19,781 research outputs found
Evolution of InAs branches in InAs/GaAs nanowire heterostructures
Branched nanowireheterostructures of InAsâGaAs were observed during Au-assisted growth of InAs on GaAsnanowires. The evolution of these branches has been determined through detailed electron microscopy characterization with the following sequence: (1) in the initial stage of InAsgrowth, the Au droplet is observed to slide down the side of the GaAsnanowire, (2) the downward movement of Aunanoparticle later terminates when the nanoparticle encounters InAsgrowing radially on the GaAsnanowire sidewalls, and (3) with further supply of In and As vapor reactants, the Aunanoparticles assist the formation of InAs branches with a well-defined orientation relationship with GaAsâInAs core/shell stems. We anticipate that these observations advance the understanding of the kink formation in axial nanowireheterostructures.The Australian Research Council is acknowledged for
the financial support of this project. One of the authors
M.P. acknowledges the support of an International Postgraduate
Research Scholarship
The nature of Ho magnetism in multiferroic HoMnO3
Using x-ray resonant magnetic scattering and x-ray magnetic circular
dichroism, techniques that are element specific, we have elucidated the role of
Ho3+ in multiferroic HoMnO3. In zero field, Ho3+ orders antiferromagnetically
with moments aligned along the hexagonal c direction below 40 K, and undergoes
a transition to another magnetic structure below 4.5 K. In applied electric
fields of up to 1x10^7 V/m, the magnetic structure of Ho3+ remains unchanged.Comment: 4 pages, 3 figures Manuscript accepted for publication in Phys. Rev.
Lett. 200
Star Formation in Disk Galaxies. I. Formation and Evolution of Giant Molecular Clouds via Gravitational Instability and Cloud Collisions
We investigate the formation and evolution of giant molecular clouds (GMCs)
in a Milky-Way-like disk galaxy with a flat rotation curve. We perform a series
of 3D adaptive mesh refinement (AMR) numerical simulations that follow both the
global evolution on scales of ~20kpc and resolve down to scales ~<10pc with a
multiphase atomic interstellar medium (ISM). In this first study, we omit star
formation and feedback, and focus on the processes of gravitational instability
and cloud collisions and interactions. We define clouds as regions with
n_H>=100cm^-3 and track the evolution of individual clouds as they orbit
through the galaxy from their birth to their eventual destruction via merger or
via destructive collision with another cloud. After ~140Myr a large fraction of
the gas in the disk has fragmented into clouds with masses ~10^6 Msun and a
mass spectrum similar to that of Galactic GMCs. The disk settles into a quasi
steady state in which gravitational scattering of clouds keeps the disk near
the threshold of global gravitational instability. The cloud collision time is
found to be a small fraction, ~1/5, of the orbital time, and this is an
efficient mechanism to inject turbulence into the clouds. This helps to keep
clouds only moderately gravitationally bound, with virial parameters of order
unity. Many other observed GMC properties, such as mass surface density,
angular momentum, velocity dispersion, and vertical distribution, can be
accounted for in this simple model with no stellar feedback.Comment: 21 pages ApJ format, including 16 figures, accepted to Ap
Green Tea Polyphenol Epigallocatechin-3-Gallate Enhance Glycogen Synthesis and Inhibit Lipogenesis in Hepatocytes
The beneficial effects of green tea polyphenols (GTP) against metabolic syndrome and type 2 diabetes by suppressing appetite and nutrient absorption have been well reported. However the direct effects and mechanisms of GTP on glucose and lipid metabolis
Star Formation in Disk Galaxies. II. The Effect of Star Formation and Photoelectric Heating on the Formation and Evolution of Giant Molecular Clouds
We investigate the effect of star formation and diffuse photoelectric heating
on the properties of giant molecular clouds (GMCs) formed in high resolution
(~< 10 pc) global (~ 20 kpc) simulations of isolated Milky Way-type galaxy
disks. The clouds are formed through gravitational fragmentation and structures
with densities n_H>=100cm^-3 are identified as GMCs. Between 1000-1500 clouds
are created in the simulations with masses M > 10^5 Msolar and 180-240 with
masses M > 10^6 Msolar in agreement with estimates of the Milky Way's
population. We find that the effect of photoelectric heating is to suppress the
fragmentation of the ISM, resulting in a filamentary structure in the warm gas
surrounding clouds. This environment suppresses the formation of a retrograde
rotating cloud population, with 88% of the clouds rotating prograde with
respect to the galaxy after 300 Myr. The diffuse heating also reduces the
initial star formation rate, slowing the conversation of gas into stars. We
therefore conclude that the interstellar environment plays an important role in
the GMCs evolution. Our clouds live between 0-20 Myr with a high infant
mortality (t' < 3 Myr) due to cloud mergers and star formation. Other
properties, including distributions of mass, size and surface density agree
well with observations. Collisions between our clouds are common, occurring at
a rate of ~1/4 of the orbital period. It is not clear whether such collisions
trigger or suppress star formation at our current resolution. Our star
formation rate is a factor of 10 higher than observations in local galaxies.
This is likely due to the absence of localized feedback in our models.Comment: 25 pages. 18 figures. Accepted for publication in Ap
Antiresistin RNA oligonucleotide ameliorates diet-induced nonalcoholic fatty liver disease in mice through attenuating proinflammatory cytokines
© 2015 Yi Tan et al. The aim of this study was to determine whether inhibition of resistin by a synthetic antiresistin RNA (oligonucleotide) oligo ameliorates metabolic and histological abnormalities in nonalcoholic fatty liver disease (NAFLD) induced by high-fat diet (HFD) in mice. The antiresistin RNA oligo and a scrambled control oligo (25 mg/kg of body weight) were i.p. injected to HFD mice. Serum metabolic parameters and hepatic enzymes were measured after 4-week treatment. The treatment significantly reduced epididymal fat and attenuated the elevated serum resistin, cholesterol, triglycerides, glucose, and insulin with an improved glucose tolerance test. Antiresistin RNA oligo also normalized serum AST and ALT levels with improved pathohistology of NAFLD. Immunoblotting and qRT-PCR revealed that decreased protein and mRNA expression of resistin in fat and liver tissues of the treated mice were associated with reduction of adipose TNF-α and IL-6 expression and secretion into circulation. mRNA and protein expression of hepatic phosphoenolpyruvate carboxykinase (PEPCK) and sterol regulatory element-binding protein-1c (SREBP-1c) were also significantly decreased in the treated mice. Our results suggest that resistin may exacerbate NAFLD in metabolic syndrome through upregulating inflammatory cytokines and hepatic PEPCK and SREBP-1c. Antiresistin RNA oligo ameliorated metabolic abnormalities and histopathology of NAFLD through attenuating proinflammatory cytokines
A Multi-Epoch Study of the Radio Continuum Emission of Orion Source I: Constraints on the Disk Evolution of a Massive YSO and the Dynamical History of Orion BN/KL
We present new 7mm continuum observations of Orion BN/KL with the VLA. We
resolve the emission from the protostar radio Source I and BN at several
epochs. Source I is highly elongated NW-SE, and remarkably stable in flux
density, position angle, and overall morphology over nearly a decade. This
favors the extended emission component arising from an ionized disk rather than
a jet. We have measured the proper motions of Source I and BN for the first
time at 43 GHz. We confirm that both sources are moving at high speed (12 and
26 km/s, respectively) approximately in opposite directions, as previously
inferred from measurements at lower frequencies. We discuss dynamical scenarios
that can explain the large motions of both BN and Source I and the presence of
disks around both. Our new measurements support the hypothesis that a close
(~50 AU) dynamical interaction occurred around 500 years ago between Source I
and BN as proposed by Gomez et al. From the dynamics of encounter we argue that
Source I today is likely to be a binary with a total mass on the order of 20
Msun, and that it probably existed as a softer binary before the close
encounter. This enables preservation of the original accretion disk, though
truncated to its present radius of ~50 AU. N-body numerical simulations show
that the dynamical interaction between a binary of 20 Msun total mass (I) and a
single star of 10 Msun mass (BN) may lead to the ejection of both and binary
hardening. The gravitational energy released in the process would be large
enough to power the wide-angle flow traced by H2 and CO emission in the BN/KL
nebula. Assuming the proposed dynamical history is correct, the smaller mass
for Source I recently estimated from SiO maser dynamics (>7 Msun) by Matthews
et al., suggests that non-gravitational forces (e.g. magnetic) must play an
important role in the circumstellar gas dynamics.Comment: 17 pages, 7 figures, 4 tables, accepted by Ap
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The interplay between thermodynamics and kinetics in the solid-state synthesis of layered oxides.
In the synthesis of inorganic materials, reactions often yield non-equilibrium kinetic byproducts instead of the thermodynamic equilibrium phase. Understanding the competition between thermodynamics and kinetics is a fundamental step towards the rational synthesis of target materials. Here, we use in situ synchrotron X-ray diffraction to investigate the multistage crystallization pathways of the important two-layer (P2) sodium oxides Na0.67MO2 (Mâ=âCo, Mn). We observe a series of fast non-equilibrium phase transformations through metastable three-layer O3, O3' and P3 phases before formation of the equilibrium two-layer P2 polymorph. We present a theoretical framework to rationalize the observed phase progression, demonstrating that even though P2 is the equilibrium phase, compositionally unconstrained reactions between powder precursors favour the formation of non-equilibrium three-layered intermediates. These insights can guide the choice of precursors and parameters employed in the solid-state synthesis of ceramic materials, and constitutes a step forward in unravelling the complex interplay between thermodynamics and kinetics during materials synthesis
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