1,405 research outputs found
Design and Setup of the Micro-Turboexpander Transcritical CO2 System
As the potential Eco-friendly refrigerant, CO2 regains more and more attentions. It has various advantages over conventional refrigerants, such as non-flammability, non-toxicity, high volumetric refrigerant capacity and excellent heat transfer properties. Because the heat rejection temperature in a transcritical CO2 heat pump or a transcritical CO2 refrigeration system is higher than the critical temperature of CO2, the transcritical vapor compression cycle becomes the best choice for transcritical CO2 systems. However, the relative low COP caused by the throttle valve limited the further development. The replacement of a throttle valve with a turboexpander, an ejector or a vortex tube is leading to the way for improving the COP of a transcritical CO2 system. With the advantages of high efficiency, high compactness, high reliability and long-life time, turboexpanders have been widely used in gas lique faction devices (below 120K) and most of the reverse Brayton refrigeration systems. It is also one of the most ideal expansion devices for transcritical CO2 systems. However, its applications are limited by the difficulties of high pressure and super high rotating speed operation. With the development of manufacturing technology and gas bearing technology, it becomes possible to use turboexpanders in transcriticalCO2 systems. In this paper, two turboexpanders with 10 mm radial reaction turbine wheel and 9 mm rotor diameter were designed for the 15 kW transcritical CO2 refrigeration system, and the rotating speed is about 200 krpm.The proposed turboexpanders outlet states are CO2 two-phase flow and subcooled CO2 liquid flow, respectively. This study will lay a foundation for the application of turboexpanders in transcritical CO2 systems
Translating solid state organic synthesis from a mixer mill to a continuous twin screw extruder
YesA study on the translation of a solid-state synthetic reaction from a mechanochemical mixer-mill to a continuous twin-screw extruder is discussed herein. The study highlights some considerations to be made and parameters to be tested in the context of a model fluorination reaction, which is the first organic fluorination to be attempted using extrusion. Upon optimization, which features the first use of grinding auxiliary solids to enable effective synthetic extrusion, the difluorination reaction was successfully translated to the extruder, leading to a 100-fold improvement in Space Time Yield (STY); 29 kg m−3 day−1 in a mixer mill to 3395 kg m−3 day−1 in a twin screw extruder.D. L. B is grateful to the EPSRC for a First Grant (D. L. B. EP/P002951/1), CRD for a studentship award to J. L. H., Queen’s University Belfast for a Visiting Research Fellowship and the School of Chemistry at Cardiff University for generous support. S. L. J. is grateful to EPSRC for support (EP/L019655/1)
Properties and Performance of Two Wide Field of View Cherenkov/Fluorescence Telescope Array Prototypes
A wide field of view Cherenkov/fluorescence telescope array is one of the
main components of the Large High Altitude Air Shower Observatory project. To
serve as Cherenkov and fluorescence detectors, a flexible and mobile design is
adopted for easy reconfiguring of the telescope array. Two prototype telescopes
have been constructed and successfully run at the site of the ARGO-YBJ
experiment in Tibet. The features and performance of the telescopes are
presented
The rare top quark decays in the topcolor-assisted technicolor model
We consider the rare top quark decays in the framework of topcolor-assisted
technicolor (TC2) model. We find that the contributions of top-pions and
top-Higgs predicted by the TC2 model can enhance the SM branching ratios by as
much as 6-9 orders of magnitude. i.e., in the most case, the orders of
magnitude of branching ratios are , , . With the reasonable values of the
parameters in TC2 model, such rare top quark decays may be testable in the
future experiments. So, rare top quark decays provide us a unique way to test
TC2 model.Comment: 14 pages, 4 figure
Global regularity criterion for the 3D Navier-Stokes equations involving one entry of the velocity gradient tensor
In this paper we provide a sufficient condition, in terms of only one of the
nine entries of the gradient tensor, i.e., the Jacobian matrix of the velocity
vector field, for the global regularity of strong solutions to the
three-dimensional Navier-Stokes equations in the whole space, as well as for
the case of periodic boundary conditions
in NonCommutative Standard Model
We study the top quark decay to b quark and W boson in the NonCommutative
Standard Model (NCSM). The lowest contribution to the decay comes from the
terms quadratic in the matrix describing the noncommutative (NC) effects while
the linear term is seen to identically vanish because of symmetry. The NC
effects are found to be significant only for low values of the NC
characteristic scale.Comment: 11 page Latex file containing 2 eps figures (redrawn). More
discussion included. To appear in PR
Virtual Effects of Split SUSY in Higgs Productions at Linear Colliders
In split supersymmetry the gauginos and higgsinos are the only supersymmetric
particles possibly accessible at foreseeable colliders like the CERN Large
Hadron Collider (LHC) and the International Linear Collider (ILC). In order to
account for the cosmic dark matter measured by WMAP, these gauginos and
higgsinos are stringently constrained and could be explored at the colliders
through their direct productions and/or virtual effects in some processes. The
clean environment and high luminosity of the ILC render the virtual effects of
percent level meaningful in unraveling the new physics effects. In this work we
assume split supersymmetry and calculate the virtual effects of the
WMAP-allowed gauginos and higgsinos in Higgs productions e+e- -> Z h and e+e-
-> \nu_e \bar_\nu_e h through WW fusion at the ILC. We find that the production
cross section of e+e- -> Zh can be altered by a few percent in some part of the
WMAP-allowed parameter space, while the correction to the WW-fusion process
e+e- -> \nu_e \bar_\nu_e h is below 1%. Such virtual effects are correlated
with the cross sections of chargino pair productions and can offer
complementary information in probing split supersymmetry at the colliders.Comment: more discussions added (7 pages, 10 figs
Supersymmetric effects in top quark decay into polarized W-boson
We investigate the one-loop supersymmetric QCD (SUSY-QCD) and electroweak
(SUSY-EW) corrections to the top quark decay into a b-quark and a longitudinal
or transverse W-boson. The corrections are presented in terms of the
longitudinal ratio \Gamma(t-->W_L b)/\Gamma(t--> W b) and the transverse ratio
\Gamma(t-->W_- b)/\Gamma(t--> W b). In most of the parameter space, both
SUSY-QCD and SUSY-EW corrections to these ratios are found to be less than 1%
in magnitude and they tend to have opposite signs. The corrections to the total
width \Gamma(t-->W b) are also presented for comparison with the existing
results in the literature. We find that our SUSY-EW corrections to the total
width differ significantly from previous studies: the previous studies give a
large correction of more than 10% in magnitude for a large part of the
parameter space while our results reach only few percent at most.Comment: Version in PRD (explanation and refs added
Three heavy jet events at hadron colliders as a sensitive probe of the Higgs sector
Assuming that a non-standard neutral Higgs with an enhanced Yukawa coupling
to a bottom quark is observed at future hadron experiments, we propose a method
for a better understanding of the Higgs sector. Our procedure is based on
"counting" the number of events with heavy jets (where "heavy" stands for a c
or b jet) versus b jets, in the final state of processes in which the Higgs is
produced in association with a single high p_T c or b jet. We show that an
observed signal of the type proposed, at either the Tevatron or the LHC, will
rule out the popular two Higgs doublet model of type II as well as its
supersymmetric version - the Minimal Supersymmetric Standard Model (MSSM), and
may provide new evidence in favor of some more exotic multi Higgs scenarios. As
an example, we show that in a version of a two Higgs doublet model which
naturally accounts for the large mass of the top quark, our signal can be
easily detected at the LHC within that framework. We also find that such a
signal may be observable at the upgraded Tevatron RunIII, if the neutral Higgs
in this model has a mass around 100 GeV and \tan\beta > 50 and if the
efficiency for distinguishing a c jet from a light jet will reach the level of
50%.Comment: Revtex, 11 pages, 4 figures embedded in the text. Main changes with
respect to Version 1: Numerical results re-calculated using the CTEQ5L pdf,
improved discussion on the experimental consequences, new references added.
Conclusions remain unchanged. As will appear in Phys. Rev.
Mathematical results for some models of turbulence with critical and subcritical regularizations
In this paper, we establish the existence of a unique "regular" weak solution
to turbulent flows governed by a general family of models with
critical regularizations. In particular this family contains the simplified
Bardina model and the modified Leray- model. When the regularizations
are subcritical, we prove the existence of weak solutions and we establish an
upper bound on the Hausdorff dimension of the time singular set of those weak
solutions. The result is an interpolation between the bound proved by Scheffer
for the Navier-Stokes equations and the regularity result in the critical case
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