Day-night high resolution infrared radiometer employing two-stage radiant cooling. Part 1 - Two-stage radiant cooler Final report

Design, thermal analysis, testing, and breadboard integration of two-stage radiant cooler for high resolution radiomete

Anion vacancies as a source of persistent photoconductivity in II-VI and chalcopyrite semiconductors

Using first-principles electronic structure calculations we identify the anion vacancies in II-VI and chalcopyrite Cu-III-VI2 semiconductors as a class of intrinsic defects that can exhibit metastable behavior. Specifically, we predict persistent electron photoconductivity (n-type PPC) caused by the oxygen vacancy VO in n-ZnO, and persistent hole photoconductivity (p-type PPC) caused by the Se vacancy VSe in p-CuInSe2 and p-CuGaSe2. We find that VSe in the chalcopyrite materials is amphoteric having two "negative-U" like transitions, i.e. a double-donor transition e(2+/0) close to the valence band and a double-acceptor transition e(0/2-) closer to the conduction band. We introduce a classification scheme that distinguishes two types of defects (e.g., donors): type-alpha, which have a defect-localized-state (DLS) in the gap, and type-beta, which have a resonant DLS within the host bands (e.g., conduction band). In the latter case, the introduced carriers (e.g., electrons) relax to the band edge where they can occupy a perturbed-host-state (PHS). Type alpha is non-conducting, whereas type beta is conducting. We identify the neutral anion vacancy as type-alpha and the doubly positively charged vacancy as type-beta. We suggest that illumination changes the charge state of the anion vacancy and leads to a crossover between alpha- and beta-type behavior, resulting in metastability and PPC. In CuInSe2, the metastable behavior of VSe is carried over to the (VSe-VCu) complex, which we identify as the physical origin of PPC observed experimentally. We explain previous puzzling experimental results in ZnO and CuInSe2 in the light of this model.Comment: submitted to Phys. Rev.

Generation of optimal trajectories for Earth hybrid pole sitters

A pole-sitter orbit is a closed path that is constantly above one of the Earth's poles, by means of continuous low thrust. This work proposes to hybridize solar sail propulsion and solar electric propulsion (SEP) on the same spacecraft, to enable such a pole-sitter orbit. Locally-optimal control laws are found with a semi-analytical inverse method, starting from a trajectory that satisfies the pole-sitter condition in the Sun-Earth circular restricted three-body problem. These solutions are subsequently used as first guess to find optimal orbits, using a direct method based on pseudospectral transcription. The orbital dynamics of both the pure SEP case and the hybrid case are investigated and compared. It is found that the hybrid spacecraft allows savings on propellant mass fraction. Finally, it is shown that for sufficiently long missions, a hybrid pole-sitter, based on mid-term technology, enables a consistent reduction in the launch mass for a given payload, with respect to a pure SEP spacecraft

Burnout in the ICU : potential consequences for staff and patient well-being

Peer reviewedAuthor versio

Magnetic oxide semiconductors

Magnetic oxide semiconductors, oxide semiconductors doped with transition metal elements, are one of the candidates for a high Curie temperature ferromagnetic semiconductor that is important to realize semiconductor spintronics at room temperature. We review in this paper recent progress of researches on various magnetic oxide semiconductors. The magnetization, magneto-optical effect, and magneto-transport such as anomalous Hall effect are examined from viewpoint of feasibility to evaluate the ferromagnetism. The ferromagnetism of Co-doped TiO2 and transition metal-doped ZnO is discussed.Comment: 26 pages, 5 tables, 6 figure

A population of gut epithelial enterochromaffin cells is mechanosensitive and requires Piezo2 to convert force into serotonin release

Enterochromaffin (EC) cells constitute the largest population of intestinal epithelial enteroendocrine (EE) cells. EC cells are proposed to be specialized mechanosensory cells that release serotonin in response to epithelial forces, and thereby regulate intestinal fluid secretion. However, it is unknown whether EE and EC cells are directly mechanosensitive, and if so, what the molecular mechanism of their mechanosensitivity is. Consequently, the role of EE and EC cells in gastrointestinal mechanobiology is unclear. Piezo2 mechanosensitive ion channels are important for some specialized epithelial mechanosensors, and they are expressed in mouse and human EC cells. Here, we use EC and EE cell lineage tracing in multiple mouse models to show that Piezo2 is expressed in a subset of murine EE and EC cells, and it is distributed near serotonin vesicles by superresolution microscopy. Mechanical stimulation of a subset of isolated EE cells leads to a rapid inward ionic current, which is diminished by Piezo2 knockdown and channel inhibitors. In these mechanosensitive EE cells force leads to Piezo2-dependent intracellular Ca(2+) increase in isolated cells as well as in EE cells within intestinal organoids, and Piezo2-dependent mechanosensitive serotonin release in EC cells. Conditional knockout of intestinal epithelial Piezo2 results in a significant decrease in mechanically stimulated epithelial secretion. This study shows that a subset of primary EE and EC cells is mechanosensitive, uncovers Piezo2 as their primary mechanotransducer, defines the molecular mechanism of their mechanotransduction and mechanosensitive serotonin release, and establishes the role of epithelial Piezo2 mechanosensitive ion channels in regulation of intestinal physiology

advanced electric propulsion diagnostic tools at iom

Abstract Recently, we have set up an Advanced Electric Propulsion Diagnostic (AEPD) platform [1] , which allows for the in-situ measurement of a comprehensive set of thruster performance parameters. The platform utilizes a five-axis-movement system for precise positioning of the thruster with respect to the diagnostic heads. In the first setup (AEPD1) an energy-selective mass spectrometer (ESMS) and a miniaturized Faraday probe for ion beam characterization, a telemicroscope and a triangular laser head for measuring the erosion of mechanical parts, and a pyrometer for surface temperature measurements were integrated. The capabilities of the AEPD1 platform were demonstrated with two electric propulsion thrusters, a gridded ion thruster RIT 22 (Airbus Defence & Space, Germany, [13]) and a Hall effect thruster SPT 100D EM1 (EDB Fakel, Russia, [1] , [4] ), in two different vacuum facilities

Cold Plasma Wave Analysis in Magneto-Rotational Fluids

This paper is devoted to investigate the cold plasma wave properties. The analysis has been restricted to the neighborhood of the pair production region of the Kerr magnetosphere. The Fourier analyzed general relativistic magnetohydrodynamical equations are dealt under special circumstances and dispersion relations are obtained. We find the $x$-component of the complex wave vector numerically. The corresponding components of the propagation vector, attenuation vector, phase and group velocities are shown in graphs. The direction and dispersion of waves are investigated.Comment: 22 pages, 18 figures, accepted for publication in Astrophys. Space Sc

Optimization of the Magnetic Field Topology in the Hall Effect Rocket with Magnetic Shielding

NASA's Hall Effect Rocket with Magnetic Shielding (HERMeS) 12.5kW Technology Demonstration Unit-1 (TDU-1) has been the subject of extensive technology maturation in preparation for flight system development. The TDU-1 thruster implements a magnetically shielded field topology and has demonstrated the elimination of the discharge channel erosion. Extensive wear testing the TDU Hall thrusters has identified the thruster front pole covers as the next life limiting component. This effort aims to explore and investigate alternate magnetic field topologies to assess whether reductions in the front pole cover erosion can be attained while still maintaining very low erosion rates on the discharge channel walls. NASA GRC and JPL have begun a magnetic field topology characterization and optimization study by designing four candidate magnetic field topologies that reduce the effectiveness of the shielding along the discharge channel walls with the intent to also reduce the erosion rates along the pole covers. Three of the four candidate magnetic field topologies have been manufactured subjected to an extensive test campaign that includes performance, plume, and stability characterization. In Phase I of the testing campaign, the thruster's oscillation magnitude and Laser Induced fluorescence (LIF) measurements of the plasma plume were performed for the three candidate topologies. In Phase I, the thruster's oscillation magnitude and LIF measurements were performed for the three candidate topologies. Phase I test results found that the B1 configuration attained lower oscillation levels than B0. Additionally, LIF measurements along the discharge chamber centerline found that upstream retraction of the thruster's peak magnetic field does result in an upstream shift of the acceleration zone but the magnitude of the shift does not correspond one-to-one to the shift in the location of the peak radial magnetic field magnitude. Phase II test segment will include performing performance, stability, plume, and erosion measurements for the various candidate magnetic field topologies