1,294 research outputs found
Probing ferroelectricity in highly conducting materials through their elastic response: persistence of ferroelectricity in metallic BaTiO3-d
The question whether ferroelectricity (FE) may coexist with a metallic or
highly conducting state, or rather it must be suppressed by the screening from
the free charges, is the focus of a rapidly increasing number of theoretical
studies and is finally receiving positive experimental responses. The issue is
closely related to the thermoelectric and multiferroic (also magnetic)
applications of FE materials, where the electrical conductivity is required or
spurious. In these circumstances, the traditional methods for probing
ferroelectricity are hampered or made totally ineffective by the free charges,
which screen the polar response to an external electric field. This fact may
explain why more than 40 years passed between the first proposals of FE metals
and the present experimental and theoretical activity. The measurement of the
elastic moduli, Young's modulus in the present case, versus temperature is an
effective method for studying the influence of doping on a FE transition
because the elastic properties are unaffected by electrical conductivity. In
this manner, it is shown that the FE transitions of BaTiO3-d are not suppressed
by electron doping through O vacancies; only the onset temperatures are
depressed, but the magnitudes of the softenings, and hence of the piezoelectric
activity, are initially even increased
A Potential of Interaction between Two- and Three-Dimensional Solitons
A general method to find an effective potential of interaction between far
separated 2D and 3D solitons is elaborated, including the case of 2D vortex
solitons. The method is based on explicit calculation of the overlapping term
in the full Hamiltonian of the system (_without_ assuming that the ``tail'' of
each soliton is not affected by its interaction with the other soliton, and, in
fact,_without_ knowing the exact form of the solution for an isolated soliton -
the latter problem is circumvented by reducing a bulk integral to a surface
one). The result is obtained in an explicit form that does not contain an
artificially introduced radius of the overlapping region. The potential applies
to spatial and spatiotemporal solitons in nonlinear optics, where it may help
to solve various dynamical problems: collisions, formation of bound states
(BS's), etc. In particular, an orbiting BS of two solitons is always unstable.
In the presence of weak dissipation and gain, the effective potential can also
be derived, giving rise to bound states similar to those recently studied in 1D
models.Comment: 29 double-spaced pages in the latex format and 1 figure in the ps
format. The paper will appear in Phys. Rev.
Stable ring vortex solitons in Bessel optical lattices
Stable ring vortex solitons, featuring a bright-shape, appear to be very rare
in nature. However, here we show that they exist and can be made dynamically
stable in defocusing cubic nonlinear media with an imprinted Bessel optical
lattice. We find the families of vortex lattice solitons and reveal their
salient properties, including the conditions required for their stability. We
show that the higher the soliton topological charge, the deeper the lattice
modulation necessary for stabilization.Comment: 14 pages, 4 figures, submitted to Physical Review Letter
Bundle Theory of Improper Spin Transformations
{\it We first give a geometrical description of the action of the parity
operator () on non relativistic spin Pauli spinors in
terms of bundle theory. The relevant bundle, , is a
non trivial extension of the universal covering group .
is the non relativistic limit of the corresponding Dirac matrix
operator and obeys . Then, from the direct
product of O(3) by , naturally induced by the structure of the galilean
group, we identify, in its double cover, the time reversal operator ()
acting on spinors, and its product with . Both, and
, generate the group . As in the case of parity,
is the non relativistic limit of the corresponding Dirac matrix
operator , and obeys .}Comment: 8 pages, Plaintex; titled changed, minor text modifications, one
reference complete
Genetic Architecture of ADHD and Overlap With Other Psychiatric Disorders And Cognition-Related Phenotypes
Attention-deficit/hyperactivity disorder (ADHD) co-occurs with many other psychiatric disorders and traits. In this review, we summarize and interpret the existing literature on the genetic architecture of these comorbidities based on hypothesis-generating approaches. Quantitative genetic studies indicate that genetic factors play a substantial role in the observed co-occurrence of ADHD with many different disorders and traits. Molecular genetic correlations derived from genome-wide association studies and results of studies based on polygenic risk scores confirm the general pattern but provide effect estimates that are smaller than those from twin studies. The identification of the specific genetic variants and biological pathways underlying co-occurrence using genome-wide approaches is still in its infancy. The first analyses of causal inference using genetic data support causal relationships between ADHD and comorbid disorders, although bidirectional effects identified in some instances point to complex relationships. While several issues in the methodology and inferences from the results are still to be overcome, this review shows that the co-occurrence of ADHD with many psychiatric disorders and traits is genetically interpretable.</p
Genetic Architecture of ADHD and Overlap With Other Psychiatric Disorders And Cognition-Related Phenotypes
Attention-deficit/hyperactivity disorder (ADHD) co-occurs with many other psychiatric disorders and traits. In this review, we summarize and interpret the existing literature on the genetic architecture of these comorbidities based on hypothesis-generating approaches. Quantitative genetic studies indicate that genetic factors play a substantial role in the observed co-occurrence of ADHD with many different disorders and traits. Molecular genetic correlations derived from genome-wide association studies and results of studies based on polygenic risk scores confirm the general pattern but provide effect estimates that are smaller than those from twin studies. The identification of the specific genetic variants and biological pathways underlying co-occurrence using genome-wide approaches is still in its infancy. The first analyses of causal inference using genetic data support causal relationships between ADHD and comorbid disorders, although bidirectional effects identified in some instances point to complex relationships. While several issues in the methodology and inferences from the results are still to be overcome, this review shows that the co-occurrence of ADHD with many psychiatric disorders and traits is genetically interpretable.</p
Few-anyon systems in a parabolic dot
The energy levels of two and three anyons in a two-dimensional parabolic
quantum dot and a perpendicular magnetic field are computed as power series in
1/|J|, where J is the angular momentum. The particles interact repulsively
through a coulombic (1/r) potential. In the two-anyon problem, the reached
accuracy is better than one part in 10^5. For three anyons, we study the
combined effects of anyon statistics and coulomb repulsion in the ``linear''
anyonic states.Comment: LaTeX, 6 pages, 4 postscript figure
Genetic Architecture of ADHD and Overlap With Other Psychiatric Disorders And Cognition-Related Phenotypes
Attention-deficit/hyperactivity disorder (ADHD) co-occurs with many other psychiatric disorders and traits. In this review, we summarize and interpret the existing literature on the genetic architecture of these comorbidities based on hypothesis-generating approaches. Quantitative genetic studies indicate that genetic factors play a substantial role in the observed co-occurrence of ADHD with many different disorders and traits. Molecular genetic correlations derived from genome-wide association studies and results of studies based on polygenic risk scores confirm the general pattern but provide effect estimates that are smaller than those from twin studies. The identification of the specific genetic variants and biological pathways underlying co-occurrence using genome-wide approaches is still in its infancy. The first analyses of causal inference using genetic data support causal relationships between ADHD and comorbid disorders, although bidirectional effects identified in some instances point to complex relationships. While several issues in the methodology and inferences from the results are still to be overcome, this review shows that the co-occurrence of ADHD with many psychiatric disorders and traits is genetically interpretable.</p
Genetic Architecture of ADHD and Overlap With Other Psychiatric Disorders And Cognition-Related Phenotypes
Attention-deficit/hyperactivity disorder (ADHD) co-occurs with many other psychiatric disorders and traits. In this review, we summarize and interpret the existing literature on the genetic architecture of these comorbidities based on hypothesis-generating approaches. Quantitative genetic studies indicate that genetic factors play a substantial role in the observed co-occurrence of ADHD with many different disorders and traits. Molecular genetic correlations derived from genome-wide association studies and results of studies based on polygenic risk scores confirm the general pattern but provide effect estimates that are smaller than those from twin studies. The identification of the specific genetic variants and biological pathways underlying co-occurrence using genome-wide approaches is still in its infancy. The first analyses of causal inference using genetic data support causal relationships between ADHD and comorbid disorders, although bidirectional effects identified in some instances point to complex relationships. While several issues in the methodology and inferences from the results are still to be overcome, this review shows that the co-occurrence of ADHD with many psychiatric disorders and traits is genetically interpretable.</p
Genetic Architecture of ADHD and Overlap With Other Psychiatric Disorders And Cognition-Related Phenotypes
Attention-deficit/hyperactivity disorder (ADHD) co-occurs with many other psychiatric disorders and traits. In this review, we summarize and interpret the existing literature on the genetic architecture of these comorbidities based on hypothesis-generating approaches. Quantitative genetic studies indicate that genetic factors play a substantial role in the observed co-occurrence of ADHD with many different disorders and traits. Molecular genetic correlations derived from genome-wide association studies and results of studies based on polygenic risk scores confirm the general pattern but provide effect estimates that are smaller than those from twin studies. The identification of the specific genetic variants and biological pathways underlying co-occurrence using genome-wide approaches is still in its infancy. The first analyses of causal inference using genetic data support causal relationships between ADHD and comorbid disorders, although bidirectional effects identified in some instances point to complex relationships. While several issues in the methodology and inferences from the results are still to be overcome, this review shows that the co-occurrence of ADHD with many psychiatric disorders and traits is genetically interpretable.</p
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