Space Station RT and E Utilization Study

Descriptive information on a set of 241 mission concepts was reviewed to establish preliminary Space Station outfitting needs for technology development missions. The missions studied covered the full range of in-space technology development activities envisioned for early Space Station operations and included both pressurized volume and attached payload requirements. Equipment needs were compared with outfitting plans for the life sciences and microgravity user communities, and a number of potential outfitting additions were identified. Outfitting implementation was addressed by selecting a strawman mission complement for each of seven technical themes, by organizing the missions into flight scenarios, and by assessing the associated outfitting buildup for planning impacts

Two-dimensional models of layered protoplanetary discs - II. The effect of a residual viscosity in the dead zone

We study axisymmetric models of layered protoplanetary discs taking radiative transfer effects into account, and allowing for a residual viscosity in the dead zone. We also explore the effect of different viscosity prescriptions. In addition to the ring instability reported in the first paper of the series we find an oscillatory instability of the dead zone, accompanied by variations of the accretion rate onto the central star. We provide a simplified analytical description explaining the mechanism of the oscillations. Finally, we find that the residual viscosity enables stationary accretion in large regions of layered discs. Based on results obtained with the help of a simple 1-D hydrocode we identify these regions, and discuss conditions in which layered discs can give rise to FU~Orionis phenomena.Comment: 9 pages, 5 figures, accepted for publication in MNRA

Heterogeneous perturbations in the Doppler-free S1 ← S0 two-photon spectrum of benzene: Evidence for intrastate coupling

Rotational perturbations are identified in Doppler-free two-photon spectra of the 1410 and 1410110 vibronic bands in C6H6. Evidence is found that Coriolis coupling between some of the rotational levels of two distinct vibrational states within S1 is the mechanism responsible. This coupling mechanism is thought to be responsible for irreversible intramolecular relaxation at higher excess energies and higher vibrational state densities

Selection and Control of Individual Domain Walls in Nanowire Arrays via Asymmetric Depinning Fields

Artificially inscribed notches are often used to pin domain walls (DWs) in ferromagnetic nanowires. The process of selecting and moving the trapped DW in nanowire arrays is an important step for potential applications. The chirality of a DW leads to a pair of pinning positions at the inscribed notches, which can be modeled by a symmetric double well. The depinning field depends on the side of the well, the DW is trapped with respect to the applied field direction, and the DWs can also be transitioned between the two wells without depinning. We demonstrate how manipulating the double well improves the DW selectivity and control in wire arrays containing multiple DWs

Casimir interactions in graphene systems

The non-retarded Casimir interaction (van der Waals interaction) between two free standing graphene sheets as well as between a graphene sheet and a substrate is determined. An exact analytical expression is given for the dielectric function of graphene along the imaginary frequency axis within the random phase approximation for arbitrary frequency, wave vector, and doping.Comment: 4 pages, 4 figure

Neural-Network Vector Controller for Permanent-Magnet Synchronous Motor Drives: Simulated and Hardware-Validated Results

This paper focuses on current control in a permanentmagnet synchronous motor (PMSM). The paper has two main objectives: The first objective is to develop a neural-network (NN) vector controller to overcome the decoupling inaccuracy problem associated with conventional PI-based vector-control methods. The NN is developed using the full dynamic equation of a PMSM, and trained to implement optimal control based on approximate dynamic programming. The second objective is to evaluate the robust and adaptive performance of the NN controller against that of the conventional standard vector controller under motor parameter variation and dynamic control conditions by (a) simulating the behavior of a PMSM typically used in realistic electric vehicle applications and (b) building an experimental system for hardware validation as well as combined hardware and simulation evaluation. The results demonstrate that the NN controller outperforms conventional vector controllers in both simulation and hardware implementation

Closed-circuit television welding- electrode guidance system

Closed-circuit TV camera is mounted parallel to electrode and moves along with it. Camera is scanned along seam so seam is viewed parallel with scan lines on TV monitor. Two fiber optics illuminators are attached to guidance system; they illuminate seam for TV camera

Dielectric function of the semiconductor hole gas

We study the dielectric function of the homogeneous hole gas in p-doped zinc-blende III-V bulk semiconductors within random phase approximation with the valence band being modeled by Luttinger's Hamiltonian in the spherical approximation. In the static limit we find a beating of Friedel oscillations between the two Fermi momenta for heavy and light holes, while at large frequencies dramatic corrections to the plasmon dispersion occur.Comment: 4 pages, 1 figure included. Version to appear in Europhys. Let

FDTD Data Extrapolation Using Multilayer Perceptron (MLP)

This work compares MLP with the matrix pencil method, a linear eigenanalysis-based extrapolator, in terms of their effectiveness in finite difference time domain (FDTD) data extrapolation. Matrix pencil method considers the signal as superposed complex exponentials while MLP considers each time step to be a nonlinear function of previous time steps

Simulations of nonlinear harmonic generation by an internal wave beam incident on a pycnocline

Internal wave beams generated by oceanic tidal flows propagate upward and interact with the increasing stratification found at the pycnocline. The nonlinear generation of harmonic modes by internal wave beams incident on a pycnocline has recently been demonstrated by laboratory experiments and numerical simulations. In these previous studies, the harmonic modes were trapped within the pycnocline because their frequencies exceeded that of the stratified fluid below. Here, two-dimensional numerical simulations are used to explore the effect of incidence angle on harmonic generation at a thin pycnocline. At incidence angles less than 30 degrees (typical of oceanic beams), the lowest harmonic mode freely radiates in the form of an internal wave beam rather than being trapped within the pycnocline. The results indicate that nonlinear refraction is the primary mechanism for harmonic generation at incidence angles exceeding 30 degrees, but that interaction of the incident and reflected beams is more important at smaller incidence angles. The simulations are compared to weakly nonlinear theory based on refraction at the pycnocline. The results yield good agreement for trapped harmonics, but weakly nonlinear theory substantially underpredicts the amplitude of the radiated harmonics