114,338 research outputs found
Effects of lags on human operator transfer functions with head-coupled systems
No full textThe effects of operator learning and target velocity on head tracking performance with and without lags has been studied. Five lags (0, 40, 80, 120, 160 ms) between head movement and target image movement, and three target velocities (2, 3.5, 5° · s-1 r.m.s.) were investigated with eight male subjects and band-limited random target motions. Head tracking transfer functions, tracking error spectra, mean radial tracking error, and subjective difficulty ratings were obtained. Head tracking performance was significantly degraded by lags greater than, or equal to, 40 ms (in addition to a system lag of 40 ms). Both the input-correlated tracking error and the uncorrelated tracking error increased with increasing lag. No significant improvement in head tracking performance was found through practice with an 80-ms lag. As the lag increased, operators increased their gains at frequencies above about 0.5 Hz and reduced their phase lags at low frequencies (about 0.1 Hz) but failed to fully compensate for the increased display lag. The increased human operator gain was associated with increased operator phase lag at higher frequencies (above 0.5 Hz). To improve head tracking performance in the presence of lags, a lag compensation technique is needed to prevent undesirable changes in tracking strategy.</p
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Liftings for noncomplete probability spaces
No full textThe current state of knowledge concerning liftings for noncomplete probability spaces is discussed. This is a somewhat expanded version of the author's talk given at the 1991 Summer Conference on General Topology and Applications in Honor of Mary Ellen Rudin and Her Work.PT: S; CR: BURKE MR, IN PRESS P AM MATH S BURKE MR, 1991, ISRAEL J MATH, V73, P33 BURKE MR, 1992, ISRAEL J MATH, V79, P289 CARLSON T, THEOREM LIFTING CHRISTENSEN JPR, 1974, TOPOLOGY BOREL STRUC FREMLIN DH, 1989, HDB BOOLEAN ALGEBRAS, P877 INOESCUTULCEA A, 1966, 5TH P BERK S MATH ST, V2 IONESCUTULCEA A, 1967, CONTRIBUTIONS PROB 1, P63 IONESCUTULCEA A, 1969, TOPICS THEORY LIFTIN JECH TJ, 1978, SET THEORY JOHNSON RA, 1980, P AM MATH SOC, V80, P234 JUST W, IN PRESS T AM MATH S KUPKA J, 1983, INDIANA U MATH J, V32, P717 LOSERT V, 1983, LNM, V1080, P95 MAHARAM D, 1958, P AM MATH SOC, V9, P987 SHELAH S, 1983, ISRAEL J MATH, V45, P90 TALAGRAND M, 1982, P AM MATH SOC, V84, P379 VONNEUMANN J, 1931, CRELLES J MATH, V165, P109; NR: 18; TC: 0; J9: ANN N Y ACAD SCI; PG: 4; GA: BZ86BSource type: Electronic(1
CONTRIBUTION TO THE STUDY OF PARTIAL DIFFERENTIAL EQUATIONS OF ELLIPTIC TYPE
No full textEn este artículo se presentan los resultados más importantes de mi trabajo de investigación en el estudio de la existencia y de las propiedades de las soluciones de ecuaciones diferenciales parciales no lineales.
Donde λ ∈ R, Ω es un dominio acotado en RN con frontera suave, ∆ = n i=0 ∂/∂x2 i es el operador de Laplace y f : R → R es una función no lineal. Se presentan teoremas obtenidos utilizando teoría de bifurcación, métodos variacionales y un principio de minimax desarrollado por el autor en colaboración con A. Castro y J. M. Neuberger ([Cas-Cos-Nu1], 1997). Además, se incluyen algunos algoritmos para construir y visualizar soluciones a problemas no lineales del tipo (1) y una serie de preguntas abiertas.In this paper I present the most important results of my research studying the solutions of nonlinear partial differential equations of the type.
In this study, we focus on nonlinear partial differential equations of the form ∆u + λf(u) = 0 in Ω, u = 0 on ∂Ω, where λ ∈ R, Ω is a smooth bounded domain in RN, ∆ = Σ ∂²/∂x²ᵢ is the Laplacian operator, and f : R → R is a nonlinear function. Our theorems were obtained using bifurcation theory, variational methods, and a minmax principle developed by the author in collaboration with A. Castro and J. M. Neuberger ([Cas-Cos-Nu1], 1997). We also present some theorems related to algorithms for approximating solutions to nonlinear problems of type (1), along with a set of open questions
Research fronts in library and information science in Spain
No full textPublications and author cocitations in library and information science in Spain during the period from 1985 to 1994 were analyzed as a measure of the structure, specificity and composition of research fronts in this country. A cocitation matrix developed from an ad hoc database was subjected to cluster analysis, multidimensional scaling and principal components analysis, The resulting cocitation maps identified specific areas of r~search and their knowledge bases. We inferred the degree of consolidation of the discipline of library and information science, and of the subdisciplines informetrics, librarianship and university affiliation, from the research activities revealed. In this respect, the conclusions from the study show the existence of several research fronts in Spanish literature the contents of which are in most cases difficult to compare with those in other countries. A lesser degree of maturity of research in this field is shown
Perturbations in the Earth's rotation induced by internal density anomalies: implications for sea-level fluctuations
No full textThe effects of internal mass anomalies on the Earth's rotation are analyzed within the framework of linearized Liouville equations and Maxwell rheology for the mantle. Our approach is appropriate for a simplified modeling of subduction. Sea-level fluctuations induced by long-term rotational instabilities are also considered. -from Author
Author Co-Citation Analysis (ACA): a powerful tool for representing implicit knowledge of scholar knowledge workers
No full textIn the last decade, knowledge has emerged as one of the most important and valuable organizational assets. Gradually this importance caused to emergence of new discipline entitled ―knowledge management‖. However one of the major challenges of knowledge management is conversion implicit or tacit knowledge to explicit knowledge. Thus Making knowledge visible so that it can be better accessed, discussed, valued or generally managed is a long-standing objective in knowledge management. Accordingly in this paper author co- citation analysis (ACA) will be proposed as an efficient technique of knowledge visualization in academia (Scholar knowledge workers)
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
Environmental impact of technology policy: R&D Subsidies versus R&D cooperation.
No full textIn this paper we study a neglected aspect ofteclmology policy, namely the adverse impact it might have on the envirol1Il1ent through increased production when R&D expenditure leads to cost reduction. Although teclmology policy measures that encourage finns to reduce their production costs would usually reduce energy inputs and therefore generate less pollution per unit of output production, we explore here the case where with reorganisation of production output gene rally increases. So even if per unit of production pollution is less, total pollution generated by the increased production induced by the innovative efforts of films increases. In this context it is therefore necessary to address the issue of tying-in teclmology and environmental policy, which is the issue we raise in this paper. We show that, irrespective of whether teclmology policy takes the fonn of R&D subsidies or R&D cooperation, R&D would gene rally lead to increased pollution and thus have a negative impact on the environment. Policies that might be optimal in the absence of concem for the enviroJUllent ceas e to be so. We claim that not only is a comparison between policy instruments more delicate but the optimal R&D subsidy might be negative. FinalIy, we propose and evaluate a speeific poliey in the form of a targeted subsidy tied-in to abatement activities and show that it is welfare improving.Technology policy; Process innovation; Pollution; R&D cooperation; R&D subsides;
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