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Fromhold TM, Patanè A, Bujkiewicz S, Wilkinson PB, Fowler D, Sherwood D, Stapleton SP, Krokhin AA, Eaves L, Henini M, Sankeshwar NS, Sheard FW. Chaotic electron diffusion through stochastic webs enhances current flow in superlattices. Nature 2004; 428:726-30. [PMID: 15085125 DOI: 10.1038/nature02445] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2003] [Accepted: 02/27/2004] [Indexed: 11/09/2022]
Abstract
Understanding how complex systems respond to change is of fundamental importance in the natural sciences. There is particular interest in systems whose classical newtonian motion becomes chaotic as an applied perturbation grows. The transition to chaos usually occurs by the gradual destruction of stable orbits in parameter space, in accordance with the Kolmogorov-Arnold-Moser (KAM) theorem--a cornerstone of nonlinear dynamics that explains, for example, gaps in the asteroid belt. By contrast, 'non-KAM' chaos switches on and off abruptly at critical values of the perturbation frequency. This type of dynamics has wide-ranging implications in the theory of plasma physics, tokamak fusion, turbulence, ion traps, and quasicrystals. Here we realize non-KAM chaos experimentally by exploiting the quantum properties of electrons in the periodic potential of a semiconductor superlattice with an applied voltage and magnetic field. The onset of chaos at discrete voltages is observed as a large increase in the current flow due to the creation of unbound electron orbits, which propagate through intricate web patterns in phase space. Non-KAM chaos therefore provides a mechanism for controlling the electrical conductivity of a condensed matter device: its extreme sensitivity could find applications in quantum electronics and photonics.
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27
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Foxon CT, Novikov SV, Belyaev AE, Zhao LX, Makarovsky O, Walker DJ, Eaves L, Dykeman RI, Danylyuk SV, Vitusevich SA, Kappers MJ, Barnard JS, Humphreys CJ. Current–voltage instabilities in GaN/AlGaN resonant tunnelling structures. ACTA ACUST UNITED AC 2003. [DOI: 10.1002/pssc.200303376] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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28
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Endicott J, Patanè A, Ibáñez J, Eaves L, Bissiri M, Hopkinson M, Airey R, Hill G. Magnetotunneling spectroscopy of dilute Ga(AsN) quantum wells. PHYSICAL REVIEW LETTERS 2003; 91:126802. [PMID: 14525385 DOI: 10.1103/physrevlett.91.126802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2003] [Indexed: 05/24/2023]
Abstract
We use magnetotunneling spectroscopy to explore the admixing of the extended GaAs conduction band states with the localized N-impurity states in dilute GaAs(1-y)N(y) quantum wells. In our resonant tunneling diodes, electrons can tunnel into the N-induced E- and E+ subbands in a GaAs(1-y)N(y) quantum well layer, leading to resonant peaks in the current-voltage characteristics. By varying the magnetic field applied perpendicular to the current direction, we can tune an electron to tunnel into a given k state of the well; since the applied voltage tunes the energy, we can map out the form of the energy-momentum dispersion curves of E- and E+. The data reveal that for a small N content (approximately 0.1%) the E- and E+ subbands are highly nonparabolic and that the heavy effective mass E+ states have a significant Gamma-conduction band character even at k=0.
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29
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Martin AM, Benedict KA, Sheard FW, Eaves L. Model for the voltage steps in the breakdown of the integer quantum Hall effect. PHYSICAL REVIEW LETTERS 2003; 91:126803. [PMID: 14525386 DOI: 10.1103/physrevlett.91.126803] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2002] [Revised: 03/12/2003] [Indexed: 05/24/2023]
Abstract
In samples used to maintain the U.S. resistance standard the breakdown of the dissipationless integer quantum Hall effect occurs as a series of dissipative voltage steps. A mechanism for this type of breakdown is proposed, based on the generation of magnetoexcitons when the quantum Hall fluid flows past an ionized impurity above a critical velocity. The calculated generation rate gives a voltage step height in good agreement with measurements on both electron and hole gases. We also compare this model to a hydrodynamic description of breakdown.
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30
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Catherall AT, Benedict KA, King PJ, Eaves L. Surface instabilities on liquid oxygen in an inhomogeneous magnetic field. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 68:037302. [PMID: 14524930 DOI: 10.1103/physreve.68.037302] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2003] [Indexed: 05/24/2023]
Abstract
Liquid oxygen exhibits surface instabilities when subjected to a sufficiently strong magnetic field. A vertically oriented magnetic field gradient both increases the magnetic field value at which the pattern forms and shrinks the length scale of the surface patterning. We show that these effects of the field gradient may be described in terms of an "effective gravity," which in our experiments may be varied from 1 g to 360 g.
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31
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Catherall AT, Eaves L, King PJ, Booth SR. Magnetic levitation: Floating gold in cryogenic oxygen. Nature 2003; 422:579. [PMID: 12686988 DOI: 10.1038/422579a] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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32
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Silberg J, Rutter M, Neale M, Eaves L. Genetic moderation of environmental risk for depression and anxiety in adolescent girls. Br J Psychiatry 2001; 179:116-21. [PMID: 11483472 DOI: 10.1192/bjp.179.2.116] [Citation(s) in RCA: 202] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
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.
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33
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Fromhold TM, Krokhin AA, Tench CR, Bujkiewicz S, Wilkinson PB, Sheard FW, Eaves L. Effects of stochastic webs on chaotic electron transport in semiconductor superlattices. PHYSICAL REVIEW LETTERS 2001; 87:046803. [PMID: 11461635 DOI: 10.1103/physrevlett.87.046803] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2000] [Indexed: 05/23/2023]
Abstract
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.
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Silberg JL, Rutter M, Eaves L. Genetic and environmental influences on the temporal association between earlier anxiety and later depression in girls. Biol Psychiatry 2001; 49:1040-9. [PMID: 11430845 DOI: 10.1016/s0006-3223(01)01161-1] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
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.
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Rutter M, Pickles A, Murray R, Eaves L. Testing hypotheses on specific environmental causal effects on behavior. Psychol Bull 2001; 127:291-324. [PMID: 11393298 DOI: 10.1037/0033-2909.127.3.291] [Citation(s) in RCA: 367] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
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.
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Eaves L, Stradling RA, Carrere G, Askenazy S, Leotin J, Portal JC, Ulmet JP. An investigation of the conduction band edge in CdSe by the magnetophonon effect. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/5/3/002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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37
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Eaves L, Stradling RA, Askenazy S, Leotin J, Portal JC, Ulmet JP. The magnetophonon effect in epitaxial films of n-type inp. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/4/2/018] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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38
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Bajaj KK, Birch JR, Eaves L, Hoult RA, Kirkman RF, Simmonds PE, Stradling RA. Spectroscopic evidence for the interaction between shallow hydrogenic donors in GaAs, InP and CdTe. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/8/4/021] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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39
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Eaves L, Hoult RA, Stradling RA, Tidey RJ, Portal JC, Askenazy S. Fourier analysis of magnetophonon and two-dimensional Shubnikov-de Haas magnetoresistance structure. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/8/7/019] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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40
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Eaves L, Hoult RA, Stradling RA, Askenazy S, Barbaste R, Carrere G, Leotin J, Portal JC, Ulmet P. An investigation of the valence bands of germanium, InSb and GaAs by means of the magnetophonon effect. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/10/15/018] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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41
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42
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Eaves L, Williams PJ. Decay of the deep-level extrinsic photoconductivity response of n-GaAs(Cr,Si) at liquid-helium temperature. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/12/18/005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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43
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Dunn-Geier J, Ho HH, Auersperg E, Doyle D, Eaves L, Matsuba C, Orrbine E, Pham B, Whiting S. Effect of secretin on children with autism: a randomized controlled trial. Dev Med Child Neurol 2000; 42:796-802. [PMID: 11132252 DOI: 10.1017/s0012162200001481] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
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.
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Maghoub AS, McCann JPJ, Eaves L, Cockayne B. The g value of Co2+(4A2) ground state in InP measured by EPR. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/16/2/006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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45
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Duncan KR, Eaves L, Ramdane A, Roys WB, Skolnick MS, Dean PJ. An investigation of the 1.36 eV photoluminescence spectrum of heat-treated InP using Zeeman spectroscopy and strain effects. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/17/7/016] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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46
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Williams PJ, Eaves L, Simmonds PE, Henry MO, Lightowlers EC, Uihlein C. High-resolution optical absorption spectroscopy on Cr-related defects in GaAs and GaP. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/15/6/026] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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47
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Eaves L, Halliday DP. A model for some defect-related bound exciton lines in the photoluminescence spectrum of GaAs layers grown by molecular beam epitaxy. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/17/27/003] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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48
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Eaves L, Halliday DP, Uihlein C. Interpretation of the 1.03 eV photoluminescence and absorption in GaP(Cr) in terms of internal transitions of Cr3+. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/18/16/002] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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49
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Eaves L, Skolnick MS, Halliday DP. Comment on the time-resolved photoluminescence study of MBE-growth-induced defect lines. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/19/20/005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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50
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Vdovin EE, Levin A, Patanè A, Eaves L, Main PC, Khanin YN, Dubrovskii YV, Henini M, Hill G. Imaging the electron wave function in self-assembled quantum dots. Science 2000; 290:122-4. [PMID: 11021794 DOI: 10.1126/science.290.5489.122] [Citation(s) in RCA: 162] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
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.
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