Showing papers by "University of Michigan published in 1980"

Social support, occupational stress, and health.

Abstract: The present paper is concerned with the buffering hypothesis that social support ameliorate. the impact of occupational stress on job-related strain and health. Previous studies of this hypothesis have yielded conflicting results. Our purpose, therefore, is twofold. First, we summarize the literature in this area and review several studies in detail, all of which found main effects of social support on perceived occupational stress and on some health outcome measures. Three of the studies were specifically designed to examine the buffering effects of support. Of the three, two found little or no evidence for buffering (LaRocco and Jones, 1978a; Pinneau, 1975), whereas the third reported buffering effects (House and Wells, 1978). Second, we attempt to reconcile these different conclusions by reanalyzing one data set-first analyzed by Caplan et al. (1975) and then by Pinneau (1975)-using a moderated regression technique identical to that used in the LaRocco and Jones (1978a) and House and Wells (1978) studies. The data usedfor this analysis consist of a randomly stratified sample of men from 23 occupations (N 636). Our review andfindings support the buffering hypothesis for mental and physical health variables (anxiety, depression, irritation, and somatic symptoms), but, as in the previous three studies, fail to support the buffering hypothesis in regard to job-related strains (job dissatisfaction, boredom, dissatisfaction with work load).

Affective discrimination of stimuli that cannot be recognized

Abstract: Animal and human subjects readily develop strong preferences for objects that have become familiar through repeated exposures. Experimental evidence is presented that these preferences can develop even when the exposures are so degraded that recognition is precluded.

On Evaluating the Performability of Degradable Computing Systems

Abstract: If the performance of a computing system is "degradable," performance and reliability issues must be dealt with simultaneously in the process of evaluating system effectiveness. For this purpose, a unified measure, called "performability," is introduced and the foundations of performability modeling and evaluation are established. A critical step in the modeling process is the introduction of a "capability function" which relates low-level system behavior to user-oriented performance levels. A hierarchical modeling scheme is used to formulate the capability function and capability is used, in turn, to evaluate performability. These techniques are then illustrated for a specific application: the performability evaluation of an aircraft computer in the environment of an air transport mission.

Spillover Versus Compensation: A Review of the Literature on the Relationship Between Work and Nonwork

Abstract: This paper reviews the evidence concerning the relationship between workers' experiences on and off the job. Of particular interest is the debate over two rival hypotheses: the "spillover" hypothesis and the "compensation" hypothesis. The former argues that workers' experiences on the job carry over into the nonwork arena, and possibly vice versa, such that there develops a similarity in the patterning of work and nonwork life. The latter marshals several arguments for a negative association between work and nonwork, for example, the contention that the work situation is likely to be deficient in needfulfillment, at least in some respects, for most workers and that they will compensate for these deficiencies in their choices of leisure and family activities. Data from relevant studies support the notions of spillover and compensation under different conditions but, overall, offer more evidence of spillover than compensation. Support for spillover, for example, is reflected in the positive correlations bet...

Homicide trends in the united states

Abstract: Unlike most other causes of death, homicide has been increasing in the United States, especially since the mid-1960s. Its impact is greatest among nonwhite men. The elimination of homicide would add approximately one and one-half years to their life span. This analysis examines trends and differentials using vital statistics data about homicide victims. A decomposition of components of change reveals that almost all of the rise in homicide mortality among nonwhites and a substantial fraction of the rise among whites results from the increasing use of firearms to kill people.

Effective Choice in the Prisoner's Dilemma:

Abstract: This is a “primer” on how to play the iterated Prisoner's Dilemma game effectively. Existing research approaches offer the participant limited help in understanding how to cope effectively with such interactions. To gain a deeper understanding of how to be effective in such a partially competitive and partially cooperative environment, a computer tournament was conducted for the iterated Prisoner's Dilemma. Decision rules were submitted by entrants who were recruited primarily from experts in game theory from a variety of disciplines: psychology, political science, economics, sociology, and mathematics. The results of the tournament demonstrate that there are subtle reasons for an individualistic pragmatist to cooperate as long as the other side does, to be somewhat for-giving, and to be optimistic about the other side's responsiveness.

A Variable Circular-Plot Method for Estimating Bird Numbers

Abstract: -A bird census method is presented that is designed for tall, structurally complex vegetation types, and rugged terrain. With this method the observer counts all birds seen or heard around a station, and estimates the horizontal distance from the station to each bird. Count periods at stations vary according to the avian community and structural complexity of the vegetation. The density of each species is determined by inspecting a histogram of the number of individuals per unit area in concentric bands of predetermined widths about the stations, choosing the band (with outside radius x) where the density begins to decline, and summing the number of individuals counted within the circle of radius x and dividing by the area (m2). Although all observations beyond radius x are rejected with this procedure, coefficients of detectability may be determined for each species using a standard fixed maximum distance. A bird census technique that estimates the number of birds per area rather than relative abundance is desirable when the objective is to estimate the number and species of birds in a community for energetic considerations (Wiens and Nussbaum 1975), for calculating species diversity (MacArthur 1960, MacArthur and MacArthur 1961), or for elucidating the effects of habitat disturbances on bird populations (Bock and Lynch 1970). Since existing methods require different amounts of effort and give results of differing accuracy (Kendeigh 1944, Emlen 1971, Robinette et al. 1974, Best 1975, Franzreb 1976), the choice of a suitable technique should be based on the species of interest, the season of the year, time and personnel available, number and types of habitats to be censused, and accuracy of the density estimate that is required. Territorial or spot-mapping methods (Williams 1936, Kendeigh 1944) require that the census be conducted during the breeding season and involve considerable time and effort. Both factors severely restrict the number of habitats that can be sampled (Franzreb 1976). Plots of fixed size (e.g., Fowler and McGinnes 1973, Anderson and Shugart 1974), whether traversed by transect or censused from a fixed point, are more easily censused since only bird occurrence needs to be noted. However, density estimates from a number of fixed plots in habitats that differ structurally may not be comparable because of differences in the detectability of birds. For this reason data from fixed plots are frequently reported as relative numbers rather than densities. One way of adjusting for varying detectability among species is to use small plots in dense ,vegetation and large plots in open habitats. Problems arise when an "optimal" plot size, in which the detectability effects are averaged across all species in the community of interest, is required. Another problem is the variance in effectiveness in which two or more observers census plots of fixed sizes (Emlen 1971). Emlen's (1971) variable strip transect count, in which right angle distances from the transect to each observation are estimated, eliminates problems of matching plot size to habitat complexity. This is so because the area used to calculate density is determined by the distance on both sides of the transect within which all individuals of a species are seen or heard. Consequently, the area surveyed is determined by the detectability of each species and observer acuity in each habitat. Additionally, the variable strip method is rapid and relatively accurate and one person can census a variety of communities during any season. For a discussion of these points and a comparison of the variable strip count with the spotmap method see Franzreb (1976). In our work we have found that a stationary observer spends more time searching for birds and less time watching the path of travel. This is particularly true in tall, dense 310 R. T. REYNOLDS, J. M. SCOTT AND R. A. NUSSBAUM vegetation and in uneven terrain. Thus. as " a result of being stationarv. estimates of density and of siecies compbsition should improve. We found, for example, that stationary observers have a greater probability of seeing and hearing birds high in the canopy than even slowly moving observers; standing observers have less effect on bird acGvity; and, because rates of travel along a transect vary with terrain, complexity of vegetation, and number of birds seen, a further advantage of being stationary is that the census periods at each station can be fixed. This aids in standardizing the time spent counting birds in each habitat. Finally, the use of stations allows more definite statements to be made concerning the relationships between the habitat variables and the abundance and occurrence of bird species. This DaDer describes a variable circularplot census technique that gives estimates of birds per unit area during all seasons. This method originated in the need for an effective techniiue for counting birds in mature conifer forests. As such, it represents an a t t em~t to combine what we feel are the best attr;butes of existing methods for habitats of this type. Following its development and use in conifer forests, we have applied it to shrub-steppe, riparian, and semi-tropical rain forests. DESCRIPTION OF THE METHOD In the variable circular-plot method, stations (points) are established within a plant community either at equal intervals along a transect or scattered (avoiding edges) in such a manner as to minimize the probability of observing the same bird from several stations. Thus, the distance between stations depends (in part) on how far away the birds can be detected and how fast they move; it will vary with vegetation and the behavior of the birds (see below). Each bird seen or heard during a fixed time period around a station is counted and the horizontal distance to its location when first observed is estimated. We adjust the time counting at stations to match the structural characteristics of the vegetation and the number of bird species in the plant community being censused. Our strategy is to select the time required to count all birds within an effective detection distance (see below) but to keep the time short enough so that the probability of counting the same bird more than once or of counting birds that move into the area being sampled is minimized. For conifer forests, 10 min at each station following a 1-min "rest period" for equilibration of bird activity after arrival at each station, appears to be sufficient. For the closed canopy rain forests of Hawaii, 8 min is sufficient (J. M. Scott and J. L. Sincock, unpubl, data). For more open habitats (e.g., shrub-steppe) less time is required. With the variable circular-plot method no maximum distance restrictions are placed on any observation. We count only those birds actively using the census area. For example, gulls flying over a stand of cottonwoods are not counted. Peregrine Falcons (Falco peregrinus) soaring over the same area are included because they may capture prey therein. Birds that are flushed while approaching a station are recorded using the distance from the station to where they were first observed as the detection distance. Species that commonly do this are quail, grouse, hawks and owls. In the analysis, we determine the distance from the stations where the number of birds observed begins to decline (the point of inflection) by plotting for each species the number of individuals seen in concentric bands around all stations in each type of habitat. Since the area in each consecutively larger band around the stations is greater (see below) the number of birds observed in each band cannot be plotted directly. Thus, we plot the number of birds per area per band and convert the density in each to a standard of birds/km2. The number of birds in the habitat is then determined by summing the number of individuals counted within the circle of radius x (the inflection point), dividing by the area (,rr2) and converting the resultant density to a standard area (birds/km). With this procedure, we reject all observations outside of the circle of radius x. However, coefficients of detectability (CDs) may be calculated from these data using a standard fixed maximum distance for all species as described by Emlen (1971). For example, we plot the density (birds/ km) of Apapane (Himatione s. sanguinea) in each band with 5-m widths from 0 to 100m, and 10-m widths from 100-m to 200-m from the stations (Fig. 1). Since the density of birds recorded in the bands may vary, we established the following criteria to provide consistency in estimating the point of inflection: choose the distance to the outermost edge of the band where the density of individuals per km2 in the next outermost band is less than 50% of the previous band, with the specified condition that the number of individuals per km in any one of the CIRCULAR-PLOT CENSUS METHOD 311 lnf lect ion Point L

More Effective Choice in the Prisoner's Dilemma

Abstract: This study reports and analyzes the results of the second round of the computer tournament for the iterated Prisoner's Dilemma. The object is to gain a deeper understanding of how to perform well in such a setting. The 62 entrants were able to draw lessons from the results of the first round and were able to design their entries to take these lessons into account. The results of the second round demonstrate a number of subtle pitfalls which specific types of decision rules can encounter. The winning rule was once again TIT FOR TAT, the rule which cooperates on the first move and then does what the other player did on the previous move. The analysis of the results shows the value of not being the first to defect, of being somewhat forgiving, but also the importance of being provocable. An analysis of hypothetical alternative tournaments demonstrates the robustness of the results. THE TOURNAMENT APPROACH This article reports and analyzes the results of the second round of the Computer Tournament for the Prisoner's Dilemma. The object of the study is to gain a deeper understanding of how to perform well in such a Prisoner's Dilemma setting. The Prisoner's Dilemma game is justifiably famous as an elegant embodiment of the tension between individual rationality (reflected in the incentive of both sides to be selfish) and group rationality (reflected in the higher payoff to both sides for mutual cooperation). A typical

Duality in field theory and statistical systems

Abstract: This paper presents a pedagogical review of duality (in the sense of Kramers and Wannier) and its application to a wide range of field theories and statistical systems. Most of the article discusses systems in arbitrary dimensions with discrete or continuous Abelian symmetry. Globally and locally symmetric interactions are treated on an equal footing. For convenience, most of the theories are formulated on a $d$-dimensional (Euclidean) lattice, although duality transformations in the continuum are briefly described. Among the familiar theories considered are the Ising model, the $x\ensuremath{-}y$ model, the vector Potts model, and the Wilson lattice gauge theory with a ${Z}_{N}$ or $U(1)$ symmetry, all in various dimensions. These theories are all members of a more general heirarchy of theories with interactions which are distinguished by their geometrical character. For all these Abelian theories it is shown that the duality transformation maps the high-temperature (or, for a field theory, large coupling constant) region of the theory into the low-temperature (small coupling constant) region of the dual theory, and vice versa. The interpretation of the dual variables as disorder parameters is discussed. The formulation of the theories in terms of their topological excitations is presented, and the role of these excitations in determining the phase structure of the theories is explained. Among the other topics discussed are duality for the Abelian Higgs model and related models, duality transformations applied to random systems (such as theories of a spin glass), duality transformations in the "lattice Hamiltonian" formalism, and a description of attempts to construct duality transformations for theories with a non-Abelian symmetry, both on the lattice and in the continuum.

Pulsatile Secretion of Luteinizing Hormone: Differential Suppression by Ovarian Steroids

Abstract: In sheep, physiological levels of estradiol and progesterone each suppress the pulses of LH characteristic of tonic LH secretion, but do so by completely different mechanisms. Estradiol treatment decreases LH pulse amplitude but not frequency and also inhibits the height of the LH peak resulting from the administration of gonadotropin-releasing hormone (GnRH). In contrast, progesterone decreases the frequency of LH pulses without reducing their amplitude or the response to exogenous GnRH. This suggests that progesterone suppresses tonic LH secretion by acting in the brain to decrease the frequency of GnRH pulses, while estradiol may suppress the response of the pituitary to GnRH and thereby decrease LH pulse amplitude.

The subgingival microbial flora during pregnancy.

Abstract: The subgingival bacterial flora from 2 gingival sites was cultured and characterized monthly in twenty periodontitis-free women during pregnancy and again post-partum. Monthly plaque samples were also cultured in eleven age and disease matched non-pregnant women. Plaque was processed anaerobically on selective and nonselective media and the predominant colony types were characterized. A portion of each plaque sample was tested for bacterial uptake of Ci4-estradiol and C^-progesterone. Plasma levels of estrogens and progesterone were measured four times in each subject. The number of gingival bleeding sites, the Gingival Index and the Plaque Index were determined at each sampling period. In the second trimester there was a significant increase in gingivitis, the ratio of anaerobic to aerobic bacteria, and the proportional levels of Bacteroides melaninogenicus ss. intermedius. In the third trimester both gingivitis and the levels of B. melaninogenicus ss. mtermedius decreased. Plaque uptake of Ci4-steroids increased significantly during pregnancy and paralleled the plaque levels of B. melaninogenicus ss. intermedius. In the second trimester, recovery of B. melaninogenicus ss. intermedius was strongly correlated with plasma levels of estrogens and progesterone. No changes were observed in clinical parameters or the subgingival flora of non-pregnant subjects. Pregnancy and specifically steroid hormones appear capable of influencing the normal bacterial flora and inducing alterations in the subgingival ecology.

Architecture of the Vessel Wall

Abstract: The sections in this article are: 1 Classification and Definition of Blood Vessels 2 Components of the Vascular Wall 21 Intima 22 Media 23 Adventitia

Polynomial approximation of functions in Sobolev spaces

Abstract: Constructive proofs and several generalizations of approximation results of J. H. Bramble and S. R. Hilbert are presented. Using an averaged Taylor series, we represent a function as a polynomial plus a remainder. The remainder can be manipulated in many ways to give different types of bounds. Approximation of functions in fractional order Sobolev spaces is treated as well as the usual integer order spaces and several nonstandard Sobolev-like spaces.

Muscle architecture and force-velocity characteristics of cat soleus and medial gastrocnemius: implications for motor control

Abstract: 1. Isometric and isotonic contractile parameters of the soleus (SOL) and medial gastrocnemius (MG) muscles of seven adult cats were studied. In addition, architectural characteristics of six contralateral pairs of these ankle extensors were determined. 2. The in situ peak isometric tetanic tension developed by the MG at the Achilles tendon is nearly 5 times (9,846 vs 2,125 g) that of the SOL muscle. However, when differences between the MG and SOL in fiber length (2.01 vs 3.66 cm), muscle mass (9.80 vs. 3.31 g), and angle of pinnation (21.4 vs. 6.4 degrees) are considered, the specific tensions of these muscles are similar (approximately 2.3 kg x cm-2). 3. When the effects of muscle architecture are eliminated, the nearly threefold greater maximum isotonic shortening velocity (Vmax) of sarcomeres of the MG (38.2 micron/s) relative to the SOL (13.4 micron/s) is presumably due to intrinsic differences in the biochemical properties of these muscle. However, the Vmax developed by the MG at the Achilles tendon (258.6 mm/s) during a shortening contraction is only 1.5 times that of the SOL (176.3 mm/s) due to the influence of these muscles' specific architectures. 4. Variations in geometrical characteristics of the SOL and MG are consonant with the relative amounts of participation of these muscles during posture, locomotion, and jumping. Posture requires the development of low forces for prolonged periods for which the SOL seems best suited both architecturally and physiologically. The MG, relatively inactive during quiet standing, becomes responsible for a greater percentage of tension and shortening speed during plantar flexion (E3) as gait speeds increase, which is consistent with this muscle's greater tension- and velocity-generating capacity. 5. At high speeds of locomotion (3.0 m/s) and jumping, the shortening velocities developed at the end of E3 (approximately 20-40 ms before paw off) exceed Vmax of the SOL. Consequently, the SOL, although electrically active, cannot contribute to the tensions required to generate the shortening velocities dictated by these movements. 6. These data demonstrate the influence of the differing geometries of the SOL and MG on the roles of these muscles in generating forces at varying velocities, as demanded by the dynamics of the movement.

Luteinizing Hormone Receptors and Testosterone Synthesis in Two Distinct Populations of Ley dig Cells

Abstract: Dispersed cells from whole testes or from isolated interstitial tissue of mature rats, yielded two distinct populations of Leydig cells when subjected to centrifugation in a 0-40% metrizamide gradient. One population (I) was found in a fractions with a density of 1.085-1.117 g/cm3, and the other population (II) was found in fractions with a density of 1.128-1.145 g/cm3. Binding of 125I-labeled hCG by each population of cells indicated a single class of binding sites with the same high binding affinity and similar concentrations of binding sites per Leydig cell. Testosterone production per fmol gonadotropin receptor site in the absence of gonadotropin stimulation was similar for cells of each population. However, when cells from each population were incubated with increasing concentrations of hCG or dibutyryl cAMP, only Leydig cells from population II exhibited a marked increase in testosterone production. The low responsiveness of Leydig cells in population I did not appear to be a result of either damage to these cells or inhibition by non-Leydig interstitial cells in population I.

Stratum identification and consciousness.

Abstract: National sample data were analyzed to describe the identification and class consciousness of people with workingand middle-class occupations, race consciousness of blacks and whites, sex consciousness of women, and age consciousness of people sixty years or older. Stratum consciousness, an ideology about the position of the stratum in society, includes a sense of power discontent, evaluation of the legitimacy of its position, and the view that collective action is the best means to realize its interests. Comparisons of the two sets of subordinate and superordinate strata showed that only along the racial dimension was identification more widespread in the lower-power stratum, but that power discontent and collectivist orientations were stronger among both identified blacks and the working class than among identified whites and the middle class. Comparisons among the identified members of lower-power strata additionally demonstrated that consciousness was strongest among blacks, weakest among women, and moderate among people with working-class occupations and older people. Multiv'ariate analyses further showed that identification, power discontent, and rejection of legitimacy influenced the collectivist orientations of women and blacks additively, rather than interactively.

Age of Patients and Morbidity Associated With Mandibular Third Molar Surgery

Abstract: The purpose of this study was to define the incidence of operative and postoperative morbidity associated with the removal of impacted mandibular third molars in patients of various ages. Results of this investigation show that there is a significant increase in surgical morbidity as patients become older. When it has been determined that the mandibular third molars must be removed, the operation should be performed on the young adult.