Magnetic levitation: Floating gold in cryogenic oxygen.
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Journal Article↗
Biomedical subjects
L Eaves
Publications and source records attributed to L Eaves.
Effects of stochastic webs on chaotic electron transport in semiconductor superlattices.
We investigate chaotic electron transport in the lowest miniband of a semiconductor superlattice with a tilted magnetic field. This experimentally accessible non-Kolmogorov-Arnol'd-Moser system involves only stationary electric and magnetic fields, but is dynamically equivalent to a time-dependent kicked harmonic oscillator. The onset of chaos strongly delocalizes the electron orbits, thus raising the electrical conductivity. When the cyclotron and Bloch frequencies are commensurate, the phase space is threaded by a stochastic web, which produces a further resonant increase in the conductivity.
Journal Article↗
Genetic and environmental influences on the temporal association between earlier anxiety and later depression in girls.
BACKGROUND: The purpose of the present study was to investigate the role of genetic and environmental factors in the association between depressive symptoms and symptoms of overanxious disorder, simple phobias, and separation anxiety in 8-13-year-old and 14-17-year-old girls. METHODS: Multivariate genetic models were fitted to child-reported longitudinal symptom data gathered from clinical interview on 415 MZ [corrected] and 194 DZ [corrected] female twin pairs from the Virginia Twin Study of Adolescent Behavioral Development (VTSABD) [corrected]. RESULTS: Model-fitting results suggest there are distinct etiological [corrected] patterns underlying the association between depression and the different anxiety syndromes during the course of development: 1) specific genetic influences on depression after age 14 reflect liability to symptoms of earlier overanxious disorder (OAD) and simple phobias; 2) aspects of the shared environment that influence symptoms of depression before age 14 contribute to symptoms of separation anxiety and simple phobias later in adolescence [corrected]; 3) the shared environmental influence on [corrected] depression in 14+ girls also affects liability to symptoms of concurrent OAD and persistent separation anxiety. CONCLUSIONS: These results suggest that depression before and after age 14 may be etiologically distinct syndromes. Earlier symptoms of OAD and (to a lesser extent phobic symptoms) [corrected] reflect the same genetic risk, and separation anxiety symptoms both before and after age 14 reflect the same environmental risk that influence liability to depressive symptoms expressed in middle to late adolescence.
Adolescent↗
Testing hypotheses on specific environmental causal effects on behavior.
There have been strong critiques of the notion that environmental influences can have an important effect on psychological functioning. The substance of these criticisms is considered in order to infer the methodological challenges that have to be met. Concepts of cause and of the testing of causal effects are discussed with a particular focus on the need to consider sample selection and the value (and limitations) of longitudinal data. The designs that may be used to test hypotheses on specific environmental risk mechanisms for psychopathology are discussed in relation to a range of adoption strategies, twin designs, various types of "natural experiments," migration designs, the study of secular change, and intervention designs. In each case, consideration is given to the need for samples that "pull-apart" variables that ordinarily go together, specific hypotheses on possible causal processes, and the specification and testing of key assumptions. It is concluded that environmental risk hypotheses can be (and have been) put to the test but that it is usually necessary to use a combination of research strategies.
Adult↗
Genetic moderation of environmental risk for depression and anxiety in adolescent girls.
BACKGROUND: There is huge individual variation in people's response to negative life events. AIMS: To test the hypothesis that genetic factors moderate susceptibility to the environmentally mediated risks associated with negative life events. METHOD: The Virginia Twin Study of Adolescent Behavioral Development (VTSABD) was used to study the effects of independent life events (assessed from maternal interview) on depression/anxiety (assessed from child interview) in 184 same-gender female twin pairs, aged 14--7 years, measured on two occasions. RESULTS: There was no genetic effect on the independent negative life events studied. A significant gene-environment interaction was found using structural equation modelling. There was no effect of independent life events on adolescents' depression in the absence of parental emotional disorder, but a significant effect in its presence. CONCLUSIONS: There is an environmentally mediated effect of life events on depression/anxiety. Genetic factors play a significant role in individual differences in susceptibility to these environmentally mediated risks.
Adolescent↗
Imaging the electron wave function in self-assembled quantum dots.
Magnetotunneling spectroscopy is used as a noninvasive and nondestructive probe to produce two-dimensional spatial images of the probability density of an electron confined in a self-assembled semiconductor quantum dot. The technique exploits the effect of the classical Lorentz force on the motion of a tunneling electron and can be regarded as the momentum (k) space analog of scanning tunneling microscopy imaging. The images reveal the elliptical symmetry of the ground state and the characteristic lobes of the higher energy states.
Journal Article↗
Landau-level spectroscopy of a two-dimensional electron system by tunneling through a quantum dot.
A single InAs self-assembled quantum dot is incorporated in the barrier of a tunnel diode and used as a spectroscopic probe of an adjacent two-dimensional electron system from the Fermi energy to the subband edge. We obtain quantitative information about the energy dependence of the quasiparticle lifetime. For magnetic field B, applied parallel to the current, we observe peaks in the current-voltage characteristics I(V) corresponding to the formation of Landau levels. Close to filling factor nu=1 we observe directly the exchange enhancement of the Lande g factor.
Journal Article↗
Self-assembling of In(Ga)As/GaAs quantum dots on (N11) substrates: the (311)A case
We have investigated the In(Ga)As island formation, in the Stranski-Krastanov growth mode, on (311)A GaAs substrates. The surface topography of InAs and InGaAs strained epilayers was studied by contact microscopies. The different substrate affects the overgrown island shape. In(Ga)As grown on (311)A gives rise to quantum wire-like islands. Quantum dots (QDs), but with highly anisotropic shapes, are the outcomes of InAs deposition. QD samples were also characterized by photoluminescence (PL) measurements. Correlation between optical and morphological properties was observed.
Journal Article↗
Effect of secretin on children with autism: a randomized controlled trial.
To determine the effect of intravenous porcine secretin on autistic behaviours in children aged 2 to 7 years, the effects of secretin on (1) performance on a standardized language measure, and (2) autistic behaviours, as rated by parents and child development professionals was examined. Employing a randomized, double-blind, placebo-controlled design, 95 participants were assigned to one of two groups and administered a single dose of either secretin or placebo. A follow-up assessment was conducted 3 weeks after the injection. No significant differences in language or autistic behaviour measures were observed at the 3-week follow-up between the groups. Also, there was no significant difference in the proportion of individuals who improved by > or = 6 points on the language measure at follow-up. This study showed no significant effects of secretin on children with autism. Our results are consistent with a systematic review of randomized controlled trials evaluating the effect of secretin in children with autism.
Animals↗
Genetic and environmental causes of covariation in interview assessments of disruptive behavior in child and adolescent twins.
Multirater, face-to-face, interview data relating to conduct disorder (CD), oppositional-defiant disorder (ODD), and inattentive, impulsive, and hyperactive components of attention-deficit hyperactivity disorder (ADHD) in a population-based sample of 1376 pairs of 8- to 16-year-old MZ and DZ twins are analyzed to examine (1) the genetic and environmental causes of correlation among ratings of ODD and CD symptoms and (2) the pattern of genetic and environmental correlation among the three components of ADHD. Parental ratings of ADHD showed marked sibling contrast effects, specific within raters but partly common across components. After these effects were removed, there was a modest genetic correlation between maternal and paternal ratings, but genetic effects were virtually uncorrelated across boys and girls. Genetic correlations among inattention, impulsivity, and hyperactivity were all large but fell well short of unity. There was little evidence that counts of symptoms of CD and ODD were genetically independent but the genetic correlations among ratings of twins, mothers, and fathers were all relatively modest. ODD and CD showed much higher genetic correlations across sexes than did the measures of ADHD. There was no evidence of rater contrast effects or of shared family environment influences in the twin resemblance for ODD and CD.
Adolescent↗
The influence of genetic factors and life stress on depression among adolescent girls.
BACKGROUND: The possible causes of greater depression among adolescent girls were investigated by examining variation in the influence of genetic and environmental risk factors among 182 prepubertal female, 237 prepubertal male, 314 pubertal female, and 171 pubertal male twin pairs from the Virginia Twin Study of Adolescent Behavioral Development. OBJECTIVES: To compare the trajectory of depressive symptoms among boys and girls from childhood to adolescence; to analyze the role of genetic, shared, and unique environmental factors in depression among prepubertal and pubertal male and female twins; and to investigate a possible link between liability to depression and one salient index of the child's environment: past-year life events. METHODS: Child-reported depression was assessed using the Child and Adolescent Psychiatric Interview and ratings of past-year life events and pubertal status obtained by maternal questionnaire and interview, respectively. RESULTS: The impact of life events on depression was particularly evident in the adolescent girls. The results from model fitting indicate increased heritability for depression in this group, and its long-term consistency was mediated primarily by latent genetic factors. Model fitting also showed that at least part of the liability to depression and to life events can be linked to a common set of genes in the adolescent girls, and there is a notable developmental increase in the genetic variance for life events. CONCLUSIONS: The greater heritability for depression in pubertal girls, its genetic mediation over time, and the increase in genetic variance for life events may be one possible explanation for the emergence of increased depression among pubertal girls and its persistence through adolescence.
Adolescent↗
Transmission of religion and attitudes.
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Attitude↗
Comparing the biological and cultural inheritance of personality and social attitudes in the Virginia 30,000 study of twins and their relatives.
Measures of four dimensions of personality (Psychoticism, Extraversion, Neuroticism, and Lie scores) and six aspects of social attitudes (to sex, taxation, militarism, politics, religion and a general conservatism scale) were obtained by mailed questionnaire from 29,691 US subjects including adult twins (n = 14,761) their parents (n = 2360), their spouses (n = 4391), siblings (n = 3184) and adult children (n = 4800). After correction for the average effects of age, sex and source of sample, familial correlations were computed for 80 distinct biological and social relationships. The data allow for the estimation of the additive and non-additive effects of genes, assortative mating, vertical cultural inheritance and other non-parental effects of the shared environment on differences in personality and social attitudes. The interaction of genetic and environmental effects with sex may also be analyzed. Model-fitting analyses show that personality and social attitude measures differ markedly in major features of family resemblance. Additive and dominant genetic effects contribute to differences in both personality and attitudes, but the effects of the family environment, including vertical cultural transmission from parent to child, are much more marked for social attitudes than for personality. There is substantial assortative mating for social attitudes and almost none for personality. The causes of family resemblance depend significantly on sex for almost every variable studied. These findings clarify and extend the more tentative findings derived from previous twin, family and adoption studies.
Adult↗
Co-occurrence of abuse of different drugs in men: the role of drug-specific and shared vulnerabilities.
BACKGROUND: Previous research has demonstrated genetic and environmental influences on abuse of individual substances, but there is less known about how these factors may influence the co-occurrence of abuse of different illicit drugs. METHODS: We studied 3372 male twin pairs from the Vietnam Era Twin Registry. They were interviewed using the Diagnostic Interview Schedule, Version III, Revised to investigate the extent to which the abuse of different categories of drugs occurs together within an individual, as well as the possibility that genetic and environmental factors are responsible for observed co-occurrence. Co-occurrence was quantified using odds ratios and conditional probabilities. Multivariate biometrical modeling analyses were used to assess genetic and environmental influences on co-occurrence. RESULTS: Abusing any category of drug was associated with a marked increase in the probability of abusing every other category of drugs. We found evidence for a shared or common vulnerability factor that underlies the abuse of marijuana, sedatives, stimulants, heroin or opiates, and psychedelics. This shared vulnerability is influenced by genetic, family environmental, and nonfamily environmental factors, but not every drug is influenced to the same extent by the shared vulnerability factor. Marijuana, more than other drugs, was influenced by family environmental factors. Each category of drug, except psychedelics, had genetic influences unique to itself (ie, not shared with other drug categories). Heroin had larger genetic influences unique to itself than did any other drug. CONCLUSION: There are genetically and environmentally determined characteristics that comprise a shared or common vulnerability to abuse a range of illicit drugs.
Adult↗
Genetic influences on childhood hyperactivity: contrast effects imply parental rating bias, not sibling interaction.
BACKGROUND: Previous twin studies of hyperactivity have supported a 'contrast effect', whereby the more hyperactive the rating of one twin, the less the rating of the other. It has not been clear whether contrast effects occur in the twins' behaviour or in the ratings made of their behaviour but the implications for hyperactivity are different under the two models. METHOD: We use hyperactivity ratings from mothers and teachers for 1644 twin pairs in the Virginia Twin Study of Adolescent Behavioral Development (VTSABD) to explore the origin of contrast effects, making use of independent teacher reports in a proportion of twins. Models were fitted separately for the two informants and jointly to ratings combined through a latent variable, using structural equation modelling. RESULTS: Models for maternal data confirm the contrast effect previously reported. Teacher ratings show a different form of bias, with both twin confusion and correlated errors representing alternative but not mutually exclusive explanations of the data. Latent variable modelling of the joint responses allowed comparison of a model in which the contrast effect was placed on maternal ratings, representing bias, versus one in which the contrast occurred in the underlying 'true' phenotype. The fit of the former model was significantly better. CONCLUSIONS: Support is provided for the notion of contrast effects as a form of rater bias in maternal hyperactivity ratings. Different bias in teacher reports highlight that no one report can be considered a gold standard. The extent to which such biases may distort information for other data sources such as sib-pair studies of concordance/discordance is discussed.
Adolescent↗
Declaration of rights and statement of needs of twins and higher order multiples.
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Human Rights↗
Integrating nature and nurture: implications of person-environment correlations and interactions for developmental psychopathology.
The developmental interplay between nature and nurture is discussed, with particular reference to implications for research in developmental psychopathology. The general principles include individual differences in reactivity to the environment, two-way interplay between intraindividual biology and environmental influences, and the need to consider broader social contextual features. Individuals actively process their experiences; they also act on their environment to shape and select their experiences, and individual characteristics change over time. Key findings on genetic effects include their ubiquitous influence, the multifactorial origin of most psychopathology, the involvement of several genes in most mental disorders, some genetic effects operate through dimensional risk features rather than directly on disorder, some genetic effects are dependent on gene-environment correlations and interactions, and genetic effects increase with age. Key findings on environmental effects include their ubiquitous influence, the genetic mediation of some supposed environmental effects, the importance of passive gene-environment correlations, the paucity of evidence regarding environmental effects on lifetime liability to psychopathology, the lack of understanding of environmental effects on the organism, and the importance of nonshared environmental effects. Research strategies to investigate environmental risk mediation include the range of genetically sensitive designs, migration studies, secular trend investigations, studies of nonfamilial environments, and examination of intraindividual change in relation to measured environmental alterations. Proximal processes involved in person-environment interplay are discussed in relation to person-environment interactions and evocative and active person-environment correlations.
Adaptation, Psychological↗
Age changes in the causes of individual differences in conservatism.
Age-related changes are analyzed in the correlation of 3416 monozygotic and 3780 dizygotic U.S. twin pairs aged between 9 and 75+ years for conservatism scores derived from a 28-item social attitude inventory. The effects of the shared environment are overwhelming in twins aged 20 years or younger. In older twins, genetic effects appear to play a larger role. A more dynamic conception of the interaction between genes and environment in the development of complex human differences is needed.
Adolescent↗