4,365 research outputs found
Possible Contribution to Electron and Positron Fluxes from Pulsars and their Nebulae
The AMS-02 experiment confirms the excess of positrons in cosmic rays (CRs)
for energy above 10 GeV with respect to the secondary production of positrons
in the interstellar medium. This is interpreted as evidence of the existence of
a primary source of these particles. Possible candidates are dark matter or
astrophysical sources. In this work we discuss the possible contribution due to
pulsars and their nebulae. Our key assumption is that the primary spectrum of
electrons and positrons at the source is the same of the well known photon
spectrum observed from gamma-rays telescopes. Using a diffusion model in the
Galaxy we propagate the source spectra up to the Solar System. We compare our
results with the recent experiments and with the LIS modelComment: To appear in the Proceedings of the 14th ICATPP Conference, Villa
Olmo 23-27 September 201
Pulsar Wind Nebulae as a source of the observed electron and positron excess at high energy: the case of Vela-X
We investigate, in terms of production from pulsars and their nebulae, the
cosmic ray positron and electron fluxes above GeV, observed by the
AMS-02 experiment up to 1 TeV. We concentrate on the Vela-X case. Starting from
the gamma-ray photon spectrum of the source, generated via synchrotron and
inverse Compton processes, we estimated the electron and positron injection
spectra. Several features are fixed from observations of Vela-X and unknown
parameters are borrowed from the Crab nebula. The particle spectra produced in
the pulsar wind nebula are then propagated up to the Solar System, using a
diffusion model. Differently from previous works, the omnidirectional intensity
excess for electrons and positrons is obtained as a difference between the
AMS-02 data and the corresponding local interstellar spectrum. An equal amount
of electron and positron excess is observed and we interpreted this excess
(above 100 GeV in the AMS-02 data) as a supply coming from Vela-X. The
particle contribution is consistent with models predicting the gamma-ray
emission at the source. The input of a few more young pulsars is also allowed,
while below 100 GeV more aged pulsars could be the main contributors.Comment: Accepted for publication in Journal of High Energy Astrophysics
(2015
Innovative experiences in teaching conservation. Involving communities’ interests on preservationtopics by fast investigations and social media dissemination
Since 2019, the authors carried out a didactical experience trough the Preservation Studio workshop in the historical center of Vimercate, a town in the north east area of Milan, implementing a convention agreement between the Municipality and the Atheneum. The convention was arranged in order to set the relationship between the three academic courses of the Politecnico di Milano and the administration of Vimercate, supporting the teaching staff by providing ac- cessibility to various services and some public properties located in the city-cen- ter.
Thanks to this kind of agreement, the courses could be supported in their activities by document centers, public associations and the members of the local community, while the teaching staff offered a constant sharing of the main activ- ities by social media and periodical disseminations through public lectures. After maturing several years of didactical workshops on the main buildings of the his- torical center of Vimercate, this paper shows the results collected with the stu- dios: the
active class strategies, the on-site survey campaigns, the evolution of the results observed by year after year inspections, ND testing activities and local community involvement. The impact coming from the researches developed by the preservation classes and specific in depth studies realized by graduation thesis showed an increasing participation of the community to the topics connected to the city center: from conservation policies to future uses, historical buildings reached the attention of the people through the development of a new sensibility and perception of new values associated to the local architectural heritage
The cool core state of Planck SZ-selected clusters versus X-ray selected samples: evidence for cool core bias
We characterized the population of galaxy clusters detected with the SZ
effect with Planck, by measuring the cool core state of the objects in a
well-defined subsample of the Planck catalogue. We used as indicator the
concentration parameter Santos et al. (2008). The fraction of cool core
clusters is and does not show significant indications of
evolution in the redshift range covered by our sample. We compare the
distribution of the concentration parameter in the Planck sample with the one
of the X-ray selected sample MACS (Mann & Ebeling, 2011): the distributions are
significantly different and the cool core fraction in MACS is much higher (). Since X-ray selected samples are known to be biased towards cool
cores due to the presence of their prominent surface brightness peak, we
simulated the impact of the "cool core bias" following Eckert et al. (2011). We
found that it plays a large role in the difference between the fractions of
cool cores in the two samples. We examined other selection effects that could
in principle bias SZ-surveys against cool cores but we found that their impact
is not sufficient to explain the difference between Planck and MACS. The
population of X-ray under-luminous objects, which are found in SZ-surveys but
missing in X-ray samples (Planck Collaboration 2016), could possibly contribute
to the difference, as we found most of them to be non cool cores, but this
hypothesis deserves further investigation.Comment: Accepted for publication in MNRA
Eating Habits of Professional Firefighters: Comparison With National Guidelines and Impact Healthy Eating Promotion Program.
Firefighters' eating habits may be an additional risk factor for metabolic diseases. We assessed eating habits of firefighters, compared them with national guidelines, and evaluated the impact of a prevention program.
Twenty-eight professional firefighters from a Swiss airport benefited from a healthy-eating program. Food intake, eating behavior, and anthropometric data were collected at baseline and 1-year follow-up using an electronic food record, questionnaires, and bio-impedance.
Participants had unbalanced diets with low-quality food choices associated with low intakes of fibers and micronutrients compared with national guidelines. Intervention did not impact eating habits or anthropometrics data at the group level, but changes were measured in sub-groups. Main reported barriers for healthy eating were lack of motivation, prioritization, or time.
Intensive and culturally tailored prevention interventions targeting nutritional behaviors are needed at the individual, group, and organizational levels
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