Showing papers by "University of Rochester published in 1997"

A hierarchical model of approach and avoidance achievement motivation

Abstract: A hierarchical model of approach and avoidance achievement motivation was proposed and tested in a college classroom. Mastery, performance-approach, and performance-avoidance goals were assessed and their antecedents and consequences examined. Results indicated that mastery goals were grounded in achievement motivation and high competence expectancies; performance-avoidance goals, in fear of failure and low competence expectancies; and performance-approach goals, in ach.ievement motivation, fear of failure, and high competence expectancies. Mastery goals facilitated intrinsic motivation, performance-approach goals enhanced graded performance, and performanceavoidance goals proved inimical to both intrinsic motivation and graded performance. The proposed model represents an integration of classic and contemporary approaches to the study of achievement motivation. Achievement motivation is a ubiquitous feature of daily life. In the classroom, at the workplace, and on the ballfield individuals strive to be competent in their effortful activities. In the past decade, many theorists have utilized a social-cognitive, achievement goal approach in accounting for individuals' competence-relevant strivings. "Achievement goal" is commonly defined as the purpose of task engagement (Maehr, 1989), and the specific type of goal adopted is posited to create a framework for how individuals interpret, experience, and act in their achievement pursuits (Dweck, 1986; Nicholls, 1989). Achievement goal theorists commonly identify two distinct orientations toward competence: a performance goal focused on the demonstration of competence relevant to others, and a mastery goal focused on the development of competence and task mastery (Ames & Archer, 1987; for similar conceptualizations with different nomenclature see Dweck, 1986; NichoUs, 1984). The adoption of a performance goal is hypothesized to produce susceptibility to a "helpless" pattern of responses in achievement settings (e.g., a preference for easy or difficult tasks, withdrawal of effort in the face of failure, and decreased task enjoyment), whereas the adoption of a mastery goal is presumed to lead to a "mastery" motivational pattern (e.g., a preference for moderately challenging tasks, persistence in the face of failure, and enhanced task enjoyment; Ames, 1992; Dweck & Leggett, 1988; Nicholls, 1989). Most achievement goal theorists conceptualize both perfor

Fiber grating spectra

Abstract: In this paper, we describe the spectral characteristics that can be achieved in fiber reflection (Bragg) and transmission gratings. Both principles for understanding and tools for designing fiber gratings are emphasized. Examples are given to illustrate the wide variety of optical properties that are possible in fiber gratings. The types of gratings considered include uniform, apodized, chirped, discrete phase-shifted, and superstructure gratings; short-period and long-period gratings; symmetric and tilted gratings; and cladding-mode and radiation-mode coupling gratings.

A Controlled Trial of Two Nucleoside Analogues plus Indinavir in Persons with Human Immunodeficiency Virus Infection and CD4 Cell Counts of 200 per Cubic Millimeter or Less

Abstract: Background The efficacy and safety of adding a protease inhibitor to two nucleoside analogues to treat human immunodeficiency virus type 1 (HIV-1) infection are not clear. We compared treatment with the protease inhibitor indinavir in addition to zidovudine and lamivudine with treatment with the two nucleosides alone in HIV-infected adults previously treated with zidovudine. Methods A total of 1156 patients not previously treated with lamivudine or protease inhibitors were stratified according to CD4 cell count (50 or fewer vs. 51 to 200 cells per cubic millimeter) and randomly assigned to one of two daily regimens: 600 mg of zidovudine and 300 mg of lamivudine, or that regimen with 2400 mg of indinavir. Stavudine could be substituted for zidovudine. The primary end point was the time to the development of the acquired immunodeficiency syndrome (AIDS) or death. Results The proportion of patients whose disease progressed to AIDS or death was lower with indinavir, zidovudine (or stavudine), and lamivudine (...

THE HEME OXYGENASE SYSTEM:A Regulator of Second Messenger Gases

Abstract: The heme oxygenase (HO) system consists of two forms identified to date: the oxidative stress-inducible protein HO-1 (HSP32) and the constitutive isozyme HO-2. These proteins, which are different gene products, have little in common in primary structure, regulation, or tissue distribution. Both, however, catalyze oxidation of heme to biologically active molecules: iron, a gene regulator; biliverdin, an antioxidant; and carbon monoxide, a heme ligand. Finding the impressive heme-degrading activity of brain led to the suggestion that "HO in brain has functions aside from heme degradation" and to subsequent exploration of carbon monoxide as a promising and potentially significant messenger molecule. There is much parallelism between the biological actions and functions of the CO- and NO-generating systems; and their regulation is intimately linked. This review highlights the current information on molecular and biochemical properties of HO-1 and HO-2 and addresses the possible mechanisms for mutual regulatory interactions between the CO- and NO-generating systems.

On Energy, Personality, and Health: Subjective Vitality as a Dynamic Reflection of Well‐Being

Abstract: Iti this article, we examine subjective vitality, a positive feeling of aliveness and energy, in six studies. Subjective vitality is hypothesized to reflect organismic well-being and thus should covary with both psychological and somatic factors that impact the energy available to the self. Associations are shown between subjective vitality and several indexes of psychological well-being; somatic factors such as physical symptoms and perceived body functioning; and basic personality traits and affective dispositions. Subse- quently, vitality is shown to be lower in people with chronic pain compared to matched controls, especially those who perceive their pain to be disabling or frightening. Subjective vitality is further associated with self-motivation and maintained weight loss among patients treated for obesity. Finally, sub- jective vitality is assessed in a diary study for its covariation with physical symptoms. Discussion focuses on the phenomenological salience of personal energy and its relations to physical and psychological well-being.

Mitosis-specific phosphorylation of histone H3 initiates primarily within pericentromeric heterochromatin during G2 and spreads in an ordered fashion coincident with mitotic chromosome condensation.

Abstract: We have generated and characterized a novel site-specific antibody highly specific for the phosphorylated form of the amino-terminus of histone H3 (Ser10). In this study, we used this antibody to examine in detail the relationship between H3 phosphorylation and mitotic chromosome condensation in mammalian cells. Our results extend previous biochemical studies by demonstrating that mitotic phosphorylation of H3 initiates nonrandomly in pericentromeric heterochromatin in late G2 interphase cells. Following initiation, H3 phosphorylation appears to spread throughout the condensing chromatin and is complete in most cell lines just prior to the formation of prophase chromosomes, in which a phosphorylated, but nonmitotic, chromosomal organization is observed. In general, there is a precise spatial and temporal correlation between H3 phosphorylation and initial stages of chromatin condensation. Dephosphorylation of H3 begins in anaphase and is complete immediately prior to detectable chromosome decondensation in telophase cells. We propose that the singular phosphorylation of the amino-terminus of histone H3 may be involved in facilitating two key functions during mitosis: (1) regulate protein-protein interactions to promote binding of trans-acting factors that "drive" chromatin condensation as cells enter M-phase and (2) coordinate chromatin decondensation associated with M-phase.

Steroid receptor interactions with heat shock protein and immunophilin chaperones.

Abstract: We have provided a historical perspective on a body of steroid receptor research dealing with the structure and physiological significance of the untransformed 9S receptor that has often confused both novice and expert investigators. The frequent controversies and equivocations of earlier studies were due to the fact that the native, hormone-free state of these receptors is a large multiprotein complex that resisted description for many years because of its unstable and dynamic nature. The untransformed 9S state of the steroid and dioxin receptors has provided a unique system for studying the function of the ubiquitous, abundant, and conserved heat shock protein, hsp90. The hormonal control of receptor association with hsp90 provided a method of manipulating the receptor heterocomplex in a manner that was physiologically meaningful. For several steroid receptors, binding to hsp90 was required for the receptor to be in a native hormone-binding state, and for all of the receptors, hormone binding promoted dissociation of the receptor from hsp90 and conversion of the receptor to the DNA-binding state. Although the complexes between tyrosine kinases and hsp90 were discovered earlier, the hormonal regulation or steroid receptor association with hsp90 permitted much more rapid and facile study of hsp90 function. The observations that hsp90 binds to the receptors through their HBDs and that these domains can be fused to structurally different proteins bringing their function under hormonal control provided a powerful linkage between the hormonal regulation of receptor binding to hsp90 and the initial step in steroid hormone action. Because the 9S receptor hsp90 heterocomplexes could be physically stabilized by molybdate, their protein composition could be readily studied, and it became clear that these complexes are multiprotein structures containing a number of unique proteins, such as FKBP51, FKBP52, CyP-40, and p23, that were discovered because of their presence in these structures. Further analysis showed that hsp90 itself exists in a variety of native multiprotein heterocomplexes independent of steroid receptors and other 'substrate' proteins. Cell-free systems can now be used to study the formation of receptor heterocomplexes. As we outlined in the scheme of Fig. 1, the multicomponent receptor-hsp90 heterocomplex assembly system is being reconstituted, and the importance of individual proteins, such as hsp70, p60, and p23, in the assembly process is becoming recognized. It should be noted that our understanding of the mechanism and purpose of steroid receptor heterocomplex assembly is still at an early stage. We can now speculate on the roles of receptor-associated proteins in receptor action, both as individuals and as a group, but their actual functions are still vague or unknown. We can make realistic models about the chaperoning and trafficking of steroid receptors, but we don't yet know how these processes occur, we don't know where chaperoning occurs in the cell (e.g. Is it limited to the cytoplasm? Is it a diffuse process or does chaperoning occur in association with structural elements?), and, with the exception of the requirement for hormone binding, we don't know the extent to which the hsp90-based chaperone system impacts on steroid hormone action. It is not yet clear how far the discovery of this hsp90 heterocomplex assembly system will be extended to the development of a general understanding of protein processing in the cell. Because this assembly system is apparently present in all eukaryotic cells, it probably performs an essential function for many proteins. The bacterial homolog of hsp90 is not an essential protein, but hsp90 is essential in eukaryotes, and recent studies indicate that the development of the cell nucleus from prokaryotic progenitors was accompanied by the duplication of genes for hsp90 and hsp70 (698). (ABSTRACT TRUNCATED)

Assessing the Effects of School Resources on Student Performance: An Update

Abstract: The relationship between school resources and student achievement has been controversial, in large part because it calls into question a variety of traditional policy approaches. This article reviews the available educational production literature, updating previous summaries. The close to 400 studies of student achievement demonstrate that there is not a strong or consistent relationship between student performance and school resources, at least after variations in family inputs are taken into account. These results are also reconciled with meta-analytic approaches and with other investigations on how school resources affect labor market outcomes. Simple resource policies hold little hope for improving student outcomes.

Capital-skill complementarity and inequality: a macroeconomic analysis

Abstract: The notion of skilled-biased technological change is often held responsible for the recent behavior of the U.S. skill premium, or the ratio between the wages of skilled and unskilled labor. This paper develops a framework for understanding this notion in terms of observable variables and uses the framework to evaluate the fraction of the skill premium's variation that is caused by changes in observables. A version of the neoclassical growth model is used in which the key feature of aggregate technology is capital-skill complementarity: the elasticity of substitution is higher between capital equipment and unskilled labor than between capital equipment and skilled labor. With this feature, changes in observables can account for nearly all the variation in the skill premium over the last 30 years. This finding suggests that increased wage inequality results from economic growth driven by new, efficient technologies embodied in capital equipment.

Supernormal vision and high-resolution retinal imaging through adaptive optics

Abstract: Even when corrected with the best spectacles or contact lenses, normal human eyes still suffer from monochromatic aberrations that blur vision when the pupil is large. We have successfully corrected these aberrations using adaptive optics, providing normal eyes with supernormal optical quality. Contrast sensitivity to fine spatial patterns was increased when observers viewed stimuli through adaptive optics. The eye's aberrations also limit the resolution of images of the retina, a limit that has existed since the invention of the ophthalmoscope. We have constructed a fundus camera equipped with adaptive optics that provides unprecedented resolution, allowing the imaging of microscopic structures the size of single cells in the living human retina.

Long-term effects of home visitation on maternal life course and child abuse and neglect : Fifteen-year follow-up of a randomized trial

Abstract: Context. —Home-visitation services have been promoted as a means of improving maternal and child health and functioning. However, long-term effects have not been examined. objective. —To examine the long-term effects of a program of prenatal and early childhood home visitation by nurses on women's life course and child abuse and neglect. Design. —Randomized trial. Setting. —Semirural community in New York. Participants. —Of 400 consecutive pregnant women with no previous live births enrolled, 324 participated in a follow-up study when their children were 15 years old. Intervention. —Families received a mean of 9 home visits during pregnancy and 23 home visits from the child's birth through the second birthday. Data Sources and Measures. —Women's use of welfare and number of subsequent children were based on self-report; their arrests and convictions were based on self-report and archived data from New York State. Verified reports of child abuse and neglect were abstracted from state records. Main Results. —During the 15-year period after the birth of their first child, in contrast to women in the comparison group, women who were visited by nurses during pregnancy and infancy were identified as perpetrators of child abuse and neglect in 0.29 vs 0.54 verified reports ( P P =.02), 65 vs 37 months between the birth of the first and a second child ( P =.001), 60 vs 90 months' receiving Aid to Families With Dependent Children ( P =.005), 0.41 vs 0.73 behavioral impairments due to use of alcohol and other drugs ( P =.03), 0.18 vs 0.58 arrests by self-report ( P P Conclusions. —This program of prenatal and early childhood home visitation by nurses can reduce the number of subsequent pregnancies, the use of welfare, child abuse and neglect, and criminal behavior on the part of low-income, unmarried mothers for up to 15 years after the birth of the first child.

New algorithms for fast discovery of association rules

Abstract: Discovery of association rules is an important problem in database mining. In this paper we present new algorithms for fast association mining, which scan the database only once, addressing the open question whether all the rules can be efficiently extracted in a single database pass. The algorithms use novel itemset clustering techniques to approximate the set of potentially maximal frequent itemsets. The algorithms then make use of efficient lattice traversal techniques to generate the frequent itemsets contained in each cluster. We propose two clustering schemes based on equivalence classes and maximal hypergraph cliques, and study two traversal techniques based on bottom-up and hybrid search. We also use a vertical database layout to cluster related transactions together. Experimental results show improvements of over an order of magnitude compared to previous algorithms.

Steroid receptor coactivator-1 is a histone acetyltransferase

Abstract: Steroid receptors and coactivator proteins are thought to stimulate gene expression by facilitating the assembly of basal transcription factors into a stable preinitiation complex What is not clear, however, is how these transcription factors gain access to transcriptionally repressed chromatin to modulate the transactivation of specific gene networks in vivo The available evidence indicates that acetylation of chromatin in vivo is coupled to transcription and that specific histone acetyltransferases (HATs) target histones bound to DNA and overcome the inhibitory effect of chromatin on gene expression The steroid-receptor coactivator SRC-1 is a coactivator for many members of the steroid-hormone receptor superfamily of ligand-inducible transcription factors Here we show that SRC-1 possesses intrinsic histone acetyltransferase activity and that it also interacts with another HAT, p300/CBP-associated factor (PCAF) The HAT activity of SRC-1 maps to its carboxy-terminal region and is primarily specific for histones H3 and H4 Acetylation by SRC-1 and PCAF of histones bound at specific promoters may result from ligand binding to steroid receptors and could be a mechanism by which the activation functions of steroid receptors and associated coactivators enhance formation of a stable preinitiation complex, thereby increasing transcription of specific genes from transcriptionally repressed chromatin templates

Emotion regulation among school-age children: The development and validation of a new criterion Q-sort scale.

Abstract: To foster the study of emotion regulation beyond infancy and toddlerhood, a new criterion Q-sort was constructed. In Study 1, Q-scales for emotion regulation and autonomy were developed, and analyses supported their discriminant validity. Study 2 further explored the construct validity of the Emotion Regulation Q-Scale within a sample of 143 maltreated and 80 impoverished children, aged 6 to 12 years. A multitrait-multimethod matrix and confirmatory factor analyses indicated impressive convergence among the Emotion Regulation Q-Scale and established measures of affect regulation. This new scale also was discriminable from measures of related constructs, including Q-sort assessments of ego resiliency. The use of this new measure was further supported by its ability to distinguish between maltreated and comparison children and between groups of well-regulated versus dysregulated children.

Risk, Financial Markets, and Human Capital in a Developing Country

Abstract: This paper explores the link between financial market incompleteness and human capital accumulation. We examine how child school attendance responds to seasonal fluctuations in the income of agrarian households using panel data from rural India. To pinpoint market imperfections, we study responses to aggregate and idiosyncratic, as well as to anticipated and unanticipated, income shocks. Our main finding is that seasonal fluctuations in school attendance are a form of self-insurance, but one which does not result in a substantial loss of human capital on average.

All-trans-Retinoic Acid in Acute Promyelocytic Leukemia

Abstract: Background All-trans-retinoic acid induces complete remission in acute promyelocytic leukemia. However, it is not clear whether induction therapy with all-trans-retinoic acid is superior to chemotherapy alone or whether maintenance treatment with all-trans-retinoic acid improves outcome. Methods Three hundred forty-six patients with previously untreated acute promyelocytic leukemia were randomly assigned to receive all-trans-retinoic acid or daunorubicin plus cytarabine as induction treatment. Patients who had a complete remission received consolidation therapy consisting of one cycle of treatment identical to the induction chemotherapy, then high-dose cytarabine plus daunorubicin. Patients still in complete remission after two cycles of consolidation therapy were then randomly assigned to maintenance treatment with all-trans-retinoic acid or to observation. Results Of the 174 patients treated with chemotherapy, 120 (69 percent) had a complete remission, as did 124 of the 172 (72 percent) given all-trans-...

Roles of Pseudomonas aeruginosa las and rhl quorum-sensing systems in control of elastase and rhamnolipid biosynthesis genes.

Abstract: Two quorum-sensing systems (las and rhl) regulate virulence gene expression in Pseudomonas aeruginosa. The las system consists of a transcriptional activator, LasR, and LasI, which directs the synthesis of the autoinducer N-(3-oxododecanoyl) homoserine lactone (PAI-1). Induction of lasB (encoding elastase) and other virulence genes requires LasR and PAI-1. The rhl system consists of a putative transcriptional activator, RhlR, and RhlI, which directs the synthesis of N-butyryl homoserine lactone (PAI-2). Rhamnolipid production in P. aeruginosa has been reported to require both the rhl system and rhlAB (encoding a rhamnosyltransferase). Here we report the generation of a delta lasI mutant and both delta lasI delta rhlI and delta lasR rhlR::Tn501 double mutants of strain PAO1. Rhamnolipid production and elastolysis were reduced in the delta lasI single mutant and abolished in the double-mutant strains. rhlAB mRNA was not detected in these strains at mid-logarithmic phase but was abundant in the parental strain. Further RNA analysis of the wild-type strain revealed that rhlAB is organized as an operon. The rhlAB transcriptional start was mapped, and putative sigma 54 and sigma 70 promoters were identified upstream. To define components required for rhlAB expression, we developed a bioassay in Escherichia coli and demonstrated that PAI-2 and RhlR are required and sufficient for expression of rhlA. To characterize the putative interaction between PAI-2 and RhlR, we demonstrated that [3H]PAI-2 binds to E. coli cells expressing RhlR and not to those expressing LasR. Finally, the specificity of the las and rhl systems was examined in E. coli bioassays. The las system was capable of mildly activating rhlA, and similarly, the rhl system partly activated lasB. However; these effects were much less than the activation of rhlA by the rhl system and lasB by the las system. The results presented here further characterize the roles of the rhl and las quorum-sensing systems in virulence gene expression.

Amelioration of Bacterial Genomes: Rates of Change and Exchange

Abstract: Although bacterial species display wide variation in their overall GC contents, the genes within a particular species' genome are relatively similar in base composition. As a result, sequences that are novel to a bacterial genome—i.e., DNA introduced through recent horizontal transfer—often bear unusual sequence characteristics and can be distinguished from ancestral DNA. At the time of introgression, horizontally transferred genes reflect the base composition of the donor genome; but, over time, these sequences will ameliorate to reflect the DNA composition of the new genome because the introgressed genes are subject to the same mutational processes affecting all genes in the recipient genome. This process of amelioration is evident in a large group of genes involved in host-cell invasion by enteric bacteria and can be modeled to predict the amount of time required after transfer for foreign DNA to resemble native DNA. Furthermore, models of amelioration can be used to estimate the time of introgression of foreign genes in a chromosome. Applying this approach to a 1.43-megabase continuous sequence, we have calculated that the entire Escherichia coli chromosome contains more than 600 kb of horizontally transferred, protein-coding DNA. Estimates of amelioration times indicate that this DNA has accumulated at a rate of 31 kb per million years, which is on the order of the amount of variant DNA introduced by point mutations. This rate predicts that the E. coli and Salmonella enterica lineages have each gained and lost more than 3 megabases of novel DNA since their divergence.

Isolation and Characterization of a cDNA from the Rat Brain that Encodes Hemoprotein Heme Oxygenase-3

Abstract: Two isozymes of heme oxygenase (HO), HO-1 or HSP32 and the constitutive form HO-2, have been characterized to date. We report the discovery of a third protein species and refer to it as HO-3. HO-3 is the product of a single transcript of approximately 2.4 kb and can encode a protein of approximately 33 kDa. The HO-3 transcript is found in the spleen, liver, thymus, prostate, heart, kidney, brain and testis and is the product of a single-copy gene. The predicted amino acid structure of HO-3 differs from both HO-1 (HSP32) and HO-2 but is closely related to HO-2 (approximately 90%). Escherichia coli expressed and purified HO-3 protein does not cross react with polyclonal antibodies to either rat HO-1 or HO-2, is a poor heme catalyst, and displays hemoprotein spectral characteristics. The predicted protein has two heme regulatory motifs that may be involved in heme binding. These motifs and the hemoprotein nature of HO-3 suggest a potential regulatory role for the protein in cellular processes which are heme-dependent.

Regulation of las and rhl quorum sensing in Pseudomonas aeruginosa.

Abstract: The production of several virulence factors by Pseudomonas aeruginosa is controlled according to cell density through two quorum-sensing systems, las and rhl. The las system is comprised of the transcriptional activator protein LasR and of LasI, which directs the synthesis of the autoinducer PAI-1. Similarly, the rhl system consists of the transcriptional activator protein RhlR and of RhlI, which directs synthesis of the autoinducer PAI-2 (formerly referred to as factor 2). To study the interrelation between the two P. aeruginosa quorum-sensing systems, we fused a lacZ reporter gene to lasR, rhlR, and rhlA and monitored expression of these three genes under various conditions. Our data indicate that lasR and rhlR are expressed in a growth-dependent manner, with activation of each gene occurring during the last half of log-phase growth. We also show that the las quorum-sensing system controls the rhl quorum-sensing system in two ways. First, we found that LasR and PAI-1 activated rhlR transcription. Second, we showed that PAI-1 blocked PAI-2 from binding to RhlR, thereby inhibiting the expression of rhlA. Our data thus indicate that the las system exerts two levels of control on RhlR, transcriptional and posttranslational.

Patterns of speciation in drosophila revisited

Abstract: In a paper published seven years ago in this journal (Coyne and Orr 1989a), we analyzed the time course of speciation in Drosophila by correlating electrophoretic genetic distance between pairs of species (a number roughly proportional to their divergence time) with the strength of reproductive isolation between them. That analysis yielded five conclusions. First, both prezygotic and postzygotic reproductive isolation increase with divergence time between taxa. Second, prezygotic (sexual) isolation evolves more rapidly than postzygotic isolation (sterility and inviability of hybrids). This difference is, however, due entirely to much stronger prezygotic isolation between sympatric than between allopatric pairs of species. We suggested that this difference was due to "reinforcement," or direct selection for sexual isolation that occurs among sympatric taxa that produce unfit hybrids (Dobzhansky 1937). Third, hybrid sterility and inviability evolve at similar rates. This conclusion now appears to be incorrect because average divergence time between taxa is not a sensitive way to measure evolutionary rates of reproductive isolation, and more sensitive analyses show that hybrid sterility may in fact evolve more rapidly than inviability (Wu 1992). Fourth, the usual pathway for the production of postzygotic isolation is the initial appearance of sterility or inviability in hybrid males, followed by its appearance in females. This explains the frequent observation of Haldane's rule: the pattern that if only one gender of hybrids is sterile or inviable in species crosses, it is nearly always the heterogametic (XY or XO) sex (Haldane 1922; Coyne and Orr 1989b). Finally, there is a large increase in genetic distance between those species pairs producing sterile or inviable males only and those producing sterile or inviable hybrids of both sexes. This implies that there is a long time lag between the evolution of postzygotic isolation in males and in females. While a similar (but much smaller) analysis has since been conducted in salamanders (Tilley et al. 1990), the data from Drosophila are unique-and are likely to remain so-because of the large number of crossable species and the ease of estimating sexual and postzygotic isolation in the laboratory. These Drosophila data have hence attracted some interest. Because of this, we have continued to accumulate new data as they have appeared. We have also found a few errors in our original data set, and have revised some estimates of reproductive isolation and phylogenetic relatedness when better data became available. We now have data for 171 interspecific hybridizations in Drosophila, an increase of 43% over the 119 hybridizations described in our previous paper. Because DNA sequencing has largely supplanted gel electrophoresis as a way of measuring divergence between species, it is unlikely that this data set will grow much larger; and it will be many years before we possess DNA-based estimates of divergence between many pairs of Drosophila species. We therefore thought it timely to check our earlier conclusions using the new and larger data set.

Consumer information search revisited: Theory and empirical analysis

Abstract: A comprehensive theoretical framework for understanding consumers' information search behavior is presented. Unlike previous research, our model identifies not only what factors affect consumers' search behavior but also how these factors interact with each other. In particular, the model emphasizes the effect of prior brand perceptions on the search process. We argue that when consumers have brand-specific prior distributions of utility, the existence of relative uncertainty among brands is necessary for search to be useful. Thus, we explain why product class involvement or low search costs may not be sufficient to induce large amounts of search activity and why there may be an inverted-U-shaped relationship between search activity and experience. We test our theory on consumers' search behavior for new automobiles, using data collected contemporaneously with consumers' actual decision process. Our data support our theory.

Aberrations and retinal image quality of the normal human eye.

Abstract: We have constructed a wave-front sensor to measure the irregular as well as the classical aberrations of the eye, providing a more complete description of the eye's aberrations than has previously been possible. We show that the wave-front sensor provides repeatable and accurate measurements of the eye's wave aberration. The modulation transfer function of the eye computed from the wave-front sensor is in fair, though not complete, agreement with that obtained under similar conditions on the same observers by use of the double-pass and the interferometric techniques. Irregular aberrations, i.e., those beyond defocus, astigmatism, coma, and spherical aberration, do not have a large effect on retinal image quality in normal eyes when the pupil is small (3 mm). However, they play a substantial role when the pupil is large (7.3-mm), reducing visual performance and the resolution of images of the living retina. Although the pattern of aberrations varies from subject to subject, aberrations, including irregular ones, are correlated in left and right eyes of the same subject, indicating that they are not random defects.

Noninvasive Doppler-derived myocardial performance index: Correlation with simultaneous measurements of cardiac catheterization measurements

Abstract: A simple, reproducible, noninvasive Doppler index for the assessment of overall cardiac function has been described previously. The purpose of this study was to correlate the Doppler index with accepted indexes of cardiac catheterization of left ventricular performance. Thirty-four patients with ischemic heart disease or idiopathic dilated cardiomyopathy prospectively underwent a simultaneous cardiac catheterization and Doppler echocardiographic study. Invasive measurements of peak +dP/dt, peak -dP/dt, and tau were obtained from the high-fidelity left ventricular pressures. A Doppler index of myocardial performance was defined as the summation of isovolumetric contraction and relaxation time divided by ejection time. There was a correlation between Doppler measurement of isovolumetric contraction time and peak +dP/dt (r = 0.842; p < 0.0001) and Doppler measurement of isovolumetric relaxation time and peak -dP/dt (r = 0.638; p < 0.001). Left ventricular ejection time correlated with both peak +dP/dt (r = 0.539; p < 0.001) and peak -dP/dt (r = 0.582; p < 0.001). The Doppler index correlated with simultaneously recorded systolic peak +dP/dt (r = 0.821; p < 0.0001) and diastolic peak -dP/dt (r = 0.833; p < 0.001) and tau (r = 0.680; p < 0.0001). This study documents that a simple, easily recordable, noninvasive Doppler index of myocardial performance correlates with invasive measurement of left ventricular systolic and diastolic function and appears to be a promising noninvasive measurement of overall cardiac function.

The Toxicology of Mercury

Abstract: The major physical forms of mercury to which humans are exposed are mercury vapor, Hg0, and methylmercury compounds, CH3HgX. Mercury vapor emitted from both natural and anthropogenic sources is globally distributed in the atmosphere. It is returned as a water-soluble form in precipitation and finds its way into bodies of fresh and ocean water. Land run-off also accounts for further input into lakes and oceans. Inorganic mercury, present in water sediments, is subject to bacterial conversion to methylmercury compounds that are bioaccumulated in the aquatic food chain to reach the highest concentration in predatory fish. Human exposure to mercury vapor is from dental amalgam and industries using mercury. Methylmercury compounds are found exclusively in seafood and freshwater fish. The health effects of mercury vapor have been known since ancient times. Severe exposure results in a triad of symptoms, erethism, tremor, and gingivitis. Today, we are concerned with more subtle effects such as preclinica...