1,282 research outputs found

    Nuclear halo of a 177 MeV proton beam in water: theory, measurement and parameterization

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    The dose distribution of a monoenergetic pencil beam in water consists of an electromagnetic "core", a "halo" from charged nuclear secondaries, and a much larger "aura" from neutral secondaries. These regions overlap, but each has distinct spatial characteristics. We have measured the core/halo using a 177MeV test beam offset in a water tank. The beam monitor was a fluence calibrated plane parallel ionization chamber (IC) and the field chamber, a dose calibrated Exradin T1, so the dose measurements are absolute (MeV/g/p). We performed depth-dose scans at ten displacements from the beam axis ranging from 0 to 10cm. The dose spans five orders of magnitude, and the transition from halo to aura is clearly visible. We have performed model-dependent (MD) and model-independent (MI) fits to the data. The MD fit separates the dose into core, elastic/inelastic nuclear, nonelastic nuclear and aura terms, and achieves a global rms measurement/fit ratio of 15%. The MI fit uses cubic splines and the same ratio is 9%. We review the literature, in particular the use of Pedroni's parametrization of the core/halo. Several papers improve on his Gaussian transverse distribution of the halo, but all retain his T(w), the radial integral of the depth-dose multiplying both the core and halo terms and motivating measurements with large "Bragg peak chambers" (BPCs). We argue that this use of T(w), which by its definition includes energy deposition by nuclear secondaries, is incorrect. T(w) should be replaced in the core term, and in at least part of the halo, by a purely electromagnetic mass stopping power. BPC measurements are unnecessary, and irrelevant to parameterizing the pencil beam.Comment: 55 pages, 4 tables, 29 figure

    Systematic review: macrophage activation syndrome in inflammatory bowel disease

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    BACKGROUND: Recently, there have been increasingly frequent reports on the occurrence of macrophage activation syndrome (MAS) in patients with inflammatory bowel disease (IBD). Clinically, MAS is characterized mainly by fever, hepatosplenomegaly, cytopenia, and elevated circulating ferritin and CD25. Mortality, even if diagnosed rapidly, is high. AIM: To identify all reports on MAS in IBD and to establish data on triggering agents, immunosuppression leading to MAS, and mortality. METHODS: A language unrestricted search on Pubmed and Scopus relating to the past 30 years was carried out by matching the following search-terms: h(a)emophagocytic lymphohistiocytosis OR h(a)emophagocytic lymphohistiocytic syndrome OR macrophage activation syndrome OR opportunistic infections OR cytomegalovirus OR Epstein-Barr virus AND Crohn's disease OR ulcerative colitis OR inflammatory bowel disease(s). RESULTS: Fifty cases were identified with an overall mortality of 30%. Virus-related MAS associated with cytomegalovirus or Epstein-Barr virus infections represents the main type of MAS, but in isolated cases bacterial infections precipitated the syndrome. In four cases (8%), a lymphoma was present at the time of MAS diagnosis or developed shortly thereafter. Thiopurine monotherapy was given before MAS onset in 56% of the patients, whereas multiple immunosuppression, including biologics, was administered to 24%. CONCLUSIONS: In IBD patients, the syndrome appears to be triggered by infections, but genetic susceptibility may contribute to its development. Since immunosuppressive therapy represents the backbone of therapeutic interventions in IBD, with the risk of new, or the reactivation of latent infections, even more frequent cases of macrophage activation syndrome may be expected

    Perceptions of College Students with Autism Spectrum Disorder on the Transition to Remote Learning During the COVID-19 Pandemic

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    COVID-19 caused a major shift in how college students, including those with disabilities, received their education during the Spring 2020 semester. The rapid shift to remote learning resulted in new challenges, but also, some benefits for students. This study presents the results of open-ended responses of a cohort of 31 students with autism spectrum disorder (ASD) who were part of a larger study and enrolled in very- to highly competitive institutions (as rated by U.S. News and World Report) during the Spring 2020 semester regarding their experiences, both positive and negative, in shifting to remote learning. The students described advantages, including personal and academic benefits with remote learning as well as disadvantages. These problematic areas included the structure and infrastructure of course delivery, environmental factors, social factors, and personal factors. Specific examples of each are presented to help richly capture the experiences of these students during an unprecedented period in history

    Cardiovascular effects in patrol officers are associated with fine particulate matter from brake wear and engine emissions

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    BACKGROUND: Exposure to fine particulate matter air pollutants (PM(2.5)) affects heart rate variability parameters, and levels of serum proteins associated with inflammation, hemostasis and thrombosis. This study investigated sources potentially responsible for cardiovascular and hematological effects in highway patrol troopers. RESULTS: Nine healthy young non-smoking male troopers working from 3 PM to midnight were studied on four consecutive days during their shift and the following night. Sources of in-vehicle PM(2.5 )were identified with variance-maximizing rotational principal factor analysis of PM(2.5)-components and associated pollutants. Two source models were calculated. Sources of in-vehicle PM(2.5 )identified were 1) crustal material, 2) wear of steel automotive components, 3) gasoline combustion, 4) speed-changing traffic with engine emissions and brake wear. In one model, sources 1 and 2 collapsed to a single source. Source factors scores were compared to cardiac and blood parameters measured ten and fifteen hours, respectively, after each shift. The "speed-change" factor was significantly associated with mean heart cycle length (MCL, +7% per standard deviation increase in the factor score), heart rate variability (+16%), supraventricular ectopic beats (+39%), % neutrophils (+7%), % lymphocytes (-10%), red blood cell volume MCV (+1%), von Willebrand Factor (+9%), blood urea nitrogen (+7%), and protein C (-11%). The "crustal" factor (but not the "collapsed" source) was associated with MCL (+3%) and serum uric acid concentrations (+5%). Controlling for potential confounders had little influence on the effect estimates. CONCLUSION: PM(2.5 )originating from speed-changing traffic modulates the autonomic control of the heart rhythm, increases the frequency of premature supraventricular beats and elicits pro-inflammatory and pro-thrombotic responses in healthy young men
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