12,101 research outputs found

    Centaur engine gimbal friction characteristics under simulated thrust load

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    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

    A preliminary check-list of the Chalcidoidea (Hymenoptera) of the Maltese Islands

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    A list of 147 species of Chalcidoidea from the Maltese Islands is presented 73 of which are here reported for the first time from this territory. They belong to 15 families as follows: Agaonidae (3); Aphelinidae (20 including 3 new records); Azotidae (1 new record); Chalcididae (3 new records); Encyrtidae (23 including 13 new records); Eulophidae (35 including 19 new records); Eupelmidae (7 including 2 new records); Eurytomidae (5 including 4 new records); Leucospidae (4); Mymaridae (2); Ormyridae (1 new record); Pteromalidae (33 including 21 new records); Signiphoridae (2); Tetracampidae (1 new record); Torymidae (7 including 5 new records). Out of the 73 new records, 55 were exclusively found in Malaise trap samples at Verdala Palace near Buskett, a semi-natural wooded area dominated by Pinus halepensis. Thirty species mentioned in the present study were reared from plant-galls, either during the present study or in former studies pertaining to Malta. Of these 8 are gall inducers and the rest are primary or secondary parasitoids of the gall inducers. This list must represent only a small proportion of the actual species richness expected to be found in the Maltese Islands since absolutely no field work was carried out in other diverse and potentially rich habitats, such as steppe, garigue, maquis, coastal habitats and valley systems, present on these islands.peer-reviewe

    Implications of Scaling Violations of F2 at HERA for Perturbative QCD

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    We critically examine the QCD predictions for the Q2Q^2 dependence of the electron-proton deep-inelastic structure function F2(x,Q2)F_2(x,Q^2) in the small xx region, which is being probed at HERA. The standard results based on next-to-leading order Altarelli-Parisi evolution are compared with those that follow from the BFKL equation, which corresponds to the resummation of the leading log(1/x)(1/x) terms. The effects of parton screening are also quantified. The theoretical predictions are confronted with each other, and with existing data from HERA. (3 Postscript figures included).Comment: (8 Latex Pages) IFJ 1653/P

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

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    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

    Preventing the development of observationally learnt fears in children by devaluing the model's negative response

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    Vicarious learning has become an established indirect pathway to fear acquisition. It is generally accepted that associative learning processes underlie vicarious learning; however, whether this association is a form of conditioned stimulus-unconditioned stimulus (CS-US) learning or stimulus-response (CS-CR) learning remains unclear. Traditionally, these types of learning can be dissociated in a US revaluation procedure. The current study explored the effects of post-vicarious learning US revaluation on acquired fear responses. Ninety-four children (46 males and 48 females) aged 6 to 10 years first viewed either a fear vicarious learning video or a neutral vicarious learning video followed by random allocation to one of three US revaluation conditions: inflation; deflation; or control. Inflation group children were presented with still images of the adults in the video and told that the accompanying sound and image of a very fast heart rate monitor belonged to the adult. The deflation group were shown the same images but with the sound and image of a normal heart rate. The control group received no US revaluation. Results indicated that inflating how scared the models appeared to be did not result in significant increases in children's fear beliefs, avoidance preferences, avoidance behavior or heart rate for animals above increases caused by vicarious learning. In contrast, US devaluation resulted in significant decreases in fear beliefs and avoidance preferences. Thus, the findings provide evidence that CS-US associations underpin vicarious learning and suggest that US devaluation may be a successful method for preventing children from developing fear beliefs following a traumatic vicarious learning episode with a stimulus

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

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    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

    Ventilation Loss in the NASA Space Shuttle Crew Protective Garments: Potential for Heat Stress

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    The potential of the National Aeronautics and Space Administration (NASA) S1035 Launch/Entry suit (LES) for producing heat stress in a simulated Space Shuttle cabin environment has been studied. The testing was designed to determine if the NASA S1035 poses a greater threat of inducing heat stress than the NASA S1032. Conditions were designed to simulate an extreme prelaunch 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. Four males, aged 28-48, were employed in this study, with three subjects having exposures in all four conditions and the fourth subject exposed to 3 conditions. Test durations in the ventilated (V) and unventilated (UV) conditions were designed for 480 minutes, which all subjects achieved. No significant differences related to experimental conditions were noted in rectal temperatures, heart rates or sweat rates. The results indicate that the S1032 and S1035 garments, in either the V or UV state, poses no danger of inducing unacceptable heat stress under the conditions expected within the Shuttle cabin during launch or re-entry

    BFKL predictions at small x from k_T and collinear factorization viewpoints

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    Hard scattering processes involving hadrons at small xx are described by a kTk_T-factorization formula driven by a BFKL gluon. We explore the equivalence of this description to a collinear-factorization approach in which the anomalous dimensions γgg\gamma_{gg} and γqg/αS\gamma_{qg}/\alpha_S are expressed as power series in αSlog(1/x)\alpha_S \log (1/x), or to be precise αS/ω\alpha_S/\omega where ω\omega is the moment index. In particular we confront the collinear-factorization expansion with that extracted from the BFKL approach with running coupling included.Comment: 11 LaTeX pages, 1 figure (uuencoded

    QCD Predictions for the Transverse Energy Flow in Deep-Inelastic Scattering in the Small x HERA Regime

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    The distribution of transverse energy, ETE_T, which accompanies deep-inelastic electron-proton scattering at small xx, is predicted in the central region away from the current jet and proton remnants. We use BFKL dynamics, which arises from the summation of multiple gluon emissions at small xx, to derive an analytic expression for the ETE_T flow. One interesting feature is an xϵx^{-\epsilon} increase of the ETE_T distribution with decreasing xx, where ϵ=(3αs/π)2log2\epsilon = (3\alpha_s/\pi)2\log 2. We perform a numerical study to examine the possibility of using characteristics of the ETE_T distribution as a means of identifying BFKL dynamics at HERA.Comment: 16 pages, REVTEX 3.0, no figures. (Hardcopies of figures available on request from Professor A.D. Martin, Department of Physics, University of Durham, DH1 3LE, England.) Durham preprint : DTP/94/0
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