876 research outputs found
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Criticality safety of low-density storage arrays
This note proposes a straightforward and simple method for the criticality safety analysis of fissionable materials configured into large arrays of standard containers. While criticality-safe storage limits have been well-established for standard containers--even under flooded conditions, it is also necessary to rule out the potential for criticality arising from neutronic interactions among multiple containers that might build up over long distances in a large array. Traditionally, the array problem has been approached by individual Monte Carlo analyses of explicit arrangements of single units and their surroundings. Here, the authors show how multiple Monte Carlo analyses can be usefully combined for wide-ranging general application. The technique takes advantage of low average density of fissionable material in typical storage arrays to separate neutron interactions that take place in the neutron`s ``birth unit`` from subsequent interactions in a highly dilute array. Effects of array size, in particular, are conservatively calculated by straightforward analyses which simply smear array contents uniformly across the extent of the array. For given unit loadings in standard containers, practical expressions for neutron multiplication depend only on overall array shape, size and reflective boundary
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Analyses with the FSTATE code: fuel performance in destructive in-pile experiments
Thermal-mechanical analysis of a fuel pin is an essential part of the evaluation of fuel behavior during hypothetical accident transients. The FSTATE code has been developed to provide this required computational ability in situations lacking azimuthal symmetry about the fuel-pin axis by performing 2-dimensional thermal, mechanical, and fission gas release and redistribution computations for a wide range of possible transient conditions. In this paper recent code developments are described and application is made to in-pile experiments undertaken to study fast-reactor fuel under accident conditions. Three accident simulations, including a fast and slow ramp-rate overpower as well as a loss-of-cooling accident sequence, are used as representative examples, and the interpretation of STATE computations relative to experimental observations is made
Corrections to the generalized vector dominance due to diffractive rho_3 production
The idea of the vector dominance is still in use in various analyses of
experimental data of photon-hadron reactions. It makes sense, therefore, to
recast results of microscopic calculations of such reactions in this language.
Here we present the diffractive DIS production as a specific
correction to the generalized vector dominance. We perform a coupled channel
analysis of spin-orbital excitations in diffractive photoproduction and
reiterate the point that rho_3 in diffractive DIS will be sensitive to a novel
aspect of diffraction.Comment: 12 pages, 2 figure
Nuclear effects in at small in deep inelastic scattering on Li and He
We suggest to use polarized nuclear targets of Li and He to study
nuclear effects in the spin dependent structure functions .
These effects are expected to be enhanced by a factor of two as compared to the
unpolarized targets.
We predict a significant dependence at of due to nuclear shadowing and nuclear
enhancement. The effect of nuclear shadowing at is of an
order of 16% for and 10% for
. By imposing the requirement that
the Bjorken sum rule is satisfied we model the effect of enhancement.
We find the effect of enhancement at to be of an
order of for and
for , if enhancement
occupies the region (). We predict
a 2% effect in the difference of the scattering cross sections of deep
inelastic scattering of an unpolarized projectile off Li with =3/2
and =1/2. We also show explicitly that the many-nucleon description of
deep inelastic scattering off Li becomes invalid in the enhancement region
.Comment: 29 pages, 5 figures, RevTe
Possible influence of the two string events on the hadron formation in a nuclear environment
One of the basic assumptions of the string model is that as a result of a DIS
in nucleus a single string arises, which then breaks into hadrons. However the
pomeron exchange considered in this work, leads to the production of two
strings in the one event. The hadrons produced in these events have smaller
formation lengths, than those with the same energy produced in the single
string events. As a consequence, they undergo more substantial absorption in
the nuclear matter
Imaging the displacement field within epitaxial nanostructures by coherent diffraction: a feasibility study
International audienceWe investigate the feasibility of applying coherent diffraction imaging to highly strained epitaxial nanocrystals using finite-element simulations of SiGe islands as input in standard phase retrieval algorithms. We discuss the specific problems arising from both epitaxial and highly strained systems and we propose different methods to overcome these difficulties. Finally, we describe a coherent microdiffraction experimental setup using extremely focused x-ray beams to perform experiments on individual nanostructures
Polypharmacy and specific comorbidities in university primary care settings.
Polypharmacy is associated with adverse events and multimorbidity, but data are limited on its association with specific comorbidities in primary care settings. We measured the prevalence of polypharmacy and inappropriate prescribing, and assessed the association of polypharmacy with specific comorbidities.
We did a cross-sectional analysis of 1002 patients aged 50-80years followed in Swiss university primary care settings. We defined polypharmacy as ≥5 long-term prescribed drugs and multimorbidity as ≥2 comorbidities. We used logistic mixed-effects regression to assess the association of polypharmacy with the number of comorbidities, multimorbidity, specific sets of comorbidities, potentially inappropriate prescribing (PIP) and potential prescribing omission (PPO). We used multilevel mixed-effects Poisson regression to assess the association of the number of drugs with the same parameters.
Patients (mean age 63.5years, 67.5% ≥2 comorbidities, 37.0% ≥5 drugs) had a mean of 3.9 (range 0-17) drugs. Age, BMI, multimorbidity, hypertension, diabetes mellitus, chronic kidney disease, and cardiovascular diseases were independently associated with polypharmacy. The association was particularly strong for hypertension (OR 8.49, 95%CI 5.25-13.73), multimorbidity (OR 6.14, 95%CI 4.16-9.08), and oldest age (75-80years: OR 4.73, 95%CI 2.46-9.10 vs.50-54years). The prevalence of PPO was 32.2% and PIP was more frequent among participants with polypharmacy (9.3% vs. 3.2%, p<0.006).
Polypharmacy is common in university primary care settings, is strongly associated with hypertension, diabetes mellitus, chronic kidney disease and cardiovascular diseases, and increases potentially inappropriate prescribing. Multimorbid patients should be included in further trials for developing adapted guidelines and avoiding inappropriate prescribing
Subclinical thyroid dysfunction and the risk for fractures: a systematic review and meta-analysis.
BACKGROUND: Data on the association between subclinical thyroid dysfunction and fractures conflict.
PURPOSE: To assess the risk for hip and nonspine fractures associated with subclinical thyroid dysfunction among prospective cohorts.
DATA SOURCES: Search of MEDLINE and EMBASE (1946 to 16 March 2014) and reference lists of retrieved articles without language restriction.
STUDY SELECTION: Two physicians screened and identified prospective cohorts that measured thyroid function and followed participants to assess fracture outcomes.
DATA EXTRACTION: One reviewer extracted data using a standardized protocol, and another verified data. Both reviewers independently assessed methodological quality of the studies.
DATA SYNTHESIS: The 7 population-based cohorts of heterogeneous quality included 50,245 participants with 1966 hip and 3281 nonspine fractures. In random-effects models that included the 5 higher-quality studies, the pooled adjusted hazard ratios (HRs) of participants with subclinical hyperthyroidism versus euthyrodism were 1.38 (95% CI, 0.92 to 2.07) for hip fractures and 1.20 (CI, 0.83 to 1.72) for nonspine fractures without statistical heterogeneity (P = 0.82 and 0.52, respectively; I2= 0%). Pooled estimates for the 7 cohorts were 1.26 (CI, 0.96 to 1.65) for hip fractures and 1.16 (CI, 0.95 to 1.42) for nonspine fractures. When thyroxine recipients were excluded, the HRs for participants with subclinical hyperthyroidism were 2.16 (CI, 0.87 to 5.37) for hip fractures and 1.43 (CI, 0.73 to 2.78) for nonspine fractures. For participants with subclinical hypothyroidism, HRs from higher-quality studies were 1.12 (CI, 0.83 to 1.51) for hip fractures and 1.04 (CI, 0.76 to 1.42) for nonspine fractures (P for heterogeneity = 0.69 and 0.88, respectively; I2 = 0%).
LIMITATIONS: Selective reporting cannot be excluded. Adjustment for potential common confounders varied and was not adequately done across all studies.
CONCLUSION: Subclinical hyperthyroidism might be associated with an increased risk for hip and nonspine fractures, but additional large, high-quality studies are needed.
PRIMARY FUNDING SOURCE: Swiss National Science Foundation
Hadron formation in high energy photonuclear reactions
We present a new method to account for coherence length effects in a
semi-classical transport model. This allows us to describe photo- and
electroproduction at large nuclei (A>12) and high energies using a realistic
coupled channel description of the final state interactions that goes beyond
simple Glauber theory. We show that the purely absorptive treatment of the
final state interactions can lead to wrong estimates of color transparency and
formation time effects in particle production. As an example, we discuss
exclusive rho^0 photoproduction on Pb at a photon energy of 7 GeV as well as
K^+ production in the photon energy range 1-7 GeV.Comment: 14 pages, 6 figures, version published in Phys. Rev.
Thyroid Dysfunction and Anemia: A Prospective Cohort Study and a Systematic Review.
Even though the association between thyroid dysfunction and anemia is commonly described, it is not known whether it is clinically relevant. This study set out to quantify the association of thyroid dysfunction on hemoglobin (Hb) concentration and risk of anemia. A systematic review (MEDLINE and EMBASE, from inception until May 15, 2017) was conducted to interpret the findings in context.
Participants from the EPIC-Norfolk cohort with available baseline thyrotropin (TSH), free thyroxine (fT4), and Hb were included. Euthyroidism was defined as TSH 0.45-4.49 mIU/L (reference category), hypothyroidism as TSH ≥4.50 mIU/L (subclinical [SHypo] with normal fT4 or overt [OHypo] with low fT4), and hyperthyroidism as TSH ≤0.44 mIU/L (subclinical [SHyper] with normal fT4 or overt [OHyper] with elevated fT4). Anemia was defined as Hb <12 g/dL in women and Hb <13 g/dL in men. In the cross-sectional analyses, multiple linear regression was used to compare Hb across TSH categories. In the prospective analysis, participants with OHypo/OHyper at baseline were excluded, as it was assumed that they were treated for overt thyroid disease. A covariance model was used to determine change in Hb concentration from baseline to last follow-up, and multivariable Cox regression was used to analyze anemia risk.
In the cross-sectional population (n = 12,337), the adjusted Hb was 0.22 g/dL lower [confidence interval (CI) 0.07-0.38] in OHypo compared to euthyroids, and 0.08 g/dL lower [CI -0.23 to 0.38] in OHyper. In the prospective analysis, 460/7031 participants developed anemia over a median follow-up of 4.7 years. The adjusted mean Hb change over time was -0.04 g/dL in SHypo [CI -0.14 to 0.06] and 0.05 g/dL in SHyper [CI -0.10 to 0.20]. The adjusted hazard ratio for anemia was 0.99 [CI 0.67-1.48] in SHypo, and 0.52 [CI 0.23-1.16] in SHyper. The systematic review returned no other prospective studies on this association, but cross-sectional and case-control studies showed comparable results.
In this first prospective population-based cohort, subclinical thyroid dysfunction was not associated with a change in Hb concentration during follow-up and was not an independent risk factor for developing anemia; variations in Hb concentration in patients with overt thyroid dysfunction were not clinically relevant
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