3,671 research outputs found
Neutron irradiation effect on SiPMs up to = 5 10 cm
Silicon Photo-Multipliers (SiPM) are becoming the photo-detector of choice
for increasingly more particle detection applications, from fundamental physics
to medical and societal applications. One major consideration for their use at
high-luminosity colliders is the radiation damage induced by hadrons, which
leads to a dramatic increase of the dark count rate. KETEK SiPMs have been
exposed to various fluences of reactor neutrons up to =
510 cm (1 MeV equivalent neutrons). Results from the I-V,
and C-V measurements for temperatures between 30C and 30C
are presented. We propose a new method to quantify the effect of radiation
damage on the SiPM performance. Using the measured dark current the single
pixel occupation probability as a function of temperature and excess voltage is
determined. From the pixel occupation probability the operating conditions for
given requirements can be optimized. The method is qualitatively verified using
current measurements with the SiPM illuminated by blue LED light
An Area of Uncertainty: Practitionersâ Experiences Working with Psychopathy
Psychopathy is an area of research that has been impacted by a great deal of prejudice and stigma. Studies pertaining to therapeutic interventions for psychopathy often argue that the condition might be untreatable. However, more recent research suggests that certain approaches are helpful as they work with strengths, weaknesses, limitations and self-interests. Moreover, qualitative research into both client and practitioner experience in treatment seems to be substantially lacking. The above conflicting opinions, combined with a lack of qualitative research in the area, motivated this research, which comprises an examination of the experience of practitioners who work with psychopathy. Six semi-structured interviews were conducted and analysed using Interpretative Phenomenological Analysis (IPA), which revealed four superordinate themes: âThereâs Something Powerful about that Labelâ, The âContinuumâ, An âArea of Uncertainty, Pessimism and Nihilismâ and Beyond âHanging in Thereâ. Each theme revealed three subordinate themes related to opinions concerning the associations and characteristics of psychopathy, while lending insight to treatment approaches. The findings showed the influence that the label could have on practitioners and clients alike, with positive and negative reactions being observed. There also seemed to be the view that psychopathy, much like other mental health diagnoses, comprised a spectrum. Treatment approaches and outcomes appeared to be met with uncertainty and pessimism, with many participants sharing the difficulty of working with psychopathy. Nonetheless, effective approaches from experience were openly shared and discussed
Constraining the true nature of an exotic binary in the core of NGC 6624
We report on the identification of the optical counterpart to Star1, the
exotic object serendipitously discovered by Deutsch et al. in the core of the
Galactic globular cluster NGC 6624. Star1 has been classified by Deutsch et al.
as either a quiescent Cataclysmic Variable or a low-mass X-ray binary. Deutsch
et al. proposed StarA as possible optical counterpart to this object. We used
high-resolution images obtained with the Hubble Space Telescope to perform a
variability analysis of the stars close to the nominal position of Star1. While
no variability was detected for StarA, we found another star, here named
COM_Star1, showing a clear sinusoidal light modulation with amplitude \Delta
m_F435W~0.7 mag and orbital period of P_orb~98 min. The shape of the light
curve is likely caused by strong irradiation by the primary heating one
hemisphere of the companion, thus suggesting a quite hot primary.Comment: Accepted for publication by ApJ Letters; 6 pages, 5 figure
Optimization of a perishable inventory system: A simulation study in a Ho.Re.Ca. company
The main goal of this paper is to describe the optimization of the inventory management process in a real context of perishable food products. The study involves one of the largest Italian HO.RE.CA. companies, located in the north of Italy and operating as a provider of the catering, commercial and welfare services. A simulation model was set up with the purpose of adapting three traditional reordering policies (i.e. Re-Order Point, Re-Order Cycle, and (s,S)) to a set of products belonging to company's assortment and evaluating the resulting economic outcomes. To this end, each policy was modelled on Microsoft ExcelTM, so as to compute the total cost of inventory management and determine of the minimum cost strategy. A comparison with the current company's performance and that achievable with the optimized policy is also proposed
Malaria sporozoite proteome leaves a trail
Comparison of the proteomes of malaria sporozoites at different stages and mutation of selected genes reveals proteins necessary for infection of the vertebrate host
The M_BH-M_star relation of obscured AGNs at high redshift
We report the detection of broad Halpha emission in three X-ray selected
obscured AGNs at z=1-2. By exploiting the Halpha width and the intrinsic X-ray
luminosity, we estimate their black hole masses, which are in the range
0.1-3x10^9 Msun. By means of multi-band photometric data, we measure the
stellar mass of their host galaxy and, therefore, infer their M_BH/M_star
ratio. These are the first obscured AGNs at high-z, selected based on their
black hole accretion (i.e. on the basis of their X-ray luminosity), that can be
located on the M_BH-M_star relation at high-z. All of these obscured high-z
AGNs are fully consistent with the local M_BH-M_star relation. This result
conflicts with those for other samples of AGNs in the same redshift range,
whose M_BH/M_star ratio departs significantly from the value observed in local
galaxies. We suggest that the obscured AGNs in our sample are in an advanced
evolutionary stage, have already settled onto the local M_BH-M_star relation,
and whose nuclear activity has been temporarily revived by recent galaxy
interactions.Comment: 4 pages, 2 figures, accepted for publication in A&A Letters, slightly
revised discussion on SMG
The primordial environment of super massive black holes: large scale galaxy overdensities around QSOs with LBT
We investigated the presence of galaxy overdensities around four
QSOs, namely SDSS J1030+0524 (z = 6.28), SDSS J1148+5251 (z = 6.41), SDSS
J1048+4637 (z = 6.20) and SDSS J1411+1217 (z = 5.95), through deep -, -
and - band imaging obtained with the wide-field () Large
Binocular Camera (LBC) at the Large Binocular Telescope (LBT). We adopted
color-color selections within the vs plane to identify samples of
-band dropouts at the QSO redshift and measure their relative abundance and
spatial distribution in the four LBC fields, each covering
physical Mpc at . The same selection criteria were then applied to
-band selected sources in the 1 deg Subaru-XMM Newton Deep Survey
to derive the expected number of dropouts over a blank LBC-sized field
(0.14 deg). The four observed QSO fields host a number of candidates
larger than what is expected in a blank field. By defining as -band dropouts
objects with and undetected in the -band, we found
16, 10, 9, 12 dropouts in SDSS J1030+0524, SDSS J1148+5251, SDSS J1048+4637,
and SDSS J1411+1217, respectively, whereas only 4.3 such objects are expected
over a 0.14 deg blank field. This corresponds to overdensity significances
of 3.3, 1.9, 1.7, 2.5, respectively. By considering the total number of
dropouts in the four LBC fields and comparing it with what is expected in four
blank fields of 0.14 deg each, we find that high-z QSOs reside in overdense
environments at the level. This is the first direct and unambiguous
measurement of the large scale structures around QSOs. [shortened]Comment: 12 pages, 8 figures. Accepted for publication in A&
Probing black hole accretion in quasar pairs at high redshift
Models and observations suggest that luminous quasar activity is triggered by
mergers, so it should preferentially occur in the most massive primordial dark
matter haloes, where the frequency of mergers is expected to be the highest.
Since the importance of galaxy mergers increases with redshift, we identify the
high-redshift Universe as the ideal laboratory for studying dual AGN. Here we
present the X-ray properties of two systems of dual quasars at z=3.0-3.3
selected from the SDSS-DR6 at separations of 6-8 arcsec (43-65kpc) and observed
by Chandra for 65ks each. Both members of each pair are detected with good
photon statistics to allow us to constrain the column density, spectral slope
and intrinsic X-ray luminosity. We also include a recently discovered dual
quasar at z=5 (separation of 21 arcsec, 136kpc) for which XMM-Newton archival
data allow us to detect the two components separately. Using optical spectra we
derived bolometric luminosities, BH masses and Eddington ratios that were
compared to those of luminous SDSS quasars in the same redshift ranges. We find
that the brighter component of both pairs at z=3.0-3.3 has high luminosities
compared to the distribution of SDSS quasars at similar redshift, with J1622A
having an order magnitude higher luminosity than the median. This source lies
at the luminous end of the z~3.3 quasar luminosity function. While we cannot
conclusively state that the unusually high luminosities of our sources are
related to their having a close companion, for J1622A there is only a 3%
probability that it is by chance.Comment: MNRAS, in pres
Does the X-ray emission of the luminous quasar RBS 1124 originate in a mildly relativistic outflowing corona?
We have observed the luminous (L2-10âkeVâ 6 Ă 1044 ergâsâ1) radio-quiet quasar RBS 1124 (z= 0.208) with Suzaku. We report the detection of a moderately broad iron (Fe) line and of a weak soft X-ray excess. The X-ray data are very well described by a simple model comprising a power-law X-ray continuum plus its reflection off the accretion disc. If the inner disc radius we measure (rin†3.8 gravitational radii) is identified with the innermost stable circular orbit of the black hole space-time, we infer that the black hole powering RBS 1124 is rotating rapidly with spin aâ„ 0.6. The soft excess contribution in the 0.5-2 keV band is âŒ15 per cent, about half than that typically observed in unobscured Seyfert 1 galaxies and quasars, in line with the low disc reflection fraction we measure (Rdiscâ 0.4). The low reflection fraction cannot be driven by disc truncation which is at odds not only with the small inner disc radius we infer but, most importantly, with the radiatively efficient nature of the source (LBol/LEddâ 1). A plausible explanation is that the X-ray corona is the base of a failed jet (RBS 1124 being radio-quiet) and actually outflowing at mildly relativistic speeds. Aberration reduces the irradiation of the disc, thus forcing a lower than standard reflection fraction, and halves the inferred source intrinsic luminosity, reducing the derived Eddington ratio from â1 to â0.5. A partial covering model provides a statistically equivalent description of the 0.3-10 keV data, but provides a worse fit above 10 keV. More importantly, its properties are not consistent with being associated to the Fe emission line, worsening the degree of self-consistency of the model. Moreover, the partial covering model implies that RBS 1124 is radiating well above its Eddington luminosity, which seems unlikely and very far off from previous estimate
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