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

Implications of Scaling Violations of F2 at HERA for Perturbative QCD

We critically examine the QCD predictions for the $Q^2$ dependence of the electron-proton deep-inelastic structure function $F_2(x,Q^2)$ in the small $x$ 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$(1/x)$ 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

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

The distribution of transverse energy, $E_T$, which accompanies deep-inelastic electron-proton scattering at small $x$, 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 $x$, to derive an analytic expression for the $E_T$ flow. One interesting feature is an $x^{-\epsilon}$ increase of the $E_T$ distribution with decreasing $x$, where $\epsilon = (3\alpha_s/\pi)2\log 2$. We perform a numerical study to examine the possibility of using characteristics of the $E_T$ 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

Black Men\u27s Perspectives on their Student-Faculty Relationships in Higher Education: A Phenomenological Study

The purpose of the phenomenological study was to explore Black men’s perspectives of their student-faculty relationships in higher education. Utilizing a qualitative research design and Noddings ethics of care theory, the findings of the inquiry are useful for institutions of higher education as they strive to facilitate effective relationships with their Black men students. The central question for this study was how do Black men describe their relationships with their faulty in higher education? The setting for this study was a social media platform that consists of 207,577 Black men; of that number, 100,000 of these men have reported being college students. From the setting, the sample was derived from a Facebook group, Black Good Men. The study was conducted using 13 participants who had experienced the phenomenon. Three themes emerged from the data: The security of Black men, desirable student-faculty relationships, and essential care all being necessary for Black men in higher education. The study concluded that Black men described their relationships with their faculty in higher education as either non-existent or a relationship built on the foundation of care. The study also concluded the effects of care was felt by Black men within personal interactions, conversations, words of affirmation, encouragement, mentorship, and acts of service from their professors

Take It or Leave It: Eminent Domain for Economic Development-Statutes, Ordinances, & Politics, Oh My!

North Texas is the focus of this Comment because it is a microcosm of the interaction between competing economic and social forces, both external, in the form of global competition, and internal, as an area of the state with one of the country\u27s fastest growing and most diverse populations. Section II of this article will examine this context, as well as federal and Texas judicial actions, to assess the economic development takings environment prior to the most recent federal case and acts of the Texas Legislature. Section III will explain the effect this combination has had in producing a constitutional imbalance. Section IV will conduct an examination of proposed solutions at the constitutional, judicial, and legislative levels from the literature and case law on the subject. Section V will conclude with predictions about the likely success of recent legislative enactments developing a brighter line between individual property rights and community economic development. The focus of this article is on the public purpose aspect of eminent domain use and strictly pertains to the taking of real property in fee simple absolute as perceived today, not on the myriad other purposes to which the eminent domain power can and has been applied,\u27 nor the various conceptions of property over time

BFKL predictions at small x from k_T and collinear factorization viewpoints

Hard scattering processes involving hadrons at small $x$ are described by a $k_T$-factorization formula driven by a BFKL gluon. We explore the equivalence of this description to a collinear-factorization approach in which the anomalous dimensions $\gamma_{gg}$ and $\gamma_{qg}/\alpha_S$ are expressed as power series in $\alpha_S \log (1/x)$, or to be precise $\alpha_S/\omega$ where $\omega$ 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

Predictions for dijet production in DIS using small x dynamics

We study the properties of dijet production in deep inelastic scattering using a unified BFKL/DGLAP framework, which includes important subleading ln (1/x) contributions. We calculate the azimuthal decorrelation between the jets. We compute the cross section for dijet production as a function of Q^2 and the jet transverse momentum, as well as calculate the total dijet rate. We compare the predictions with HERA data.Comment: 7 pages, LaTeX with 4 eps figure

Links between soil microbial communities and plant traits in a species-rich grassland under long-term climate change

Climate change can influence soil microorganisms directly by altering their growth and activity but also indirectly via effects on the vegetation, which modifies the availability of resources. Direct impacts of climate change on soil microorganisms can occur rapidly, whereas indirect effects mediated by shifts in plant community composition are not immediately apparent and likely to increase over time. We used molecular fingerprinting of bacterial and fungal communities in the soil to investigate the effects of 17 years of temperature and rainfall manipulations in a species‐rich grassland near Buxton, UK. We compared shifts in microbial community structure to changes in plant species composition and key plant traits across 78 microsites within plots subjected to winter heating, rainfall supplementation, or summer drought. We observed marked shifts in soil fungal and bacterial community structure in response to chronic summer drought. Importantly, although dominant microbial taxa were largely unaffected by drought, there were substantial changes in the abundances of subordinate fungal and bacterial taxa. In contrast to short‐term studies that report high resistance of soil fungi to drought, we observed substantial losses of fungal taxa in the summer drought treatments. There was moderate concordance between soil microbial communities and plant species composition within microsites. Vector fitting of community‐weighted mean plant traits to ordinations of soil bacterial and fungal communities showed that shifts in soil microbial community structure were related to plant traits representing the quality of resources available to soil microorganisms: the construction cost of leaf material, foliar carbon‐to‐nitrogen ratios, and leaf dry matter content. Thus, our study provides evidence that climate change could affect soil microbial communities indirectly via changes in plant inputs and highlights the importance of considering long‐term climate change effects, especially in nutrient‐poor systems with slow‐growing vegetation

Some monodontomerinae and megastigminae torymidae associated with cynipidae in spain hymenoptera

5 paginas y 7 figurasMicrodontomerus impolitus sp. n. and Liodontomerus centaureae sp. n. are described from cynipid galls on Tragopogon and Centaurea respectively. New host and distributional data are given for M. crassipes Bouček. L. papaveris (Förster), Chalcimerus borceai Steffan & Andriescu and Megastigmus dumicola Bouček, and generic characters of Microdontomerus and Liodontomerus are commented upon.Peer reviewe

Properties of the BFKL equation and structure function predictions for HERA

The general properties of the Lipatov or BFKL equation are reviewed. Modifications to the infrared region are proposed. Numerical predictions for the deep-inelastic electron-proton structure functions at small $x$ are presented and confronted with recent HERA measurements.Comment: 21 pages, 11 figures, Latex file, Durham preprint DTP 92/2