24,937 research outputs found

    Orbital debris measurements

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    What is currently known about the orbital debris flux is from a combination of ground based and in-space measurements. These measurements have revealed an increasing population with decreasing size. A summary of measurements is presented for the following sources: the North American Aerospace Defense Command Catalog, the Perimeter Acquisition and Attack Characterization System Radar, ground based optical telescopes, the Explorer 46 Meteoroid Bumper Experiment, spacecraft windows, and Solar Max surfaces

    Origin of orbital debris impacts on LDEF's trailing surfaces

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    A model was developed to determine the origin of orbital impacts measured on the training surfaces of LDEF. The model calculates the expected debris impact crater distribution around LDEF as a function of debris orbital parameters. The results show that only highly elliptical, low inclination orbits could be responsible for these impacts. The most common objects left in this type of orbit are orbital transfer stages used by the U.S. and ESA to place payloads into geosynchronous orbit. Objects in this type of orbit are difficult to catalog by the U.S. Space Command; consequently there are independent reasons to believe that the catalog does not adequately represent this population. This analysis concludes that the relative number of cataloged objects with highly elliptical, low inclination orbits must be increased by a factor of 20 to be consistent with the LDEF data

    Universal transloader moves delicate equipment without stress

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    Transloader moves delicate or heavy items over irregular surfaces without transmitting stress to the load. The loader is supported on three pivot points which produce a wrap free base. The base is supported by an artificial four-wheel frame

    The Global Employer: The Labor Relations and Collective Agreements Issue

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    [Excerpt] Baker & McKenzie’s Global Employment Practice Group is pleased to present its 56th issue of The Global Employerℱ entitled “The Labor Relations and Collective Agreements Issue.” In this issue you will find the first report from our Future of Work Series. Labor Relations Report - Brand Attack: How to avoid becoming the target of a corporate campaign and what actions to take if you do. The Future of Work is a series of client reports based on panel discussions at our Global Employer Forum, a two-day thought leadership conference. During the forum, nearly 70 clients, academics and consultants gathered with our employment partners to discuss pressing workplace topics like talent shortages, data privacy, global mobility assignments, globalization of unions and managing the employment aspects of M&A deals. Rather than the traditional “how to” legal format of most law firm conferences, the Global Employer Forum features panel discussions of in-house counsel and senior-level executives from some of the world’s largest multinational organizations who discussed their personal experiences addressing these challenges and the solutions they have found to overcome them. Following the Labor Relations Report, you will also find information pertaining to the current state of labor relations and union negotiations in Argentina and a general overview of the current state of collective bargaining in Brazil. In Germany, we take a look at some of the numbers behind collective bargaining agreements; and a review of the impacts on labor benefits of the January 2014, Income Tax Law reform in Mexico. From Spain we bring you articles that discuss negotiating with representatives bodies in collective lay-offs and the new role of company level collective bargaining agreements; and from the US, recent efforts by the NLRB as it Targets Successor Issues in US Mergers and Acquisitions

    Nonlinear lattice model of viscoelastic Mode III fracture

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    We study the effect of general nonlinear force laws in viscoelastic lattice models of fracture, focusing on the existence and stability of steady-state Mode III cracks. We show that the hysteretic behavior at small driving is very sensitive to the smoothness of the force law. At large driving, we find a Hopf bifurcation to a straight crack whose velocity is periodic in time. The frequency of the unstable bifurcating mode depends on the smoothness of the potential, but is very close to an exact period-doubling instability. Slightly above the onset of the instability, the system settles into a exactly period-doubled state, presumably connected to the aforementioned bifurcation structure. We explicitly solve for this new state and map out its velocity-driving relation

    Human operator identification model and related computer programs

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    Four computer programs which provide computational assistance in the analysis of man/machine systems are reported. The programs are: (1) Modified Transfer Function Program (TF); (2) Time Varying Response Program (TVSR); (3) Optimal Simulation Program (TVOPT); and (4) Linear Identification Program (SCIDNT). The TV program converts the time domain state variable system representative to frequency domain transfer function system representation. The TVSR program computes time histories of the input/output responses of the human operator model. The TVOPT program is an optimal simulation program and is similar to TVSR in that it produces time histories of system states associated with an operator in the loop system. The differences between the two programs are presented. The SCIDNT program is an open loop identification code which operates on the simulated data from TVOPT (or TVSR) or real operator data from motion simulators

    The Effects of Competition on Variation in the Quality and Cost of Medical Care

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    We estimate the effects of hospital competition on the level of and the variation in quality of care and hospital expenditures for elderly Medicare beneficiaries with heart attack. We compare competition's effects on more-severely ill patients, whom we assume value quality more highly, to the effects on less-severely ill, low-valuation patients. We find that low-valuation patients in less-competitive markets receive more intensive treatment than in more-competitive markets, but have statistically similar health outcomes. In contrast, high-valuation patients in less-competitive markets receive less intensive treatment than in more-competitive markets, and have significantly worse health outcomes. Since this competition-induced increase in variation in expenditures is, on net, expenditure-decreasing and outcome-beneficial, we conclude that it is welfare-enhancing. These findings are inconsistent with conventional models of vertical differentiation, although they can be accommodated by more recent models.

    A Generalization of the Brodsky-Lepage Formalism

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    We present an approach that generalizes in a natural way the perturbative QCD formalism developed by Brodsky and Lepage for the study of exclusive hadronic processes to the case of L≠0L\neq 0 mesons. As an application of our approach we consider here the production of meson pairs, involving tensor and pseudotensor mesons, in photon-photon collisions.Comment: LaTeX, 5 pages, 1 embedded ps figure, uses macros sprocl.sty, epsfig.sty. Talk delivered by F. Murgia at the PHOTON'97 Conference, Egmond aan Zee, The Netherlands, May 10-15, 1997. To be published in the proceedings by World Scientifi

    Superradiance-like Electron Transport through a Quantum Dot

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    We theoretically show that intriguing features of coherent many-body physics can be observed in electron transport through a quantum dot (QD). We first derive a master equation based framework for electron transport in the Coulomb-blockade regime which includes hyperfine (HF) interaction with the nuclear spin ensemble in the QD. This general tool is then used to study the leakage current through a single QD in a transport setting. We find that, for an initially polarized nuclear system, the proposed setup leads to a strong current peak, in close analogy with superradiant emission of photons from atomic ensembles. This effect could be observed with realistic experimental parameters and would provide clear evidence of coherent HF dynamics of nuclear spin ensembles in QDs.Comment: 21 pages, 10 figure
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