Simulation and experimental study of the multichanneling rimfire gas switch

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file viewed on (July 10, 2006)Includes bibliographical references.Thesis (M.S.) University of Missouri-Columbia 2005.Dissertations, Academic -- University of Missouri--Columbia -- Electrical engineering.Since 1985, the Rimfire switch has been used extensively in accelerators at Sandia National Laboratories. Demands for increased future accelerator performance require improvements to the Rimfire switch. This thesis is both a theoretical and experimental study of this switch. Theoretical study was achieved utilizing an advanced circuit model. Through this model, insight was gained into some of the intricacies of switch operation. In addition, past models were verified and extended. Utilizing the University of Missouri Terawatt Test Stand, experiments were conducted studying the multichanneling cascade section of the switch. The electrical affects of multichanneling and a method to force multichanneling was presented. In addition, an objective curve fitting method was used to deduce switch inductance from the measured data. Many conclusions were made with regard to the Rimfire switch. Specific topics included advanced triggering schemes, immersion dielectric changes, jitter reduction, electrical affects of multichanneling, factors effecting multichanneling, and switch impedance calculations

The ferroelectric plasma thruster

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file (viewed on June 9, 2009)Vita.Thesis (Ph. D.) University of Missouri-Columbia 2008.Micropropulsion is an enabling technology for microspacecraft. As requirements for microspacecraft missions become more demanding, so do the requirements for micropropulsion. Therefore, existing technologies require improvement, or new technologies need to be developed. The Ferroelectric Plasma Thruster (FEPT) is a new technology for microspacecraft propulsion. This dissertation is a demonstration of this technology and its characteristics. To produce thrust, the FEPT produces a plasma and a beam of ions. The acceleration of these ions away from the thruster is the mass-transfer mechanism of the thruster. Plasma parameters were measured such as average ion current, ion energy, ion species, and average power dissipated. Photography was performed including open-shutter photography and framing photography. These measured parameters were used to make a calculation of the thrust due to ions.For a more direct measurement of thrust, a micro-thrust stand was designed, built, and characterized. In addition, the mass flow rate from the thruster was measured by weighing the FEPT before and after operation. Combining these two measurements leads to a calculation of the specific impulse. Measured parameters include a thrust of [approximately] 70[micro]N, specific impulse of [approximately] 400 s, average power of [approximately] 6 W, and impulse bits of [less than] 1 nN [multiple] s. Advantages of the FEPT include its small mass of less than 6 g and its inherent simplicity. Only a single, low-power rf power supply is needed to form plasma and accelerate particles. Also, electrons are also expelled from the thruster which potentially removes the necessity of a separate neutralizer. Finally, the impulse bits delivered by the FEPT are extremely small which leads to very fine control of microspacecraft attitude.Includes bibliographical reference

Reduced glycogen availability is associated with increased AMPKα2 activity, nuclear AMPKα2 protein abundance, and GLUT4 mRNA expression in contracting human skeletal muscle

Glycogen availability can influence glucose transporter 4 (GLUT4) expression in skeletal muscle through unknown mechanisms. The multisubstrate enzyme AMP-activated protein kinase (AMPK) has also been shown to play an important role in the regulation of GLUT4 expression in skeletal muscle. During contraction, AMPK [alpha]2 translocates to the nucleus and the activity of this AMPK isoform is enhanced when skeletal muscle glycogen is low. In this study, we investigated if decreased pre-exercise muscle glycogen levels and increased AMPK [alpha]2 activity reduced the association of AMPK with glycogen and increased AMPK [alpha]2 translocation to the nucleus and GLUT4 mRNA expression following exercise. Seven males performed 60 min of exercise at ~70% [VO.sub.2] peak on 2 occasions: either with normal (control) or low (LG) carbohydrate pre-exercise muscle glycogen content. Muscle samples were obtained by needle biopsy before and after exercise. Low muscle glycogen was associated with elevated AMPK [alpha]2 activity and acetyl-CoA carboxylase [beta] phosphorylation, increased translocation of AMPK [alpha]2 to the nucleus, and increased GLUT4 mRNA. Transfection of primary human myotubes with a constitutively active AMPK adenovirus also stimulated GLUT4 mRNA, providing direct evidence of a role of AMPK in regulating GLUT4 expression. We suggest that increased activation of AMPK [alpha]2 under conditions of low muscle glycogen enhances AMPK [alpha]2 nuclear translocation and increases GLUT4 mRNA expression in response to exercise in human skeletal muscle. <br /

Inverse Marx modulators for self-biasing klystron depressed collectors

A novel pulsed depressed collector biasing scheme is proposed. This topology feeds forward energy recovered during one RF pulse for use on the following RF pulse. The presented &quot;inverse&quot; Marx charges biasing capacitors in series, and discharges them in parallel. Simulations are shown along with experimental demonstration on a 62kW klystron. Introduction: SLAC National Accelerator Laboratory (SLAC) is actively developing next-generation high-power RF sources. In response to a US Federal mandate [1] and growing particle accelerator demands, RF power source efficiency is gaining importance. One method for increasing efficiency, a depressed collector, is studied for application in pulsed RF systems. In low duty cycle, high peak power (&gt;1MW), short pulse (&lt;1µs) RF systems, traditional depressed collector stage biasing methods can introduce cathode oscillations, affecting RF output phase and output. Decoupling the collector biasing from the driving modulator avoids these deleterious cathode oscillations and enables recovering the wasted energy in the rise and fall time; critical in short-pulse applications. A self-biasing depressed collector was recently developed. In this method, collector stages dynamically float to potentials according to the impedance of the biasing network and the collected stage current. During the pulse, a step-down transformer builds up energy in a storage capacitor. This energy is then recovered back to the driving modulator in the inter-pulse time perio

The surface area and reactivity of granitic soils: I. Dissolution rates of primary minerals as a function of depth and age deduced from field observations

Surface area-normalised dissolution rates of the primary minerals in two distinct granitic soils located in 1) the Dartmoor National Park, England and 2) Glen Dye, Scotland were determined as a function of depth. Each soil was sampled to a depth of ~ 1 m. The maximum soil ages based on 14C analysis of the humin fraction of the soil are 15,600 and 4400 years for the Dartmoor and Glen Dye soil profiles, respectively. The measured BET surface areas of the soil minerals are close to 5 m2/g in the B and C horizons, but decrease to less than 1 m2/g close to the surface. Retrieved geometric surface area normalised mineral dissolution rates are most rapid at the surface and at the bedrock–soil interface; this behaviour is interpreted to stem from a combination of the approach to equilibrium of the soil waters with depth and more rapid dissolution rates of fresh versus weathered surfaces. At the soil surface, the relative mineral dissolution rate order is found to be quartz > feldspar > mica, with quartz geometric surface area dissolution rates as fast as 2.6 to 4.1 × 10− 13 mol/m2/s. As observed in a number of past studies, field based rates obtained in this study are significantly slower than corresponding rates obtained from laboratory studies, suggesting that these latter rates may not accurately describe the reactivity of primary minerals in soils

Oral dosing for antenatal corticosteroids in the Rhesus macaque.

Antenatal corticosteroids (ACS) are standard of care for women at risk of preterm delivery, although choice of drug, dose or route have not been systematically evaluated. Further, ACS are infrequently used in low resource environments where most of the mortality from prematurity occurs. We report proof of principle experiments to test betamethasone-phosphate (Beta-P) or dexamethasone-phosphate (Dex-P) given orally in comparison to the clinical treatment with the intramuscular combination drug beta-phosphate plus beta-acetate in a Rhesus Macaque model. First, we performed pharmacokinetic studies in non-pregnant monkeys to compare blood levels of the steroids using oral dosing with Beta-P, Dex-P and an effective maternal intramuscular dose of the beta-acetate component of the clinical treatment. We then evaluated maternal and fetal blood steroid levels with limited fetal sampling under ultrasound guidance in pregnant macaques. We found that oral Beta is more slowly cleared from plasma than oral Dex. The blood levels of both drugs were lower in maternal plasma of pregnant than in non-pregnant macaques. Using the pharmacokinetic data, we treated groups of 6-8 pregnant monkeys with oral Beta-P, oral Dex-P, or the maternal intramuscular clinical treatment and saline controls and measured pressure-volume curves to assess corticosteroid effects on lung maturation at 5d. Oral Beta-P improved the pressure-volume curves similarly to the clinical treatment. Oral Dex-P gave more variable and nonsignificant responses. We then compared gene expression in the fetal lung, liver and hippocampus between oral Beta-P and the clinical treatment by RNA-sequencing. The transcriptomes were largely similar with small gene expression differences in the lung and liver, and no differences in the hippocampus between the groups. As proof of principle, ACS therapy can be effective using inexpensive and widely available oral drugs. Clinical dosing strategies must carefully consider the pharmacokinetics of oral Beta-P or Dex-P to minimize fetal exposure while achieving the desired treatment responses

Exposure of Salmonella enterica Serovar Typhimurium to High Level Biocide Challenge Can Select Multidrug Resistant Mutants in a Single Step

Biocides are crucial to the prevention of infection by bacteria, particularly with the global emergence of multiply antibiotic resistant strains of many species. Concern has been raised regarding the potential for biocide exposure to select for antibiotic resistance due to common mechanisms of resistance, notably efflux.Salmonella enterica serovar Typhimurium was challenged with 4 biocides of differing modes of action at both low and recommended-use concentration. Flow cytometry was used to investigate the physiological state of the cells after biocide challenge. After 5 hours exposure to biocide, live cells were sorted by FACS and recovered. Cells recovered after an exposure to low concentrations of biocide had antibiotic resistance profiles similar to wild-type cells. Live cells were recovered after exposure to two of the biocides at in-use concentration for 5 hours. These cells were multi-drug resistant and accumulation assays demonstrated an efflux phenotype of these mutants. Gene expression analysis showed that the AcrEF multidrug efflux pump was de-repressed in mutants isolated from high-levels of biocide.These data show that a single exposure to the working concentration of certain biocides can select for mutant Salmonella with efflux mediated multidrug resistance and that flow cytometry is a sensitive tool for identifying biocide tolerant mutants. The propensity for biocides to select for MDR mutants varies and this should be a consideration when designing new biocidal formulations

Titanium sapphire : A decade of diode-laser pumping

For many years, Ti:sapphire was the prototypical example of a solid-state laser material that could not be diode pumped. The rationale for this assessment follows from the laser properties of Ti:sapphire, which combine to demand high brightness pumping in the blue-green region (see fig. 1 [1]). The development of efficient Gallium Nitride (GaN) based laser diodes eroded this logic [2], and improvements in the spatial brightness of GaN diode lasers subsequently enabled the first demonstration of a directly diode-laser pumped Ti:sapphire laser in 2009 [3], This presentation will outline the physics that makes diode-pumping difficult, and the developments that mean, it is, nonetheless, possible. Interestingly, diode-pumping of CW and modelocked Ti:sapphire lasers was achieved not by a radical redesign of the laser, but by careful optimisation of existing approaches that enabled the rapidly improving brightness of GaN diode lasers to be exploited [3-5]

Ultrafast diode-pumped Ti:sapphire laser with broad tunability

We report a broadly wavelength-tunable femtosecond diode-pumped Ti:sapphire laser, passively mode-locked using both semiconductor saturable absorber mirror (SESAM) and Kerr-lens mode-locking (KLM) techniques. Using two pump laser diodes (operating at 450 nm), an average output power as high as 433 mW is generated during mode-locking with the SESAM. A tunability range of 37 nm (788-825 nm) was achieved with the shortest pulse duration of 62 fs at 812 nm. In the KLM regime, an average output power as high as 382 mW, pulses as short as 54 fs, and a tunability of 120 nm (755-875 nm) are demonstrated

A broadly tunable ultrafast diode-pumped Ti:sapphire laser

We report a diode-pumped ultrafast Ti:sapphire laser tunable over a 50 nm range. Sub-100 fs pulses are generated at a pulse repetition rate of 139 MHz with a maximum average output power of 430 mW