1,721,237 research outputs found
MYSCE, a new Monte Carlo code for star cluster simulations. Axion-like particles and very-high energy astrophysics
Get PDFThis thesis focuses on two different topics: (i) star clusters, as favourite environments for the formation of black holes of very high mass, and (ii) the implications of axionlike particles for very-high energy astrophysics by considering -ray observations from blazars.
In the first part of this thesis we develop a new Monte Carlo code MYSCE (Montecarlo Young Star Cluster Evolution) which improves and solves some problems of the original scheme presented by Hénon. We use our code to simulate star clusters and to inquire if an episode of gas infall during the cluster lifetime can lead to the formation of an intermediate mass black hole and/or a super massive black hole seed.
In the second part of this thesis we explore axion-like particles in an astrophysical context. We describe their origin and properties within extensions of the Standard Model of elementary particle physics. We show how axion-like particles can in principle solve the cosmic opacity problem for distant blazars and naturally explain the emission of very-high energy photons from at spectrum radio quasar
Observability of the Very-High-Energy Emission from GRB 221009A
Get PDFThe LHAASO Collaboration detected the gamma ray burst GRB 221009A at energies above 500 GeV with a tail extending up to 18 TeV, whose spectral analysis has presently been performed up to 7 TeV for the lower energy instrument LHAASO-WCDA only, with no indication of a cutoff. Soon thereafter, Carpet-2 at Baksan Neutrino Observatory reported the observation of an air shower consistent with being caused by a photon of energy 251 TeV from the same GRB. Given the source redshift z =0.151 , the expected attenuation due to the extragalactic background light is very severe so that these detections have proven very hard to explain. In this Letter, we show that the existence of axionlike particles with mass ma≃(10-11- 10-7) eV and two-photon coupling ga γ γ≃(3 -5 )×10-12 GeV-1 strongly reduce the optical depth of TeV photons, thus explaining the observations. Our ALPs meet all available constraints, are consistent with two previous hints at their existence, and are good candidates for cold dark matter. Moreover, we show that Lorentz invariance violation can explain the Carpet-2 result but not the LHAASO observations
Evidence for an axion-like particle from PKS 1222+216?
No full textThe surprising discovery by Major Atmospheric Gamma Imaging Cherenkov Telescope (MAGIC) of an intense, rapidly varying emission in the energy range 70-400 GeV from the flat spectrum radio quasar PKS 1222+216 represents a challenge for all interpretative scenarios. Indeed, in order to avoid absorption of γ rays in the dense ultraviolet radiation field of the broad line region, one is forced to invoke some unconventional astrophysical picture, like for instance the existence of a very compact (r∼1014cm) emitting blob at a large distance (R∼1018cm) from the jet base. We offer the investigation of a scenario based on the standard blazar model for PKS 1222+216 where γ rays are produced close to the central engine, but we add the new assumption that inside the source photons can oscillate into axion-like particles (ALPs), which are a generic prediction of several extensions of the Standard Model of elementary particle interactions. As a result, a considerable fraction of very-high-energy photons can escape absorption from the broad line region through the mechanism of photon-ALP oscillations much in the same way as they largely avoid absorption from extragalactic background light when propagating over cosmic distances in the presence of large-scale magnetic fields in the nG range. In addition we show that the above Major Atmospheric Gamma Imaging Cherenkov Telescope (MAGIC) observations and the simultaneous Fermi/Large Area Telescope (LAT) observations in the energy range 0.3-3 GeV can both be explained by a standard spectral energy distribution for experimentally allowed values of the model parameters. In particular, we need a very light ALP just like in the case of photon-ALP oscillations in cosmic space. Moreover, we find it quite tantalizing that the most favorable value of the photon-ALP coupling happens to be the same in both situations. Although our ALPs cannot contribute to the cold dark matter, they are a viable candidate for the quintessential dark energy. An astrophysical test of our scenario is proposed and an independent laboratory check for the existence of an ALP with the properties required by our picture will be performed with the planned upgrade of the photon regeneration experiment ALPS at Deutsches Elektronen-Synchrotron (DESY) and with the next generation of solar axion detectors like International Axion Observatory (IAXO). © 2012 American Physical Society
2D longitudinal LV speckle tracking strain pattern in breast cancer survivors: sports activity vs exercise as prescription model
No full textPrevention strategies are important to optimize and to manage heart care in breast cancer survivors. Regular physical activity at moderate intensity is normally
proposed to maintain myocardial performance; however, no data is available about the different impact of different levels of physical exercise. 2D speckle tracking echocardiography (2DSTE) is an accepted method for early detection of myocardial dysfunction. The study aims to monitor the cardiac performances in breast cancer survivors
by 2DSTE analysis to manage sports activity vs physical activity. Two groups of previous breast cancer survivors (33 BCS) trained at moderate intensity and 55 athletes practicing dragon boat (DBA) sport were enrolled. They were matched with two healthy subjects groups: 23 competitive female athletes practicing different sports and 20 healthy women trained with exercise as prescription model. All women were studied by a complete echo examination including LV global longitudinal strain (GLS) assessment (XStrain-Esaote). EF and GS are only significantly higher in healthy subjects (-25.4 ± 2.1). Nevertheless, GLS values are within the normal range for all groups. Particularly, GS does not show any significant differences among subjects (-19.93 ± 4) practicing exercise as prescription when compared to the DBA competitive trained group. 2DSTE method is an appropriate
method to supervise the intensity of exercise in breast cancer patients. Particularly, GLS can optimize and improve cancer therapy supporting and creating efficiencies within the health system confirming the role of the exercise prescription therapy in maintaining normal heart function
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Morphological Characteristics of Elite International Soccer Referees: Somatotype and Bioelectrical Impedance Vector Analysis
Get PDFThis study aimed to assess the physical characteristics of elite international soccer referees, compare them with other referee populations in the literature, and establish reference tolerance ellipses for the bioelectrical impedance vector analysis (BIVA) point graph. Forty-one elite international soccer referees (age 38.8 ± 3.6 years) participated in the study. The participants underwent body composition assessments, including dual-energy X-ray absorptiometry, BIVA, and somatotype. The Somatotype Attitudinal Distance (SAD), the two-sample Hotelling’s T2 test and the Mahalanobis test were used to determine somatotype and bioelectrical vector differences with the literature. The average somatotype of the referees was a balanced mesomorph (2.8, 6.5, 2.8). Elite international referees significantly differed from other samples in the literature (SAD = 2.1, 2.6, 2.9 with respect to Zimbabwean, Brazilian, and South African referees, respectively). The bioelectrical vector was significantly different from the general population (T2 ≤ 76.6; F = 38.8; D = 1.44; p 2 ≤ 25.3; F = 12.6; D = 0.8; p < 0.001). Somatotype values and tolerance ellipses from this study may be useful as a reference for developing training programs and improving the selection process of referees in soccer
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Female athletes and menstrual disorders: A pilot study
No full textBackground: There is a greater incidence of menstrual disorders in female athletes than in their sedentary counterparts. The menstrual disorder is reported in female athletes suffering from athletic triad syndrome, while few data in those free of this syndrome are available. The study aims to ascertain the presence of menstrual disorders and the eventual relationship with myocardial performance in female athletes practicing different sports. Methods: A sample of 64 subjects aged 18.5±2 was selected and divided into 3 groups (37 subjects practicing rhythmic gymnastics, 11 swimmers, and 16 volleyball players). All underwent echocardiography, biompendance analysis, and answered a questionnaire. Results: All anthropometrics parameters were normal. Few athletes reported menstrual disorders. No association between the presence of menstrual disorders and BMI. All echo results were within the normal range. Cardiac Mass Index (CMI) was normal for all athletes despite in swimmers significantly higher values (90.64±14.9 g/m2) compared to the volleyball players (78.25±14.0 g/m2; p<.04) and rhythmic gymnasts (77.89±13.4 g/m2; p<.009) were found. Conclusions: Despite menstrual disorders are represented among female athletes, the eventual relationship with the sport practiced is not so evident. Questionnaire should be used to identify menstrual disorders in non-elite athletically active females
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