Showing papers by "Virginia Tech published in 1984"
TL;DR: In this paper, a higher-order shear deformation theory of laminated composite plates is developed, which accounts for parabolic distribution of the transverse shear strains through the thickness of the plate.
Abstract: A higher-order shear deformation theory of laminated composite plates is developed. The theory contains the same dependent unknowns as in the first-order shear deformation theory of Whitney and Pagano (1970), but accounts for parabolic distribution of the transverse shear strains through the thickness of the plate. Exact closed-form solutions of symmetric cross-ply laminates are obtained and the results are compared with three-dimensional elasticity solutions and first-order shear deformation theory solutions. The present theory predicts the deflections and stresses more accurately when compared to the first-order theory.
3,504 citations
TL;DR: A variety of new investigations of the helplessness reformulation that employ five research strategies that converge in their support for the learned helplesshood reformulation are described.
Abstract: The attributional reformulation of the learned helplessness model claims that an explanatory style in which bad events are explained by internal, stable, and global causes is associated with depressive symptoms. Furthermore, this style is claimed to be a risk factor for subsequent depression when bad events are encountered. We describe a variety of new investigations of the helplessness reformulation that employ five research strategies: (a) cross-sectional correlational studies, (b) longitudinal studies, (c) experiments of nature, (d) laboratory experiments, and (e) case studies. Taken together, these studies converge in their support for the learned helplessness reformulation.
1,517 citations
TL;DR: The facet model is used to accomplish step edge detection and the Marr-Hildreth zero crossing of the Laplacian operator is found that it is the best performer; next is the Prewitt gradient operator.
Abstract: We use the facet model to accomplish step edge detection. The essence of the facet model is that any analysis made on the basis of the pixel values in some neighborhood has its final authoritative interpretation relative to the underlying gray tone intensity surface of which the neighborhood pixel values are observed noisy samples. With regard to edge detection, we define an edge to occur in a pixel if and only if there is some point in the pixel's area having a negatively sloped zero crossing of the second directional derivative taken in the direction of a nonzero gradient at the pixel's center. Thus, to determine whether or not a pixel should be marked as a step edge pixel, its underlying gray tone intensity surface must be estimated on the basis of the pixels in its neighborhood. For this, we use a functional form consisting of a linear combination of the tensor products of discrete orthogonal polynomials of up to degree three. The appropriate directional derivatives are easily computed from this kind of a function. Upon comparing the performance of this zero crossing of second directional derivative operator with the Prewitt gradient operator and the Marr-Hildreth zero crossing of the Laplacian operator, we find that it is the best performer; next is the Prewitt gradient operator. The Marr-Hildreth zero crossing of the Laplacian operator performs the worst.
1,130 citations
TL;DR: Because of increased interest in milk proteins of species other than bovine, the Committee suggests that these be identified as homologs of those already characterized in European, Bos taurus , and Indian, Bos indicus , cattle.
870 citations
TL;DR: In this paper, a higher-order shear deformation theory of plates accounting for the von Karman strain was presented, which contains the same dependent unknowns as in the Hencky-Mindlin type first-order deformation theories and accounts for parabolic distribution of the transverse shear strains through the thickness of the plate.
695 citations
TL;DR: A new acetotrophic marine methane-producing bacterium that was isolated from the methane-evolving sediments of a marine canyon is described, and Methanosarcina acetivorans is the proposed species.
Abstract: A new acetotrophic marine methane-producing bacterium that was isolated from the methane-evolving sediments of a marine canyon is described. Exponential phase cultures grown with sodium acetate contained irregularly shaped cocci that aggregated in the early stationary phase and finally differentiated into communal cysts that released individual cocci when ruptured or transferred to fresh medium. The irregularly shaped cocci (1.9 +/- 0.2 mm in diameter) were gram negative and occurred singly or in pairs. Cells were nonmotile, but possessed a single fimbria-like structure. Micrographs of thin sections showed a monolayered cell wall approximately 10 nm thick that consisted of protein subunits. The cells in aggregates were separated by visible septation. The communal cysts contained several single cocci encased in a common envelope. An amorphous form of the communal cyst that had incomplete septation and internal membrane-like vesicles was also present in late exponential phase cultures. Sodium acetate, methanol, methylamine, dimethylamine, and trimethylamine were substrates for growth and methanogenesis; H(2)-CO(2) (80:20) and sodium formate were not. The optimal growth temperature was 35 to 40 degrees C. The optimal pH range was 6.5 to 7.0. Both NaCl and Mg were required for growth, with maximum growth rates at 0.2 M NaCl and 0.05 M MgSO(4). The DNA base composition was 41 +/- 1% guanine plus cytosine. Methanosarcina acetivorans is the proposed species. C2A is the type strain (DSM 2834, ATCC 35395).
316 citations
TL;DR: The geometry of the ideal pyrochlore structure type (8A26B24X64Y, Fd3m) has been examined using a data base of 440 synthetic samples as discussed by the authors.
271 citations
229 citations
TL;DR: It was found that regression analysis, subjective techniques, exponential smoothing, and moving average were well known and used for specific situations and accuracy was relatively high for aggregate short range forecasts, but decreased for longer range and product level forecasts.
Abstract: This article presents the results of a survey to determine the degree of familiarity and usage, accuracy obtained, and evaluation of different forecasting techniques. It was found that regression analysis, subjective techniques, exponential smoothing, and moving average were well known and used for specific situations. Accuracy was relatively high for aggregate short range forecasts, but decreased for longer range and product level forecasts.
224 citations
TL;DR: Data to indicate the possible involvement of the raffinose family of oligosaccharides in flatulence production are given and molecular and physicochemical properties of legume starches are discussed.
214 citations
01 Jan 1984
TL;DR: In this article, an experimental and theoretical investigation has been made of the primary resonances of the system, which occur when the frequency of excitation is near one of the natural frequencies, ω 1 and ω 2.
TL;DR: The results clearly indicate that if these organisms exist, and if their metabolic reactions occur in an aqueous environment, they could not survive at this temperature if they were composed of biomolecules such as proteins and nucleic acids, due to the very rapid rate of decomposition of such molecules.
Abstract: The upper temperature at which a living system can exist is limited by the hydrolytic breakdown rate of its chemical constituents. The peptide bonds of proteins, the phosphodiester and N-glycosyl bonds in RNA and DNA, and the pyrophosphate and N-glycosyl bonds in nucleotides such as ATP and NAD are among the more important bonds that will undergo hydrolysis. The decomposition of biomolecules via non-hydrolytic pathways such as decarboxylations and dehydrations may also be critical factors in determining this upper temperature limit. Baross and Deming recently reported 'black smoker' bacteria, which they isolated from deep-sea hydrothermal vents, growing at 250 degrees C. Here I have attempted to establish the rates for the hydrolysis and/or decomposition of critical biomolecules to determine their ability to exist at this temperature. My results clearly indicate that if these organisms exist, and if their metabolic reactions occur in an aqueous environment, they could not survive at this temperature if they were composed of biomolecules such as proteins and nucleic acids, due to the very rapid rate of decomposition of such molecules.
TL;DR: A simple analysis using two dimensional lamination theory combined with the appropriate three dimensional anisotropic constitutive equation is presented to show some rather surprising results for the range of values of the through-the-thickness effective Poisson's ratio nu sub xz for angle ply laminates as mentioned in this paper.
Abstract: A simple analysis using two dimensional lamination theory combined with the appropriate three dimensional anisotropic constitutive equation is presented to show some rather surprising results for the range of values of the through-the-thickness effective Poisson's ratio nu sub xz for angle ply laminates. Results for graphite-epoxy show that the through-the-thickness effective Poisson's ratio can range from a high of 0.49 for a 90 laminate to a low of -0.21 for a + or - 25s laminate. It is shown that negative values of nu sub xz are also possible for other laminates.
TL;DR: In this article, the effects of seller concession behavior, seller information, and buying firm monitoring of the buyer on the negotiation behavior and outcomes of industrial buyers were investigated, and the authors posited and tested the effect of concession behavior and seller information on industrial buyers.
Abstract: The author posits and tests the effects of seller concession behavior, seller information, and buying firm monitoring of the buyer on the negotiation behavior and outcomes of industrial buyers. Pra...
TL;DR: In this paper, the synthesis and physical characteristics of sulfonated polysulfone are addressed and a detailed synthesis route is provided and methods that yield determinable levels of SPSF sulfonation are described.
Abstract: Ionic groups incorporated into a polymer have a decided effect on its physical properties. A number of ionomers and polyelectrolytes have been widely applied. In particular, sulfonated bisphenol-A polysulfone (SPSF) has been used as a composite or single-component membrane for the desalination of water. In this article, the synthesis and physical characteristics of sulfonated polysulfone are addressed. A detailed synthesis route is provided and methods that yield determinable levels of sulfonation are described. These ion-containing polymers retain an excessive amount of residual salts, which, of course, are impurities to the system. Therefore, before any analyses were made the polymers were subjected to a thorough soxhlet extraction process with boiling water, which appeared to be quite effective. The degree of sulfonation was assessed by several methods such as 1H NMR and FT-IR. A new 1H NMR method was derived because the method cited in the literature proved to be too inconsistent for our work. The new 1H NMR method used a quaternary ammonium counterion [N(CH3)4]. These methyl protons are easily measured and may be ratioed against the isopropylidene protons in the polymer backbone that act as an internal standard. Characterization of the physical properties of SPSF consisted of water uptake, differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and solubility studies. Its physical appearance and mechanical behavior were improved by the solution procedure. Also addressed were the effects of different counterions (Na+ & Mg++) with SPSFs of low levels of sulfonation. The variation in physical properties between the divalent and monovalent counterions is dramatic, especially when observed by TMA in the rubber plateau above the apparent glass temperature.
TL;DR: A new multiple leader-follower model that is a consistent extension of Stackelberg's leader- follower duopoly is presented that contrasts with other existing extensions by demonstrating how the leader-Firms can utilize the true reaction curve of the follower-firms.
Abstract: This paper presents a new multiple leader-follower model that is a consistent extension of Stackelberg's leader-follower duopoly. The development contrasts with other existing extensions by demonstrating how the leader-firms can utilize the true reaction curve of the follower-firms; it also provides sufficient conditions for some useful convexity and differentiability properties of this function. For the proposed model, we conduct a static analysis and discuss the existence, uniqueness, and computation of an equilibrium solution, as well as study certain issues regarding the relative profits of leader and follower-firms. Since the Cournot oligopoly and the Stackelberg leader-follower models are special cases of this model, the analysis in this paper hopefully provides some further insights about these types of models.
TL;DR: The relationship between Dairy Herd Improvement program test-day milk yield and somatic cell counts in milk was analyzed in 34 dairy herds over 3 yr and estimates were more accurate when somaticcell counts were transformed to natural logarithms rather than actual.
TL;DR: The characteristic fatigue behavior of carburized and quenched steel with internal oxides and non-martensitic microstructure near the surface was presented through rotating bending fatigue test as discussed by the authors.
Abstract: The characteristic fatigue behavior of carburized and quenched steel with internal oxides and non-martensitic microstructure near the surface was presented through rotating bending fatigue test. The S-N diagram revealed two knees and the specimens continued to fail over 107 stress cycles. The fatigue limit could not be obtained even at 108 stress cycles. The test results were compared to those for the specimens without surface structure anomalies to show the effect of structure anomalies on the fatigue behavior of carburized steel.
TL;DR: In this paper, the importance of the differences between industrial and consumer marketing is discussed. But, the fundamental question raised in this paper is whether the importance is suffi cient.
Abstract: Academicians have traditionally acknowledged that industrial and consumer marketing are different. A fundamental question raised in this paper is whether the importance of these differences is suff...
TL;DR: The ability of all isolates to metabolize formate below the detection limit of 10 microM indicated that, in contrast to previous reports, methanogenic bacteria have the potential to directly metabolized formate in the rumen.
Abstract: Methanogenic bacteria with a coccobacillus morphology similar to Methanobrevibacter ruminantium were isolated from the bovine rumen. One isolate, 10-16B, represented a previously undescribed rumen population that, unlike M. ruminantium, synthesized coenzyme M, grew rapidly (mu = 0.24 h-1) on H2-CO2 in a complex medium, had simple nutritional requirements, and metabolized formate at reported rumen concentrations. H2 was metabolized to partial pressures 10-fold lower than those reported for the rumen. After H2 starvation for 26 h, strain 10-16B rapidly resumed growth when H2 was made available. The minimum concentrations of acetate (6 mM) and ammonia (less than 7 mM) that were required for optimal growth were lower than the reported acetate and ammonia concentrations in the rumen. Isoleucine and leucine stimulated growth, but only at concentrations (greater than 50 microM) higher than those reported for the rumen. Another coccobacillary methanogenic organism that synthesized coenzyme M was isolated from a different animal as were organisms that required an exogenous supply of coenzyme M. In general, methanogenic bacteria that required an exogenous supply of coenzyme M had lower maximum growth rates and more complex nutritional requirements than organisms that synthesized the cofactor. The ability of all isolates to metabolize formate below the detection limit of 10 microM indicated that, in contrast to previous reports, methanogenic bacteria have the potential to directly metabolize formate in the rumen. This study demonstrated that there are physiologically diverse populations of coccobacillary methanogenic bacteria in the rumen that can interact competitively and cooperatively.
01 Nov 1984
TL;DR: In searching for a general "zero-current-Switching" technique for DC-DC converters, the concept of resonant switches is developed and application of the resonant switch concept to conventional converters leads to the discovery of a host of new converter circuits.
Abstract: In searching for a general "zero-current-Switching" technique for DC-DC converters, the concept of resonant switches is developed. As a combination of switching device and LC network, the resonant switch offers advantages of quasi-sinusoidal current waveforms, zero switching stresses, zero switching losses, self-commutation, and reduced EMI. Furthermore, application of the resonant switch concept to conventional converters leads to the discovery of a host of new converter circuits.
TL;DR: In this paper, analytical solutions are developed for the hyperbolic heat conduction equation describing the wave nature of thermal energy transport in a finite slab with insulated boundaries subjected to a volumetric energy source in the medium.
TL;DR: In this article, the relative reactivities of pulverized samples of 3 marcasite and 7 pyrite specimens from various sources were determined at 25°C and pH 2.0 in ferric chloride solutions with initial ferric iron concentrations of 10−3 molal.
TL;DR: In this article, a batch reaction of lignin in a batch reactor under alkaline conditions at 180°C was studied using propylene oxide (PO) by itself, and PO in combination with several LN-like model compounds and with kraft LN.
Abstract: Hydroxypropylation of lignin in a batch reactor under alkaline conditions at 180°C was studied using propylene oxide (PO) by itself, and PO in combination with several ligninlike model compounds and with kraft lignin. While the PO homopolymerization rate increased rapidly at temperatures above 85°C, and was too fast to be determined accurately at 180°C, the addition of model compounds and lignin was found to delay homopolymerization in relation to the presence of ionizable functional groups. The observations are consistent with a reaction mechanism involving first order kinetics with regard to each alkoxide and PO concentrations. Where the reaction rates toward PO increase with increasing pKa values, the reaction sequence proceeds in the order of declining basicity. Thus lignins with high acidity were found to be subject to greater degrees of modification than those with more neutral character. This explains the earlier observed beneficial effect of lignin carboxylation on the properties of lignin–PO reaction mixtures.
TL;DR: In this article, Amino-propyl terminated poly(dimethylsiloxane) oligomers were reacted with various diisocynates to form segmented copolymers with urea linkages.
TL;DR: No scientifically justifiable evidence exists to indicate the degree of reliability with which one may use single species tests to predict responses at higher levels of biological organization, which makes it all the more remarkable that in the field of toxicity testing an assumption is made that responses at levels of Biological organization above single species can be reliably predicted.
Abstract: Most biologists agree that at each succeeding level of biological organization new properties appear that would not have been evident by even the most intense and careful examination of lower levels of organization. These levels might be crudely characterized as subcellular, cellular, organ, organism, population, multispecies, community, and ecosystem. The field of ecology developed because even the most meticulous study of single species could not accurately predict how several such species might interact competitively or in predator-prey interactions and the like. Moreover, interactions of biotic and abiotic materials at the level of organization called ecosystem are so complex that they could not be predicted from a detailed examination of isolated component parts. This preamble may seem platitudinous to most biologists who have heard this many times before. This makes it all the more remarkable that in the field of toxicity testing an assumption is made that responses at levels of biological organization above single species can be reliably predicted with single species toxicity tests. Unfortunately, this assumption is rarely explicitly stated and, therefore, often passes unchallenged. When the assumption is challenged, a response is that single species tests have been used for years and no adverse ecosystem or multispecies effects were noted. This could be because single species tests are overly protective when coupled with an enormous application factor or that such effects were simply not detected because there were no systematic, scientifically sound studies carried out to detect them. Probably both of these possibilities occur. However, the important factor is that no scientifically justifiable evidence exists to indicate the degree of reliability with which one may use single species tests to predict responses at higher levels of biological organization. One might speculate that the absence of such information is due to the paucity of reliable tests at higher levels of organization. This situation certainly exists but does not explain the lack of pressure to develop such tests. The most pressing need in the field of toxicity testing is not further perfection of single species tests, but rather the development of parallel tests at higher levels of organization. These need not be inordinately expensive, time consuming, or require any more skilled professionals than single species tests. Higher level tests merely require a different type of biological background. Theoretical ecologists have been notoriously reluctant to contribute to this effort, and, as a consequence, such tests must be developed by this and other organizations with similar interests.
TL;DR: In this paper, surface characteristics of ultraviolettreated wood were analyzed by infrared and ultraviolet spectroscopy, and it was shown that ultraviolet-treated wood is rich in carboxylic and carbonyl chromophoric groups and poor in aromatic functional groups.
Abstract: Wood is beautiful but sensitive to light. Because of the chromophoric system at its surface, ultraviolet light cannot penetrate it deeper than 80 μm. Surface characteristics of ultraviolettreated wood were analyzed by infrared and ultraviolet spectroscopy. Analyses of infrared spectra revealed that ultraviolet-treated wood is rich in carboxylic and carbonyl chromophoric groups and poor in aromatic functional groups. Ultraviolet spectral studies suggest that water-soluble low molecular weight fractions of degraded products from the wood surface are mainly derived from lignin. These degradation products contained carbonyl conjugated phenolic hydroxyl groups and had a weight-average molecular weight of about 900, confirmed by gel permeation chromatography.
TL;DR: In this article, the effect of synthesis variables on polyurethane properties was examined. But, the authors focused on the properties of the synthesis variables and did not consider the effects of other synthesis variables, such as lignin type, diisocyanate type and composition.
Abstract: Lignin-based polyurethane films were synthesized by solution casting from hydroxypropyl lignin derivatives and either an aliphatic or an aromatic isocyanate. Two lignins, kraft and steam explosion lignin, and two diisocyanates, hexamethylene diisocyanate (HDI) and tolylene diisocyanate (TDI), were chosen for the study. It was found necessary to use stoichiometric excess diisocyanate in the synthesis of the thermosetting polyurethanes. This part of the series addresses the effect of synthesis variables on film properties. The study examines the effect of lignin type, of diisocyanate type, and of composition in terms of NCO to OH stoichiometry on thermal and mechanical properties. Stoichiometric NCO-excess was found to cause a more significant increase in the glass transition temperature of TDI-based films than of films made with HDI. The films swelled less with increasing NCO/OH ratio. Use of aliphatic diisocyanate (HDI) resulted in films with lower moduli as compared to aromatic diisocyanate (TDI). Kraft-lignin-based polyurethanes had slightly inferior strength characteristics (Young's modulus and tensile strength) in comparison with those derived from steam explosion lignin. Variation in the NCO/OH stoichiometry had no noticeable effect on modulus or tensile strength, but did significantly influence glass transition temperature, swelling, and strain at break. It is observed that the properties of these thermosetting polyurethanes are very sensitive to their composition. The study illustrates that materials of satisfactory performance characteristics can be engineered by proper selection of synthesis variables and modification of network architecture.