No abstract available
Topics: Arnold, Bradley, Choa, Fow-Sen, Maryland Univ. Baltimore County, NASA Marshall Space Flight Center,...
We examined the various likely processes for creating the cavities and found that the mirror force acting on the transversely heated ions is the most likely mechanism. The pondermotive force causing the wave collapse was found to be a much weaker force than the mirror force on the transversely heated ions observed inside the cavities along with the lower hybrid waves. Using a hydrodynamic model for the polar wind we modeled the cavity formation and found that for the heating rate obtained from...
Topics: NASA Technical Reports Server (NTRS), EARTH IONOSPHERE, IONOSPHERIC HEATING, IONS, PLASMA HEATING,...
We present brief overview of our study on the low temperature flux growth of two very important novel wide bandgap materials 2H-SiC and Beta-gallium oxide (Beta-Ga2O3). We have synthesized and grown 5 millimeter to 1 centimeter size single crystals of Beta-gallium oxide (Beta-Ga2O3). We used a flux and semi wet method to grow transparent good quality crystals. In the semi-wet method Ga2O3 was synthesized with starting gallium nitrate solution and urea as a nucleation agent. In the flux method...
Topics: Arnold, Bradley, Choa, Fow-Sen, Kelly, Lisa, Maryland Univ. Baltimore County, NASA Marshall Space...
Material is the key component and controls the performance of the detectors, devices and sensors. The materials design, processing, growth and fabrication of bulk and nanocrystals and fabrication into devices and sensors involve multidisciplinary team of experts. This places a large burden on the cost of the novel materials development. Due to this reason there is a big thrust for the prediction of multifunctionality of materials before design and development. Up to some extent design can...
Topics: Arnold, Brad, Bohorfous, Sara, Choa, Fow-Sen, Maryland Univ. Baltimore County, NASA Marshall Space...
No abstract available
Topics: Arnold, B., Chao, Fow-Sen, Kelly, Lisa, Maryland Univ. Baltimore County, NASA Marshall Space Flight...
Increasing threats of radiological weapons have revitalized the researches for low cost large volume -ray and neutron ray sensors In the past few years we have designed and grown ternary and quaternary lead and thallium chalcogenides and lead selenoiodides for detectors to meet these challenges. These materials are congruent, can be tailored to enhance the parameters required for radiation sensors. In addition, this class of compounds can be grown by Bridgman method which promises for large...
Topics: Arnold, Brad, Choa, Fow-Sen, Maryland Univ. Baltimore County, NASA Marshall Space Flight Center,...
A major laboratory dedicated to biological-medical research is proposed for the Space Platform. The laboratory would focus on sensor physiology and biochemistry since sensory physiology represents the first impact of the new space environment on living organisms. Microgravity and the high radiation environment of space would be used to help solve the problems of prolonged sojourns in space but, more importantly, to help solve terrestrial problems of human health and agricultural productivity....
Topics: NASA Technical Reports Server (NTRS), BIOCHEMISTRY, MICROGRAVITY, PHYSIOLOGY, SPACE LABORATORIES,...
Arcing and other types of electrical discharges are likely to occur in high-voltage subsystems of the Space Station. Results from ground and space experiments on the arcing of solar cell arrays are briefly reviewed, showing that the arcing occurs when the conducting interconnects in the arrays are at negative potential above a threshold, which decreases with the increasing plasma density. Furthermore, above the threshold voltages the arcing rate increases with the plasma density. At the...
Topics: NASA Technical Reports Server (NTRS), AEROSPACE ENVIRONMENTS, ARC DISCHARGES, ELECTRIC DISCHARGES,...
During the last 10 months of the grant, both laminar and anomalous plasma processes occurring during the refilling of the outer plasmasphere after magnetic storms are investigated. Theoretical investigations were based on two types of models: (1) two-stream hydrodynamic model in which plasma flows from the conjugate ionospheres are treated as separate fluids and the ion temperature anisotropies are treated self-consistently; and (2) large-scale particle-in-cell code.
Topics: NASA Technical Reports Server (NTRS), ANISOTROPY, ION TEMPERATURE, MAGNETOSPHERE-IONOSPHERE...
Semiconductor nanowires exhibit very exciting optical and electrical properties including high transparency and a several order of magnitude better photocurrent than thin film and bulk materials. We present here the mechanism of nanowire growth from the melt-liquid-vapor medium. We describe preliminary results of binary and ternary selenide materials in light of recent theories. Experiments were performed with lead selenide and thallium arsenic selenide systems which are multifunctional...
Topics: Arnold, B., Choa, Fow-Sen, Coriell, S. R., Cullum, Brian, Hopkins, Inc., Hopkins, R. H., Maryland...
Investigations dealing with the generation of waves by contaminant ions are reported. The studies included the properties of the velocity distribution function of such ions. It was found that it takes about one ion-cyclotron period for the distribution function to transform from a beam to a ring distribution. A linear instability analysis was performed to examine the possibility of wave excitation by an ion beam streaming perpendicular to the ambient magnetic field in an ionospheric type of...
Topics: NASA Technical Reports Server (NTRS), CONTAMINANTS, DISTRIBUTION FUNCTIONS, ION BEAMS, IONS,...
In the past two decades there has been a large rise in the investment and expectations for nanotechnology use. Almost every area of research has projected improvements in sensors, or even a promise for the emergence of some novel device technologies. For these applications major focuses of research are in the areas of nanoparticles and graphene. Although there are some near term applications with nanowires in photodetectors and other low light detectors, there are few papers on the growth...
Topics: Arnold, B., Choa, Fow-Sen, Coriell, S. R., Cullum, Brian, Hopkins, Inc., Hopkins, R. H., Maryland...
Physical vapor transport processes were studied for the purpose of identifying the magnitude of convective effects on the crystal growth process. The effects of convection on crystal quality were were studied by varying the aspect ratio and those thermal conditions which ultimately affect thermal convection during physical vapor transport. An important outcome of the present study was the observation that the convection growth rate increased up to a certain value and then dropped to a constant...
Topics: NASA Technical Reports Server (NTRS), CRYSTAL GROWTH, CRYSTALS, KINETICS, OPTOELECTRONIC DEVICES,...
There is a strong need for developing multifunctional materials to reduce the cost of applied material without compromising the performance of the detectors, devices and sensors. The materials design, processing, growth and fabrication of bulk and nanocrystals and fabrication into devices and sensors involve huge cost and resources including a multidisciplinary team of experts. Because of this reason, prediction of multifunctionality of materials before design and development should be...
Topics: NASA Technical Reports Server (NTRS), 4e91d8daa3224fbf8bc09ecffef19666,...
No abstract available
Topics: NASA Technical Reports Server (NTRS), ACOUSTO-OPTICS, HALIDES, SELENIDES, ANISOTROPY, CRYSTALS,...
Heavy metal halides and selenides have unique properties which make them excellent materials for chemical, biological and radiological sensors. Recently it has been shown that selenohalides are even better materials than halides or selenides for gamma-ray detection. These materials also meet the strong needs of a wide band imaging technology to cover ultra-violet (UV), midwave infrared wavelength (MWIR) to very long wavelength infrared (VLWIR) region for hyperspectral imager components such as...
Topics: NASA Technical Reports Server (NTRS), ACOUSTO-OPTICS, HALIDES, SELENIDES, ANISOTROPY, CRYSTALS,...
Experiments were carried out to grow 3.Nitroaniline (m.NA) crystals doped with 4.Nitroaniline (p.NA) and 2.chloro 4.Nitroaniline (CNA). The measured undercooling for m.NA, p.NA, and CNA were 0.21 tm K, 0.23 tm K, and 0.35 tm K respectively, where tm represents the melting temperature of the pure component. Because of the crystals' large heat of fusion and large undercooling, it was not possible to grow good quality crystals with low thermal gradients. In the conventional two-zone Bridgman...
Topics: NASA Technical Reports Server (NTRS), ANILINE, BRIDGMAN METHOD, DOPED CRYSTALS, NITRO COMPOUNDS,...
Several mechanisms which can cause electric (E) and magnetic (B) field contaminations of the Space Station environment are identified. The level of E and B fields generated by some of them such as the motion of the vehicle across the ambient magnetic field B(0) and the 20-kHz leakage currents and charges can be controlled by proper design considerations. On the other hand, there are some mechanisms which are inherent to the interaction of large vehicles with the plasma and probably their...
Topics: NASA Technical Reports Server (NTRS), EARTH ORBITAL ENVIRONMENTS, ELECTRIC FIELDS, ELECTROMAGNETIC...
A detailed study on the effect of convection on crystal quality was carried out by growing lead bromide crystals in transparent Bridgman furnace. Direct observations were made on the solid-liquid interface and a new kind of instability was observed. This could be explained on the basis of toroidal flow in the AgBr-doped lead bromide sample. With the increasing translation velocity, the interface changed from flat to depressed, and then formed a cavity in the center of the growth tube. The...
Topics: NASA Technical Reports Server (NTRS), BRIDGMAN METHOD, DOPED CRYSTALS, CRYSTAL GROWTH, MORPHOLOGY,...
No abstract available
Topics: NASA Technical Reports Server (NTRS), SINGLE CRYSTALS, ARSENIC COMPOUNDS, SELENIDES, THALLIUM...
Measurements from the space shuttle flights have revealed that a large spacecraft in a low earth orbit is accompanied by an extensive gas cloud which is primarily made up of water. The charge exchange between the water molecule and the ionospheric O(+) ions produces a water ion beam traversing downstream of the spacecraft. In this report we present results from a study on the generation of plasma waves by the interaction of the water ion beams with the ionospheric plasma. Since velocity...
Topics: NASA Technical Reports Server (NTRS), CHARGE EXCHANGE, CYCLOTRON FREQUENCY, EARTH ORBITAL...
The Al-Si material system is an important and has been studied for over half century with a focus on industrial applications in high strength and high conductivity alloys. A great deal of researches have been focused on controlling the morphology and hence performance through the addition of small impurities and by processing conditions. Most of the structure-property correlations are based on the post solidified micromorphology and growth conditions. This material system is unique and has been...
Topics: NASA Technical Reports Server (NTRS), 2d103458298f41978c8aa40aa98d830a,...
No abstract available
Topics: NASA Technical Reports Server (NTRS), 2c61284d1e3348ab86b0eee511e5d592,...
The local bifurcation of the flow field, during physical vapor transport for a parametric range of experimental interest, shows that its dynamical state ranges from steady to aperiodic. Comparison of computationally predicted velocity profiles with laser doppler velocimetry measurements shows reasonable agreement in both magnitude and planform. Correlation of experimentally measured crystal quality with the predicted dynamical state of the flow field shows a degradation of quality with an...
Topics: NASA Technical Reports Server (NTRS), CRYSTAL GROWTH, FLOW DISTRIBUTION, MERCURY COMPOUNDS,...
Investigations based on small-scale simulations of microprocesses occurring when a magnetic flux tube refills with a cold plasma are summarized. Results of these investigations are reported in the following attached papers: (1) 'Numerical Simulation of Filling a Magnetic Flux Tube with a Cold Plasma: The Role of Ion Beam-Driven Instabilities'; and (2) 'Numerical Simulation of Filling a Magnetic Flux Tube with a Cold Plasma: Effects of Magnetically Trapped Hot Plasma'. Other papers included are:...
Topics: NASA Technical Reports Server (NTRS), BEAM INTERACTIONS, COLD PLASMAS, HIGH TEMPERATURE PLASMAS,...
Thin film and nanocrystalline materials of oxides have been very attractive choice as low cost option for gamma-ray detection and have shown great promise. Our studies on pure oxide films indicated that thickness and microstructure have pronounced effect on sensitivity. Since the interaction of gamma-ray with composites involves all three interaction processes; photoelectric effect, Compton scattering, and pair production, composites containing ionic organics have better chance for enhancing...
Topics: NASA Technical Reports Server (NTRS), 1902665e7bf44746866ca0d6183674ca,...
