55 research outputs found
Declines in prevalence of adolescent substance use disorders and delinquent behaviors in the USA: A unitary trend?
AbstractBackgroundDownward trends in a number of adolescent risk behaviors including violence, crime, and drug use have been observed in the USA in recent years. It is unknown whether these are separate trends or whether they might relate to a general reduction in propensity to engage in such behaviors. Our objectives were to quantify trends in substance use disorders (SUDs) and delinquent behaviors over the 2003–2014 period and to determine whether they might reflect a single trend in an Externalizing-like trait.MethodsWe analyzed data from 12 to 17 year old participants from the National Survey on Drug Use and Health, a representative survey of the household dwelling population of the USA, across the 2003–2014 period (N = 210 599). Outcomes included past-year prevalence of six categories of substance use disorder and six categories of delinquent behavior.ResultsTrend analysis suggested a net decline of 49% in mean number of SUDs and a 34% decline in delinquent behaviors over the 12-year period. Item Response Theory models were consistent with the interpretation that declines in each set of outcomes could be attributed to changes in mean levels of a latent, Externalizing-like trait.ConclusionsOur findings suggest that declines in SUDs and some delinquent behaviors reflect a single trend related to an Externalizing-like trait. Identifying the factors contributing to this trend may facilitate continued improvement across a spectrum of adolescent risk behaviors.</jats:sec
Considering Fluctuation Energy as a Measure of Gyrokinetic Turbulence
In gyrokinetic theory there are two quadratic measures of fluctuation energy,
left invariant under nonlinear interactions, that constrain the turbulence. The
recent work of Plunk and Tatsuno [Phys. Rev. Lett. 106, 165003 (2011)] reported
on the novel consequences that this constraint has on the direction and
locality of spectral energy transfer. This paper builds on that work. We
provide detailed analysis in support of the results of Plunk and Tatsuno but
also significantly broaden the scope and use additional methods to address the
problem of energy transfer. The perspective taken here is that the fluctuation
energies are not merely formal invariants of an idealized model
(two-dimensional gyrokinetics) but are general measures of gyrokinetic
turbulence, i.e. quantities that can be used to predict the behavior of the
turbulence. Though many open questions remain, this paper collects evidence in
favor of this perspective by demonstrating in several contexts that constrained
spectral energy transfer governs the dynamics.Comment: Final version as published. Some cosmetic changes and update of
reference
Assessing global ion thermal confinement in critical-gradient-optimized stellarators
We investigate the confinement properties of two recently devised
quasi-helically symmetric stellarator configurations, HSK and QSTK. Both have
been optimized for large critical gradients of the ion temperature gradient
mode, which is an important driver of turbulent transport in magnetic
confinement fusion devices. To predict the resulting core plasma profiles, we
utilize an advanced theoretical framework based on the gyrokinetic codes GENE
and GENE-3D, coupled to the transport code TANGO. Compared to the HSX
stellarator, both HSK and QSTK achieve significantly higher core-to-edge
temperature ratios, partly thanks to their smaller aspect ratios, with the
other part due to more detailed shaping of the magnetic geometry achieved
during optimization. The computed confinement time, however, is less sensitive
to core temperature than edge temperature, simply due to the disproportionate
influence the edge has on stored plasma energy. We therefore emphasize the
possible benefits of further optimizing turbulence in the outer core region,
and the need to include accurate modelling of confinement in the edge region in
order to assess overall plasma performance of turbulence optimized
stellarators
The impact of adolescent exposure to medical marijuana laws on high school completion, college enrollment and college degree completion
Background: There is concern that medical marijuana laws (MMLs) could negatively affect adolescents. To better understand these policies, we assess how adolescent exposure to MMLs is related to educational attainment. Methods: Data from the 2000 Census and 2001-2014 American Community Surveys were restricted to individuals who were of high school age (14-18) between 1990 and 2012 (n = 5,483,715). MML exposure was coded as: (i) a dichotomous any MML indicator, and (ii) number of years of high school age exposure. We used logistic regression to model whether MMLs affected: (a) completing high school by age 19; (b) beginning college, irrespective of completion; and (c) obtaining any degree after beginning college. A similar dataset based on the Youth Risk Behavior Survey (YRBS) was also constructed for confirmatory analyses assessing marijuana use. Results: MMLs were associated with a 0.40 percentage point increase in the probability of not earning a high school diploma or GED after completing the 12th grade (from 3.99% to 4.39%). High school MML exposure was also associated with a 1.84 and 0.85 percentage point increase in the probability of college non-enrollment and degree non-completion, respectively (from 31.12% to 32.96% and 45.30% to 46.15%, respectively). Years of MML exposure exhibited a consistent dose response relationship for all outcomes. MMLs were also associated with 0.85 percentage point increase in daily marijuana use among 12th graders (up from 1.26%). Conclusions: Medical marijuana law exposure between age 14 to 18 likely has a delayed effect on use and education that persists over time. (C) 2016 Elsevier Ireland Ltd. All rights reserved
Gyrokinetic turbulence: a nonlinear route to dissipation through phase space
This paper describes a conceptual framework for understanding kinetic plasma
turbulence as a generalized form of energy cascade in phase space. It is
emphasized that conversion of turbulent energy into thermodynamic heat is only
achievable in the presence of some (however small) degree of collisionality.
The smallness of the collision rate is compensated by the emergence of
small-scale structure in the velocity space. For gyrokinetic turbulence, a
nonlinear perpendicular phase mixing mechanism is identified and described as a
turbulent cascade of entropy fluctuations simultaneously occurring at spatial
scales smaller than the ion gyroscale and in velocity space. Scaling relations
for the resulting fluctuation spectra are derived. An estimate for the
collisional cutoff is provided. The importance of adequately modeling and
resolving collisions in gyrokinetic simulations is biefly discussed, as well as
the relevance of these results to understanding the dissipation-range
turbulence in the solar wind and the electrostatic microturbulence in fusion
plasmas.Comment: iop revtex style, 14 pages, 1 figure; submitted to PPCF; invited talk
for EPS Conference on Plasma Physics, Crete, June 2008; Replaced to match
published versio
Kinetic Turbulence
The weak collisionality typical of turbulence in many diffuse astrophysical
plasmas invalidates an MHD description of the turbulent dynamics, motivating
the development of a more comprehensive theory of kinetic turbulence. In
particular, a kinetic approach is essential for the investigation of the
physical mechanisms responsible for the dissipation of astrophysical turbulence
and the resulting heating of the plasma. This chapter reviews the limitations
of MHD turbulence theory and explains how kinetic considerations may be
incorporated to obtain a kinetic theory for astrophysical plasma turbulence.
Key questions about the nature of kinetic turbulence that drive current
research efforts are identified. A comprehensive model of the kinetic turbulent
cascade is presented, with a detailed discussion of each component of the model
and a review of supporting and conflicting theoretical, numerical, and
observational evidence.Comment: 31 pages, 3 figures, 99 references, Chapter 6 in A. Lazarian et al.
(eds.), Magnetic Fields in Diffuse Media, Astrophysics and Space Science
Library 407, Springer-Verlag Berlin Heidelberg (2015
Publisher Correction: Demonstration of reduced neoclassical energy transport in Wendelstein 7-X
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