2,174 research outputs found
Nonfactorizable decay and QCD factorization
We study the unexpectedly large rate for the factorization-forbidden decay
within the QCD factorization approach. We use a non-zero
gluon mass to regularize the infrared divergences in vertex corrections. The
end-point singularities arising from spectator corrections are regularized and
carefully estimated by the off-shellness of quarks. We find that the
contributions arising from the vertex and leading-twist spectator corrections
are numerically small, and the twist-3 spectator contribution with chiral
enhancement and linear end-point singularity becomes dominant. With reasonable
choices for the parameters, the branching ratio for decay is
estimated to be in the range , which is compatible with
the Belle and BaBar data.Comment: Appendix added; it is emphasized that in the dominant twist-3
spectator corrections the end-point singularity contributions may be
estimated by the off-shellness of the charm quark (by the binding energy in
charmonium) and the gluon (by the transverse momentum of the light quark in
the kaon
Towards Efficient Data Valuation Based on the Shapley Value
"How much is my data worth?" is an increasingly common question posed by
organizations and individuals alike. An answer to this question could allow,
for instance, fairly distributing profits among multiple data contributors and
determining prospective compensation when data breaches happen. In this paper,
we study the problem of data valuation by utilizing the Shapley value, a
popular notion of value which originated in coopoerative game theory. The
Shapley value defines a unique payoff scheme that satisfies many desiderata for
the notion of data value. However, the Shapley value often requires exponential
time to compute. To meet this challenge, we propose a repertoire of efficient
algorithms for approximating the Shapley value. We also demonstrate the value
of each training instance for various benchmark datasets
Double-loop sliding mode control of reentry hypersonic vehicle with RCS
In order to solve the problem of insufficient aerodynamic moment caused by thin air in the re-entry stage of hypersonic vehicle, this paper establishes an attitude angle model of hypersonic vehicle with reaction control system (RCS), and derives its affine linear model to decoupled the internal and external loop. According to the dead zone and saturation characteristics of RCS thruster, a control method to convert continuous moment into discrete switching instruction using pulse width modulation (PWM) is proposed. Since the number of thrusters is usually redundant, the installation matrix of thrusters in the body coordinate is established, and the command moment is coordinately distributed to the individual thrusters. Then a double-loop sliding mode controller (DSMC) is designed to achieve attitude stability and trajectory tracking. Finally, the simulation results show that DSMC has higher maneuverability, fewer thruster switches and stronger robustness to interference
Size dependent electric voltage-controlled magnetic anisotropy in multiferroic heterostructures: Interface-charge and strain co-mediated magnetoelectric coupling
We present a phenomenological scheme to study the size-dependent electric
voltage-controlled magnetic anisotropy in ferromagnetic (FM)/ferroelectric (FE)
heterostructures. The FM layers are either metallic Fe(001), Ni(001), Co(0001),
or half-metallic (La, Sr)MnO3 films. Two magnetoelectric mechanisms, i.e.,
interface-charge and strain-mediated couplings, are considered. We show that
the interface-charge mediated coupling is the main mechanism for the
magnetoelectic coupling when the FM film thickness is below a certain
transition thickness dtr while the strain-mediated coupling dominates above
dtr.Comment: 10 pages, 4 figure
A fluidic platform for mobility evaluation of zebrafish with gene deficiency
IntroductionZebrafish is a suitable animal model for molecular genetic tests and drug discovery due to its characteristics including optical transparency, genetic manipulability, genetic similarity to humans, and cost-effectiveness. Mobility of the zebrafish reflects pathological conditions leading to brain disorders, disrupted motor functions, and sensitivity to environmental challenges. However, it remains technologically challenging to quantitively assess zebrafish's mobility in a flowing environment and simultaneously monitor cellular behavior in vivo.MethodsWe herein developed a facile fluidic device using mechanical vibration to controllably generate various flow patterns in a droplet housing single zebrafish, which mimics its dynamically flowing habitats.ResultsWe observe that in the four recirculating flow patterns, there are two equilibrium stagnation positions for zebrafish constrained in the droplet, i.e., the “source” with the outward flow and the “sink” with the inward flow. Wild-type zebrafish, whose mobility remains intact, tend to swim against the flow and fight to stay at the source point. A slight deviation from streamline leads to an increased torque pushing the zebrafish further away, whereas zebrafish with motor neuron dysfunction caused by lipin-1 deficiency are forced to stay in the “sink,” where both their head and tail align with the flow direction. Deviation angle from the source point can, therefore, be used to quantify the mobility of zebrafish under flowing environmental conditions. Moreover, in a droplet of comparable size, single zebrafish can be effectively restrained for high-resolution imaging.ConclusionUsing the proposed methodology, zebrafish mobility reflecting pathological symptoms can be quantitively investigated and directly linked to cellular behavior in vivo
GlnR-Mediated Regulation of Short-Chain Fatty Acid Assimilation in Mycobacterium smegmatis
Assimilation of short-chain fatty acids (SCFAs) plays an important role in the survival and lipid biosynthesis of Mycobacteria. However, regulation of this process has not been thoroughly described. In the present work, we demonstrate that GlnR as a well-known nitrogen-sensing regulator transcriptionally modulates the AMP-forming propionyl-CoA synthetase (MsPrpE), and acetyl-CoA synthetases (MsAcs) is associated with SCFAs assimilation in Mycobacterium smegmatis, a model Mycobacterium. GlnR can directly activate the expression of MsprpE and Msacs by binding to their promoter regions based upon sensed nitrogen starvation in the host. Moreover, GlnR can activate the expression of lysine acetyltransferase encoding Mspat, which significantly decreases the activity of MsPrpE and MsAcs through increased acylation. Next, growth curves and resazurin assay show that GlnR can further regulate the growth of M. smegmatis on different SCFAs to control the viability. These results demonstrate that GlnR-mediated regulation of SCFA assimilation in response to the change of nitrogen signal serves to control the survival of M. smegmatis. These findings provide insights into the survival and nutrient utilization mechanisms of Mycobacteria in their host, which may enable new strategies in drug discovery for the control of tuberculosis
and meson exclusive decay in QCD factorization
Belle has observed surprisingly copious production of in
meson decay , of which the rate is comparable to that of
. We study this puzzling process in the QCD factorization
approach with the effect of S-D mixing considered. We find that the soft
scattering effects in the spectator interactions play an essential role. With a
proper parametrization for the higher twist soft end-point singularities
associated with kaon, and with the S-D mixing angle , the
calculated decay rates can be close to the data. Implications of these soft
spectator effects to other charmonium production in exclusive decays are
also emphasized.Comment: journal versio
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