191 research outputs found
Universality Classes for Interface Growth with Quenched Disorder
We present numerical evidence that there are two distinct universality
classes characterizing driven interface roughening in the presence of quenched
disorder. The evidence is based on the behavior of , the coefficient
of the nonlinear term in the growth equation. Specifically, for three of the
models studied, at the depinning transition, while
for the two other models, .Comment: 11 pages and 3 figures (upon request), REVTeX 3.0, (submitted to PRL
Singularities and Avalanches in Interface Growth with Quenched Disorder
A simple model for an interface moving in a disordered medium is presented.
The model exhibits a transition between the two universality classes of
interface growth phenomena. Using this model, it is shown that the application
of constraints to the local slopes of the interface produces avalanches of
growth, that become relevant in the vicinity of the depinning transition. The
study of these avalanches reveals a singular behavior that explains a recently
observed singularity in the equation of motion of the interface.Comment: 4 pages. REVTEX. 4 figs available on request from [email protected]
Delocalization Transition of a Rough Adsorption-Reaction Interface
We introduce a new kinetic interface model suitable for simulating
adsorption-reaction processes which take place preferentially at surface
defects such as steps and vacancies. As the average interface velocity is taken
to zero, the self- affine interface with Kardar-Parisi-Zhang like scaling
behaviour undergoes a delocalization transition with critical exponents that
fall into a novel universality class. As the critical point is approached, the
interface becomes a multi-valued, multiply connected self-similar fractal set.
The scaling behaviour and critical exponents of the relevant correlation
functions are determined from Monte Carlo simulations and scaling arguments.Comment: 4 pages with 6 figures, new comment
2017 Nevada Middle School Youth Risk Behavior Survey (YRBS): Adverse Childhood Experiences (ACEs) Special Report
Priority health risk behaviors (i.e. preventable behaviors that contribute to the leading causes of morbidity and mortality) are often established during childhood and adolescence and extend into adulthood. Ongoing surveillance of youth risk behaviors is critical for the design, implementation, and evaluation of public health interventions to improve adolescent health. The Youth Risk Behavior Survey (YRBS) is a national surveillance system that was established in 1991 by the Centers for Disease Control and Prevention (CDC) to monitor the prevalence of health risk behaviors among youth. YRBS data are routinely collected on middle school students, but only a few states collect data in middle schools. The Nevada Middle School YRBS is biennial, anonymous and voluntary survey of students in 6th through 8th grade in regular public, charter, and alternative schools. Students self-report their behaviors in five major areas of health that directly lead to morbidity and mortality. The Nevada Middle School YRBS provides prevalence estimates for priority risk behaviors and can be used to monitor trends over time.This research was partially supported by a grant from the Centers for Disease Control and Prevention (CDC-PS13-1308). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the CD
2017 Nevada High School Youth Risk Behavior Survey (YRBS): Adverse Childhood Experiences (ACEs) Special Report
Priority health risk behaviors (i.e. preventable behaviors that contribute to the leading causes of morbidity and mortality) are often established during childhood and adolescence and extend into adulthood. Ongoing surveillance of youth risk behaviors is critical for the design, implementation, and evaluation of public health interventions to improve adolescent health. The Youth Risk Behavior Survey (YRBS) is a national surveillance system that was established in 1991 by the Centers for Disease Control and Prevention (CDC) to monitor the prevalence of health risk behaviors among youth. The Nevada High School YRBS is a biennial, anonymous, and voluntary survey of students in 9th through 12th grade in regular public, charter, and alternative schools. Students self-report their behaviors in six major areas of health that directly lead to morbidity and mortality. The Nevada High School YRBS provides prevalence estimates for priority risk behaviors and can be used to monitor trends over time.This research was partially supported by a grant from the Centers for Disease Control and Prevention (CDC-PS13-1308). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the CD
2017 Nevada High School Youth Risk Behavior Survey (YRBS): Sexual Identity Special Report
Priority health risk behaviors (i.e. preventable behaviors that contribute to the leading causes of morbidity and mortality) are often established during childhood and adolescence and extend into adulthood. Ongoing surveillance of youth risk behaviors is critical for the design, implementation, and evaluation of public health interventions to improve adolescent health. The Youth Risk Behavior Survey (YRBS) is a national surveillance system that was established in 1991 by the Centers for Disease Control and Prevention (CDC) to monitor the prevalence of health risk behaviors among youth. The Nevada High School YRBS is a biennial, anonymous, and voluntary survey of students in 9th through 12th grade in regular public, charter, and alternative schools. Students self-report their behaviors in six major areas of health that directly lead to morbidity and mortality.The Nevada High School YRBS provides prevalence estimates for priority risk behaviors and can be used to monitor trends over time.This surveillance project was partially supported by a grant from the Centers for Disease Control and Prevention (CDC-PS13-1308). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the CDC
Collective Particle Flow through Random Media
A simple model for the nonlinear collective transport of interacting
particles in a random medium with strong disorder is introduced and analyzed. A
finite threshold for the driving force divides the behavior into two regimes
characterized by the presence or absence of a steady-state particle current.
Below this threshold, transient motion is found in response to an increase in
the force, while above threshold the flow approaches a steady state with motion
only on a network of channels which is sparse near threshold. Some of the
critical behavior near threshold is analyzed via mean field theory, and
analytic results on the statistics of the moving phase are derived. Many of the
results should apply, at least qualitatively, to the motion of magnetic bubble
arrays and to the driven motion of vortices in thin film superconductors when
the randomness is strong enough to destroy the tendencies to lattice order even
on short length scales. Various history dependent phenomena are also discussed.Comment: 63 preprint pages plus 6 figures. Submitted to Phys Rev
Static and Dynamic Properties of Inhomogeneous Elastic Media on Disordered Substrate
The pinning of an inhomogeneous elastic medium by a disordered substrate is
studied analytically and numerically. The static and dynamic properties of a
-dimensional system are shown to be equivalent to those of the well known
problem of a -dimensional random manifold embedded in -dimensions.
The analogy is found to be very robust, applicable to a wide range of elastic
media, including those which are amorphous or nearly-periodic, with local or
nonlocal elasticity. Also demonstrated explicitly is the equivalence between
the dynamic depinning transition obtained at a constant driving force, and the
self-organized, near-critical behavior obtained by a (small) constant velocity
drive.Comment: 20 pages, RevTeX. Related (p)reprints also available at
http://matisse.ucsd.edu/~hwa/pub.htm
Stochastic Growth Equations and Reparametrization Invariance
It is shown that, by imposing reparametrization invariance, one may derive a
variety of stochastic equations describing the dynamics of surface growth and
identify the physical processes responsible for the various terms. This
approach provides a particularly transparent way to obtain continuum growth
equations for interfaces. It is straightforward to derive equations which
describe the coarse grained evolution of discrete lattice models and analyze
their small gradient expansion. In this way, the authors identify the basic
mechanisms which lead to the most commonly used growth equations. The
advantages of this formulation of growth processes is that it allows one to go
beyond the frequently used no-overhang approximation. The reparametrization
invariant form also displays explicitly the conservation laws for the specific
process and all the symmetries with respect to space-time transformations which
are usually lost in the small gradient expansion. Finally, it is observed, that
the knowledge of the full equation of motion, beyond the lowest order gradient
expansion, might be relevant in problems where the usual perturbative
renormalization methods fail.Comment: 42 pages, Revtex, no figures. To appear in Rev. of Mod. Phy
Scaling properties of driven interfaces in disordered media
We perform a systematic study of several models that have been proposed for
the purpose of understanding the motion of driven interfaces in disordered
media. We identify two distinct universality classes: (i) One of these,
referred to as directed percolation depinning (DPD), can be described by a
Langevin equation similar to the Kardar-Parisi-Zhang equation, but with
quenched disorder. (ii) The other, referred to as quenched Edwards-Wilkinson
(QEW), can be described by a Langevin equation similar to the Edwards-Wilkinson
equation but with quenched disorder. We find that for the DPD universality
class the coefficient of the nonlinear term diverges at the depinning
transition, while for the QEW universality class either or
as the depinning transition is approached. The identification
of the two universality classes allows us to better understand many of the
results previously obtained experimentally and numerically. However, we find
that some results cannot be understood in terms of the exponents obtained for
the two universality classes {\it at\/} the depinning transition. In order to
understand these remaining disagreements, we investigate the scaling properties
of models in each of the two universality classes {\it above\/} the depinning
transition. For the DPD universality class, we find for the roughness exponent
for the pinned phase, and
for the moving phase. For the growth exponent, we find for the pinned phase, and for the moving phase.
Furthermore, we find an anomalous scaling of the prefactor of the width on the
driving force. A new exponent , characterizing the
scaling of this prefactor, is shown to relate the values of the roughnessComment: Latex manuscript, Revtex 3.0, 15 pages, and 15 figures also available
via anonymous ftp from ftp://jhilad.bu.edu/pub/abms/ (128.197.42.52
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