Showing papers by "University of Oregon published in 1993"

The mental representation of parity and number magnitude.

Abstract: Nine experiments of timed odd-even judgments examined how parity and number magnitude are accessed from Arabic and verbal numerals. With Arabic numerals, Ss used the rightmost digit to access a store of semantic number knowledge. Verbal numerals went through an additional stage of transcoding to base 10. Magnitude information was automatically accessed from Arabic numerals. Large numbers preferentially elicited a rightward response, and small numbers a leftward response. The Spatial-Numerical Association of Response Codes (SNARC) effect depended only on relative number magnitude and was weaker or absent with letters or verbal numerals. Direction did not vary with handedness or hemispheric dominance but was linked to the direction of writing, as it faded or even reversed in right-to-left writing Iranian Ss

Goal-directed requirements acquisition

Abstract: Requirements analysis includes a preliminary acquisition step where a global model for the specification of the system and its environment is elaborated This model, called requirements model, involves concepts that are currently not supported by existing formal specification languages, such as goals to be achieved, agents to be assigned, alternatives to be negotiated, etc The paper presents an approach to requirements acquisition which is driven by such higher-level concepts Requirements models are acquired as instances of a conceptual meta-model The latter can be represented as a graph where each node captures an abstraction such as, eg, goal, action, agent, entity, or event, and where the edges capture semantic links between such abstractions Well-formedness properties on nodes and links constrain their instances-that is, elements of requirements models Requirements acquisition processes then correspond to particular ways of traversing the meta-model graph to acquire appropriate instances of the various nodes and links according to such constraints Acquisition processes are governed by strategies telling which way to follow systematically in that graph; at each node specific tactics can be used to acquire the corresponding instances The paper describes a significant portion of the meta-model related to system goals, and one particular acquisition strategy where the meta-model is traversed backwards from such goals The meta-model and the strategy are illustrated by excerpts of a university library system

Configurational approaches to organizational analysis

Abstract: The 1993 Special Research Forum on Configurations is dedicated to the proposition that configurational theory and research can significantly advance understanding of people, groups, and organizations. In this introductory essay, we define configurational approaches to organizational analysis, trace the history of configurational thinking, distinguish the contingency approach from the configurational approach, and highlight key contributions of the five empirical articles that make up the special research forum. Most of these articles report research conducted at the organizational level of analysis, but we argue that the configurational perspective has unrealized potential at other levels as well and suggest some configurational approaches to revitalizing theory and research at the individual and group levels.

Successive combination jet algorithm for hadron collisions

Abstract: Jet finding algorithms, as they are used in ${e}^{+}{e}^{\ensuremath{-}}$ and hadron collisions, are reviewed and compared. It is suggested that a successive combination style algorithm, similar to that used in ${e}^{+}{e}^{\ensuremath{-}}$ physics, might be useful also in hadron collisions, where cone style algorithms have been used previously.

Measurement of the Wigner distribution and the density matrix of a light mode using optical homodyne tomography: Application to squeezed states and the vacuum.

Abstract: We have measured probability distributions of quadrature-field amplitude for both vacuum and quadrature-squeezed states of a mode of the electromagnetic field. From these measurements we demonstrate the technique of optical homodyne tomography to determine the Wigner distribution and the density matrix of the mode. This provides a complete quantum mechanical characterization of the measured mode.

Measurement of the Wigner distribution and the density matrix of a light mode by using optical homodyne tomography: application to squeezed states and vacuum

Abstract: We report measurements of the Wigner distribution and the density matrix of an electromagnetic field mode, for both vacuum and quadrature-squeezed states. As proposed by Vogel and Risken,1 we obtained the Wigner distribution by tomographic inversion of a set of probability distributions of field-quadrature amplitudes measured by using balanced homodyne detection. A Fourier transform of the Wiener function yields the density matrix, which, according to the standard interpretation of quantum mechanics, contains all knowable information about a given quantum system.

Structure of the zebrafish snail1 gene and its expression in wild-type, spadetail and no tail mutant embryos

Abstract: Mesoderm formation is critical for the establishment of the animal body plan and in Drosophila requires the snail gene. This report concerns the cloning and expression pattern of the structurally similar gene snail1 from zebrafish. In situ hybridization shows that the quantity of snail1 RNA increases at the margin of the blastoderm in cells that involute during gastrulation. As gastrulation begins, snail1 RNA disappears from the dorsal axial mesoderm and becomes restricted to the paraxial mesoderm and the tail bud. snail1 RNA increases in cells that define the posterior border of each somite and then disappears when somitic cells differentiate. Later in development, expression appears in cephalic neural crest derivatives. Many snail1-expressing cells were missing from mutant spadetail embryos and the quantity of snail1 RNA was greatly reduced in mutant no tail embryos. The work presented here suggests that snail1 is involved in morphogenetic events during gastrulation, somitogenesis and development of the cephalic neural crest, and that no tail may act as a positive regulator of snail1.

The zebrafish midblastula transition

Abstract: The zebrafish midblastula transition (MBT) begins at cycle 10. It is characterized by cell cycle lengthening, loss of cell synchrony, activation of transcription and appearance of cell motility. Superceding a 15 minute oscillator that controls the first nine cycles, the nucleocytoplasmic ratio appears to govern the MBT. This timing mechanism operates cell autonomously: clones of labeled cells initiate cell cycle lengthening independently of neighbors but dependent on immediate lineal ancestors. Unequal divisions, when they occur, produce asymmetric cell cycle lengthening based on the volume of each daughter. During the several cycles after the MBT begins, cycle length is correlated with the reciprocal of the blastomere volume, suggesting a continuation of cell cycle regulation by the nucleocytoplasmic ratio during an interval that we term the 'MBT period'.

Quantum trajectory theory for cascaded open systems.

Abstract: The quantum trajectory theory of an open quantum system driven by a photoemissive source is formulated. The formalism is illustrated by applying it to photon scattering from an atom driven by strongly focused coherent light.

The mutational meltdown in asexual populations

Abstract: Loss of fitness due to the accumulation of deleterious mutations appears to be inevitable in small, obligately asexual populations, as these are incapable of reconstituting highly fit genotypes by recombination or back mutation. The cumulative buildup of such mutations is expected to lead to an eventual reduction in population size, and this facilitates the chance accumulation of future mutations. This synergistic interaction between population size reduction and mutation accumulation leads to an extinction process known as the mutational meltdown, and provides a powerful explanation for the rarity of obligate asexuality. We give an overview of the theory of the mutational meltdown, showing how the process depends on the demographic properties of a population, the properties of mutations, and the relationship between fitness and number of mutations incurred.

Attentional and Nonattentional Forms of Sequence Learning

Abstract: This research investigated the hypothesis that sequential patterns of behavior can be learned by 2 independent mechanisms. One requires attention to the relation between successive events, whereas the other operates independently of such attention. In 4 experiments, subjects learned visuospatial sequences in a serial reaction time task. The relation between attentional and nonattentional learning was explored by assessing the extent to which learning transferred between conditions with or without distraction. The results suggest that attentional and nonattentional learning operate independently, in parallel, do not share information, and represent sequential information in qualitatively different ways. A fundamental type of learning in which humans excel is the learning of sequential patterns of behavior. In four experiments, we investigated the hypothesis that humans exhibit two forms of sequential learning. One form of learning requires attention to the relation between successive events in the sequence, not only for acquisition but also for the expression of the learning in performance. We hypothesized that the other type of sequential learning did not require attention to these relations. Furthermore, these two forms of learning are independent of one another, with no communication or sharing of information between them. If subjects perform a series of behavioral acts that occur in a predictable order and under conditions relatively free of distraction, we suppose that attentionally based and nonattentionally based learning of the sequence occur in parallel. If distraction is added during learning, the attentional form is disabled, but the nonattentional one is unmodified. That is, attention is neither necessary nor helpful to the nonattentional form of learning. This hypothesis is similar to ideas examined by other investigators but is also different in several ways. Nissen and her colleagues (Nissen & Bullemer, 1987; Willingham, Nissen, & Bullemer, 1989; see also Lewicki, Hill, & Bizot, 1988; Stadler, 1989) have suggested that learning of sequences can be either procedural (without awareness) or declarative (with awareness). Both of these, according to Nissen, require attention. We distinguish both of those forms from a third, nonattentional type of learning.

Dynamic backtracking

Abstract: Because of their occasional need to return to shallow points in a search tree, existing backtracking methods can sometimes erase meaningful progress toward solving a search problem. In this paper, we present a method by which backtrack points can be moved deeper in the search space, thereby avoiding this difficulty. The technique developed is a variant of dependency-directed backtracking that uses only polynomial space while still providing useful control information and retaining the completeness guarantees provided by earlier approaches.

Occurrence of UV-Absorbing, Mycosporine-Like Compounds among Cyanobacterial Isolates and an Estimate of Their Screening Capacity

Abstract: A survey of 20 strains of cyanobacteria (belonging to 13 genera) isolated from habitats exposed to strong insolation revealed that 13 strains contained one or more water-soluble, UV-absorbing, mycosporine amino acid (MAA)-like compounds. Some of the compounds were identical in several strains. In all, 13 distinct compounds were found. The UV absorption spectra of MAAs complemented well that of the extracellular sunscreen pigment scytonemin, which many of the strains also produced. Even though the specific MAA contents were variable among strains, they were invariably higher when the cultures were grown with UV radiation than when it was absent. In five strains tested, the MAA complement accumulated as a solute in the cytoplasmic cell fraction. The sunscreen capacities of MAA and scytonemin and their combined capacity were estimated for each strain and condition on the basis of the specific contents, cell size, and cellular location of the compounds. The estimates suggested that significant, albeit not complete, protection from UV photodamage could be gained from the possession of either MAA or scytonemin but especially from simultaneous screening by both types of compounds.

Children's temperament in the US and China: similarities and differences

Abstract: We report the results of research investigating temperamental characteristics of children in the People's Republic of China and the US using a parent-report instrument, the Children's Behavior Questionnaire (CBQ), defining temperament as individual differences in emotional, motoric, and attentional reactivity and self-regulation. Subjects were 624 6- to 7-year-old children, from Shanghai and the north-western region of the US. The 15 CBQ scales were factored for both samples, employing a principal axis factor analysis with an oblique rotation. Our findings indicated considerable similarity of factor structure in the two cultures, obtaining three factors labelled Surgency, Negative Affect, and Attentional Self-Regulation or Effortful Control. Differences across cultures were also found, with Surgency and Effortful Control scores being relatively higher than Negative Affect in the US sample and Negative Affect being relatively higher than Surgency and Effortful Control in the Chinese sample. Gender differences were also found to vary across cultures. Our findings are congruent with a view of underlying cultural similarities in temperamental variability across these cultures, influenced over time by the children's culturally varied experience.

The structure of scytonemin, an ultraviolet sunscreen pigment from the sheaths of cyanobacteria.

Abstract: Despite knowledge of the existence of the pigment called scytonemin for over 100 years, its structure has remained unsolved until now. This pigment, the first shown to be an effective, photo-stable ultraviolet shield in prokaryotes, is a novel dimeric molecule (molec. wt. 544) of indolic and phenolic subunits and is known only from the sheaths enclosing the cells of cyanobacteria. It is probable that scytonemin is formed from a condensation of tryptophan-and phenylpropanoid-derived subunits. The linkage between these units is unique among natural products and this novel ring structure is here termed the ‘scytoneman skeleton’. Scytonemin absorbs strongly and broadly in the spectral region 325–425 nm (UV-A-violet-blue, with an in vivo maximum at 370 nm). However, there is also major absorption in the UV-C (λ max=250nm) and UV-B (280–320 nm). The pigment has been recently shown to provide significant protection to cyanobacteria against damage by ultraviolet radiation. The pigment occurs in all phylogenetic lines of sheathed cyanobacteria and possibly represents a UV screening strategy far more ancient than that of plant flavonoids and animal melanins. How diverse organisms deal with UV radiation is considered of vital importance to global ecology.

Betaine can eliminate the base pair composition dependence of DNA melting

Abstract: We show that the amino acid analogue betaine shares with small tetraalkylammonium ions [Melchior, W. B., Jr., & von Hippel, P. H. (1973) Proc. Natl. Acad. Sci. U.S.A. 70, 298-302] the ability to reduce or even eliminate the base pair composition dependence of DNA thermal melting transitions. The "isostabilizing" concentration of betaine (at which AT and GC base pairs are equally stable) is approximately 5.2 M. Betaine exerts its isostabilizing effect without appreciably altering the conformation of double-stranded DNA from the B form. The presence of > 5 M betaine also does not greatly change the behavior of DNA as a polyelectrolyte; this lack of effect on electrostatic interactions is expected because betaine exists as a zwitterion near neutral pH. Study of DNA melting transitions in high concentrations of betaine thus allows the experimental separation of compositional and polyelectrolyte effects on DNA melting. As a consequence, betaine solutions can also be used to investigate DNA-protein interactions under isostabilizing (or close to isostabilizing) conditions, which has not been possible using isostabilizing salts. This potential is illustrated by examining the highly salt concentration-dependent interaction of ribonuclease A with DNA in concentrated betaine solutions.

Muller's ratchet and mutational meltdowns.

Abstract: We extend our earlier work on the role of deleterious mutations in the extinction of obligately asexual populations. First, we develop analytical models for mutation accumulation that obviate the need for time-consuming computer simulations in certain ranges of the parameter space. When the number of mutations entering the population each generation is fairly high, the number of mutations per individual and the mean time to extinction can be predicted using classical approaches in quantitative genetics. However, when the mutation rate is very low, a fixation-probability approach is quite effective. Second, we show that an intermediate selection coefficient (s) minimizes the time to extinction. The critical value of s can be quite low, and we discuss the evolutionary implications of this, showing that increased sensitivity to mutation and loss of capacity for DNA repair can be selectively advantageous in asexual organisms. Finally, we consider the consequences of the mutational meltdown for the extinction of mitochondrial lineages in sexual species.

Reconstructive democratic theory

Abstract: While the idea of democracy has never been more universal or more popular, both democratic theory and the empirical study of democratic possibilities are in some disarray. We seek a productive reconnection of these two endeavors with democratic discourse through close attention to the language of democracy as used by ordinary people and political actors. Reconstructive inquiry determines how the individuals who are the potential constituents of any democratic order themselves conceptualize democracy and their own political roles and competences. We deploy an intensive method—Q methodology—for the study of individual characteristics, capabilities, and dispositions in combination with political discourse analysis. Four discourses are discovered in an analysis of selected U.S. subjects: contented republicanism, deferential conservatism, disaffected populism, and private liberalism. These results can be used to relate democratic theory to live possibilities in democratic discourse.

Evidence Regarding the UV Sunscreen Role of a Mycosporine-Like Compound in the Cyanobacterium Gloeocapsa sp.

Abstract: The UV sunscreen role commonly ascribed to mycosporine-like amino acids (MAAs) was investigated with an isolate of the terrestrial cyanobacterium Gloeocapsa sp. strain C-90-Cal-G.(2), which accumulates intracellularly an MAA with absorbance maximum at 326 nm but produces no extracellular sunscreen compound (i.e., scytonemin). The intracellular concentrations of MAA achieved were directly related to the intensity of the UV radiation (maximum at 320 nm) received by the cells. However, the presence of high concentrations of MAA was not necessary for the physiological acclimation of the cultures to UV radiation. The measured sunscreen factor due to MAA in single cells was 0.3 (the MAA prevented 3 out of 10 photons from hitting potential cytoplasmic targets). High contents of MAA in the cells correlated with increased resistance to UV radiation. However, when resistance was gauged under conditions of desiccation, with inoperative physiological photoprotective and repair mechanisms, cells with high MAA specific contents were only 20 to 25% more resistant. Although UV radiation centered around both 320 and 365 nm resulted in chlorophyll a photobleaching and photoinhibition of photosynthesis, the difference in sensitivity correlated with MAA accumulation occurred only at 320 nm (absorbed by MAA) and not at 365 nm (not absorbed by MAA). This difference represents the maximal protection ascribable to the presence of MAA for single cells, i.e., if one does not consider the enhancing effects of colony formation on protection by sunscreens.

Social welfare, cooperators' advantage, and the option of not playing the game.

Abstract: The AA outline a model of how freedom to choose between playing and not playing particular Pisoner's dilemma games can (1) increase social welfare and (2) provide relative gains to intending cooperators When cooperators are relatively more willing to play, they will interact more frequently with each other and their pay off per encounter will be higher - potentially higher than that of intending defectors The AA speculate about the cognitive processes that underlie this result

Multiple RNA polymerase conformations and GreA: control of the fidelity of transcription.

Abstract: Pre-steady state kinetics of misincorporation were used to investigate the addition of single nucleotides to nascent RNA by Escherichia coli RNA polymerase during transcription elongation. The results were fit with a branched kinetic mechanism that permits conformational switching, at each template position, between an activated and an unactivated enzyme complex, both of which can bind nucleotide triphosphates (NTPs) from solution. The complex exists most often in the long-lived activated state, and only becomes unactivated when transcription is slowed. This model permits multiple levels of nucleotide discrimination in transcription, since the complex can be "kinetically trapped" in the unactivated state in the absence of the correct NTP or if the 3' terminal residue is incorrectly matched. The transcription cleavage factor GreA (or an activity enhanced by GreA) increased the fidelity of transcription by preferential cleavage of transcripts containing misincorporated residues in the unactivated state of the elongation complex. This cleavage mechanism by GreA may prevent the formation of "dead-end" transcription complexes in vivo.

Spatial calcium buffering in saccular hair cells

Abstract: The potential importance of intracellular calcium-binding proteins in rapid and highly localized Ca2+ signalling is poorly understood. During fast synaptic transmission, which occurs at specialized active zones where Ca2+ diffuses only a few tens of nanometers from channels to neurotransmitter release sites, a cytoplasmic Ca2+ buffer would have to be extremely fast or present in millimolar concentrations to intercept a significant fraction of the calcium ions en route to their targets. Therefore, Ca2+ buffers have been presumed to be unimportant in fast exocytosis and another fast calcium-mediated process, electrical resonance in hair cells. Here I present evidence to the contrary by showing that hair cells in the frog sacculus contain millimolar concentrations of a mobile cytoplasmic calcium buffer that captures Ca2+ within a few microseconds after it enters through presynaptic Ca2+ channels and carries it away from the point of entry. This spatial buffering reduces the presynaptic free Ca2+ by up to 60 per cent and probably restricts the region in which the internal calcium ion concentration exceeds 1 microM to within < 250 nm of each synaptic site. The buffer can thus influence both electrical resonance and synaptic transmission. Calbindin-D28K or a related protein may serve as the mobile calcium buffer, an action similar to its function in transporting Ca2+ across intestinal epithelial cells.

Star formation thresholds in low surface brightness galaxies

Abstract: Low Surface Brightness (LSB) galaxies appear to have low star formation rates despite their often quite normal H I contents as judged from global H I properties such as M(H I)/L and M(H I)/M(T) ratios. H I imaging with the Very Large Array of the National Radio Astronomy Observatory (the NRAO is operated by Associated Universities Inc. under contract with the National Science Foundation) of eight LSB galaxies shows that the H I is extended compared with the optical size and has average surface densities which are about a factor 2 lower than in High Surface Brightness (HSB) galaxies of the same type. The resolution of the H I imaging allows a rough rotation curve analysis for evaluating the critical density for star formation as formulated by Kennicutt [ApJ, 344, 685 (1989)]. The observed H I surface densities systematically fall below this critical density for most of the galaxies in this sample, in agreement with the low current star formation rates. From the optical surface photometry we conclude that the galaxies studied are in general late-type galaxies dominated by an exponential disk with a typical scale length of a few kpc. The B-R and V-I colors of the LSB galaxies are a few tenths of a magnitude bluer than those of HSB galaxies indicating that the disks of these galaxies have a mean young age.