2,014 research outputs found
Observational evidence for buffeting induced kink waves in solar magnetic elements
The role of diffuse photospheric magnetic elements in the energy budget of
the upper layers of the Sun's atmosphere has been the recent subject of many
studies. This was made possible by the availability of high temporal and
spatial resolution observations of the solar photosphere, allowing large
numbers of magnetic elements to be tracked to study their dynamics. In this
work we exploit a long temporal series of seeing-free magnetograms of the solar
photosphere to study the effect of the turbulent convection in the excitation
of kink oscillations in magnetic elements. We make use of the empirical mode
decomposition technique (EMD) in order to study the transverse oscillations of
several magnetic flux tubes. This technique permits the analysis of
non-stationary time series like those associated to the horizontal velocities
of these flux tubes which are continuously advected and dispersed by granular
flows.
Our primary findings reveal the excitation of low frequency modes of kink
oscillations, which are sub-harmonics of a fundamental mode with a minute periodicity. These results constitute a strong case for
observational proof of the excitation of kink waves by the buffeting of the
convection cells in the solar photosphere, and are discussed in light of their
possible role in the energy budget of the upper Sun's atmosphere.Comment: A&A accepte
Reduced lysosomal acid lipase activity: A new marker of liver disease severity across the clinical continuum of non-alcoholic fatty liver disease?
Lysosomal acid lipase (LAL) plays a key role in intracellular lipid metabolism. Reduced LAL activity promotes increased multi-organ lysosomal cholesterol ester storage, as observed in two recessive autosomal genetic diseases, Wolman disease and Cholesterol ester storage disease. Severe liver steatosis and accelerated liver fibrosis are common features in patients with genetic LAL deficiency. By contrast, few reliable data are available on the modulation of LAL activity in vivo and on the epigenetic and metabolic factors capable of regulating its activity in subjects without homozygous mutations of the Lipase A gene. In the last few years, a less severe and non-genetic reduction of LAL activity was reported in children and adults with non-alcoholic fatty liver disease (NAFLD), suggesting a possible role of LAL reduction in the pathogenesis and progression of the disease. Patients with NAFLD show a significant, progressive reduction of LAL activity from simple steatosis to non-alcoholic steatohepatitis and cryptogenic cirrhosis. Among cirrhosis of different etiologies, those with cryptogenic cirrhosis show the most significant reductions of LAL activity. These findings suggest that the modulation of LAL activity may become a possible new therapeutic target for patients with more advanced forms of NAFLD. Moreover, the measurement of LAL activity may represent a possible new marker of disease severity in this clinical setting
A new photometric technique for the joint selection of star-forming and passive galaxies at 1.4<z<2.5
A simple two color selection based on B-, z-, and K- band photometry is
proposed for culling galaxies at 1.4<z<2.5 in K-selected samples and
classifying them as star-forming or passive systems. The method is calibrated
on the highly complete spectroscopic redshift database of the K20 survey,
verified with simulations and tested on other datasets. Requiring
BzK=(z-K)-(B-z)>-0.2 (AB) allows to select actively star-forming galaxies at
z>1.4, independently on their dust reddening. Instead, objects with BzK<-0.2
and (z-K)>2.5 (AB) colors include passively evolving galaxies at z>1.4, often
with spheroidal morphologies. Simple recipes to estimate the reddening, SFRs
and masses of BzK-selected galaxies are derived, and calibrated on K<20
galaxies. Based on their UV (reddening-corrected), X-ray and radio
luminosities, the BzK-selected star-forming galaxies with K<20 turn out to have
average SFR ~ 200 Msun yr^-1, and median reddening E(B-V)~0.4. Besides missing
the passively evolving galaxies, the UV selection appears to miss some relevant
fraction of the z~2 star-forming galaxies with K<20, and hence of the
(obscured) star-formation rate density at this redshift. The high SFRs and
masses add to other existing evidence that these z=2 star-forming galaxies may
be among the precursors of z=0 early-type galaxies. Theoretical models cannot
reproduce simultaneously the space density of both passively evolving and
highly star-forming galaxies at z=2. In view of Spitzer Space Telescope
observations, an analogous technique based on the RJL photometry is proposed to
complement the BzK selection and to identify massive galaxies at 2.5<z<4.0.
These color criteria should help in completing the census of the stellar mass
and of the star-formation rate density at high redshift (abridged).Comment: 19 pages, 17 figures, to appear on ApJ (20 December 2004 issue
The Visible and Near Infrared module of EChO
The Visible and Near Infrared (VNIR) is one of the modules of EChO, the
Exoplanets Characterization Observatory proposed to ESA for an M-class mission.
EChO is aimed to observe planets while transiting by their suns. Then the
instrument had to be designed to assure a high efficiency over the whole
spectral range. In fact, it has to be able to observe stars with an apparent
magnitude Mv= 9-12 and to see contrasts of the order of 10-4 - 10-5 necessary
to reveal the characteristics of the atmospheres of the exoplanets under
investigation. VNIR is a spectrometer in a cross-dispersed configuration,
covering the 0.4-2.5 micron spectral range with a resolving power of about 330
and a field of view of 2 arcsec. It is functionally split into two channels
respectively working in the 0.4-1 and 1.0-2.5 micron spectral ranges. Such a
solution is imposed by the fact the light at short wavelengths has to be shared
with the EChO Fine Guiding System (FGS) devoted to the pointing of the stars
under observation. The spectrometer makes use of a HgCdTe detector of 512 by
512 pixels, 18 micron pitch and working at a temperature of 45K as the entire
VNIR optical bench. The instrument has been interfaced to the telescope optics
by two optical fibers, one per channel, to assure an easier coupling and an
easier colocation of the instrument inside the EChO optical bench.Comment: 26 page
Ground-based monitoring of comet 67P/Churyumov-Gerasimenko gas activity throughout the <i>Rosetta</i> mission
Simultaneously to the ESA Rosetta mission, a world-wide ground-based campaign provided measurements of the large scale activity of comet 67P/Churyumov-Gerasimenko through measurement of optically active gas species and imaging of the overall dust coma. We present more than two years of observations performed with the FORS2 low resolution spectrograph at the VLT, TRAPPIST, and ACAM at the WHT. We focus on the evolution of the CN production, as a tracer of the comet activity. We find that it is asymmetric with respect to perihelion and different from that of the dust. The CN emission is detected for the first time at 1.34 au pre-perihelion and production rates then increase steeply to peak about two weeks after perihelion at (1.00±0.10) ×1025 molecules s−1, while the post-perihelion decrease is more shallow. The evolution of the comet activity is strongly influenced by seasonal effects, with enhanced CN production when the Southern hemisphere is illuminated
Preliminary report on the amphibians and reptiles from the lower Palaeolithic palaeoanthropological site of Visogliano (NE Italy)
Polarimetry of transneptunian objects (136472) Makemake and (90482) Orcus
Context. We study the surface properties of transneptunian populations of
Solar-system bodies. Aims. We investigate the surface characteristics of the
dwarf planet (136472) Makemake and the resonant object (90482) Orcus. Methods.
Using the FORS2 instrument of the ESO-VLT we have carried out linear
polarisation measurements of Makemake and Orcus. Results. Polarisation of Orcus
is similar to that of smaller size objects. The polarimetric properties of
Makemake are very close to those of Eris and Pluto. We have not found any
significant differences in the polarisation properties of objects from
different dynamical classes. However, there are significant differences in
polarisation of large and smaller size objects, and between large TNOs with
water-ice and methane-ice dominated surfaces. Conclusions. We confirm the
different types of polarisation phase behavior for the largest and smaller size
TNOs. To explain subtle surface polarisation of Pluto, Makemake and Eris we
assume that their surfaces are covered by a thin layer of hoarfrost masking the
surface structure
Cobertura de testes unitários no SIGI.
Técnicas de teste. Ferramenta para cobertura de testes unitários. Diretrizes para utilização da Discover. Cobertura dos testes unitários do SIGI.bitstream/CNPTIA/9884/1/comuntec25.pdfAcesso em: 30 maio 2008
Star formation properties of sub-mJy radio sources
We investigate the star formation properties of ~800 sources detected in one
of the deepest radio surveys at 1.4 GHz. Our sample spans a wide redshift range
(~0.1 - 4) and about four orders of magnitude in star formation rate (SFR). It
includes both star forming galaxies (SFGs) and active galactic nuclei (AGNs),
further divided into radio-quiet and radio-loud objects. We compare the SFR
derived from the far infrared luminosity, as traced by Herschel, with the SFR
computed from their radio emission. We find that the radio power is a good SFR
tracer not only for pure SFGs but also in the host galaxies of RQ AGNs, with no
significant deviation with redshift or specific SFR. Moreover, we quantify the
contribution of the starburst activity in the SFGs population and the
occurrence of AGNs in sources with different level of star formation. Finally
we discuss the possibility of using deep radio survey as a tool to study the
cosmic star formation history.Comment: 18 pages, 14 figures, 1 table (available in its entirety as ancillary
data
The comet 17P/Holmes 2007 outburst: the early motion of the outburst material
Context. On October 24, 2007 the periodic comet 17P/Holmes underwent an
astonishing outburst that increased its apparent total brightness from
magnitude V\sim17 up to V\sim2.5 in roughly two days. We report on Wendelstein
0.8 m telescope (WST) photometric observations of the early evolution stages of
the outburst. Aims. We studied the evolution of the structure morphology, its
kinematic, and estimated the ejected dust mass. Methods. We analized 126 images
in the BVRI photometric bands spread between 26/10/2007 and 20/11/2007. The
bright comet core appeared well separated from that one of a quickly expanding
dust cloud in all the data, and the bulk of the latter was contained in the
field of view of our instrument. The ejected dust mass was derived on the base
of differential photometry on background stars occulted by the moving cloud.
Results. The two cores were moving apart from each other at a relative
projected constant velocity of (9.87 +/- 0.07) arcsec/day (0.135 +/-0.001
km/sec). In the inner regions of the dust cloud we observed a linear increase
in size at a mean constant velocity of (14.6+/-0.3) arcsec/day (0.200+/-0.004
km/sec). Evidence of a radial velocity gradient in the expanding cloud was also
found. Our estimate for the expanding coma's mass was of the order of 10^{-2}-1
comet's mass implying a significant disintegration event. Conclusions. We
interpreted our observations in the context of an explosive scenario which was
more probably originated by some internal instability processes, rather than an
impact with an asteroidal body. Due to the peculiar characteristics of this
event, further observations and investigations are necessary in order to
enlight the nature of the physical processes that determined it.Comment: 5 pages, 3 figures, A&A accepte
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