8,702 research outputs found
Location Choice by Households and Polluting Firms: An Evolutionary Approach
environmental policy;game theory;household economics;pollution;location choice
Remarks on Global Anomalies in RCFT Orientifolds
We check the list of supersymmetric standard model orientifold spectra of
Dijkstra, Huiszoon and Schellekens for the presence of global anomalies, using
probe branes. Absence of global anomalies is found to impose strong
constraints, but in nearly all cases they are automatically satisfied by the
solutions to the tadpole cancellation conditions.Comment: 10 page
Micromachined two dimensional resistor arrays for determination of gas parameters
A resistive sensor array is presented for two dimensional temperature distribution measurements in a micromachined flow channel. This allows simultaneous measurement of flow velocity and fluid parameters, like thermal conductivity, diffusion coefficient and viscosity. More general advantages of measuring temperature distributions are the inherent compensation of heat losses to the support and the insensitivity to variations in the temperature coefficient of resistance
The Correlation Between Star Formation and 21cm Emission During the Reionization Epoch
Reionization is thought to be dominated by low mass galaxies, while direct
observations of resolved galaxies probe only the most massive, rarest objects.
The cross-correlation between fluctuations in the surface brightness of the
cumulative Ly-alpha emission (which serves as a proxy for the star formation
rate) and the redshifted 21cm signal from neutral hydrogen in the intergalactic
medium (IGM), will directly probe the causal link between the production of
ionizing photons in galaxies and the reionization of the IGM. We discuss the
prospects for detecting this cross-correlation for unresolved galaxies. We find
that on angular scales <10 arc-minutes, detection will be practical using
widefield near-IR imaging from space in combination with the forthcoming
Mileura Widefield Array - Low Frequency Demonstrator. When redshifted 21cm
observations of the neutral IGM are combined with space-based near-IR imaging
of Ly-alpha emission, the detection on angular scales <3 arc-minutes will be
limited by the sensitivity of the 21cm signal, even when a small aperture
optical telescope (~2m) and a moderate field of view (~10 square degrees) are
used. On scales >3 arc-minutes, the measurement of cross-correlation will be
limited by the accuracy of the foreground sky subtraction.Comment: 12 pages. 5 figures. Submitted to MNRA
Healthiness from Duality
Healthiness is a good old question in program logics that dates back to
Dijkstra. It asks for an intrinsic characterization of those predicate
transformers which arise as the (backward) interpretation of a certain class of
programs. There are several results known for healthiness conditions: for
deterministic programs, nondeterministic ones, probabilistic ones, etc.
Building upon our previous works on so-called state-and-effect triangles, we
contribute a unified categorical framework for investigating healthiness
conditions. We find the framework to be centered around a dual adjunction
induced by a dualizing object, together with our notion of relative
Eilenberg-Moore algebra playing fundamental roles too. The latter notion seems
interesting in its own right in the context of monads, Lawvere theories and
enriched categories.Comment: 13 pages, Extended version with appendices of a paper accepted to
LICS 201
Theory of asymmetric non-additive binary hard-sphere mixtures
We show that the formal procedure of integrating out the degrees of freedom
of the small spheres in a binary hard-sphere mixture works equally well for
non-additive as it does for additive mixtures. For highly asymmetric mixtures
(small size ratios) the resulting effective Hamiltonian of the one-component
fluid of big spheres, which consists of an infinite number of many-body
interactions, should be accurately approximated by truncating after the term
describing the effective pair interaction. Using a density functional treatment
developed originally for additive hard-sphere mixtures we determine the zero,
one, and two-body contribution to the effective Hamiltonian. We demonstrate
that even small degrees of positive or negative non-additivity have significant
effect on the shape of the depletion potential. The second virial coefficient
, corresponding to the effective pair interaction between two big spheres,
is found to be a sensitive measure of the effects of non-additivity. The
variation of with the density of the small spheres shows significantly
different behavior for additive, slightly positive and slightly negative
non-additive mixtures. We discuss the possible repercussions of these results
for the phase behavior of binary hard-sphere mixtures and suggest that
measurements of might provide a means of determining the degree of
non-additivity in real colloidal mixtures
Small-scale Intensity Mapping: Extended Halos as a Probe of the Ionizing Escape Fraction and Faint Galaxy Populations during Reionization
We present a new method to quantify the value of the escape fraction of
ionizing photons, and the existence of ultra-faint galaxies clustered around
brighter objects during the epoch of cosmic reionization, using the diffuse
Ly, continuum and H emission observed around galaxies at
. We model the surface brightness profiles of the diffuse halos
considering the fluorescent emission powered by ionizing photons escaping from
the central galaxies, and the nebular emission from satellite star-forming
sources, by extending the formalisms developed in Mas-Ribas & Dijkstra (2016)
and Mas-Ribas et al. (2017). The comparison between our predicted profiles and
Ly observations at and favors a low ionizing escape
fraction, , for galaxies in the range . However, uncertainties and possible systematics in
the observations do not allow for firm conclusions. We predict H and
rest-frame visible continuum observations with JWST, and show that JWST will be
able to detect extended (a few tens of kpc) fluorescent H emission
powered by ionizing photons escaping from a bright, , galaxy.
Such observations can differentiate fluorescent emission from nebular emission
by satellite sources. We discuss how observations and stacking of several
objects may provide unique constraints on the escape fraction for faint
galaxies and/or the abundance of ultra-faint radiation sources.Comment: 9 pages, 4 figures, re-submitted after referee report to Ap
On the Detectability of the Hydrogen 3-cm Fine Structure Line from the EoR
A soft ultraviolet radiation field, 10.2 eV < E <13.6 eV, that permeates
neutral intergalactic gas during the Epoch of Reionization (EoR) excites the 2p
(directly) and 2s (indirectly) states of atomic hydrogen. Because the 2s state
is metastable, the lifetime of atoms in this level is relatively long, which
may cause the 2s state to be overpopulated relative to the 2p state. It has
recently been proposed that for this reason, neutral intergalactic atomic
hydrogen gas may be detected in absorption in its 3-cm fine-structure line
(2s_1/2 -> 2p_3/2) against the Cosmic Microwave Background out to very high
redshifts. In particular, the optical depth in the fine-structure line through
neutral intergalactic gas surrounding bright quasars during the EoR may reach
tau~1e-5. The resulting surface brightness temperature of tens of micro K (in
absorption) may be detectable with existing radio telescopes. Motivated by this
exciting proposal, we perform a detailed analysis of the transfer of Lyman
beta,gamma,delta,... radiation, and re-analyze the detectability of the
fine-structure line in neutral intergalactic gas surrounding high-redshift
quasars. We find that proper radiative transfer modeling causes the
fine-structure absorption signature to be reduced tremendously to tau< 1e-10.
We therefore conclude that neutral intergalactic gas during the EoR cannot
reveal its presence in the 3-cm fine-structure line to existing radio
telescopes.Comment: 7 pages, 4 figures, MNRAS in press; v2. some typos fixe
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