4,342 research outputs found
Quantification of food intake in Drosophila
Measurement of food intake in the fruit fly Drosophila melanogaster is often necessary for studies of behaviour, nutrition and drug administration. There is no reliable and agreed method for measuring food intake of flies in undisturbed, steady state, and normal culture conditions. We report such a method, based on measurement of feeding frequency by proboscis-extension, validated by short-term measurements of food dye intake. We used the method to demonstrate that (a) female flies feed more frequently than males, (b) flies feed more often when housed in larger groups and (c) fly feeding varies at different times of the day. We also show that alterations in food intake are not induced by dietary restriction or by a null mutation of the fly insulin receptor substrate chico. In contrast, mutation of takeout increases food intake by increasing feeding frequency while mutation of ovoD increases food intake by increasing the volume of food consumed per proboscis-extension. This approach provides a practical and reliable method for quantification of food intake in Drosophila under normal, undisturbed culture conditions
Radio Wavelength Constraints on the Sources of the Far Infrared Background
The cosmic far infrared background detected recently by the COBE-DIRBE team
is presumably due, in large part, to the far infrared (FIR) emission from all
galaxies. We take the well-established correlation between FIR and radio
luminosity for individual galaxies and apply it to the FIR background. We find
that these sources make up about half of the extragalactic radio background,
the other half being due to AGN. This is in agreement with other radio
observations, which leads us to conclude that the FIR-radio correlation holds
well for the very faint sources making up the FIR background, and that the FIR
background is indeed due to star-formation activity (not AGN or other possible
sources). If these star-forming galaxies have a radio spectral index between
0.4 and 0.8, and make up 40 to 60% of the extragalactic radio background, we
find that they have redshifts between roughly 1 and 2, in agreement with recent
estimates by Madau et al. of the redshift of peak star-formation activity. We
compare the observed extragalactic radio background to the integral over the
logN-logS curve for star-forming radio sources, and find that the slope of the
curve must change significantly below about 1 microjansky. At 1 microjansky,
the faint radio source counts predict about 25 sources per square arcminute,
and these will cause SIRTF to be confusion limited at 160micron.Comment: 10 pages including 1 figure, AASTeX, accepted by Ap
Planck Observations of M33
We have performed a comprehensive investigation of the global integrated flux
density of M33 from radio to ultraviolet wavelengths, finding that the data
between 100 GHz and 3 THz are accurately described by a single modified
blackbody curve with a dust temperature of = 21.670.30 K
and an effective dust emissivity index of = 1.350.10,
with no indication of an excess of emission at millimeter/sub-millimeter
wavelengths. However, sub-dividing M33 into three radial annuli, we found that
the global emission curve is highly degenerate with the constituent curves
representing the sub-regions of M33. We also found gradients in
and across the disk of M33, with both
quantities decreasing with increasing radius. Comparing the M33 dust emissivity
with that of other Local Group members, we find that M33 resembles the
Magellanic Clouds rather than the larger galaxies, i.e., the Milky Way and M31.
In the Local Group sample, we find a clear correlation between global dust
emissivity and metallicity, with dust emissivity increasing with metallicity. A
major aspect of this analysis is the investigation into the impact of
fluctuations in the Cosmic Microwave Background (CMB) on the integrated flux
density spectrum of M33. We found that failing to account for these CMB
fluctuations would result in a significant over-estimate of
by 5 K and an under-estimate of by 0.4.Comment: Accepted for publication in MNRA
The Planck Surveyor mission: astrophysical prospects
Although the Planck Surveyor mission is optimized to map the cosmic microwave
background anisotropies, it will also provide extremely valuable information on
astrophysical phenomena. We review our present understanding of Galactic and
extragalactic foregrounds relevant to the mission and discuss on one side,
Planck's impact on the study of their properties and, on the other side, to
what extent foreground contamination may affect Planck's ability to accurately
determine cosmological parameters. Planck's multifrequency surveys will be
unique in their coverage of large areas of the sky (actually, of the full sky);
this will extend by two or more orders of magnitude the flux density interval
over which mm/sub-mm counts of extragalactic sources can be determined by
instruments already available (like SCUBA) or planned for the next decade (like
the LSA-MMA or the space mission FIRST), which go much deeper but over very
limited areas. Planck will thus provide essential complementary information on
the epoch-dependent luminosity functions. Bright radio sources will be studied
over a poorly explored frequency range where spectral signatures, essential to
understand the physical processes that are going on, show up. The
Sunyaev-Zeldovich effect, with its extremely rich information content, will be
observed in the direction of a large number of rich clusters of Galaxies.
Thanks again to its all sky coverage, Planck will provide unique information on
the structure and on the emission properties of the interstellar medium in the
Galaxy. At the same time, the foregrounds are unlikely to substantially limit
Planck's ability to measure the cosmological signals. Even measurements of
polarization of the primordial Cosmic Microwave background fluctuations appear
to be feasible.Comment: 20 pages, Latex (use aipproc2.sty, aipproc2.cls, epsfig.sty), 10
PostScript figures; invited review talk, Proc. of the Conference: "3 K
Cosmology", Roma, Italy, 5-10 October 1998, AIP Conference Proc, in press
Note: Figures 6 and 7 have been replaced by new and correct version
Optically Faint Microjansky Radio Sources
We report on the identifications of radio sources from our survey of the
Hubble Deep Field and the SSA13 fields, both of which comprise the deepest
radio surveys to date at 1.4 GHz and 8.5 GHz respectively. About 80% of the
microjansky radio sources are associated with moderate redshift starburst
galaxies or AGNs within the I magnitude range of 17 to 24 with a median of I =
22 mag. Thirty-one (20%) of the radio sources are: 1) fainter than 25 mag,
with two objects in the HDF 28.5, 2) often identified with very red
objects 4, and 3) not significantly different in radio properties than
the brighter objects. We suggest that most of these objects are associated with
heavily obscured starburst galaxies with redshifts between 1 and 3. However,
other mechanisms are discussed and cannot be ruled out with the present
observations.Comment: to appear in Astrophysical Journal Letters, 3 figures, 1 tabl
The Heumann-Hotzel model for aging revisited
Since its proposition in 1995, the Heumann-Hotzel model has remained as an
obscure model of biological aging. The main arguments used against it were its
apparent inability to describe populations with many age intervals and its
failure to prevent a population extinction when only deleterious mutations are
present. We find that with a simple and minor change in the model these
difficulties can be surmounted. Our numerical simulations show a plethora of
interesting features: the catastrophic senescence, the Gompertz law and that
postponing the reproduction increases the survival probability, as has already
been experimentally confirmed for the Drosophila fly.Comment: 11 pages, 5 figures, to be published in Phys. Rev.
Microstructural evolution of silicate immiscible liquids in ferrobasalts
Abstract: An experimental study of the microstructural evolution of an immiscible basaltic emulsion shows that the Fe-rich liquid forms homogeneously nucleated droplets dispersed in a continuous Si-rich liquid, together with droplets heterogeneously nucleated on plagioclase, magnetite, and pyroxene. Heterogeneous nucleation is likely promoted by localised compositional heterogeneities around growing crystals. The wetting angle of Fe-rich droplets on both plagioclase and magnetite increases with decreasing temperature. Droplet coarsening occurs by a combination of diffusion-controlled growth and Ostwald ripening, with an insignificant contribution from coalescence. Characteristic microstructures resulting from the interaction of immiscible Fe-rich liquid with crystal grains during crystal growth can potentially be used as an indicator of liquid unmixing in fully crystallised natural samples. In magma bodies < ~ 10 m in size, gravitationally driven segregation of immiscible Fe-rich droplets is unlikely to be significant
The Radio/Optical Catalog of the SSA13 Field
We present a 1.4-GHz catalog of 810 radio sources (560 sources in the
complete sample) with 1.8" resolution found within a 17' radius in the SSA13
field (RA=13h12m,DEC=42d38'). The radio image from the VLA has an rms noise
level of 4.82 microJy/beam at the field center, and Subaru optical images in
r-band (6300A) and z-band (9200A) have a three-sigma detection magnitude of
26.1 and 24.9, respectively. 88% of the radio sources are identified with an
optical counterpart, and there is significantly more reddening for objects
fainter than 24-mag. The radio and optical parameters are tabulated, and source
morphologies are displayed by radio contours overlaying optical false-color
images. The radio structures show a wealth of complexity and these are
classified into a small number of categories. About one-third of the radio
sources are larger than 1.2" and their orientation is often similar to that of
the associated galaxy or binary-galaxy system. The density of sources in the
SSA13 field above 75 microJy is 0.40 per square arcmin, with a slope of -2.43
in the differential counts. The radio spectral index may steepen for sources
below 75 microJy. We estimate that at most 40% of the microJansky radio sources
are dominated by AGN processes.Comment: 50 pages, 14 figures of which fig 6 contains 33 parts. In press,
Astrophysical Journal, Supp
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