38,135 research outputs found
Dosimetry for radiobiological studies of the human hematopoietic system
A system for estimating individual bone marrow doses in therapeutic radiation exposures of leukemia patients was studied. These measurements are used to make dose response correlations and to study the effect of dose protraction on peripheral blood cell levels. Three irradiators designed to produce a uniform field of high energy gamma radiation for total body exposures of large animals and man are also used for radiobiological studies
Lagrangian acceleration statistics in turbulent flows
We show that the probability densities af accelerations of Lagrangian test
particles in turbulent flows as measured by Bodenschatz et al. [Nature 409,
1017 (2001)] are in excellent agreement with the predictions of a stochastic
model introduced in [C. Beck, PRL 87, 180601 (2001)] if the fluctuating
friction parameter is assumed to be log-normally distributed. In a generalized
statistical mechanics setting, this corresponds to a superstatistics of
log-normal type. We analytically evaluate all hyperflatnes factors for this
model and obtain a flatness prediction in good agreement with the experimental
data. There is also good agreement with DNS data of Gotoh et al. We relate the
model to a generalized Sawford model with fluctuating parameters, and discuss a
possible universality of the small-scale statistics.Comment: 10 pages, 2 figure
A new method for the determination of thin film porosity
Internal reflection spectroscopy may be used to determine presence of water in thin film pores. Presence of water in such pores is function of relative humidity and pore size. Thus, one can determine pore size by controlling humidity. Fluids with surface tension different from that of water can be used to detect pores
Application of pushbroom altimetry from space using large space antennas
The capabilities of multibeam altimetry are discussed and an interferometric multibeam technique for doing precision altimetry is described. The antenna feed horn arrangement and the resulting footprint lube pattern are illustrated. Plans for a shuttle multibeam altimetry mission are also discussed
Magneto-acoustic waves in sunspots from observations and numerical simulations
We study the propagation of waves from the photosphere to the chromosphere of
sunspots. From time series of cospatial Ca II H (including its line blends)
intensity spectra and polarimetric spectra of Si I 1082.7 nm and He I 1083.0 nm
we retrieve the line-of-sight velocity at several heights. The analysis of the
phase difference and amplification spectra shows standing waves for frequencies
below 4 mHz and propagating waves for higher frequencies, and allows us to
infer the temperature and height where the lines are formed. Using these
observational data, we have constructed a model of sunspot, and we have
introduced the velocity measured with the photospheric Si I 1082.7 nm line as a
driver. The numerically propagated wave pattern fits reasonably well with the
observed using the lines formed at higher layers, and the simulations reproduce
many of the observed features. The observed waves are slow MHD waves
propagating longitudinally along field lines.Comment: proceedings of GONG 2010/SOHO 24 meeting, June 27 - July 2, 2010,
Aix-en-Provence, Franc
The eight micron band of silicon monoxide in the expanding cloud around VY Canis Majoris
Observations of vibration-rotation transitions of silicon monoxide in VY CMa show that the lines originate in accelerating, expanding, and cool (600 K) layers of a circumstellar cloud at a distance of roughly 0.15 minutes from the central star. The central stellar velocity, as estimated from observed SiO P Cygni line profiles, is somewhat redshifted from the midpoint of the maser emission features. Most of the silicon is probably in the form of dust grains. The isotopic ratios of silicon are nearly terrestrial
What measurable zero point fluctuations can(not) tell us about dark energy
We show that laboratory experiments cannot measure the absolute value of dark
energy. All known experiments rely on electromagnetic interactions. They are
thus insensitive to particles and fields that interact only weakly with
ordinary matter. In addition, Josephson junction experiments only measure
differences in vacuum energy similar to Casimir force measurements. Gravity,
however, couples to the absolute value. Finally we note that Casimir force
measurements have tested zero point fluctuations up to energies of ~10 eV, well
above the dark energy scale of ~0.01 eV. Hence, the proposed cut-off in the
fluctuation spectrum is ruled out experimentally.Comment: 4 page
Infrared spectroscopy of star formation in galaxies
The Brackett alpha and beta lines with 7.2 seconds angular and 350 km/s velocity resolution were observed in 11 infrared-bright galaxies. From these measurements extinctions, Lyman continuum fluxes, and luminosities due to OB stars were derived. The galaxies observed to date are NGC3690, M38, NGC 5195, Arp 220, NGC 520, NGC660, NGC1614, NGC 3079, NGC 6946, NGC 7714, and Maffei 2, all of which were suggested at some time to be starburst ogjects. The contributions of OB stars to the luminosities of these galaxies can be quantified from the measurements and range from insignificant to sufficient to account for the total energy output. The OB stellar luminosities observed are as high as 10 to the 12th solar luminosities in the galaxy NGC 1614. It is noteworthy that star formation can play very different roles in the infrared energy output of galaxies of similar luminosity, as for example Arp 220 and NGC 1614. In addition to probing the star formation process in these galaxies, the Brackett line measurements, when compared to radio and infrared continuum results, have revealed some unexpected and at present imperfectly understood phenomena: in some very luminous sources the radio continuum appears to be suppressed relative to the infrared recombination lines; in many galaxies there is a substantial excess of 10 micron flux over that predicted from simple models of Lyman alpha heating of dust if young stars are the only significant energy source
Measuring non-extensitivity parameters in a turbulent Couette-Taylor flow
We investigate probability density functions of velocity differences at
different distances r measured in a Couette-Taylor flow for a range of Reynolds
numbers Re. There is good agreement with the predictions of a theoretical model
based on non-extensive statistical mechanics (where the entropies are
non-additive for independent subsystems). We extract the scale-dependent
non-extensitivity parameter q(r, Re) from the laboratory data.Comment: 8 pages, 5 figure
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