15,054 research outputs found
Sub-femtosecond electron bunches created by direct laser acceleration in a laser wakefield accelerator with ionization injection
In this work, we will show through three-dimensional particle-in-cell
simulations that direct laser acceleration in laser a wakefield accelerator can
generate sub-femtosecond electron bunches. Two simulations were done with two
laser pulse durations, such that the shortest laser pulse occupies only a
fraction of the first bubble, whereas the longer pulse fills the entire first
bubble. In the latter case, as the trapped electrons moved forward and
interacted with the high intensity region of the laser pulse, micro-bunching
occurred naturally, producing 0.5 fs electron bunches. This is not observed in
the short pulse simulation.Comment: AAC 201
Anglo-American Relations Before 1580
Paper read before the Historical Society of the Rice Institute on April 12, 195
The population of hot subdwarf stars studied with Gaia II. The Gaia DR2 catalogue of hot subluminous stars
Based on data from the ESA Gaia Data Release 2 (DR2) and several
ground-based, multi-band photometry surveys we compiled an all-sky catalogue of
hot subluminous star candidates selected in Gaia DR2 by means of
colour, absolute magnitude and reduced proper motion cuts. We expect the
majority of the candidates to be hot subdwarf stars of spectral type B and O,
followed by blue horizontal branch stars of late B-type (HBB), hot post-AGB
stars, and central stars of planetary nebulae. The contamination by cooler
stars should be about . The catalogue is magnitude limited to Gaia
and covers the whole sky. Except within the Galactic plane
and LMC/SMC regions, we expect the catalogue to be almost complete up to about
. The main purpose of this catalogue is to serve as input
target list for the large-scale photometric and spectroscopic surveys which are
ongoing or scheduled to start in the coming years. In the long run, securing a
statistically significant sample of spectroscopically confirmed hot subluminous
stars is key to advance towards a more detailed understanding of the latest
stages of stellar evolution for single and binary stars.Comment: 13 pages, A&A, accepte
Analysis of B and Be Star Populations of the Double Cluster h and chi Persei
We present blue optical spectra of 92 members of h and chi Per obtained with
the WIYN telescope at Kitt Peak National Observatory. From these spectra,
several stellar parameters were measured for the B-type stars, including V sin
i, T_eff, log g_polar, M_star, and R_star. Stromgren photometry was used to
measure T_eff and log g_polar for the Be stars. We also analyze photometric
data of cluster members and discuss the near-to-mid IR excesses of Be stars.Comment: 4 pages, to appear in the proceedings of IAU Symposium 266: Star
Cluster
A STRUCTURAL-EQUATION GME ESTIMATOR
A generalized maximum entropy estimator is developed for the linear simultaneous equations systems model. We provide results on large and small sample properties of the estimator. Empirical results illustrate efficiency advantages of the generalized maximum entropy estimator proposed in this study over traditional estimators (e.g., 2SLS and 3SLS).Research Methods/ Statistical Methods,
Studies of Intestinal Lymphoid Tissue. XI – The Immunopathology of Cell-Mediated Reactions in Gluten Sensitivity and Other Enteropathies
Computerised image-analysis was used to quantitate small intestinal mucosae from celiac sprue and dermatitis herpetiformis patients, Gambian children with tropical-sprue-like malabsorption, first-degree celiac sprue relatives, and treated celiac sprue patients during challenge with a peptic-tryptic digest of gluten. A wide range of mucosal appearances was observed. Typically, \u27flat\u27 lesions (Type 2) revealed a reduced number of epithelial lymphocytes that were large and mitotically active. At the other extreme, mucosal architecture was relatively well preserved (Type 1) but surface epithelium contained an expanded population of small, non-mitotic lymphocytes, with or without crypt hyperplasia. Similar changes were observed in one-third of celiac relatives and following small dose gluten challenge. Larger dose challenges revealed a transition from Type 1 to Type 2 lesions over a 5-day period. Studies in a few patients over 2-4 years showed a similar type of progression. A major feature of this sequence was early appearance of crypt hypertrophy while villi persisted, indicating a role for factors other than increased loss of enterocytes from surface epithelium. These changes parallel the T lymphocyte-mediated events in graft-versus-host reactions in animals. It is thus concluded that the spectrum of immunopathologic changes observed in gluten sensitivity is fundamentally a cell-mediated effect, the degree of change being controlled by host genetic factors. In becoming flat, it appears obligatory for the mucosa to evolve through the earlier Type 1 lesion in which crypt hypertrophy is a prominent response
The Grassmannian Sigma Model in SU(2) Yang-Mills Theory
Spin-charge separation in pure SU(2) Yang-Mills theory was recently found to
involve the dynamics of an O(3) non-linear sigma model and, seemingly, a
Grassmannian non-linear sigma model. In this article we explicitly construct
the Grassmannian sigma model of the form appearing in the the spin-charge
separated SU(2) theory through a quaternionic decomposition of the manifold,
thus verifying its relevance in this context. The coupling between this model
and the O(3) non-linear sigma model is further commented upon.Comment: 11 pages, undergraduate research project; version published in J.
Phys.
Geologic applications of thermal inertia image using HCMM data
The author has identified the following significant results. Comparison of a simulated HCMM image of the Pisgah Crater, California test site obtained from aircraft data with an image generated from the preliminary satellite data tape of the area indicates that the HCMM satellite data appears much as predicted by the simulation
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