Showing papers by "University at Buffalo published in 1991"

Control of Machines with Friction

Abstract: 1. Introduction.- 2. Friction in Machines.- 2.1. The Contemporary Model of Machine Friction.- 2.2. Boundary Lubricants: a Domain of Many Choices.- 2.3. Relaxation Oscillations.- 2.4. Friction Modeling in the Controls Literature.- 2.5. An Integrated Friction Model.- 3. Experiment Design.- 4. Repeatability.- 5. Break-Away Experiments.- 5.1. Experimental Issues in Measuring Break-Away Torque.- 5.2. Building the Compensation Table.- 6. Friction as a Function of Velocity.- 6.1. Analysis of Variance in the Motion Friction Data.- 6.2. Friction at Low Velocities.- 6.3. Friction During Compliant Motion.- 6.4. The Dahl Effect.- 6.5. The Stribeck Effect.- 6.6. Temporal Effects in the Rise and Decay of Friction.- 6.7. Variance in Friction as Process Noise.- 7. Analysis of Stick-Slip.- 7.1. Dimensional Analysis.- 7.2. Perturbation Analysis.- 7.3. The Impact of Static Friction Rising as a Function of Dwell Time.- 7.4. Integral Control.- 8. Demonstrations of Friction Compensation.- 8.1. Open-Loop Motion of One Joint.- 8.2. Open-Loop Motion of Three Joints.- 8.3. Friction Compensated Force Control.- 9. Suggestions Toward Friction Modeling and Compensation.- 9.1. Suggestions on Experimental Technique.- 9.2. Suggestions on Control.- 9.3. Conclusion.- Appendix A: Small Studies.- A.1 Friction as a Function of Motor Angle.- A.2 Joint 2 Motor Alone and Joint 2 Link Alone.- A.3 Trials with Dither.- A.4 Friction as a Function of Load.- A.5 Creep.- A.6 Effects that were not Observed.

Periodontal Disease in Non‐Insulin‐Dependent Diabetes Mellitus

Abstract: The relationship between diabetes mellitus and oral health status was determined in Pima Indians from the Gila River Indian Community in Arizona. This tribe of native Americans has the world's highest reported incidence and prevalence of non-insulin-dependent (type 2) diabetes mellitus. The probing attachment level, alveolar bone loss, age, sex, Calculus Index, Plaque Index, Gingival Index, fluorosis, and DMFT as well as the diabetic status was assessed in 1,342 Pima Indians who were at least partially dentate. The prevalence and severity of destructive periodontal disease was determined by measuring probing attachment loss and radiographically apparent interproximal crestal alveolar bone loss, two independent but correlated indicators of periodontal destruction. Only diabetic status, age, and the presence of subgingival calculus were significantly associated with both increased prevalence and greater severity of destructive periodontal disease in this population. Diabetic status was significantly and strongly related to both the prevalence and severity of disease after adjusting for the effects of demographic variables and several indices of oral health including the Plaque Index. Subjects with type 2 diabetes have an increased risk of destructive periodontitis with an odds ratio of 2.81 (95% confidence interval 1.91 to 4.13) when attachment loss is used to measure the disease. The odds ratio for diabetic subjects was 3.43 (95% confidence interval 2.28 to 5.16) where bone loss was used to measure periodontal destruction. These findings demonstrate tht diabetes increases the risk of developing destructive periodontal disease about threefold. Furthermore, diabetes increases the risk of developing periodontal disease in a manner which cannot be explained on the basis of age, sex, and hygiene or other dental measures.(ABSTRACT TRUNCATED AT 250 WORDS)

The Pacific/North American Teleconnection Pattern and United States Climate. Part I: Regional Temperature and Precipitation Associations

Abstract: The Pacific/North American (PNA) teleconnection index, a measure of the strength and phase of the PNA teleconnection pattern, is related to the variations of the surface climate of the United States from 1947 through 1982 for the autumn, winter, and spring months when the PNA is a main mode of Northern Hemisphere midtropospheric variability. The results demonstrate that the PNA index is highly correlated with both regional temperature and precipitation. The strongest, most extensive correlations between the index and temperature are observed in winter, but large areas of the country show important associations during the spring and autumn as well. Although the centers of highest correlation migrate systematically with changes in the circumpolar vortex over the course of the annual cycle, the southeastern and northwestern parts of the United States possess consistently high index-temperature correlations. Correlations between the PNA index and precipitation are weaker and less extensive than those...

Gap junctions formed by connexins 26 and 32 alone and in combination are differently affected by applied voltage.

Abstract: Gap junctions are formed by a family of homologous proteins termed connexins. Their channels are dodecamers, and homomeric forms differ in their properties with respect to control by voltage and other gating stimuli. We report here the properties of coupling from expression of connexin complementary RNAs (cRNAs; sense to mRNA, antisense to cDNA) in Xenopus oocyte pairs in which endogenous coupling was blocked by injection of DNA oligonucleotides antisense to the mRNA of Cx38, the principal endogenous connexin. We found that a connexin recently sequenced from rat liver, Cx26, formed functional gap junctions whose conductance exhibited voltage dependence with unusual characteristics suggestive of two gating mechanisms. Junctional conductance (gj) was increased to a small degree by depolarization and decreased by hyperpolarization of either cell in a coupled pair, indicating dependence on the potential between the inside and outside of the cells (Vi-o). These changes were fast compared with the resolution of their measurement (ca. 10 ms). On a slower timescale, large transjunctional potentials (Vj) of either sign caused a more substantial decrease in conductance similar to that previously reported for several other gap junctions. Homotypic junctions formed of another connexin, Cx32, exhibited a similar slow dependence on Vj but no dependence on Vi-o. In contrast, heterotypic junctions between an oocyte expressing Cx26 and one expressing Cx32 were electrically asymmetric; they exhibited a greater fast change in gj, which depended, however, on Vj, such that gj increased with relative positivity on the Cx26 side and decreased with relative negativity on the Cx26 side. There was also a large slow decrease in gj in response to Vj for relative positivity on the Cx26 side but not for Vj of the opposite sign. These data indicate that properties of the hemichannels contributed by the two connexins in the heterotypic case were changed from their properties in homotypic junctions. The fast change in gj may involve a mechanism analogous to that at fast rectifying electrical synapses. Experiments in which oocytes expressing Cx32 were paired with oocytes expressing both Cx26 and Cx32 demonstrated that asymmetric junctions would form between oocytes expressing both connexins, thereby confirming their potential relevance in vivo, where the same coupled cells are known to express both proteins.

Attachment Styles, Gender and Parental Problem Drinking:

Abstract: Bartholomew's (1990) four-category typology of adult attachment styles was compared with Hazan & Shaver's (1987) three-category typology in terms of three substantive issues. First, the same two dimensions were found to underlie both typologies, and the Bartholomew and Hazan & Shaver measures corresponded as predicted. Second, there were no gender differences on Hazan & Shaver's measure, in line with previous studies, but there were gender differences on Bartholomew's measure, especially in her two avoidant categories. More males than females were dismissing avoidants; more females than males were fearful avoidants. Third, a hypothesis advanced by Latty-Mann & Davis (1988) was confirmed. Adult children of alcoholics scored high on both avoidant and anxious-ambivalent scales of Hazan & Shaver's measure, and fell predominantly into Bartholomew's fearful-avoidant category, suggesting that at least some fearful adults are grown-up versions of the `disorganized, disoriented' children identified by Crittenden (...

Folate Intake and Carcinogenesis of the Colon and Rectum

Abstract: Experimental evidence suggests that folate depletion plays a role in carcinogenesis. A case-control study examining folate intake was conducted. Some 428 colon and 372 rectal cancer cases with matched neighbourhood controls were interviewed regarding usual intake of foods, including food preparation. Unadjusted folate was not associated with risk of either cancer. Controlling for kilocalories, odds ratios (ORs) for those with the highest folate intake were 0.5 (95% confidence interval (CI): 0.24-1.03) and 0.31 (95% CI: 0.16-0.59) for females and males for rectal cancer. There was no change in colon cancer risk associated with folate intake. There was an indication of an interaction of folate and alcohol intake; the difference in risk associated with low and high folate intake was highest for males in the highest alcohol category. Associations were of similar magnitude for other dietary factors correlated with folate. It appears that intake of folate or a correlated factor may be negatively related to risk of rectal cancer.

Children’s Testimony About a Stressful Event: Improving Children’s Reports

Abstract: Age differences in children's ability to recount a stressful event were explored, as were several ways to improve children's reports. Seventy 3- to 7 year olds were videotaped while receiving inoculations at a medical clinic. It was predicted that multiple interviews would maintain memory and strengthen resistance to sugges-tion. It was also predicted that social support would ease intimidation and thus lessen children's suggestibility. To test these predictions, children were inter-viewed either once after a 4-week delay or twice, following 2- and 4-week delays, and under either "reinforcing" or "nonreinforcing" conditions. Age differences in answers to specific and misleading questions and in performance on a photo identification task were prevalent. However, multiple interviews and reinforce-ment supported more accurate reports. Training was effective in reducing false identifications on the photo identification task, especially for older children. Children's accuracy was unrelated to parental ratings of the stressfulness of the event. Our findings have implications for the testimony of child victim witnesses and for child-adult reconstruction of a child's past history. (Psychology)

Measurement of extensional viscosity of polymer solutions

Abstract: A filament stretching technique for measuring the extensional viscosity of polymer solutions at constant stretch rate is presented. The liquid sample is held between two coaxial discs and stretched by moving the bottom disc downwards with a speed that increases exponentially with time. This is illustrated using a constant viscosity, elastic fluid consisting of 0.185% polyisobutylene in a solvent of kerosene and polybutene. For the case of this particular fluid, two distinct stretch rate regions are found to arise. The stretch rate in the first region is much higher than in the second, which is, in most cases, close to the overall stretch rate imposed on the sample. Nonetheless, all the results of any given run can be represented using an average extensional rate. The extensional stress growth data, plotted as the Trouton ratio against time, show an initial linear viscoelastic region where TR rises to a value of 3, independent of extensional rate. Beyond this region, TR depends on the stretch rate and rises dramatically to values in excess of 103; the higher the extensional rate, the faster is the increase in TR. These data do not seem to reach a steady state and appear to be similar to polymer melt data obtained by others in the past. The reproducibility of the results is very good and all this suggests that it is now possible to obtain unambiguous constant-stretch-rate stress-growth data for polymer solutions stretched from a state of rest.

Bistatic synthetic aperture radar inversion with application in dynamic object imaging

Abstract: An inversion method is presented for bistatic synthetic aperture radar imaging. The method is based on a Fourier analysis (Doppler processing) of the bistatic synthesized array's data followed by a phase modulation analysis of the Doppler data. The approach incorporates the phase information of the wavefront curvature in the transmitted waves as well as the resultant echoed signals. The Doppler data are shown to provide samples of the reflectivity function's spatial Fourier transform within a band that depends upon the bistatic angles and ranges. Associated resolution, reconstruction, and sampling constraints for the imaging problem are discussed. The bistatic SAR inversion is also utilized to formulate an inversion for multistatic measurements made along a physical linear array due to a single transmission to image a dynamic object. >

Locally axisymmetric turbulence

Abstract: The failure of local isotropy to describe the experimentally obtained derivative moments in turbulent shear flows has previously been well-documented, but is briefly reviewed. The same data are then used to evaluate the hypothesis that the turbulence is locally axisymmetric. Locally axisymmetric turbulence is defined herein as turbulence which is locally invariant to rotations about a preferred axis.The derivative moment relations are derived from the general form of the two-point velocity correlation tensor near the origin for axisymmetric turbulence. These are used to derive relations for the rate of dissipation of kinetic energy, the mean-square vorticity, and the components of each. Almost all of the experimental derivative moment data are shown to be consistent with these equations, and thus with local axisymmetry.

Construct Measurement in Information Systems Research: An Illustration in Strategic Systems

Abstract: This study seeks to highlight construct measurement issues in information systems (IS) research. It describes the normative process of construct measurement and identifies the difficult problems involved in measurement and some ways in which these difficulties may be overcome. An illustrative construct-operationalization study in the area of strategic systems outlines how the normative guidelines may be applied to IS. Some specific recommendations for IS include developing a preliminary model of the construct even if there is little previous measurement research, devoting greater attention to predictive validity because a lack of theories in IS precludes the examination of nomological validity, verifying the assumptions underlying the computation of an overall index, and examining the measurement properties of the index.

2-D shape classification using hidden Markov model

Abstract: The authors present a planar shape recognition approach based on the hidden Markov model and autoregressive parameters. This approach segments closed shapes to make classifications at a finer level. The algorithm can tolerate a lot of shape contour perturbation and a moderate amount of occlusion. An orientation scheme is described to make the overall classification insensitive to shape orientation. Excellent recognition results have been reported. A distinct advantage of the approach is that the classifier does not have to be trained again when a new class of shapes is added. >

Nonlinear optical properties of p-nitroaniline: An ab initio time-dependent coupled perturbed Hartree-Fock study

Abstract: For p‐nitroaniline the ab initio method with a double‐zeta basis set which includes semidiffuse polarization functions has been used to calculate the dipole moment μ, frequency‐dependent linear polarizability α, and nonlinear hyperpolarizabilities β and γ using the time‐dependent coupled perturbed Hartree–Fock approach. The computation procedure used here yields information on the dispersion behavior of all the tensor components of polarizability and various hyperpolarizability terms. The largest dispersion effect is observed for the diagonal components of the polarizability and hyperpolarizability tensors along the long in‐plane axis. The magnitudes of the various hyperpolarizability terms which describe the various second‐order nonlinear processes show the following trend: β(−2ω;ω,ω) ≳β(0;ω,−ω)=β(−ω;0,ω) ≳β(0;0,0), with β(−2ω;ω,ω) exhibiting the largest frequency dispersion. The various second hyperpolarizability terms which describe the various third‐order nonlinear optical processes show the following trend: γ(−3ω;ω,ω,ω) ≳γ(−2ω;0,ω,ω) ≳γ(−ω;ω,−ω,ω) ≳γ(−ω;0,0,ω) ≊ γ(0;0,ω,−ω) ≳γ(0;0,0,0). Again γ(−3ω;ω,ω,ω) shows the largest dispersion effect. The results of existing semiempirical calculations on p‐nitroaniline are compared with that of the present ab initio calculation, and the problem due to the arbitrary parametrization procedure adopted in the past for semiempirical calculation is discussed. The computed values of the first resonance energy, the dipole moment, and the polarizability are in good agreement with the respective values experimentally observed, within the spread of the existing experimental data. In contrast, the computed β and γ values are considerably smaller than the respective experimentally determined values. We attribute this discrepancy to two sources. First, in the theoretical calculation electron correlation has been neglected, and the basis set used, although large, may not still be adequate. Second, there is a considerable spread in the reported experimental values for a given nonlinear coefficient making any comparison between the theory and the experiment difficult.

Mouse connexin37: cloning and functional expression of a gap junction gene highly expressed in lung.

Abstract: The coding sequence (333 amino acids) of a new connexin protein, designated mouse connexin37 (Cx37 or Cx37.6) due to the deduced theoretical molecular mass of 37.600 kD, has been determined from cDNA and genomic clones. As seen in other connexins, its gene has no introns within the coding region and the deduced amino acid sequence is predicted to have similar topology to other connexins that form intercellular channels. The amino acid sequence of mouse Cx37 is most similar to rat connexin43 (59% identity) and Xenopus connexin38 (66% identity) when compared from the NH2 terminus to the end of the fourth putative transmembrane region. When expressed in Xenopus oocytes Cx37 forms functional intercellular channels that exhibit more sensitive and rapid gating in response to voltage than any previously characterized vertebrate gap junction. Under stringent conditions the Cx37 cDNA hybridizes to an mRNA of 1.7 kb that is found highly abundant in lung and to progressively lesser extents in brain, kidney, skin, spleen, liver, intestine, and heart. Embryonic brain, kidney, and skin express two to fivefold higher levels of the Cx37 transcript than the corresponding adult tissues. Cx37 transcripts were also found to increase two to threefold in response to retinoic acid treatment of cultured embryonic carcinoma F9 cells.

Research on cooperative learning: implications for practice

Abstract: This article provides an overview of research on cooperative learning with an emphasis on issues related to the implementation of cooperative learning groups. Specific benefits of cooperative learn...

Impact and adjustment: foreign students in comparative perspective*

Abstract: Foreign study is a multifaceted phenomenon - its impact is felt on academic institutions in both the ‘host’ and ‘sending’ countries, on the economies of nations, and of course on the individuals involved. With more than one million students studying abroad, foreign study has assumed considerable importance in higher education planning. This article considers the many aspects of foreign study and discusses the interrelationships of these elements. The policies of the ‘host’ nations, for example, have an impact on higher education planning in the sending countries. The non-return of foreign students, traditionally referred to as the ‘brain drain’, is considerably more complex than was once thought since Third World graduates settled in the industrialized nations often retain contacts with their home countries and increasingly return after a period abroad. This article also considers the various ‘push’ and ‘pull’ factors which determine the constantly changing flow of foreign students.

Critical Dimensions of Strategic Information Systems Planning

Abstract: Strategic information systems planning (SISP) is the process whereby an organization establishes a long-range plan of computer-based applications in order to achieve its goals. A number of problems can potentially impede information systems planners as they carry out the process. A survey of 80 firms who completed the SISP process revealed that the problems constitute five factors: the organization, implementation, database, hardware, and cost. A discriminant analysis showed that three factors—the organization, implementation, and database—best distinguished satisfied from dissatisfied information systems planners. A research application of the five factors suggested that organizations with more sophisticated business planning endure significantly less severe hardware and implementation problems.