Accurate Modeling of Weak Lensing with the sGL Method

We revise and extend the stochastic approach to cumulative weak lensing (hereafter the sGL method) first introduced in Ref. [1]. Here we include a realistic halo mass function and density profiles to model the distribution of mass between and within galaxies, galaxy groups and galaxy clusters. We also introduce a modeling of the filamentary large-scale structures and a method to embed halos into these structures. We show that the sGL method naturally reproduces the weak lensing results for the Millennium Simulation. The strength of the sGL method is that a numerical code based on it can compute the lensing probability distribution function for a given inhomogeneous model universe in a few seconds. This makes it a useful tool to study how lensing depends on cosmological parameters and its impact on observations. The method can also be used to simulate the effect of a wide array of systematic biases on the observable PDF. As an example we show how simple selection effects may reduce the variance of observed PDF, which could possibly mask opposite effects from very large scale structures. We also show how a JDEM-like survey could constrain the lensing PDF relative to a given cosmological model. The updated turboGL code is available at turboGL.org.Comment: PRD style: 20 pages, 10 figures; replaced to match the improved version accepted for publication in PRD. The updated turboGL code can be downloaded at http://www.turbogl.org

Observational constraints on inhomogeneous cosmological models without dark energy

It has been proposed that the observed dark energy can be explained away by the effect of large-scale nonlinear inhomogeneities. In the present paper we discuss how observations constrain cosmological models featuring large voids. We start by considering Copernican models, in which the observer is not occupying a special position and homogeneity is preserved on a very large scale. We show how these models, at least in their current realizations, are constrained to give small, but perhaps not negligible in certain contexts, corrections to the cosmological observables. We then examine non-Copernican models, in which the observer is close to the center of a very large void. These models can give large corrections to the observables which mimic an accelerated FLRW model. We carefully discuss the main observables and tests able to exclude them.Comment: 27 pages, 7 figures; invited contribution to CQG special issue "Inhomogeneous Cosmological Models and Averaging in Cosmology". Replaced to match the improved version accepted for publication. Appendix B and references adde

Spatially structured brown-headed cowbird control measures and their effects on Kirtland’s warbler long-term population sustainability

Context: Brown-headed cowbirds (Molothrus ater), through brood parasitism, can exert extrinsic population growth pressures on North American songbirds. Cowbird removal programs may reduce parasitism rates on host species but can be expensive and difficult to implement throughout a host species’ breeding range. Aim: We estimated cowbird abundance and nest parasitism rates within Kirtland’s warbler (Setophaga kirtlandii) primary breeding range in Michigan, USA, and determined the maximum sustainable parasitism rate for Kirtland’s warblers under several spatially structured cowbird removal designs. Methods: We conducted point counts to estimate cowbird abundance and monitored nests to quantify nest parasitism rates during 2019–2021. We used the modelling software STELLA to determine the maximum sustainable parasitism rate for Kirtland’s warblers under different spatially structured cowbird removal scenarios (complete, core-only, and no removal). Key results: Cowbird abundance and parasitism rates remained low following cowbird trap closures in 2018. In the simulation study, complete removal was the most robust scenario with no replications having \u3c1000 Kirtland’s warbler males. The core-only removal scenario had a substantially higher sustainable parasitism rate in the peripheral breeding area than the no removal scenario. Assumed hatch-year dispersal distance had the greatest impact on the maximum sustainable parasitism rate in the core-only scenario. Conclusions: Low cowbird abundance and nest parasitism following suspension of cowbird removal efforts showed resuming the removal program may not be required in the short-term. If cowbird abundance increases, however, adaptive cowbird removal programs can be used to sustain Kirtland’s warbler populations long-term. Implications: Our results indicate that incorporating spatial structure of host species’ habitat into designing cowbird removal programs may minimise costs of cowbird management while sustaining populations of Kirtland’s warbler and possibly other host species that are affected by brood parasitism

Brief communication: The potential use of low-cost acoustic sensors to detect rainfall for short-term urban flood warnings

Floods in urban areas are one of the most common natural hazards. Due to climate change enhancing extreme rainfall and cities becoming larger and denser, the frequency, magnitude, and impact of these events are expected to increase. Pluvial floods can occur in urban areas within minutes. A fast and reliable rainfall detection system should thus be implemented in flood-prone cities to warn the public of upcoming floods and save lives and reduce damage. The purpose of this brief communication is to discuss the potential implementation of low-cost acoustic rainfall sensors in short-term flood warning systems.</p

High phytoplankton growth and production rates in oligotrophic Hawaiian coastal waters

Plankton biomass, material fluxes, e.g. 14C uptake, and specific growth rates are related quantities. In the course of comparing various methods of measuring these properties in September 1982 off Oahu, Hawaii, we found specific growth rates of 1–2·d−1. Such rates approach the maximum expected values observed in laboratory cultures

Modelling the impact of women’s education on fertility in Malawi

Many studies have suggested that there is an inverse relationship between education and number of children among women from sub-Saharan Africa countries, including Malawi. However, a crucial limitation of these analyses is that they do not control for the potential endogeneity of education. The aim of our study is to estimate the role of women’s education on their number of children in Malawi, accounting for the possible presence of endogeneity and for nonlinear effects of continuous observed confounders. Our analysis is based on micro data from the 2010 Malawi Demographic Health Survey, and uses a flexible instrumental variable regression approach. The results suggest that the relationship of interest is affected by endogeneity and exhibits an inverted U-shape among women living in rural areas of Malawi, whereas it exhibits an inverse (nonlinear) relationship for women living in urban areas

Averaging inhomogeneities in scalar-tensor cosmology

The backreaction of inhomogeneities on the cosmic dynamics is studied in the context of scalar-tensor gravity. Due to terms of indefinite sign in the non-canonical effective energy tensor of the Brans-Dicke-like scalar field, extra contributions to the cosmic acceleration can arise. Brans-Dicke and metric f(R) gravity are presented as specific examples. Certain representation problems of the formalism peculiar to these theories are pointed out.Comment: Comments and references added. 14 page