4,488 research outputs found
New mechanism for primordial black hole formation during reheating
In the scalar field dark matter model virialized halos present condensed central cores called boson stars. Considering the equivalent process during reheating, we look at the formation of primordial black holes (PBHs) through the gravitational collapse of structures virialized in this era. We present the criteria necessary for collapse of either the whole structure, or that of the central core, in terms of the threshold amplitude for the primordial density contrast. This is computed for both the free and the self-interacting scalar fields. We discuss the relevance of our results for the abundance of PBHs
Assessing development strategies and Africa's food and nutrition security
"On average, a typical developing country in Africa is assisted by about 30 aid institutions in the implementation of development strategies, yet Africa is still far from achieving food and nutrition security. Adequate access to food that is necessary for food security must be complemented with provision of health services, education, sanitary environments, and safe water sources, among other resources, to achieve nutrition security." from TextDevelopment assistance ,Food security Africa ,Nutrition Security ,Health services ,Water quality ,Sanitation ,Development strategies ,
Development strategies and food and nutrition security in Africa: an assessment
"Momentum is building in and around Africa today for policy action to decisively confront hunger and malnutrition. If we are to succeed, it is vital that food and nutrition security strategies be both sound and able to be implemented. Ultimately, strategies deficient in either of these two areas will be ineffectual. Lessons from past strategies provide a valuable resource in the design of future strategies, yet there is a dearth of programmatic information and rigorous evaluations of the approaches used in the past. With this in mind, the authors of this 2020 discussion paper review the multitude of approaches and strategies for achieving food and nutrition security in Africa within the context of development over the past four decades. They assess the extent to which these plans have been implemented and identify the key constraints and limitations, along with the priority investments needed for more effective design and implementation in the future." Foreword by Joachim von Braun, Director General, IFPRIFood policy, Hunger, Malnutrition Africa, Food security Africa, Development policies, Assessment, Investments,
Impact de pulvérisations de deltaméthrine dans un foyer de leishmaniose de Bolivie
Une unique pulvérisation domiciliaire de K-Othrine à 0,025 g/m2, en début de saison humide, contrÎle efficacement les populations domestiques et péridomestiques de #Lutzomyia longipalpis, le vecteur de la leishmaniose viscérale, dans un village submontagnard de la province Nord-Yungas, Bolivie. Ce phlébotome est éliminé des habitations et des poulaillers durant, respectivement, 9 et 10 mois. Par contre, l'impact des traitements sur #Lu. nuneztovari anglesi, le vecteur présumé de la leishmaniose tégumentaire, est beaucoup moins marqué. Il se traduit, plus par une baisse de 50 % du taux de gorgement des populations capturées dans les maisons, que par une diminution de leur densité, difficile à apprécier du fait des variations saisonniÚres naturelles, et de l'absence de témoin représentatif. Ce résultat n'est pas inattendu, étant donné la forte exophilie de #Lu. n. anglesi$ dans la région. (Résumé d'auteur
Visualising COVID-19 Research
The world has seen in 2020 an unprecedented global outbreak of SARS-CoV-2, a
new strain of coronavirus, causing the COVID-19 pandemic, and radically
changing our lives and work conditions. Many scientists are working tirelessly
to find a treatment and a possible vaccine. Furthermore, governments,
scientific institutions and companies are acting quickly to make resources
available, including funds and the opening of large-volume data repositories,
to accelerate innovation and discovery aimed at solving this pandemic. In this
paper, we develop a novel automated theme-based visualisation method, combining
advanced data modelling of large corpora, information mapping and trend
analysis, to provide a top-down and bottom-up browsing and search interface for
quick discovery of topics and research resources. We apply this method on two
recently released publications datasets (Dimensions' COVID-19 dataset and the
Allen Institute for AI's CORD-19). The results reveal intriguing information
including increased efforts in topics such as social distancing; cross-domain
initiatives (e.g. mental health and education); evolving research in medical
topics; and the unfolding trajectory of the virus in different territories
through publications. The results also demonstrate the need to quickly and
automatically enable search and browsing of large corpora. We believe our
methodology will improve future large volume visualisation and discovery
systems but also hope our visualisation interfaces will currently aid
scientists, researchers, and the general public to tackle the numerous issues
in the fight against the COVID-19 pandemic.Comment: 11 pages. 10 figures. Preprint paper made available here prior to
submission. Update: special characters correcte
SODES: Solving ordinary differential equations step by step
In this paper, we introduce SODES (Stepwise Ordinary Differential Equations Solver) a new solver for Ordinary Differential Equations (ODE). SODES can optionally provide the solution displaying all the steps needed to obtain it. This way, SODES is an important tool not only for researchers who need solving ODE but also constitutes an important tool for the teaching and learning process of ODE. SODES has been developed using programming with a Computer Algebra System (CAS). Specifically, we use the CAS Derive but it can be easily adapted to any other CAS supporting programming.
SODES provides, step by step, the solution of the following types of ODE: separable, homogeneous, exact, integrating factors, linear, Bernoulli, Riccati, first order ODE of nth degree, Cauchyâs problems of first order ODE, higher order linear homogeneous
equations with constant coefficients, Lagrangeâs method for particular solutions of higher order linear equations with constant coefficients, higher order linear equations with constant coefficients and Cauchyâs problems of higher order linear equations with
constant coefficients. SODES also deals with two generic programs which determine the type or types of a given ODE and provides the solution.
In this paper we will also introduce a draft of a Graphical User Interface (GUI) for SODES in a local web application using programming in Python (using its CAS module SymPy) which is a more portable and free CAS. This draft can be used in English, French and Spanish, and can be easily extended to other languages.
The code of SODES and the GUI are freely available so that it can be used by users who also will be able to adapt it to their needsFunding for open access charge: Universidad de MĂĄlaga / CBU
Clustering and descendants of MUSYC galaxies at z<1.5
We measure the evolution of galaxy clustering out to a redshift of z~1.5
using data from two MUSYC fields, the Extended Hubble Deep Field South (EHDF-S)
and the Extended Chandra Deep Field South (ECDF-S). We use photometric redshift
information to calculate the projected-angular correlation function,
omega(sigma), from which we infer the projected correlation function Xi(sigma).
We demonstrate that this technique delivers accurate measurements of clustering
even when large redshift measurement errors affect the data. To this aim we use
two mock MUSYC fields extracted from a LambdaCDM simulation populated with
GALFORM semi-analytic galaxies which allow us to assess the degree of accuracy
of our estimates of Xi(sigma) and to identify and correct for systematic
effects in our measurements. We study the evolution of clustering for volume
limited subsamples of galaxies selected using their photometric redshifts and
rest-frame r-band absolute magnitudes. We find that the real-space correlation
length r_0 of bright galaxies, M_r<-21 (rest-frame) can be accurately recovered
out to z~1.5, particularly for ECDF-S given its near-infrared photometric
coverage. There is mild evidence for a luminosity dependent clustering in both
fields at the low redshift samples (up to =0.57), where the correlation
length is higher for brighter galaxies by up to 1Mpc/h between median
rest-frame r-band absolute magnitudes of -18 to -21.5. As a result of the
photometric redshift measurement, each galaxy is assigned a best-fit template;
we restrict to E and E+20%Sbc types to construct subsamples of early type
galaxies (ETGs). Our ETG samples show a strong increase in r_0 as the redshift
increases, making it unlikely (95% level) that ETGs at median redshift
z_med=1.15 are the direct progenitors of ETGs at z_med=0.37 with equivalent
passively evolved luminosities. (ABRIDGED)Comment: 16 pages, 12 figures, 2 tables, accepted for publication in MNRA
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