scispace - formally typeset
Search or ask a question

Showing papers by "Rensselaer Polytechnic Institute published in 1975"


Journal ArticleDOI
TL;DR: In this paper, experimental data on the interdiffusion of hydrogen and alkali ions in glass were examined using a concentration-dependent inter-diffusion coefficient, taking into account surface dissolution.
Abstract: Experimental data on the interdiffusion of hydrogen and alkali ions in glass are examined using a concentration-dependent interdiffusion coefficient, taking into account surface dissolution. The comparisons between calculated and experimental concentration profiles and diffusion coefficients are more satisfactory than for a concentration-independent diffusion coefficient, and support the use of the interdiffusion coefficient.

352 citations


Journal ArticleDOI
TL;DR: In this article, the authors concluded that the top management of any profit-seeking organization is delinquent if they do not engage in fully integrated long-range planning (LRR) planning.

221 citations


Journal ArticleDOI
TL;DR: In this paper, the modulus of the difference between the empirical and theoretical characteristic functions is weighted and integrated over the real line; this function of the sample values and the parameters is then minimized with respect to the parameters via a gradient search routine nested within a sequential search.
Abstract: SUMMARY Estimation of the parameters of the stable laws is considered for samples of size at least 50. The modulus of the difference between the empirical and theoretical characteristic functions is weighted and integrated over the real line; this function of the sample values and the parameters is then minimized with respect to the parameters via a gradient search routine nested within a sequential search. Extensive simulation experiments validate the effectiveness of the estimation procedure over the entire parameter space. Application of the procedure to stock market price behaviour is made.

201 citations


Journal ArticleDOI
TL;DR: In this paper, the processes used to produce high-performance carbon fibers are described from fundamentals, and the resulting fiber microstructures and the consequences of these structures on properties are presented.
Abstract: Graphite has a hexagonal close-packed crystal structure which is strong and stiff in the two directions of the basal plane and, in the third direction—perpendicular to the basal plane—is weak and compliant. High-performance carbon fibers must make use of the strong directions while suffering from the poor properties of the third. This paper describes, from fundamentals, the processes used to produce high-performance carbon fibers. The resulting fiber microstructures and the consequences of these structures on properties are presented.

186 citations


Journal ArticleDOI
TL;DR: In this article, a dilatometric investigation was conducted to determine the effect of carbon on the volume expansion accompanying the martensite transformation in iron-carbon alloys, and it was found that volume expansion at the m ∼ s ∼ temperature varies from 2.0 pct at 0.19 wt pct carbon to 3.1 pet at 1.01 pct.
Abstract: A dilatometric investigation was conducted to determine the effect of carbon on the volume expansion accompanying the martensite transformation in iron-carbon alloys. It was found that the volume expansion at theM s temperature varies from 2.0 pct at 0.19 wt pct carbon to 3.1 pet at 1.01 pct carbon, largely due to the effect of carbon on lowering the temperature at which the transformation occurs. Also of importance is the solid solution effect of carbon on altering the lattice parameters of both the austenite and martensite phases at theMs.

157 citations


Journal ArticleDOI
TL;DR: In this paper, a method for measuring solid/liquid surface energies, with a total systematic and random error of well under 10%, is described, derived from measurements of grain-boundary grooves in solid and liquid interfaces which are maintained in shallow temperature gradients.
Abstract: A new method for measuring solid/liquid surface energies, with a total systematic and random error of well under 10%, is described. The surface energies are derived from measurements of grain-boundary grooves in solid/liquid interfaces which are maintained in shallow temperature gradients. The gradients are established by an axial heater wire in a cylindrical specimen chamber. Applying the method to highly-purified succinonitrile, a solid/liquid surface energy of 8·94±0·5 erg/cm2 was determined. This corresponds to 37% of the heat of fusion per surface molecule.

154 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of heat treatment on the microstructure of Li2O-Al2O3·SiO2 glass-ceramics which contain crystals of either Li2SiO3, Li 2Si2O5, or both was investigated quantitatively.
Abstract: The effect of heat treatment on the microstructure of Li2O-Al2O3·SiO2 glass-ceramics which contain crystals of either Li2SiO3, Li2Si2O5, or both was investigated quantitatively. Strength determinations for abraded rods were correlated with heat treatment on the basis of both size and distribution of crystals and the type and amount of crystal phases present. The presence of Li2Si2O5 crystals enhanced the strength, whereas the presence of Li2SiO3 crystals did not change the strength of the abraded parent glass. The interrelation between strength and microstructure is discussed.

148 citations



Journal ArticleDOI
TL;DR: In this paper, the authors consider the case when the mean free path is small compared to typical lengths in the domain (e.g., the size of a reactor) and derive a uniform asymptotic expansion of the solution of the problem.
Abstract: We consider initial−boundary value and boundary value problems for transport equations in inhomogeneous media. We consider the case when the mean free path is small compared to typical lengths in the domain (e.g., the size of a reactor). Employing the boundary layer technique of matched asymptotic expansions, we derive a uniform asymptotic expansion of the solution of the problem. In so doing we find that in the interior of the domain, i.e., away from boundaries and away from the initial line, the leading term of the expansion satisfies a diffusion equation which is the basis of most computational work in reactor design. We also derive boundary conditions appropriate to the diffusion equation. Comparisons with existing results such as the asymptotic and P1 diffusion theories, the PN approximation, and the extrapolated end point condition for these approximations, are made. Finally the uniform validity of our expansions is proved, thus yielding the desired error estimates.

132 citations


Journal ArticleDOI
TL;DR: In this paper, the authors apply the Barker's method to the reduction of VLE data on a routine basis, and demonstrate the validity of the method through application to several sets of data from the literature, and new experimental data are presented for six diverse binary systems in vapor liquid equilibrium at 50°C.
Abstract: Through an empirical but rational appraoch to the development of equations to represent the composition dependence of the excess Gibbs function for binary liquid systems, it has been found possible to correlate VLE data precisely, even for highly nonideal systems. This makes possible the application of Barker's method to the reduction of VLE data on a routine basis. The validity of the method is demonstrated through application to several sets of data from the literature, and new experimental data are presented for six diverse binary systems in vapor-liquid equilibrium at 50°C.

129 citations



Journal ArticleDOI
TL;DR: The performance of the poor readers was equivalent to that of the normals on the non-verbal tasks but inferior on the verbal tasks, interpreted as consistent with the possibility of select language (intrahemispheric) disorder, in poor readers.

Journal ArticleDOI
TL;DR: In this article, the critical molecular weight-crystallization temperature relationship shows a 1/ΔT2 dependence and the equilibrium segregation on crystallization to hypothetical fully extended chain crystals yields a lower limit of segregation.
Abstract: Polyethylenes of six different molecular weights and distributions have been crystallized isothermally from the melt at 90 to 129 °C and under elevated pressure (5,000 bar) at 225 to 240 °C. The crystallized polymer and the supernatant melt have been analyzed after quenching to low temperature, by selective dissolution using DSC and viscometry. In addition, data on solution crystallization of the literature were analysed. It was observed that fractionation occurs according to molecular weight. Melt and solution data on the critical molecular weight, chosen so that 90% by weight of the supernatant melt or solution has lower molecular weight and 90% of the crystals have higher molecular weight, agree when shifting the crystallization temperatures by 36 °C. The critical molecular weight-crystallization temperature relationship shows a 1/ΔT2 dependence. The equilibrium segregation on crystallization to hypothetical fully extended chain crystals yields a lower limit of segregation. At low supercooling, molecular lengths many times the equilibrium length and many times the lamellar thickness are reproducibly, selectively and permanently excluded from the crystal. Molecular nucleation is proposed to be the explanation for the observed facts.

Book ChapterDOI
01 Jan 1975

Journal ArticleDOI
TL;DR: A procedure for preparing derivatives of bovine superoxide dismutase in which primarily the Cu binding sites are occupied by Cu2+ (2 Cu2--) and in which both the Zn and Cu binding Sites are occupiedby Cu2+, finding an antiferro-magnetic interaction between Cu2+.

Journal ArticleDOI
TL;DR: It was concluded that deficient visual memory is an unlikely source of specific reading disability, and alternative explanations of the disorder were considered.

Journal ArticleDOI
TL;DR: In this paper, a computer-based method is developed to perform the numerical analysis of the measured adsorption isotherm in order to determine the quantitative distribution of potential energies displayed by a solid substrate for a physically-adsorbed gas.

Journal ArticleDOI
TL;DR: In this paper, total pressure measurements taken for the ternay systems of acetone-chloroform-methanol and chloroform -ethanol-n-heptane at 50°C were reduced by Barker's method and correlated by an equation similar to one proposed by Wohl.
Abstract: Total pressure measurements taken for the ternay systems acetone-chloroform-methanol and chloroform-ethanol-n-heptane at 50°C are reduced by Barker's method and correlated by an equation similar to one proposed by Wohl (1953).

Journal ArticleDOI
TL;DR: In this article, the growth rate constants for crystal growth were independent of stirring rate and temperature for oxalate monohydrate and trihydrate in stirred and unstirred aqueous solutions.

Journal ArticleDOI
TL;DR: Results are presented which strongly suggest that the species formed during the oxidation of dialuric acid which is active toward the cell is neither superoxide ion nor hydrogen peroxide nor a product of these substances.

Journal ArticleDOI
TL;DR: In modern unconsolidated carbonate sediments, the volume of pore space may exceed that of sedimentary particles as discussed by the authors, which is the missing link in the source of calcite cement.
Abstract: In modern unconsolidated carbonate sediments the volume of pore space may exceed that of sedimentary particles. During lithification calcium carbonate is introduced from the outside. Surprisingly compaction accounts for only little reduction in pore space. In cementation the waters may be (1) percolating freshwaters on surface or in subsurface, (2) seawaters, and (3) formation waters. Percolating freshwaters may affect carbonate sediments as the generally subsiding sea floor at times rises ("yo-yo tectonics") or as sea level falls ("yo-yo oscillations") or as freshwaters circulate in the subsurface through carbonate sediments. In the phreatic zone (below the groundwater table), especially in moist climatic belts, the original pore space between particles as well as any secondary moldic pore space fill with cements of various fabrics. As carbonate sediments in the phreatic zone are converted to limestone, they not only lose their pore space and become tight, but they may acquire, as their depositional texture vanishes, a xenotopic and poikilotopic fabric of recrystallization. Phreatic diagenesis, however, may also follow a different sequence: reefs micritize beyond recognition; geologists mistake such reefs for "lime mud." Phreatic diagenesis, however, does not always lead to a lack of porosity; carbonates, including reefs, may "chalkify" into porous micron-size, soft, friable calcite. In the vadose zone, (above the groundwater table) which in arid regions may be thousands of feet thick, the pores remain largely open. In fact secondary pores may develop, and stay open, as the aragonite of ooids or of "critters" is leached to form oo- or "crittermolds." Porous strata as products of vadose diagenesis may occur interbedded, as cyclic sequences, with tight strata of phreatic diagenesis. Cements in limestones may also be derived from the effects of dissolution which stylolitization provides. On the sea bottom cementation may be related to bacterial activity. By such activity organic matter can yield methane or other gases that oxidize on the sea floor and are effective in generating bicarbonate ions which then combine with calcium to deposit a a cemented calcium-carbonate deposit. Sulfate-reducing bacteria use sulfate from seawater as an oxidant for that part of organic matter which they oxidize for energy production. Calcium carbonate as a cement is formed when CO 2 produced in the bacterial oxidation of organic matter combines with calcium ions. In the subsurface this reaction involving formation waters is probably even more important than in seawater and may be the missing link in our explanation of the source of calcite cement. In reefs photosynthesis and respiration of the biomass cause a shift in the bicarbonate buffer system of seawater with the uptake of CO 2 . In this process micro-levels of pH 10 and even 10.5 may be reached and maintained in thin jell-like or monomolecular layers. Such high pH levels trigger the precipitation of carbonate cements. In response to increasing salinities during periods of falling sea level carbonate cements likewise are precipitated.

Journal ArticleDOI
TL;DR: In this paper, the asymmetric stable laws rather than the symmetric stable law provide a closer representation of the behavior of security prices, and the empirical results indicate that the Asymmetric laws are more appropriate than the Symmetric Stable Law.
Abstract: A point of considerable interest is whether the asymmetric stable laws rather than the symmetric stable laws provide for a closer representation of the behavior of security prices. Our empirical results indicate that the asymmetric laws are more appropriate than the symmetric stable laws. A new estimation procedure is used to obtain the estimates of parameters of the stable laws for 20 randomly selected stocks from the New York Stock Exchange. Estimates of the skewness parameter are explicitly obtained for the first time. The estimates are compared with those obtained under the assumption of symmetry and are also compared with the estimates provided by the method of Fama and Roll [13].

Journal ArticleDOI
TL;DR: Constraints imposed on the functions μ, χ, and k constitute the necessary and sufficient conditions for the existence of travelling bands of chemotactic bacteria.
Abstract: Traveling band solutions of the differential equations for chemotactic bacteria are exhibited for arbitrary motility μ( s ), chemotactic sensitivity χ( s ), and substrate consumption rate k ( s ). The requirements that the total number of bacteria in the band be finite, and that these bands behave appropriately at ± ∞, impose stringent constraints on the functions μ, χ, and k . These constraints are exhibited, and constitute the necessary and sufficient conditions for the existence of travelling bands of chemotactic bacteria.

Journal ArticleDOI
TL;DR: In this paper, the influence of the thermal gradient (thermomigration) and of electric current (electromigration) on atom motions in the solid phase are treated. But only the influences of thermal gradient and electric current are considered.


Journal ArticleDOI
TL;DR: The strong Burnside problem has an affirmative answer for semigroups of finite dimensional matrices over a skew field as discussed by the authors, and it follows that a torsion semigroup embeddable in the multiplicative semigroup of an algebra over a field satisfying a polynomial identity is locally finite.

Journal ArticleDOI
TL;DR: In this paper, the authors considered the possibility of a large number of molecular degrees of freedom associated with condensation shock wave discontinuities for which the upstream state is vapour and the downstream state is liquid and found that the ideal gas specific heat cv [ges ] 24R at the critical temperature satisfies the usual stability conditions.
Abstract: Shock discontinuities for which the upstream state is vapour and the downstream state is liquid are considered. The possibility of such shock waves is associated with a large number of molecular degrees of freedom: it is necessary that the ideal-gas specific heat cv [ges ] 24R at the critical temperature, a condition which is met by several common fluids. Shock properties are found from a corresponding-states thermodynamic model and from several calculations based on data for particular fluids. Condensation shock waves satisfy the usual stability conditions and should be found in laboratory experiments.

Journal ArticleDOI
TL;DR: The thermal expansion of GeSe has been studied above room temperature up to the melting point of 670 plus or minus 5 C by X-ray diffraction techniques using a 190 mm Unicam high temperature camera.
Abstract: The thermal expansion of GeSe has been studied above room temperature up to the melting point of 670 plus or minus 5 C by X-ray diffraction techniques using a 190 mm Unicam high temperature camera. The thermal expansion of the crystallographic axes is linear with a distinct change in the expansion coefficients for all axes above 400 C. The relative changes in the axes indicate a rearrangement of the structure towards cubic symmetry with increasing temperature. The transformation of GeSe from the orthorhombic to a normal NaCl-type structure is observed at 651 plus or minus 5 C. The lattice parameter of the cubic form of GeSe is a 0 ? 5.730 plus or minus 0.003 A at 656 C. The GeSe lattice remains cubic up to the melting point.

Journal ArticleDOI
TL;DR: Of a variety of purine and pyrimidine nucleotides tested, only ADP and 5'AMP significantly inhibited the Mg(2+)-dependent activity of pea leaf glutamine synthetase.
Abstract: Of a variety of purine and pyrimidine nucleotides tested, only ADP and 5′AMP significantly inhibited the Mg 2+ -dependent activity of pea leaf glutamine synthetase. They were less effective inhibitors where Mn 2+ replaced Mg 2+ . They were competitive inhibitors with respect to ATP, with inhibition constant (K i ) values of 1.2 and 1.8 mm, respectively. The energy charge significantly affects the activity of glutamine synthetase, especially with Mg 2+ . Of a variety of amino acids tested, l-histidine and l-ornithine were the most inhibitory, but significant inhibition was seen only where Mn 2+ was present. Both amino acids appeared to compete with l-glutamate, and the K i values were 1.9 mm for l-histidine (pH 6.2) and 7.8 mm for l-ornithine (pH 6.2). l-Alanine, glycine, and l-serine caused slight inhibition (Mn 2+ -dependent activity) and were not competitive with ATP or l-glutamate. Carbamyl phosphate was an effective inhibitor only when Mn 2+ was present, and did not compete with substrates. Inorganic phosphate and pyrophosphate caused significant inhibition of the Mg 2+ -dependent activity.

Journal ArticleDOI
TL;DR: In this paper, the history dependence of structural metals is examined and it is shown that prior deformation can change the response of structural metal to the same forcing function permanently but only in degree and not in kind.
Abstract: In slow motions, such as occur in repeated creep, relaxation and low-cycle fatigue loadings, rate and history dependence interact and the conventional metallic material idealizations do not appear to be appropriate. For later use an operational definition of aging, rate and history dependence is given. Constitutive equations capable of reproducing history dependence must not only depend on the forcing function in the present time interval but must also have a not completely fading memory of prior loadings. It is demonstrated that certain forms of integral constitutive equations and defined history dependence. The history dependence of structural metals is examined and it is shown that prior deformation can change the response of structural metals to the same forcing function permanently but only in degree and not in kind; the variable hereditary property of structural metals is limited and is caused by deformation-induced changes of the microstructure. Variant and invariant response properties under prior loading are stated.