1,954 research outputs found
The Impact of Migration on Family Left Behind
This paper addresses the effects of migration on families left behind and offers new evidence on the impact of migration on elderly parents. After discussing the identification issues involved in estimation, I review the literature on the effects of migration on the education and health of non-migrant children as well as the labor supply of non-migrant spouses. Finally, I address the impact of adult child migration on contributions toward non-migrant parents as well as the effects on parental health. Results show that elderly parents receive lower time contributions from all of their children when one child migrates.migration, left behind, elderly, children
Discrete Formulation for the dynamics of rods deforming in space
We describe the main ingredients needed to create, from the smooth lagrangian
density, a variational principle for discrete motions of a discrete rod, with
corresponding conserved Noether currents. We describe all geometrical objects
in terms of elements on the linear Atiyah bundle, using a reduced forward
difference operator. We show how this introduces a discrete lagrangian density
that models the discrete dynamics of a discrete rod. The presented tools are
general enough to represent a discretization of any variational theory in
principal bundles, and its simplicity allows to perform an iterative
integration algorithm to compute the discrete rod evolution in time, starting
from any predefined configurations of all discrete rod elements at initial
times
Spatial chaos of an extensible conducting rod in a uniform magnetic field
The equilibrium equations for the isotropic Kirchhoff rod are known to form
an integrable system. It is also known that the effects of extensibility and
shearability of the rod do not break the integrable structure. Nor, as we have
shown in a previous paper does the effect of a magnetic field on a conducting
rod. Here we show, by means of Mel'nikov analysis, that, remarkably, the
combined effects do destroy integrability; that is, the governing equations for
an extensible current-carrying rod in a uniform magnetic field are
nonintegrable. This result has implications for possible configurations of
electrodynamic space tethers and may be relevant for electromechanical devices
Curvature condensation and bifurcation in an elastic shell
We study the formation and evolution of localized geometrical defects in an
indented cylindrical elastic shell using a combination of experiment and
numerical simulation. We find that as a symmetric localized indentation on a
semi-cylindrical shell increases, there is a transition from a global mode of
deformation to a localized one which leads to the condensation of curvature
along a symmetric parabolic crease. This process introduces a soft mode in the
system, converting a load-bearing structure into a hinged, kinematic mechanism.
Further indentation leads to twinning wherein the parabolic crease bifurcates
into two creases that move apart on either side of the line of symmetry. A
qualitative theory captures the main features of the phenomena and leads to
sharper questions about the nucleation of these defects.Comment: 4 pages, 5 figures, submitted to Physical Review Letter
Elastic cavitation, tube hollowing, and differential growth in plants and biological tissues
Elastic cavitation is a well-known physical process by which elastic materials under stress can open cavities. Usually, cavitation is induced by applied loads on the elastic body. However, growing materials may generate stresses in the absence of applied loads and could induce cavity opening. Here, we demonstrate the possibility of spontaneous growth-induced cavitation in elastic materials and consider the implications of this phenomenon to biological tissues and in particular to the problem of schizogenous aerenchyma formation
Scoping studies: towards a methodological framework
This paper focuses on scoping studies, an approach to reviewing the literature which to date has received little attention in the research methods literature. We distinguish between different types of scoping studies and indicate where these stand in relation to full systematic reviews. We outline a framework for conducting a scoping study based on our recent experiences of reviewing the literature on services for carers for people with mental health problems. Where appropriate, our approach to scoping the field is contrasted with the procedures followed in systematic reviews. We emphasize how including a consultation exercise in this sort of study may enhance the results, making them more useful to policy makers, practitioners and service users. Finally, we consider the advantages and limitations of the approach and suggest that a wider debate is called for about the role of the scoping study in relation to other types of literature reviews
Integrability of a conducting elastic rod in a magnetic field
We consider the equilibrium equations for a conducting elastic rod placed in
a uniform magnetic field, motivated by the problem of electrodynamic space
tethers. When expressed in body coordinates the equations are found to sit in a
hierarchy of non-canonical Hamiltonian systems involving an increasing number
of vector fields. These systems, which include the classical Euler and
Kirchhoff rods, are shown to be completely integrable in the case of a
transversely isotropic rod; they are in fact generated by a Lax pair. For the
magnetic rod this gives a physical interpretation to a previously proposed
abstract nine-dimensional integrable system. We use the conserved quantities to
reduce the equations to a four-dimensional canonical Hamiltonian system,
allowing the geometry of the phase space to be investigated through Poincar\'e
sections. In the special case where the force in the rod is aligned with the
magnetic field the system turns out to be superintegrable, meaning that the
phase space breaks down completely into periodic orbits, corresponding to
straight twisted rods.Comment: 19 pages, 1 figur
Graphene-Based Nanomaterials for Neuroengineering: Recent Advances and Future Prospective
Graphene unique physicochemical properties made it prominent among other allotropic forms of carbon, in many areas of research and technological applications. Interestingly, in recent years, many studies exploited the use of graphene family nanomaterials (GNMs) for biomedical applications such as drug delivery, diagnostics, bioimaging, and tissue engineering research. GNMs are successfully used for the design of scaffolds for controlled induction of cell differentiation and tissue regeneration. Critically, it is important to identify the more appropriate nano/bio material interface sustaining cells differentiation and tissue regeneration enhancement. Specifically, this review is focussed on graphene-based scaffolds that endow physiochemical and biological properties suitable for a specific tissue, the nervous system, that links tightly morphological and electrical properties. Different strategies are reviewed to exploit GNMs for neuronal engineering and regeneration, material toxicity, and biocompatibility. Specifically, the potentiality for neuronal stem cells differentiation and subsequent neuronal network growth as well as the impact of electrical stimulation through GNM on cells is presented. The use of field effect transistor (FET) based on graphene for neuronal regeneration is described. This review concludes the important aspects to be controlled to make graphene a promising candidate for further advanced application in neuronal tissue engineering and biomedical use
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