1,120 research outputs found
A Large Mass of H_2 in the Brightest Cluster Galaxy in Zwicky 3146
We present the Spitzer/IRS mid-infrared spectrum of the infrared-luminous (L_(IR) = 4 × 10^(11) L_☉) brightest cluster galaxy (BCG) in the X-ray-luminous cluster Zwicky 3146 (Z3146; z = 0.29). The spectrum shows strong aromatic emission features, indicating that the dominant source of the infrared luminosity is star formation. The most striking feature of the spectrum, however, is the exceptionally strong molecular hydrogen (H_2) emission lines, which seem to be shock-excited. The line luminosities and inferred warm H_2 gas mass (~10^(10) M_☉) are 6 times larger than those of NGC 6240, the most H_2-luminous galaxy at z ≲ 0.05. Together with the large amount of cold H_2 detected previously (~10^(11) M_☉), this indicates that the Z3146 BCG contains disproportionately large amounts of both warm and cold H_2 gas for its infrared luminosity, which may be related to the intracluster gas cooling process in the cluster core
A Large Mass of H2 in the Brightest Cluster Galaxy in Zwicky 3146
We present the Spitzer/IRS mid-infrared spectrum of the infrared-luminous
(L_{IR}=4e11 L_sun) brightest cluster galaxy (BCG) in the X-ray-luminous
cluster Z3146 (z=0.29). The spectrum shows strong aromatic emission features,
indicating that the dominant source of the infrared luminosity is star
formation. The most striking feature of the spectrum, however, is the
exceptionally strong molecular hydrogen (H2) emission lines, which seem to be
shock-excited. The line luminosities and inferred warm H2 gas mass (~1e10
M_sun) are 6 times larger than those of NGC 6240, the most H2-luminous galaxy
at z <~ 0.1. Together with the large amount of cold H2 detected previously
(~1e11 M_sun), this indicates that the Z3146 BCG contains disproportionately
large amounts of both warm and cold H2 gas for its infrared luminosity, which
may be related to the intracluster gas cooling process in the cluster core.Comment: 13 pages, 3 figures, 1 table; Accepted for publication in ApJ
Crowding effect on helix-coil transition: beyond entropic stabilization
We report circular dichroism measurements on the helix-coil transition of
poly(L-glutamic acid) in solution with polyethylene glycol (PEG) as a crowding
agent. Using small angle neutron scattering, PEG solutions have been
characterized and found to be well described by the picture of a transient
network of mesh size , usual for semi-diluted chains in good solvent. We
show that the increase of PEG concentration stabilizes the helices and
increases the transition temperature. But more unexpectedly we also notice that
the increase of crowding agent concentration reduces the mean helix extent at
the transition, or in other words reduces its cooperative feature. This result
cannot be accounted for by an entropic stabilization mechanism. Comparing the
mean length of helices at the transition and the mesh size of the PEG network,
our results strongly suggest two regimes: helices shorter or longer than the
mesh size
Unravelling cellular mechanisms of stem cell senescence: An aid from natural bioactive molecules
Cellular senescence plays a role in the onset of age-related pathologies and in the loss of tissue homeostasis. Natural compounds of food or plants exert an important antioxidant activity, counteracting the formation of harmful free radicals. In the presence of an intense stressing event, cells activate specific responses to counteract senescence or cell death. In the present paper, we aimed at evaluating the levels of expression of specific markers of senescence, in order to demonstrate that extracts from Myrtus Communis L. can prevent premature senescence in ADSCs exposed to oxidative stress. Cells were cultured in the presence of Myrtus extracts for 12–24 and 48 h and then incubated with H2O2 to induce senescence. We then evaluated the expression of senescence-related markers p16, p19, p21, p53, TERT, c-Myc, and the senescence-associated β-Galactoidase activity. Our results showed that pre-treatment with Myrtus extracts protects cells from premature senescence, by regulating the cell cycle, and inducing the expression of TERT and c-Myc. These findings suggest a potential application of these natural compounds in the prevention and treatment of various diseases, counteracting premature senescence and preserving tissue functions
Pacman percolation: a model for enzyme gel degradation
We study a model for the gel degradation by an enzyme, where the gel is
schematized as a cubic lattice, and the enzyme as a random walker, that cuts
the bonds over which it passes. The model undergoes a (reverse) percolation
transition, which for low density of enzymes falls in a universality class
different from random percolation. In particular we have measured a gel
fraction critical exponent beta=1.0+-0.1, in excellent agreement with
experiments made on the real system.Comment: 4 pages, 7 eps figure
Strategies in Outsourcing R&D Processes to Maintain Market Competitiveness
In the 21st century, managing outsourced research and development (R&D) processes is critical to an organization\u27s success. Guided by the logistic outsourcing theory developed by de Boer, Gaytan, and Arroyo, the purpose of this single case study was to explore strategies and processes organizational leaders used to manage outsourced R&D to maintain market competitiveness. Semistructured interviews were conducted with 5 purposefully selected business leaders who were responsible for outsourcing R&D in a single Fortune 500 corporation in the Mid-Atlantic region of the United States. Company records were also gathered as data. Yin\u27s 5-step process for a case study and key words in context analysis were used to analyze the data. Findings included 3 main themes: (a) the outsourcing decision-making process with internal and external constraints, (b) the effectiveness of managing outsourcing services and processes, and (c) the influence of outsourcing on business effectiveness and new products. Findings also indicated no practical system to measure effectiveness of outsourced R&D services on market competitiveness. The lack of measurement effectiveness was due to a lack of processes in place to measure R&D performance and no practical approach to measure impact of R&D on market competitiveness. Findings offered insight into strategies used by business leaders to manage outsourced R&D processes. Findings may also have implications for positive social change such as impacting communities through employment, generating government revenues through taxes, and creating a positive impact on job creation in the industries that promote R&D outsourcing
ISOCAM observations in the Lockman Hole - II The 14.3 micron deep survey: data reduction, catalogue and source counts
We present a new analysis of the ISOCAM 14.3 micron deep survey in a 20x20
square arcmins area in the Lockman Hole. This survey is intermediate between
the ultra-deep surveys and the shallow surveys in the ELAIS fields. The data
have been analyzed with the method presented by Lari et al. (2001). We have
produced a catalogue of 283 sources detected above the 5-sigma threshold, with
fluxes in the interval 0.1-8 mJy. The catalogue is 90% complete at 1 mJy. The
positional accuracy, estimated from the cross-correlation of infrared and
optical sources, is around 1.5 arcsec. The search for the optical counterparts
of the sources in the survey is performed on a medium-deep r' band optical
image (5-sigma depth of r'=25), making use of the radio detections when
available. The photometry has been checked through simulations and by comparing
the data with those presented in a shallower and more extended ISOCAM survey in
the Lockman Hole, that we have presented in a companion paper. Only 15% of the
14.3 micron sources do not have an optical counterpart down to r'=25 mag. We
use the 6.7/14.3 micron colour as a star/galaxy separator, together with a
visual inspection of the optical image and an analysis of the observed Spectral
Energy Distribution of the ISOCAM sources. The stars in the sample turn out to
be only 6% of the sample. We discuss the 14.3 micron counts of extragalactic
sources, combining our catalogue with that obtained from the shallower ISOCAM
survey. The data in the two surveys are consistent, and our results fully
support the claims in previous works for the existence of an evolving
population of infrared galaxies, confirming the evident departure from
non-evolutionary model predictions.Comment: Version accepted by Astronomy and Astrophysics. Images have been
heavily degraded to fill the archive size. A full resolution version can be
downloaded at the following link
http://dipastro.pd.astro.it/giulia/Deep/1252.ps.g
ISO investigates the nature of extremely-red hard X-ray sources responsible for the X-ray background
We analyse very deep X-ray and mid-IR surveys in common areas of the Lockman
Hole and the HDF North to study the sources of the X-ray background (XRB) and
to test the standard obscured accretion paradigm. We detect with ISO a rich
population of X-ray luminous sources with red optical colours, including a
fraction identified with Extremely Red Objects (R-K > 5) and galaxies with SEDs
typical of normal massive ellipticals or spirals at z ~ 1. The high 0.5-10 keV
X-ray luminosities of these objects (1E43-1E45 erg/s) indicate that the
ultimate energy source is gravitational accretion, while the X-ray to IR flux
ratios and the X-ray spectral hardness show evidence of photoelectric
absorption at low X-ray energies. An important hint on the physics comes from
the mid-IR data at 6.7 and 15 um, well reproduced by model spectra of
completely obscured quasars under standard assumptions and l.o.s. optical
depths tau ~ 30-40. Other predictions of the standard XRB picture, like the
distributions of intrinsic bolometric luminosities and the relative fractions
of type-I and -II objects (1:3), are also consistent with our results. Obscured
gravitational accretion is then confirmed as being responsible for the bulk of
the X-ray background, since we detect in the IR the down-graded energy
photoelectrically absorbed in X-rays: 63% of the faint 5-10 keV XMM sources are
detected in the mid-IR by Fadda et al. (2001). However, although as much as 90%
of the X-ray energy production could be converted to IR photons, no more than
20% of the Cosmic IR Background can be attributed to X-ray loud AGNs.Comment: 7 pages, 5 postscript figures, ApJ submitte
Online learning of physics during a pandemic: A report from an academic experience in Italy
The arrival of the Sars-Cov II has opened a new window on teaching physics in academia.
Frontal lectures have left space for online teaching, teachers have been faced with a new way
of spreading knowledge, adapting contents and modalities of their courses. Students have
faced up with a new way of learning physics, which relies on free access to materials and
their informatics knowledge. We decided to investigate how online didactics has influenced
students’ assessments, motivation, and satisfaction in learning physics during the pandemic
in 2020. The research has involved bachelor (n = 53) and master (n = 27) students of
the Physics Department at the University of Cagliari (N = 80, 47 male; 33 female). The
MANOVA supported significant mean differences about gender and university level with
higher values for girls and master students in almost all variables investigated. The path
analysis showed that student-student, student-teacher interaction, and the organization of
the courses significantly influenced satisfaction and motivation in learning physics. The
results of this study can be used to improve the standards of teaching in physics at the
University of Cagliar
Counting individual galaxies from deep 24-μm Spitzer surveys
We address the question of how to deal with confusion-limited surveys in the mid-infrared (MIR) domain by using information from shorter-wavelength observations over the same sky regions. Such information, once applied to apparently extended MIR sources, which are indeed ‘blends’ of two or more different sources, allow us to disentangle the single counterparts and to split the measured flux density into different components. We present the application of this method to the 24-μm Spitzer archival data in the Great Observatories Origins Deep Survey ELAIS-N1 (GOODS EN1) test field, where apparently extended, ‘blended’ sources constitute about 20 per cent of a reliable sample of 983 sources detected above the 5σ threshold down to 40 μJy. As a shorter-wavelength data set, we have considered the public Infrared Array Camera (IRAC) images and catalogues of the same field. We show that the 24-μm sample is almost unbiased down to ~40 μJy and the careful application of the deblending procedure does not require any statistical completeness correction (at least at the flux level considered). This is probed by direct comparison of our results with results in the literature that analysed the same data set through extensive Monte Carlo simulations. The extrapolation of the source counts down to fainter fluxes suggests that our 24-μm sample is able to resolve ~62 per cent of the cosmic background down to a flux level of 38 μJy
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