Showing papers by "University of Oregon published in 1987"

Complexity of finding embeddings in a k -tree

Abstract: A k-tree is a graph that can be reduced to the k-complete graph by a sequence of removals of a degree k vertex with completely connected neighbors. We address the problem of determining whether a graph is a partial graph of a k-tree. This problem is motivated by the existence of polynomial time algorithms for many combinatorial problems on graphs when the graph is constrained to be a partial k-tree for fixed k. These algorithms have practical applications in areas such as reliability, concurrent broadcasting and evaluation of queries in a relational database system. We determine the complexity status of two problems related to finding the smallest number k such that a given graph is a partial k-tree. First, the corresponding decision problem is NP-complete. Second, for a fixed (predetermined) value of k, we present an algorithm with polynomially bounded (but exponential in k) worst case time complexity. Previously, this problem had only been solved for $k = 1,2,3$.

Roundtable: what is temperament? Four approaches

Abstract: 4 current approaches to understanding temperament are discussed in the roundtable. In an introductory overview, Goldsmith outlines some of the major convergences and divergences in the understanding of this concept. Theorists representing 4 positions--Goldsmith, Buss and Plomin, Rothbart, and Thomas and Chess--outline their views by responding to each of 6 questions: How do you define temperament and explain the boundaries of the concept? What are the elements of temperatment? How does the construct of temperament permit you to approach issues or organize data in ways that are possible only if this construct is invoked? How does temperament develop? To what extent do you consider temperament to be a personological versus a relational or an interactional construct? and How does your approach deal with issues of temperamental "difficulty"? In 2 commentaries on the theorists' answers, Hinde highlights differences among their positions and indicates issues that current theories of temperament must take into consideration, and McCall draws on common aspects to propose a synthesizing definition that draws on all 4 approaches.

Protein stability curves

Abstract: The stability curve of a protein is defined as the plot of the free energy of unfolding as a function of temperature. For most proteins the change in heat capacity on denaturation, or unfolding, is large but approximately constant. When unfolding is s two-state process, most of the salient features of the stability curves of proteins can be derived from this fact. A number of relations are obtained, including the special features of low-temperature denaturation, the properties of the maximum in stability, and the interrelationships of the characteristic temperatures of the protein. The paper closes with a formula that permits one to calculate small changes in stabilization free energy from changes in the melting temperature of the protein.

Four Genes Responsible for a Position Effect on Expression From HML and HMR in Saccharomyces cerevisiae

Abstract: Mating type interconversion in Saccharomyces cerevisiae occurs by transposition of copies of the a or ci mating type cassettes from inactive loci, HML and HMR, to an active locus, MAT. The lack of expression of the a and LY genes at the silent loci results from repression by trans-acting regulators encoded by SIR @lent information Regulator) genes. In this paper we present evidence for the existence of four SIR genes. Inactivation of any of these genes leads to expression of cassettes at both HML and HMR. Unusual complementation properties are observed for a number of sir mutations. Specifically, some recessive mutations in different genes fail to complement. The correspondence between SIRI, SIR2, SIR3, SIR4 and other genes with similar roles (MAR, CMT, STE8 and STEP) is presented. ELL type in the unicellular eucaryote SaccharoC myces cerevisiae is under control of a single genetic locus, the mating type locus (MAT). The two mating types of yeast, a and a, are determined by the MATa and MATa alleles, respectively (LINDEGREN and LINDEGREN 1943). The gene products that are encoded by both MATa and MATa are regulatory proteins UOHNSON and HERSKOWITZ 1985). The genetic and physical structure of the mating type locus is known (SPRAGUE, RINE and HERSKOWITZ 198 1, a, b; ASTELL et al. 198 1 ; NASMYTH and TATCHELL 1980). MAT consists of a block of DNA approximately 2 kilobase pairs (kb) in length. The structural details of MATa and MATa are indicated in Figure 1 [adapted from ASTELL et al. (1 98 1) and ABRAHAM et al. (1984)]. Two points are particularly relevant to this work: (1) the central regions of MATa and MATa are nonhomologous; (2) both MATa and MATa encode two transcripts, a1 and a2 in a celIs and a1 and a2 in a cells, that are transcribed from divergent promoters located in the regions of nonhomology between a and a. Certain strains of yeast, namely those containing the HO gene (WINCE and ROBERTS 1949), are capable of switching from one cell type to another as frequently as once per generation (HICKS and HERSKOWITZ 1976; STRATHERN and HERSKOWITZ 1979; RINE et al. 1981). When a cell switches from a to a, MATa is replaced by MATa; switching from a to a results from the opposite change. HMLa and HMRa are additional genes required for mating type intercon

Voluntarily Leaving an Organization: An Empirical Investigation of Steers and Mowday's Model of Turnover

Abstract: This study tested propositions derived from Steers and Mow day's (1981) model. A group of 445 employees of a financial institution responded to a mailed survey. Through access to their personnel re...

Isolating attentional systems: A cognitive-anatomical analysis

Abstract: Recently our knowledge of the mechanisms of visual-spatial attention has improved because of studies employing single cell recording with alert monkeys and others using performance analysis of neurological patients. These studies suggest that a complex neural network that includes parts of the posterior parietal lobe and midbrain is involved in covert shifts of visual attention. Is this system an isolated visual attentional module or is it part of a more general attentional system? Our studies employ the dual-task technique to determine whether covert visual orienting can take place while a person’s attention is engaged in a language processing task. We find clear evidence of interference between the two tasks, which suggests some common operations. However, the results also indicate that whatever is common to the two tasks does not have the same anatomical location as that of visual-spatial attention.

Rational Ecology: Environment and Political Economy

Abstract: The book describes the variety of institutional arrangements through which collective decisions can be achieved and makes special reference to decision-making on ecology. According to the author, the means employed by societies to make collective choices have far-reaching ramifications for the kind of world which exists or develops. He assesses those means in connection with various forms of rationality used to make decisions and to act: markets, bureaucracies, and polyarchies are among the institutional arrangements evaluated. He examines their capacity for intelligent decision-making, based on notions of justice, individual liberty or economic efficiency, and measures these against the yardstick of environmental concerns, a pressing set of problems which transcend particular political and institutional arrangements. The analysis extends beyond the realm of environmental choice to elucidate more fully the characteristics of the world's social choice mechanisms and proposes innovations for improving these forms.

Oryzalin, a dinitroaniline herbicide, binds to plant tubulin and inhibits microtubule polymerization in vitro

Abstract: The effects of oryzalin, a dinitroaniline herbicide, on chromosome behavior and on cellular microtubules (MTs) were examined by light microscopy and immunogold staining, respectively, in endosperm cells from Haemanthus katherinae Bak. Brief treatments with 1.0·10-8 M oryzalin reduced markedly the migration rate of anaphase chromosomes and 1.0·10-7 M oryzalin stopped migration abruptly. Oryzalin (1.0·10-7 M) depolymerized MTs and prevented the polymerization of new MTs at all stages of the mitotic cycle. The chromosome condensation cycle was unaffected by oryzalin. Endothelial cells from the heart of Xenopus leavis showed no chromosomal or microtubular rearrangements after oryzalin treatment. The inhibition by oryzalin of the polymerization of tubulin isolated from cultured cells of Rosa sp. cv. Paul's scarlet was examined in vitro by turbidimetry, electron microscopy and polymer sedimentation analysis. Oryzalin inhibited the rapid phase of taxol-induced polymerization of rose MTs at 24°C with an apparent inhibition constant (K i ) of 2.59·106 M. Shorter and fewer MTs were formed with increasing oryzalin concentrations, and maximum inhibition of taxol-induced polymerization occurred at approx. 1:1 molar ratios of oryzalin and tubulin. Oryzalin partially depolymerized taxol-stabilized rose MTs. Ligand-binding experiments with [14C]oryzalin demonstrated the formation of a tubulin-oryzalin complex that was time- and pH-dependent. The tubulin-oryzalin interaction (24°C, pH 7.1) had an apparent affinity constant (K app) of 1.19·105 M-1. Oryzalin did not inhibit taxol-induced polymerization of bovinebrain MTs and no appreciable binding of oryzalin to brain tubulin or other proteins was detected. The results demonstrate pharmacological differences between plant and animal tubulins and indicate that the most sensitive mode of action of the dinitroaniline herbicides is the direct poisoning of MT dynamics in cells of higher plants.

High-resolution photoemission study of the electronic structure of the noble-metal (111) surfaces.

Abstract: High-resolution angle-resolved photoemission studies of the (111) surfaces of copper, silver, and gold are reported which investigate in detail the properties of the intrinsic surface states located in the projected sp-band gaps at the center of the surface Brillouin zones. Accurate two-dimensional energy dispersion relations are reported for each surface state and are quantified in terms of effective masses at the surface Brillouin-zone center. The masses for the three metals are found to be remarkably similar when normalized to the effective mass of the lower edge of the bulk continuum. The decay length of the surface state wave function into the surface was determined for all three surfaces. These results are expressed in terms of an effective mass of the complex dispersion relation within the projected band gap. In accord with our previous results on the copper state, these effective masses are found to be anomalously large by approximately a factor of 2 relative to expectations based on effective mass theory coupled to first-principles bulk band calculations. An explanation of this anomaly involving the nonorthogonality of effective-mass-theory-derived states is explored. All experimental results are compared to the predictions of recent self-consistent surface electronic structure calculations for these surfaces.

Selective binding and solvent denaturation.

Abstract: A primitive model for solvent denaturation is that the denaturant binds independently to sites exposed by the unfolding of the protein. For reagents like urea and guanidinium salts, this binding must be very weak since denaturation occurs only at very high concentrations. Standard formulas for very weak binding lead to thermodynamic inconsistencies. In this paper, binding by denaturants is treated as selective solvation. This introduces a factor of K 1 into the binding isotherm and binding free energy, where K is the equilibrium constant for selective interaction with the sites. This leads to a thermodynamically consistent description of the binding and the denaturation since, when K = 1, there is no selective interaction and no effect on denaturation, even in concentrated solutions where site occupancy is inevitable.

The Intergeniculate Leaflet Partially Mediates Effects of Light on Circadian Rhythms

Abstract: Photic signals affect circadian activity rhythms by both phasic and tonic mechanisms that modulate pacemaker phase and period. In mammals, the effects of light on circadian activity are mediated by the retina, which communicates with the suprahiasmatic nucleus (SCN) by two different anatomical routes: the retino-hypothalamic tract (RHT), originating in the retina, and the geniculo-hypothalamic tract (GHT), arising from a retino-recipient nucleus, the intergeniculate leaflet (IGL). We assessed the roles of these two afferent systems in mediating phasic and tonic effects of light on circadian activity in IGL-lesioned animals. Destruction of the IGL significantly affected phase shifts produced by brief light pulses (phasic effect) and modified the change in period (tau) of the free-running activity rhythm produced by changing the level of constant light (LL) (tonic effect). Phase advances produced by brief light pulses were decreased in amplitude while phase delays were increased in IGL-lesioned animals as compared to controls. The free-running period in constant dark (tau DD) of IGL-lesioned animals was greater than tau DD of controls, and the lengthening of tau normally produced by LL was not observed or was greatly reduced in IGL-lesioned animals. Entrainment to light-dark cycles was unaffected by the lesions, as were other aspects of the circadian activity rhythm that normally change in response to LL (e.g., activity-rest ratio, total activity, splitting). Our data support the interpretation that the IGL plays a significant role in relaying information regarding illumination intensity to the SCN.

Identification and regulation of a gene required for cell fusion during mating of the yeast Saccharomyces cerevisiae.

Abstract: We have devised a screen for genes from the yeast Saccharomyces cerevisiae whose expression is affected by cell type or by the mating pheromones. From this screen we identified a gene, FUS1, whose pattern of expression revealed interesting regulatory strategies and whose product was required for efficient cell fusion during mating. Transcription of FUS1 occurred only in a and alpha cells, not in a/alpha cells, where it was repressed by a1 X alpha 2, a regulatory activity present uniquely in a/alpha cells. Transcription of FUS1 showed an absolute requirement for the products of five STE genes, STE4, STE5, STE7, STE11, and STE12. Since the activators STE4, STE5, and STE12 are themselves repressed by a1 X alpha 2, the failure to express FUS1 in a/alpha cells is probably the result of a cascade of regulatory activities; repression of the activators by a1 X alpha 2 in turn precludes transcription of FUS1. In addition to regulation of FUS1 by cell type, transcription from the locus increased 10-fold or more when a or alpha cells were exposed to the opposing mating pheromone. To investigate the function of the Fus1 protein, we created fus1 null mutants. In fus1 X fus1 matings, the cells of a mating pair adhered tightly and appeared to form zygotes. However, the zygotes were abnormal. Within the conjugation bridge the contained a partition that prevented nuclear fusion and mixing of organelles. The predicted sequence of the Fus1 protein (deduced from the FUS1 DNA sequence) and subcellular fractionation studies with Fus1-beta-galactosidase hybrid proteins suggest that Fus1 is a membrane or secreted protein. Thus, Fus1 may be located at a position within the cell where it is poised to catalyze cell wall or plasma membrane fusion.

Temperature-sensitive mutations of bacteriophage T4 lysozyme occur at sites with low mobility and low solvent accessibility in the folded protein.

Abstract: Twenty-five different temperature-sensitive point mutations at 20 sites in the lysozyme gene of bacteriophage T4 have been identified. All of the mutations alter amino acid side chains that have lower than average crystallographic thermal factors and reduced solvent accessibility in the folded protein. This suggests that the amino acids with well-defined conformations can form specific intramolecular interactions that make relatively large contributions to the thermal stability of the protein. Residues with high mobility or high solvent accessibility are much less susceptible to destabilizing substitutions, suggesting that, in general, such amino acids contribute less to protein stability. The pattern of the sites of ts substitutions observed in the folded conformation of T4 lysozyme suggests that severe destabilizing mutations that primarily affect the free energy of the unfolded state are rare. These results indicate that proteins can be stabilized by adding new interactions to regions that are rigid or buried in the folded conformation.

Measuring and Interpreting Organizational Culture

Abstract: This article offers a triangulation approach to the study of organizational culture by employing reliably coded interviews to help interpret and place in context the results of statistical analyses...

Spatial frequency channels and perceptual grouping in texture segregation

Abstract: The literature suggests that both spatial frequency components and grouping processes affect texture segregation. The experiments we report investigated texture segregation in a three-part (tripartite) pattern in which each part contains equal numbers of two different squares that are arranged in vertical stripes in the top and bottom parts and in a checkerboard in the center part. We found: (1) A difference in sign of contrast yields strong texture segregation. (2) Texture segregation is a negatively accelerated function of the ratio of the Rayleigh contrasts of the low-luminance and high-luminance squares. (3) Size and contrast are not independent attributes but can cancel each other. High spatial frequency differences are not sufficient to cause segregation in the presence of contradictory information from the low spatial frequency channels. (4) Hue is a weak feature relative to contrast. Hue differences are not sufficient to cause texture segregation in the presence of contradictory contrast information. The results of the experiments support the argument that the higher order processes in texture segregation have access to information corresponding to the outputs of the spatial frequency channels. They are qualitatively consistent with the hypothesis that tripartite segregation is primarily a function of spatial frequency components and not of grouping processes.

Developmental models of supervision: Is it development?

Abstract: Developmental models of supervision have become the Zeitgeist of supervision thinking and research. Eighteen different models of supervision that refer to developmental principles have been cited in the psychiatric, psychological, and social work disciplines (Worthington, 1984). Numerous empirical studies have been designed to investigate developmental paradigms (Roehlke, 1984). If these models are to continue to influence research and practice, it seems warranted that the underlying assumptions and principles of the proposed models be critically examined. This article contains such a critical examination, and the conceptual and methodological approaches currently applied in the research of this topic are discussed from a developmental perspective.

How do financial analysts make decisions? A process model of the investment screening decision

Abstract: This article examines the decision making processes of professional financial analysts who are screening prospective investments. The analysts were provided with a package of financial materials that reflected the magnitude and the types of information that they normally review. They were asked to verbalize “whatever came to mind” during their evaluation. The resulting transcripts, called protocols, formed the basis for the analysis. The protocol analysis produced a descriptive model of the financial screening process, including the identification of the decision making processes, the decision rules, and the types of knowledge that are required to perform the task. Particular attention is given to factors that differentiate among individual analysts.