Computation of H2/air reacting flowfields in drag-reduction external combustion

Numerical simulation and analysis of the solution are presented for a laminar reacting flowfield of air and hydrogen in the case of external combustion employed to reduce base drag in hypersonic vehicles operating at transonic speeds. The flowfield consists of a transonic air stream at a Mach number of 1.26 and a sonic transverse hydrogen injection along a row of 26 orifices. Self-sustained combustion is computed over an expansion ramp downstream of the injection and a flameholder, using the recently developed RPLUS code. Measured data is available only for surface pressure distributions and is used for validation of the code in practical 3D reacting flowfields. Pressure comparison shows generally good agreements, and the main effects of combustion are also qualitatively consistent with experiment

Sheath ionization model of beam emissions from large spacecraft

An analytical model of the charging of a spacecraft emitting electron and ion beams has been applied to the case of large spacecraft. In this model, ionization occurs in the sheath due to the return current. Charge neutralization of spherical space charge flow is examined by solving analytical equations numerically. Parametric studies of potential large spacecraft are performed. As in the case of small spacecraft, the ions created in the sheath by the returning current play a large role in determining spacecraft potential

Asteroseismology of the δ\delta Scuti star HD 50844

Aims. We aim to probe the internal structure and investigate more detailed information of the $\delta$ Scuti star HD 50844 with asteroseismology. Methods. We analyse the observed frequencies of the $\delta$ Scuti star HD 50844 obtained by Balona (2014), and search for possible multiplets based on the rotational splitting law of g-mode. We tried to disentangle the frequency spectra of HD 50844 by means of the rotational splitting only. We then compare them with theoretical pulsation modes, which correspond to stellar evolutionary models with various sets of initial metallicity and stellar mass, to find the best-fitting model. Results. There are three multiplets including two complete triplets and one incomplete quintuplet, in which mode identifications for spherical harmonic degree $l$ and azimuthal number $m$ are unique. The corresponding rotational period of HD 50844 is found to be 2.44$^{+0.13}_{-0.08}$ days. The physical parameters of HD 50844 are well limited in a small region by three modes identified as nonradial ones ($f_{11}$, $f_{22}$, and $f_{29}$) and by the fundamental radial mode ($f_{4}$). Our results show that the three nonradial modes ($f_{11}$, $f_{22}$, and $f_{29}$) are all mixed modes, which mainly represent the property of the helium core. The fundamental radial mode ($f_{4}$) mainly represents the property of the stellar envelope. In order to fit these four pulsation modes, both the helium core and the stellar envelope must be matched to the actual structure of HD 50844. Finally, the mass of the helium core of HD 50844 is estimated to be 0.173 $\pm$ 0.004 $M_{\odot}$ for the first time. The physical parameters of HD 50844 are determined to be $M=$ 1.81 $\pm$ 0.01 $M_{\odot}$, $Z=$ 0.008 $\pm$ 0.001. $T_{\rm eff}=$ 7508 $\pm$ 125 K, log$g=$ 3.658 $\pm$ 0.004, $R=$ 3.300 $\pm$ 0.023 $R_{\odot}$, $L=$ 30.98 $\pm$ 2.39 $L_{\odot}$.Comment: 11 pages, 7 figures, 6 tables, accepted for publication in A&

Two-dimensional viscous flow computations of hypersonic scramjet nozzle flowfields at design and off-design conditions

The PARC2D code has been selected to analyze the flowfields of a representative hypersonic scramjet nozzle over a range of flight conditions from Mach 3 to 20. The flowfields, wall pressures, wall skin friction values, heat transfer values and overall nozzle performance are presented

Viscous three-dimensional analyses for nozzles for hypersonic propulsion

A Navier-Stokes computer code was validated using a number of two- and three-dimensional configurations for both laminar and turbulent flows. The validation data covers a range of freestream Mach numbers from 3 to 14, includes wall pressures, velocity profiles, and skin friction. Nozzle flow fields computed for a generic scramjet nozzle from Mach 3 to 20, wall pressures, wall skin friction values, heat transfer values, and overall performance are presented. In addition, three-dimensional solutions obtained for two asymmetric, single expansion ramp nozzles at a pressure ratio of 10 consists of the internal expansion region in the converging/diverging sections and the external supersonic exhaust in a quiescent ambient environment. The fundamental characteristics that were captured successfully include expansion fans; Mach wave reflections; mixing layers; and nonsymmetrical, multiple inviscid cell, supersonic exhausts. Comparison with experimental data for wall pressure distributions at the center planes shows good agreement

New signals of a R-parity violating model of neutrino mass at the Tevatron

In a variety models of neutrino masses and mixings the lighter top squark decays into competing R - parity violating and R - parity conserving channels. Using Pythia we have estimated in a model independent way the minimum value of P $\equiv$ BR($\widetilde t_1 \to c \widetilde \chi_1^0$) $\times$ BR($\widetilde t_1 \to l^+_i b$), where $l_i = e^+$ and $\mu^+$, corresponding to an observable signal involving the final state 1$l$ + jets +\met (carried by the neutrinos from the $\tilde \chi_1^0$ decay) at Tevatron Run II. For the kinematical cuts designed in this paper P depends on $m_{\widetilde t_1}$ only. We then compute P for representative choices of the model parameters constrained by the oscillation data and find that over a significant region of the allowed parameter space P is indeed larger than $P_{min}$. This signal is complementary to the dilepton + dijet signal studied in several earlier experimental and phenomenological analyses and may be observed even if BR($\widetilde t_1 \to l^+_i b$) is an order of magnitude smaller than BR($\widetilde t_1 \to c \widetilde \chi_1^0$). The invariant mass distribution of the hardest lepton and the hardest jet may determine $m_{\widetilde t_1}$ and reveal the lepton number violating nature of the underlying interaction. The invariant mass distribution of the two lowest energy jets may determine $m_{\widetilde \chi_1^0}$.Comment: Some minor changes in language are made at pages 1,2,8 and 18 respectivel

Analyzing powers in inclusive pion production at high energy and the nucleon spin structure

Analyzing powers in inclusive pion production in high energy transversely polarized proton-proton collisions are studied theoretically in the framework of the quark recombination model. Calculations by assuming the SU(6) spin-flavor symmetry for the nucleon structure disagree with the experiments. We solve this difficulty by taking into account the %We overcome this difficulty by taking into account the realistic spin distribution functions of the nucleon, which differs from the SU(6) expectation at large $x$, %but coincides with a perturbative QCD constraint on the ratio of the unpolarized valence distributions, $u/d \to 5$ as $x \to 1$. We also discuss the kaon spin asymmetry and find $A_N(K^+) = -A_N(K^0)$ in the polarized proton-proton collisions at large $x_F$.Comment: 13 pages, 4 figures, late

Exterior optical cloaking and illusions by using active sources: a boundary element perspective

Recently, it was demonstrated that active sources can be used to cloak any objects that lie outside the cloaking devices [Phys. Rev. Lett. \textbf{103}, 073901 (2009)]. Here, we propose that active sources can create illusion effects, so that an object outside the cloaking device can be made to look like another object. invisibility is a special case in which the concealed object is transformed to a volume of air. From a boundary element perspective, we show that active sources can create a nearly "silent" domain which can conceal any objects inside and at the same time make the whole system look like an illusion of our choice outside a virtual boundary. The boundary element method gives the fields and field gradients (which can be related to monopoles and dipoles) on continuous curves which define the boundary of the active devices. Both the cloaking and illusion effects are confirmed by numerical simulations