109,237 research outputs found

    The RHIC azimuth quadrupole: "perfect liquid" or gluonic radiation?

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    Large elliptic flow at RHIC seems to indicate that ideal hydrodynamics provides a good description of Au-Au collisions, at least at the maximum RHIC energy. The medium formed has been interpreted as a nearly perfect (low-viscosity) liquid, and connections have been made to gravitation through string theory. Recently, claimed observations of large flow fluctuations comparable to participant eccentricity fluctuations seem to confirm the ideal hydro scenario. However, determination of the azimuth quadrupole with 2D angular autocorrelations, which accurately distinguish ``flow'' (quadrupole) from ``nonflow'' (minijets), contradicts conventional interpretations. Centrality trends may depend only on the initial parton geometry, and methods used to isolate flow fluctuations are sensitive instead mainly to minijet correlations. The results presented in this paper suggest that the azimuth quadrupole may be a manifestation of gluonic multipole radiation.Comment: 11 pages, 6 figure

    Does drying affect gel networks?

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    The properties of low molecular weight gels are determined by the underlying, self-assembled network. To access information on the network, it is common for techniques to be used that require the gel to be dried, such as transmission electron microscopy or scanning electron microscopy. The implicit assumption is that this drying has no bearing on the data collected. Here, we discuss the validity of this assumption

    Flight-test verification of a pictorial display for general aviation instrument approach

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    Results of flight tests of the pictorial "follow me" box display results of the simulator study. The most important item of agreement was the frequency of the vertical and lateral models of motion of the pilot-aircraft-display system, which was 0.4 rad/sec in each study. Successful short, curved, descending approaches, such as are often suggested for use with microwave landing systems, can be executed with the "follow me" box display. Variations of the value of distance from the aircraft to the box were also examined using values of 736 m, 368 m, and 184 m. The results show that successful approaches can be made with all of these values. A sharper final turn and greater precision of position control are obtained with the shorter distance. Deletion of distance measuring equipment from the system was also studies. It was shown that successful approaches can be made with no distance measures included in the system, but the values of distance from the aircraft to the box that can be used are restricted

    Simulator study of a flight director display

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    A six degree of freedom, fixed base simulation study of the use of a flight director by general aviation pilots in an instrument landing system approach was conducted. An autopilot command law was used to drive the flight director needles. Time histories of the pilot aircraft display system responses and standard deviations and means of the glide slope and localizer errors were obtained. The pilot aircraft display system responses with the flight director were very similar to the autopilot aircraft responses. Without the flight director, the pilot aircraft display system exhibited less damping than with the flight director. The sensitivity of the flight director command laws was judged to be about as high as it could be by the test subjects. Thus, further improvement in the pilot aircraft display system performance by increasing the gains in the command laws was precluded

    Simulator study of conventional general aviation instrument displays in path-following tasks with emphasis on pilot-induced oscillations

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    A study of the use of conventional general aviation instruments by general aviation pilots in a six degree of freedom, fixed base simulator was conducted. The tasks performed were tracking a VOR radial and making an ILS approach to landing. A special feature of the tests was that the sensitivity of the displacement indicating instruments (the RMI, CDI, and HSI) was kept constant at values corresponding to 5 n. mi. and 1.25 n. mi. from the station. Both statistical and pilot model analyses of the data were made. The results show that performance in path following improved with increases in display sensitivity up to the highest sensitivity tested. At this maximum test sensitivity, which corresponds to the sensitivity existing at 1.25 n. mi. for the ILS glide slope transmitter, tracking accuracy was no better than it was at 5 n. mi. from the station and the pilot aircraft system exhibited a marked reduction in damping. In some cases, a pilot induced, long period unstable oscillation occurred

    Study of the use of a nonlinear, rate limited, filter on pilot control signals

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    The use of a filter on the pilot's control output could improve the performance of the pilot-aircraft system. What is needed is a filter with a sharp high frequency cut-off, no resonance peak, and a minimum of lag at low frequencies. The present investigation studies the usefulness of a nonlinear, rate limited, filter in performing the needed function. The nonlinear filter is compared with a linear, first order filter, and no filter. An analytical study using pilot models and a simulation study using experienced test pilots was performed. The results showed that the nonlinear filter does promote quick, steady maneuvering. It is shown that the nonlinear filter attenuates the high frequency remnant and adds less phase lag to the low frequency signal than does the linear filter. It is also shown that the rate limit in the nonlinear filter can be set to be too restrictive, causing an unstable pilot-aircraft system response

    Goalposts on the Move

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    The impact profile of recent UK geoscience research is set to change, say Nick Petford & Jonathan Adam

    First Result of Net-Charge Jet-Correlations from STAR

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    We presented results on azimuthal correlation of net-charge with high pTp_T trigger particles. It is found that the net-charge correlation shape is similar to that of total-charge. On the near-side, the net-charge and total-charge pTp_T spectra have similar shape and both are harder than the inclusives. On the away-side, the correlated spectra are not much harder than the inclusives, and the net-charge/total-charge ratio increases with pTp_T and is similar to the inclusive ratio
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