21,039 research outputs found
Determining Reactor Flux from Xenon-136 and Cesium-135 in Spent Fuel
The ability to infer the reactor flux from spent fuel or seized fissile
material would enhance the tools of nuclear forensics and nuclear
nonproliferation significantly. We show that reactor flux can be inferred from
the ratios of xenon-136 to xenon-134 and cesium-135 to cesium-137. If the
average flux of a reactor is known, the flux inferred from measurements of
spent fuel could help determine whether that spent fuel was loaded as a blanket
or close to the mid-plane of the reactor. The cesium ratio also provides
information on reactor shutdowns during the irradiation of fuel, which could
prove valuable for identifying the reactor in question through comparisons with
satellite reactor heat monitoring data. We derive analytic expressions for
these correlations and compare them to experimental data and to detailed
reactor burn simulations. The enrichment of the original uranium fuel affects
the correlations by up to 3 percent, but only at high flux.Comment: 10 pages, 9 figure
Cultures maraichères en zone soudano-sahélienne : recueil de fiches techniques
Ce recueil résume le bilan vulgarisable des recherches sur les cultures maraîchères à la station de Farako-Ba, au Burkina Faso. Simple et précis, il propose, après quelques données générales sur la culture des plantes en maraîchage, 22 fiches techniques. Destiné en priorité aux producteurs de la zone soudano-sahélienne, il associe les réponses à leurs questions et les résultats du programme maraîcher au Burkina Fas
Spectral radius of finite and infinite planar graphs and of graphs of bounded genus
It is well known that the spectral radius of a tree whose maximum degree is
cannot exceed . In this paper we derive similar bounds for
arbitrary planar graphs and for graphs of bounded genus. It is proved that a
the spectral radius of a planar graph of maximum vertex degree
satisfies . This result is
best possible up to the additive constant--we construct an (infinite) planar
graph of maximum degree , whose spectral radius is . This
generalizes and improves several previous results and solves an open problem
proposed by Tom Hayes. Similar bounds are derived for graphs of bounded genus.
For every , these bounds can be improved by excluding as a
subgraph. In particular, the upper bound is strengthened for 5-connected
graphs. All our results hold for finite as well as for infinite graphs.
At the end we enhance the graph decomposition method introduced in the first
part of the paper and apply it to tessellations of the hyperbolic plane. We
derive bounds on the spectral radius that are close to the true value, and even
in the simplest case of regular tessellations of type we derive an
essential improvement over known results, obtaining exact estimates in the
first order term and non-trivial estimates for the second order asymptotics
Stable incidence rates of tuberculosis (TB) among human immunodeficiency virus (HIV)-negative South African gold miners during a decade of epidemic HIV-associated TB.
During the last decade, annual tuberculosis (TB) case-notification rates increased 4-fold, to >4000 cases/100000 person-years, in the study workforce, among whom prevalence of human immunodeficiency virus (HIV) was 30% in 2000. Three separate cohort studies, totalling 6454 HIV-negative participants, were combined and analyzed for time trends. Observed incidence of TB varied between 962 (1991-1994) and 1589 (1999-2000) cases/100000 person-years (P=.17, test for trend). There was, however, a progressive increase in age, and, for each period, older age was associated with increased incidence rates of TB (P<.001). Having adjusted for age differences, there was no significant association between incidence of TB and calendar period (P=.81, test for trend). Relative to 1991-1994, multivariate-adjusted incidence-rate ratios were 0.94, for 1995-1997, 0.96, for 1998-1999, and 1.05, for 1999-2000. Preventing a secondary epidemic of TB among HIV-negative individuals may be achievable with conventional means, even in settings with a high burden of HIV-associated TB
Recommended from our members
Bump start needed: linking guidelines, policy and practice in promoting physical activity during and beyond pregnancy
First paragraph: There is compelling evidence that regular physical activity (PA) during pregnancy benefits both mother and baby.1 2 Notably, physical and psychological benefits are evident in the literature, such as marked reductions in the development of gestational diabetes and hypertensive disorders, alongside improvements in depressive symptoms and cardiorespiratory fitness.1 2 The evidence base has been reflected by recent policy initiatives, for example, in 2017 (relaunched in 2019), the UK‘s chief medical officers (CMOs) published PA guidelines for pregnant women, which made substantial strides in unifying and translating the evidence into recommendations.1 The CMO guidelines are aimed at supporting health professionals to provide consistent, evidence-based PA messages to women throughout pregnancy.1 Recently, the Chartered Institute for the Management of Sport and Physical Activity have updated their professional standards for working with antenatal and postnatal clients to align with these CMO guidelines.3 However, not all women have access to professionals with this level of expertise and training, potentially limiting the impact of the CMO guidelines
Local and Central Differential Privacy for Robustness and Privacy in Federated Learning
Federated Learning (FL) allows multiple participants to train machine
learning models collaboratively by keeping their datasets local while only
exchanging model updates. Alas, this is not necessarily free from privacy and
robustness vulnerabilities, e.g., via membership, property, and backdoor
attacks. This paper investigates whether and to what extent one can use
differential Privacy (DP) to protect both privacy and robustness in FL. To this
end, we present a first-of-its-kind evaluation of Local and Central
Differential Privacy (LDP/CDP) techniques in FL, assessing their feasibility
and effectiveness. Our experiments show that both DP variants do d fend against
backdoor attacks, albeit with varying levels of protection-utility trade-offs,
but anyway more effectively than other robustness defenses. DP also mitigates
white-box membership inference attacks in FL, and our work is the first to show
it empirically. Neither LDP nor CDP, however, defend against property
inference. Overall, our work provides a comprehensive, re-usable measurement
methodology to quantify the trade-offs between robustness/privacy and utility
in differentially private FL
Extension Programming for Food Entrepreneurs: An Indiana Needs Assessment
The objective of the research reported here was to identify the needs of food entrepreneurs in the state of Indiana. To attain this objective, Purdue Extension educators from 86 counties in Indiana were surveyed. Topics of interest from the survey results included marketing, new business start-up, food regulations, and food safety. This assessment tool has directed Purdue Extension in developing a Food Entrepreneur Engagement Program. The survey results were used to develop a statewide workshop for food entrepreneurs. Resources provided by this program ultimately helped several food entrepreneurs create value-added food businesses in Indiana
Occurrence of preterm calving in Great Britain and associations with milk production and reproductive performance in dairy cattle
This study describes the occurrence of preterm calving in Great Britain and evaluates its associations with subsequent milk production and reproductive performances and survival on farm of dairy cows. A total of 53 British dairy farms and 5759 animals with detailed breeding and milk recording data available were used to form two study groups: preterm calving (calving occurring between days 266 and 277 of gestation) and full-term calving (calving occurring at 278 days of gestation and over). Mixed effects models were implemented to compare milk production, clinical cases of mastitis and number of services per conception between groups. Kaplan-Meier curves and Cox regression analyses compared time from calving to conception, calving interval and survival on farm between groups. Preterm calving cows showed significantly lower milk yield (P<0.01) and butter fat per cent (P=0.02), increased milk protein per cent (P=0.01), longer survival on farm (P<0.01), and a tendency for shorter calving to conception intervals and fewer services per conception, although other factors were involved in the reproduction outcomes. Experiencing a preterm calving is associated with lower milk production and longer survival times on farm. Potential risk factors for preterm calving, such as infectious diseases, diet and husbandry practices, should be further investigated
Edge effects in electrostatic calibrations for the measurement of the Casimir force
We have performed numerical simulations to evaluate the effect on the
capacitance of finite size boundaries realistically present in the parallel
plane, sphere-plane, and cylinder-plane geometries. The potential impact of
edge effects in assessing the accuracy of the parameters obtained in the
electrostatic calibrations of Casimir force experiments is then discussed
- …