895 research outputs found
A food chain ecoepidemic model: infection at the bottom trophic level
In this paper we consider a three level food web subject to a disease
affecting the bottom prey. The resulting dynamics is much richer with respect
to the purely demographic model, in that it contains more transcritical
bifurcations, gluing together the various equilibria, as well as persistent
limit cycles, which are shown to be absent in the classical case. Finally,
bistability is discovered among some equilibria, leading to situations in which
the computation of their basins of attraction is relevant for the system
outcome in terms of its biological implications
Numerical simulations of stellar jets and comparison between synthetic and observed maps: clues to the launch mechanism
High angular resolution spectra obtained with the Hubble Space Telescope
Imaging Spectrograph (HST/STIS) provide rich morphological and kinematical
information about the stellar jet phenomenon, which allows us to test
theoretical models efficiently. In this work, numerical simulations of stellar
jets in the propagation region are executed with the PLUTO code, by adopting
inflow conditions that arise from former numerical simulations of magnetized
outflows, accelerated by the disk-wind mechanism in the launching region. By
matching the two regions, information about the magneto-centrifugal
accelerating mechanism underlying a given astrophysical object can be
extrapolated by comparing synthetic and observed position-velocity diagrams
(PVDs). We show that quite different jets, like those from the young T Tauri
stars DG-Tau and RW-Aur, may originate from the same disk-wind model for
different configurations of the magnetic field at the disk surface. This result
supports the idea that all the observed jets may be generated by the same
mechanism.Comment: 15 pages, 18 figures, accepted for publication by A&
Reflectionless tunneling in planar Nb/GaAs hybrid junctions
Reflectionless-tunneling was observed in Nb/GaAs superconductor/semiconductor
junctions fabricated through a two-step procedure. First, periodic
-doped layers were grown by molecular beam epitaxy near the GaAs
surface, followed by an As cap layer to protect the surface during {\it
ex-situ} transfer. Second, Nb was deposited by dc-magnetron sputtering onto the
GaAs(001) 2 4 surface {\it in-situ} after thermal desorption of the
cap layer. The magnetotransport behavior of the resulting hybrid junctions was
successfully analyzed within the random matrix theory of phase-coherent Andreev
transport. The impact of junction morphology on reflectionless tunneling and
the applicability of the fabrication technique to the realization of complex
superconductor/semiconductor mesoscopic systems are discussed.Comment: 10 pages, 3 figures, to be published in Appl. Phys. Let
Safety culture to improve accidental events reporting in radiotherapy
The potential for unintended and adverse radiation exposure in radiotherapy is real and should be studied because radiotherapy is a highly complex, multistep process which requires input from numerous individuals from different areas and steps of the radiotherapy workflow. The 'Incident' (I) is a consequence of which are not negligible from the point of view of protection or safety. A 'near miss' (NM) is defined as an event which is highly likely to happen but did not occur. The purpose of this work is to show that through a systematic reporting and analysis of these adverse events, their occurrence can be reduced
Monitoring of the declining trend of Polychlorobifenyls concentration in milk of contaminated dairy cows
Six pregnant heifers, coming from a herd with a history of high concentration of polychlorobifenyls (PCB) into the milk, were fed with a very low-PCB diet starting from the 6th month of pregnancy. After parturition cows were milked for at least 190 d with a maximum of 270 d. Diet was made of: corn silage (31.7% of DMI), dehydrated alfalfa (13.3% of DMI), grass hay (3.7% of DMI) and concentrate (51.3% of DMI). The average DMI was 23.12 kg/d. Milk production was recorded and samples of milk and blood were taken and analyzed for PCB (18, 28, 31, 52, 44, 101, 149, 118, 153, 138, 180 and 194 congeners) content using a GC-MS technique. The average milk yield (kg/d) of the 6 cows was 26.0, 22.5, 23.2, 24.5, 28.9, 29.3. The maximum PCB concentration of 100 ng/g of fat allowed by the Italian law was reached after 144-209 d of lactation. One animal after 204 days had a PCB concentration of 102 ng/g fat. If log10 of PCB concentration (ppb) in milk fat is regressed against days in milking (DIM) the following significant equation was obtained: log10 PCB (ng/g of milk fat)= 2.796 -0.00474 DIM; r2 0.72; P<0.01 The initial level of contamination is not the main factor affecting the time required in order for PCB to return to below the legal threshold of 100 ng/g fat, while daily milk yield significantly affects PCB excretion. Body condition and energy balance could be important factors affecting PCB excretion. In the presence of high contamination, about 6 months of lactation are required in order to obtain milk with a sufficiently low PCB content. Among the seven congeners considered by Italian legislation, PCB 101, PCB 118, PCB 138, PCB 153 constitute almost all the PCBs found in tissues and milk, with a much smaller presence of PCB 180, and the numbers of the congeners PCB 28 and PCB 52 are almost insignificant, probably because they accumulate little in the body. The congeners PCB 138 and PCB 153 are those most frequently found. For PCB 138 the liver is the principal organ of accumulation, while for PCB 153 we found equal accumulations in the liver, kidneys and tail, but a low presence in milk. The PCBs 118 and 138 are those most abundant in milks
S100A8 calcium-binding expression in radicular and dentigerous cysts and in keratocystic odontogenic tumors
Introduction: Recently the term Keratocystic Odontogenic Tumor (KCOT) has been recommended for Odontogenic Keratocysts (OKC) to address the neoplastic nature of the lesion compared to radicular and dentigerous cysts. S100 are calcium-binding proteins involved in cell differentiation and inflammation, with a potential role in neoplastic transformation. Aim: The aim of this study was to evaluate whether S100A8 protein expression is different in KCOT compared to radicular cysts (RC) and dentigerous cysts (DC). Methods: A total of 84 consecutive odontogenic cysts, 34 RC, 25 DC, and 25 KCOT, were analyzed in this study. Results: Epithelial cells in KCOT cases were not immunoreactive for S100A8 except focally in cases associated with inflammation, while RC cases showed a variable positivity of all the epithelial layers from the basal to the superficial in 19/34 cases and DC cases showed a weak positivity of the intermediate and superficial layers in 7/25 cases. Conclusion: The lack of S100A8 protein expression seems to be observed more frequently in KCOT compared to RC and DC. This difference might be related to their neoplastic nature and a potential aggressive biological behavior for odontogenic cystic lesions
An X-ray polarimeter for hard X-ray optics
Development of multi-layer optics makes feasible the use of X-ray telescope
at energy up to 60-80 keV: in this paper we discuss the extension of
photoelectric polarimeter based on Micro Pattern Gas Chamber to high energy
X-rays. We calculated the sensitivity with Neon and Argon based mixtures at
high pressure with thick absorption gap: placing the MPGC at focus of a next
generation multi-layer optics, galatic and extragalactic X-ray polarimetry can
be done up till 30 keV.Comment: 12 pages, 7 figure
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