Showing papers by "University of Illinois at Urbana–Champaign published in 1981"

Assessment of Biotic Integrity Using Fish Communities

Abstract: Man's activities have had profound, and usually negative, influences on freshwater fishes from the smallest streams to the largest rivers. Some negative effects are due to contaminants, while others are associated with changes in watershed hydrology, habitat modifications, and alteration of energy sources upon which the aquatic biota depends. Regrettably, past efforts to evaluate effects of man's activities on fishes have attempted to use water quality as a surrogate for more comprehensive biotic assessment. A more refined biotic assessment program is required for effective protection of freshwater fish resources. An assessment system proposed here uses a series of fish community attributes related to species composition and ecological structure to evaluate the quality of an aquatic biota. In preliminary trials this system accurately reflected the status of fish communities and the environment supporting them.

In Praise of Paradox: A Social Policy of Empowerment over Prevention

Abstract: The thesis of this paper is that the most important and interesting aspects of community life are by their very nature paradoxical; and that our task as researchers, scholars, and professionals should be to “unpack” and influence contemporary resolutions of paradox. Within this general theme I will argue that in order to do so we will need to be more a social movement than a profession, regain our sense of urgency, and avoid the tendency to become “one-sided.” I will suggest that the paradoxical issue which demands our attention in the foreseeable future is a conflict between “rights” and “needs” models for viewing people in trouble.

A metric for thought: a comparison of P300 latency and reaction time

Abstract: We confirm that the latency of the P300 component of the human event-related potential is determined by processes involved in stimulus evaluation and categorization and is relatively independent of response selection and execution. Stimulus discriminability and stimulus-response compatibility were manipulated independently in an "additive-factors" design. Choice reaction time and P300 latency were obtained simultaneously for each trial. Although reaction time was affected by both discriminability and stimulus-response compatibility, P300 latency was affected only by stimulus discriminability.

The cube-connected cycles: a versatile network for parallel computation

Abstract: An interconnection pattern of processing elements, the cube-connected cycles (CCC), is introduced which can be used as a general purpose parallel processor. Because its design complies with present technological constraints, the CCC can also be used in the layout of many specialized large scale integrated circuits (VLSI). By combining the principles of parallelism and pipelining, the CCC can emulate the cube-connected machine and the shuffle-exchange network with no significant degradation of performance but with a more compact structure. We describe in detail how to program the CCC for efficiently solving a large class of problems that include Fast Fourier transform, sorting, permutations, and derived algorithms.

Ecological perspective on water quality goals

Abstract: The central assumption of nonpoint source pollution control efforts in agricultural watersheds is that traditional erosion control programs are sufficient to insure high quality water resources. We outline the inadequacies of that assumption, especially as they relate to the goal of attaining ecological integrity. The declining biotic integrity of our water resources over the past two decades is not exclusively due to water quality (physical/chemical) degradation. Improvement in many aspects of the quality of our water resources must be approached with a much broader perspective than improvement of physical/chemical conditions. Other deficiencies in nonpoint pollution control programs are discussed and a new approach to the problem is outlined.

Performance of Processor-Memory Interconnections for Multiprocessors

Abstract: A class of interconnection networks based on some existing permutation networks is described with applications to processor to memory communication in multiprocessing systems. These networks, termed delta networks, allow a direct link between any processor to any memory module. The delta networks and full crossbars are analyzed with respect to their effective bandwidth and cost. The analysis shows that delta networks have a far better performance per cost than crossbars in large multiprocessing systems.

Dependence graphs and compiler optimizations

Abstract: Dependence graphs can be used as a vehicle for formulating and implementing compiler optimizations. This paper defines such graphs and discusses two kinds of transformations. The first are simple rewriting transformations that remove dependence arcs. The second are abstraction transformations that deal more globally with a dependence graph. These transformations have been implemented and applied to several different types of high-speed architectures.

On sharing secrets and Reed-Solomon codes

Abstract: Shamir's scheme for sharing secrets is closely related to Reed-Solomon coding schemes. Decoding algorithms for Reed-Solomon codes provide extensions and generalizations of Shamir's method.

Chloroplast protein phosphorylation couples plastoquinone redox state to distribution of excitation energy between photosystems

Abstract: In photosynthetic membranes isolated from pea leaves, the redox state of the plastoquinone pool controls both the level of phosphorylation of the chloroplast light-harvesting pigment–protein complex (LHC) and distribution of absorbed excitation energy between the two photosystems. Phosphorylation of LHC polypeptides is proposed as the regulatory mechanism by which photosynthetic systems adapt to changing wavelengths of light.

Thermal Stress and Low Cycle Fatigue

Abstract: Text on thermal stress and low-cycle fatigue covering elastic stresses, plastic flow and creep, stress cycling, etc

Disorder of an AlAs‐GaAs superlattice by impurity diffusion

Abstract: Data are presented showing that Zn diffusion into an AlAs‐GaAs superlattice (41 Lz∼45‐A GaAs layers, 40 LB∼150‐A AlAs layers), or into AlxGa1−xAs‐GaAs quantum‐well heterostructures, increases the Al‐Ga interdiffusion at the heterointerfaces and creates, even at low temperature (<600 °C), uniform compositionally disordered AlxGa1−xAs. For the case of the superlattice, the diffusion‐induced disordering causes a change from direct‐gap AlAs‐GaAs (Eg∼1.61 eV) to indirect‐gap AlxGa1−xAs (x∼0.77, EgX∼2.08 eV).

Tidier Drawings of Trees

Abstract: Various algorithms have been proposed for producing tidy drawings of trees–drawings that are aesthetically pleasing and use minimum drawing space. We show that these algorithms contain some difficulties that lead to aesthetically unpleasing, wider than necessary drawings. We then present a new algorithm with comparable time and storage requirements that produces tidier drawings. Generalizations to forests and m-ary trees are discussed, as are some problems in discretization when alphanumeric output devices are used.

Species variation in the specificity of ribulose biphosphate carboxylase/oxygenase

Abstract: The balance between photosynthesis and photorespiration in many species, including most crop plants, is determined by the kinetic properties of ribulose-l,5-bisphosphate (RuBP) carboxylase/oxygenase1,2. Photosynthesis is initiated by the carboxylase activity3 while the oxygenase activity catalyses the first reaction in the photorespiratory pathway1,2,4. In these reactions, CO2 and O2 are competitive substrates2. Because O2 inhibits carboxylation, and photorespiration oxidizes reduced carbon to CO2 with no known benefit to the plant, it has been suggested that photosynthetic efficiency and thus productivity might be increased by chemical or genetic alterations of the enzyme which increase carboxylation or decrease oxygenation5–7. On the other hand, it has been argued that RuBP carboxylase/oxygenase cannot completely discriminate between CO2 and O2, so that photorespiration is unavoidable8. From analyses of RuBP carboxylase/oxygenase enzymes purified from several different species, we report here large differences in specificity towards the substrates CO2 and O2. Evolutionary pressures seem to have directed the enzyme towards more efficient utilization of CO2.

Syntrophomonas wolfei gen. nov. sp. nov., an Anaerobic, Syntrophic, Fatty Acid-Oxidizing Bacterium

Abstract: An anaerobic, nonphototrophic bacterium that beta-oxidizes saturated fatty acids (butyrate through octanoate) to acetate or acetate and propionate using protons as the electron acceptor (H(2) as electron sink product) was isolated in coculture with either a non-fatty acid-degrading, H(2)-utilizing Desulfovibrio sp. or methanogens. Three strains of the bacterium were characterized and are described as a new genus and species, Syntrophomonas wolfei. S. wolfei is a gram-negative, slightly helical rod with round ends that possesses between two to eight flagella laterally inserted along the concave side of the cell. It has a multilayered cell wall of the gram-negative type. The presence of muramic acid, inhibition of growth by penicillin, and increased sensitivity of the cells to lysis after treatment with lysozyme indicate that peptidoglycan is present in the cell wall. Cells of S. wolfei contain poly-beta-hydroxybutyrate. Isoheptanoate was degraded to acetate, isovalerate, and H(2). Carbohydrates, proteinaceous materials, alcohols, or other tested organic compounds do not support growth. Common electron acceptors are not utilized with butyrate as the electron donor. Growth and degradation of fatty acids occur only in syntrophic association with H(2)-using bacteria. The most rapid generation time obtained by cocultures of S. wolfei with Desulfovibrio and Methanospirillum hungatei is 54 and 84 h, respectively. The addition of Casamino Acids but neither Trypticase nor yeast extract stimulated growth and resulted in a slight decrease in the generation time of S. wolfei cocultured with M. hungatei. The addition of H(2) to the medium stopped growth and butyrate degradation by S. wolfei.

Krylov subspace methods for solving large unsymmetric linear systems

Abstract: Some algorithms based upon a projection process onto the Krylov subspace K/sub m/ = Span(r/sub 0/, Ar/sub 0/,..., A/sup m-1/r/sub 0/) are developed, generalizing the method of conjugate gradients to unsymmetric systems. These methods are extensions of Arnoldi's algorithm for solving eigenvalue problems. The convergence is analyzed in terms of the distance of the solution to the subspace K/sub m/ and some error bounds are established showing in particular a similarity with the conjugate gradient method (for symmetric matrices) when the eigenvalues are real. Several numerical experiments are described and discussed.

The Mating System of the Prairie Vole, Microtus-Ochrogaster - Field and Laboratory Evidence for Pair-Bonding

Abstract: 1. Field and experimental evidence is provided for the existence of pair-bonding or monogamy in prairie voles (Microtus ochrogaster). 2. Multiple-capture live-trap data indicated that male and female pairs of M. ochrogaster were repeatedly captured together. (A comparable analysis for data from M. pennsylvanicus revealed no indications of long-term male-female associations.) 3. Male-female pair captures of M. ochrogaster were equally likely during either the breeding or nonbreeding seasons, further suggesting a relative stability of pairs. 4. In laboratory dyadic encounters, both males and females from breeding pairs tended to show relatively high levels of aggression toward unfamiliar animals of the opposite sex. In contrast, aggression was rarely observed between members of established breeding pairs. Nonpaired animals of either sex infrequently initiated aggressive encounters. 5. When pairs were separated for 8 days (during which time the females lived with a new male) the apparent pair-bond with the original male was broken. These females became aggressive toward the male with which they had previously bred, and rarely fought with their new mate. This suggests that the pair-bonding process is reversible. 6. Females in postpartum estrus preferentially showed high levels of sexual receptivity and low levels of aggression toward familiar males and were less likely to mate with unfamiliar sexually experienced males. The presence of pups at the time of testing did not appear to influence female-initiated aggression.

Random vibration of hysteretic degrading systems

Abstract: A differential equation model for hysteretic systems with strength, stiffness or combined degradation is presented. Solution under white noise, Kanai filtered white noise and temporally modulated filtered white noise is obtained by equivalent linearization, without recourse to the Krylov-Bogoliubov approximation typically required for hysteretic systems. Resulting zero time lag covariance response matrices agree well with simulated solutions at all excitation levels. First passage predictions are nonconservative, because of the non-Gaussian character of the response.

Estimating three-dimensional motion parameters of a rigid planar patch

Abstract: We present a new direct method of estimating the three-dimensional motion parameters of a rigid planar patch from two time-sequential perspective views (image frames). First, a set of eight pure parameters are defined. These parameters can be determined uniquely from the two given image frames by solving a set of linear equations. Then, the actual motion parameters are determined from these pure parameters by a method which requires the solution of a sixth-order polynomial of one variable only, and there exists a certain efficient algorithm for solving a sixth-order polynomial. Aside from a scale factor for the translation parameters, the number of real solutions never exceeds two. In the special case of three-dimensional translation, the motion parameters can be expressed directly as some simple functions of the eight pure parameters. Thus, only a few arithmetic operations are needed.

Secondary structure model for 23S ribosomal RNA.

Abstract: A secondary structure model for 23S ribosomal RNA has been constructed on the basis of comparative sequence data, including the complete sequences from E. coli. Bacillus stearothermophilis, human and mouse mitochondria and several partial sequences. The model has been tested extensively with single strand-specific chemical and enzymatic probes. Long range base-paired interactions organize the molecule into six major structural domains containing over 100 individual helices in all. Regions containing the sites of interaction with several ribosomal proteins and 5S RNA have been located. Segments of the 23S RNA structure corresponding to eucaryotic 5.8S and 25 RNA have been identified, and base paired interactions in the model suggest how they are attached to 28S RNA. Functionally important regions, including possible sites of contact with 30S ribosomal subunits, the peptidyl transferase center and locations of intervening sequences in various organisms are discussed. Models for molecular 'switching' of RNA molecules based on coaxial stacking of helices are presented, including a scheme for tRNA-23S RNA interaction.

Didemnins: antiviral and antitumor depsipeptides from a caribbean tunicate

Abstract: Extracts of samples of a Caribbean tunicate (ascidian, sea squirt) of the family Didemnidae inhibit in vitro at low concentrations the growth of DNA and RNA viruses as well as L1210 leukemic cells. The active compounds isolated from the tunicate, didemnins A, B, and C, are depsipeptides, and didemnin B (a derivative of didemnin A) is the component active at the lowest concentration in inhibiting viral replication in vitro and P388 leukemia in vivo.

Band-structure-dependent transport and impact ionization in GaAs

Abstract: We have performed a Monte Carlo simulation of high-field transport in GaAs including a realistic band structure to study the band-structure dependence of electron transport and impact ionization. The band structure has been calculated using the empirical pseudopotential method. Unlike previous theories of impact ionization, our method is capable of calculating various parameters, such as mean free path, from first principles. The calculated electron mean free path, drift velocity, and impact ionization rate are in reasonable agreement with the experimental data in spite of several simplifications of the model. Within statistical uncertainty we do not observe any orientation dependence of the ionization rate in contradiction to the interpretation of recently reported experimental results. We also find that the contribution of ballistic electrons to impact ionization is negligibly small. Based on the results of the calculation, a general discussion of impact ionization is given.