20,172 research outputs found
Shuttle electrical environment
Part of an AFGL payload flown on the STS-4 mission consisted of experiments to measure in-situ electric fields, electron densities, and vehicle charging. During this flight some 11 hours of data were acquired ranging from 5 minute snapshots up to continuous half-orbits. These experiments are described and results presented for such vehicle induced events as a main engine burn, thruster firings and water dumps in addition to undisturbed periods. The main characteristic of all the vehicle induced events is shown to be an enhancement in the low frequency noise (less than 2 kHz), in both the electrostatic and electron irregularity (delta N/N) spectra. The non-event results indicate that the electrostatic broadband emissions show a white noise characteristic in the low frequency range up to 2 kHz at an amplitude of 10 db above the shuttle design specification limit, falling below that limit above 10 kHz. The vehicle potential remained within the range of -3 to +1 volt throughout the flight which exhibits normal behavior for a satellite in a low equatorial orbit
Bose-Einstein Correlations and the Equation of State of Nuclear Matter
Within a relativistic hydrodynamic framework, we use four different equations
of state of nuclear matter to compare to experimental spectra from CERN/SPS
experiments NA44 and NA49. Freeze-out hypersurfaces and Bose-Einstein
correlation functions for identical pion pairs are discussed. We find that
two-pion Bose-Einstein interferometry measures the relationship between the
temperature and the energy density in the equation of state during the late
hadronic stage of the fireball expansion. Little sensitivity of the
light-hadron data to a quark-gluon plasma phase-transition is seen.Comment: 4 pages, including 4 figures. You can also download a PostScript file
of the manuscript from http://p2hp2.lanl.gov/people/schlei/eprint.htm
An experimentally robust technique for halo measurement using the IPM at the Fermilab Booster
We propose a model-independent quantity, , to characterize non-Gaussian
tails in beam profiles observed with the Fermilab Booster Ion Profile Monitor.
This quantity can be considered a measure of beam halo in the Booster. We use
beam dynamics and detector simulations to demonstrate that is superior to
kurtosis as an experimental measurement of beam halo when realistic beam
shapes, detector effects and uncertainties are taken into account. We include
the rationale and method of calculation for in addition to results of the
experimental studies in the Booster where we show that is a useful halo
discriminator
Can cluster environment modify the dynamical evolution of spiral galaxies?
Over the past decade many effects of the cluster environment on member galaxies have been established. These effects are manifest in the amount and distribution of gas in cluster spirals, the luminosity and light distributions within galaxies, and the segregation of morphological types. All these effects could indicate a specific dynamical evolution for galaxies in clusters. Nevertheless, a more direct evidence, such as a different mass distribution for spiral galaxies in clusters and in the field, is not yet clearly established. Indeed, Rubin, Whitmore, and Ford (1988) and Whitmore, Forbes, and Rubin (1988) (referred to as RWF) presented evidence that inner cluster spirals have falling rotation curves, unlike those of outer cluster spirals or the great majority of field spirals. If falling rotation curves exist in centers of clusters, as argued by RWF, it would suggest that dark matter halos were absent from cluster spirals, either because the halos had become stripped by interactions with other galaxies or with an intracluster medium, or because the halos had never formed in the first place. Even if they didn't disagree with RWF, other researchers pointed out that the behaviour of the slope of the rotation curves of spiral galaxies (in Virgo) is not so clear. Amram, using a different sample of spiral galaxies in clusters, found only 10% of declining rotation curves (2 declining vs 17 flat or rising) in opposition to RWF who find about 40% of declining rotation curves in their sample (6 declining vs 10 flat or rising), we will hereafter briefly discuss the Amram data paper and compare it to the results of RWF. We have measured the rotation curves for a sample of 21 spiral galaxies in 5 nearby clusters. These rotation curves have been constructed from detailed two-dimensional maps of each galaxy's velocity field as traced by emission from the Ha line. This complete mapping, combined with the sensitivity of our CFHT 3.60 m. + Perot-Fabry + CCD observations, allows the construction of high-quality rotation curves. Details concerning the acquisition and reduction procedures of the data are given in Amram. We present and discuss our preliminary analysis and compare them with RWF's results
Wind turbine generator rotor blade concepts with low cost potential
Four processed for producing blades are examined. Two use filament winding techniques and two involve filling a mold or form to produce all or part of a blade. The processes are described and a comparison is made of cost, material properties, design and free vibration characteristics. Conclusions are made regarding the feasibility of each process to produce low cost, structurally adequate blades
Probing the Interstellar Medium using HI absorption and emission towards the W3 HII region
HI spectra towards the W3 HII complex are presented and used to probe the
Galactic structure and interstellar medium conditions between us and this
region. The overall shape of the spectra is consistent with the predictions of
the Two-Arm Spiral Shock model wherein the gas found in the -40 km/s to -50
km/s range has been accelerated by some 20 km/s from its rotation curve
velocity. Spin temperatures of ~100 K are derived for the Local Arm gas, lower
than found in a previous, similar study towards DR 7. For the interarm region,
values on the order of 300 K are found, implying a negligible filling factor
for the Cold Neutral Medium (<< 1%). Some of the absorbing gas at velocities
near -40 km/s is confirmed to be associated with the HII regions.Comment: 23 pages, 6 figures, accepted for publication in the Astronomical
Journa
Recommended from our members
Crossing Chronotopes in the Polyphonic Organisation: A dialogical analysis of the comedy industry
YesThe ‘Polyphonic Organisation’ is an emerging root-metaphor for the multiple voices that
constitute an organisation. In this article, we explore the narrative concept of the
‘chronotope’ as a feature of the ‘polyphonic organisation’. The ‘chronotope’, in a general
sense, refers to the matrix of time-space-value in organisations. We argue that the
chronotope is important because it introduces boundaries between voices within
organisations and helps to explain the difficulties in getting to dialogue with voices in
different spaces in the ‘Polyphonic Organisation’. More particularly, there are multiple
kinds of chronotopes which lead to different kinds of time-spaces matrices within the
polyphonic organisation. Our aim is to examine chronotope crossings within polyphonic
organisations as part of the work of being heard. This is a theoretical argument drawing
significantly from Bakhtin’s work on chronotope. To examine the argument in practice we
draw on original fieldwork within the comedy industry. Here we found three kinds of
chronotopes: 1) The comedy-offense boundary; 2) The commissioning landscape 3)
Platform spaces. We also found that moving within and between these involved a variety
of adventures in experience (such as hope and disappointment), which also have their own
specific chronotopes. Overall, we argue that the polyphonic organisation is significantly
enhanced as an organisational concept through a turn to the role of chronotope. This is
because chronotope helpfully describes the barriers and porous boundaries between voice
MicroRNA regulation of natural killer cells
Natural killer (NK) cells are innate immune lymphocytes critical for host defense against viral infection and surveillance against malignant transformation. MicroRNAs (miRNAs) are a family of small, non-coding RNAs that regulate a wide variety of cellular processes. Recent advances have highlighted the importance of miRNA-mediated post-transcriptional regulation in NK cell development, maturation, and function. This review focuses on several facets of this regulatory mechanism in NK cells: (1) the expressed NK cell miRNA transcriptome; (2) the impact of total miRNA deficiency on NK cells; (3) the role of specific miRNAs regulating NK cell development, survival, and maturation; (4) the intrinsic role of miRNAs regulating NK cell function, including cytokine production, proliferation, and cytotoxicity; and (5) the role of NK cell miRNAs in disease. Currently our knowledge of how miRNAs regulate NK cell biology is limited, and thus we also explore key open questions in the field, as well as approaches and techniques to ascertain the role of individual miRNAs as important molecular regulators
- …