Centaur engine gimbal friction characteristics under simulated thrust load

An investigation was performed to determine the friction characteristics of the engine gimbal system of the Centaur upper stage rocket. Because the Centaur requires low-gain autopilots in order to meet all stability requirements for some configurations, control performance (response to transients and limit-cycle amplitudes) depends highly on these friction characteristics. Forces required to rotate the Centaur engine gimbal system were measured under a simulated thrust load of 66,723 N (15,000 lb) and in an altitude/thermal environment. A series of tests was performed at three test conditions; ambient temperature and pressure, ambient temperature and vacuum, and cryogenic temperature and vacuum. Gimbal rotation was controlled, and tests were performed in which rotation amplitude and frequency were varied by using triangular and sinusoidal waveforms. Test data revealed an elastic characteristic of the gimbal, independent of the input signal, which was evident prior to true gimbal sliding. The torque required to initiate gimbal sliding was found to decrease when both pressure and temperature decreased. Results from the low amplitude and low frequency data are currently being used in mathematically modeling the gimbal friction characteristics for Centaur autopilot performance studies

Saltbush-associated Asphondylia species (Diptera: Cecidomyiidae) in the Mediterranean Basin and their chalcidoid parasitoids (Hymenoptera: Chalcidoidea)

Numerous species of gall midges (Diptera: Cecidomyiidae) have been recorded from saltbush (Chenopodiaceae: Atriplex) around the world but only 11 of them belong to the large cecidomyiid genus Asphondylia. Of these, two species were de-scribed in the late 19th century from complex bud galls on Atriplex halimus in the Mediterranean Basin. In the present study Asphondylia punica is redescribed, A. conglomerata is synonymized with it, and Asphondylia scopuli is described from Atriplex lanfrancoi, an endemic plant to the Maltese Islands. Descriptions are accompanied by information about the galls and life history of the gall midges, and a review of the parasitic Hymenoptera associated with A. scopuli is provided. Four species of parasitoids were found and attributed to the families Eurytomidae, Pteromalidae, Eupelmidae and Eulophidae, of which the pteromalid Mesopolobus melitensis is described as new.peer-reviewe

Effect of vicarious fear learning on children's heart rate responses and attentional bias for novel animals

Research with children has shown that vicarious learning can result in changes to 2 of Lang's (1968) 3 anxiety response systems: subjective report and behavioral avoidance. The current study extended this research by exploring the effect of vicarious learning on physiological responses (Lang's final response system) and attentional bias. The study used Askew and Field's (2007) vicarious learning procedure and demonstrated fear-related increases in children's cognitive, behavioral, and physiological responses. Cognitive and behavioral changes were retested 1 week and 1 month later, and remained elevated. In addition, a visual search task demonstrated that fear-related vicarious learning creates an attentional bias for novel animals, which is moderated by increases in fear beliefs during learning. The findings demonstrate that vicarious learning leads to lasting changes in all 3 of Lang's anxiety response systems and is sufficient to create attentional bias to threat in children

Silicon device performance measurements to support temperature range enhancement

Semiconductor power devices are typically rated for operation below 150 C. Little data is known for power semiconductors over 150 C. In most cases, the device is derated to zero operating power at 175 C. At the high temperature end of the temperature range, the intrinsic carrier concentration increases to equal the doping concentration level and the silicon behaves as an intrinsic semiconductor. The increase in intrinsic carrier concentration results in a shift of the Fermi level toward mid-bandgap at elevated temperatures. This produces a shift in devices characteristics as a function of temperature. By increasing the doping concentration higher operating temperatures can be achieved. This technique was used to fabricate low power analog and digital devices in silicon with junction operating temperatures in excess of 300 C. Additional temperature effects include increased p-n junction leakage with increasing temperature, resulting in increased resistivity. The temperature dependency of physical properties results in variations in device characteristics. These must be quantified and understood in order to develop extended temperature range operation

Yesterday

In lieu of an abstract, below is the essay\u27s first paragraph. Yesterday you said you loved me, tonight you say you don\u27t need me. Where did it go? Why did you stay, what made you decide to treat me this way. Did I hurt you without realizing, I search my mind\u27s eyes looking for answers, not finding a clue. Where did our love go? Tell me what did I do

Ventilation loss and pressurization in the NASA launch/entry suit: Potential for heat stress

The potential of the NASA Launch/Entry Suit (LES) for producing heat stress in a simulated Space Shuttle cabin environment was studied. The testing was designed to identify potential heat stress hazards if the LES were pressurized or if ventilation were lost. Conditions were designed to simulate an extreme pre-launch situation with chamber temperatures maintained at dry bulb temperature = 27.2 +/- 0.1 C, globe temperature = 27.3 +/- 0.1 C, and wet bulb temperature = 21.1 +/- 0.3 C. Two females and two males, 23 to 34 years of age, were employed in this study, with two subjects having exposures in all 3 conditions. Test durations in the ventilated (V) and unventilated (UV) conditions were designed for 480 minutes, which all subjects achieved. Pressurized runs (Pr) were designed for 45 minutes, which all subjects also achieved. While some significant differences related to experimental conditions were noted in rectal and mean skin temperatures, evaporation rates, sweat rates, and heart rate, these differences were not thought to be physiologically significant. The results indicate that the LES garment, in either the Pr or UV state, poses no danger of inducing unacceptable heat stress under the conditions expected within the Space Shuttle cabin during launch or reentry

Small xx Contributions to the Structure Function FL(x,Q2)F_L(x,Q^2)

The gluon contributions to $F_L(x,Q^2)$ in ${\cal O}(\alpha_s)$ are calculated taking into account the transverse momentum of the initial state parton. In comparison with collinear factorization $F_L(x,Q^2)$, is not affected at large $x$ but takes smaller values in the small $x$ range. The onset of the $k_{\perp}$ effect is a function of $Q^2$.Comment: 4 p., postscript encoded with uufiles; DESY 94--14