12,330 research outputs found
Direct Observation of Condon Domains in Silver by Hall Probes
Using a set of micro Hall probes for the detection of the local induction,
the inhomogeneous Condon domain structure has been directly observed at the
surface of a pure silver single crystal under strong Landau quantization in
magnetic fields up to 10 T. The inhomogeneous induction occurs in the
theoretically predicted part of the H-T Condon domain phase diagram.
Information about size, shape and orientation of the domains is obtained by
analyzing Hall probes placed along and across the long sample axis and by
tilting the sample. On a beryllium surface the induction inhomogeneity is
almost absent although the expected induction splitting here is at least ten
times higher than in silver.Comment: 4 pages, 6 figures, submitted to PR
Spherical Orbifolds for Cosmic Topology
Harmonic analysis is a tool to infer cosmic topology from the measured
astrophysical cosmic microwave background CMB radiation. For overall positive
curvature, Platonic spherical manifolds are candidates for this analysis. We
combine the specific point symmetry of the Platonic manifolds with their deck
transformations. This analysis in topology leads from manifolds to orbifolds.
We discuss the deck transformations of the orbifolds and give eigenmodes for
the harmonic analysis as linear combinations of Wigner polynomials on the
3-sphere. These provide new tools for detecting cosmic topology from the CMB
radiation.Comment: 17 pages, 9 figures. arXiv admin note: substantial text overlap with
arXiv:1011.427
Hysteresis in the de Haas-van Alphen Effect
A hysteresis loop is observed for the first time in the de Haas-van Alphen
(dHvA) effect of beryllium at low temperatures and quantizing magnetic field
applied parallel to the hexagonal axis of the single crystal. The irreversible
behavior of the magnetization occurs at the paramagnetic part of the dHvA
period in conditions of Condon domain formation arising by strong enough dHvA
amplitude. The resulting extremely nonlinear response to a very small
modulation field offers the possibility to find in a simple way the Condon
domain phase diagram. From a harmonic analysis, the shape and size of the
hysteresis loop is constructed.Comment: 4 pages, 5 figures, submitted to PR
Exponential localization in one-dimensional quasiperiodic optical lattices
We investigate the localization properties of a one-dimensional bichromatic
optical lattice in the tight binding regime, by discussing how exponentially
localized states emerge upon changing the degree of commensurability. We also
review the mapping onto the discrete Aubry-Andre' model, and provide evidences
on how the momentum distribution gets modified in the crossover from extended
to exponentially localized states. This analysis is relevant to the recent
experiment on Anderson localization of a noninteracting Bose-Einstein
condensate in a quasiperiodic optical lattice [G. Roati et al., Nature 453, 895
(2008)].Comment: 13 pages, 6 figure
Physical interpretation of NUT solution
We show that the well-known NUT solution can be correctly interpreted as
describing the exterior field of two counter-rotating semi-infinite sources
possessing negative masses and infinite angular momenta which are attached to
the poles of a static finite rod of positive mass.Comment: 7 pages, 1 figure, submitted to Classical and Quantum Gravit
Current-voltage characteristics of quasi-one-dimensional superconductors: An S-curve in the constant voltage regime
Applying a constant voltage to superconducting nanowires we find that its
IV-characteristic exhibits an unusual S-behavior. This behavior is the direct
consequence of the dynamics of the superconducting condensate and of the
existence of two different critical currents: j_{c2} at which the pure
superconducting state becomes unstable and j_{c1}<j_{c2} at which the phase
slip state is realized in the system.Comment: 4 pages, 5 figures, replaced with minor change
Wigner Molecules in Nanostructures
The one-- and two-- particle densities of up to four interacting electrons
with spin, confined within a quasi one--dimensional ``quantum dot'' are
calculated by numerical diagonalization. The transition from a dense
homogeneous charge distribution to a dilute localized Wigner--type electron
arrangement is investigated. The influence of the long range part of the
Coulomb interaction is studied. When the interaction is exponentially cut off
the ``crystallized'' Wigner molecule is destroyed in favor of an inhomogeneous
charge distribution similar to a charge density wave .Comment: 10 pages (excl. Figures), Figures available on request LaTe
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The experiences of adolescents and adults conceived by sperm donation: Comparisons by age of disclosure and family type
Abstract
BACKGROUND
This study presents findings from a large sample of donor offspring who are aware of the nature of their conception. Importantly, this is one of the first studies to compare the views of offspring told of their origins during childhood to those who found out during adulthood.
METHODS
Online questionnaires were completed anonymously by donor offspring who were members of the Donor Sibling Registry, a US-based worldwide registry that helps donor-conceived individuals search for and contact their donor and donor siblings (i.e. half-siblings). Data were obtained on offspring’s feelings about being donor conceived and their feelings towards their parents.
RESULTS
Offspring of single mothers and lesbian couples learnt of their donor origins earlier than offspring of heterosexual couples. Those told later in life reported more negative feelings regarding their donor conception than those told earlier. Offspring’s feelings towards their parents were less clear, with some of those told later reporting more positive feelings and others reporting more negative feelings. Offspring from heterosexual-couple families were more likely to feel angry at being lied to by their mothers than by their fathers. The most common feeling towards fathers was ‘sympathetic’.
CONCLUSIONS
Age of disclosure is important in determining donor offspring’s feelings about their donor conception. It appears it is less detrimental for children to be told about their donor conception at an early age.Supported by the Nuffield Foundation, U
Condon Domain Phase Diagram for Silver
We present the Condon domain phase diagram for a silver single crystal
measured in magnetic fields up to 28 T and temperatures down to 1.3 K. A
standard ac method with a pickup coil system is used at low frequency for the
measurements of the de Haas-van Alphen effect (dHvA). The transition point from
the state of homogeneous magnetization to the inhomogeneous Condon domain state
(CDS) is found as the point where a small irreversibility in the dHvA
magnetization arises, as manifested by an extremely nonlinear response in the
pickup voltage showing threshold character. The third harmonic content in the
ac response is used to determine with high precision the CDS phase boundary.
The experimentally determined Condon domain phase diagram is in good agreement
with the theoretical prediction calculated by the standard Lifshitz-Kosevich
(LK) formula
Electron propagation in crossed magnetic and electric fields
Laser-atom interaction can be an efficient mechanism for the production of
coherent electrons. We analyze the dynamics of monoenergetic electrons in the
presence of uniform, perpendicular magnetic and electric fields. The Green
function technique is used to derive analytic results for the field--induced
quantum mechanical drift motion of i) single electrons and ii) a dilute Fermi
gas of electrons. The method yields the drift current and, at the same time it
allows us to quantitatively establish the broadening of the (magnetic) Landau
levels due to the electric field: Level number k is split into k+1 sublevels
that render the th oscillator eigenstate in energy space. Adjacent Landau
levels will overlap if the electric field exceeds a critical strength. Our
observations are relevant for quantum Hall configurations whenever electric
field effects should be taken into account.Comment: 11 pages, 2 figures, submitte
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