Sub-Optimal Control of Rigid Spacecraft Reorientation Using Three Momentum Wheels

This thesis addresses sub-optimal employment of 3 momentum wheels for large angle reorientation of rigid spacecraft with minimal induced spacecraft motion during maneuvers. In addition to development of general theory for 3 wheel vehicles, simulation results for a vehicle using momentum wheels for secondary attitude control (GPS Block IIR) are compared to results for a vehicle using them for primary attitude control (the Hubble Space Telescope), to demonstrate practical applications and limitations. While the control laws were developed assuming no external perturbing torques on the vehicle, reorientation scenarios were run both in a torque free environment as well as an environment with simulated gravity gradient and solar pressure torques. The goal was primarily to show the growth of vehicle angular velocities and again demonstrate limitations of the derived control laws. The results indicate that for real spacecraft with limited wheel momentum storage capacities, there is a significant trade-off between maneuver times and required wheel torques, and that final state errors (angular velocities) increase with increasing wheel torques. Nonetheless, the simulations demonstrated that large angle maneuvers can be performed for both GPS Block lift and Hubble Space Telescope in reasonable times and with small angular velocities using the sub-optimal control law. However, gravity gradient and solar pressure torques tended to cause larger fluctuations in total angular momentum, angular velocities, and final state errors for the Hubble Space Telescope

AAV5-mediated targeted decorin gene therapy : effective and safe for corneal fibrosis [abstract]

Corneal fibrosis is 3rd leading cause of global blindness according to WHO report. At present, no agents are proven to clinically reduce corneal fibrosis without causing significant side effects. It was hypothesized that decorin gene delivered into keratocytes prevents corneal fibrosis in the cornea in vivo by blocking transforming growth factor β (TGFb), which converts keratocyte to myofibroblasts and cause fibrosis

Tissue-selective controlled decorin gene delivery in the rabbit cornea significantly retards corneal angiogenesis in vivo [abstract]

Recent studies have shown that decorin gene therapy inhibits neovascularization in many non-ocular tissues. We tested the efficacy of decorin gene delivery into stroma with AAV5 to impede vascular endothelial growth factor (VEGF)-induced angiogenesis in rabbit cornea in vivo

The fundamental problem of command : plan and compliance in a partially centralised economy

When a principal gives an order to an agent and advances resources for its implementation, the temptations for the agent to shirk or steal from the principal rather than comply constitute the fundamental problem of command. Historically, partially centralised command economies enforced compliance in various ways, assisted by nesting the fundamental problem of exchange within that of command. The Soviet economy provides some relevant data. The Soviet command system combined several enforcement mechanisms in an equilibrium that shifted as agents learned and each mechanism's comparative costs and benefits changed. When the conditions for an equilibrium disappeared, the system collapsed.Comparative Economic Studies (2005) 47, 296–314. doi:10.1057/palgrave.ces.810011

Targeted Decorin Gene Therapy Delivered with Adeno-Associated Virus Effectively Retards Corneal Neovascularization \u3cem\u3ein vivo\u3c/em\u3e

Decorin, small leucine-rich proteoglycan, has been shown to modulate angiogenesis in nonocular tissues. This study tested a hypothesis that tissue-selective targeted decorin gene therapy delivered to the rabbit stroma with adeno-associated virus serotype 5 (AAV5) impedes corneal neovascularization (CNV) in vivo without significant side effects. An established rabbit CNV model was used. Targeted decorin gene therapy in the rabbit stroma was delivered with a single topical AAV5 titer (100 μl; 5x10^12 vg/ml) application onto the stroma for two minutes after removing corneal epithelium. The levels of CNV were examined with stereomicroscopy, H&E staining, lectin, collagen type IV, CD31 immunocytochemistry and CD31 immunoblotting. Real-time PCR quantified mRNA expression of pro- and anti-angiogenic genes. Corneal health in live animals was monitored with clinical, slit-lamp and optical coherence tomography biomicroscopic examinations. Selective decorin delivery into stroma showed significant 52% (p\u3c0.05), 66% (p\u3c0.001), and 63% (p\u3c0.01) reduction at early (day 5), mid (day 10), and late (day 14) stages of CNV in decorin-delivered rabbit corneas compared to control (no decorin delivered) corneas in morphometric analysis. The H&E staining, lectin, collagen type IV, CD31 immunostaining (57–65, p\u3c0.5), and CD31 immunoblotting (62–67%, p\u3c0.05) supported morphometric findings. Quantitative PCR studies demonstrated decorin gene therapy down-regulated expression of VEGF, MCP1 and angiopoietin (pro-angiogenic) and up-regulated PEDF (anti-angiogenic) genes. The clinical, biomicroscopy and transmission electron microscopy studies revealed that AAV5– mediated decorin gene therapy is safe for the cornea. Tissue-targeted AAV5-mediated decorin gene therapy decreases CNV with no major side effects, and could potentially be used for treating patients

Chemical characteristics of air from differing source regions during the Pacific Exploratory Mission‐Tropics A (PEM‐Tropics A)

Ten‐day backward trajectories are used to determine the origins of air parcels arriving at airborne DC‐8 chemical measurement sites during NASA\u27s Pacific Exploratory Mission‐Tropics A (PEM‐T) that was conducted during August‐October 1996. Those sites at which the air had a common geographical origin and transport history are grouped together, and statistical measures of chemical characteristics are computed. Temporal changes in potential temperature are used to determine whether trajectories experience a significant convective influence during the 10‐day period. Those trajectories that do not experience a significant convective influence are divided into four geographical categories depending on their origins and paths. Air parcels originating over Africa and South America are characterized by enhanced mixing ratios of O3, CO, HNO3, and PAN. The backward trajectories travel at high altitudes (∼10–11 km), covering long distances due to strong upper‐tropospheric westerly winds. The observed enhancement of combustion‐related species is attributed to biomass burning from distant sources to the west, extending even to South America. The relatively large value of Be‐7 probably is due either to less efficient removal of aerosols from upper tropospheric air or to small stratospheric contributions. Aged marine parcels are found to have relatively small concentrations of burning‐related species. Although these trajectories arrive at a wide range of aircraft altitudes, they do not pass over a land mass during the preceding 10‐day period. Air passing over Australia but no other land mass exhibits a combustion signature; however, photochemical product species such as O3 and PAN are less enhanced than in the long‐range transport category. These trajectories travel shorter distances and are at lower altitudes (∼5–8 km) than those reaching Africa and/or South America. The combustion influence on these parcels is attributed to biomass burning emissions injected over Australia. That burning is less widespread than in Africa and South America. Finally, trajectories originating over Southeast Asia appear to receive a weak combustion influence. However, compared to Africa and South America, Southeast Asia has a relatively small incidence of biomass burning. There is little combustion input from Australia due to the high transport altitudes compared to the lower heights of the convection. The Southeast Asian parcels exhibit the greatest NOx to ∑NOi ratio of any category, perhaps due to lightning. Parcels experiencing a significant convective influence also are examined. Most of these parcels pass through widespread, persistent convection along either the South Pacific Convergence Zone or Intertropical Convergence Zone approximately 5 days prior to arriving at the aircraft locations. Thus the category mostly represents marine convection. Mixing ratios of peroxides and acids in the convective category are found to be smaller than in parcels not experiencing convection. Small mixing ratios of Be‐7 and Pb‐210 suggest particle removal by precipitation

Vorinostat: A Potent Agent to Prevent and Treat Laser-Induced Corneal Haze

PURPOSE—This study investigated the efficacy and safety of vorinostat, a deacetylase (HDAC) inhibitor, in the treatment of laser-induced corneal haze following photorefractive keratectomy (PRK) in rabbits in vivo and transforming growth factor beta 1 (TGFβ1) -induced corneal fibrosis in vitro. METHODS—Corneal haze in rabbits was produced with −9.00 diopters (D) PRK. Fibrosis in cultured human and rabbit corneal fibroblasts was activated with TGFβ1. Vorinostat (25 μm) was topically applied once for 5 minutes on rabbit cornea immediately after PRK for in vivo studies. Vorinostat (0 to 25 μm) was given to human/rabbit corneal fibroblasts for 5 minutes or 48 hours for in vitro studies. Slit-lamp microscopy, TUNEL assay, and trypan blue were used to determined vorinostat toxicity, whereas real-time polymerase chain reaction, immunocytochemistry, and immunoblotting were used to measure its efficacy. RESULTS—Single 5-minute vorinostat (25 μm) topical application on the cornea following PRK significantly reduced corneal haze (Pin vivoscreened 4 weeks after PRK. Vorinostat reduced TGFβ1-induced fibrosis in human and rabbit corneas in vitro in a dose-dependent manner without altering cellular viability, phenotype, or proliferation. CONCLUSIONS—Vorinostat is non-cytotoxic and safe for the eye and has potential to prevent laser-induced corneal haze in patients undergoing PRK for high myopia

System Parameters of the Transiting Extrasolar Planet HD 209458b

We derive improved system parameters for the HD 209458 system using a model that simultaneously fits both photometric transit and radial velocity observations. The photometry consists of previous Hubble Space Telescope STIS and FGS observations, twelve I-band transits observed between 2001-2003 with the Mt. Laguna Observatory 1m telescope, and six Stromgren b+y transits observed between 2001-2004 with two of the Automatic Photometric Telescopes at Fairborn Observatory. The radial velocities were derived from Keck/HIRES observations. The model properly treats the orbital dynamics of the system, and thus yields robust and physically self-consistent solutions. Our set of system parameters agrees with previously published results though with improved accuracy. For example, applying robust limits on the stellar mass of 0.93-1.20Msun, we find 1.26 < Rplanet < 1.42 Rjup and 0.59 < Mplanet < 0.70 Mjup. We can reduce the uncertainty on these estimates by including a stellar mass-radius relation constraint, yielding Rplanet = 1.35 +/- 0.07 Rjup and Mplanet = 0.66 +/- 0.04 Mjup. Our results verify that the planetary radius is 10-20% larger than predicted by planet evolution models, confirming the need for an additional mechanism to slow the evolutionary contraction of the planet. A revised ephemeris is derived, T0=2452854.82545 + 3.52474554E (HJD), which now contains an uncertainty in the period of 0.016s and should facilitate future searches for planetary satellites and other bodies in the HD 209458 system.Comment: 30 pages, 5 figures. To appear in ApJ, 2005 Oct 2

Functional MRI in Awake Unrestrained Dogs

Because of dogs' prolonged evolution with humans, many of the canine cognitive skills are thought to represent a selection of traits that make dogs particularly sensitive to human cues. But how does the dog mind actually work? To develop a methodology to answer this question, we trained two dogs to remain motionless for the duration required to collect quality fMRI images by using positive reinforcement without sedation or physical restraints. The task was designed to determine which brain circuits differentially respond to human hand signals denoting the presence or absence of a food reward. Head motion within trials was less than 1 mm. Consistent with prior reinforcement learning literature, we observed caudate activation in both dogs in response to the hand signal denoting reward versus no-reward