Showing papers by "University of Illinois at Urbana–Champaign published in 1980"

Crosscorrelation properties of pseudorandom and related sequences

Abstract: Binary maximal-length linear feedback shift register sequences (m-sequences) have been successfully employed in communications, navigation, and related systems over the past several years. For the early applications, m-sequences were used primarily because of their excellent periodic autocorrelation properties. For many of the recent systems applications, however, the crosscorrelation properties of such sequences are at least as important as the autocorrelation properties, and the system performance depends upon the aperiodic correlation in addition to the periodic correlation. This paper presents a survey of recent results and provides several new results on the periodic and aperiodic crosscorrelation functions for pairs of m-sequences and for pairs of related (but not maximal-length) binary shift register sequences. Also included are several recent results on correlation for complex-valued sequences as well as identities relating the crosscorrelation functions to autocorrelation functions. Examples of problems in spread-spectrum communications are employed to motivate the choice of correlation parameters that are considered in the paper.

Neural basis of rhythmic behavior in animals

Abstract: Timing of the repetitive movements that constitute any rhythmic behavior is regulated by intrinsic properties of the central nervous system rather than by sensory feedback from moving parts of the body. Evidence of this permits resolution of the long-standing controversy over the neural basis of rhythmic behavior and aids in the identification of this mechanism as a general principle of neural organization applicable to all animals with central nervous systems.

Phytic acid interactions in food systems

Abstract: Phytic acid is present in many plant systems, constituting about 1 to 5% by weight of many cereals and legumes. Concern about its presence in food arises from evidence that it decreases the bioavailability of many essential minerals by interacting with multivalent cations and/or proteins to form complexes that may be insoluble or otherwise unavailable under physiologic conditions. The precise structure of phytic acid and its salts is still a matter of controversy and lack of a good method of analysis is also a problem. It forms fairly stable chelates with almost all multivalent cations which are insoluble above pH 6 to 7, although pH, type, and concentration of cation have a tremendous influence on their solubility characteristics. In addition, at low pH and low cation concentration, phytate‐protein complexes are formed due to direct electrostatic interaction, while at pH >6 to 7, a ternary phytic acid‐mineral‐protein complex is formed which dissociates at high Na concentrations. These complexes appear to...

Effects of Peer Models' Food Choices and Eating Behaviors on Preschoolers' Food Preferences.

Abstract: Preschooler food preferences can be strongly influenced by outside forces, namely, peer pressure, hero worship, role models, etc., but whether the changed preferences persist or not is slightly harder to assess. Experimental taste tests of 9 vegetables were tried on 39 children; they were asked to taste each one, decide whether it tasted good, bad, or OK, and then were helped to rank them by preference. The next step was to determine the effects of social influence by peers--this was done in a lunch-room situation where one child with a strong preference was placed with 3 peers of opposite tastes for 4 days. Data was obtained on 17 different subjects in 17 situations. The first step was then repeated. The target children showed a distinct increase in preference for previously spurned food, as well as a decrease in desire for the favorite vegetable, though not of an equal amount. The social influence thus demonstrated indicates that children will learn to accept a broader range of foods when exposed to preferences other than their own

An analysis of learned helplessness: II. The processing of success.

Abstract: Helpless children attribute their failures to lack of ability and view them as insurmountable. Mastery-oriented children, in contrast, tend to emphasize motivational factors and to view failure as surmountable. Although the performance of the two groups is usually identical during success of prior to failure, past research suggests that these groups may well differ in the degree to which they perceive that their successes are replicable and hence that their failures are avoidable. The present study was concerned with the nature of such differences. Children performed a task on which they encountered success and then failure. Half were asked a series of questions about their performance after success and half after failure. Striking differences emerged: Compared to mastery-oriented children, helpless children underestimated the number of success (and overestimated the number of failures), did not view successes as indicative of ability, and did not expect the successes to continue. subsequent failure led them to devalue ;their performance but left the mastery-oriented children undaunted. Thus, for helpless children, successes are less salient, less predictive, and less enduring--less successful.

P300 and Tracking Difficulty: Evidence For Multiple Resources in Dual‐Task Performance

Abstract: Subjects performed a visual tracking task while performing a concurrent task in which tones were covertly counted. The P300 component of the event-related potentials elicited by the tones was examined to determine the extent to which its amplitude was affected by variations in the forcing-function bandwidth, or difficulty, of the tracking task. P300 decreased in magnitude when tones were counted in conjunction with the performance of the tracking task, relative to a single-task counting condition. Increasing tracking difficulty failed to reduce P300 amplitude further. A second experiment obviated the possibility that movement-related potentials caused the P300 attenuation resulting from the introduction of the tracking task. In Experiment 3, subjects performed a reaction time task in conjunction with tracking in order to establish the validity of the tracking difficulty manipulation. The results are interpreted in terms of a theory of functionally-specific processing resources.

A Mixed-Mode Crack Analysis of Isotropic Solids Using Conservation Laws of Elasticity

Abstract: A simple and convenient method of analysis for studying two-dimensional mixed-mode crack problems is presented. The analysis is formulated on the basis of conservation laws of elasticity and of fundamental relationships in fracture mechanics. The problem is reduced to the determination of mixed-mode stress-intensity factor solutions in terms of conservation integrals involving known auxiliary solutions. One of the salient features of the present analysis is that the stress-intensity solutions can be determined directly by using information extracted in the far field. Several examples with solutions available in the literature are solved to examine the accuracy and other characteristics of the current approach. This method is demonstrated to be superior in its numerical simplicity and computational efficiency to other approaches. Solutions of more complicated and practical engineering fracture problems dealing with the crack emanating from a circular hole are presented also to illustrate the capacity of this method

Propionate-Degrading Bacterium, Syntrophobacter wolinii sp. nov. gen. nov., from Methanogenic Ecosystems

Abstract: A new genus and species of a nonmotile gram-negative rod, Syntrophobacter wolinii, is the first bacterium described which degrades propionate only in coculture with an H(2)-using organism and in the absence of light or exogenous electron acceptors such as O(2), sulfate, or nitrate. It was isolated from methanogenic enrichments from an anaerobic municipal sewage digestor, using anaerobic roll tubes containing a medium with propionate as the energy source in association with an H(2)-using, sulfate-reducing Desulfovibrio sp. which cannot utilize fatty acids other than formate. S. wolinii produced acetate and, presumably, CO(2) and H(2) (or formate) from propionate. In media without sulfate and with Methanospirillum hungatei, a methanogen that uses only H(2)-CO(2) or formate as an energy source, acetate, methane, and, presumably, CO(2) were produced from propionate and only small amounts of Desulfovibrio sp. were present. Isolation in coculture with the methanogen was not successful. S. wolinii does not use other saturated fatty acids as energy sources.

The Northern Hemisphere Sea-Level Pressure Data Set: Trends, Errors and Discontinuities

Abstract: A detailed examination of the Northern Hemisphere monthly mean sea-level grid-point pressures shows a disappointingly large number of problems. The data set extends from 1899–1977 but has originated from eight different sources and discontinuities have been identified with every change in source. We have documented corrections for many of these and have also catalogued 3263 serious errors. These have been corrected or set to missing. Most of the errors are over Asia and are predominant before 1922 or during World War II. Analyses of several different aspects of the data that reveal both the problems and real changes in the atmospheric circulation are presented, along with a comparison of the monthly mean operational U.S. Navy versus U.S. National Meteorological Center analyses. A plea is made for a greater effort in archiving quality controlled climatological data.

Human ecology and crime: A routine activity approach

Abstract: Prior explanations of the distributions of crime have tended to emphasize the criminal intentions of people without considering adequately the circumstances in which criminal acts occur. This paper examines how community structure generates these circumstances and applies Amos Hawley's human ecological theory in treating criminal acts as routine activities which feed upon other routine activities. For example, we consider how married women in the labor force, persons living alone, and lightweight durable goods provide offenders with circumstances favorable for carrying out certain illegal acts. We examine in particular how directcontact predatory violations require the convergence in space and time of offenders, suitable targets,and the absence of effective guardians.Various trends in the social structure can alter crime rates by affecting the likelihood of this convergence, without necessarily requiring changes in the criminal inclinations of individuals.

Postsurgical pain relief: patients' status and nurses' medication choices.

Abstract: This study consisted of two interrelated parts. In the first part, the adequacy of pain relief in hospitalized post-surgical patients was assessed and described and in the second part ways in which nurses on the same units chose analgesic medications were examined and analyzed. Pain was considered a subjective experience. Patients were interviewed, and their charts reviewed on the third postoperative day. The sample included 109 patients in 5 central Illinois hospitals. After all patient interviews were completed, 121 nurses on the same units responded to a questionnaire which included clinical vignettes. Results of the patient interviews indicated that 75.2% of these patients were in moderate or marked pain distress and that a general question did not adequately assess pain. Chart review indicated that these patients were actually receiving less narcotic analgesics than they could receive. Nurses were overly concerned about the possibility of addiction; choices of analgesic medications seemed irrational; and knowledge of the drugs was inadequate. Moreover, these nurses indicated that complete pain relief after surgery was not their major goal. In 2 sets of identical vignettes where the only difference was the sex of the patient, nurses selected less medication for pain for female patients (P < 0.001 and P < 0.025 respectively). Factors that nurses consider in administering and choosing postoperative analgesia are described.

Quantum-well heterostructure lasers

Abstract: The various features peculiar to the operation of quantum-well semiconductor lasers are described and illustrated with data on single- and multiple-quantum-well Al x Ga 1-x As-GaAs heterostructures grown by metalorganic chemical vapor deposition (MO-CVD). Photo-pumped and p-n diode lasers (injection lasers) are described that are capable of continuous room temperature (CW 300 K) operation. The basic problems of carrier collection, thermalization, and quantum-well band filling are considered and have made clear the limits on single quantum-well laser operation and how these can be overcome with multiple quantum-well active regions. The idea that the steplike density-of-states of a quantum-well heterostructure can improve the operation of a semiconductor laser is shown to be valid. Also, it is shown that phonon participation in the operation of a quantum-well laser, which was not anticipated, is a major (even dominant) effect, with perhaps the phonon emission itself in the compact active region being stimulated. Besides the obvious freedom that quantum-well layers offer in how the active region of a semiconductor laser can be designed, quantum-well lasers are shown to exhibit a lesser sensitivity of the threshold current density on temperature, which is explained in terms of the step-like density-of-states and the disturbed electron and phonon distributions in the quantum-well active regions. Values as high as \sim437\deg C have been obtained for T 0 in the usual expression J_{th}(T) = J_{th}(0) \exp (T/T_{0}) . Since photopumped multiple-quantum-well MO-CVD Al x Ga 1-x As-GaAs heterostructures have operated as CW 300 K lasers with only 5-10 mW of photoexcitation (uncorrected for focusing and window losses, \lambda \sim 5145 A), it is suggested that quantum-well laser diodes can be made that will operate at ∼1 mA or even less excitation.

Microvascular contributions in tissue heat transfer.

Abstract: Many mathematical formulations of the heat transfer in living tissues'-' have been for the purposes of studying thermal regulation, comfort, or other phenomenon where significant localized (as opposed to whole-body or regional) variations in temperature and heat flux were of little interest. The advent of intensified interest in hyperthermia as a cancer therapy and the safety associated with ultrasound and microwave radiation, as well as attempts at a quantitative interpretation of thermographic measurements, however, have made it highly desirable to have formulations that are valid also for small-scale temperature variations. Living tissues differ from nonbiological materials primarily because of the presence of the vasculature. The large number and the architectural and dimensional variety of blood vessels clearly make it impractical to account for their individual contribution to heat transfer processes in the tissue with the exception, of course, of the larger arteries and veins. In the fields of heat transfer and fluid flow, when one encounters problems with a large number of structures whose individual dimensions are small relative to the macroscopic phenomenon under study, a common practice is to adopt the so-called continuum description. In this description, only the collective behavior of the small structures is taken into consideration in a certain statistical manner. Usually the influence of the small structures are ultimately expressed in terms of continuum properties of the medium, in our case, the thermal conductivity, specific heat, and blood perfusion rate of the tissue. It is the purpose of this report to explore the theoretical basis for the relationship between these properties and the architecture and function of the vasculature. It will be shown that because of the vasculature, and the large rate of blood perfusion, living biological tissues are fundamentally different from inert materials. Consequently, the familiar thermal properties can no longer be assumed to be independent of the parameters of the temperature field. In other words, these properties may vary, depending on the nature of the application. In view of the fact that existing formulations of the bio-heat transfer problem have been found to be more or less satisfactory for the description of heat transfer involving large-scale tempera-

Pattern Recognition as Rule-Guided Inductive Inference

Abstract: The determination of pattern recognition rules is viewed as a problem of inductive inference, guided by generalization rules, which control the generalization process, and problem knowledge rules, which represent the underlying semantics relevant to the recognition problem under consideration. The paper formulates the theoretical framework and a method for inferring general and optimal (according to certain criteria) descriptions of object classes from examples of classification or partial descriptions. The language for expressing the class descriptions and the guidance rules is an extension of the first-order predicate calculus, called variable-valued logic calculus VL21. VL21 involves typed variables and contains several new operators especially suited for conducting inductive inference, such as selector, internal disjunction, internal conjunction, exception, and generalization. Important aspects of the theory include: 1) a formulation of several kinds of generalization rules; 2) an ability to uniformly and adequately handle descriptors (i.e., variables, functions, and predicates) of different type (nominal, linear, and structured) and of different arity (i.e., different number of arguments); 3) an ability to generate new descriptors, which are derived from the initial descriptors through a rule-based system (i.e., an ability to conduct the so called constructive induction); 4) an ability to use the semantics underlying the problem under consideration. An experimental computer implementation of the method is briefly described and illustrated by an example.

Equivalences Among Relational Expressions with the Union and Difference Operators

Abstract: Queries in relational databases can be formulated in terms of relational expressions using the relational operations select, project, join, union, and difference The equivalence problem for these queries is studied with query optimization m mind It ts shown that testmg eqmvalence of relational expressions with the operators select, project, join, and union is complete m the class FIt of the polynomial-time hierarchy A nonprocedural representation for queries formulated by these expressions is proposed This method of query representation can be viewed as a generahzatlon of tableaux or conjunctive queries (which are used to represent expressions with only select, project, and join) Furthermore, this method is extended to queries formulated by relatmnal expressions that also contain the difference operator, provided that the project operator is not applied to subexpresstons with the difference operator A procedure for testing eqmvalence of these queries is given It ts shown that testmg containment of tableaux is a necessary step in testing equivalence of queries with union and difference Three important cases m which containment of tableaux can be tested m polynomial time are described, although the containment problem is shown to be NP-complete even for tableaux that correspond to expressions with only one project and several join operators

Theory of Substitutional Deep Traps in Covalent Semiconductors

Abstract: The energies of substitutional deep ${A}_{1}$ impurity levels in zinc-blende semiconductors are predicted and related to the impurities' atomic energies and to host dangling bond (ideal vacancy) energies.

Test Generation for Microprocessors

Abstract: The goal of this paper is to develop test generation procedures for testing microprocessors in a user environment. Classical fault detection methods based on the gate and flip-flop level or on the state diagram level description of microprocessors are not suitable for test generation. The problem is further compounded by the availability of a large variety of microprocessors which differ widely in their organization, instruction repertoire, addressing modes, data storage, and manipulation facilities, etc. In this paper, a general graph-theoretic model is developed at the register transfer level. Any microprocessor can be easily modeled using information only about its instruction set and the functions performed. This information is readily available in the user's manual. A fault model is developed on a functional level quite independent of the implementation details. The effects of faults in the fault model are investigated at the level of the graph-theoretic model. Test generation procedures are proposed which take the microprocessor organization and the instruction set as parameters and generate tests to detect all the faults in the fault model. The complexity of the test sequences measured in terms of the number of instructions is given. Our effort in generating tests for a real microprocessor and evaluating their fault coverage is described.

Quantum mechanical tunnelling in biological systems

Abstract: ‘Tunnelling’ is the metaphorical name given to the process, possible in quantum mechanics, but not in classical mechanics, whereby a particle can disappear from one side of a potential-energy barrier and appear on the other side without having enough kinetic energy to mount the barrier. One can think of this as a manifestation of the wave-nature of particles. The wavelength is larger if a particle is lighter. In particular electrons, being very light compared to atoms, have wavelengths as large or larger than atoms at energies found in the valence shells of molecules. Thus, they easily ooze through and around atoms and molecules. We are also concerned with the tunnelling of heavy particles: nuclei, atoms, molecules.

Effects of Ownership and Performance on Executive Tenure in U.S. Corporations

Abstract: The relationship between executive tenure and selected company characteristics was examined for 84 U.S. corporations. Among other findings, performance measures were related to the tenure of the ch...

On the problem of diffusion in solids

Abstract: We rationalize diffusion in solids on the basis of a differential equation of balance expressing conservation of momentum for the diffusing species. The balance equation contains a tensor, modelling the stress supported by the diffusing species, and a diffusive force vector, modelling the exchange of momentum between the diffusing species and the species of the solid matrix. These two quantities, which are not identified in classical diffusion interpretations, are the basic ingredients of the theory. The effect of state and constitution of interdiffusing materials is reflected in the form of the constitutive equations for the stress and the diffusive force. Within our framework, the main results of classical theories are rigorously derived in a unified manner. New interesting findings are also deduced and their implications are discussed. The applicability of the theory to a variety of problems, ranging from metallurgy to polymer physics and geophysics, is illustrated.

Secondary structure model for bacterial 16S ribosomal RNA: phylogenetic, enzymatic and chemical evidence

Abstract: We have derived a secondary structure model for 16S ribosomal RNA on the basis of comparative sequence analysis, chemical modification studies and nuclease susceptibility data. Nucleotide sequences of the E. coli and B. brevis 16S rRNA chains, and of RNAse T1 oligomer catalogs from 16S rRNAs of over 100 species of eubacteria were used for phylogenetic comparison. Chemical modification of G by glyoxal, A by m-chloroperbenzoic acid and C by bisulfite in naked 16S rRNA, and G by kethoxal in active and inactive 30S ribosomal subunits was taken as an indication of single stranded structure. Further support for the structure was obtained from susceptibility to RNases A and T1. These three approaches are in excellent agreement. The structure contains fifty helical elements organized into four major domains, in which 46 percent of the nucleotides of 16S rRNA are involved in base pairing. Phylogenetic comparison shows that highly conserved sequences are found principally in unpaired regions of the molecule. No knots are created by the structure.

Heat transfer to blood vessels

Abstract: Heat transfer to individual blood vessels has been investigated in three configurations: a single vessel, two vessels in counterflow, and a single vessel near the skin surface. For a single vessel the Graetz number is the controlling parameter. The arterioles, capillaries, and venules have very low Graetz numbers, Gz < 0.4, and act as perfect heat exchangers in which the blood quickly reaches the tissue temperature. The large arteries and veins with Graetz numbers over 10(3) have virtually no heat exchange with the tissue, and blood leaves them at near the entering temperature. Heat transfer between parallel vessels in counterflow is influenced most strongly by the relative distance of separation anad by the mass transferred from the artery to the vein along the length. These two effects are of the same order of magnitude, whereas the film coefficients in the blood flow are of significant but lesser importance. The effect of a blood vessel on the temperature distribution of the skin directly above it and on the heat transfer to the environment increases with decreasing depth-to-radius ratio and decreasing Biot number based on radius. The absolute magnitude of these effects is independent of other linear effects, such as internal heat generation or a superimposed one-dimensional heat flux.