Development and performance of power processor system for 2-gigahertz, 200-watt amplifier for communications technology satellite

The electrical and environmental requirements for a power processor system (PPS) designed to supply the appropriate voltages and currents to a 200-watt traveling wave tube (TWT) for a communication technology satellite is described. A block diagram of the PPS, the interface requirements between the PPS and spacecraft, the interface requirements between the PPS and 200-watt TWT, and the environmental requirements of the PPS are presented. Also included are discussions of protection circuits, interlocking sequences, and transient requirements. Predictions of the flight performance, based on ground test data, are provided

Large-scale Simulation of the Two-dimensional Kinetic Ising Model

We present Monte Carlo simulation results for the dynamical critical exponent $z$ of the two-dimensional kinetic Ising model using a lattice of size $10^6 \times 10^6$ spins. We used Glauber as well as Metropolis dynamics. The $z$-value of $2.16\pm 0.005$ was calculated from the magnetization and energy relaxation from an ordered state towards the equilibrium state at $T_c$.Comment: 6 pages + 2 figures as separate uuencoded compressed tar file, Postscipt also available at http://wwwcp.tphys.uni-heidelberg.de/papers

Using supply chain management techniques to make wind plant and energy storage operation more profitable

Thesis (M. Eng. in Logistics)--Massachusetts Institute of Technology, Engineering Systems Division, 2009.Includes bibliographical references (leaves 161-164).Our research demonstrates that supply chain management techniques can improve the incremental gross profits of wind plant and storage operations by up to five times. Using Monte-Carlo simulation we create and test scenarios that achieve incremental operating profits of up to 15 percent of base case revenue, and show pre-tax profit. We show that energy storage-specifically in the form of utility-scale batteries - can become economically-viable today when using supply chain management strategies under certain scenarios. To achieve these results we have built a simulation model with three data inputs. First, we synthesized the output of a 120 MW wind plant in Maine for both summer and winter seasons. Second, we simulated New England ISO market pricing data for both the Day-Ahead and Real-Time markets in summer and winter seasons using Monte Carlo simulations. Third, using actual data from two existing battery companies, we incorporated the technical and cost specifications for two energy storage facilities. All of these data inputs feature adjustable parameters so we can test various plant configurations, market volatilities and storage capabilities, among other inputs. Using our model, we then employed supply chain management network design strategies and daily operating policies to test profitability improvements on our wind plant-plus-storage operation. For example, we ran simulations for scenarios where our storage facility is either located in Maine next to our wind plant, or located in another state.(cont.) Also, since storage can make wind generation a predictable capacity resource, we ran simulations to test results in both the Day-Ahead and Real-Time markets. In addition we developed four (4) inventory management policies with dynamic input (charge) and output (discharge) strategies for our storage units. For each policy, we had to conceptualize the policy - while considering planning horizon, lead time, holding costs, shortage costs, market pricing and storage capabilities - and then build functionality in our model to execute those strategies in dynamic pricing and wind plant output environments. The outcomes of our simulation model include incremental gross profit, operating profit and pre-tax profit for each of 54 scenarios, as well as 11 management insights for wind plant and storage operators, storage technology manufacturers and New England ISO leadership.by Prashant Saran and Clayton W. Siegert.M.Eng.in Logistic

Coarsening Dynamics of Crystalline Thin Films

The formation of pyramid-like structures in thin-film growth on substrates with a quadratic symmetry, e.g., {001} surfaces, is shown to exhibit anisotropic scaling as there exist two length scales with different time dependences. Analytical and numerical results indicate that for most realizations coarsening of mounds is described by an exponent n=0.2357. However, depending on material parameters, n may lie between 0 (logarithmic coarsening) and 1/3. In contrast, growth on substrates with triangular symmetries ({111} surfaces) is dominated by a single length scale and an exponent n=1/3.Comment: RevTeX, 4 pages, 3 figure

Strong Resonance of Light in a Cantor Set

The propagation of an electromagnetic wave in a one-dimensional fractal object, the Cantor set, is studied. The transfer matrix of the wave amplitude is formulated and its renormalization transformation is analyzed. The focus is on resonant states in the Cantor set. In Cantor sets of higher generations, some of the resonant states closely approach the real axis of the wave number, leaving between them a wide region free of resonant states. As a result, wide regions of nearly total reflection appear with sharp peaks of the transmission coefficient beside them. It is also revealed that the electromagnetic wave is strongly enhanced and localized in the cavity of the Cantor set near the resonant frequency. The enhancement factor of the wave amplitude at the resonant frequency is approximately $6/|\eta_\mathrm{r}|$, where $\eta_\mathrm{r}$ is the imaginary part of the corresponding resonant eigenvalue. For example, a resonant state of the lifetime $\tau_\mathrm{r}=4.3$ms and of the enhancement factor $M=7.8\times10^7$ is found at the resonant frequency $\omega_\mathrm{r}=367$GHz for the Cantor set of the fourth generation of length L=10cm made of a medium of the dielectric constant $\epsilon=10$.Comment: 20 pages, 11 figures, to be published in Journal of the Physical Society of Japa

INTEGRAL/SPI γ -ray line spectroscopy : Response and background characteristics

© 2018 ESO. Reproduced with permission from Astronomy & Astrophysics. Content in the UH Research Archive is made available for personal research, educational, and non-commercial purposes only. Unless otherwise stated, all content is protected by copyright, and in the absence of an open license, permissions for further re-use should be sought from the publisher, the author, or other copyright holder.Context. The space based γ-ray observatory INTEGRAL of the European Space Agency (ESA) includes the spectrometer instrument "SPI". This is a coded mask telescope featuring a 19-element Germanium detector array for high-resolution γ-ray spectroscopy, encapsulated in a scintillation detector assembly that provides a veto for background from charged particles. In space, cosmic rays irradiate spacecraft and instruments, which, in spite of the vetoing detectors, results in a large instrumental background from activation of those materials, and leads to deterioration of the charge collection properties of the Ge detectors.Aim. We aim to determine the measurement characteristics of our detectors and their evolution with time, that is, their spectral response and instrumental background. These incur systematic variations in the SPI signal from celestial photons, hence their determination from a broad empirical database enables a reduction of underlying systematics in data analysis. For this, we explore compromises balancing temporal and spectral resolution within statistical limitations. Our goal is to enable modelling of background applicable to spectroscopic studies of the sky, accounting separately for changes of the spectral response and of instrumental background.Methods. We use 13.5 years of INTEGRAL/SPI data, which consist of spectra for each detector and for each pointing of the satellite. Spectral fits to each such spectrum, with independent but coherent treatment of continuum and line backgrounds, provides us with details about separated background components. From the strongest background lines, we first determine how the spectral response changes with time. Applying symmetry and long-term stability tests, we eliminate degeneracies and reduce statistical fluctuations of background parameters, with the aim of providing a self-consistent description of the spectral response for each individual detector. Accounting for this, we then determine how the instrumental background components change in intensities and other characteristics, most-importantly their relative distribution among detectors.Results. Spectral resolution of Ge detectors in space degrades with time, up to 15% within half a year, consistently for all detectors, and across the SPI energy range. Semi-annual annealing operations recover these losses, yet there is a small long-term degradation. The intensity of instrumental background varies anti-correlated to solar activity, in general. There are significant differences among different lines and with respect to continuum. Background lines are found to have a characteristic, well-defined and long-term consistent intensity ratio among detectors. We use this to categorise lines in groups of similar behaviour. The dataset of spectral-response and background parameters as fitted across the INTEGRAL mission allows studies of SPI spectral response and background behaviour in a broad perspective, and efficiently supports precision modelling of instrumental background.Peer reviewedFinal Published versio

Suppression of Tcf1 by Inflammatory Cytokines Facilitates Effector CD8 T Cell Differentiation.

The formation of central CD8 T cell memory in response to infection depends on the transcription factor Tcf1 (Tcf7). Tcf1 is expressed at high levels in naive CD8 T cells but downregulated in most CD8 T cells during effector differentiation. The relevance of Tcf1 downregulation for effector differentiation and the signals controlling Tcf1 expression have not been elucidated. Here, we show that systemic inflammatory signals downregulated Tcf1 in CD8 T cells during dendritic cell vaccination and bacterial infections. The suppressive effect was mediated by the inflammatory cytokine interleukin 12 (IL-12), which acted via STAT4 in CD8 T cells. IL-12-induced Tcf1 downregulation required cell cycling, occurred at the transcriptional level, and was prevented in part by inhibiting DNA methyltransferases. Absence of Tcf1 during T cell priming circumvented the need of systemic inflammation for effector differentiation. We conclude that silencing of Tcf1 by systemic inflammation facilitates effector CD8 T cell differentiation

The role of step edge diffusion in epitaxial crystal growth

The role of step edge diffusion (SED) in epitaxial growth is investigated. To this end we revisit and extend a recently introduced simple cubic solid-on-solid model, which exhibits the formation and coarsening of pyramid or mound like structures. By comparing the limiting cases of absent, very fast (significant), and slow SED we demonstrate how the details of this process control both the shape of the emerging structures as well as the scaling behavior. We find a sharp transition from significant SED to intermediate values of SED, and a continuous one for vanishing SED. We argue that one should be able to control these features of the surface in experiments by variation of the flux and substrate temperature.Comment: revised and enlarged version 12 pages, 5 figures, to appear in Surface Scienc

Nonmonotonic roughness evolution in unstable growth

The roughness of vapor-deposited thin films can display a nonmonotonic dependence on film thickness, if the smoothening of the small-scale features of the substrate dominates over growth-induced roughening in the early stage of evolution. We present a detailed analysis of this phenomenon in the framework of the continuum theory of unstable homoepitaxy. Using the spherical approximation of phase ordering kinetics, the effect of nonlinearities and noise can be treated explicitly. The substrate roughness is characterized by the dimensionless parameter $Q = W_0/(k_0 a^2)$, where $W_0$ denotes the roughness amplitude, $k_0$ is the small scale cutoff wavenumber of the roughness spectrum, and $a$ is the lattice constant. Depending on $Q$, the diffusion length $l_D$ and the Ehrlich-Schwoebel length $l_{ES}$, five regimes are identified in which the position of the roughness minimum is determined by different physical mechanisms. The analytic estimates are compared by numerical simulations of the full nonlinear evolution equation.Comment: 16 pages, 6 figures, to appear on Phys. Rev.

Local gauge invariance implies Siegert's hypothesis

The nonrelativistic Ward-Takahashi identity, a consequence of local gauge invariance in quantum mechanics, shows the necessity of exchange current contributions in case of nonlocal and/or isospin-dependent potentials. It also implies Siegert's hypothesis: in the nonrelativistic limit, two-body charge densities identically vanish. Neither current conservation, which follows from global gauge invariance, nor the constraints of (lowest order) relativity are sufficient to arrive at this result. Furthermore, a low-energy theorem for exchange contributions is established.Comment: 5 pages, REVTE