4,567 research outputs found
Time-resolved density correlations as probe of squeezing in toroidal Bose-Einstein condensates
I study the evolution of mean field and linear quantum fluctuations in a
toroidal Bose-Einstein condensate, whose interaction strength is quenched from
a finite (repulsive) value to zero. The azimuthal equal-time density-density
correlation function is calculated and shows temporal oscillations with twice
the (final) excitation frequencies after the transition. These oscillations are
a direct consequence of positive and negative frequency mixing during
non-adiabatic evolution. I will argue that a time-resolved measurement of the
equal-time density correlator might be used to calculate the moduli of the
Bogoliubov coefficients and thus the amount of squeezing imposed on a mode,
i.e., the number of atoms excited out of the condensate.Comment: 18 pages, IOP styl
Surface spin-flop transition in a uniaxial antiferromagnetic Fe/Cr superlattice induced by a magnetic field of arbitrary direction
We studied the transition between the antiferromagnetic and the surface
spin-flop phases of a uniaxial antiferromagnetic [Fe(14 \AA)/Cr(11 \AA] superlattice. For external fields applied parallel to the in-plane easy
axis, the layer-by-layer configuration, calculated in the framework of a
mean-field one-dimensional model, was benchmarked against published polarized
neutron reflectivity data. For an in-plane field applied at an angle with the easy axis, magnetometry shows that the magnetization
vanishes at H=0, then increases slowly with increasing . At a critical value
of , a finite jump in is observed for , while a
smooth increase of is found for . A dramatic
increase in the full width at half maximum of the magnetic susceptibility is
observed for . The phase diagram obtained from
micromagnetic calculations displays a first-order transition to a surface
spin-flop phase for low values, while the transition becomes continuous
for greater than a critical angle, . This is in fair agreement with the experimentally observed results.Comment: 24 pages, 7 figure
Electronic structure and optical properties of ZnX (X=O, S, Se, Te)
Electronic band structure and optical properties of zinc monochalcogenides
with zinc-blende- and wurtzite-type structures were studied using the ab initio
density functional method within the LDA, GGA, and LDA+U approaches.
Calculations of the optical spectra have been performed for the energy range
0-20 eV, with and without including spin-orbit coupling. Reflectivity,
absorption and extinction coefficients, and refractive index have been computed
from the imaginary part of the dielectric function using the Kramers--Kronig
transformations. A rigid shift of the calculated optical spectra is found to
provide a good first approximation to reproduce experimental observations for
almost all the zinc monochalcogenide phases considered. By inspection of the
calculated and experimentally determined band-gap values for the zinc
monochalcogenide series, the band gap of ZnO with zinc-blende structure has
been estimated.Comment: 17 pages, 10 figure
Conductance Quantization and Magnetoresistance in Magnetic Point Contacts
We theoretically study the electron transport through a magnetic point
contact (PC) with special attention to the effect of an atomic scale domain
wall (DW). The spin precession of a conduction electron is forbidden in such an
atomic scale DW and the sequence of quantized conductances depends on the
relative orientation of magnetizations between left and right electrodes. The
magnetoresistance is strongly enhanced for the narrow PC and oscillates with
the conductance.Comment: 4 pages, 4 figures, revised version with new figure
Human neural stem cell transplantation into the corpus callosum of Alzheimer’s mice
The hippocampus has been the target of stem cell transplantations in preclinical studies focused on Alzheimer’s disease, with results showing improvements in histological and behavioral outcomes. The corpus callosum is another structure that is affected early in Alzheimer’s disease. Therefore, we hypothesize that this structure is a novel target for human neural stem cell transplantation in transgenic Alzheimer’s disease mouse models. This study demonstrates the feasibility of targeting the corpus callosum and identifies an effective immunosuppression regimen for transplanted neural stem cell survival. These results support further preclinical development of the corpus callosum as a therapeutic target in Alzheimer’s disease.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138852/1/acn3443_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138852/2/acn3443.pd
Multi-component Transparent Conducting Oxides: Progress in Materials Modelling
Transparent conducting oxides (TCOs) play an essential role in modern
optoelectronic devices through their combination of electrical conductivity and
optical transparency. We review recent progress in our understanding of
multi-component TCOs formed from solid-solutions of ZnO, In2O3, Ga2O3 and
Al2O3, with a particular emphasis on the contributions of materials modelling,
primarily based on Density Functional Theory. In particular, we highlight three
major results from our work: (i) the fundamental principles governing the
crystal structures of multi-component oxide structures including (In2O3)(ZnO)n,
named IZO, and (In2O3)m(Ga2O3)l(ZnO)n, named IGZO; (ii) the relationship
between elemental composition and optical and electrical behaviour, including
valence band alignments; (iii) the high-performance of amorphous oxide
semiconductors. From these advances, the challenge of the rational design of
novel electroceramic materials is discussed.Comment: Part of a themed issue of Journal of Physics: Condensed Matter on
"Semiconducting Oxides". In Press (2011
A lattice in more than two Kac--Moody groups is arithmetic
Let be an irreducible lattice in a product of n infinite irreducible
complete Kac-Moody groups of simply laced type over finite fields. We show that
if n is at least 3, then each Kac-Moody groups is in fact a simple algebraic
group over a local field and is an arithmetic lattice. This relies on
the following alternative which is satisfied by any irreducible lattice
provided n is at least 2: either is an S-arithmetic (hence linear)
group, or it is not residually finite. In that case, it is even virtually
simple when the ground field is large enough.
More general CAT(0) groups are also considered throughout.Comment: Subsection 2.B was modified and an example was added ther
Wave: A New Family of Trapdoor One-Way Preimage Sampleable Functions Based on Codes
We present here a new family of trapdoor one-way Preimage Sampleable
Functions (PSF) based on codes, the Wave-PSF family. The trapdoor function is
one-way under two computational assumptions: the hardness of generic decoding
for high weights and the indistinguishability of generalized -codes.
Our proof follows the GPV strategy [GPV08]. By including rejection sampling, we
ensure the proper distribution for the trapdoor inverse output. The domain
sampling property of our family is ensured by using and proving a variant of
the left-over hash lemma. We instantiate the new Wave-PSF family with ternary
generalized -codes to design a "hash-and-sign" signature scheme which
achieves existential unforgeability under adaptive chosen message attacks
(EUF-CMA) in the random oracle model. For 128 bits of classical security,
signature sizes are in the order of 15 thousand bits, the public key size in
the order of 4 megabytes, and the rejection rate is limited to one rejection
every 10 to 12 signatures.Comment: arXiv admin note: text overlap with arXiv:1706.0806
Spectrum of Paediatric Lysosomal Storage Disorders in Oman
Objectives: The aim of this study was to look at the spectrum of paediatric lysosomal disorders in Oman. Lysosomal storage disorders (LSDs) are a heterogeneous group of inherited metabolic diseases. Few studies on the birth prevalence and prevalence of LSDs have been reported from the Arabian Peninsula. Methods: We studied 86 children with LSDs diagnosed over a period of nine years, from June 1998 to May 2007. Detailed clinical data, including age of onset, sex, age and mode of first presentation, and presence of consanguinity were collected. Results: Our data showed the combined birth prevalence for all LSDs in Oman to be around 1 in 4,700 live births. Sphingolipidoses was the most common group of disorder encountered (47.7%), followed by neuronal ceroid lipofuscinoses (NCL) (23.2%) and mucopolysaccharidoses (MPS) (23.2%). The proportion of consanguineous marriages in our series was found to be 87.5%. Conclusion: Our data represent the birth prevalence and clinicalspectrum of such disorders in Oman, one of the highly consanguineous societies in the Middle East.
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