Formulation and Implementation of Inflow/Outflow Boundary Conditions to Simulate Propulsive Effects

Boundary conditions appropriate for simulating flow entering or exiting the computational domain to mimic propulsion effects have been implemented in an adaptive Cartesian simulation package. A robust iterative algorithm to control mass flow rate through an outflow boundary surface is presented, along with a formulation to explicitly specify mass flow rate through an inflow boundary surface. The boundary conditions have been applied within a mesh adaptation framework based on the method of adjoint-weighted residuals. This allows for proper adaptive mesh refinement when modeling propulsion systems. The new boundary conditions are demonstrated on several notional propulsion systems operating in flow regimes ranging from low subsonic to hypersonic. The examples show that the prescribed boundary state is more properly imposed as the mesh is refined. The mass-flowrate steering algorithm is shown to be an efficient approach in each example. To demonstrate the boundary conditions on a realistic complex aircraft geometry, two of the new boundary conditions are also applied to a modern low-boom supersonic demonstrator design with multiple flow inlets and outlets

Spin-dependent phenomena and device concepts explored in (Ga,Mn)As

Over the past two decades, the research of (Ga,Mn)As has led to a deeper understanding of relativistic spin-dependent phenomena in magnetic systems. It has also led to discoveries of new effects and demonstrations of unprecedented functionalities of experimental spintronic devices with general applicability to a wide range of materials. In this article we review the basic material properties that make (Ga,Mn)As a favorable test-bed system for spintronics research and discuss contributions of (Ga,Mn)As studies in the general context of the spin-dependent phenomena and device concepts. Special focus is on the spin-orbit coupling induced effects and the reviewed topics include the interaction of spin with electrical current, light, and heat.Comment: 47 pages, 41 figure

The anomalous Cepheid XZ Ceti

XZ Ceti is the only known anomalous Cepheid in the Galactic field. Being the nearest and brightest such variable star, a detailed study of XZ Ceti may shed light on the behaviour of anomalous Cepheids whose representatives have been mostly detected in external galaxies. CCD photometric and radial velocity observations have been obtained. The actual period and amplitude of pulsation were determined by Fourier analysis. The long time scale behaviour of the pulsation period was studied by the method of the O-C diagram using the archival Harvard photographic plates and published photometric data. XZ Ceti differs from the ordinary classical Cepheids in several respects. Its most peculiar feature is cycle-to-cycle variability of the light curve. The radial velocity phase curve is not stable either. The pulsation period is subjected to strong changes on various time scales including a very short one. The ratio of amplitudes determined from the photometric and radial velocity observations indicates that this Cepheid performs an overtone pulsation, in accord with the other known anomalous Cepheid in our Galaxy, BL Boo (V19 in the globular cluster NGC 5466). Continued observations are necessary to study the deviations from regularity, to determine their time scale, as well as to confirm binarity of XZ Ceti and to study its role in the observed peculiar behaviour.Comment: 7 pages, 4 figures. accepted for Astron. Astrophy

Distributed-Flap Layout Trade Study on a Highly Flexible Common Research Model

The results of a layout trade study of a full-span, trailing-edge flap system for the NASACommon Research Model (CRM) are presented. Previously developed analysis and design tools areused to determine the potential performance benefits of several flap layouts on a highlyflexible version of the aircraft wing. The wing is first re-twisted for optimal aerodynamicperformance at the design cruise condition while addressing aeroelastic effects. Several flaplayouts are then installed on the new baseline wing. The deflection of each segment on allflap layouts is then optimized for aerodynamic performance at an overspeed flight conditionto ascertain the effectiveness of each flap system. The results indicate that employing two-segmentflaps greatly improves overspeed performance as compared to using no or justsingle-segment flaps. The study also showed that additional segments offer only incrementalimprovements in performance. The results also show that using only four spanwise flaps canproduce meaningful performance gains. Overall, the trade study results suggest a simpledistributed flap system (four spanwise flaps with two segments each) can reduce the drag ofthe Common Research Model by 13 counts at a Mach number that is 3.5 percent higher than thedesign cruise point

V39: an unusual object in the field of IC 1613

The variable star V39 in the field of IC 1613 is discussed in the light of the available photometric and new spectroscopic data. It has strong emission Balmer lines, and the observed characteristics could be explained by a W Vir pulsating star with a period of 14.341 d, located at more than 115 kpc, that is in the very outer halo of our Galaxy. It should have an apparent companion, a long period (1118d) red variable, belonging to IC 1613. The main uncertainty in this interpretation is an emission feature at 668.4 nm, which we tentatively identified as a He I line.Comment: 5 pages; accepted for publication in Astronomy & Astrophysic

Static Aeroelastic Analysis with an Inviscid Cartesian Method

An embedded-boundary, Cartesian-mesh flow solver is coupled with a three degree-of-freedom structural model to perform static, aeroelastic analysis of complex aircraft geometries. The approach solves a nonlinear, aerostructural system of equations using a loosely-coupled strategy. An open-source, 3-D discrete-geometry engine is utilized to deform a triangulated surface geometry according to the shape predicted by the structural model under the computed aerodynamic loads. The deformation scheme is capable of modeling large deflections and is applicable to the design of modern, very-flexible transport wings. The coupling interface is modular so that aerodynamic or structural analysis methods can be easily swapped or enhanced. After verifying the structural model with comparisons to Euler beam theory, two applications of the analysis method are presented as validation. The first is a relatively stiff, transport wing model which was a subject of a recent workshop on aeroelasticity. The second is a very flexible model recently tested in a low speed wind tunnel. Both cases show that the aeroelastic analysis method produces results in excellent agreement with experimental data

Spin Hall effect transistor

Spin transistors and spin Hall effects have been two separate leading directions of research in semiconductor spintronics which seeks new paradigms for information processing technologies. We have brought the two directions together to realize an all-semiconductor spin Hall effect transistor. Our scheme circumvents semiconductor-ferromagnet interface problems of the original Datta-Das spin transistor concept and demonstrates the utility of the spin Hall effects in microelectronics. The devices use diffusive transport and operate without electrical current, i.e., without Joule heating in the active part of the transistor. We demonstrate a spin AND logic function in a semiconductor channel with two gates. Our experimental study is complemented by numerical Monte Carlo simulations of spin-diffusion through the transistor channel.Comment: 11 pages, 3 figure