141 research outputs found
Debris disk size distributions: steady state collisional evolution with P-R drag and other loss processes
We present a new scheme for determining the shape of the size distribution,
and its evolution, for collisional cascades of planetesimals undergoing
destructive collisions and loss processes like Poynting-Robertson drag. The
scheme treats the steady state portion of the cascade by equating mass loss and
gain in each size bin; the smallest particles are expected to reach steady
state on their collision timescale, while larger particles retain their
primordial distribution. For collision-dominated disks, steady state means that
mass loss rates in logarithmic size bins are independent of size. This
prescription reproduces the expected two phase size distribution, with ripples
above the blow-out size, and above the transition to gravity-dominated
planetesimal strength. The scheme also reproduces the expected evolution of
disk mass, and of dust mass, but is computationally much faster than evolving
distributions forward in time. For low-mass disks, P-R drag causes a turnover
at small sizes to a size distribution that is set by the redistribution
function (the mass distribution of fragments produced in collisions). Thus
information about the redistribution function may be recovered by measuring the
size distribution of particles undergoing loss by P-R drag, such as that traced
by particles accreted onto Earth. Although cross-sectional area drops with
1/age^2 in the PR-dominated regime, dust mass falls as 1/age^2.8, underlining
the importance of understanding which particle sizes contribute to an
observation when considering how disk detectability evolves. Other loss
processes are readily incorporated; we also discuss generalised power law loss
rates, dynamical depletion, realistic radiation forces and stellar wind drag.Comment: Accepted for publication by Celestial Mechanics and Dynamical
Astronomy (special issue on EXOPLANETS
The prevalence of mild cognitive impairment in diverse geographical and ethnocultural regions: The COSMIC Collaboration
Background Changes in criteria and differences in populations studied and methodology have produced a wide range of prevalence estimates for mild cognitive impairment (MCI). Methods Uniform criteria were applied to harmonized data from 11 studies from USA, Europe, Asia and Australia, and MCI prevalence estimates determined using three separate definitions of cognitive impairment. Results The published range of MCI prevalence estimates was 5.0%-36.7%. This was reduced with all cognitive impairment definitions: performance in the bottom 6.681% (3.2%-10.8%); Clinical Dementia Rating of 0.5 (1.8%-14.9%); Mini-Mental State Examination score of 24-27 (2.1%-20.7%). Prevalences using the first definition were 5.9% overall, and increased with age (P < .001) but were unaffected by sex or the main races/ethnicities investigated (Whites and Chinese). Not completing high school increased the likelihood of MCI (P = .01). Conclusion Applying uniform criteria to harmonized data greatly reduced the variation in MCI prevalence internationally
Psychosocial Treatment of Children in Foster Care: A Review
A substantial number of children in foster care exhibit psychiatric difficulties. Recent epidemiologi-cal and historical trends in foster care, clinical findings about the adjustment of children in foster care, and adult outcomes are reviewed, followed by a description of current approaches to treatment and extant empirical support. Available interventions for these children can be categorized as either symptom-focused or systemic, with empirical support for specific methods ranging from scant to substantial. Even with treatment, behavioral and emotional problems often persist into adulthood, resulting in poor functional outcomes. We suggest that self-regulation may be an important mediat-ing factor in the appearance of emotional and behavioral disturbance in these children
Customer emotions in service failure and recovery encounters
Emotions play a significant role in the workplace, and considerable attention has been given to the study of employee emotions. Customers also play a central function in organizations, but much less is known about customer emotions. This chapter reviews the growing literature on customer emotions in employeeâcustomer interfaces with a focus on service failure and recovery encounters, where emotions are heightened. It highlights emerging themes and key findings, addresses the measurement, modeling, and management of customer emotions, and identifies future research streams. Attention is given to emotional contagion, relationships between affective and cognitive processes, customer anger, customer rage, and individual differences
Impact of different eddy covariance sensors, site set-up, and maintenance on the annual balance of CO2 and CH4 in the harsh Arctic environment
Improving year-round data coverage for CO2 and CH4 fluxes in the Arctic is critical for refining the global C budget but continuous measurements are very sparse due to the remote location limiting instrument maintenance, to low power availability, and to extreme weather conditions. The need for tailoring instrumentation, site set up, and maintenance at different sites can add uncertainty to estimates of annual C budgets from different ecosystems. In this study, we investigated the influence of different sensor combinations on fluxes of sensible heat, CO2, latent heat (LE), and CH4, and assessed the differences in annual CO2 and CH4 fluxes estimated with different instrumentation at the same sites. Using data from four sites across the North Slope of Alaska, we found that annual CO2 fluxes estimated with heated (7.5 ± 1.4 gC mâ2 yrâ1) and non-heated (7.9 ± 1.3 gC mâ2 yrâ1) anemometers were within uncertainty bounds. Similarly, despite elevated noise in 30-min flux data, we found that summer CO2 fluxes from open (â17.0 ± 1.1 gC mâ2 yrâ1) and close-path (â14.2 ± 1.7 gC mâ2 yrâ1) gas analyzers were not significantly different. Annual CH4 fluxes were also within uncertainty bounds when comparing both open (4.5 ± 0.31 gC mâ2 yrâ1) and closed-path (4.9 ± 0.27 gC mâ2 yrâ1) gas analyzers as well as heated (3.7 ± 0.26 gC mâ2 yrâ1) and non-heated (3.7 ± 0.28 gC mâ2 yrâ1) anemometers. A continuously heated anemometer increased data coverage (64%) relative to non-heated anemometers (47â52%). However, sensible heat fluxes were over-estimated by 12%, on average, with the heated anemometer, contributing to the overestimation of CO2, CH4, and LE fluxes (mean biases of â0.03 ÎŒmol mâ2 sâ1, â0.05 mgC mâ2 hâ1, and â3.77 W mâ2, respectively). To circumvent this potential bias and reduce power consumption, we implemented an intermittent heating strategy whereby activation only occurred when ice or snow blockage of the transducers was detected. This resulted in comparable coverage (50%) during winter to the continuously heated anemometer (46%), while avoiding flux over-estimation. Closed and open-path analyzers showed good agreement, but data coverage was generally greater when using closed-path, especially during winter. Winter data coverage of 26â32% was obtained with closed-path devices, vs 10â14% for the open-path devices with unheated anemometers or up to 46% and 35% using closed and open-path analyzers, respectively with heated anemometers. Accurate estimation of LE remains difficult in the Arctic due to strong attenuation in closed-path systems, even when intake tubes are heated, and due to poor data coverage from open-path sensors in such a harsh environment
Estimação de parĂąmetros da cinĂ©tica de trĂąnsito de partĂculas em bovinos sob pastejo por diferentes seqĂŒĂȘncias amostrais
New insights into the genetic etiology of Alzheimer's disease and related dementias
Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE Δ4 allele
Massa das sementes de Tecoma stans L. Juss. ex Kunth (Bignoniaceae): efeitos na emergĂȘncia e desenvolvimento de suas plĂąntulas no sol e na sombra
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