2,315 research outputs found
Evolution of Non-Equilibrium Profile in Adsorbate Layer under Compressive Strain
We investigate the time evolution of an initial step profile separating a
bare substrate region from the rest of the compressively strained adsorbate
layer near a commensurate to incommensurate transition. The rate of profile
evolution as a function of the mismatch, coverage and the strength of the
substrate potential are determined by Brownian molecular dynamics simulations.
We find that the results are qualitatively similar to those observed for the
Pb/Si(111) system. The anomalously fast time evolution and sharpness of the
non-equilibrium profile can be understood through the domain wall creation at
the boundary and its subsequent diffusion into the interior of the adsorbate
layer.Comment: 6 pages, 7 figures, Tribology Letter
Precision Localization of Lipid-Based Nanoparticles by Dual-Fluorescent Labeling for Accurate and High-Resolution Imaging in Living Cells
In nanomedicine, lipid-based nanoparticles (NPs) such as liposomes (LPs) have established an important position. Precise delineation of NP interaction with cells and detailed characterization of activity are becoming essential, which mainly rely on labeling with lipophilic fluorescent molecules and assuming stable association with NPs. However, because of label separation from NPs in (biological) media, or when processed by cells, fluorescence-based detection of an NP incorporating a single label may not necessarily indicate the actual presence of an NP but may be from the dissociated label, rendering results unreliable. Herein, flow cytometry and confocal microscopy are employed to demonstrate that to verify the localization of LPs in a cell with perfect accuracy, dual-labeling, and contemporaneous detection of both fluorescent signals in one pixel are required. This is combined with size exclusion chromatography (SEC) and mass spectrometry measurements to indicate factors involved in label dissociation, which helps to understand the possible conditions of dissociated label and NP. It is shown that determining label colocalization with, and label dissociation from, dual-labeled NPs are needed to provide accurate spatiotemporal insight into targeting destination (colocalized signals) and disintegration (separated signals) of NPs during intracellular processing and in studying payload delivery with precision in nanomedicine.</p
Some (further) Comments on the Theta(1540) Pentaquark
Additional broader I=0 states in the KN channel near (1540) are
expected in many models, making the absence of any signature in the
K-deuteron scattering data even more puzzling.
In an ideal "three-body" picture the is viewed as two compact
ud(1)ud(2) color diquarks and an quark. A "QCD-type"
inequality involving , the mass of the L=1 excitation and that of a new I=0 tetraquark vector meson then follows.
The inequality suggests a very light new vector meson, and is violated.
We note that "associated production" of the pentaquark with another
quadriquark or anti-pentaquark may be favored. This along with some estimates
of the actual production cross sections suggest that the can be found
in BaBar or Belle e-e colliders.Comment: 6 page
Radiative Corrections to Double Dalitz Decays: Effects on Invariant Mass Distributions and Angular Correlations
We review the theory of meson decays to two lepton pairs, including the cases
of identical as well as non-identical leptons, as well as CP-conserving and
CP-violating couplings. A complete lowest-order calculation of QED radiative
corrections to these decays is discussed, and comparisons of predicted rates
and kinematic distributions between tree-level and one-loop-corrected
calculations are presented for both pi-zero and K-zero decays.Comment: 25 pages, 18 figures, added figures and commentar
Manifestation of photonic band structure in small clusters of spherical particles
We study the formation of the photonic band structure in small clusters of
dielectric spheres. The first signs of the band structure, an attribute of an
infinite crystal, can appear for clusters of 5 particles. Density of resonant
states of a cluster of 32 spheres may exhibit a well defined structure similar
to the density of electromagnetic states of the infinite photonic crystal. The
resonant mode structure of finite-size aggregates is shown to be insensitive to
random displacements of particles off the perfect lattice positions as large as
half-radius of the particle. The results were obtained by an efficient
numerical method, which relates the density of resonant states to the the
scattering coefficients of the electromagnetic scattering problem. Generalized
multisphere Mie (GMM) solution was used to obtain scattering matrix elements.
These results are important to miniature photonic crystal design as well as
understanding of light localization in dense random media.Comment: 4 pages, 2 figure
Isocurvature perturbations in extra radiation
Recent cosmological observations, including measurements of the CMB
anisotropy and the primordial helium abundance, indicate the existence of an
extra radiation component in the Universe beyond the standard three neutrino
species. In this paper we explore the possibility that the extra radiation has
isocurvatrue fluctuations. A general formalism to evaluate isocurvature
perturbations in the extra radiation is provided in the mixed inflaton-curvaton
system, where the extra radiation is produced by the decay of both scalar
fields. We also derive constraints on the abundance of the extra radiation and
the amount of its isocurvature perturbation. Current observational data favors
the existence of an extra radiation component, but does not indicate its having
isocurvature perturbation. These constraints are applied to some particle
physics motivated models. If future observations detect isocurvature
perturbations in the extra radiation, it will give us a hint to the origin of
the extra radiation.Comment: 41 pages, 8 figures; version accepted for publication in JCA
Mechanisms of repeat-associated non-AUG translation in neurological microsatellite expansion disorders
Repeat-associated non-AUG (RAN) translation was discovered in 2011 in spinocerebellar ataxia type 8 (SCA8) and myotonic dystrophy type 1 (DM1). This non-canonical form of translation occurs in all reading frames from both coding and non-coding regions of sense and antisense transcripts carrying expansions of trinucleotide to hexanucleotide repeat sequences. RAN translation has since been reported in 7 of the 53 known microsatellite expansion disorders which mainly present with neurodegenerative features. RAN translation leads to the biosynthesis of low-complexity polymeric repeat proteins with aggregating and cytotoxic properties. However, the molecular mechanisms and protein factors involved in assembling functional ribosomes in absence of canonical AUG start codons remain poorly characterised while secondary repeat RNA structures play key roles in initiating RAN translation. Here, we briefly review the repeat expansion disorders, their complex pathogenesis and the mechanisms of physiological translation initiation together with the known factors involved in RAN translation. Finally, we discuss research challenges surrounding the understanding of pathogenesis and future directions that may provide opportunities for the development of novel therapeutic approaches for this group of incurable neurodegenerative diseases
Unusual magnetic relaxation behavior in La0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3
We have carried out a systematic magnetic relaxation study, measured after
applying and switching off a 5 T magnetic field to polycrystalline samples of
La0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3. The long time logarithmic relaxation rate
(LTLRR), decreased from 10 K to 150 K and increased from 150 K to 195 K in
La0.5Ca0.5MnO3. This change in behavior was found to be related to the complete
suppression of the antiferromagnetic phase above 150 K and in the presence of a
5 T magnetic field. At 195 K, the magnetization first decreased, and after a
few minutes increased slowly as a function of time. Moreover, between 200 K and
245 K, the magnetization increased throughout the measured time span. The
change in the slope of the curves, from negative to positive at about 200 K was
found to be related to the suppression of antiferromagnetic fluctuations in
small magnetic fields. A similar temperature dependence of the LTLRR was found
for the Nd0.5Sr0.5MnO3 sample. However, the temperature where the LTLRR reached
the minimum in Nd0.5Sr0.5MnO3 was lower than that of La0.5Ca0.5MnO3. This
result agrees with the stronger ferromagnetic interactions that exist in
Nd0.5Sr0.5MnO3 in comparison to La0.5Ca0.5MnO3. The above measurements
suggested that the general temperature dependence of the LTLRR and the
underlying physics were mainly independent of the particular charge ordering
system considered. All relaxation curves could be fitted using a logarithmic
law at long times. This slow relaxation was attributed to the coexistence of
ferromagnetic and antiferromagnetic interactions between Mn ions, which
produced a distribution of energy barriers.Comment: Accepted to PRB as a regular article, 10 figures, Scheduled Issue: 01
June 200
Relativistic Mass Ejecta from Phase-transition-induced Collapse of Neutron Stars
We study the dynamical evolution of a phase-transition-induced collapse
neutron star to a hybrid star, which consists of a mixture of hadronic matter
and strange quark matter. The collapse is triggered by a sudden change of
equation of state, which result in a large amplitude stellar oscillation. The
evolution of the system is simulated by using a 3D Newtonian hydrodynamic code
with a high resolution shock capture scheme. We find that both the temperature
and the density at the neutrinosphere are oscillating with acoustic frequency.
However, they are nearly 180 out of phase. Consequently, extremely
intense, pulsating neutrino/antineutrino fluxes will be emitted periodically.
Since the energy and density of neutrinos at the peaks of the pulsating fluxes
are much higher than the non-oscillating case, the electron/positron pair
creation rate can be enhanced dramatically. Some mass layers on the stellar
surface can be ejected by absorbing energy of neutrinos and pairs. These mass
ejecta can be further accelerated to relativistic speeds by absorbing
electron/positron pairs, created by the neutrino and antineutrino annihilation
outside the stellar surface. The possible connection between this process and
the cosmological Gamma-ray Bursts is discussed.Comment: 40 pages, 11 figures, accepted for publication in JCA
- …