Control and dynamics of a flexible spacecraft during stationkeeping maneuvers

A case study of a spacecraft having flexible solar arrays is presented. A stationkeeping attitude control mode using both earth and rate gyro reference signals and a flexible vehicle dynamics modeling and implementation is discussed. The control system is designed to achieve both pointing accuracy and structural mode stability during stationkeeping maneuvers. Reduction of structural mode interactions over the entire mode duration is presented. The control mode using a discrete time observer structure is described to show the convergence of the spacecraft attitude transients during Delta-V thrusting maneuvers without preloading thrusting bias to the onboard control processor. The simulation performance using the three axis, body stabilized nonlinear dynamics is provided. The details of a five body dynamics model are discussed. The spacecraft is modeled as a central rigid body having cantilevered flexible antennas, a pair of flexible articulated solar arrays, and to gimballed momentum wheels. The vehicle is free to undergo unrestricted rotations and translations relative to inertial space. A direct implementation of the equations of motion is compared to an indirect implementation that uses a symbolic manipulation software to generate rigid body equations

Ultrastructural Studies On Stomata Development In Internodes Of Avena Sativa

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141606/1/ajb209789.pd

Heat Transfer and Pressure Drop in Concentric Annular Flows of Binary Inert Gas Mixtures

Studies of heat transfer and pressure drop of binary inert gas mixtures flowing through smooth concentric circular annuli, tubes with fully developed velocity profiles, and constant heating rate are described. There is a general lack of agreement among the constant property heat transfer correlations for such mixtures. No inert gas mixture data exist for annular channels. The intent of this study was to develop highly accurate and benchmarked pressure drop and heat transfer correlations that can be used to size heat exchangers and cores for direct gas Brayton nuclear power plants. The inside surface of the annular channel is heated while the outer surface of the channel is insulated. Annulus ratios range 0.5 < r* < 0.83. These smooth tube data may serve as a reference to the heat transfer and pressure drop performance in annuli, tubes, and channels having helixes or spacer ribs, or other surfaces

Steady-state measurements of respiration rate with an oxygen electrode

An oxygen electrode was developed which measures steady-state respiration rates in a volume of 0.25 ml and at oxygen concentrations as low as 0.1 [mu]. The steady state was achieved by pumping air-equilibrated buffer into the respirometer at various rates. The method is most suitable for tissue slices.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22139/1/0000568.pd

Measurement of oxygen partial pressure within soybean nodules by oxygen microelectrodes

The internal pO 2 of soybean ( Glycine max Merr.) nodules was measured with oxygen microelectrodes. For nodules in air at 23°, the pO 2 decreased sharply across the nodule cortex, and was too low to measure in the central tissue. At 1° in 1.0 atm O 2 , the pO 2 in the central tissue was measurable, and was approximately uniform from the center to the edge of the central tissue. This uniformity was probably due to the intercellular air spaces of the central tissue, since infiltrating the spaces with water substantially decreased the pO 2 in the central tissue. The results strongly suggest that most of the resistance to O 2 diffusion into the nodule occurs within the cortex.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47462/1/425_2004_Article_BF00388335.pd

Aqua­{2,2-[ethane-1,2-diylbis(nitrilo­methyl­idyne)]diphenolato}(3-nitro­benzoato)manganese(III)

The title compound, [Mn(C16H14N2O2)(C7H4NO4)(H2O)], is a Jahn–Teller-distorted manganese(III) monomer with an octa­hedral geometry. The tetra­dentate Schiff base accommodates the MnIII ion at the centre of a nearly planar square. The axial positions are occupied by a monodentate carboxyl­ate group and a water mol­ecule. Adjacent monomers inter­act through hydrogen bonding between the noncoordinated C=O group of the carboxyl­ate and the coordinated water mol­ecule to produce chains extending parallel to the b axis

Redefining genomic privacy: trust and empowerment

Fulfilling the promise of the genetic revolution requires the analysis of large datasets containing information from thousands to millions of participants. However, sharing human genomic data requires protecting subjects from potential harm. Current models rely on de-identification techniques in which privacy versus data utility becomes a zero-sum game. Instead, we propose the use of trust-enabling techniques to create a solution in which researchers and participants both win. To do so we introduce three principles that facilitate trust in genetic research and outline one possible framework built upon those principles. Our hope is that such trust-centric frameworks provide a sustainable solution that reconciles genetic privacy with data sharing and facilitates genetic research

Experimental constraints on a dark matter origin for the DAMA annual modulation effect

A claim for evidence of dark matter interactions in the DAMA experiment has been recently reinforced. We employ a new type of germanium detector to conclusively rule out a standard isothermal galactic halo of Weakly Interacting Massive Particles (WIMPs) as the explanation for the annual modulation effect leading to the claim. Bounds are similarly imposed on a suggestion that dark pseudoscalars mightlead to the effect. We describe the sensitivity to light dark matter particles achievable with our device, in particular to Next-to-Minimal Supersymmetric Model candidates.Comment: v4: introduces recent results from arXiv:0807.3279 and arXiv:0807.2926. Sensitivity to pseudoscalars is revised in light of the first. Discussion on the subject adde

Chronic hindlimb ischemia impairs functional vasodilation and vascular reactivity in mouse feed arteries

Vasodilation of lower leg arterioles is impaired in animal models of chronic peripheral ischemia. In addition to arterioles, feed arteries are a critical component of the vascular resistance network, accounting for as much as 50% of the pressure drop across the arterial circulation. Despite the critical importance of feed arteries in blood flow control, the impact of ischemia on feed artery vascular reactivity is unknown. At 14 days following unilateral resection of the femoral–saphenous artery–vein pair, functional vasodilation of the profunda femoris artery was severely impaired, 11 ± 9 versus 152 ± 22%. Although endothelial and smooth muscle-dependent vasodilation were both impaired in ischemic arteries compared to control arteries (Ach: 40 ± 14 versus 81 ± 11%, SNP: 43 ± 12 versus and 85 ± 11%), the responses to acetylcholine and sodium nitroprusside were similar, implicating impaired smooth muscle-dependent vasodilation. Conversely, vasoconstriction responses to norepinephrine were not different between ischemic and control arteries, −68 ± 3 versus −66 ± 3%, indicating that smooth muscle cells were functional following the ischemic insult. Finally, maximal dilation responses to acetylcholine, ex vivo, were significantly impaired in the ischemic artery compared to control, 71 ± 9 versus 97 ± 2%, despite a similar generation of myogenic tone to the same intravascular pressure (80 mmHg). These data indicate that ischemia impairs feed artery vasodilation by impairing the responsiveness of the vascular wall to vasodilating stimuli. Future studies to examine the mechanistic basis for the impact of ischemia on vascular reactivity or treatment strategies to improve vascular reactivity following ischemia could provide the foundation for an alternative therapeutic paradigm for peripheral arterial occlusive disease