3,106 research outputs found
Approaches to Estimating the Health State Dependence of the Utility Function
If the marginal utility of consumption depends on health status, this will affect the economic analysis of a number of central problems in public finance, including the optimal structure of health insurance and optimal life cycle savings. In this paper, we describe the promises and challenges of various approaches to estimating the effect of health on the marginal utility of consumption. Our basic conclusion is that while none of these approaches is a panacea, many offer the potential to shed important insights on the nature of health state dependence.
Localized to extended states transition for two interacting particles in a two-dimensional random potential
We show by a numerical procedure that a short-range interaction induces
extended two-particle states in a two-dimensional random potential. Our
procedure treats the interaction as a perturbation and solve Dyson's equation
exactly in the subspace of doubly occupied sites. We consider long bars of
several widths and extract the macroscopic localization and correlation lengths
by an scaling analysis of the renormalized decay length of the bars. For ,
the critical disorder found is , and the critical
exponent . For two non-interacting particles we do not find any
transition and the localization length is roughly half the one-particle value,
as expected.Comment: 4 two-column pages, 4 eps figures, Revtex, to be published in
Europhys. Let
One-dimensional collision carts computer model and its design ideas for productive experiential learning
We develop an Easy Java Simulation (EJS) model for students to experience the
physics of idealized one-dimensional collision carts. The physics model is
described and simulated by both continuous dynamics and discrete transition
during collision. In the field of designing computer simulations, we discuss
briefly three pedagogical considerations such as 1) consistent simulation world
view with pen paper representation, 2) data table, scientific graphs and
symbolic mathematical representations for ease of data collection and multiple
representational visualizations and 3) game for simple concept testing that can
further support learning. We also suggest using physical world setup to be
augmented complimentary with simulation while highlighting three advantages of
real collision carts equipment like tacit 3D experience, random errors in
measurement and conceptual significance of conservation of momentum applied to
just before and after collision. General feedback from the students has been
relatively positive, and we hope teachers will find the simulation useful in
their own classes. 2015 Resources added:
http://iwant2study.org/ospsg/index.php/interactive-resources/physics/02-newtonian-mechanics/02-dynamics/46-one-dimension-collision-js-model
http://iwant2study.org/ospsg/index.php/interactive-resources/physics/02-newtonian-mechanics/02-dynamics/195-elastic-collisionComment: 6 pages, 8 figures, 1 table, 1 L. K. Wee, Physics Education 47 (3),
301 (2012); ISSN 0031-912
Variation of the density of states in amorphous GdSi at the metal-insulator transition
We performed detailed conductivity and tunneling mesurements on the
amorphous, magnetically doped material -GdSi (GdSi), which
can be driven through the metal-insulator transition by the application of an
external magnetic field. Conductivity increases linearly with field near the
transition and slightly slower on the metallic side. The tunneling conductance,
proportional to the density of states , undergoes a gradual change with
increasing field, from insulating, showing a soft gap at low bias, with a
slightly weaker than parabolic energy dependence, i.e. , , towards metallic behavior, with , energy
dependence. The density of states at the Fermi level appears to be zero at low
fields, as in an insulator, while the sample shows already small, but
metal-like conductivity. We suggest a possible explanation to the observed
effect.Comment: 6 pages, 6 figure
Faint AGNs at z>4 in the CANDELS GOODS-S field: looking for contributors to the reionization of the Universe
In order to derive the AGN contribution to the cosmological ionizing
emissivity we have selected faint AGN candidates at in the CANDELS
GOODS-South field which is one of the deepest fields with extensive
multiwavelength coverage from Chandra, HST, Spitzer and various groundbased
telescopes. We have adopted a relatively novel criterion. As a first step high
redshift galaxies are selected in the NIR band down to very faint levels
() using reliable photometric redshifts. This corresponds at to
a selection criterion based on the galaxy rest-frame UV flux. AGN candidates
are then picked up from this parent sample if they show X-ray fluxes above a
threshold of cgs (0.5-2 keV). We have found 22 AGN
candidates at and we have derived the first estimate of the UV luminosity
function in the redshift interval and absolute magnitude interval
typical of local Seyfert galaxies. The
faint end of the derived luminosity function is about two/four magnitudes
fainter at than that derived from previous UV surveys. We have then
estimated ionizing emissivities and hydrogen photoionization rates in the same
redshift interval under reasonable assumptions and after discussion of possible
caveats, the most important being the large uncertainties involved in the
estimate of photometric redshift for sources with featureless, almost power-law
SEDs and/or low average escape fraction of ionizing photons from the AGN host
galaxies. We argue that, under reasonable evaluations of possible biases, the
probed AGN population can produce at photoionization rates consistent
with that required to keep highly ionized the intergalactic medium observed in
the Lyman- forest of high redshift QSO spectra, providing an important
contribution to the cosmic reionization.Comment: 15 pages, 8 figures, A&A accepted, updated figure 6, corrected typo
in table 3, updated reference
Simplicial quantum dynamics
Present-day quantum field theory can be regularized by a decomposition into
quantum simplices. This replaces the infinite-dimensional Hilbert space by a
high-dimensional spinor space and singular canonical Lie groups by regular spin
groups. It radically changes the uncertainty principle for small distances.
Gaugeons, including the gravitational, are represented as bound fermion-pairs,
and space-time curvature as a singular organized limit of quantum
non-commutativity.
Keywords: Quantum logic, quantum set theory, quantum gravity, quantum
topology, simplicial quantization.Comment: 25 pages. 1 table. Conference of the International Association for
Relativistic Dynamics, Taiwan, 201
The Role of Bulge Formation in the Homogenization of Stellar Populations at as revealed by Internal Color Dispersion in CANDELS
We use data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy
Survey to study how the spatial variation in the stellar populations of
galaxies relate to the formation of galaxies at . We use the
Internal Color Dispersion (ICD), measured between the rest-frame UV and optical
bands, which is sensitive to age (and dust attenuation) variations in stellar
populations. The ICD shows a relation with the stellar masses and morphologies
of the galaxies. Galaxies with the largest variation in their stellar
populations as evidenced by high ICD have disk-dominated morphologies (with
S\'{e}rsic indexes ) and stellar masses between . There is a marked decrease in the ICD as the stellar mass and/or
the S\'ersic index increases. By studying the relations between the ICD and
other galaxy properties including sizes, total colors, star-formation rate, and
dust attenuation, we conclude that the largest variations in stellar
populations occur in galaxies where the light from newly, high star-forming
clumps contrasts older stellar disk populations. This phase reaches a peak for
galaxies only with a specific stellar mass range, , and prior to the formation of a substantial bulge/spheroid. In contrast,
galaxies at higher or lower stellar masses, and/or higher S\'{e}rsic index () show reduced ICD values, implying a greater homogeneity of their stellar
populations. This indicates that if a galaxy is to have both a quiescent bulge
along with a star forming disk, typical of Hubble Sequence galaxies, this is
most common for stellar masses and when the
bulge component remains relatively small ().Comment: 15 pages, 14 figure
Stellar Populations of Lyman Break Galaxies at z=1-3 in the HST/WFC3 Early Release Science Observations
We analyze the spectral energy distributions (SEDs) of Lyman break galaxies
(LBGs) at z=1-3 selected using the Hubble Space Telescope (HST) Wide Field
Camera 3 (WFC3) UVIS channel filters. These HST/WFC3 observations cover about
50 sq. arcmin in the GOODS-South field as a part of the WFC3 Early Release
Science program. These LBGs at z=1-3 are selected using dropout selection
criteria similar to high redshift LBGs. The deep multi-band photometry in this
field is used to identify best-fit SED models, from which we infer the
following results: (1) the photometric redshift estimate of these dropout
selected LBGs is accurate to within few percent; (2) the UV spectral slope
(beta) is redder than at high redshift (z>3), where LBGs are less dusty; (3) on
average, LBGs at z=1-3 are massive, dustier and more highly star-forming,
compared to LBGs at higher redshifts with similar luminosities
(0.1L*<~L<~2.5L*), though their median values are similar within 1-sigma
uncertainties. This could imply that identical dropout selection technique, at
all redshifts, find physically similar galaxies; and (4) stellar masses of
these LBGs are directly proportional to their UV luminosities with a
logarithmic slope of ~0.46, and star-formation rates are proportional to their
stellar masses with a logarithmic slope of ~0.90. These relations hold true ---
within luminosities probed in this study --- for LBGs from z~1.5 to 5. The
star-forming galaxies selected using other color-based techniques show similar
correlations at z~2, but to avoid any selection biases, and for direct
comparison with LBGs at z>3, a true Lyman break selection at z~2 is essential.
The future HST UV surveys, both wider and deeper, covering a large luminosity
range are important to better understand LBG properties, and their evolution.Comment: Accepted for publication in ApJ (29 pages, 9 figures
Right eigenvalue equation in quaternionic quantum mechanics
We study the right eigenvalue equation for quaternionic and complex linear
matrix operators defined in n-dimensional quaternionic vector spaces. For
quaternionic linear operators the eigenvalue spectrum consists of n complex
values. For these operators we give a necessary and sufficient condition for
the diagonalization of their quaternionic matrix representations. Our
discussion is also extended to complex linear operators, whose spectrum is
characterized by 2n complex eigenvalues. We show that a consistent analysis of
the eigenvalue problem for complex linear operators requires the choice of a
complex geometry in defining inner products. Finally, we introduce some
examples of the left eigenvalue equations and highlight the main difficulties
in their solution.Comment: 24 pages, AMS-Te
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