118 research outputs found
Superfluids and Supersolids on Frustrated 2D Lattices
We study the ground state of hard-core bosons with nearest-neighbor hopping
and nearest-neighbor interactions on the triangular and Kagom\'e lattices by
mapping to a system of spins (), which we analyze using spin-wave
theory. We find that the both lattices display superfluid and supersolid (a
coexistence of superfluid and solid) order as the parameters and filling are
varied. Quantum fluctuations seem large enough in the Kagom\'e system to raise
the interesting possibility of a disordered ground state.Comment: Latex format, 24 figures available by email upon request. Submitted
to Physical Review
Quantum-Phase Transitions of Interacting Bosons and the Supersolid Phase
We investigate the properties of strongly interacting bosons in two
dimensions at zero temperature using mean-field theory, a variational Ansatz
for the ground state wave function, and Monte Carlo methods. With on-site and
short-range interactions a rich phase diagram is obtained. Apart from the
homogeneous superfluid and Mott-insulating phases, inhomogeneous charge-density
wave phases appear, that are stabilized by the finite-range interaction.
Furthermore, our analysis demonstrates the existence of a supersolid phase, in
which both long-range order (related to the charge-density wave) and
off-diagonal long-range order coexist. We also obtain the critical exponents
for the various phase transitions.Comment: RevTex, 20 pages, 10 PostScript figures include
The relations between DISC-IV DSM diagnoses of ADHD and multi-informant CBCL-AP syndrome scores
Background: Previous studies have examined the relation between attention problems (APs) obtained with the Child Behavior Checklist (CBCL) and attention deficit hyperactivity disorder (ADHD) assessed with the Diagnostic and Statistical Manual of Mental Disorders (DSM). We will examine this relation across sex using multi-informant data. Methods: Parents of 12 538 twins, aged 7, 10, and 12 years, and teachers of twins, aged 10 years, completed the questionnaires. The mothers of a sample of 283 boys and 291 girls who scored either low or high on longitudinal maternal CBCL-AP were interviewed. Results: Children with a low AP score obtained a negative ADHD diagnosis in 96% of cases. Children with a high AP score obtained a positive diagnosis in 36% (girls) and 59% (boys) of cases. The association between paternal and maternal AP ratings and ADHD was the same, whereas the association between teacher AP ratings and ADHD was low. Conclusions: The association between AP and ADHD is higher in boys than girls, possibly because of a bias toward the male manifestation of ADHD. © 2006 Elsevier Inc. All rights reserved
Classification of a supersolid: Trial wavefunctions, Symmetry breakings and Excitation spectra
A state of matter is characterized by its symmetry breaking and elementary
excitations.
A supersolid is a state which breaks both translational symmetry and internal
symmetry.
Here, we review some past and recent works in phenomenological
Ginsburg-Landau theories, ground state trial wavefunctions and microscopic
numerical calculations. We also write down a new effective supersolid
Hamiltonian on a lattice.
The eigenstates of the Hamiltonian contains both the ground state
wavefunction and all the excited states (supersolidon) wavefunctions. We
contrast various kinds of supersolids in both continuous systems and on
lattices, both condensed matter and cold atom systems. We provide additional
new insights in studying their order parameters, symmetry breaking patterns,
the excitation spectra and detection methods.Comment: REVTEX4, 19 pages, 3 figure
Solid 4He and the Supersolid Phase: from Theoretical Speculation to the Discovery of a New State of Matter? A Review of the Past and Present Status of Research
The possibility of a supersolid state of matter, i.e., a crystalline solid
exhibiting superfluid properties, first appeared in theoretical studies about
forty years ago. After a long period of little interest due to the lack of
experimental evidence, it has attracted strong experimental and theoretical
attention in the last few years since Kim and Chan (Penn State, USA) reported
evidence for nonclassical rotational inertia effects, a typical signature of
superfluidity, in samples of solid 4He. Since this "first observation", other
experimental groups have observed such effects in the response to the rotation
of samples of crystalline helium, and it has become clear that the response of
the solid is extremely sensitive to growth conditions, annealing processes, and
3He impurities. A peak in the specific heat in the same range of temperatures
has been reported as well as anomalies in the elastic behaviour of solid 4He
with a strong resemblance to the phenomena revealed by torsional oscillator
experiments. Very recently, the observation of unusual mass transport in hcp
solid 4He has also been reported, suggesting superflow. From the theoretical
point of view, powerful simulation methods have been used to study solid 4He,
but the interpretation of the data is still rather difficult; dealing with the
question of supersolidity means that one has to face not only the problem of
the coexistence of quantum coherence phenomena and crystalline order, exploring
the realm of spontaneous symmetry breaking and quantum field theory, but also
the problem of the role of disorder, i.e., how defects, such as vacancies,
impurities, dislocations, and grain boundaries, participate in the phase
transition mechanism.Comment: Published on J. Phys. Soc. Jpn., Vol.77, No.11, p.11101
Reactive and Regulative Temperament in Youths: Psychometric Evaluation of the Early Adolescent Temperament Questionnaire-Revised
The present study examined the psychometric properties of the self-report version of the Early Adolescent Temperament Questionnaire-Revised (EATQ-R), which is a scale for measuring reactive and regulative temperament traits, in a large sample of children and adolescents (N = 1,055). The results indicated that the internal consistency was acceptable for most EATQ-R temperament scales. Further, principal components analysis of the instrument yielded a structure with nine components, which generally reflected the temperament scales of the EATQ-R. The test–retest stability of the scale was moderate to good, whereas the parent–child agreement was rather low. Finally, the scale correlated in a theoretically meaningful way with children’s self-reports of personality and psychopathology. It can be concluded that the EATQ-R is a useful scale for measuring aspects of reactive and regulative temperament in children and adolescents, although there is certainly room for improving the instrument
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