1,451 research outputs found
Chirality transfer and stereo-selectivity of imprinted cholesteric networks
Imprinting of cholesteric textures in a polymer network is a method of
preserving a macroscopically chiral phase in a system with no molecular
chirality. By modifying the elastics properties of the network, the resulting
stored helical twist can be manipulated within a wide range since the
imprinting efficiency depends on the balance between the elastics constants and
twisting power at network formation. One spectacular property of phase
chirality imprinting is the created ability of the network to adsorb
preferentially one stereo-component from a racemic mixture. In this paper we
explore this property of chirality transfer from a macroscopic to the molecular
scale. In particular, we focus on the competition between the phase chirality
and the local nematic order. We demonstrate that it is possible to control the
subsequent release of chiral solvent component from the imprinting network and
the reversibility of the stereo-selective swelling by racemic solvents
Imprinted Networks as Chiral Pumps
We investigate the interaction between a chirally imprinted network and a
solvent of chiral molecules. We find, a liquid crystalline polymer network is
preferentially swollen by one component of a racemic solvent. This ability to
separate is linked to the chiral order parameter of the network, and can be
reversibly controlled via temperature or a mechanical deformation. It is
maximal near the point at which the network loses its imprinted structure. One
possible practical application of this effect would be a mechanical device for
sorting mixed chiral molecules.Comment: 4 pages, 5 figure
Unaccompanied Children in the United States: Mental Health, Adversity and Employment as Markers of Immigrant Integration
Thesis advisor: Thomas M. CreaUnaccompanied children have arrived at the US border in increasing numbers since 2012, reaching a peak of 59,692 children apprehended at the US border in 2016. This dissertation includes three studies to better understand the characteristics of integration as experienced by unaccompanied children who arrive to the US. The first study examines rates of PTSD in a sample of unaccompanied children receiving post release services. This study also includes a confirmatory factor analysis to examine the theoretical structure of the Child PTSD Symptom Scale (CPSS). The second study examines factors associated with adversity experienced by unaccompanied children who are exiting a long term foster care program. The third study examines factors associated with employment outcomes for unaccompanied children exiting the Unaccompanied Refugee Minor (URM) federal foster care program. Together, the three studies comprise an exploratory dissertation that sheds light on the characteristics of two primary features of immigrant integration, namely mental health and employment.Thesis (PhD) — Boston College, 2019.Submitted to: Boston College. Graduate School of Social Work.Discipline: Social Work
Contributor to the November Issue/Notes
Notes by Charles G. Hasson, Robert J. Mahoney, Robert E. Sullivan, John Kelly, John D. O\u27Neill, John M. Anderton, Charles R. Gerard, R. A. Macdonell, William B. Ball, Robert E. Sullivan, and Leonard D. Bodkin
Stereo-selective swelling of imprinted cholesteric networks
Molecular chirality, and the chiral symmetry breaking of resulting
macroscopic phases, can be topologically imprinted and manipulated by
crosslinking and swelling of polymer networks. We present a new experimental
approach to stereo-specific separation of chiral isomers by using a cholesteric
elastomer in which a helical director distribution has been topological
imprinted by crosslinking. This makes the material unusual in that is has a
strong phase chirality, but no molecular chirality at all; we study the nature
and parameters controlling the twist-untwist transition. Adding a racemic
mixture to the imprinted network results in selective swelling by only the
component of ``correct'' handedness. We investigate the capacity of demixing in
a racemic environment, which depends on network parameters and the underlying
nematic order
Untwisting of a cholesteric elastomer by a mechanical field
A mechanical strain field applied to a monodomain cholesteric elastomer will
unwind the helical director distribution. There is an analogy with the
classical problem of an electric field applied to a cholesteric liquid crystal,
but with important differences. Frank elasticity is of minor importance unless
the gel is very weak. The interplay is between director anchoring to the rubber
elastic matrix and the external mechanical field. Stretching perpendicular to
the helix axis induces the uniform unwound state via the elimination of sharp,
pinned twist walls above a critical strain. Unwinding through conical director
states occurs when the elastomer is stretched along the helical axis.Comment: 4 pages, RevTeX 3 style, 3 EPS figure
Contributor to the November Issue/Notes
Notes by Charles G. Hasson, Robert J. Mahoney, Robert E. Sullivan, John Kelly, John D. O\u27Neill, John M. Anderton, Charles R. Gerard, R. A. Macdonell, William B. Ball, Robert E. Sullivan, and Leonard D. Bodkin
Coping with information style and family burden:Possible roles of self-stigma and hope among parents of children in a psychiatric inpatient unit
Objective: Parents of children who are hospitalized in inpatient psychiatric units must cope with significant challenges. One of these challenges relates to the way in which they cope with illness-related information. The current study examined the relationship between two such coping styles - monitoring and blunting - and family burden among parents of children in a psychiatric inpatient unit. Moreover, the possible moderating roles.played by hope and self-stigma in these associations were also examined. Methods: Questionnaires regarding coping with information style, self-stigma, hope and family burden were administered to 70 parents. Results: A main positive effect of hope and a main negative effect of self-stigma were uncovered. An interaction between self-stigma and monitoring was also revealed, suggesting that for parents with high self-stigma, compared to those with low self-stigma, more monitoring was related to more burden. Conclusions: Tailoring family interventions according to coping style and self-stigma is highly recommended as a mean to reduce the family burden of parents whose child is hospitalized in a psychiatric inpatient unit. (C) 2016 Elsevier Masson SAS. All rights reserved
Contributors to the November Issue/Notes
Notes by Leo L. Linck, Anthony M. Bernard, Richard F. Swisher, Charles G. Hasson, James H. Neu, William J. Syring, and John H. Verdonk
Contributors to the November Issue/Notes
Notes by Leo L. Linck, Anthony M. Bernard, Richard F. Swisher, Charles G. Hasson, James H. Neu, William J. Syring, and John H. Verdonk
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