16,892 research outputs found
Review of Seabird Demographic Rates and Density Dependence. JNCC Report no. 552
Introduction
This report presents individual species accounts for a selection of British seabirds, sea ducks, divers and grebes. Each account gathers the most up to date published estimates on the following demographic parameters: age-specific survival, age-specific productivity, age of recruitment, incidence of missed breeding, and natal and adult breeding dispersal. Particular attention has been given to regional variation in demographic rates, indicating the extent to which estimates may be applied to other less-well studied colonies. Where possible, the intrinsic and extrinsic factors that influence demographic rates are also detailed.
The reported rates should enable population models that assess the impacts of offshore wind farms to be developed as reliably and realistically as possible. Where sufficient data could not be gathered using UK examples, data from colonies outside of the UK have been presented, or a proxy species has been identified. The evidence for density-dependent regulation of seabird demographic rates is also reviewed using examples from the UK, as well as non-UK studies on similar species
Patterns of Financing: A Comparison Between White- and African-American Young Firms
Based on Kauffman Firm Survey data, examines differences in start-up and follow-on capital injections into and capital use by firms with African-American and white owners. Explores how access to capital affects the racial gap in new business formation
Motion of a distinguishable impurity in the Bose gas: Arrested expansion without a lattice and impurity snaking
We consider the real time dynamics of an initially localized distinguishable
impurity injected into the ground state of the Lieb-Liniger model. Focusing on
the case where integrability is preserved, we numerically compute the time
evolution of the impurity density operator in regimes far from analytically
tractable limits. We find that the injected impurity undergoes a stuttering
motion as it moves and expands. For an initially stationary impurity, the
interaction-driven formation of a quasibound state with a hole in the
background gas leads to arrested expansion -- a period of quasistationary
behavior. When the impurity is injected with a finite center of mass momentum,
the impurity moves through the background gas in a snaking manner, arising from
a quantum Newton's cradle-like scenario where momentum is exchanged
back-and-forth between the impurity and the background gas.Comment: v1: 13 pages, 10 figures; v2: 14 pages, 13 figures and change of
titl
Night Moment and Spring
Poems include: Night Moment , by Robert Schalk and Spring , by Wyoming Robinso
Derivatives of the Incomplete Beta Function
The incomplete beta function is defined as where Beta(p, q) is the beta function. Dutka (1981) gave a history of the development and numerical evaluation of this function. In this article, an algorithm for computing first and second derivatives of Ix,p,q with respect to p and q is described. The algorithm is useful, for example, when fitting parameters to a censored beta, truncated beta, or a truncated beta-binomial model.
Modeling the Infrared Reverberation Response of the Circumnuclear Dusty Torus in AGN: The Effects of Cloud Orientation and Anisotropic Illumination
The obscuring circumnuclear torus of dusty molecular gas is one of the major
components of active galactic nuclei (AGN). The torus can be studied by
analyzing the time response of its infrared (IR) dust emission to variations in
the AGN continuum luminosity, a technique known as reverberation mapping. The
IR response is the convolution of the AGN ultraviolet/optical light curve with
a transfer function that contains information about the size, geometry, and
structure of the torus. Here, we describe a new computer model that simulates
the reverberation response of a clumpy torus. Given an input optical light
curve, the code computes the emission of a 3D ensemble of dust clouds as a
function of time at selected IR wavelengths, taking into account light travel
delays. We present simulated dust emission responses at 3.6, 4.5, and 30 m
that explore the effects of various geometrical and structural properties, dust
cloud orientation, and anisotropy of the illuminating radiation field. We also
briefly explore the effects of cloud shadowing (clouds are shielded from the
AGN continuum source). Example synthetic light curves have also been generated,
using the observed optical light curve of the Seyfert 1 galaxy NGC 6418 as the
input. The torus response is strongly wavelength-dependent, due to the gradient
in cloud surface temperature within the torus, and because the cloud emission
is strongly anisotropic at shorter wavelengths. Anisotropic illumination of the
torus also significantly modifies the torus response, reducing the lag between
the IR and optical variations.Comment: 17 pages, 14 figures, published in the Astrophysical Journal (2017
July 1
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Matrix Metalloproteinases and Glaucoma Treatment.
Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that degrade extracellular matrix (ECM) components such as collagen and have important roles in multiple biological processes, including development and tissue remodeling, both in health and disease. The activity of MMPs is influenced by the expression of MMPs and tissue inhibitors of metalloproteinase (TIMPs). In the eye, MMP-mediated ECM turnover in the juxtacanalicular region of the trabecular meshwork (TM) reduces outflow resistance in the conventional outflow pathway and helps maintain intraocular pressure (IOP) homeostasis. An imbalance in the MMP/TIMP ratio may be involved in the elevated IOP often associated with glaucoma. The prostaglandin analog/prostamide (PGA) class of topical ocular hypotensive medications used in glaucoma treatment reduces IOP by increasing outflow through both conventional and unconventional (uveoscleral) outflow pathways. Evidence from in vivo and in vitro studies using animal models and anterior segment explant and cell cultures indicates that the mechanism of IOP lowering by PGAs involves increased MMP expression in the TM and ciliary body, leading to tissue remodeling that enhances conventional and unconventional outflow. PGA effects on MMP expression are dependent on the identity and concentration of the PGA. An intracameral sustained-release PGA implant (Bimatoprost SR) in development for glaucoma treatment can reduce IOP for many months after expected intraocular drug bioavailability. We hypothesize that the higher concentrations of bimatoprost achieved in ocular outflow tissues with the implant produce greater MMP upregulation and more extensive, sustained MMP-mediated target tissue remodeling, providing an extended duration of effect
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