Magnetic Field Induced Charged Exciton Studies in a GaAs/Al(0.3)Ga(0.7)As Single Heterojunction

The magnetophotoluminescence (MPL) behavior of a GaAs/Al(0.3)Ga(0.7)As single heterojunction has been investigated to 60T. We observed negatively charged singlet and triplet exciton states that are formed at high magnetic fields beyond the nu=1 quantum Hall state. The variation of the charged exciton binding energies are in good agreement with theoretical predictions. The MPL transition intensities for these states showed intensity variations (maxima and minima) at the nu=1/3 and 1/5 fractional quantum Hall (FQH) state as a consequence of a large reduction of electron-hole screening at these filling factors.Comment: submitted to Phys. Rev. Let

Atmosphere Revitalization Technology Development for Crewed Space Exploration

As space exploration objectives extend human presence beyond low Earth orbit, the solutions to technological challenges presented by supporting human life in the hostile space environment must build upon experience gained during past and present crewed space exploration programs. These programs and the cabin atmosphere revitalization process technologies and systems developed for them represent the National Aeronautics and Space Administration s (NASA) past and present operational knowledge base for maintaining a safe, comfortable environment for the crew. The contributions of these programs to the NASA s technological and operational working knowledge base as well as key strengths and weaknesses to be overcome are discussed. Areas for technological development to address challenges inherent with the Vision for Space Exploration (VSE) are presented and a plan for their development employing unit operations principles is summarize

Neutronics parameter variation studies for the Los Alamos ATW concept

The purpose of the Los Alamos ATW (Accelerator Transmutation of nuclear Waste) project is to utilize a high-energy (800--1600 MeV), high current (25--60mA) proton beam to generate a large neutron flux for the transmutation of nuclear wastes. Our theoretical modeling efforts have been directed toward designing a device that will transmute the 2000 kg of Tc and I in the Hanford waste depository along with significant quantities of actinides. Previous system studies have indicated the feasibility of such a device. However, it required thirty years to transmute 2000 kg of Tc and 400 kg of Np. In the present work, we have expanded on the previous study and focused on a device which will significantly reduce the time required for the transmutation of the fission products. 3 refs., 1 tab

What does the evidence tell us about merit principles and government performance?

In October 2020, President Donald Trump sought to convert many US federal civil servants to at-will employees by executive order. Trump's initiative, referred to as Schedule F, has stimulated a partisan debate about dismantling the merit system in the US federal government. A substantial international body of evidence has developed during the last three decades about the effects of administrative practices associated with meritocracy and the likely consequences of changes to civil service systems, such as those embedded in Schedule F. This article employs guidelines established under the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) to conduct a systematic review of the evidence to address the question: What does the evidence tell us about merit principles and government performance? This systematic review summarizes what empirical research tells us about effects of civil service practices, such as meritocratic appointments, meritocratic advancement, and tenure protection, for government performance and the quality of government. The findings indicate that factors such as meritocratic appointments/recruitment, tenure protection, impartiality, and professionalism are strongly associated with higher government performance and lower corruption. We conclude by discussing implications of our findings for public policy and management and for future research.The politics and administration of institutional chang

An action for the exact string black hole

A local action is constructed describing the exact string black hole discovered by Dijkgraaf, Verlinde and Verlinde in 1992. It turns out to be a special 2D Maxwell-dilaton gravity theory, linear in curvature and field strength. Two constants of motion exist: mass M>1, determined by the level k, and U(1)-charge Q>0, determined by the value of the dilaton at the origin. ADM mass, Hawking temperature T_H \propto \sqrt{1-1/M} and Bekenstein-Hawking entropy are derived and studied in detail. Winding/momentum mode duality implies the existence of a similar action, arising from a branch ambiguity, which describes the exact string naked singularity. In the strong coupling limit the solution dual to AdS_2 is found to be the 5D Schwarzschild black hole. Some applications to black hole thermodynamics and 2D string theory are discussed and generalizations - supersymmetric extension, coupling to matter and critical collapse, quantization - are pointed out.Comment: 41 pages, 2 eps figures, dedicated to Wolfgang Kummer on occasion of his Emeritierung; v2: added ref; v3: extended discussion in sections 3.2, 3.3 and at the end of 5.3 by adding 2 pages of clarifying text; updated refs; corrected typo

On the variability of simulated source-receptor relationships for sulfur deposition

The use of Lagrangian models to estimate source-receptor relationships for ambient SO 4 = concentrations and S deposition has become fairly widespread over the past several years. This paper addresses the sensitivity of long-term simulations of a Lagrangian S transport and deposition model to actual variations in SO 2 emissions and meteorological conditions. The variations of predicted source-receptor relationships due to (1) the inclusion of day to day variations in emissions strength as opposed to the use of the annual average daily emission rate and (2) year-to-year variations in meteorological conditions were studied to identify causes of uncertainty in a Lagrangian model. The results suggested that adding information on day to day emission variations for a specific point source resulted in variations in estimated S wet deposition of the order of only 20% within 500 km of the source.Year-to-year variations in meteorological conditions, on the other hand, resulted in variations in predicted S wet deposition of the order of 50% for some receptors. The variation in estimated source-receptor relationships for a given source/receptor combination was found to range as high as 70% over a 5-yr modeling period.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43900/1/11270_2004_Article_BF00303346.pd

Plant Growth Optimization by Vegetable Production System in HI-SEAS Analog Habitat

The Vegetable Production System (Veggie) is a scientific payload designed to support plant growth for food production under microgravity conditions. The configuration of Veggie consists of an LED lighting system with modular rooting pillows designed to contain substrate media and time-release fertilizer. The pillows were designed to be watered passively using capillary principles but have typically been watered manually by the astronauts in low-Earth orbit (LEO). The design of Veggie allows cabin air to be drawn through the plant enclosure for thermal and humidity control and for supplying CO2 to the plants. Since its delivery to the International Space Station (ISS) in 2014, Veggie has undergone several experimental trials by various crews. Ground unit testing of Veggie was conducted during an 8-month Mars analog study in a semi-contained environment of a simulated habitat located at approximately 8,200 feet (2,500 m) elevation on the Mauna Loa volcano on the Island of Hawaii. The Hawaii Space Exploration Analog and Simulation (HI-SEAS) offered conditions (habitat, mission, communications, etc.) intended to simulate a planetary exploration mission. This paper provides data and analyses to show the prospect for optimized use of the current Veggie design for human habitats. Lessons learned during the study may provide opportunities for updating the system design and operational parameters for current Veggie experiments being conducted onboard the ISS and for payloads on future deep space missions

Magneto-Transport Properties of Doped RuSr2_2GdCu2_2O8_8

RuSr$_2$GdCu$_2$O$_8$, in which magnetic order and superconductivity coexist with $T_{Magnetic}$$\gg$$T_c$, is a complex material which poses new and important questions to our understanding of the interplay between magnetic and superconducting (SC) order. Resistivity, Hall effect and thermopower measurements on sintered ceramic RuSr$_2$GdCu$_2$O$_8$ are presented, together with results on a broad range of substituted analogues. The Hall effect and thermopower both show anomalous decreases below $T_{Magnetic}$ which may be explained within a simple two-band model by a transition from localized to more itinerant behavior in the RuO$_2$ layer at $T_{Magnetic}$.Comment: 10 pages, 7 figures, submitted to Phys. Rev. B., correspondence to [email protected]