Showing papers by "University of Oregon published in 1991"
TL;DR: Theories of the self from both psychology and anthropology are integrated to define in detail the difference between a construal of self as independent and a construpal of the Self as interdependent as discussed by the authors, and these divergent construals should have specific consequences for cognition, emotion, and motivation.
Abstract: People in different cultures have strikingly different construals of the self, of others, and of the interdependence of the 2. These construals can influence, and in many cases determine, the very nature of individual experience, including cognition, emotion, and motivation. Many Asian cultures have distinct conceptions of individuality that insist on the fundamental relatedness of individuals to each other. The emphasis is on attending to others, fitting in, and harmonious interdependence with them. American culture neither assumes nor values such an overt connectedness among individuals. In contrast, individuals seek to maintain their independence from others by attending to the self and by discovering and expressing their unique inner attributes. As proposed herein, these construals are even more powerful than previously imagined. Theories of the self from both psychology and anthropology are integrated to define in detail the difference between a construal of the self as independent and a construal of the self as interdependent. Each of these divergent construals should have a set of specific consequences for cognition, emotion, and motivation; these consequences are proposed and relevant empirical literature is reviewed. Focusing on differences in self-construals enables apparently inconsistent empirical findings to be reconciled, and raises questions about what have been thought to be culture-free aspects of cognition, emotion, and motivation.
18,178 citations
TL;DR: Advances in the conceptualization and measurement of life stress in the past 2 decades raise several questions concerning traditional diathesis-stress theories of psychopathology, and information is available on diatheses and stress for specific disorders to provide a foundation for more empirically based hypotheses about diathetic-stress interactions.
Abstract: Advances in the conceptualization and measurement of life stress in the past 2 decades raise several questions concerning traditional diathesis— stress theories of psychopathology. First, comprehensive measures of life stress force investigators to become more precise about the particular stressful circumstances hypothesized to interact with diatheses. Second, the influence of the diathesis on a person's life is typically ignored, which results in several types of possible bias in the assessment of life stress. Finally, information is available on diatheses and stress for specific disorders to provide a foundation for more empirically based hypotheses about diathesis—stress interactions. This possibility is outlined for depression. Such an approach provides the basis for developing broader, yet more specific, frameworks for investigating diathesis—stress theories of psychopathology in general and of depression in particular.
1,649 citations
TL;DR: Results of a laboratory experiment in which response times and verbal protocols were used to examine processes related to the evaluation of brand extensions showed that subjects’ attitudes toward brand extensions were correlated highly with their ratings of brand extension typicality.
Abstract: The authors explore the implications of considering a brand as representing a category consisting of its products. They report results of a laboratory experiment in which response times and verbal ...
890 citations
TL;DR: In this paper, the authors have studied experimentally the vapour-absent melting behavior of a natural metapelitic rock and their results differ greatly from those of previous experimental and theoretical investigations of melt productivity from metamorphic rocks.
Abstract: Peraluminous granitoid magmas are a characteristic product of ultrametamorphism leading to anatexis of aluminous metasedimentary rocks in the continental crust. The mechanisms and characteristic length-scales over which these magmas can be mobilized depend strongly on their melt fraction, because of their high viscosities. Thus, it is of fundamental importance to understand the controls exerted by pressure, temperature and bulk composition of the source material on melt productivity. We have studied experimentally the vapour-absent melting behaviour of a natural metapelitic rock and our results differ greatly from those of previous experimental and theoretical investigations of melt productivity from metamorphic rocks. Under H2O-undersaturated conditions, bulk composition of the source material is the overriding factor controlling melt fraction at temperatures on the order of 850–900° C. Granitoid melts formed in this temperature interval by the peritectic dehydration-melting reaction:
$$\begin{gathered} Biotite + plagioclase + aluminosilicate + quartz \hfill \\ = melt + garnet \hfill \\ \end{gathered} $$
have a restricted compositional range. As a consequence, melt fractions will be maximized from protoliths whose modes coincide with the stoichiometry of the melting reaction. This “optimum mode” (approximately 38% biotite, 32% quartz, 22% plagioclase and 8% aluminosilicate) reflects the fact that generation of low-temperature granitoid liquids requires both fusible quartzo-feldspathic components and H2O (from hydrous minerals). Metapelitic rocks rich in mica and aluminosilicate and poor in plagioclase contain an excess of refractory material (Al2O3, FeO, MgO) with low solubility in low-temperature silicic melts, and will therefore be poor magma sources. Melt fraction varies inversely with pressure in the range 7–13 kbar, but the effect is not strong: the decrease (at constant temperature) over this pressure range is of at most 15 vol% (absolute). The liquids produced in our experiments are silicarich (68–73 wt% SiO2), strongly peraluminous (2–5 wt% normative corundum) and very felsic (MgO+FeO* +TiO2 less than 3 wt%, even at temperatures above 1000° C). The last observation suggests that peraluminous granitoids with more than 10% mafic minerals (biotite, cordierite, garnet) contain some entrained restite. Furthermore, because liquids are also remarkably constant in composition, we believe that restite separation is more important than fractional crystallization in controlling the variability within and among peraluminous granitoids. We present liquidus phase diagrams that allow us to follow the phase relationships of melting of silica-and alumina-saturated rocks at pressures corresponding to the mid- to deep-continental crust. Garnet, aluminosilicate, quartz and ilmenite are the predominant restitic phases at temperatures of about 900° C, but Ti-rich biotite or calcic plagioclase can also be present, depending on the bulk composition of the protolith. At temperatures above 950–1050° C (depending on the pressure) the restitic assemblage is: hercynitic spinel+ilmenite+quartz±aluminosilicate. Our results therefore support the concept that aluminous granulites (garnet-spinel-plagioclase-aluminosilicate-quartz) can be the refractory residuum of anatectic events.
828 citations
TL;DR: A general expression is presented for the expected phenotype of an individual under the joint influence of inbreeding and crossbreeding, a simple function of the inbreeding coefficient, of source and hybridity indices ofCrossbreeding, and of specific forms of gene action.
Abstract: Inbreeding with close relatives and outbreeding with members of distant populations can both result in deleterious shifts in the means of fitness-related characters, most likely for very different reasons. Such processes often occur simultaneously and have important implications for the evolution of mating systems, dispersal strategies, and speciation. They are also relevant to the design of breeding strategies for captive populations of endangered species. A general expression is presented for the expected phenotype of an individual under the joint influence of inbreeding and crossbreeding. This expression is a simple function of the inbreeding coefficient, of source and hybridity indices of crossbreeding, and of specific forms of gene action. Application of the model may be of use in identifying the mechanistic bases for a number of evolutionary phenomena such as the shift from outbreeding enhancement to outbreeding depression that occurs with population divergence.
737 citations
TL;DR: In this article, the question of whether the psychological status of the basic level can be modified by experience was addressed in three experiments comparing the performance of subjects in expert and novice domains.
722 citations
TL;DR: Results strongly suggest that scytonemin production constitutes an adaptive strategy of photoprotection against short‐wavelength solar irradiance.
Abstract: Scytonemin, the yellow-brown pigment of cyanobacterial (blue-green algal) extracellular sheaths, was found in species thriving in habitats exposed to intense solar radiation. Scytonemin occurred predominantly in sheaths of the outermost parts or top layers of cyanobacterial mats, crusts, or colonies. Scytonemin appears to be a single compound identified in more than 30 species of cyanobacteria from cultures and natural populations. It is lipid soluble and has a prominent absorption maximum in the near-ultraviolet region of the spectrum (384 nm in acetone; ca. 370 nm in vivo) with a long tail extending to the infrared region. Microspectrophotometric measurements of the transmittance of pigmented sheaths and the quenching of ultraviolet excitation of phycocyanin fluorescence demonstrate that the pigment was effective in shielding the cells from incoming near-ultraviolet-blue radiation, but not from green or red light. High light intensity (between 99 and 250 μmol photon · m−2· S−1, depending on species) promoted the synthesis of scytonemin in cultures of cyanobacteria. In cultures, high light intensity caused reduction in the specific content of Chl a and phycobilins, increase in the ratio of total carotenoids to Chl a, and scytonemin increase. UV-A (320–400 nm) radiation was very effective in eliciting scytonemin synthesis. Scytonemin production was physiological and not due to a mere photochemical conversion. These results strongly suggest that scytonemin production constitutes an adaptive strategy of photoprotection against short-wavelength solar irradiance.
633 citations
TL;DR: Postponing the permanent repository and employing dry-cask storage of wastes on site would provide the time necessary for difficult social and political issues to be resolved.
Abstract: The Department of Energy's program for disposing of high-level radioactive wastes has been impeded by overwhelming political opposition fueled by public perceptions of risk. Analysis of these perceptions shows them to be deeply rooted in images of fear and dread that have been present since the discovery of radioactivity. The development and use of nuclear weapons linked these images to reality and the mishandling of radioactive wastes from the nation's military weapons facilities has contributed toward creating a profound state of distrust that cannot be erased quickly or easily. Postponing the permanent repository and employing dry-cask storage of wastes on site would provide the time necessary for difficult social and political issues to be resolved.
628 citations
TL;DR: The initial phenotypic characterization of an Arabidopsis mutation, terminal flower 1-1 (tfl1-1), that identifies a new genetic locus, TFL1, is presented, suggesting that tFL1 perturbs the establishment and maintenance of the inflorescence meristem.
Abstract: We present the initial phenotypic characterization of an Arabidopsis mutation, terminal flower 1-1 (tfl1-1), that identifies a new genetic locus, TFL1. The tfl1-1 mutation causes early flowering and limits the development of the normally indeterminate inflorescence by promoting the formation of a terminal floral meristem. Inflorescence development in mutant plants often terminates with a compound floral structure consisting of the terminal flower and one or two subtending lateral flowers. The distal-most flowers frequently contain chimeric floral organs. Light microscopic examination shows no structural aberrations in the vegetative meristem or in the inflorescence meristem before the formation of floral buttresses. The wild-type appearance of lateral flowers and observations of double mutant combinations of tfl1-1 with the floral morphogenesis mutations apetala 1-1 (ap1-1), ap2-1, and agamous (ag) suggest that the tfl1-1 mutation does not affect normal floral meristems. Secondary flower formation usually associated with the ap1-1 mutation is suppressed in the terminal flower, but not in the lateral flowers, of tfl1-1 ap1-1 double mutants. Our results suggest that tfl1-1 perturbs the establishment and maintenance of the inflorescence meristem. The mutation lies on the top arm of chromosome 5 approximately 2.8 centimorgans from the restriction fragment length polymorphism marker 217.
546 citations
TL;DR: An overview of distributed shared memory issues covers memory coherence, design choices, and implementation methods, and algorithms that support process synchronization and memory management are discussed.
Abstract: An overview of distributed shared memory (DSM) issues is presented. Memory coherence, design choices, and implementation methods are included. The discussion of design choices covers structure and granularity, coherence semantics, scalability, and heterogeneity. Implementation issues concern data location and access, the coherence protocol, replacement strategy, and thrashing. Algorithms that support process synchronization and memory management are discussed. >
524 citations
TL;DR: Results indicated that only the 4--month-old group was easily able to disengage from an attractive central stimulus to orient toward a simultaneously presented target, consistent with the predictions of matura-tional accounts of the development of visual orienting.
Abstract: Three aspects of the development of visual orienting in infants of 2, 3, and 4 months of age are examined in this paper. These are the age of onset and sequence of development of (1) the ability to readily disengage gaze from a stimulus, (2) the ability to consistently show “anticipatory” eye movements, and (3) the ability to use a central cue to predict the spatial location of a target. Results indicated that only the 4--month-old group was easily able to disengage from an attractive central stimulus to orient toward a simultaneously presented target. The 4--month-old group also showed more than double the percentage of “anticipatory” looks than did the other age groups. Finally, only the 4--month-old group showed significant evidence of being able to acquire the contingent relationship between a central cue and the spatial location (to the right or to the left) of a target. Measures of anticipatory looking and contingency learning were not correlated. These findings are, in general terms, consistent with the predictions of matura-tional accounts of the development of visual orienting.
TL;DR: It is suggested that less skilled comprehenders suffer from a less efficient suppression mechanism, which is an important component of general comprehension skill.
Abstract: We investigated whether the cognitive mechanism of suppression underlies differences in adult comprehension skill. Less skilled comprehenders reject less efficiently the inappropriate meanings of ambiguous words (e.g., the playing card vs. garden tool meaning of spade), the incorrect forms of homophones (e.g., patients vs. patience), the highly typical but absent members of scenes (e.g., a tractor in a farm scene), and words superimposed on pictures or pictures surrounding words. However, less skilled comprehenders are not less cognizant of what is contextually appropriate; in fact, they benefit from a biasing context just as much (and perhaps more) as more skilled comprehenders do. Thus, less skilled comprehenders do not have difficulty enhancing contextually appropriate information. Instead, we suggest that less skilled comprehenders suffer from a less efficient suppression mechanism, which we conclude is an important component of general comprehension skill.
TL;DR: The success of helix–coil theory in describing the unfolding transitions of short peptides in water indicates that helical propensities, or s values, can be determined from substitution experiments in short alanine‐based peptides.
Abstract: Thermal unfolding curves have been measured for a series of short alanine-based peptides that contain repeating sequences and varying chain lengths. Standard helix-coil theory successfully fits the observed transition curves, even for these short peptides. The results provide values for sigma, the helix nucleation constant, delta H0, the enthalpy change on helix formation, and for s (0 degree C), the average helix propagation parameter at 0 degree C. The enthalpy change agrees with the value determined calorimetrically. The success of helix-coil theory in describing the unfolding transitions of short peptides in water indicates that helical propensities, or s values, can be determined from substitution experiments in short alanine-based peptides.
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01 Jan 1991TL;DR: The physical, chemical, and biologic properties of sedimentary rocks, as revealed by petrographic microscopy, geochemical techniques, and field study, are discussed in this paper.
Abstract: This textbook outlines the physical, chemical, and biologic properties of the major sedimentary rocks, as revealed by petrographic microscopy, geochemical techniques, and field study It covers the mineralogy, chemistry, textures, and sedimentary structures that characterise sedimentary rocks, and relates these features to the depositional origin of the rocks and their subsequent alteration by diagenetic processes during burial In addition to detailed sections on siliciclastic and carbonate rocks, it also discusses evaporites, cherts, iron-rich sedimentary rocks, phosphorites, and carbonaceous sedimentary rocks such as oil shales This second edition maintains the comprehensive treatment of sedimentary petrography and petrology provided in the first edition, and has been updated with new concepts and cutting-edge techniques like cathodoluminescence imaging of sedimentary rocks and backscattered electron microscopy It is ideal for advanced undergraduate and graduate courses in sedimentary petrology, and is a key reference for researchers and professional petroleum geoscientists
TL;DR: It is reported here that in wild-type embryos the floor plate develops as a simply organized single cell row, but that its development fails in embryos bearing the newly discovered zygotic lethal 'cyclops' mutation, cyc-1(b16).
Abstract: The floor plate is a set of epithelial cells present in the ventral midline of the neural tube in vertebrates that seems to have an important role in the developmental patterning of central nervous system fibre pathways, and arrangements of specific neurons. The floor plate arises from dorsal ectodermal cells closely associated with the mesoderm that forms notochord, and it may depend on interactions from the notochord for its specification. To learn the nature of these interactions we have analysed mutations in zebrafish (Brachydanio rerio). We report here that in wild-type embryos the floor plate develops as a simply organized single cell row, but that its development fails in embryos bearing the newly discovered zygotic lethal 'cyclops' mutation, cyc-1(b16). Mosaic analysis establishes that cyc-1 blocks floor plate development autonomously and reveals the presence of homeogenetic induction between floor plate cells.
TL;DR: Methods are presented for the estimation of phylogenywide means of characters, the variance‐covariance structure of the components of taxon‐specific means, and the mean phenotypes of ancestral taxa and it is argued that the covarianceructure of phylogenetic effects provides a description of a macroevolutionary pattern.
Abstract: Inferences regarding phylogenetic patterns and constraints on the evolution of characters often can be derived only from comparisons of extant species. If the phylogeny of these species is known, then the mean phenotypes of taxa can be partitioned into heritable phylogenetic effects and nonheritable residual components. Methods are presented for the estimation of phylogeny- wide means of characters, the variance-covariance structure of the components of taxon-specific means, and the mean phenotypes of ancestral taxa. These methods, which are largely an extension of maximum-likelihood techniques used in quantitative genetics, make an efficient use of the data, are unbiased by phylogenetically uninformative contributions to mean phenotypes, and take into account fully the nonindependence of data resulting from evolutionary relationships. Statistical tests are introduced for evaluating the significance of phylogenetic heritability and of correlations between traits, and expressions are given for the standard errors of ancestral mean phenotype estimates. It is argued that the covariance structure of phylogenetic effects provides a description of a macroevolutionary pattern, whereas that for the residual effects, when corrected for sampling error, is more closely related to a microevolutionary pattern.
TL;DR: The role of response efficiency in functional equivalence training was examined in terms of three variables: physical effort, schedule of reinforcement, and the time delay between presentation of the discriminative stimulus and reinforcer delivery.
Abstract: Three experiments addressed the role of response efficiency in the application of functional equivalence training. Functional equivalence training includes conducting a functional assessment of the problem behavior. Variables that predict and maintain the problem behavior are defined, and socially appropriate, functionally equivalent skills are identified and taught. The logic is that if the learner has a socially appropriate way to achieve the same function, he or she will be less likely to use problem behaviors. This study examined the role of response efficiency in functional equivalence training. Response efficiency was examined in terms of three variables: (a) physical effort, (b) schedule of reinforcement, and (c) the time delay between presentation of the discriminative stimulus and reinforcer delivery. Each of the three experiments involved a person who performed a set of problem behaviors and a functional assessment of the problem behaviors. A socially appropriate alternative response was taught, but this new response was less efficient than the problem behavior on one of the efficiency variables (effort, schedule, delay in time). The new behaviors did not compete successfully with the problem behaviors until a new, more efficient, alternative behavior was taught. These results are discussed in terms of our understanding of response covariation and the need in applied contexts to include response efficiency in any functional analysis assessment.
TL;DR: The new phototrophs are described as a new species of the genus Chlorobium, Ch chlorobium tepidum, which is positioned phylogenetically within the green sulfur bacterial branch of the domain Bacteria.
Abstract: Thermophilic green sulfur bacteria of the genus Chlorobium were isolated from certain acidic high sulfide New Zealand hot springs. Cells were Gram-negative nonmotile rods of variable length and contained bacteriochlorophyll c and chlorosomes. Cultures of thermophilic chlorobia grew only under anaerobic, phototrophic conditions, either photoautotrophically or photoheterotrophically. The optimum growth temperature for the strains of thermophilic green sulfur bacteria isolated was 47–48°C with generation times of about 2 h being observed. The upper temperature limit for growth was about 52°C. Thiosulfate was a major electron donor for photoautotrophic growth while sulfide alone was only poorly used. N2 fixation was observed at 48°C and cell suspensions readily reduced acetylene to ethylene. The G+C content of DNA from strains of thermophilic chlorobia was 56.5–58.2 mol% and the organisms positioned phylogenetically within the green sulfur bacterial branch of the domain Bacteria. The new phototrophs are described as a new species of the genus Chlorobium, Chlorobium tepidum.
01 Aug 1991
TL;DR: The notion of extensibility of a finite set of Laurent polynomials is shown to be central in the construction of wavelet decompositions by decomposition of spaces in a multiresolution analysis.
Abstract: We study basic questions of wavelet decompositions associated with multiresolution analysis. A rather complete analysis of multiresolution associated with the solution of a refinement equation is presented. The notion of extensibility of a finite set of Laurent polynomials is shown to be central in the construction of wavelets by decomposition of spaces. Two examples of extensibility, first over the torus and then in complex space minus the coordinate axes are discussed. In each case we are led to a decomposition of the fine space in a multiresolution analysis as a sum of the adjacent coarse space plus an additional space spanned by the multiinteger translates of a finite number of pre-wavelets. Several examples are provided throughout to illustrate the general theory.
TL;DR: The ratio of the helix propensities ofAlanine to glycine is large, about 100, in substitution experiments with a 17-residue reference peptide containing alanine and lysine, and the results are interpreted by the Lifson–Roig theory.
Abstract: The standard view of alpha helix formation in water, based on helix propensities determined by the host-guest method, is that differences in helix propensity among the amino acids are small, except for proline, and that the average value of the helix propagation parameter s is near 1. A contradictory view of alpha helix formation in water is emerging from substitution experiments with short, unique-sequence peptides that contain only naturally occurring amino acids. Short peptides that contain only alanine and lysine, or alanine and glutamate, form surprisingly stable monomeric helices in water and substitution of a single alanine residue by another amino acid in these or related peptides produces a wide range of changes in helix content, depending on which amino acid is substituted for alanine. We show here that the ratio of the helix propensities of alanine to glycine is large, about 100, in substitution experiments with a 17-residue reference peptide containing alanine and lysine. The helix propensity is identified with s, the helix propagation parameter of the statistical mechanics model for alpha helix formation, and the results are interpreted by the Lifson-Roig theory. Single alanine----glycine substitutions have been made at a series of positions in individual peptides. The helix-destabilizing effect of an Ala----Gly substitution depends strongly on its position in the helix, as predicted by the Lifson-Roig theory if the ratio of s values for Ala:Gly is large.
01 Jan 1991
TL;DR: A battery of laboratory temperament assessment techniques have been reviewed and evaluated from several perspectives (e g, Bornstein, Gaughran, & Homel, 1986; Crockenberg & Acredolo, 1983; Goldsmith & Rieser-Danner, 1990; Hubert, Wachs, Peters-Martin, & Gandour, 1982; Neale & Stevenson, 1989; Rothbart & Goldsmith, 1985; Seifer & Sameroff, 1986, Slabach, Morrow, & WachS, this volume) as mentioned in this paper.
Abstract: Research in behavioral science often succeeds or fails depending on the quality of its assessment instruments Recognizing this, many temperament researchers have proposed questionnaires, interview schedules, home observation coding systems, and laboratory methods for assessing early temperament These assessment instruments have been reviewed and evaluated from several perspectives (e g, Bornstein, Gaughran, & Homel, 1986; Crockenberg & Acredolo, 1983; Goldsmith & Rieser-Danner, 1990; Hubert, Wachs, Peters-Martin, & Gandour, 1982; Neale & Stevenson, 1989; Rothbart & Goldsmith, 1985; Seifer & Sameroff, 1986; Slabach, Morrow, & Wachs, this volume) In this chapter, we preview some new instruments and review recent data on an established questionnaire, all developed in our laboratories These instruments include the Infant Behavior Questionnaire, the Toddler Behavior Assessment Questionnaire, and the Children’s Behavior Questionnaire, as well as a battery of laboratory temperament assessment techniques
TL;DR: The three-dimensional structure of human basic fibroblast growth factor (bFGF) has been determined by x-ray crystallography and refined to a crystallographic residual of 17.4% at 2.2-A resolution.
Abstract: The three-dimensional structure of human basic fibroblast growth factor (bFGF) has been determined by x-ray crystallography and refined to a crystallographic residual of 17.4% at 2.2-A resolution. The structure was initially solved at a nominal resolution of 2.8 A by multiple isomorphous replacement using three heavy-atom derivatives. Although the map clearly showed the overall fold of the molecule, electron density was not observed for the first 19 amino-terminal and the last 3 carboxyl-terminal amino acids, suggesting that they are disordered. The bFGF crystals were grown from 2.0 M ammonium sulfate at pH 8.1 in space group P1 with cell dimensions a = 30.9 A, b = 33.4 A, c = 35.9 A, alpha = 59.5 degrees, beta = 72.0 degrees, and gamma = 75.6 degrees. There is one molecule per unit cell and the crystals diffract to spacings beyond 1.9 A. The overall structure of bFGF can be described as a trigonal pyramid with a fold very similar to that reported for interleukin 1 beta, interleukin 1 alpha, and soybean trypsin inhibitor. An apparent sulfate ion is bound within a basic region on the surface of the molecule and has a ligands the main-chain amide of Arg-120 and the side chains of Asn-27, Arg-120, and Lys-125. This is suggested as the presumed binding site for heparin. Residues 106-115, which are presumed to bind to the bFGF receptor [Baird, A., Schubert, D., Ling, N. & Guillemin, R. (1988) Proc. Natl. Acad. Sci. USA 85, 2324-2328], include an irregular loop that extends somewhat from the surface of the protein and is about 25 A from the presumed heparin binding site. The backbone structure of this putative receptor-binding loop is very similar, although not identical, to the corresponding region of interleukin 1 beta.
TL;DR: Investigations into landing are necessary to more thoroughly understand the force attenuation mechanisms and critical performance variables associated with lower extremity injuries.
Abstract: Many sport and movement activities contain a jumping component which necessitates landing. Several injury surveys across a variety of jump sports have identified the lower extremities and specifically the knee joint as being a primary injury site. Factors which might contribute to the frequency and severity of such injuries include stresses to which the body is subjected during performance (forces and torques), body position at landing, performance execution and landing surface. Most of the initial landing studies were primarily descriptive in nature with many of the more recent efforts being directed toward identifying the specific performance factors that could account for the observed system stresses. Continued investigations into landing are necessary to more thoroughly understand the force attenuation mechanisms and critical performance variables associated with lower extremity injuries.
TL;DR: Overall, the necessity of performing a complete minimization of the Higgs sector {ital before} extracting phenomenology is emphasized, which leads to a highly restrictive range of possibilities for global minima that are simultaneously consistent with all experimental observations.
Abstract: We examine the predictions of the conventional SU(2${)}_{\mathit{L}}$\ensuremath{\bigotimes}SU(2${)}_{\mathit{R}}$\ensuremath{\bigotimes}U(1${)}_{\mathit{B}\mathrm{\ensuremath{-}}\mathit{L}}$ left-right-symmetric model in the case where the minimal Higgs sector (containing one bidoublet, one L-triplet, and one R-triplet Higgs field) and the standard lepton representations (incorporating right-handed partners for the observed neutrinos) are adopted. We show that a complete analysis of spontaneous symmetry breaking for the Higgs sector leads to a highly restrictive range of possibilities for global minima that are simultaneously consistent with all experimental observations (such as lepton masses, ${\mathit{K}}_{\mathit{L}}$-${\mathit{K}}_{\mathit{S}}$ mixing, etc.). As a result, the possible phenomenologies for the gauge and Higgs bosons of the model are very limited. For instance, we demonstrate that in the absence of explicit CP violation in the Higgs potential, spontaneous CP violation does not arise and the fermion couplings exhibit ``manifest'' left-right symmetry. Further, we find no entirely natural solutions other than ones in which all of the extra (non-standard-model) gauge and Higgs bosons associated with the left-right-symmetric extension are extremely heavy (typically, more massive than ${10}^{7}$ GeV). Only by ``fine-tuning'' certain parameters of the Higgs potential is it possible to bring these extra particles down to an observable mass scale. Alternatively, symmetries can be introduced to eliminate the terms in the Higgs potential associated with these parameters, but only at the sacrifice of introducing undesirable consequences for fermion masses. Many of the pitfalls and problems are illustrated using a simplified model. Overall, we emphasize the necessity of performing a complete minimization of the Higgs sector before extracting phenomenology.
TL;DR: A thermodynamic analysis of the elongation phase of transcription in Escherichia coli closely predicts the exact sites of termination at a number of intrinsic terminators (and attenuators) in the E. coli genome.
Abstract: In the first part of this paper we present a thermodynamic analysis of the elongation phase of transcription in Escherichia coli. The stability of the elongation complex is described by a "free energy of formation" function (delta G zero f) that is a sum of terms for forming (i) a locally denatured 17-base-pair DNA "bubble"; (ii) a constant-length hybrid between the 3'-terminal 12-nucleotide residues of the RNA transcript and the corresponding region of the DNA template strand; and (iii) a set of binding interactions between the polymerase and certain DNA and RNA residues within and near the "transcription bubble". The transcriptional elongation complex is very stable at most positions along a natural DNA template and moves in a highly processive fashion. At these positions, the delta G zero f function provides a quantitative measure of the stability of the elongation complex. Besides allowing for the polymerization of the RNA transcript, the elongation complex also serves to define the context within which transcript termination occurs. In the second part of the paper the thermodynamic analysis is extended to discriminate between template positions at which the elongation complex is stable and positions at which it is rendered relatively unstable by the presence of a string of rU residues at the 3'-terminus of the RNA together with the formation of a specific RNA hairpin just upstream of this point. Most factor-independent (intrinsic) termination events are thermodynamically disallowed at the former positions and are thermodynamically allowed at the latter positions. The extended form of the analysis closely predicts the exact sites of termination at a number of intrinsic terminators (and attenuators) in the E. coli genome. It also correctly predicts bidirectional function for a number of bidirectional terminators. In some cases it may identify terminators that are similar to the intrinsic type but that require additional protein factors, unusual polymerase-nucleic acid interactions, or rate-limiting conformational changes in order to function. Finally, it successfully locates intrinsic terminators within a number of E. coli operons and discriminates between these terminators and the surrounding DNA sequence.
TL;DR: It is concluded that pairs of oppositely charged residues that are on the surface of a protein and have freedom to adopt different conformations do not tend to come together to form structurally localized salt bridges, and instead remain mobile, interact weakly if at all, and do not contribute significantly to protein stability.
Abstract: Six designed mutants of T4 lysozyme were created in an attempt to create putative salt bridges on the surface of the protein. The first three of the mutants, T115E (Thr 115 to Glu), Q123E, and N144E, were designed to introduce a new charged side chain close to one or more existing charged groups of the opposite sign on the surface of the protein. In each of these cases the putative electrostatic interactions introduced by the mutation include possible salt bridges between residues within consecutive turns of an alpha-helix. Effects of the mutations ranged from no change in stability to a 1.5 degrees C (0.5 kcal/mol) increase in melting temperature. In two cases, secondary (double) mutants were constructed as controls in which the charge partner was removed from the primary mutant structure. These controls proteins indicate that the contributions to stability from each of the engineered salt bridges is very small (about 0.1-0.25 kcal/mol in 0.15 M KCl). The structures of the three primary mutants were determined by X-ray crystallography and shown to be essentially the same as the wild-type structure except at the site of the mutation. Although the introduced charges in the T115E and Q123E structures are within 3-5 A of their intended partner, the introduced side chains and their intended partners were observed to be quite mobile. It has been shown that the salt bridge between His 31 and Asp 70 in T4 lysozyme stabilizes the protein by 3-5 kcal/mol [Anderson, D. E., Becktel, W. J., & Dahlquist, F. W. (1990) Biochemistry 29, 2403-2408]. To test the effectiveness of His...Asp interactions in general, three additional double mutants, K60H/L13D, K83H/A112D, and S90H/Q122D, were created in order to introduce histidine-aspartate charge pairs on the surface of the protein. Each of these mutants destabilizes the protein by 1-3 kcal/mol in 0.15 M KCl at pH values from 2 to 6.5. The X-ray crystallographic structure of the mutant K83H/A112D has been determined and shows that there are backbone conformational changes of 0.3-0.6 A extending over several residues. The introduction of the histidine and aspartate presumably introduces strain into the folded protein that destabilizes this variant. It is concluded that pairs of oppositely charged residues that are on the surface of a protein and have freedom to adopt different conformations do not tend to come together to form structurally localized salt bridges. Rather, such residues tend to remain mobile, interact weakly if at all, and do not contribute significantly to protein stability. It is argued that the entropic cost of localizing a pair of solvent-exposed charged groups on the surface of a protein largely offsets the interaction energy expected from the formation of a defined salt bridge. There are examples of strong salt bridges in proteins, but such interactions require that the folding of the protein provides the requisite driving energy to hold the interacting partners in the correct rigid alignment.
TL;DR: Application of climate-pollen response surfaces to three climate model simulations of doubled preindustrial atmospheric CO2 levels shows that the change in the equilibrium distribution of natural vegetation over eastern North America over the next 200 to 500 years could be larger than the overall change during the past 7,000 to 10,000 years and equivalent to the change that took place over the 1,000- to 3,000 year period of most rapid deglaciation.
Abstract: Increases in atmospheric trace gas concentrations could warm the global average temperature 1.5° to 4.5°C by the end of the next century. Application of climate-pollen response surfaces to three climate model simulations of doubled preindustrial atmospheric CO 2 levels shows that the change in the equilibrium distribution of natural vegetation over eastern North America over the next 200 to 500 years could be larger than the overall change during the past 7,000 to 10,000 years and equivalent to the change that took place over the 1,000- to 3,000-year period of most rapid deglaciation. Some plant ranges and abundance maxima could shift as much as 500 to 1000 km during the next 200 to 500 years; such changes would have dramatic impacts on silvicultural and natural ecosystems. Although unprecedented vegetation change is likely if climate changes as predicted, forecasting the exact timing and patterns of change will be difficult.
01 Jan 1991
TL;DR: In this article, a new model of cooperators' advantage is proposed, which depends on players' making the play-no-play decision by the heuristic of projecting their own "cooperate-defect" choices onto potential partners.
Abstract: We propose a new model of cooperators' advantage depending neither on supplementary incentives nor on cooperators' capacity to recognize, and play selectively with, other cooperators. It depends, rather, on players' making the play-no play decision by the heuristic of projecting their own “cooperate-defect” choices onto potential partners. Cooperators offer to play more often, and fellow cooperators will more often accept their offer. When certain boundary conditions are met, this results in a higher expected payoff for cooperators than for defectors. Empirical support for this heuristic is suggested by expectations data from related social dilemma experiments. Moreover, its use can be justified in Bayesean terms. Our model brings behavioral decision theory's “cognitive miser” paradigm to bear on interdisciplinary concern with the evolution of cooperative behavior and shows how, if other mechanisms provide a suitable “initial kick,” cooperation can evolve in the absence of iteration and in large, mobile societies.