Showing papers by "University of Colorado Boulder published in 1992"

Solitons, Nonlinear Evolution Equations and Inverse Scattering

Abstract: Solitons have been of considerable interest to mathematicians since their discovery by Kruskal and Zabusky. This book brings together several aspects of soliton theory currently only available in research papers. Emphasis is given to the multi-dimensional problems arising and includes inverse scattering in multi-dimensions, integrable nonlinear evolution equations in multi-dimensions and the ∂ method. Thus, this book will be a valuable addition to the growing literature in the area and essential reading for all researchers in the field of soliton theory.

Foundations for the study of software architecture

Abstract: The purpose of this paper is to build the foundation for software architecture. We first develop an intuition for software architecture by appealing to several well-established architectural disciplines. On the basis of this intuition, we present a model of software architecture that consists of three components: elements, form, and rationale. Elements are either processing, data, or connecting elements. Form is defined in terms of the properties of, and the relationships among, the elements --- that is, the constraints on the elements. The rationale provides the underlying basis for the architecture in terms of the system constraints, which most often derive from the system requirements. We discuss the components of the model in the context of both architectures and architectural styles and present an extended example to illustrate some important architecture and style considerations. We conclude by presenting some of the benefits of our approach to software architecture, summarizing our contributions, and relating our approach to other current work.

Monsoon and Enso: Selectively Interactive Systems

Abstract: We attempt to construct a logical framework for the deciphering of the physical processes that determine the interannual variability of the coupled climate system. of particular interest are the causes of the ‘predictability barrier’ in the boreal spring when observation-prediction correlations rapidly decline. the barrier is a property of many models and occurs irrespective of what time of year a forecast is initiated. Noting that most models used in interannual prediction emphasize the coupled physics of the Pacific Ocean basin, with the intent of encapsulating the essential structure of the El Nino-Southern Oscillation (ENSO) system, lagged Southern Oscillation Index (SOI) correlations are compared with the model results. the lagged SOI correlations also decrease rapidly in springtime. In that sense, the coupled ocean-atmosphere models are behaving in a manner very similar to the real system, at least as it is defined by the SOI. We propose that (i) the springtime is a period where errors may grow most rapidly in a coupled ocean-atmosphere forecast model or (ii) there are other influences on the system that are not included in the simple coupled-model formulations. Both propositions are based on observations. By examining the period of correlation decrease, it is noticed that the equatorial pressure gradients tend to be a minimum at the time of the correlation decrease, suggesting that the ocean-atmosphere system may be least robust during the spring and, thus, subject to error growth. At the same time the south Asian summer monsoon is growing very rapidly. As the monsoon circulation is highly variable in both phase and amplitude from year to year, the ocean-atmosphere system may be subject to variable and impulsive forcing each spring. A monsoon intensity index, based on the magnitude of the mean summer vertical shear in the ‘South Asia’ region, was defined for the broad-scale monsoon. ‘Strong’ and ‘weak’ monsoon seasons were determined by the index and were shown to be consistent with the independent broad-scale outgoing long-wave-radiation fields. Associated with the anomalous monsoons were global scale, coherent summer circulation patterns. of particular importance was that stronger (weaker) than average summer trade winds were associated with strong (weak) monsoon periods. Thus, a signal of the variable monsoon was detected in the low-level wind fields over the Pacific Ocean that would be communicated to the Pacific Ocean through surface stresses. A longer-period context for the anomalous summer monsoon circulation fields was sought. Based on the summer monsoon index, annual cycles for the years in which there were strong and weak monsoon seasons were composited. Large-scale coherent differences were apparent in the circulation fields over most of the globe including south Asia and the tropical Indian Ocean as far as the previous winter and spring. Although the limited data period renders the absoluteness of the conclusions difficult to confirm, the results indicate that the variable monsoon (and hence the signal in the Pacific Ocean trade regime) are immersed in a larger scale and slowly evolving circulation system. Based on the observation that the monsoon and the Walker circulation appear to be in quadrature, it is proposed that these two circulations are selectively interactive. During the springtime, the rapidly growing monsoon dominates the near-equatorial Walker circulation. During autumn and winter, the monsoon is weakest with convection fairly close to the equator; the Walker circulation is then strongest and may dominate the winter monsoon. During the summer the monsoon may dominate. Numerical experiments are proposed to test both propositions.

Impaired spatial learning in alpha-calcium-calmodulin kinase II mutant mice

Abstract: Although long-term potentiation (LTP) has been studied as the mechanism for hippocampus-dependent learning and memory, evidence for this hypothesis is still incomplete. The mice with a mutation in the alpha-calcium-calmodulin-dependent kinase II (alpha-CaMKII), a synaptic protein enriched in the hippocampus, are appropriate for addressing this issue because the hippocampus of these mice is deficient in LTP but maintains intact postsynaptic mechanisms. These mutant mice exhibit specific learning impairments, an indication that alpha-CaMKII has a prominent role in spatial learning, but that it is not essential for some types of non-spatial learning. The data considerably strengthen the contention that the synaptic changes exhibited in LTP are the basis for spatial memory.

Cognitive change, strategic action, and organizational renewal

Abstract: Organizational renewal requires that a firm's top managers make timely adjustments in their mental models following significant changes in the environment. Our initial propositions about the difference between renewal and decline focused on whether similar organizations in similar contexts differ in their ability to recognize significant changes in their environments. Analysis of longitudinal data from a matched pair of U.S. railroads suggested, however, that renewal hinges not so much on noticing new conditions, but on being able to link environmental change to corporate strategy and to modify that linkage over time. In the successful company we studied organizational renewal is a continuous process of first and second order changes in cognitive maps.

Discrimination among semi-arid landscape endmembers using the Spectral Angle Mapper (SAM) algorithm

Abstract: Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data were acquired during three consecutive seasons of the year (26 Sep. 1989, 22 Mar. 1990, and 7 Aug. 1990) over an area of the High Plains east of Greeley, Colorado. This region contains extensive eolian deposits in the form of stabilized dune complexes (small scale parabolic dunes superimposed on large scale longitudinal and parabolic dunes). Due to the dunes' large scale (2-10 km) and low relief (1-5 m), the scaling relationships that contribute to the evolution of this landscape are nearly impossible to understand without the use of remote sensing. Additionally, climate models indicate that the High Plains could be one of the first areas to experience changes in climate caused by either global warming or cooling. During the past 10,000 years there were at least three periods of extensive sand activity, followed by periods of landscape stability, as shown in the stratigraphic record of this area. Therefore, if the past is an indication of the future, the monitoring of this landscape and its sensitive ecosystem is important for early detection of regional and global climate change.

Cognitive walkthroughs: a method for theory-based evaluation of user interfaces

Abstract: This paper presents a new methodology for performing theory-based evaluations of user interface designs early in the design cycle. The methodology is an adaptation of the design walkthrough techniques that have been used for many years in the software engineering community. Traditional walkthroughs involve hand simulation of sections of code to ensure that they implement specified functionality. The method we present involves hand simulation of the cognitive activities of a user, to ensure that the user can easily learn to perform tasks that the system is intended to support. The cognitive walkthrough methodology, described in detail, is based on a theory of learning by exploration presented in this paper. There is a summary of preliminary results of effectiveness and comparisons with other design methods.

Sulfur Emissions to the Atmosphere from Natural Sources

Abstract: Emissions of sulfur gases from both natural and anthropogenic sources strongly influence the chemistry of the atmosphere. To assess the relative importance of these sources we have combined the measurements of sulfur gases and fluxes during the past decade to create a global emission inventory. The inventory, which is divided into 12 latitude belts, takes into account the seasonal dependence of sulfur emissions from biogenic sources. The total emissions of sulfur gases from natural sources are approximately 0.79 Tmol S/a. These emissions are 16% of the total sulfur emissions in the Northern Hemisphere and 58% in the Southern Hemisphere. The inventory clearly shows the impact of anthropogenic sulfur emissions in the region between 35° and 50°N.

Determinants of faculty pay: An agency theory perspective.

Abstract: This study tested 12 hypotheses on the determinants of faculty pay using an agency theory perspective. The sample consisted of 353 professors of management. Data were collected from survey response...

Symplectic maps, variational principles, and transport

Abstract: Symplectic maps are the discrete-time analog of Hamiltonian motion. They arise in many applications including accelerator, chemical, condensed-matter, plasma, and fluid physics. Twist maps correspond to Hamiltonians for which the velocity is a monotonic function of the canonical momentum. Twist maps have a Lagrangian variational formulation. One-parameter families of twist maps typically exhibit the full range of possible dynamics-from simple or integrable motion to complex or chaotic motion. One class of orbits, the minimizing orbits, can be found throughout this transition; the properties of the minimizing orbits are discussed in detail. Among these orbits are the periodic and quasiperiodic orbits, which form a scaffold in the phase space and constrain the motion of the remaining orbits. The theory of transport deals with the motion of ensembles of trajectories. The variational principle provides an efficient technique for computing the flux escaping from regions bounded by partial barriers formed from minimizing orbits. Unsolved problems in the theory of transport include the explanation for algebraic tails in correlation functions, and its extension to maps of more than two dimensions.

Nicotine binding and nicotinic receptor subunit RNA after chronic nicotine treatment.

Abstract: DBA mice were chronically treated with nicotine by continuous intravenous infusion of 4.0 mg/kg/hr for 10 d. Drug-treated mice were tolerant to the acute effects of nicotine on locomotor activity and body temperature. The effect of chronic treatment on the amount of L-3H-nicotine binding and RNA encoding for alpha 4, the most widely expressed nicotinic alpha-subunit, was measured in three brain regions. Chronic treatment increased L-3H-nicotine binding in cortex and midbrain but had no effect in cerebellum. In contrast, chronic treatment had no effect on the levels of mRNA encoding for alpha 4 in any of the three brain regions. Subsequently brains were sectioned and L-3H-nicotine binding was measured using quantitative autoradiographic methods. In addition, the relative amounts of mRNA for the major nicotinic receptor subunits (alpha 4 and beta 2), as well as for three additional minor subunits (alpha 2, alpha 3, and alpha 5), were determined by in situ hybridization histochemistry followed by quantitation of image intensity. Chronic nicotine treatment resulted in increases in the amount of L-3H-nicotine binding in many but not all brain areas measured. In contrast, chronic treatment had little effect on the intensity of the hybridization signal for the nicotinic subunit mRNA. The results suggest that chronic treatment with nicotine under conditions resulting in maximal steady-state increases in L-3H-nicotine binding has little effect on RNA levels encoding any of four nicotinic alpha-subunits and the beta 2-subunit.

Maps for managers: where are we? where do we go from here?

Abstract: Research on managerial cognition in genetal, and on cognitive mapping in particular, is receving a great deal of attention in Europe and the US, but the work being done is currently disparate and loosely coupled. Furthermor, the development of maps as a decision aid has tended to focus on specific sub-areas of cognition. In this article we argue that the broad strategic concerns of managers require a portfolio of different kinds of cognitive maps. The interactions among these maps are as important as the functions of each one separately. We develop a framework for classifying cognitice maps and argue for the importance of managing multiple maps.

Are adolescents the victims of raging hormones: evidence for activational effects of hormones on moods and behavior at adolescence.

Abstract: The literatures on hormone changes at adolescence, hormonal influences on moods and behavior in nonhuman animals and adult humans, and mood and behavioral changes at adolescence and the small but burgeoning literature on hormonal influences at adolescence are examined. The focus is on moods and behaviors often identified as typically adolescent (e.g., mood lability, mood intensity, irritability, conflict with parents) and the primary hormones of puberty (i.e., the adrenal androgens, gonadotropins, and sex steroids). Through an integration of these literatures evidence is assessed for specific hormone-mood and hormone-behavior associations, as well as for more general types of hormone-outcome relations that transcend specific hormones or outcomes. Non-biological factors that appear to be important in moderating the role of hormones in adolescent moods and behavior are identified. Implications for the design of future studies in this area are detailed.

Learning to Teach Hard Mathematics: Do Novice Teachers and Their Instructors Give Up Too Easily?

Abstract: This article analyzes from several vantage points a classroom lesson in which a student teacher was unsuccessful in providing a conceptually based justification for the standard division-offractions algorithm. We attempt to understand why the lesson failed, what it reveals about learning to teach, and what the implications are for mathematics teacher education. We focus on (a) the student teacher's beliefs about good mathematics teaching, her knowledge related to division of fractions, and her beliefs about learning to teach; and (b) the treatment of division of fractions in the mathematics methods course she took. The student teacher's conception of good mathematics teaching included components compatible with current views of effective mathematics teaching. However, these beliefs are difficult to achieve without a stronger conceptual knowledge base and a greater commitment to use available resources and to engage in hard thinking than she possessed. Further, the mathematics methods course did not require the student teacher to reconsider her knowledge base, to confront the contradictions between her knowledge base and at least some of her beliefs, or to reassess her beliefs about how she would learn to teach. These findings suggest that mathematics teacher education programs should reconsider how they provide subject matter knowledge and opportunities to teach it, and whether and how they challenge student teachers' existing beliefs.

Monte Carlo simulation of the atomic master equation for spontaneous emission.

Abstract: A Monte Carlo simulation of the atomic master equation for spontaneous emission in terms of atomic wave functions is developed. Realizations of the time evolution of atomic wave functions are constructed that correspond to an ensemble of atoms driven by laser light undergoing a sequence of spontaneous emissions. The atomic decay times are drawn according to the photon count distribution of the driven atom. Each quantum jump of the atomic electron projects the atomic wave function to the ground state of the atom. Our theory is based on a stochastic interpretation and generalization of Mollow's pure-state analysis of resonant light scattering, and the Srinivas-Davies theory of continuous measurements in photodetection. An extension of the theory to include mechanical light effects and a generalization to atomic systems with Zeeman substructure are given. We illustrate the method by simulating the solutions of the optical Bloch equations for two-level systems, and laser cooling of a two-level atom in an ion trap where the center-of-mass motion of the atom is described quantum mechanically.

RNA pseudoknots that inhibit human immunodeficiency virus type 1 reverse transcriptase

Abstract: High-affinity ligands of the reverse transcriptase of human immunodeficiency virus type 1 (HIV-1) were isolated by the SELEX procedure (systematic evolution of ligands by exponential enrichment) from RNA populations randomized at 32 positions. Analysis of these ligands revealed a pseudoknot consensus with primary sequence bias at some positions. We demonstrated that at least one of the ligands inhibits cDNA synthesis by HIV reverse transcriptase but fails to inhibit other reverse transcriptases. These experiments highlight the power of SELEX to yield highly specific ligands that reduce the activity of target proteins. Such ligands may provide therapeutic reagents for viral and other diseases.

School and family effects on the ontogeny of children's interests, self-perceptions, and activity choices.

Abstract: In this chapter we have presented two perspectives on the link between social context and the following motivational constructs: self-concept of ability and sense of personal efficacy in specific activity domains; perceptions of the value of skills in various domains; interest in various activities; activity choice; persistence; performance; and general self-esteem. In the first section, we discussed how social-contextual variables in both the family and the home could produce individual differences in the motivational constructs of interest. We presented a general framework for thinking about this issue and summarized our recent empirical work. In the second section, we discussed how systematic changes in the social environments that confront children as they develop could explain age-related changes in the motivational constructs of interest. Again we presented a general framework for thinking about this issue and summarized our empirical work testing the hypotheses generated from this framework. Throughout this section we have argued that optimal development takes place when there is good stage-environment fit between the needs of developing individuals and the opportunities afforded in their social environments. Furthermore, we suggested that the negative changes in motivational variables often associated with early adolescent development result from regressive changes in school and home environments. For example, the transition to junior high school, in particular, often confronts early adolescents with regressive environmental changes such as a decrease in the opportunity to participate in classroom decision making, a decrease in teacher support and teacher efficacy, and an increase in teaching styles and reporting practices likely to induce a focus on relative ability and comparative performance as well as excessive social comparison. Not surprisingly, there is also a decrease in intrinsic motivation and an increase in school misbehavior associated with this transition, and these changes are most apparent among adolescents who report regressive changes in the characteristics of classroom and school social environment. Such motivational changes are not apparent in adolescents who report the more developmentally appropriate shifts in the social context at school. Although our analysis of the family data is not as complete as our analysis of the classroom data, we have found evidence that a similar process may be going on in the family in relation to issues of control and autonomy. Excessive parental control is linked to lower intrinsic school motivation, to more negative change in self-esteem following the junior high school transition, to more school misbehavior, and to relatively greater investment in peer social attachments.(ABSTRACT TRUNCATED AT 400 WORDS)

Learning complex, extended sequences using the principle of history compression

Abstract: Previous neural network learning algorithms for sequence processing are computationally expensive and perform poorly when it comes to long time lags. This paper first introduces a simple principle for reducing the descriptions of event sequences without loss of information. A consequence of this principle is that only unexpected inputs can be relevant. This insight leads to the construction of neural architectures that learn to “divide and conquer” by recursively decomposing sequences. I describe two architectures. The first functions as a self-organizing multilevel hierarchy of recurrent networks. The second, involving only two recurrent networks, tries to collapse a multilevel predictor hierarchy into a single recurrent net. Experiments show that the system can require less computation per time step and many fewer training sequences than conventional training algorithms for recurrent nets.

Strategic renewal and the interaction of cumulative stress and inertia

Abstract: Strategic renewal is accomplished in large and small ways. This paper proposes a four phase characterization of how organizations move between state sustaining renewal and the more radical reconceptualizations that significantly alter organization activity. The argument juxtaposes inertia (or commitment to current strategy) and stress, the dissatisfactions that signal the need for renewal. To explore the details of this interaction, and its implications for the evolution of strategy over time, a formal model is developed. Quite plausible organization paths of renewal are simulated via the model which help illustrate our main theoretic arguments.

Translation initiation in Escherichia coli: sequences within the ribosome-binding site.

Abstract: The translational roles of the Shine-Dalgarno sequence, the initiation codon, the space between them, and the second codon have been studied. The Shine-Dalgarno sequence UAAGGAGG initiated translation roughly four times more efficiently than did the shorter AAGGA sequence. Each Shine-Dalgarno sequence required a minimum distance to the initiation codon in order to drive translation; spacing, however, could be rather long. Initiation at AUG was more efficient than at GUG or UUG at each spacing examined; initiation at GUG was only slightly better than UUG. Translation was also affected by residues 3' to the initiation codon. The second codon can influence the rate of initiation, with the magnitude depending on the initiation codon. The data are consistent with a simple kinetic model in which a variety of rate constants contribute to the process of translation initiation.

Integrated high quality rectifier-regulators

Abstract: A family of AC-to-DC converters which integrate the functions of low harmonic rectification, low frequency energy storage, and wide bandwidth output voltage control into a single converter containing one, two, or four active switches is presented. These converters utilize a discontinuous conduction mode input inductor, an internal energy storage capacitor, and transformer secondary circuits which resemble the bridge, forward, flyback, or Cuk DC-DC converters. A large-signal equivalent circuit model for this family which uses the loss-free resistor concept is presented. Design strategies and experimental results are given. High performance regulation with satisfactory line current harmonics is demonstrated with conventional duty ratio control. Further improvements in line current are possible by simultaneous duty ratio and switching frequency control. >

Functional Compartmentation of the Golgi Apparatus of Plant Cells : Immunocytochemical Analysis of High-Pressure Frozen- and Freeze-Substituted Sycamore Maple Suspension Culture Cells

Abstract: The Golgi apparatus of plant cells is engaged in both the processing of glycoproteins and the synthesis of complex polysaccharides. To investigate the compartmentalization of these functions within individual Golgi stacks, we have analyzed the ultrastructure and the immunolabeling patterns of high-pressure frozen and freeze-substituted suspension-cultured sycamore maple (Acer pseudoplatanus L.) cells. As a result of the improved structural preservation, three morphological types of Golgi cisternae, designated cis, medial, and trans, as well as the trans Golgi network, could be identified. The number of cis cisternae per Golgi stack was found to be fairly constant at approximately 1, whereas the number of medial and trans cisternae per stack was variable and accounted for the varying number of cisternae (3-10) among the many Golgi stacks examined. By using a battery of seven antibodies whose specific sugar epitopes on secreted polysaccharides and glycoproteins are known, we have been able to determine in which types of cisternae specific sugars are added to N-linked glycans, and to xyloglucan and polygalacturonic acid/rhamnogalacturonan-I, two complex polysaccharides. The findings are as follows. The β-1,4-linked d-glucosyl backbone of xyloglucan is synthesized in trans cisternae, and the terminal fucosyl residues on the trisaccharide side chains of xyloglucan are partly added in the trans cisternae, and partly in the trans Golgi network. In contrast, the polygalacturonic/rhamnogalacturonan-I backbone is assembled in cis and medial cisternae, methylesterification of the carboxyl groups of the galacturonic acid residues in the polygalacturonic acid domains occurs mostly in medial cisternae, and arabinose-containing side chains of the polygalacturonic acid domains are added to the nascent polygalacturonic acid/rhamnogalacturonan-I molecules in the trans cisternae. Double labeling experiments demonstrate that xyloglucan and polygalacturonic acid/rhamnogalacturonan-I can be synthesized concomitantly within the same Golgi stack. Finally, we show that the xylosyl residue-linked β-1,2 to the β-linked mannose of the core of N-linked glycans is added in medial cisternae. Taken together, our results indicate that in sycamore maple suspension-cultured cells, different types of Golgi cisternae contain different sets of glycosyl transferases, that the functional organization of the biosynthetic pathways of complex polysaccharides is consistent with these molecules being processed in a cis to trans direction like the N-linked glycans, and that the complex polysaccharide xyloglucan is assembled exclusively in trans Golgi cisternae and the trans Golgi network.