26,309 research outputs found
Strategy for Cost-Effective Reduction of the Sum of Health Risk Estimates for Exposures to Mixtures of Toxic Substances
The authors argue that a minimization approach can provide guidance for effective use of funds to reduce the sum of estimated risks or the upper limit of the sum of risk estimates for mixtures of chemicals
Optimal realizations of floating-point implemented digital controllers with finite word length considerations.
The closed-loop stability issue of finite word length (FWL) realizations is
investigated for digital controllers implemented in floating-point arithmetic.
Unlike the existing methods which only address the effect of the mantissa bits
in floating-point implementation to the sensitivity of closed-loop stability,
the sensitivity of closed-loop stability is analysed with respect to both the
mantissa and exponent bits of floating-point implementation. A computationally
tractable FWL closed-loop stability measure is then defined, and the method of
computing the value of this measure is given. The optimal controller realization
problem is posed as searching for a floating-point realization that maximizes
the proposed FWL closed-loop stability measure, and a numerical optimization
technique is adopted to solve for the resulting optimization problem. Simulation
results show that the proposed design procedure yields computationally efficient
controller realizations with enhanced FWL closed-loop stability performance
Effect of Socio-Demographics, Health-Related Problems, and Family Structure on Chronic Absenteeism Among Children
Purpose/Background: From 5 to 7.5 million school children are chronically absent, defined as missing ā„15 days of school within a year. Students miss schools due to various reasons such as health, socioeconomic status, and environmental factors. We examined childās health and behavior, family structure, and socio-demographics to understand chronic absenteeism.
Materials & Methods: The population included children ages 6 to 17 years from the Medical Expenditure Panel Survey (MEPS) years 2008-2013. Multivariable logistic regressions were used to identify the risk factors of chronic absenteeism, adjusting for the complex sampling design.
Results: Among socio-demographic variables, age ā„14 years, race/ethnicity, lower-income family, public health insurance, US-born, and speaking English at home were associated with chronic absenteeism. Asians, Mexican Hispanics, and blacks have lower chronic absenteeism than whites. Among health-related variables, children using an inhaler for asthma, having behavioral problems, and less healthy than other children were more likely to be chronically absent. Among family variables, a smaller family size was a risk factor for chronic absenteeism.
Discussion/Conclusion: Asthma and behavioral problems were highly associated with chronic absenteeism. The identification of children at risk for chronic absenteeism will help the educational professionals identify the barriers to academic achievements and develop integrated educational interventions and policies to support disadvantaged children
Leptons from Dark Matter Annihilation in Milky Way Subhalos
Numerical simulations of dark matter collapse and structure formation show
that in addition to a large halo surrounding the baryonic component of our
galaxy, there also exists a significant number of subhalos that extend hundreds
of kiloparsecs beyond the edge of the observable Milky Way. We find that for
dark matter (DM) annihilation models, galactic subhalos can significantly
modify the spectrum of electrons and positrons as measured at our galactic
position. Using data from the recent Via Lactea II simulation we include the
subhalo contribution of electrons and positrons as boundary source terms for
simulations of high energy cosmic ray propagation with a modified version of
the publicly available GALPROP code. Focusing on the DM DM -> 4e annihilation
channel, we show that including subhalos leads to a better fit to both the
Fermi and PAMELA data. The best fit gives a dark matter particle mass of 1.2
TeV, for boost factors of 90 in the main halo and 1950-3800 in the subhalos
(depending on assumptions about the background), in contrast to the 0.85 TeV
mass that gives the best fit in the main halo-only scenario. These fits suggest
that at least a third of the observed electron cosmic rays from DM annihilation
could come from subhalos, opening up the possibility of a relaxation of recent
stringent constraints from inverse Compton gamma rays originating from the
high-energy leptons.Comment: 8 pages, 13 figures; added referenc
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