907 research outputs found
Who Invests in Home Equity to Exempt Wealth from Bankruptcy?
Homestead exemptions to personal bankruptcy allow households to retain their home equity up to a limit determined at the state level. Households that may experience bankruptcy thus have an incentive to bias their portfolios towards home equity. Using US household data from the Survey of Income and Program Participation for the period 1996-2006, we find that especially households with low net worth maintain a larger share of their wealth as home equity if a larger homestead exemption applies. This home equity bias is also more pronounced if the household head is in poor health, increasing the chance of bankruptcy on account of unpaid medical bills. The bias is further stronger for households with mortgage finance, shorter house tenures, and younger household heads, which taken together reflect households that face more financial uncertainty.Homestead exemptions;Personal bankruptcy;Portfolio allocation;Home ownership
The factor structure, metrical properties, and convergent validity of the third edition (1999) of the Locus of Control Inventory.
The principal objective of the study was to examine the factor structure and metrical properties of the third edition (1999) of the Locus of Control Inventory (LCI). A corollary of the study was to examine the convergent validity of the instrument. After a thorough revision and extension of the scale to 88 items it was applied to a sample of 2091 first-year university students. Particular attention was paid to the shortcomings revealed in a study by de Bruin (2004). An iterative principal factor analysis of the scale was done. The three-factor-structure previously found was substantiated by the analysis. The obtained factors were interpreted as Autonomy, External Control and Internal Control. Highly acceptable reliabilities were obtained. As far as validity is concerned it was found that Internal Control and Autonomy are strongly related to Psychological Wellness and External Control negatively to Stress Management. The implications of the findings are discussed
Formation of toxic oligomers of polyQ-expanded Huntingtin by prion-mediated cross-seeding
Manifestation of aggregate pathology in Huntington's disease is thought to be facilitated by a preferential vulnerability of affected brain cells to age-dependent proteostatic decline. To understand how specific cellular backgrounds may facilitate pathologic aggregation, we utilized the yeast model in which polyQ-expanded Huntingtin forms aggregates only when the endogenous prion-forming protein Rnq1 is in its amyloid-like prion [PIN+] conformation. We employed optogenetic clustering of polyQ protein as an orthog-onal method to induce polyQ aggregation in prion-free [pin-] cells. Optogenetic aggregation circumvented the prion requirement for the formation of detergent-resistant polyQ inclusions but bypassed the formation of toxic polyQ oligomers, which accumulated specifically in [PIN+] cells. Reconstitution of aggregation in vitro suggested that these polyQ oligomers formed through direct templating on Rnq1 prions. These findings shed light on the mechanism of prion-mediated formation of oligomers, which may play a role in triggering polyQ pathology in the patient brain
Sis1 potentiates the stress response to protein aggregation and elevated temperature
Cells adapt to conditions that compromise protein conformational stability by activating various stress response pathways, but the mechanisms used in sensing misfolded proteins remain unclear. Moreover, aggregates of disease proteins often fail to induce a productive stress response. Here, using a yeast model of polyQ protein aggregation, we identified Sis1, an essential Hsp40 co-chaperone of Hsp70, as a critical sensor of proteotoxic stress. At elevated levels, Sis1 prevented the formation of dense polyQ inclusions and directed soluble polyQ oligomers towards the formation of permeable condensates. Hsp70 accumulated in a liquid-like state within this polyQ meshwork, resulting in a potent activation of the HSF1 dependent stress response. Sis1, and the homologous DnaJB6 in mammalian cells, also regulated the magnitude of the cellular heat stress response, suggesting a general role in sensing protein misfolding. Sis1/DnaJB6 functions as a limiting regulator to enable a dynamic stress response and avoid hypersensitivity to environmental changes. Identifying factors that enable cells to induce a potent stress response to amyloid-like aggregation can provide further insight into the mechanism of stress regulation. Here, the authors express polyglutamine-expanded Huntingtin as a model disease protein in yeast cells and perform a genetic screen for chaperone factors that allow yeast cells to activate a potent stress response. They identify Sis1, an essential Hsp40 co-chaperone of Hsp70, as a critical sensor of proteotoxic stress and further show that both Sis1 and its mammalian homolog DnaJB6 regulate the magnitude of the cellular heat stress response, indicating that this mechanism is conserved
A framework for large-scale relativistic simulations in the characteristic approach
We present a new computational framework (LEO), that enables us to carry out
the very first large-scale, high-resolution computations in the context of the
characteristic approach in numerical relativity. At the analytic level, our
approach is based on a new implementation of the ``eth'' formalism, using a
non-standard representation of the spin-raising and lowering angular operators
in terms of non-conformal coordinates on the sphere; we couple this formalism
to a partially first-order reduction (in the angular variables) of the Einstein
equations. The numerical implementation of our approach supplies the basic
building blocks for a highly parallel, easily extensible numerical code. We
demonstrate the adaptability and excellent scaling of our numerical code by
solving, within our numerical framework, for a scalar field minimally coupled
to gravity (the Einstein-Klein-Gordon problem) in 3-dimensions. The nonlinear
code is globally second-order convergent, and has been extensively tested using
as reference a calibrated code with the same boundary-initial data and radial
marching algorithm. In this context, we show how accurately we can follow
quasi-normal mode ringing. In the linear regime, we show energy conservation
for a number of initial data sets with varying angular structure. A striking
result that arises in this context is the saturation of the flow of energy
through the Schwarzschild radius. As a final calibration check we perform a
large simulation with resolution never achieved before.Comment: RevTeX4, 22 pages, 21 figures, to appear in Phys. Rev.
Finding apparent horizons and other two-surfaces of constant expansion
Apparent horizons are structures of spacelike hypersurfaces that can be
determined locally in time. Closed surfaces of constant expansion (CE surfaces)
are a generalisation of apparent horizons. I present an efficient method for
locating CE surfaces. This method uses an explicit representation of the
surface, allowing for arbitrary resolutions and, in principle, shapes. The CE
surface equation is then solved as a nonlinear elliptic equation.
It is reasonable to assume that CE surfaces foliate a spacelike hypersurface
outside of some interior region, thus defining an invariant (but still
slicing-dependent) radial coordinate. This can be used to determine gauge modes
and to compare time evolutions with different gauge conditions. CE surfaces
also provide an efficient way to find new apparent horizons as they appear e.g.
in binary black hole simulations.Comment: 21 pages, 8 figures; two references adde
R.A.Fisher, design theory, and the Indian connection
Design Theory, a branch of mathematics, was born out of the experimental
statistics research of the population geneticist R. A. Fisher and of Indian
mathematical statisticians in the 1930s. The field combines elements of
combinatorics, finite projective geometries, Latin squares, and a variety of
further mathematical structures, brought together in surprising ways. This
essay will present these structures and ideas as well as how the field came
together, in itself an interesting story.Comment: 11 pages, 3 figure
Polariton propagation in weak confinement quantum wells
Exciton-polariton propagation in a quantum well, under centre-of-mass
quantization, is computed by a variational self-consistent microscopic theory.
The Wannier exciton envelope functions basis set is given by the simple
analytical model of ref. [1], based on pure states of the centre-of-mass wave
vector, free from fitting parameters and "ad hoc" (the so called additional
boundary conditions-ABCs) assumptions. In the present paper, the former
analytical model is implemented in order to reproduce the centre-of-mass
quantization in a large range of quantum well thicknesses (5a_B < L < inf.).
The role of the dynamical transition layer at the well/barrier interfaces is
discussed at variance of the classical Pekar's dead-layer and ABCs. The Wannier
exciton eigenstates are computed, and compared with various theoretical models
with different degrees of accuracy. Exciton-polariton transmission spectra in
large quantum wells (L>> a_B) are computed and compared with experimental
results of Schneider et al.\cite{Schneider} in high quality GaAs samples. The
sound agreement between theory and experiment allows to unambiguously assign
the exciton-polariton dips of the transmission spectrum to the pure states of
the Wannier exciton center-of-mass quantization.Comment: 15 pages, 15 figures; will appear in Phys.Rev.
An Application of Molecular Genotyping in Mice
Microsatellite markers are simple sequence repeats within the mammalian genome that can be used for identifying disease loci, mapping genes of interest as well as studying segregation patterns related to meiotic nondisjunction. Different strains of mice have variable CA repeat lengths and PCR based methods can be used to identify them, thus allowing for specific genotypes to be assigned. Molecular genotyping offers such identification at any developmental stage, which allows for a broad range of anomalies to be studied. We studied chromosomal segregation in relation to nondisjunction in early-gestation mouse embryos using molecular genotyping. Information on the parental origin as well as the number of chromosomes a given progeny carried was obtained in our analysis
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