Showing papers by "Pennsylvania State University published in 1993"

Estimation of the number of nucleotide substitutions in the control region of mitochondrial DNA in humans and chimpanzees.

Abstract: Examining the pattern of nucleotide substitution for the control region of mitochondrial DNA ( mtDNA ) in humans and chimpanzees, we developed a new mathematical method for estimating the number of transitional and transversional substitutions per site, as well as the total number of nucleotide substitutions. In this method, excess transitions, unequal nucleotide frequencies, and variation of substitution rate among different sites are all taken into account. Application of this method to human and chimpanzee data suggested that the transition / transversion ratio for the entire control region was - 15 and nearly the same for the two species. The 95% confidence interval of the age of the common ancestral mtDNA was estimated to be 80,000-480,000 years in humans and 0.57-2.72 Myr in common chimpanzees.

Conducting Interorganizational Research Using Key Informants

Abstract: In this article, we examine the use of the key informant methodology by researchers investigating interorganizational relationships. Authors have advocated the use of multiple informants to increase the reliability and validity of informant reports. However, interorganizational research still tends to rely on single informants. We investigated informant selection and obtaining perceptual agreement among multiple informants, two problems that may have inhibited widespread use of multiple informants. We suggest procedures for dealing with those problems and provide an illustrative application of our proposals.

Convective parameterization for mesoscale models : The Kain-Fritsch Scheme

Abstract: The Kain-Fritsch (KF) convective parameterization scheme (CPS) is based on the same fundamental closure assumption as the Fritsch-Chappell (FC) (1980) scheme—convective effects are assumed to remove convective available potential energy in a grid element within an advective time period. Its development was motivated by ongoing observational and numerical investigations of mesoscale convective systems that have revealed the potentially significant impact of certain physical processes that were not represented in the FC scheme. For example, in the FC scheme, detrainment from convective clouds to their environment occurs over a limited vertical depth near cloud top. Yet, it has become evident from diagnostic studies (e.g., Leary and Houze 1980; Gamache and Houze 1983) that midlevel detrainment of mass and moisture from deep convective clouds plays an important role in the development of some mesoscale convective systems.

A Nonhydrostatic Version of the Penn State–NCAR Mesoscale Model: Validation Tests and Simulation of an Atlantic Cyclone and Cold Front

Abstract: A nonhydrostatic extension to the Pennsylvania State University-NCAR Mesoscale Model is presented. This new version employs reference pressure as the basis for a terrain-following vertical coordinate and the fully compressible system of equations. In combination with the existing initialization techniques and physics of the current hydrostatic model, this provides a model capable of real-data simulations on any scale, limited only by data resolution and quality and by computer resources. The model uses pressure perturbation and temperature as prognostic variables as well as a B-grid staggering in contrast to most current nonhydrostatic models. The compressible equations are solved with a split-time- step approach where sound waves are treated semi-implicitly on the shorter step. Numerical techniques and finite differencing are described. Two-dimensional tests of flow over a bell-shaped hill on a range of scales were carded out with the hydrostatic and nonhydrostatic models to contrast the two and...

Etiology of child maltreatment: a developmental-ecological analysis.

Abstract: This article applies a developmental-ecological perspective to the question of the etiology of physical child abuse and neglect by organizing the paper around a variety of "contexts of maltreatment." The roles of parent and child characteristics and processes are considered ("developmental context"), including an examination of intergenerational transmission. The "immediate interactional context" of maltreatment, which focuses on the parenting and parent-child interactional processes associated with abuse and neglect, is analyzed. Finally, the "broader context" is discussed with 3 specific subsections dealing with the community, cultural, and evolutionary contexts of child maltreatment. Implications for intervention are considered and future research directions are outlined.

Strategic Sensemaking and Organizational Performance: Linkages Among Scanning, Interpretation, Action, and Outcomes

Abstract: This study investigated the strategic "sensemaking" processes of scanning, interpretation, and action and how those activities are linked to organizational performance. Using path analyses on data from 156 hospitals, we tested the direct and indirect effects among these sensemaking processes and performance outcomes and developed a model of their relationships. In a more general sense, the research represents an attempt to provide insight not only into relationships between cognition and action, but also into the links between those fundamental processes and organizational performance outcomes.

Abrupt increase in Greenland snow accumulation at the end of the Younger Dryas event

Abstract: THE warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate, the best-known of which is the Younger Dryas event1. Despite much study of the causes of this event and the mechanisms by which it ended, many questions remain unresolved1. Oxygen isotope data from Greenland ice cores2–4 suggest that the Younger Dryas ended abruptly, over a period of about 50 years; dust concentrations2,4 in these cores show an even more rapid transition (≲20 years). This extremely short timescale places severe constraints on the mechanisms underlying the transition. But dust concentrations can reflect subtle changes in atmospheric circulation, which need not be associated with a large change in climate. Here we present results from a new Greenland ice core (GISP2) showing that snow accumulation doubled rapidly from the Younger Dryas event to the subsequent Preboreal interval, possibly in one to three years. We also find that the accumulation-rate change from the Oldest Dryas to the Bo11ing/Allerod warm period was large and abrupt. The extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the North Atlantic climate system.

Ceramic Powder Synthesis by Spray Pyrolysis

Abstract: A variety of spray pyrolysis (SP) techniques have been developed to directly produce ceramic powders from solutions. This paper reviews the current status of these processes in terms of the process parameters that enable the formation of particles with controlled morphology and composition. A model incorporating solute diffusion in the droplet and solvent evaporation from the droplet surface is presented to establish the critical parameters leading to solid particle formation. The model illustrates that solid particles can be obtained if solutes with high solubility and a large difference between the critical supersaturation and equilibrium concentration are used and if the process is designed to avoid solvent boiling. It is demonstrated that mixed metal oxide, non-oxide, and composite particles that are solid, hollow, porous, or fibrous can be produced by modifying the precursor characteristics, solution properties, and process parameters. The physical and chemical flexibility of SP processes offers numerous opportunities for the controlled synthesis of advanced ceramic powders and films. However, production rates are limited by the need to produce <5-[mu]m-diameter droplets and to avoid subsequent droplet coagulation. Developments in process controls, atomization, and system design are required for wider commercialization of SP-type processes.

Potential power and power use: an investigation of structure and behavior

Abstract: behavioral tactics. Results indicate that structural position, measured as an individual's network centrality and level in the organizational hierarchy, and behavior-use of assertiveness, ingratiation, exchange, upward appeal, rationality, and coalition formation-relate independently and significantly to others' perceptions of the individual's power. In addition, structure partially mediated the relationship between behavior and power, and the behavioral strategies partially mediated the structure-power relationship. Significant interaction effects were also found. The study of power in organizations has been both plagued and blessed by the multitude of theories and approaches that have been offered. Although the variety of approaches makes convergence difficult, consideration of its subtle complexities leads to a more comprehensive overview of the phenomenon of power. However, the proliferation of conceptual subtleties has also resulted in a fragmentation of empirical research (Astley & Sachdeva, 1984). Nowhere is this more evident than in the research agendas of organizational psychologists, who take a micro-level view, and organizational sociologists, who take a macro-level view. Micro research has focused on the behavior of individuals, macro research on the larger organizational context. In investigating power in organizations, the micro-macro split is exemplified in the distinction between potential power and power use.

A review of catalytically grown carbon nanofibers

Abstract: Carbon nanofibers (sometimes known as carbon filaments) can be produced in a relative large scale by the catalytic decomposition of certain hydrocarbons on small metal particles. The diameter of the nanofibers is governed by that of the catalyst particles responsible for their growth. By careful manipulation of various parameters it is possible to generate carbon nanofibers in assorted conformations and at the same time also control the degree of their crystalline order. This paper is a review of the recent advances made in the development of these nanostructures, with emphasis both on the fundamental aspects surrounding the growth of the material and a discussion of the key factors which enable one to control their chemical and physical properties. Attention is also given to some of the possible applications of the nanostructures which center around the unique blend of properties exhibited by the material.

Efficacy of Applied Relaxation and Cognitive-Behavioral Therapy in the Treatment of Generalized Anxiety Disorder

Abstract: Nondirective (ND), applied relaxation (AR), and cognitive behavioral (CBT) therapies for generalized anxiety disorder (GAD) were compared. The latter 2 conditions were generally equivalent in outcome but superior to ND at postassessment. The 3 conditions did not differ on several process measures, and ND created the greatest depth of emotional processing. Follow-up results indicated losses in gains in ND, maintained gains in the other 2 conditions, especially CBT, and highest endstate functioning for CBT. AR and CBT thus contain active ingredients in the treatment of GAD; support exists for further development of imagery exposure methods or cognitive therapy because of their likely role in promoting maintenance of change with this disorder. Expectancy for improvement was also associated with outcome, suggesting the need for further research on this construct for understanding the nature of GAD and its amelioration.

Phenolics in ecological interactions: The importance of oxidation.

Abstract: The ecological activities of plant phenolics are diverse and highly variable. Although some variation is attributable to differences in concentration, structure, and evolutionary history of association with target organisms, much of it is unexplained, making it difficult to predict when and where phenolics will be active. I suggest that our understanding is limited by a failure to appreciate the importance of oxidative activation and the conditions that influence it. I summarize examples of oxidative activation of phenolics in ecological interactions, and argue that physicochemical conditions of the environment that control phenolic oxidation generate variation in ecological activity. Finally, I suggest that measurements of oxidative conditions can improve our predictions of phenolic activity and that experiments must be designed with conditions appropriate to the biochemical mode of phenolic action.

Negotiation of leisure constraints

Abstract: Virtually all past leisure constraints research has been based on a conception of constraints as insurmountable obstacles to leisure participation. Thus, it has typically been assumed that if an individual encounters a constraint, the outcome will be nonparticipation. This article elaborates an alternative view of constraints that has recently begun to appear in the literature, summarized in the central proposition that leisure participation is dependent not on the absence of constraints but on negotiation through them. Such negotiation may modify participation rather than foreclosing it. Evidence from the existing literature for the negotiation proposition is examined, and five additional propositions are defined concerning relative success in negotiating constraints, interactions between different types of constraints, and balance between constraints and motivations.

Theoretical foundation of the minimum-evolution method of phylogenetic inference.

Abstract: The minimum-evolution (ME) method of phylogenetic inference is based on the assumption that the tree with the smallest sum of branch length estimates is most likely to be the true one. In the past this assumption has been used without mathematical proof. Here we present the theoretical basis of this method by showing that the expectation of the sum of branch length estimates for the true tree is smallest among all possible trees, provided that the evolutionary distances used are statistically unbiased and that the branch lengths are estimated by the ordinary least-squares method. We also present simple mathematical formulas for computing branch length estimates and their standard errors for any unrooted bifurcating tree, with the least-squares approach. As a numerical example, we have analyzed mtDNA sequence data obtained by Vigilant et al. and have found the ME tree for 95 human and 1 chimpanzee (outgroup) sequences. The tree was somewhat different from the neighbor-joining tree constructed by Tamura and Nei, but there was no statistically significant difference between them.

Organizational Configurations and Performance: A Comparison of Theoretical Approaches

Abstract: Two major approaches to examining the relationship between organizational configurations and performance are found in the strategic management literature. The first, rooted in the concept of strate...

Conformational Coupling in DNA Polymerase Fidelity

Abstract: The fidelity of DNA polymerases is largely attributable to a two-step nucleotide binding mechanism. In the first step, binding contacts are initially made between the template and the incoming dNTP. The selectivity of this ground-state binding is similar in magnitude to the selectivity seen in forming base pairs in solution. In the second step, a change in protein conformation occurs, which leads to rapid incorporation of the dNTP into the growing polymer. This conformational change appears to occur globally in that it is inhibited by mismatches in the dNTP or in any of the three terminal base pairs of the primer/template. The open conformation allows rapid binding of the dNTP from solution, while the closed conformation provides steric checks for the proper Watson-Crick base pair geometry. This conformational change accounts for the extraordinary fidelity of polymerization and also provides selectivity to the exonuclease by inhibiting polymerization over a mismatch in the primer/template. The overall fidelity approaches one error in 10(10) by a combination of selectivity in polymerization (10(5)-10(6)) and in proofreading (10(3)-10(4)). This paradigm provides the theoretical basis for further investigation of the structural basis for fidelity by pointing to the essential elements of the polymerization reaction that need to be examined in order to evaluate active-site-directed mutants of polymerases to test appropriate structure/function relationships.

The ‘flickering switch’ of late Pleistocene climate change

Abstract: POLAR ice contains a unique record of past climate variations; previous Greenland ice cores have documented relatively warm ‘interstadial’ periods during the last glaciation and short (centuryscale) returns to colder conditions during the glacial to interglacial warming (see, for example, ref. 1). These climate features have also been observed to varying degrees in ocean sediment cores2–4 and terrestrial pollen and insect records5–7. Here we report electrical conductivity measurements from a new Greenland ice core, which confirm these previous observations, and also reveal a hitherto unrecognized mode of rapid climate variation. Fluctuations in ice conductivity on the scales of <5–20 years reflect rapid oscillations in the dust content of the atmosphere. This ‘flickering’ between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation.

Lesbian, gay, and bisexual youth in community settings: personal challenges and mental health problems.

Abstract: Studied 194 lesbian, gay, and bisexual youth aged 21 and younger who attended programs in 14 community centers to determine the personal challenges they face due to their sexual orientation and their responses to these stresses. First awareness of sexual orientation typically occurred at age 10, but disclosure to another person did not occur until about age 16. There was much variability in sexual behavior, and many youths reported both same-sex and opposite-sex sexual experiences. Although most had told at least one family member about their sexual orientation, there remained much concern about family reactions. Suicide attempts were acknowledged by 42% of the sample. Attempters significantly differed from nonattempters on several milestones of sexual orientation development, social aspects of sexual orientation, parents' knowledge of sexual orientation, and mental health problems.

The Structure of Intergenerational Exchanges in American Families

Abstract: Intergenerational support is analyzed using data from the National Survey of Families and Households. The authors find evidence that a systematic latent structure of intergenerational exchange characterizes the giving and receiving of support. Overall, one-half of Americans do not routinely engage in giving or receiving relationships with their parents and only about one in 10 are engaged in extensive exchange relationships. Parents are assisted more often in situations of poor health, and more often receive assistance when they have young children. Assistance in time of need is not uniform and is rarely extensive. Intergenerational assistance is constrained by family structure and the needs and resources of each generation. African-Americans are consistently less likely than whites to be involved in intergenerational assistance. In each generation, men receive as much altruistic support as women; higher levels of giving and receiving of aid among American women are due to their greater involvement in exc...

The Contact Hypothesis Revisited: Black-White Interaction and Positive Racial Attitudes

Abstract: The contact hypothesis the idea that contact between members of different races fosters positive racial attitudes has performed indifferently in research conducted over the past four decades, leading to a recommendation that the hypothesis be discarded and that attention turn to other sources of positive and negative racial attitudes. However, most of this research is now badly dated and focuses solely on the racial attitudes of whites. We present a new test of the contact hypothesis, drawing on a national survey of blacks and whites conducted in 1989. Analysis reveals that in several instances interracial contact is associated with more positive racial attitudes, especially among whites, and that some effects are appreciable. Although familiarity may breed contempt and absence make the heart grow fonder, students of race relations have long assumed that close contact between members of different races promotes positive racial attitudes and that the lack of such contact fosters prejudice and ill will (Allport 1954). Adherents of this contact hypothesis view racial segregation as a source of ignorance and ignorance as a breeding ground for derogatory stereotypes and racial hostility. If stronger social bonds could be forged between blacks and whites, they contend, racial attitudes would improve dramatically. Blacks are known to be more likely than whites to engage in various types of informal personal contact (Lee, Campbell & Miller 1991), but less is known about racial differences in the frequency and consequences of interracial contact. Although many researchers have observed lower levels of racial prejudice among whites who maintain closer contact with blacks (Aberbach & Walker 1973; Deutsch & Collins 1951; Meer & Freedman 1966; Robinson 1980; Wilner, Walkley & Cook 1955), the contact hypothesis has not always withstood rigorous testing (Ford 1973; Robinson & Preston 1976). In the classic "Robbers * Thanks are due to two anonymous reviewersfor their helpful suggestions. Direct correspondence to Lee Sigelman, Department of Political Science, The George Washington University, Washington, DC 20052. @ The University of North Carolina Press Social Forces, March 1993, 71(3):781-795 This content downloaded from 207.46.13.176 on Mon, 20 Jun 2016 06:28:59 UTC All use subject to http://about.jstor.org/terms 782 / Social Forces 71:3, March 1993 Cave" experiment by Sherif and his colleagues, prejudice lessened only when members of two hostile groups wereforced to cooperate with one another (Sherif et al. 1961). Subsequent experimental studies have generally concluded that only when intergroup contact occurs under highly auspicious circumstances should favorable attitude change be anticipated (see Desforges et al. 1991 and the studies cited therein). In a nonexperimental context, a major nationwide survey of whites conducted in the mid-1970s found that the racial views of whites whose circle of friends included a black person closely paralleled the views of whites with no black friends Uackman & Crane 1986). Only when blacks and whites of more or less equal status shared a wide variety of contacts did white hostility toward blacks abate an idea that hearkened back to Allport's (1954) original formulation but provided little basis for optimism, since blacks and whites often have only minimal contact and typically do not interact as social equals Jackman & Crane 1986). Based on their own findings and the results of prior research, Jackman and Crane conclude that the time has come to fashion a new explanation of interracial hostility. But it seems premature to either embrace or discard the contact hypothesis on the basis of the existing evidence. Though provocative, experimental tests of the contact hypothesis are of questionable external validity. In some cases such extreme intergroup antagonisms have been created for experimental purposes that probably not even the most fervent proponent of the contact hypothesis would expect closer intergroup contact under the same conditions to produce more positive intergroup relations. More generally, although researchers working in the experimental tradition have often couched their studies in terms of, or have extrapolated from their findings to, race relations, the experiments themselves have generally lacked a racial component. As for tests of the contact hypothesis conducted outside of the laboratory, many preceded the civil rights revolution of the late 1950s and early 1960s, and most others were undertaken during the turbulent late 1960s and early 1970s. Whites' racial attitudes have undergone considerable change since then (Schuman, Steeh & Bobo 1985), and in the dynamic context of race relations in the United States it is legitimate to ask whether conclusions based on research conducted a decade or more ago are still applicable. Because the contact hypothesis focuses generically on intergroup attitudes rather than specifically on the attitudes of one group (whites) toward another (blacks), it is also important to know whether interracial contact affects the racial attitudes of blacks toward whites. This question has received little attention, and again, a high proportion of the pertinent studies are now extremely dated. In early studies of the attitudinal impact of integrated public housing, a reduction in black prejudice following close contact with whites was sometimes observed (Works 1961), but there were also reports of an increase in black prejudice (Ford 1973; Robinson & Preston 1976). No clear patterns emerged in research conducted in other settings (Brown & Albee 1966; Tsukashima & Montero 1976). Schuman and Hatchett (1974), examining data from the 1968 Detroit Area Survey, found that blacks who socialized with white neighbors or coworkers harbored fewer feelings of alienation and distrust toward white society than blacks who lacked these experiences; however, simply having casual contact with whites as neighbors or coworkers had no This content downloaded from 207.46.13.176 on Mon, 20 Jun 2016 06:28:59 UTC All use subject to http://about.jstor.org/terms Positive Racial Attitudes / 783 appreciable effect on blacks' racial attitudes. More recently, Sigelman and Welch (1991), drawing on national surveys conducted in 1981 and 1986, included interracial friendship as one predictor in a multivariate model of blacks' and whites' perceptions of white prejudice against blacks, but they observed no appreciable effects. What psychological mechanisms might mediate the linkage between interracial contact and positive racial attitudes? One is availability (Kahneman, Slovic & Tversky 1982). For whites, having a black friend or living in an area where one comes into frequent contact with blacks serves as a source of information about blacks their outlooks, the problems they face, and so on. Such firsthand information almost inevitably influences one's perceptions of and feelings about blacks in general. Thus, for example, when whites are asked how many blacks harbor antiwhite feelings, they may think first of their own black friends, if they have any, and the very fact of their friendship should shape their response. Or they may think of blacks in the area where they live, and here again their impressions are likely to be fairly positive, because black-white relations are usually perceived as less problematic in one's local area than nationwide (Sigelman & Welch 1991). Lacking such firsthand information, whites must base their responses on whatever other information they may have at their disposal. Given the tendency of media coverage to focus on cases of intense, dramatic conflict, the secondhand information whites have about blacks is apt to accentuate the negative. This availability-based interpretation suggests, in short, that whites' perceptions and expressions of racial hostility should be materially affected by personal contact with blacks, because such contact is a key source of positive information about blacks; in the absence of this source, whites must fall back on other information sources, including long-standing racial stereotypes and media reports, which are more likely to be negative. For blacks, too, interracial contact presumably affects the availability of information about whites, though perhaps in a somewhat more muted fashion than for whites. Living in a white-dominated society, blacks have an easier time amassing a variety of firstand secondhand information about whites than the average white does about blacks. Thus, simply being in neighborhoods or school cachement areas with whites may have little bearing on perceptions of racial attitudes generally. However, interracial friendship may deter racial stereotyping by providing blacks with counterexamples to the stereotype of whites as prejudiced and hostile. Our purpose in this study is to subject the contact hypothesis to further testing. Drawing on a biracial national survey conducted in 1989, we examine two aspects of the hypothesis. Do blacks and whites who come into closer contact with members of the other race perceive less hostility between the races than do those who are more isolated from the other race? Second, do blacks and whites who come into closer contact with members of the other race express a deeper commitment to the maintenance of interracial social ties than do others? While the contact hypothesis suggests affirmative answers to both questions, prior studies have left these issues very much in doubt. This content downloaded from 207.46.13.176 on Mon, 20 Jun 2016 06:28:59 UTC All use subject to http://about.jstor.org/terms 784 / Social Forces 71:3, March 1993

Emerging Varieties of Action Research: Introduction to the Special Issue

Abstract: Action research is defined and its scientific basis is noted but not argued. Although its original, classical form established almost a half century ago still exists, there has recently emerged a variety of new models for doing action research today. The basic classical model is described in terms of five elements. These are, in turn, used to introduce the present collection of reports on new, emergent varieties of contemporary action research that complement and extend the classic model. The reports come from projects in hundreds of organizations, in communities and regions, and in numerous countries. The ideas behind the basic model of action research may remain viable today only because they are being practiced in new ways, in innovative research designs, and applied to new problems. The collection of cases presented in this special issue illustrates the rich variety of new thinking available in contemporary action research.

Calcium Supplementation and Bone Mineral Density in Adolescent Girls

Abstract: Objective. —To evaluate the effect of calcium supplementation on bone acquisition in adolescent white girls. Design. —A randomized, double-blind, placebo-controlled trial of the effect of 18 months of calcium supplementation on bone density and bone mass. Subjects. —Ninety-four girls with a mean age of 11.9+0.5 years at study entry. Setting. —University hospital in a small town. Interventions. —Calcium supplementation, 500 mg/d calcium as calcium citrate malate; controls received placebo pills. Main Outcome Measures. —Bone mineral density and bone mineral content of the lumbar spine and total body were measured by dual-energy x-ray absorptiometry and calcium excretion from 24-hour urine specimens. Results. —Calcium intake from dietary sources averaged 960 mg/d for the entire study group. The supplemented group received, on average, an additional 354 mg/d of calcium. The supplemented group compared with the placebo group had greater increases of lumbar spine bone density (18.7% vs 15.8%; P =.03), lumbar spine bone mineral content (39.4% vs 34.7%; P =.06), total body bone mineral density (9.6% vs 8.3%; P =.05), and 24-hour urinary calcium excretion (90.4 vs 72.9 mg/d; P =.02), respectively. Conclusions. —Increasing daily calcium intake from 80% of the recommended daily allowance to 110% via supplementation with calcium citrate malate resulted in significant increases in total body and spinal bone density in adolescent girls. The increase of 24 g of bone gain per year among the supplemented group translates to an additional 1.3% skeletal mass per year during adolescent growth, which may provide protection against future osteoporotic fracture. ( JAMA . 1993;270:841-844)