29,055 research outputs found
Rough Approximate subgroups
Given a -rough definably amenable -rough approximate subgroup of a
group in some first-order structure, there is a type-definable subgroup
normalised by and contained in of bounded index in
Non-universality of artificial frustrated spin systems
Magnetic frustration effects in artificial kagome arrays of nanomagnets with
out-of-plane magnetization are investigated using Magnetic Force Microscopy and
Monte Carlo simulations. Experimental and theoretical results are compared to
those found for the artificial kagome spin ice, in which the nanomagnets have
in-plane magnetization. In contrast with what has been recently reported, we
demonstrate that long range (i.e. beyond nearest-neighbors) dipolar
interactions between the nanomagnets cannot be neglected when describing the
magnetic configurations observed after demagnetizing the arrays using a field
protocol. As a consequence, there are clear limits to any universality in the
behavior of these two artificial frustrated spin systems. We provide arguments
to explain why these two systems show striking similarities at first sight in
the development of pairwise spin correlations.Comment: 7 pages, 6 figure
Vacancy complexes in nonequilibrium germanium-tin semiconductors
Understanding the nature and behavior of vacancy-like defects in epitaxial
GeSn metastable alloys is crucial to elucidate the structural and
optoelectronic properties of these emerging semiconductors. The formation of
vacancies and their complexes is expected to be promoted by the relatively low
substrate temperature required for the epitaxial growth of GeSn layers with Sn
contents significantly above the equilibrium solubility of 1 at.%. These
defects can impact both the microstructure and charge carrier lifetime. Herein,
to identify the vacancy-related complexes and probe their evolution as a
function of Sn content, depth-profiled pulsed low-energy positron annihilation
lifetime spectroscopy and Doppler broadening spectroscopy were combined to
investigate GeSn epitaxial layers with Sn content in the 6.5-13.0 at.% range.
The samples were grown by chemical vapor deposition method at temperatures
between 300 and 330 {\deg}C. Regardless of the Sn content, all GeSn samples
showed the same depth-dependent increase in the positron annihilation line
broadening parameters, which confirmed the presence of open volume defects. The
measured average positron lifetimes were the highest (380-395 ps) in the region
near the surface and monotonically decrease across the analyzed thickness, but
remain above 350 ps. All GeSn layers exhibit lifetimes that are 85 to 110 ps
higher than the Ge reference layers. Surprisingly, these lifetimes were found
to decrease as Sn content increases in GeSn layers. These measurements indicate
that divacancies are the dominant defect in the as-grown GeSn layers. However,
their corresponding lifetime was found to be shorter than in epitaxial Ge thus
suggesting that the presence of Sn may alter the structure of divacancies.
Additionally, GeSn layers were found to also contain a small fraction of
vacancy clusters, which become less important as Sn content increases
Acute and chronic exercise in patients with HFrEF: Evidence of structural and functional plasticity and intact angiogenic signaling in skeletal muscle
This study examined the response to acute submaximal exercise and the effect of training in patients with heart failure with reduced ejection fraction (HFrEF). The acute angiogenic response to submaximal exercise in HFrEF after small muscle mass training is debated. The direct Fick method, with vascular pressures, was performed across the leg during knee-extensor exercise (KE) at 50% of maximum work rate (WRmax) in patients (n = 6) and controls (n = 6) and then after KE training in patients. Muscle biopsies facilitated the assessment of skeletal muscle structure and vascular endothelial growth factor (VEGF) mRNA levels. Prior to training, HFrEF exhibited significantly higher leg vascular resistance (LVR) (approximate to 15%) and significantly greater noradrenaline spillover (approximate to 385%). Apart from mitochondrial volume density, which was significantly lower (approximate to 22%) in HFrEF, initial skeletal muscle structure, including capillarity, was not different between groups. Resting VEGF mRNA levels, and the increase with exercise, was not different between patients and controls. Following training, LVR was no longer elevated and noradrenaline spillover was curtailed. Skeletal muscle capillarity increased with training, as assessed by capillary-to-fibre ratio (approximate to 13%) and number of capillaries around a fibre (N-CAF) (approximate to 19%). VEGF mRNA was now not significantly increased by acute exercise. Muscle fibre cross-sectional area and percentage area of type I fibres both increased significantly with training (approximate to 18% and approximate to 21%, respectively), while the percentage area of type II fibres fell significantly (approximate to 11%), and mitochondrial volume density now exceeded that of controls. These data reveal structural and functional plasticity and appropriate angiogenic signalling in skeletal muscle of HFrEF patients
Broadband multi-wavelength campaign on PKS 2005-489
The spectral energy distribution (SED) of high-frequency peaked BL Lac
objects (HBL) is characterized by two peaks: one in the UV-X-ray and one in the
GeV-TeV regime. An interesting object for analyzing these broadband
characteristics is PKS 2005-489, which in 2004 showed the softest TeV spectrum
ever measured. In 2009, a multi-wavelength campaign has been conducted with,
for the first time, simultaneous observations by H.E.S.S. (TeV), Fermi/LAT
(GeV), RXTE (keV), Swift (keV, UV, optical) and ATOM (optical) to cover the two
peaks of the SED. During this campaign PKS 2005-489 underwent a high state in
all wavebands which gives the opportunity to study in detail the emission
processes of a high state of this interesting HBL.Comment: 2009 Fermi Symposium; eConf Proceedings C09112
Systematic Study of Two-Pion Production in NN Collisions -- from Single-Baryon to Di-Baryon Excitations
The two-pion production in nucleon-nucleon collisions has been studied by
exclusive and kinematically complete experiments from threshold up to =
1.36 GeV at CELSIUS-WASA. At near-threshold energies the total and differential
distributions for the and channels are dominated by
Roper excitation and its decay into and channels. At beam
energies 1.1 GeV the excitation governs the two-pion
production process. In the channel evidence is found for the
excitation of a higher-lying I=3/2 resonance, favorably the . The
isovector fusion processes leading to the deuteron and to quasi-stable He,
respectively, %with the production of an isovector pion-pair exhibit no or only
a modest ABC-effect, {\it i.e.} low-mass enhancement in the -invariant
mass spectrum, and can be described by conventional -channel
excitation. On the other hand, the isoscalar fusion process to the deuteron
%with the production of an isoscalar pion-pair exhibits a dramatic ABC-effect
correlated with a narrow resonance-like energy dependence in the total cross
section with a width of only 50 MeV and situated at a mass 90 MeV below the
mass.Comment: Proceedings HADRON0
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