27,250 research outputs found

    Effects of a 50 Hz magnetic field on human visual duration discrimination and recognition memory : a thesis presented in partial fulfilment of the requirements for the degree of Master of Arts in Psychology at Massey University

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    The purpose of this study was to investigate the direct and delayed effects of a sinusoidal 100 μ;T, 50 Hz intermittent magnetic field on human performance measures. Eighty participants (aged 19-53) completed the experiment which involved a visual duration discrimination task and a recognition memory task. Initially all participants completed the study phase of the recognition memory task in which 40 abstract shapes were presented in a random order. A two alternative forced choice visual duration discrimination task followed in which participants had to decide which of two consecutive light flashes was longer in duration. The duration discrimination task had only one hard level of difficulty over the 200 trials with a standard flash duration of 50 ms paired with an alternative hard flash duration of 65 ms. During the duration discrimination task, 40 participants were sham exposed while the remaining 40 were exposed to a 100 μT, 50 Hz magnetic field. Participants were randomly assigned to either the sham or exposure groups and the study was conducted under double-blind procedures. Reaction time and percentage of correct decisions were recorded during a total exposure time lasting approximately 11 minutes. The two alternative forced choice recognition memory testing phase was then conducted in which participants viewed 40 pairs of abstract shapes, each pair presented for six seconds. Participants had to decide which of the two shapes (left or right) they had previously seen during the study phase. In addition, participants had to rate their confidence in each of the 40 decisions on a four point rating scale (1 = very sure to 4 = unsure). Both percentage of correct decisions and confidence ratings were recorded for each participant Participants were only exposed to the magnetic field during the visual duration discrimination task. The results of an earlier investigation were unsupported as the present results found no field-effects between sham and exposure groups on both measures of reaction time and percentage of correct decisions during the visual duration discrimination task. However, a reduction in the percentage of correct decisions and confidence during the recognition memory task was observed for participants who had been previously exposed to a magnetic field. Differences in experimental parameters and insufficient power render comparisons with other human magnetic field studies impossible. The need for exact replication studies with maximum design sensitivity was discussed within the context of a research field that is to produce small effect sizes

    Extending group actions on metric spaces

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    We address the following natural extension problem for group actions: Given a group GG, a subgroup H≤GH\le G, and an action of HH on a metric space, when is it possible to extend it to an action of the whole group GG on a (possibly different) metric space? When does such an extension preserve interesting properties of the original action of HH? We begin by formalizing this problem and present a construction of an induced action which behaves well when HH is hyperbolically embedded in GG. Moreover, we show that induced actions can be used to characterize hyperbolically embedded subgroups. We also obtain some results for elementary amenable groups

    Hot spot abundance, ridge subduction and the evolution of greenstone belts

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    A number of plate tectonic hypotheses have been proposed to explain the origin of Archaean and Phanerozoic greenstone/ophiolite terranes. In these models, ophiolites or greenstone belts represent the remnants of one or more of the following: island arcs, rifted continental margins, oceanic crustal sections, and hot spot volcanic products. If plate tectonics has been active since the creation of the Earth, it is logical to suppose that the same types of tectonic processes which form present day ophiolites also formed Archaean greenstone belts. However, the relative importance of the various tectonic processes may well have been different and are discussed

    Thermodynamic energy exchange in a moving plate capacitor

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    In this paper we describe an apparent paradox concerning a moving plate capacitor driven by thermal noise from a resistor. The plates are attracted together, but a demon restores the plates of the capacitor to their original position when the voltage across the capacitor is small-hence only small forces are present for the demon to work against. The demon has to work harder than this to avoid the situation of perpetual motion, but the open question is how? This is unsolved, however we explore the concept of a moving plate capacitor by examining the case where it is still excited by thermal noise, but where the restoring force on the capacitor plates is provided by a simple spring rather than some unknown demon. We display simulation results with interesting behavior, particularly where the capacitor plates collide with each other. (c) 2001 American Institute of Physics.B. R. Davis, D. Abbott, and J. M. R. Parrond

    Using the INSPIRAL program to search for gravitational waves from low-mass binary inspiral

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    The INSPIRAL program is the LIGO Scientific Collaboration's computational engine for the search for gravitational waves from binary neutron stars and sub-solar mass black holes. We describe how this program, which makes use of the FINDCHIRP algorithm (discussed in a companion paper), is integrated into a sophisticated data analysis pipeline that was used in the search for low-mass binary inspirals in data taken during the second LIGO science run.Comment: 11 pages, 3 figures, submitted to Classical and Quantum Gravity for the special issue of the GWDAW9 Proceeding

    The Background Field Method as a Canonical Transformation

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    We construct explicitly the canonical transformation that controls the full dependence (local and non-local) of the vertex functional of a Yang-Mills theory on a background field. After showing that the canonical transformation found is nothing but a direct field-theoretic generalization of the Lie transform of classical analytical mechanics, we comment on a number of possible applications, and in particular the non perturbative implementation of the background field method on the lattice, the background field formulation of the two particle irreducible formalism, and, finally, the formulation of the Schwinger-Dyson series in the presence of topologically non-trivial configurations.Comment: 11 pages, REVTeX. References added, some explanations extended. Final version to appear in the journa

    Computer modeling of a two-junction, monolithic cascade solar cell

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    The theory and design criteria for monolithic, two-junction cascade solar cells are described. The departure from the conventional solar cell analytical method and the reasons for using the integral form of the continuity equations are briefly discussed. The results of design optimization are presented. The energy conversion efficiency that is predicted for the optimized structure is greater than 30% at 300 K, AMO and one sun. The analytical method predicts device performance characteristics as a function of temperature. The range is restricted to 300 to 600 K. While the analysis is capable of determining most of the physical processes occurring in each of the individual layers, only the more significant device performance characteristics are presented

    Parrondo's games with chaotic switching

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    This paper investigates the different effects of chaotic switching on Parrondo's games, as compared to random and periodic switching. The rate of winning of Parrondo's games with chaotic switching depends on coefficient(s) defining the chaotic generator, initial conditions of the chaotic sequence and the proportion of Game A played. Maximum rate of winning can be obtained with all the above mentioned factors properly set, and this occurs when chaotic switching approaches periodic behavior.Comment: 11 pages, 9 figure

    Aerodynamic and directional acoustic performance of a scoop inlet

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    Aerodynamic and directional acoustic performances of a scoop inlet were studied. The scoop inlet is designed with a portion of the lower cowling extended forward to direct upward any noise that is propagating out the front of the engine toward the ground. The tests were conducted in an anechoic wind tunnel facility at free stream velocities of 0, 18, 41, and 61 m/sec and angles of attack from -10 deg to 120 deg. Inlet throat Mach number was varied from 0.30 to 0.75. Aerodynamically, at a free stream velocity of 41 m/sec, the design throat Mach number (0.63), and an angle of attack of 50 deg, the scoop inlet total pressure recovery was 0.989 and the total pressure distortion was 0.15. The angles of attack where flow separation occurred with the scoop inlet were higher than those for a conventional symmetric inlet. Acoustically, the scoop inlet provided a maximum noise reduction of 12 to 15 db below the inlet over the entire range of throat Mach number and angle of attack at a free-stream velocity of 41 m/sec
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