2,975 research outputs found
Analysis of Two-Body Decays of Charmed Baryons Using the Quark-Diagram Scheme
We give a general formulation of the quark-diagram scheme for the nonleptonic
weak decays of baryons. We apply it to all the decays of the antitriplet and
sextet charmed baryons and express their decay amplitudes in terms of the
quark-diagram amplitudes. We have also given parametrizations for the effects
of final-state interactions. For SU(3) violation effects, we only parametrize
those in the horizontal -loop quark diagrams whose contributions are solely
due to SU(3)-violation effects. In the absence of all these effects, there are
many relations among various decay modes. Some of the relations are valid even
in the presence of final-state interactions when each decay amplitude in the
relation contains only a single phase shift. All these relations provide useful
frameworks to compare with future experiments and to find out the effects of
final-state interactions and SU(3) symmetry violations.Comment: 28 pages, 20 Tables in landscape form, 4 figures. Main changes are:
(i) some errors in the Tables and in the relations between the quark-diagram
amplitudes of this paper and those of Ref.[10] are corrected, (ii)
improvements are made in the presentation so that comparisons with previous
works and what have been done to include SU(3) breaking and final-state
interactions are more clearly stated; to appear in the Physical Review
Functional changes in motor endplates of the target muscle after amputation of the C7 nerve root
There are limited data on structural and functional changes in motor endplates and
muscle fibers in the target muscle following amputation of the 7th cervical nerve root, a
transplantation-related procedure in surgical treatment in the case of avulsions of the brachial
plexus roots. We examined functional changes in these structures using stimulated singlefiber electromyography (sSF-EMG) in an animal model. Unilateral amputation of the 7th
cervical nerve root was performed in 36 male rats, and the m. triceps brachii muscle was
tested by sSF-EMG at different time points. We observed significant differences in the jitter
(mean consecutive difference, MCD, of the latencies between adjacent muscle fibers) at postamputation weeks 1, 2, 4, and 6. The post-operation fiber density (FD) values within the
zone of effective stimulation also gradually increased. At post-amputation weeks 8 and 12,
the jitter values returned to normal levels, whereas FD values continued to rise. Our results
indicate that the post-amputation compensatory processes in the target muscles of the 7th
cervical nerve root are completed at 9-12 weeks after amputation.Дані щодо структурних та функціональних змін у моторних
кінцевих пластинках та м’язових волокнах м’яза-цілі після ампутації сьомого шийного нервового корінця (процедури в рамках трансплантаційного хірургічного лікування
наслідків відриву корінців брахіального сплетіння) поки
що обмежені. Ми досліджували функціональні зміни в згаданих структурах, використовуючи методику стимуляційної „одноволоконної” електроміографії в умовах експериментальної моделі на тваринах. Унілатеральну ампутацію
сьомого цервікального нервового корінця було виконано на
36 щурах-самцях, і триголові м’язи плеча тестувалися за допомогою згаданої ЕМГ-методики в різні часові інтервали.
Ми виявили істотні відмінності середніх варіацій („дрижання”, jitter, різниць між послідовними величинами) латентних періодів, характерних для прилеглих одне до одного
м’язових волокон, у перший, другий, четвертий та шостий
тижні після операційного періоду. В цей час щільність волокон у зоні ефективної стимуляції також поступово зростала.
На восьмий–12-й тижні післяопераційного періоду значення варіацій („дрижання”) поверталися до нормальних, тоді
як значення щільності активованих волокон продовжували
зростати. Наші результати свідчать про те, що післяампутаційні компенсаторні процеси в м’язах-цілях волокон нервового корінця С7 завершуються через дев’ять–12 тижнів після ампутації останнього
Nonleptonic Weak Decays of Bottom Baryons
Cabibbo-allowed two-body hadronic weak decays of bottom baryons are analyzed.
Contrary to the charmed baryon sector, many channels of bottom baryon decays
proceed only through the external or internal W-emission diagrams. Moreover,
W-exchange is likely to be suppressed in the bottom baryon sector.
Consequently, the factorization approach suffices to describe most of the
Cabibbo-allowed bottom baryon decays. We use the nonrelativistic quark model to
evaluate heavy-to-heavy and heavy-to-light baryon form factors at zero recoil.
When applied to the heavy quark limit, the quark model results do satisfy all
the constraints imposed by heavy quark symmetry. The decay rates and up-down
asymmetries for bottom baryons decaying into and
are calculated. It is found that the up-down asymmetry is negative except for
decay and for decay modes with in the final
state. The prediction for
is consistent with the recent CDF measurement. We also present
estimates for decays and compare with various model
calculations.Comment: 24 pages, to appear in Phys. Rev. Uncertainties with form factor q^2
dependence are discusse
On the flow-level stability of data networks without congestion control: the case of linear networks and upstream trees
In this paper, flow models of networks without congestion control are
considered. Users generate data transfers according to some Poisson processes
and transmit corresponding packet at a fixed rate equal to their access rate
until the entire document is received at the destination; some erasure codes
are used to make the transmission robust to packet losses. We study the
stability of the stochastic process representing the number of active flows in
two particular cases: linear networks and upstream trees. For the case of
linear networks, we notably use fluid limits and an interesting phenomenon of
"time scale separation" occurs. Bounds on the stability region of linear
networks are given. For the case of upstream trees, underlying monotonic
properties are used. Finally, the asymptotic stability of those processes is
analyzed when the access rate of the users decreases to 0. An appropriate
scaling is introduced and used to prove that the stability region of those
networks is asymptotically maximized
On the Heisenberg invariance and the Elliptic Poisson tensors
We study different algebraic and geometric properties of Heisenberg invariant
Poisson polynomial quadratic algebras. We show that these algebras are
unimodular. The elliptic Sklyanin-Odesskii-Feigin Poisson algebras
are the main important example. We classify all quadratic
invariant Poisson tensors on with and show that
for they coincide with the elliptic Sklyanin-Odesskii-Feigin Poisson
algebras or with their certain degenerations.Comment: 14 pages, no figures, minor revision, typos correcte
Manganese-enhanced magnetic resonance imaging depicts brain activity in models of acute and chronic pain: a new window to study experimental spontaneous pain?
Application of functional imaging techniques to animal models is vital to understand pain mechanisms, but is often confounded by the need to limit movement artefacts with anaesthesia, and a focus on evoked responses rather than clinically relevant spontaneous pain and related hyperalgesia. The aim of the present study was to investigate the potential of manganese-enhanced magnetic resonance imaging (MEMRI) to measure neural responses during on-going pain that underpins hyperalgesia in pre-clinical models of nociception. As a proof of concept that MEMRI is sensitive to the neural activity of spontaneous, intermittent behaviour, we studied a separate positive control group undergoing a voluntary running wheel experiment.
In the pain models, pain behaviour (weight bearing asymmetry and hindpaw withdrawal thresholds (PWTs)) was measured at baseline and following either intra-articular injection of nerve growth factor (NGF, 10 µg/50 µl; acute pain model, n=4 rats per group), or the chondrocyte toxin monosodium iodoacetate (MIA, 1 mg/50 µl; chronic model, n=8 rats per group), or control injection. Separate groups of rats underwent a voluntary wheel running protocol (n=8 rats per group). Rats were administered with paramagnetic ion Mn2+ as soluble MnCl2 over seven days (subcutaneous osmotic pump) to allow cumulative activity-dependent neural accumulation in the models of pain, or over a period of running. T1-weighted MR imaging at 7 T was performed under isoflurane anaesthesia using a receive-only rat head coil in combination with a 72 mm volume coil for excitation.
The pain models resulted in weight bearing asymmetry (NGF: 20.0 ± 5.2%, MIA: 15 ± 3%), and a reduction in PWT in the MIA model (8.3 ± 1.5 g) on the final day of assessment before undergoing MR imaging. Voxel-wise and region-based analysis of MEMRI data did not identify group differences in T1 signal. However, MnCl2 accumulation in the VTA, right Ce amygdala, and left cingulate was negatively correlated with pain responses (greater differences in weight bearing), similarly MnCl2 accumulation was reduced in the VTA in line with hyperalgesia (lower PWTs), which suggests reduced regional activation as a result of the intensity and duration of pain experienced during the 7 days of MnCl2 exposure. Motor cortex T1-weighted signal increase was associated with the distance ran in the wheel running study, while no between group difference was seen. Our data suggest that on-going pain related signal changes identified using MEMRI offers a new window to study the neural underpinnings of spontaneous pain in rats
Thermodynamic properties of thin films of superfluid 3He-A
The pairing correlations in superfluid He-3 are strongly modified by
quasiparticle scattering off a surface or an interface. We present theoretical
results and predictions for the order parameter, the quasiparticle excitation
spectrum and the free energy for thin films of superfluid He-3. Both specular
and diffuse scattering by a substrate are considered, while the free surface is
assumed to be a perfectly reflecting specular boundary. The results are based
on self-consistent calculations of the order parameter and quasiparticle
excitation spectrum at zero pressure. We obtain new results for the phase
diagram, free energy, entropy and specific heat of thin films of superfluid
He-3.Comment: Replaced with an updated versio
Molecular localization of a ribosome-dependent ATPase on Escherichia coli ribosomes
We have previously isolated and described an Escherichia coli ribosome-bound ATPase, RbbA, that is required for protein synthesis in the presence of ATP, GTP and the elongation factors, EF-Tu and EF-G. The gene encoding RbbA, yhih, has been cloned and the deduced protein sequence harbors two ATP-motifs and one RNA-binding motif and is homologous to the fungal EF-3. Here, we describe the isolation and assay of a truncated form of the RbbA protein that is stable to overproduction and purification. Chemical protection results show that the truncated RbbA specifically protects nucleotide A937 on the 30S subunit of ribosomes, and the protected site occurs at the E-site where the tRNA is ejected upon A-site occupation. Other weakly protected bases in the region occur at or near the mRNA binding site. Using radiolabeled tRNAs, we study the stimulating effect of this truncated RbbA on the binding and release of different tRNAs bound to the (aminoacyl) A-, (peptidyl) P- and (exit) E-sites of 70S ribosomes. The combined data suggest plausible mechanisms for the function of RbbA in translation
The effect of the spin-orbit interaction on the band gap of half-metals
The spin-orbit interaction can cause a nonvanishing density of states (DOS)
within the minority-spin band gap of half-metals around the Fermi level. We
examine the magnitude of the effect in Heusler alloys, zinc-blende half metals
and diluted magnetic semiconductors, using first-principles calculations. We
find that the ratio of spin-down to spin-up DOS at the Fermi level can range
from below 1% (e.g. 0.5% for NiMnSb) over several percents (4.2% for (Ga,Mn)As)
to 13% for MnBi.Comment: 5 pages, 3 figure
Exploring morphological correlations among H2CO, 12CO, MSX and continuum mappings
There are relatively few H2CO mappings of large-area giant molecular cloud
(GMCs). H2CO absorption lines are good tracers for low-temperature molecular
clouds towards star formation regions. Thus, the aim of the study was to
identify H2CO distributions in ambient molecular clouds. We investigated
morphologic relations among 6-cm continuum brightness temperature (CBT) data
and H2CO (111-110; Nanshan 25-m radio telescope), 12CO (1--0; 1.2-m CfA
telescope) and midcourse space experiment (MSX) data, and considered the impact
of background components on foreground clouds. We report simultaneous 6-cm H2CO
absorption lines and H110\alpha radio recombination line observations and give
several large-area mappings at 4.8 GHz toward W49 (50'\times50'), W3
(70'\times90'), DR21/W75 (60'\times90') and NGC2024/NGC2023 (50'\times100')
GMCs. By superimposing H2CO and 12CO contours onto the MSX color map, we can
compare correlations. The resolution for H2CO, 12CO and MSX data was about 10',
8' and 18.3", respectively. Comparison of H2CO and 12CO contours, 8.28-\mu m
MSX colorscale and CBT data revealed great morphological correlation in the
large area, although there are some discrepancies between 12CO and H2CO peaks
in small areas. The NGC2024/NGC2023 GMC is a large area of HII regions with a
high CBT, but a H2CO cloud to the north is possible against the cosmic
microwave background. A statistical diagram shows that 85.21% of H2CO
absorption lines are distributed in the intensity range from -1.0 to 0 Jy and
the \Delta V range from 1.206 to 5 km/s.Comment: 18 pages, 22 figures, 5 tables. Accepted to be published in
Astrophysics and Space Scienc
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