2,168 research outputs found
The Presbyter John Controversy
The purpose of this paper is to investigate the problem of the Presbyter John by following the controversy that has raged around his name, by taking a look at the status of the controversy today, and by considering the evidence in regard to some of the chief matters in the controversy
Stealing Cars: Technology and Society from the Model T to the Gran Torino
Stealing Cars brings together expertise from the history of technology and cultural history as well as city planning and transborder studies to produce a compelling and detailed work that raises questions concerning American priorities and values. Drawing on sources that include interviews, government documents, patents, sociological and psychological studies, magazines, monographs, scholarly periodicals, film, fiction, and digital gaming, Heitmann and Morales tell a story that highlights both human creativity and some of the paradoxes of American life
Three-Dimensionally Confined Optical Modes in Quantum Well Microtube Ring Resonators
We report on microtube ring resonators with quantum wells embedded as an
optically active material. Optical modes are observed over a broad energy
range. Their properties strongly depend on the exact geometry of the microtube
along its axis. In particular we observe (i) preferential emission of light on
the inside edge of the microtube and (ii) confinement of light also in
direction of the tube axis by an axially varying geometry which is explained in
an expanded waveguide model.Comment: 5 pages, 4 figure
An inclusion result for dagger closure in certain section rings of abelian varieties
We prove an inclusion result for graded dagger closure for primary ideals in
symmetric section rings of abelian varieties over an algebraically closed field
of arbitrary characteristic.Comment: 11 pages, v2: updated one reference, fixed 2 typos; final versio
Picovoltmeter for probing vortex dynamics in a single weak-pinning Corbino channel
We have developed a picovoltmeter using a Nb dc Superconducting QUantum
Interference Device (SQUID) for measuring the flux-flow voltage from a small
number of vortices moving through a submicron weak-pinning superconducting
channel. We have applied this picovoltmeter to measure the vortex response in a
single channel arranged in a circle on a Corbino disk geometry. The circular
channel allows the vortices to follow closed orbits without encountering any
sample edges, thus eliminating the influence of entry barriers.Comment: 4 pages, 3 figures, submitted to Review of Scientific Instrument
Robustness of Cosmological Simulations I: Large Scale Structure
The gravitationally-driven evolution of cold dark matter dominates the
formation of structure in the Universe over a wide range of length scales.
While the longest scales can be treated by perturbation theory, a fully
quantitative understanding of nonlinear effects requires the application of
large-scale particle simulation methods. Additionally, precision predictions
for next-generation observations, such as weak gravitational lensing, can only
be obtained from numerical simulations. In this paper, we compare results from
several N-body codes using test problems and a diverse set of diagnostics,
focusing on a medium resolution regime appropriate for studying many
observationally relevant aspects of structure formation. Our conclusions are
that -- despite the use of different algorithms and error-control methodologies
-- overall, the codes yield consistent results. The agreement over a wide range
of scales for the cosmological tests is test-dependent. In the best cases, it
is at the 5% level or better, however, for other cases it can be significantly
larger than 10%. These include the halo mass function at low masses and the
mass power spectrum at small scales. While there exist explanations for most of
the discrepancies, our results point to the need for significant improvement in
N-body errors and their understanding to match the precision of near-future
observations. The simulation results, including halo catalogs, and initial
conditions used, are publicly available.Comment: 32 pages, 53 figures, data from the simulations is available at
http://t8web.lanl.gov/people/heitmann/arxiv, accepted for publication in
ApJS, several minor revisions, reference added, main conclusions unchange
The Impact of Cluster Structure and Dynamical State on Scatter in the Sunyaev-Zel'dovich Flux-Mass Relation
Cosmological constraints from cluster surveys rely on accurate mass estimates
from the mass-observable relations. In order to avoid systematic biases and
reduce uncertainties, we study the form and physical origin of the intrinsic
scatter about the mean Sunyaev-Zel'dovich (SZ) flux-mass relation using a
hydrodynamical simulation of galaxy cluster formation. We examine the
assumption of lognormal scatter and detect non-negligible positive skewness and
kurtosis (> 0.5) for a wide range of limiting masses and redshifts. These
higher-order moments should be included in the parametrization of scatter in
order not to bias cosmological constraints. We investigate the sources of the
scatter by correlating it with measures of cluster morphology, halo
concentration, and dynamical state, and we quantify the individual contribution
from each source. We find that statistically the impact of dynamical state is
weak, so the selection bias due to mergers is negligible. On the other hand,
there is a strong correlation between the scatter and halo concentration, which
can be used to reduce the scatter significantly (from 12.07% to 7.34% or by
~40% for clusters at z = 0). We also show that a cross-calibration by combining
information from X-ray followups can be used to reduce the scatter in the
flux-mass relation and also identify outliers in both X-ray and SZ cluster
surveys.Comment: 14 pages, 12 figures; accepted for publication in Ap
The Halo Mass Function: High-Redshift Evolution and Universality
We study the formation of dark matter halos in the concordance LCDM model
over a wide range of redshifts, from z=20 to the present. Our primary focus is
the halo mass function, a key probe of cosmology. By performing a large suite
of nested-box N-body simulations with careful convergence and error controls
(60 simulations with box sizes from 4 to 256 Mpc/h, we determine the mass
function and its evolution with excellent statistical and systematic errors,
reaching a few percent over most of the considered redshift and mass range.
Across the studied redshifts, the halo mass is probed over 6 orders of
magnitude (10^7 - 10^13.5 M_sun/h). Historically, there has been considerable
variation in the high redshift mass function as obtained by different groups.
We have made a concerted effort to identify and correct possible systematic
errors in computing the mass function at high redshift and to explain the
discrepancies between some of the previous results. We discuss convergence
criteria for the required force resolution, simulation box size, halo mass
range, initial and final redshift, and time stepping. Because of conservative
cuts on the mass range probed by individual boxes, our results are relatively
insensitive to simulation volume, the remaining sensitivity being consistent
with extended Press-Schechter theory. Previously obtained mass function fits
near z=0, when scaled by linear theory, are in good agreement with our results
at all redshifts, although a mild redshift dependence consistent with that
found by Reed and collaborators exists at low redshifts.Comment: 20 pages, 15 figures. Minor changes to the text and figures; results
and conclusions unchange
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