Application of the DSMC Method for Design of a Coaxial Microthruster Nozzle

The Direct Simulation Monte Carlo (DSMC) method is used to numerically simulate and design a micronozzle with improved performance. Thrust calculations using the DSMC method demonstrate that the coaxial micronozzles can achieve milli-Newton thrust levels with specific impulses on the order of 45 s using argon in a cold gas expansion. Improved micronozzle designs of coaxial microthrusters are also proposed. Coaxial micronozzles utilizing center-body geometries to exploit pressure thrust show about 140% increase in specific impulse at low Reynolds numbers compared to a traditional converging nozzle

Bostonia Perplexa Gen. Et Sp. Nov., A Calamopityan Axis From The New Albany Shale Of Kentucky

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141922/1/ajb206093.pd

Plasma-Neutral Heat Transfer in Coaxial RF Argon Discharges

Particle-in-cell/Monte Carlo Collision (PIC/MCC) algorithms comprise a numerical model to assess the discharge characteristics of an RF plasma microthruster concept that exploits an RF capacitively coupled discharge (RFCCD) to heat a propellant. The effects of heat transfer between the discharge and the neutral species on microthruster performance are discussed. Heat transfer within the plasma discharge has been shown to greatly affect the discharge characteristics and thruster performance. Increasing the neutral temperature reduces the amount of power transmitted into the fluid through a reduction of the neutral density, and thus reduces effectiveness of the discharge. The PIC/MCC modeling showed that the power transmitted into the fluid increases faster than linear with respect to an increase in applied potential, but the total power absorbed increases on the order of a linear trend. The power transmission efficiency is found to be directly proportional to the applied potential, making the discharge more efficient at higher voltages. The theoretical specific impulse also increases as the applied potential or discharge pressure is increased

RFCCD Microthruster Performance via Numerical Simulation

Particle-in-cell/Monte Carlo (PIC/MCC) and Direct Simulation Monte Carlo (DSMC) algorithms comprise a numerical model to assess the propulsive capability of a RF plasma microthruster concept. This thruster concept is an electrothermal device and exploits RF capacitively coupled discharge (RFCCD) to heat a propellant. This RF plasma microthruster has potential to alleviate some severe constraints on microsatellite propulsion systems such as power, mass, volume and lifetime. The discharge characteristics are investigated by permuting electrode geometry (0.5 - 10 mm) and applied voltage (10 - 500 V) at a constant RF frequency of 200 MHz and a pressure of 3 Torr. PIC/MCC simulations determine the overall trends in plasma characteristics within this parameter space. The PIC/MCC modeling showed that increases in applied potential and inner radius transmit more power to the fluid. A gas heat transfer model enhanced the original PIC/MCC code to reflect effects of neutral gas temperature in the plasma

Performance Modeling of an RF Coaxial Plasma Thruster

The RF plasma thruster has considerable potential to ease the impact of severe constraints on power, mass, volume and lifetime of microsatellite propulsion systems. This concept is classified as an electrothermal propulsion system and exploits RF capacitively coupled discharge (RFCCD) for heating of a propellant. The plasma is characterized as a low-power discharge possessing a low-current density with high uniformity and propagating through low-pressure gas. To assess computationally the thruster’s propulsive capabilities as a function of mass flow rate, electrode separation, RF frequency and power input, a numerical model comprises particle-in-cell/Monte Carlo (PIC/MCC) and Direct Simulation Monte Carlo (DSMC) algorithms. Thruster performance is investigated by permuting electrode geometry (0.5 - 2 cm), chamber pressure (0.05 - 50 Torr), applied voltage (100 - 500 V), and frequency (10 - 1000 MHz). For this parameter space, PIC/MCC determines overall trends in plasma characteristics. One selected case (3 Torr, 500 V, 200 MHz) and its set of conditions (plasma density, plasma heating, gas temperature, etc.) form the basis for an in-depth flow field and thrust performance analysis with DSMC. Assuming adiabatic wall conditions, the RF plasma thruster achieves a specific impulse of 104.4 s with Argon at the throat Reynolds number of 25. The RF heating increases the specific impulse by 125 %. This study shows that propulsive capability of the RF plasma thruster can be enhanced by increasing the discharge chamber length, redesigning the nozzle contour, and using propellants with lower molecular weights

Distribution and Length Frequency of Invasive Lionfish (Pterois sp.) in the Northern Gulf of Mexico

The purpose of this communication is to document continued spatial expansion of lionfish farther west into the northern Gulf of Mexico. Furthermore, we provide the first length— mass relationships and length frequency information for lionfishes captured within the northern GOM based on data collected as part of a broader on—going study of lionfish life history in this region

New information on Bostonia perplexa--an unusual member of the calamopityaceae from North America

A calamopityacean axis exhibiting multiple segments of primary xylem surrounded by secondary vascular tissue is analyzed here for its morphological and systematic significance. The plant is fundamentally protostelic with a deeply three-ribbed column of primary xylem. Each rib consists of a semi-discrete bundle of tracheids at the tip, intermittently connected to the stelar center by an extensive primary xylem parenchyma. The appearance of separate vascular segments at some levels is associated with departure of paired leaf traces. Between levels of trace departure, the three-ribbed protostele is reconstituted with primary xylem ribs following a helical course through the stem and supplying a regular Fibonacci phyllotaxis. Attached petiole bases are broadly of the Kalymma-type but exhibit a distinctly three-ribbed medial petiole bundle. The new specimen is assigned to Bostonia perplexa requiring an expanded concept of the taxon. A restricted cladistic analysis of stelar architecture and nodal anatomy within the Calamopityaceae produces two phylogenetic hypotheses. One is preferred on morphological grounds but necessitates viewing at least some protostelic calamopityaceans as exhibiting a derived condition within the group. The redefinition of Bostonia proposed here, a protostelic calamopityacean with medullosan-like vascular segments, reinforces long-standing views of a calamopityacean origin of Medullosales. Cladistic interpretation of stelar form and petiole anatomy in members of these groups, however, reveals character incompatibility hinging upon whether Quaestora (a protostelic medullosan) or Bostonia (a calamopityacean with medullosan-like dissected vascular system) should be preferred as a candidate for medullosan ancestor.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30042/1/0000410.pd

Bone mineral density and risk of heart failure in older adults: The Cardiovascular Health Study

Background Despite increasing evidence of a common link between bone and heart health, the relationship between bone mineral density ( BMD ) and heart failure ( HF ) risk remains insufficiently studied. Methods and Results We investigated whether BMD measured by dual‐energy x‐ray absorptiometry was associated with incident HF in an older cohort. Cox models were stratified by sex and interactions of BMD with race assessed. BMD was examined at the total hip and femoral neck separately, both continuously and by World Health Organization categories. Of 1250 participants, 442 (55% women) developed HF during the median follow‐up of 10.5 years. In both black and nonblack women, neither total hip nor femoral neck BMD was significantly associated with HF ; there was no significant interaction by race. In black and nonblack men, total hip, but not femoral neck, BMD was significantly associated with HF , with evidence of an interaction by race. In nonblack men, lower total hip BMD was associated with higher HF risk (hazard ratio, 1.13 [95% CI, 1.01–1.26] per 0.1 g/cm 2 decrement), whereas in black men, lower total hip BMD was associated with lower HF risk (hazard ratio, 0.74 [95% CI, 0.59–0.94]). There were no black men with total hip osteoporosis. Among nonblack men, total hip osteoporosis was associated with higher HF risk (hazard ratio, 2.83 [95% CI, 1.39–5.74]) compared with normal BMD . Conclusions Among older adults, lower total hip BMD was associated with higher HF risk in nonblack men but lower risk in black men, with no evidence of an association in women. Further research is needed to replicate these findings and to study potential underlying pathways. </jats:sec

Predicting Ares I Reaction Control System Performance by Utilizing Analysis Anchored with Development Test Data

The Ares I launch vehicle is an integral part of NASA s Constellation Program, providing a foundation for a new era of space access. The Ares I is designed to lift the Orion Crew Module and will enable humans to return to the Moon as well as explore Mars.1 The Ares I is comprised of two inline stages: a Space Shuttle-derived five-segment Solid Rocket Booster (SRB) First Stage (FS) and an Upper Stage (US) powered by a Saturn V-derived J-2X engine. A dedicated Roll Control System (RoCS) located on the connecting interstage provides roll control prior to FS separation. Induced yaw and pitch moments are handled by the SRB nozzle vectoring. The FS SRB operates for approximately two minutes after which the US separates from the vehicle and the US Reaction Control System (ReCS) continues to provide reaction control for the remainder of the mission. A representation of the Ares I launch vehicle in the stacked configuration and including the Orion Crew Exploration Vehicle (CEV) is shown in Figure 1. Each Reaction Control System (RCS) design incorporates a Gaseous Helium (GHe) pressurization system combined with a monopropellant Hydrazine (N2H4) propulsion system. Both systems have two diametrically opposed thruster modules. This architecture provides one failure tolerance for function and prevention of catastrophic hazards such as inadvertent thruster firing, bulk propellant leakage, and over-pressurization. The pressurization system on the RoCS includes two ambient pressure-referenced regulators on parallel strings in order to attain the required system level single Fault Tolerant (FT) design for function while the ReCS utilizes a blow-down approach. A single burst disk and relief valve assembly is also included on the RoCS to ensure single failure tolerance for must-not-occur catastrophic hazards. The Reaction Control Systems are designed to support simultaneously firing multiple thrusters as require

Integrated chronostratigraphy of Proterozoic-Cambrian boundary beds in the western Anabar region, northern Siberia

Carbonate-rich sedimentary rocks of the western Anabar region, northern Siberia, preserve an exceptional record of evolutionary and biogeochemical events near the Proterozoic/Cambrian boundary. Sedimentologically, the boundary succession can be divided into three sequences representing successive episodes of late transgressive to early highstand deposition; four parasequences are recognized in the sequence corresponding lithostratigraphically to the Manykai Formation. Small shelly fossils are abundant and include many taxa that also occur in standard sections of southeastern Siberia. Despite this coincidence of faunal elements, biostratigraphic correlations between the two regions have been controversial because numerous species that first appear at or immediately above the basal Tommotian boundary in southeastern sections have first appearances scattered through more than thirty metres of section in the western Anabar. Carbon- and Sr-isotopic data on petrographically and geochemically screened samples collected at one- to two-metre intervals in a section along the Kotuikan River, favour correlation of the Staraya Reckha Formation and most of the overlying Manykai Formation with sub-Tommotian carbonates in southeastern Siberia. In contrast, isotopic data suggest that the uppermost Manykai Formation and the basal 26 m of the unconformably overlying Medvezhya Formation may have no equivalent in the southeast; they appear to provide a sedimentary and palaeontological record of an evolutionarily significant time interval represented in southeastern Siberia only by the sub-Tommotian unconformity. Correlations with radiometrically dated horizons in the Olenek and Kharaulakh regions of northern Siberia suggest that this interval lasted approximately three to six million years, during which essentially all 'basal Tommotian' small shelly fossils evolved