Development of a high power microwave thruster, with a magnetic nozzle, for space applications

This paper describes the current development of a high-power microwave electrothermal thruster (MET) concept at the NASA Lewis Research Center. Such a thruster would be employed in space for applications such as orbit raining, orbit maneuvering, station change, and possibly trans-lunar or trans-planetary propulsion of spacecraft. The MET concept employs low frequency continuous wave (CW) microwave power to create and continuously pump energy into a flowing propellant gas at relative high pressure via a plasma discharge. The propellant is heated to very high bulk temperatures while passing through the plasma discharge region and then is expanded through a throat-nozzle assembly to produce thrust, as in a conventional rocket engine. Apparatus, which is described, is being assembled at NASA Lewis to test the MET concept to CW power levels of 30 kW at a frequency of 915 MHz. The microwave energy is applied in a resonant cavity applicator and is absorbed by a plasma discharge in the flowing propellant. The ignited plasma acts as a lossy load, and with optimal tuning, energy absorption efficiencies over 95 percent (based on the applied microwave power) are expected. Nitrogen, helium, and hydrogen will be tested as propellants in the MET, at discharge chamber pressures to 10 atm

Fabrication and Characterization of Controllable Grain Boundary Arrays in Solution Processed Small Molecule Organic Semiconductor Films

We have produced solution-processed thin films of 6,13-bis(triisopropyl-silylethynyl) pentacene with grain sizes from a few micrometers up to millimeter scale by lateral crystallization from a rectangular stylus. Grains are oriented along the crystallization direction, and the grain size transverse to the crystallization direction depends inversely on the writing speed, hence forming a regular array of oriented grain boundaries with controllable spacing. We utilize these controllable arrays to systematically study the role of large-angle grain boundaries in carrier transport and charge trapping in thin film transistors. The effective mobility scales with the grain size, leading to an estimate of the potential drop at individual large-angle grain boundaries of more than one volt. This result indicates that the structure of grain boundaries is not molecularly abrupt, which may be a general feature of solution processed small molecule organic semiconductor thin films where relatively high energy grain boundaries are typically formed. This may be due to the crystal Transient measurements after switching from positive to negative gate bias or between large and small negative gate bias reveal reversible charge trapping with time constants on the order of 10 s, and trap densities that are correlated with grain boundary density. We suggest that charge diffusion along grain boundaries and other defects is the rate determining mechanism of the reversible trapping.Comment: 12 pages, 11 figure

Iodine sorption study on the proposed use of Viton A in a shuttle galley water accumulator

The installation of a Viton A accumulator in the Shuttle galley has been proposed to prevent overpressurization of the hot water supply system. A laboratory study has been conducted to determine if there would be any interaction between the Viton A material and the iodine used to disinfect the water. Coupons of Viton A were exposed for 24 hours to aqueous iodine solutions similar in quality to the Shuttle's potable water. Changes in the iodine residual were monitored to determine the rate of iodine sorption by the coupon. Total organic carbon (TOC) was monitored to determine the rate of desorption of organic materials from the Viton A. The same coupons were then soaked in reagent-grade water for 24 hours, and iodine was monitored to determine the rate of iodine desorption. The coupons were again exposed to iodine solutions for 24 hours and iodine and TOC were monitored. No significant change in the iodine sorption rate was detected between the first and second exposures. A triangle taste test indicated at a 1 percent confidence level that the water exposed to Viton A had a different taste which was less acceptable to the panelists

Xwnt-5A: a maternal Wnt that affects morphogenetic movements after overexpression in embryos of Xenopus laevis

To contribute to an understanding of the roles and mechanisms of action of Wnts in early vertebrate development, we have characterized the normal expression of Xenopus laevis Wnt-5A, and investigated the consequences of misexpression of this putative signalling factor. Xwnt-5A transcripts are expressed throughout development, and are enriched in both the anterior and posterior regions of embryos at late stages of development, where they are found primarily in ectoderm, with lower levels of expression in mesoderm. Overexpression of Xwnt-5A in Xenopus embryos leads to complex malformations distinct from those achieved by ectopic expression of Xwnts −1, −3A, or −8. This phenotype is unlikely to result from Xwnt-5A acting as an inducing agent, as overexpression of Xwnt-5A does not rescue dorsal structures in UV-irradiated embryos, does not induce mesoderm in blastula caps, and Xwnt-5A does not alter the endogenous patterns of expression of goosecoid, Xbra, or Xwnt-8. To pursue whether Xwnt-5A has the capacity to affect morphogenetic movements, we investigated whether overexpression of Xwnt-5A alters the normal elongation of blastula cap explants induced by activin. Intriguingly, Xwnt-5A blocks the elongation of blastula caps in response to activin, without blocking the differentiation of either dorsal or ventral mesoderm within these explants. The data are consistent with Xwnt-5A having the potential activity of modifying the morphogenetic movements of tissues

Influence of Sacubitril/Valsartan (LCZ696) on 30-day readmission after heart failure hospitalization

Background: Patients with heart failure (HF) are at high risk for hospital readmission in the first 30 days following HF hospitalization. Objectives: This study sought to determine if treatment with sacubitril/valsartan (LCZ696) reduces rates of hospital readmission at 30-days following HF hospitalization compared with enalapril. Methods: We assessed the risk of 30-day readmission for any cause following investigator-reported hospitalizations for HF in the PARADIGM-HF trial, which randomized 8,399 participants with HF and reduced ejection fraction to treatment with LCZ696 or enalapril. Results: Accounting for multiple hospitalizations per patient, there were 2,383 investigator-reported HF hospitalizations, of which 1,076 (45.2%) occurred in subjects assigned to LCZ696 and 1,307 (54.8%) occurred in subjects assigned to enalapril. Rates of readmission for any cause at 30 days were 17.8% in LCZ696-assigned subjects and 21.0% in enalapril-assigned subjects (odds ratio: 0.74; 95% confidence interval: 0.56 to 0.97; p = 0.031). Rates of readmission for HF at 30-days were also lower in subjects assigned to LCZ696 (9.7% vs. 13.4%; odds ratio: 0.62; 95% confidence interval: 0.45 to 0.87; p = 0.006). The reduction in both all-cause and HF readmissions with LCZ696 was maintained when the time window from discharge was extended to 60 days and in sensitivity analyses restricted to adjudicated HF hospitalizations. Conclusions: Compared with enalapril, treatment with LCZ696 reduces 30-day readmissions for any cause following discharge from HF hospitalization

The Gulf Surgeon, Acanthurus randalli, a Junior Synonym of the Ocean Surgeon, Acanthurus bahianus (Teleostei: Acanthuridae)

We compared 62 specimens, 48-126.5 mm standard length, of Acanthurus bahianus from the northeastern Gulf of Mexico with 95 specimens from other localities to determine if the distinguishing characters in the original description of the Gulf of Mexico endemic surgeonfish Acanthurus randalli were valid. No color pattern or meristic differences were found, and the only measurement that allowed distinction (91% percent concordance) was the shallower caudal concavity of northeastern Gulf of Mexico specimens. Acanthurus chirurgus from the northeastern Gulf of Mexico also have shallower caudal concavities (93.7% percent concordance) than do conspecifics from other areas, suggesting that this trend may be correlated with some unknown environmental influence. Considering the extended planktonic larval dispersal capabilities of Atlantic surgeonfishes, and that the single divergent morphological character state is also exhibited in a sympatric northeastern Gulf of Mexico population of A. chirurgus, recognition of A. randalli is untenable, and the name is considered a junior synonym of A. bahianus. An identification key to western Atlantic species of Acanthurus that incorporates the results of this study is given

The Gulf Surgeon, Acanthurus randalli, a Junior Synonym of the Ocean Surgeon, Acanthurus bahianus (Teleostei: Acanthuridae)

We compared 62 specimens, 48-126.5 mm standard length, of Acanthurus bahianus from the northeastern Gulf of Mexico with 95 specimens from other localities to determine if the distinguishing characters in the original description of the Gulf of Mexico endemic surgeonfish Acanthurus randalli were valid. No color pattern or meristic differences were found, and the only measurement that allowed distinction (91% percent concordance) was the shallower caudal concavity of northeastern Gulf of Mexico specimens. Acanthurus chirurgus from the northeastern Gulf of Mexico also have shallower caudal concavities (93.7% percent concordance) than do conspecifics from other areas, suggesting that this trend may be correlated with some unknown environmental influence. Considering the extended planktonic larval dispersal capabilities of Atlantic surgeonfishes, and that the single divergent morphological character state is also exhibited in a sympatric northeastern Gulf of Mexico population of A. chirurgus, recognition of A. randalli is untenable, and the name is considered a junior synonym of A. bahianus. An identification key to western Atlantic species of Acanthurus that incorporates the results of this study is given

Bulk Scalar Stabilization of the Radion without Metric Back-Reaction in the Randall-Sundrum Model

Generalizations of the Randall-Sundrum model containing a bulk scalar field $\Phi$ interacting with the curvature $R$ through the general coupling $R f(\Phi)$ are considered. We derive the general form of the effective 4D potential for the spin-zero fields and show that in the mass matrix the radion mixes with the Kaluza-Klein modes of the bulk scalar fluctuations. We demonstrate that it is possible to choose a non-trivial background form $\Phi_0(y)$ (where $y$ is the extra dimension coordinate) for the bulk scalar field such that the exact Randall-Sundrum metric is preserved (i.e. such that there is no back-reaction). We compute the mass matrix for the radion and the KK modes of the excitations of the bulk scalar relative to the background configuration $\Phi_0(y)$ and find that the resulting mass matrix implies a non-zero value for the mass of the radion (identified as the state with the lowest eigenvalue of the scalar mass matrix). We find that this mass is suppressed relative to the Planck scale by the standard warp factor needed to explain the hierarchy puzzle, implying that a mass \sim 1\tev is a natural order of magnitude for the radion mass. The general considerations are illustrated in the case of a model containing an $R\Phi^2$ interaction term.Comment: 22 pages, 3 figure

An X-Ray Study of the Supernova Remnant G290.1-0.8

G290.1-0.8 (MSH 11-61A) is a supernova remnant (SNR) whose X-ray morphology is centrally bright. However, unlike the class of X-ray composite SNRs whose centers are dominated by nonthermal emission, presumably driven by a central pulsar, we show that the X-ray emission from G290.1-0.8 is thermal in nature, placing the remnant in an emerging class which includes such remnants as W44, W28, 3C391, and others. The evolutionary sequence which leads to such X-ray properties is not well understood. Here we investigate two scenarios for such emission: evolution in a cloudy interstellar medium, and early-stage evolution of a remnant into the radiative phase, including the effects of thermal conduction. We construct models for these scenarios in an attempt to reproduce the observed center-filled X-ray properties of G290.1-0.8, and we derive the associated age, energy, and ambient density conditions implied by the models. We find that for reasonable values of the explosion energy, the remnant age is of order (1 - 2) x 10^{4} yr. This places a fairly strong constraint on any association between G290.1-0.8 and PSR J1105-610, which would require an anomalously large velocity for the pulsar.Comment: 7 pages, 7 figures, ApJ, accepte