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

Investigation of direct solar-to-microwave energy conversion techniques

Identification of alternative methods of producing microwave energy from solar radiation for purposes of directing power to the Earth from space is investigated. Specifically, methods of conversion of optical radiation into microwave radiation by the most direct means are investigated. Approaches based on demonstrated device functioning and basic phenomenologies are developed. There is no system concept developed, that is competitive with current baseline concepts. The most direct methods of conversion appear to require an initial step of production of coherent laser radiation. Other methods generally require production of electron streams for use in solid-state or cavity-oscillator systems. Further development is suggested to be worthwhile for suggested devices and on concepts utilizing a free-electron stream for the intraspace station power transport mechanism

Dynamical polarization, screening, and plasmons in gapped graphene

The one-loop polarization function of graphene has been calculated at zero temperature for arbitrary wavevector, frequency, chemical potential (doping), and band gap. The result is expressed in terms of elementary functions and is used to find the dispersion of the plasmon mode and the static screening within the random phase approximation. At long wavelengths the usual square root behaviour of plasmon spectra for two-dimensional (2D) systems is obtained. The presence of a small (compared to a chemical potential) gap leads to the appearance of a new undamped plasmon mode. At greater values of the gap this mode merges with the long-wavelength one, and vanishes when the Fermi level enters the gap. The screening of charged impurities at large distances differs from that in gapless graphene by slower decay of Friedel oscillations ($1/r^2$ instead of $1/r^3$), similarly to conventional 2D systems.Comment: 8 pages, 8 figures, v2: to match published versio

Hydrogen Production from the LOHC Perhydro-Dibenzyl-Toluene and Purification using a 5 µm PdAg-Membrane in a coupled Microstructured System

Hydrogen bound in organic liquid hydrogen carriers (LOHC) such as dibenzyl-toluene enables simple and safe handling as well as long-term storage. This idea is particularly interesting in the context of the energy transition, where hydrogen is considered a key energy carrier. The LOHC technology serves as a storage between volatile energy and locally and timely independent consumption. Depending on the type of application, decisive specifications are placed on the hydrogen purity. In the product gas from dehydrogenation, however, concentrations of 100 to a few 1000 ppm can be found from low boiling substances, which partly originate from the production of the LOHC material, but also from the decomposition and evaporation of the LOHC molecules in the course of the enormous volume expansion due to hydrogen release. For the removal of undesired traces in the LOHC material, a pre-treatment and storage under protective gas is necessary. For purification, the use of Pd-based membranes might be useful, which makes these steps less important or even redundant. Heat supply and phase contacting of the liquid LOHC and catalyst is also crucial for the process. Within the contribution, the first results from a coupled microstructured system—consisting of a radial flow reactor unit and membrane separation unit—are shown. In a first step, the 5 m thick PdAg-membrane was characterized and a high Sieverts exponent of 0.9 was determined, indicating adsorption/desorption driven permeation. It can be demonstrated that hydrogen is first released with high catalyst-related productivity in the reactor system and afterwards separated and purified. Within the framework of limited analytics, we found that by using a Pd-based membrane, a quality of 5.0 (99.999% purity) or higher can be achieved. Furthermore, it was found that after only 8 hours, the membrane can lose up to 30% of its performance when exposed to the slightly contaminated product gas from the dehydrogenation process. However, the separation efficiency can almost completely be restored by the treatment with pure hydrogen

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

Attack of the Flying Snakes : Formation of Isolated HI Clouds By Fragmentation of Long Streams

The existence of long (> 100 kpc) HI streams and small (< 20 kpc) free-floating HI clouds is well-known. While the formation of the streams has been investigated extensively, and the isolated clouds are often purported to be interaction debris, little research has been done on the formation of optically dark HI clouds that are not part of a larger stream. One possibility is that such features result from the fragmentation of more extended streams, while another idea is that they are primordial, optically dark galaxies. We test the validity of the fragmentation scenario (via harassment) using numerical simulations. In order to compare our numerical models with observations, we present catalogues of both the known long HI streams (42 objects) and free-floating HI clouds suggested as dark galaxy candidates (51 objects). In particular, we investigate whether it is possible to form compact features with high velocity widths (> 100 km/s), similar to observed clouds which are otherwise intriguing dark galaxy candidates. We find that producing such features is possible but extremely unlikely, occurring no more than 0.2% of the time in our simulations. In contrast, we find that genuine dark galaxies could be extremely stable to harassment and remain detectable even after 5 Gyr in the cluster environment (with the important caveat that our simulations only explore harassment and do not yet include the intracluster medium, heating and cooling, or star formation). We also discuss the possibility that such objects could be the progenitors of recently discovered ultra diffuse galaxies.Comment: 46 pages, 27 figures, accepted for publication in MNRA

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

Nonlinear electromagnetic response of graphene: Frequency multiplication and the self-consistent-field effects

Graphene is a recently discovered carbon based material with unique physical properties. This is a monolayer of graphite, and the two-dimensional electrons and holes in it are described by the effective Dirac equation with a vanishing effective mass. As a consequence, electromagnetic response of graphene is predicted to be strongly non-linear. We develop a quasi-classical kinetic theory of the non-linear electromagnetic response of graphene, taking into account the self-consistent-field effects. Response of the system to both harmonic and pulse excitation is considered. The frequency multiplication effect, resulting from the non-linearity of the electromagnetic response, is studied under realistic experimental conditions. The frequency up-conversion efficiency is analysed as a function of the applied electric field and parameters of the samples. Possible applications of graphene in terahertz electronics are discussed.Comment: 14 pages, 7 figures, invited paper written for a special issue of JPCM "Terahertz emitters

Nagaoka ferromagnetism observed in a quantum dot plaquette

Engineered, highly-controllable quantum systems hold promise as simulators of emergent physics beyond the capabilities of classical computers. An important problem in many-body physics is itinerant magnetism, which originates purely from long-range interactions of free electrons and whose existence in real systems has been subject to debate for decades. Here we use a quantum simulator consisting of a four-site square plaquette of quantum dots to demonstrate Nagaoka ferromagnetism. This form of itinerant magnetism has been rigorously studied theoretically but has remained unattainable in experiment. We load the plaquette with three electrons and demonstrate the predicted emergence of spontaneous ferromagnetic correlations through pairwise measurements of spin. We find the ferromagnetic ground state is remarkably robust to engineered disorder in the on-site potentials and can induce a transition to the low-spin state by changing the plaquette topology to an open chain. This demonstration of Nagaoka ferromagnetism highlights that quantum simulators can be used to study physical phenomena that have not yet been observed in any system before. The work also constitutes an important step towards large-scale quantum dot simulators of correlated electron systems.Comment: This version: main (8 pages, 6 figures) + supplementary (15 pages, 8 figures

Spatial and Temporal Scales of Sverdrup Balance

Sverdrup balance underlies much of the theory of ocean circulation and provides a potential tool for describing the interior ocean transport from only the wind stress. Using both a model state estimate and an eddy-permitting coupled climate model, this study assesses to what extent and over what spatial and temporal scales Sverdrup balance describes the meridional transport. The authors find that Sverdrup balance holds to first order in the interior subtropical ocean when considered at spatial scales greater than approximately 5°. Outside the subtropics, in western boundary currents and at short spatial scales, significant departures occur due to failures in both the assumptions that there is a level of no motion at some depth and that the vorticity equation is linear. Despite the ocean transport adjustment occurring on time scales consistent with the basin-crossing times for Rossby waves, as predicted by theory, Sverdrup balance gives a useful measure of the subtropical circulation after only a few years. This is because the interannual transport variability is small compared to the mean transports. The vorticity input to the deep ocean by the interaction between deep currents and topography is found to be very large in both models. These deep transports, however, are separated from upper-layer transports that are in Sverdrup balance when considered over large scales