained by back extrapolation from the high pressure measurements.
108 citations
TL;DR: In this article, thermal conductivity measurements were made on polyethylene samples which had been crystallized at different temperatures in order to vary density and lamellar crystal thickness, showing that the conductivity increased linearly by 50% as the density went from 0.96 to 0.99 gm/cc.
Abstract: Thermal conductivity measurements were made on polyethylene samples which had been crystallized at different temperatures in order to vary density and lamellar crystal thickness. Tests were also made on polyethylenes which were oriented by mechanical shearing and by crystallization in a temperature gradient. The thermal conductivity increased linearly by 50% as the density went from 0.96 to 0.99 gm/cc. By orientation the conductivity was increased ten fold in the direction of molecular orientation and decreased two fold in the perpendicular direction. For samples oriented by deformation at different temperatures, the conductivity apparently correlates with birefringence.
TL;DR: Bada and Miller as discussed by the authors showed that an ammonium ion concentration of 10−2 to 10−3 M is necessary for the synthesis of these biomolecules, while Rasool and McGovern suggest that a methane-ammonia atmosphere could have been maintained for 109 years by a low leakage rate of hydrogen.
Abstract: THE suggestion that the primitive atmosphere was highly reducing and consisted mainly of methane, ammonia and water vapour1 is supported by Miller's observation that amino-acids are formed by electrical discharges through such a mixture2 and the synthesis of various biomolecules under presumed primitive Earth atmospheres containing ammonia3. Bada and Miller4 point out that an ammonium ion concentration of 10−2 to 10−3 M is necessary for the synthesis of these biomolecules while Rasool and McGovern5 suggest that a methane–ammonia atmosphere could have been maintained for 109 years by a low leakage rate of hydrogen.
TL;DR: In this paper, the flow between eccentric rotating cylinders was studied using a modified bipolar coordinate system and the Sommerfeld pressure distribution and associated flow in a journal bearing were derived from the Navier-Stokes equations by a straightforward and systematic expansion in the clearance ratio (assumed small).
Abstract: The flow between eccentric rotating cylinders is studied using a modified bipolar coordinate system. The Sommerfeld pressure distribution and associated flow in a journal bearing are derived from the Navier-Stokes equations by a straightforward and systematic expansion in the clearance ratio (assumed small). First order corrections for curvature and inertial effects are given. There is no restriction on the eccentricity. (Author)
TL;DR: Buckling of axially compressed circular cylindrical shells with localized or random axisymmetric imperfections, deriving asymptotic approximation formulas for stress calculation.
Abstract: Buckling of axially compressed circular cylindrical shells with localized or random axisymmetric imperfections, deriving asymptotic approximation formulas for stress calculation
TL;DR: In this article, the linear stability of the flow between two long eccentric rotating circular cylinders is considered, which is an extension of the classical Taylor problem for concentric cylinders, and a global solution to the stability problem is obtained.
Abstract: The linear stability of the flow between two long eccentric rotating circular cylinders is considered The problem, which is of interest in lubrication technology, is an extension of the classical Taylor problem for concentric cylinders The basic flow has components in the radial and azimuthal directions and depends on both of these co-ordinates As a consequence the linearized stability equations are partial differential equations rather than ordinary differential equations Thus standard methods of stability theory are not immediately useful By letting the clearance ratio and eccentricity tend to zero in a given way a global solution to the stability problem is obtained
TL;DR: In this article, a mechanism based upon electron charging due to the electron beam was proposed to explain the nucleation, growth, coalescence, disappearance, and geometry of the aluminium islands, which showed either a lateral growth with eventual coalescence with other islands, or a reoxidation process which caused the islands to disappear.
Abstract: Thin foils of high purity aluminium and an Al-Al2O3 SAP type of alloy were oxidised in a specially designed hot stage specimen chamber in an electron microscope. Below 450 C, amorphous aluminium oxide formed on the foil surface and was first detectable at foil edges, holes, and pits. Islands of aluminium then nucleated in this amorphous oxide. The aluminium islands displayed either a lateral growth with eventual coalescence with other islands, or a reoxidation process which caused the islands to disappear. The aluminium island formation was determined to be related to the presence of the electron beam. A mechanism based upon electron charging due to the electron beam was proposed to explain the nucleation, growth, coalescence, disappearance, and geometry of the aluminium islands.
01 May 1972
TL;DR: The morphology of extended chain lamellae and fibrous polytetrafluoroethylene has been analyzed by electron microscopy and compared to polyethylene as discussed by the authors, and the crystal growth mechanism of initial folding on molecular nucleation followed by chain extension is applicable to both polymers and seems to be a general mechanism for crystallization of prepolymerized linear macromolecules.
Abstract: The morphology of extended chain lamellae and fibrous polytetrafluoroethylene has been analyzed by electron microscopy and compared to polyethylene. The crystal growth mechanism of initial folding on molecular nucleation followed by chain extension is applicable to both polymers and seems to be a general mechanism for crystallization of prepolymerized linear macromolecules. Differences arise from the branching mechanism of the spherulites. Annealing the striated surface created on fracture could be shown to lead to folded chain “ripples” of time and temperature dependent thickness. Fibrous crystals of smooth and shish-kebob-type appearance were grown from gaseous tetrafluoroethylene.
TL;DR: In this paper, a study of the non-linear effects of the flanges and the behavior of the adhesion was carried out in the case of two bogie-models, as well as the system of external forces applied, based on the interactions between the rail and the wheel tread, and the reactions of flanges.
Abstract: A study of hunting, taking into account the non-linear effects, such as the intervention of the flanges, and the behaviour of the adhesion. The author shows the equations covering the system, in the case of two bogie-models, as well as the system of external forces applied, based on the interactions between the rail and the wheel tread, and the reactions of the flanges. The systems of equations were resolved by means of a computer. The author shows the conclusions reached, as a result of the calculations made, concerning the hunting frequencies, the riding stability, and the contacts between the flanges and the rail, which are different from those reached as a result of a study based on linear hypotheses. Reference is made in the bibliography to a number of basic studies of the subject.
TL;DR: In this article, the specific heat of amorphous polystyrene and polymethyl methacrylate was found to vary as AT + BT3 and thermal conductivity as T 1.8 in agreement with measurements on inorganic glasses, demonstrating that this phenomenon is not sensitive to details of morphology.
TL;DR: In this paper, a normal coordinate calculation of the fundamental vibrations of phenazine was performed from infrared and Raman spectra, compared to the vibrational assignments of anthracene.
01 Jul 1972-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
Abstract: The effects of air and vacuum on the fatigue behavior of a nickel-base superalloy, Mar-M200, in single crystal form were investigated. Between 800° and 1400°F fracture is entirely in the Stage I mode in air and vacuum, and fatigue life is unaffected by environment. At 1700° F in both environments, fracture is predominantly in the Stage II mode and fatigue life in air is greater than that in vacuum. At both temperatures, fatigue cracking in air is internally initiated, whereas in vacuum cracking is generally initiated at the specimen surface. Identical fatigue lives in air and in vacuum between 800° and 1400° F are attributed to the fact that internally initiated cracks in air are actually propagating in a high vacuum, surface cracking being inhibited by dynamic oxidation of emerging surface slip offsets. The subsurface portion of the Stage I fracture surface produced in air tests and all of the Stage I fracture produced in vacuum tests shows a dimpled structure, whereas the Stage I fracture surface produced while the crack propagation is in air shows a cleavage appearance. At 1700° F, bulk oxidation of surface initiated cracks interferes with the plastic blunting mechanism of Stage II crack growth normally observed at this temperature, internally initiated cracks causing ultimate failure. Shorter lives in vacuum are thought to result from enhanced Stage II surface crack propagation.
TL;DR: In this article, the authors observed the segregation of sulfur to the surface of a (111) oriented nickel single crystal, and the kinetics of the reaction of this sulfur with oxygen at temperatures near ambient.
TL;DR: In this paper, conditions have been found for the etching of poly(ethylene terephthalate) with water so that the crystalline portions alone remain, and the morphology of melt-crystallized poly (ethylene Terephthalates) and the melting behavior of oligomer lamellae are discussed.
Abstract: Conditions have been found for the etching of poly(ethylene terephthalate) with water so that the crystalline portions alone remain. Initial sample and hydrolysis products are analyzed by extraction of low molecular weight products; density, viscosity molecular weight, and endgroup determination; heating-rate-dependent thermal analysis; low-angle and wide-angle x-ray analysis; and electron microscopy. On hydrolysis of a 67% crystalline polymer at 180°C for about 300 min, almost fully crystalline extended-chain oligomers can be obtained with about 65% yield. The morphology of melt-crystallized poly(ethylene terephthalate) and the melting behavior of oligomer lamellae are discussed.
TL;DR: Utilizing whole-cell preparations of Escherichia coli, it appears that 670 atm inhibits protein synthesis during elongation, while not affecting aminoacyl transfer ribonucleic acid formation, polysomal integrity, or amino acid permeability.
Abstract: Utilizing whole-cell preparations of Escherichia coli, it appears that 670 atm inhibits protein synthesis during elongation, while not affecting aminoacyl transfer ribonucleic acid formation, polysomal integrity, or amino acid permeability.
TL;DR: The mechanism of homotypic plaque exclusion in both cell lines was shown to occur beyond the virion adsorption stage, and the original infecting virus genome persisted in bothcell lines after standard virus was no longer detectable.
Abstract: Persistent infections were established in suspension cultures of BHK21/13S cells with both Parana and lymphocytic choriomeningitis viruses. Four generations after infection with either virus, more than 90% of the cells scored as infective centers, with concomitant peaks in extracellular virus yields. In both cultures the synthesis of detectable plaque-forming units (PFU) ceased about the 50th generation postinfection, and this condition was maintained until the 350th cell generation when the cultures were discontinued. The generation time of each culture was identical to that of uninfected parent controls, and at no time were cytopathic effects evident. In spite of the absence of infectivity, over 90% of the cells sampled at various times contained viral antigen demonstrable by immunofluorescence. When either of these persistently infected cell lines was substituted for normal cells in the standard plaque assay, very low efficiencies of plating were observed for homotypic and heterotypic viruses. Plaque formation by several heterologous viruses was virtually unaffected. The mechanism of homotypic plaque exclusion in both cell lines was shown to occur beyond the virion adsorption stage. The original infecting virus genome persisted in both cell lines after standard virus was no longer detectable. This was shown with the lymphocytic choriomeningitis virus-infected cells after storage in liquid nitrogen. After thawing, such cells were found to synthesize standard virus for a brief period. Although the Parana virus-infected cells did not behave this way, the growth medium from these cells would initiate PFU synthesis in normal cells within 36 hr after infection.
TL;DR: The inability of AA-tRNA to bind to ribosomes and mRNA under pressure, possibly in conjunction with translocation, appears to be responsible for the observed inhibition of the translational mechanism.
Abstract: Pressure inhibition of cell-free polypeptide synthesis is manifested in the same manner as that observed in the intact cell: (i) starting at approximately 200 atm, there is a progressive inhibition with increasing pressures; (ii) there is complete inhibition at 680 atm; (iii) incorporation into polypeptide is instantaneously reversible after pressure release and proceeds at a rate parallel to an atmospheric control; and (iv) the volume change of activation (DeltaV*) is 100 cm(3)/mole. Peptide bond formation per se can occur at a pressure level which is totally inhibitory to polypeptide synthesis. The one investigated step in translation that is inhibited in an identical manner is the binding of aminoacyl-transfer ribonucleic acid (AA-tRNA) to the ribosome-messenger RNA (mRNA) complex. The volume change of activation (DeltaV*) calculated for the binding reaction is also 100 cm(3)/mole. Thus, the inability of AA-tRNA to bind to ribosomes and mRNA under pressure, possibly in conjunction with translocation, appears to be responsible for the observed inhibition of the translational mechanism.
TL;DR: In this article, the authors measured the activation volumes associated with the basal and nonbasal vacancy mechanisms and found that activation volumes for diffusion are temperature dependent, isotropic, and approximately proportional to $T. The activation entropy is pressure dependent whereas the activation enthalpy is pressure independent to within the experimental uncertainty.
Abstract: The coefficient of self-diffusion along the principal axes in zinc was obtained over the temperature range 300-400\ifmmode^\circ\else\textdegree\fi{}C, and over the pressure range 0-9 kbar. The unusually high precision of 2% in the measurement of the vacancy activation volumes was achieved by means of a novel technique that insured temperature reproducibility in the diffusion zone of \ifmmode\pm\else\textpm\fi{} 0.2\ifmmode^\circ\else\textdegree\fi{}C at high pressure. The activation volumes for diffusion, associated with the basal and nonbasal vacancy mechanisms are found to be temperature dependent, isotropic, and approximately proportional to $T$. Hence the thermal coefficient of expansion of an activated vacancy is given by ${\ensuremath{\alpha}}_{v}={T}^{\ensuremath{-}1}$, and is about 15 times larger than the thermal coefficient of expansion of the perfect lattice. The activation entropy is pressure dependent, whereas the activation enthalpy is pressure independent to within the experimental uncertainty.
TL;DR: In this article, the annealing behavior and the uniaxial stress responses of the radiation-induced defect causing the 0.18$-eV photoconductivity energy levels in $n$-type silicon were studied after 1.5-MeV electron and Co$-gamma$-ray irradiation at 300 \ifmmode^\circ\else\textdegree\fi{}K.
Abstract: The annealing behavior and the uniaxial-stress responses of the radiation-induced defect causing the ${E}_{c}\ensuremath{-}0.75$-, ${E}_{c}\ensuremath{-}0.54$-, ${E}_{c}\ensuremath{-}0.42$-, and ${E}_{c}\ensuremath{-}0.18$-eV photoconductivity energy levels in $n$-type silicon were studied after 1.5-MeV electron and $^{60}\mathrm{Co}$ $\ensuremath{\gamma}$-ray irradiation at 300 \ifmmode^\circ\else\textdegree\fi{}K. The results suggest that the ${E}_{c}\ensuremath{-}0.75$-eV level arises from the electronic transition of the neutral charge state of the divacancy to the conduction band. This level also occurs in heavily irradiated $p$-type silicon when the Fermi level is too high to observe the divacancy-associated 0.32-eV photoconductivity band. The ${E}_{c}\ensuremath{-}0.75$-eV level is found to be correlated with the 0.32-eV band, indicating that they are due to two different charge states of the same defect. The ${E}_{c}\ensuremath{-}0.18$-eV level arises from the $A$-center defect which exhibits only one kind of stress response, i.e., the atomic redistribution among the allowable orientations. No electronic response was observed for the $A$ center in our photoconductivity measurements. Our data fit very well with the $A$-center model derived from electron-paramagnetic-resonance studies. The ${E}_{c}\ensuremath{-}0.42$-eV level was quite complicated. Besides the radiation-induced divacancy defect located near this level, we present evidence that some additional trap center inherent as an in-grown defect in the sample also gives rise to this level. The ${E}_{c}\ensuremath{-}0.54$-eV level anneals out around 150 \ifmmode^\circ\else\textdegree\fi{}C. Whether it really arises from the singly charged state of the divacancy or not is still a question.
01 Apr 1972-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the recovery and recrystallization behavior of two commercial quality steels, a Cb(Nb) strengthened high-strength low-alloy (HSLA) steel and a 304 stainless steel, was studied following hot-working.
Abstract: The recovery and recrystallization behavior of two commercial quality steels, a Cb(Nb) strengthened high-strength low-alloy (HSLA) steel and a 304 stainless steel, was studied following hot-working. Specimens were deformed in tension at a constant head velocity of 2 in.Js to reductions-in-area of 30 to 50 pct at temperatures in the austenite range from 1600° to 1900°F. The subsequent annealing behavior was observed at the temperature of deformation. Decreasing recrystallization rates with decreasing temperature andJor deformation were observed. It is suggested that CbC precipitation occurred during annealing of the HSLA steel and accounted for an arrest in the softening behavior. For the 304 stainless steel it is concluded that dynamic recrystallization took place during deformation, that thermal microtwinning was an active recovery mechanism during annealing, and that there was a preference for grain boundaries as nucleation sites for recrystallized grains. These conclusions regarding the annealing behavior of 304 stainless steel were supported by metallographic analysis of specimens water quenched from the temperature of deformation.