19,541 research outputs found
Azimuthal distributions of radial momentum and velocity in relativistic heavy ion collisions
Azimuthal distributions of radial (transverse) momentum, mean radial
momentum, and mean radial velocity of final state particles are suggested for
relativistic heavy ion collisions. Using transport model AMPT with string
melting, these distributions for Au + Au collisions at 200 GeV are presented
and studied. It is demonstrated that the distribution of total radial momentum
is more sensitive to the anisotropic expansion, as the anisotropies of final
state particles and their associated transverse momentums are both counted in
the measure. The mean radial velocity distribution is compared with the radial
{\deg}ow velocity. The thermal motion contributes an isotropic constant to mean
radial velocity
Feedback noncausal model predictive control of wave energy converters
In this paper, a novel feedback noncausal model predictive control (MPC) strategy for sea wave energy converters (WECs) is proposed, where the wave prediction information can be explicitly incorporated into the MPC strategy to improve the WEC control performance. The main novelties of the MPC strategy proposed in this paper include: (i) the recursive feasibility and robust constraints satisfaction are guaranteed without a significant increase in the computational burden; (ii) the information of short-term wave prediction is incorporated into the feedback noncausal MPC method to maximise the potential energy output; (iii) the sea condition for the WEC to safely operate in can be explicitly calculated. The proposed feedback noncausal MPC algorithm can also be extended to a wide class of control design problems, especially to the energy maximisation problems with constraints to be satisfied and subject to persistent but predictable disturbances. Numerical simulations are provided to show the efficacy of the proposed feedback noncausal MPC
Two-particle azimuthal angle correlations and azimuthal charge balance function in relativistic heavy ion collisions
The two-particle azimuthal angle correlation (TPAC) and azimuthal charge balance function (ACBF) are used to study the anisotropic expansion in relativistic heavy ion collisions. It is demonstrated by the relativistic quantum molecular dynamics (RQMD) model and a multi-phase transport (AMPT) model that the small-angle correlation in TPAC indeed presents anisotropic expansion, and the large-angle (or back-to-back) correlation is mainly due to global momentum conservations. The AMPT model reproduces the observed TPAC, but the RQMD model fails to reproduce the strong correlations in both small and large azimuthal angles. The width of ACBF from RQMD and AMPT models decreases from peripheral to central collisions, consistent with experimental data, but in contrast to the expectation from thermal model calculations. The ACBF is insensitive to anisotropic expansion. It is a probe for the mechanism of hadronization, similar to the charge balance function in rapidity
Numerical and physical simulation of rapid microstructural evolution of gas atomised Ni superalloy powders
The rapid microstructural evolution of gas atomised Ni superalloy powder compacts over timescales of a few seconds was studied using a Gleeble 3500 thermomechanical simulator, finite element based numerical model and electron microscopy. The study found that the microstructural changes were governed by the characteristic temperatures of the alloy. At a temperature below the γ' solvus, the powders maintained dendritic structures. Above the γ' solvus temperature but in the solid-state, rapid grain spheroidisation and coarsening occurred, although the fine-scale microstructures were largely retained. Once the incipient melting temperature of the alloy was exceeded, microstructural change was rapid, and when the temperature was increased into the solid + liquid state, the powder compact partially melted and then re-solidified with no trace of the original structures, despite the fast timescales. The study reveals the relationship between short, severe thermal excursions and microstructural evolution in powder processed components, and gives guidance on the upper limit of temperature and time for powder-based processes if desirable fine-scale features of powders are to be preserved
The Study of Noncollectivity by the Forward-Backward Multiplicity Correlation Function
We propose a forward-backward multiplicity correlation function ,
which is experimentally accessible, to measure the noncollectivity
contribution. We find that is sensitive to the jet contribution for
the particle-rich case. Surprisingly, it will automatically decrease for the
particle-rare case. Our study indicates that similar decreasing trend observed
previously is mainly driven by particle scarcity instead of jets. The function
is studied in Au+Au collision at GeV with a multiphase
transport model (AMPT). We find that the jet fraction is about 10% at
transverse momentum () around 2.5 GeV/ and reaches up to 30% at 3.5
GeV/. The implication of this study in the investigation of the
noncollectivity contribution in elliptic anisotropy parameter is also
discussed.Comment: 5 pages, 4 figure
Vortices in multiphoton pair production revisited
Vortices in multiphoton pair production are revisited by two counter-rotating
fields with time delay for different cycles in pulse. Novel findings include
that for subcycle fields, the remarkable vortex structure in the momentum
spectrum can be still caused by a large time delay compared to the previous
study for supercycle case where it is easier to be generated by a small time
delay. And also there exist a range of critical polarization values for the
vortices appearance corresponding to the different cycle number. The relative
phase difference between two fields causes not only severe symmetry breaking of
the momentum spectra pattern and vortex, but also a significant change for the
shape and the number of vortex spiral. Upon the number density, it is found a
more sensitive to the cycle number, in particularly, it is enhanced by more
than one order of magnitude for small cycle pulse, while it is increased about
few times when the time delay is small. These results provide an abundant
theoretical testbed for the possible experimental observation on the
multiphoton pair production in future. Meanwhile, it is applicable to regard
the particles momentum signatures as a new probing to the laser field
information with it from the vacuum.Comment: 29 pages, 12 figures, 2 table
Characterization of a broad-based mosquito yeast interfering RNA larvicide with a conserved target site in mosquito semaphorin-1a genes
BACKGROUND:
RNA interference (RNAi), which has facilitated functional characterization of mosquito neural development genes such as the axon guidance regulator semaphorin-1a (sema1a), could one day be applied as a new means of vector control. Saccharomyces cerevisiae (baker's yeast) may represent an effective interfering RNA expression system that could be used directly for delivery of RNA pesticides to mosquito larvae. Here we describe characterization of a yeast larvicide developed through bioengineering of S. cerevisiae to express a short hairpin RNA (shRNA) targeting a conserved site in mosquito sema1a genes.
RESULTS:
Experiments conducted on Aedes aegypti larvae demonstrated that the yeast larvicide effectively silences sema1a expression, generates severe neural defects, and induces high levels of larval mortality in laboratory, simulated-field, and semi-field experiments. The larvicide was also found to induce high levels of Aedes albopictus, Anopheles gambiae and Culex quinquefasciatus mortality.
CONCLUSIONS:
The results of these studies indicate that use of yeast interfering RNA larvicides targeting mosquito sema1a genes may represent a new biorational tool for mosquito control
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