18,689 research outputs found
Phase structures of the black D-D-brane system in various ensembles II: electrical and thermodynamic stability
By incorporating the electrical stability condition into the discussion, we
continue the study on the thermodynamic phase structures of the D-D
black brane in GG, GC, CG, CC ensembles defined in our previous paper
arXiv:1502.00261. We find that including the electrical stability conditions in
addition to the thermal stability conditions does not modify the phase
structure of the GG ensemble but puts more constraints on the parameter space
where black branes can stably exist in GC, CG, CC ensembles. In particular, the
van der Waals-like phase structure which was supposed to be present in these
ensembles when only thermal stability condition is considered would no longer
be visible, since the phase of the small black brane is unstable under
electrical fluctuations. However, the symmetry of the phase structure by
interchanging the two kinds of brane charges and potentials is still preserved,
which is argued to be the result of T-duality.Comment: 34 pages, 17 figure
Phase structures of the black D-D-brane system in various ensembles I: thermal stability
When the D-brane () with delocalized D charges is put into
equilibrium with a spherical thermal cavity, the two kinds of charges can be
put into canonical or grand canonical ensemble independently by setting
different conditions at the boundary. Using the thermal stability condition, we
discuss the phase structures of various ensembles of this system formed in this
way and find out the situations that the black brane could be the final stable
phase in these ensembles. In particular, van der Waals-like phase transitions
can happen when D0 and D4 charges are in different kinds of ensembles.
Furthermore, our results indicate that the D-branes and the delocalized
D-branes are equipotent.Comment: 45 pages, 16 figures, accepted by JHEP; A section added to briefly
discuss more general stability conditions, various typos correcte
Numerical Simulation of Flow Past NACA 0012 Airfoil Using a Co-Flow Jet at Different Injection Angles to Control Lift and Drag
ABSTRACT OF THE THESIS
Numerical Simulation of flow Past NACA 0012 Airfoil Using a Co-Flow Jet at Different Injection Angles to Control Lift and Drag
by
Da Xiao
Master of Science in Mechanical Engineering
Washington University in St. Louis, 2019
Research Advisor: Professor Ramesh K. Agarwal
The focus of this thesis is to numerically study the aerodynamic performance of an airfoil by employing the active flow control from a co-flow jet (CFJ) near the leading edge. The study is conducted by changing the injection angle of CFJ on a location close to the leading edge on the upper surface of a most widely used NACA 0012 airfoil. The compressible Reynolds-Averaged Navier-Stokes (RANS) equations with Spalart-Allmaras (SA) turbulence model are solved using the commercial CFD solver ANSYS FLUENT. Steady state solver is employed in the simulations with pseudo-transient numerical method. The study is performed at free stream angles of attack from 0Β° and 10Β° for momentum coefficients = 0.1, 0.2 and 0.3 with injection slot located at 5%, 15% and 25% chord length from the leading edge of the airfoil. It is shown that for given free stream conditions, the lift coefficient can be substantially increased and drag coefficient can be decreased with suitable choice of , injection angle and location of co-flow jet on the airfoil surface and different injection angles can have different aerodynamic coefficients performance. Thus, Changeable Injection Angle CFJ technology can be used for AFC to achieve the desired outcome of increasing the lift of an airfoil, decreasing drag of an airfoil and at the same time, to have a control of aerodynamic coefficients
Anatomy of decays and effects of next-to-leading order contributions in the perturbative QCD factorization approach
In this paper, we will make systematic calculations for the branching ratios
and the CP-violating asymmetries of the twenty one decays
by employing the perturbative QCD (PQCD) factorization approach. Besides the
full leading-order (LO) contributions, all currently known next-to-leading
order (NLO) contributions are taken into account. We found numerically that:
(a) the NLO contributions can provide enhancement to the LO PQCD
predictions for and , or a reduction to
\calb(\bar{B}_s^0 \to \pi^{-} K^{*+}), and we confirmed that the inclusion of
the known NLO contributions can improve significantly the agreement between the
theory and those currently available experimental measurements, (b) the total
effects on the PQCD predictions for the relevant transition form
factors after the inclusion of the NLO twist-2 and twist-3 contributions is
generally small in magnitude: less than enhancement respect to the
leading order result, (c) for the "tree" dominated decay and the "color-suppressed-tree" decay ,
the big difference between the PQCD predictions for their branching ratios are
induced by different topological structure and by interference effects among
the decay amplitude and : constructive for the
first decay but destructive for the second one, and (d) for \bar{B}_s^0 \to
V(\eta, \etar) decays, the complex pattern of the PQCD predictions for their
branching ratios can be understood by rather different topological structures
and the interference effects between the decay amplitude \cala(V\eta_q) and
\cala(V\eta_s) due to the \eta-\etar mixing.Comment: 18 pages, 2 figures, 3 tables. Some modifications of the text.
Several new references are adde
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