11,580 research outputs found
Stabilization of multidimensional behaviors
We consider three types of stabilizability defined for discrete nD systems within the behavioral framework, namely: trajectory stabilizability, set-controllability to a stable behavior and stabilizability by interconnection. As a first step, we introduce and fully characterize the underlying stability notion. Then, we formalize the definitions of these properties and investigate what is the relationship among them
Periodic behaviors
This paper studies behaviors that are defined on a torus, or equivalently,
behaviors defined in spaces of periodic functions, and establishes their basic
properties analogous to classical results of Malgrange, Palamodov, Oberst et
al. for behaviors on R^n. These properties - in particular the Nullstellensatz
describing the Willems closure - are closely related to integral and rational
points on affine algebraic varieties.Comment: 13 page
Too Many Teens: Preventing Unnecessary Out-Of-Home Placements
The child welfare system was created to care for abused and neglected children. But too often, teenagers are landing in the system because they simply aren't getting along with their parents. This paper traces Casey's efforts to learn from communities that are preventing teens from landing in the system by helping families while the teen remains at home. A survey of the states, interviews with experts, secondary research and visits to several communities show common elements of successful programs.The paper presents information on related laws and policies, funding sources and programs for families while including the infrastructure and services needed to support such initiatives
A Behavioral Approach to the Control of Discrete Linear Repetitive Processes
This paper formulates the theory of linear discrete time repetitive processes in the setting of behavioral systems theory. A behavioral, latent variable model for repetitive processes is developed and for the physically defined inputs and outputs as manifest variables, a kernel representation of their behavior is determined. Conditions for external stability and controllability of the behavior are then obtained. A sufficient condition for stabilizability is also developed for the behavior and it is shown under a mild restriction that, whenever the repetitive system is stabilizable, a regular constant output feedback stabilizing controller exists. Next a notion of eigenvalues is defined for the repetitive process under an action of a closed loop controller. It is then shown how under controllability of the original repetitive process, an arbitrary assignment of eigenvalues for the closed loop response can be achieved by a constant gain output feedback controller under the above restriction. These results on the existence of constant gain output feedback controllers are among the most striking properties enjoyed by repetitive systems, discovered in this paper. Results of this paper utilize the behavioral model of the repetitive process which is an analogue of the 1D equivalent model of the dynamics studied in earlier work on repetitive processes
Use of harm reduction strategies in an occupational therapy life skills intervention
Thesis (M.S.)--Boston UniversityObjectives of Study: Harm reduction intervention strategies have the potential to support positive health outcomes. However, no studies have explored how these strategies can be implemented in an occupational therapy intervention. This study addresses this knowledge gap by examining harm reduction strategies that were discussed during group and individual sessions of an occupational therapist-led life skills intervention for people who have a mental illness and are or were homeless.
Methods: This study is a secondary analysis of a larger study that used a longitudinal repeated measures design to implement a life skills intervention. This secondary analysis uses a mixed methods design. Qualitative methods were used for data collection and initial analysis. Quantitative methods were then used to analyze differences between settings.
Results: Three major themes emerged from the data: Financial, Physical, and Psychosocial Hann Reduction. The most prevalent theme was Financial Harm Reduction. All three themes were present throughout all of the different life skills intervention modules. There was no significant difference in the themes used between settings.
Limitations and Recommendations for Further Research: This study was limited to what
was documented in the therapy notes. Although the notes may not include every discussion that occurred, these results suggest that harm-reduction strategies can be utilized in an occupational therapy intervention. Additional research is needed to investigate how harm reduction can be implemented in other areas of occupational therapy practice
The MHD Kelvin-Helmholtz Instability II: The Roles of Weak and Oblique Fields in Planar Flows
We have carried out high resolution MHD simulations of the nonlinear
evolution of Kelvin-Helmholtz unstable flows in 2 1/2 dimensions. The modeled
flows and fields were initially uniform except for a thin shear layer with a
hyperbolic tangent velocity profile and a small, normal mode perturbation. The
calculations consider periodic sections of flows containing magnetic fields
parallel to the shear layer, but projecting over a full range of angles with
respect to the flow vectors. They are intended as preparation for fully 3D
calculations and to address two specific questions raised in earlier work: 1)
What role, if any, does the orientation of the field play in nonlinear
evolution of the MHD Kelvin-Helmholtz instability in 2 1/2 D. 2) Given that the
field is too weak to stabilize against a linear perturbation of the flow, how
does the nonlinear evolution of the instability depend on strength of the
field. The magnetic field component in the third direction contributes only
through minor pressure contributions, so the flows are essentially 2D. Even a
very weak field can significantly enhance the rate of energy dissipation. In
all of the cases we studied magnetic field amplification by stretching in the
vortex is limited by tearing mode, ``fast'' reconnection events that isolate
and then destroy magnetic flux islands within the vortex and relax the fields
outside the vortex. If the magnetic tension developed prior to reconnection is
comparable to Reynolds stresses in the flow, that flow is reorganized during
reconnection. Otherwise, the primary influence on the plasma is generation of
entropy. The effective expulsion of flux from the vortex is very similar to
that shown by Weiss for passive fields in idealized vortices with large
magnetic Reynolds numbers. We demonstrated that thisComment: 23 pages of ApJ Latex (aaspp4.sty) with 10 figures, high resolution
postscript images for figs 4-9 available through anonymous at
ftp://ftp.msi.umn.edu/pub/twj To appear in the June 10, 1997 Ap
Causal and Stable Input/Output Structures on Multidimensional Behaviours
In this work we study multidimensional (nD) linear differential behaviours with a distinguished independent variable called "time". We define in a natural way causality and stability on input/output structures with respect to this distinguished direction. We make an extension of some results in the theory of partial differential equations, demonstrating that causality is equivalent to a property of the transfer matrix which is essentially hyperbolicity of the Pc operator defining the behaviour (Bc)0,y We also quote results which in effect characterise time autonomy for the general systems case. Stability is likewise characterized by a property of the transfer matrix. We prove this result for the 2D case and for the case of a single equation; for the general case it requires solution of an open problem concerning the geometry of a particular set in Cn. In order to characterize input/output stability we also develop new results on inclusions of kernels, freeness of variables, and closure with respect to S,S' and associated spaces, which are of independent interest. We also discuss stability of autonomous behaviours, which we beleive to be governed by a corresponding condition
Stability Properties of 1-Dimensional Hamiltonian Lattices with Non-analytic Potentials
We investigate the local and global dynamics of two 1-Dimensional (1D)
Hamiltonian lattices whose inter-particle forces are derived from non-analytic
potentials. In particular, we study the dynamics of a model governed by a
"graphene-type" force law and one inspired by Hollomon's law describing
"work-hardening" effects in certain elastic materials. Our main aim is to show
that, although similarities with the analytic case exist, some of the local and
global stability properties of non-analytic potentials are very different than
those encountered in systems with polynomial interactions, as in the case of 1D
Fermi-Pasta-Ulam-Tsingou (FPUT) lattices. Our approach is to study the motion
in the neighborhood of simple periodic orbits representing continuations of
normal modes of the corresponding linear system, as the number of particles
and the total energy are increased. We find that the graphene-type model is
remarkably stable up to escape energy levels where breakdown is expected, while
the Hollomon lattice never breaks, yet is unstable at low energies and only
attains stability at energies where the harmonic force becomes dominant. We
suggest that, since our results hold for large , it would be interesting to
study analogous phenomena in the continuum limit where 1D lattices become
strings.Comment: Accepted for publication in the International Journal of Bifurcation
and Chao
- …