1,191 research outputs found
High School Studentsâ Performances in Transitions between Different Representations of Linear Relationships in Mathematics and Physics
This study involved 643 high school students to assess their performance in using different representations of linear functionsâgraphs, tables, and algebraic relationshipsâin mathematics and kinematics. The results show that students encounter greater difficulties when they have to interpret representations involving algebraic relations in mathematics. Furthermore, it is shown how the ability to switch from one type of representation to another is influenced by spatial reasoning skills, orientation toward physics, and self-confidence in the field of mathematics and physics. Implications for teaching kinematics and linear functions are briefly discussed
Thermal Relics in Modified Cosmologies: Bounds on Evolution Histories of the Early Universe and Cosmological Boosts for PAMELA
Alternative cosmologies, based on extensions of General Relativity, predict
modified thermal histories in the Early Universe during the pre Big Bang
Nucleosynthesis (BBN) era, epoch which is not directly constrained by
cosmological observations. When the expansion rate is enhanced with respect to
the standard case, thermal relics typically decouple with larger relic
abundances. The correct value of the relic abundance is therefore obtained for
larger annihilation cross--sections, as compared to standard cosmology. A
direct consequence is that indirect detection rates are enhanced. Extending
previous analyses of ours, we derive updated astrophysical bounds on the dark
matter annihilation cross sections and use them to constrain alternative
cosmologies in the pre--BBN era. We also determine the characteristics of these
alternative cosmologies in order to provide the correct value of relic
abundance for a thermal relic for the (large) annihilation cross--section
required to explain the PAMELA results on the positron fraction, therefore
providing a "cosmological boost" solution to the dark matter interpretation of
the PAMELA data.Comment: 19 pages, 27 figures, matches published versio
Constraints on massive gravity theory from big bang nucleosynthesis
The massive gravity cosmology is studied in the scenario of big bang
nucleosynthesis. By making use of current bounds on the deviation from the
fractional mass, we derive the constraints on the free parameters of the
theory. The cosmological consequences of the model are also discussed in the
framework of the PAMELA experiment.Comment: 5 page
New Constraints from PAMELA anti-proton data on Annihilating and Decaying Dark Matter
Recently the PAMELA experiment has released its updated anti-proton flux and
anti-proton to proton flux ratio data up to energies of ~200GeV. With no clear
excess of cosmic ray anti-protons at high energies, one can extend constraints
on the production of anti-protons from dark matter. In this letter, we consider
both the cases of dark matter annihilating and decaying into standard model
particles that produce significant numbers of anti-protons. We provide two sets
of constraints on the annihilation cross-sections/decay lifetimes. In the one
set of constraints we ignore any source of anti-protons other than dark matter,
which give the highest allowed cross-sections/inverse lifetimes. In the other
set we include also anti-protons produced in collisions of cosmic rays with
interstellar medium nuclei, getting tighter but more realistic constraints on
the annihilation cross-sections/decay lifetimes.Comment: 7 pages, 3 figures, 3 table
Small bowel emergency surgery: literature's review
Emergency surgery of the small bowel represents a challenge for the surgeon, in the third millennium as well. There is a wide number of pathologies which involve the small bowel. The present review, by analyzing the recent and past literature, resumes the more commons. The aim of the present review is to provide the main indications to face the principal pathologies an emergency surgeon has to face with during his daily activity
Fermi Gamma-ray Haze via Dark Matter and Millisecond Pulsars
We study possible astrophysical and dark matter (DM) explanations for the
Fermi gamma-ray haze in the Milky Way halo. As representatives of various DM
models, we consider DM particles annihilating into W+W-, b-bbar, and e+e-. In
the first two cases, the prompt gamma-ray emission from DM annihilations is
significant or even dominant at E > 10 GeV, while inverse Compton scattering
(ICS) from annihilating DM products is insignificant. For the e+e- annihilation
mode, we require a boost factor of order 100 to get significant contribution to
the gamma-ray haze from ICS photons. Possible astrophysical sources of high
energy particles at high latitudes include type Ia supernovae (SNe) and
millisecond pulsars (MSPs). Based on our current understanding of Ia SNe rates,
they do not contribute significantly to gamma-ray flux in the halo of the Milky
Way. As the MSP population in the stellar halo of the Milky Way is not well
constrained, MSPs may be a viable source of gamma-rays at high latitudes
provided that there are ~ 20 000 - 60 000 of MSPs in the Milky Way stellar
halo. In this case, pulsed gamma-ray emission from MSPs can contribute to
gamma-rays around few GeV's while the ICS photons from MSP electrons and
positrons may be significant at all energies in the gamma-ray haze. The
plausibility of such a population of MSPs is discussed. Consistency with the
Wilkinson Microwave Anisotropy Probe (WMAP) microwave haze requires that either
a significant fraction of MSP spin-down energy is converted into e+e- flux or
the DM annihilates predominantly into leptons with a boost factor of order 100.Comment: 18 pages, 1 table, 5 figures; v2: references and a few discussions
added, v3: minor change
Association of non-alcoholic fatty liver disease with left ventricular changes in treatment-naive patients with uncomplicated hypertension
Background and aims: Cardiac structural and functional changes have been demonstrated in patients with non-alcoholic fatty liver disease (NAFLD). Because of the frequent association of NAFLD with hypertension, we aimed to examine the relationship of liver steatosis with left ventricular (LV) changes in patients with hypertension. Materials and methods: In a cross-sectional study, we included 360 untreated, essential hypertensive patients who were free of major cardiovascular and renal complications. Liver steatosis was assessed by three different biochemical scores (NAFLD Liver Fat Score, LFS; Fatty Liver Index, FLI; Hepatic Steatosis Index, HSI). Echocardiography was performed with standard B-mode and tissue-Doppler imaging. Results: LV hypertrophy was present in 19.4% and LV diastolic dysfunction in 49.2% of patients who had significantly higher body mass index (BMI), blood pressure (BP), and homeostatic model assessment (HOMA) index and higher frequency of the metabolic syndrome and liver steatosis that was defined by presence of 2 or more positive scores. LV mass index increased progressively across patients who had none, 1, or 2 or more liver steatosis scores, with associated progressive worsening of LV diastolic function. LV mass index was significantly and positively correlated with age, BMI, BP, HOMA-index, LFS, and HSI. Logistic regression analysis showed that age, BP, and liver steatosis scores independently predicted LV hypertrophy and diastolic dysfunction. Liver steatosis independently predicted LV dysfunction but not LV hypertrophy even after inclusion in analysis of the HOMA-index. Conclusion: NAFLD is associated with LV hypertrophy and diastolic dysfunction in untreated patients with hypertension. In hypertension, NAFLD could contribute to LV diastolic dysfunction with mechanisms unrelated to insulin resistance
Executive function abnormalities in pathological gamblers
Background: Pathological gambling (PG) is an impulse control disorder characterized by persistent and maladaptive gambling behaviors with disruptive consequences for familial, occupational and social functions. The pathophysiology of PG is still unclear, but it is hypothesized that it might include environmental factors coupled with a genetic vulnerability and dysfunctions of different neurotransmitters and selected brain areas. Our study aimed to evaluate a group of patients suffering from PG by means of some neuropsychological tests in order to explore the brain areas related to the disorder. Methods: Twenty outpatients (15 men, 5 women), with a diagnosis of PG according to DSM-IV criteria, were included in the study and evaluated with a battery of neuropsychological tests: the Wisconsin Card Sorting Test (WCST), the Wechsler Memory Scale revised (WMS-R) and the Verbal Associative Fluency Test (FAS). The results obtained in the patients were compared with normative values of matched healthy control subjects. Results: The PG patients showed alterations at the WCST only, in particular they had a great difficulty in finding alternative methods of problem-solving and showed a decrease, rather than an increase, in efficiency, as they progressed through the consecutive phases of the test. The mean scores of the other tests were within the normal range. Conclusion: Our findings showed that patients affected by PG, in spite of normal intellectual, linguistic and visual-spatial abilities, had abnormalities emerging from the WCST, in particular they could not learn from their mistakes and look for alternative solutions. Our results would seem to confirm an altered functioning of the prefrontal areas which might provoke a sort of cognitive "rigidity" that might predispose to the development of impulsive and/or compulsive behaviors, such as those typical of PG. Š 2008 Marazziti et al; licensee BioMed Central Ltd
Learning progressions: An overview and how-to guide for researchers in physics education
Learning progressions are a well established model in science education research to represent the learning process. It lies at the heart of the learning progressions the idea that students develop their knowledge of a subject from naive conceptions and, through a series of intermediate stages of increasingly sophisticated understanding, come to master a scientifically correct body of knowledge. Starting from a learning progression, it is possible to develop entire curricula and large-scale evaluation tools based on empirical data. We will present a review of the literature on learning progressions and discuss possible implications for research in physics education and teaching practice
Sustained virologic response to direct-acting antiviral agents predicts better outcomes in hepatitis C virus-infected patients: A retrospective study
Direct-acting antiviral agents (DAAs) are extremely effective in eradicating hepatitis C virus (HCV) in chronically infected patients. However, the protective role of the sustained virologic response (SVR) achieved by second- and third-generation DAAs against the onset of hepatocellular carcinoma (HCC) and mortality is less well established
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