5,676 research outputs found
Lensed: a code for the forward reconstruction of lenses and sources from strong lensing observations
Robust modelling of strong lensing systems is fundamental to exploit the
information they contain about the distribution of matter in galaxies and
clusters. In this work, we present Lensed, a new code which performs forward
parametric modelling of strong lenses. Lensed takes advantage of a massively
parallel ray-tracing kernel to perform the necessary calculations on a modern
graphics processing unit (GPU). This makes the precise rendering of the
background lensed sources much faster, and allows the simultaneous optimisation
of tens of parameters for the selected model. With a single run, the code is
able to obtain the full posterior probability distribution for the lens light,
the mass distribution and the background source at the same time. Lensed is
first tested on mock images which reproduce realistic space-based observations
of lensing systems. In this way, we show that it is able to recover unbiased
estimates of the lens parameters, even when the sources do not follow exactly
the assumed model. Then, we apply it to a subsample of the SLACS lenses, in
order to demonstrate its use on real data. The results generally agree with the
literature, and highlight the flexibility and robustness of the algorithm.Comment: v2: major revision; accepted by MNRAS; lens reconstruction code
available at http://glenco.github.io/lensed
Environmental, human health and socio-economic effects of cement powders: The multicriteria analysis as decisional methodology
The attention to sustainability-related issues has grown fast in recent decades. The experience gained with these themes reveals the importance of considering this topic in the construction industry, which represents an important sector throughout the world. This work consists on conducting a multicriteria analysis of four cement powders, with the objective of calculating and analysing the environmental, human health and socio-economic effects of their production processes. The economic, technical, environmental and safety performances of the examined powders result from official, both internal and public, documents prepared by the producers. The Analytic Hierarchy Process permitted to consider several indicators (i.e., environmental, human health related and socio-economic parameters) and to conduct comprehensive and unbiased analyses which gave the best, most sustainable cement powder. As assumed in this study, the contribution of each considered parameter to the overall sustainability has a different incidence, therefore the procedure could be used to support on-going sustainability efforts under different conditions. The results also prove that it is not appropriate to regard only one parameter to identify the ‘best’ cement powder, but several impact categories should be considered and analysed if there is an interest for pursuing different, often conflicting interests
Zooming into the Cosmic Horseshoe: new insights on the lens profile and the source shape
The gravitational lens SDSS J1148+1930, also known as the Cosmic Horseshoe,
is one of the biggest and of the most detailed Einstein rings ever observed. We
use the forward reconstruction method implemented in the lens fitting code
Lensed to investigate with great detail the properties of the lens and of the
background source. We model the lens with different mass distributions,
focusing in particular on the determination of the slope of the dark matter
component. The inherent degeneracy between the lens slope and the source size
can be broken when we can isolate separate components of each lensed image, as
in this case. For an elliptical power law model, , the
results favour a flatter-than-isothermal slope with a maximum-likelihood value
t = 0.08. Instead, when we consider the contribution of the baryonic matter
separately, the maximum-likelihood value of the slope of the dark matter
component is t = 0.31 or t = 0.44, depending on the assumed Initial Mass
Function. We discuss the origin of this result by analysing in detail how the
images and the sources change when the slope t changes. We also demonstrate
that these slope values at the Einstein radius are not inconsistent with recent
forecast from the theory of structure formation in the LambdaCDM model.Comment: 13 pages, 9 figures, accepted for publication in MNRA
AMICO: optimised detection of galaxy clusters in photometric surveys
We present AMICO (Adaptive Matched Identifier of Clustered Objects), a new
algorithm for the detection of galaxy clusters in photometric surveys. AMICO is
based on the Optimal Filtering technique, which allows to maximise the
signal-to-noise ratio of the clusters. In this work we focus on the new
iterative approach to the extraction of cluster candidates from the map
produced by the filter. In particular, we provide a definition of membership
probability for the galaxies close to any cluster candidate, which allows us to
remove its imprint from the map, allowing the detection of smaller structures.
As demonstrated in our tests, this method allows the deblending of close-by and
aligned structures in more than of the cases for objects at radial
distance equal to or redshift distance equal to , being the typical uncertainty of photometric redshifts.
Running AMICO on mocks derived from N-body simulations and semi-analytical
modelling of the galaxy evolution, we obtain a consistent mass-amplitude
relation through the redshift range , with a logarithmic slope
and a logarithmic scatter . The fraction of false
detections is steeply decreasing with S/N, and negligible at S/N > 5.Comment: 18 pages, accepted for publication in MNRA
Scinax granulatus (NCN). Argentina: Buenos Aires
Partido de General Pueyrredon. Sierra de Los Padres (37° 56' 25"S 57 °47' 41" W). 24 July 2010. L. E.Vega & P. J.Bellagamba. Verified by J. Faivovich. Herpetological Collection of Laboratorio Vertebrados, Departamento de BiologÃa, Universidad Nacional de Mar del Plata (UNMdP 1809, UNMdP 1810). Two adult individuals were captured under rocks in the ridge of mountains of Sierra de los Padres of the Tandilia Mountain Range System. Another five individuals were detected inactive in similar microhabitats (under rocks). Barrasso and Cajade (Barraso, D. and R. Cajade. 2007. Geographic distribution: Scinax granulatus. Herpetol. Rev. 38: 1) pointed out that Gallardo mentioned two specimens from Sierra de la Ventana, but such citation is not supported by voucher specimens, therefore this is the first documentation of this frog inhabiting mountain environments at 170 MASL...Fil: Vega, Laura Estela. Universidad Nacional de Mar del Plata. Instituto de BiologÃa; ArgentinaFil: Bellagamba, Patricio J.. Universidad Nacional de Mar del Plata. Instituto de BiologÃa; ArgentinaFil: Stellatelli, Oscar AnÃbal. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de Mar del Plata. Instituto de BiologÃa; ArgentinaFil: Natale, Guillermo Sebastian. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de QuÃmica. Centro de Investigaciones del Medio Ambiente; Argentin
Legacies of Slavery and Popular Traditions of Freedom in Southern Senegal (1860–1960)
This study examines the historical linkages that developed between experiences of enslavement, the legacies of slavery, and ideas of freedom before and after abolition in the early twentieth century in an area of southern Senegal known today as the Kolda region. In the Fulfulde language, spoken by the majority of the population, there are several terms and expressions to talk about freedom. The first is ndimaaku, which people tend to equate with nobility and dignity. This is the freedom of the olden days of slavery, when the capacities and qualities of the male or female freeborn stood in stark contrast to those of the slave, and being free meant not having been a slave in the first place. The second term is heɓtaare, i.e., freedom in the sense of tranquility, economic well-being, and a general ease in life and social relations. The expression jeyaal-hoore mun conveys a sense of independence, self-mastery and autonomy, while heɓtugol hoore mun literally means to retrieve one's head, the center of individual thought and capacity for independent action. Politically, heɓtugol hoore mun stands for the end of colonial rule and the achievement of national independence. Socially, it refers to the emancipation of subordinated groups, like the youth and women, and it describes slaves who freed themselves from their masters. Drawing from archival sources and oral history, this essay attempts to reconstruct the discursive reconfigurations of local ideas of freedom within the context of the political and social changes that affected the Kolda region in the late nineteenth century, the early colonial period, and the years before decolonization. Each historical period had its own actors, dynamics and complexities in which slavery and then legacies of slavery played a role in the definition of freedom and the entitlement of people to its benefits. As demonstrated here, however, liberation paved the way for other forms of subjugation
Ideazione e sviluppo di una tecnica, a costi d’investimento trascurabili, per la valutazione della viabilità stradale utilizzando dati estraibili dalla rete cellulare
Utilizzando solo dati di cui una società di telefonia mobile dispone è possibile valutare la congestione del traffico veicolare.
La tecnica, sviluppata nella Tesi, è in grado di produrre, a costi d’investimento trascurabili, informazioni sulla viabilità stradale e può essere utilizzata per penetrare nel mercato dei "content provider" per i servizi di infotraffico
Weighing simulated galaxy clusters using lensing and X-ray
We aim at investigating potential biases in lensing and X-ray methods to
measure the cluster mass profiles. We do so by performing realistic simulations
of lensing and X-ray observations that are subsequently analyzed using
observational techniques. The resulting mass estimates are compared among them
and with the input models. Three clusters obtained from state-of-the-art
hydrodynamical simulations, each of which has been projected along three
independent lines-of-sight, are used for this analysis. We find that strong
lensing models can be trusted over a limited region around the cluster core.
Extrapolating the strong lensing mass models to outside the Einstein ring can
lead to significant biases in the mass estimates, if the BCG is not modeled
properly for example. Weak lensing mass measurements can be largely affected by
substructures, depending on the method implemented to convert the shear into a
mass estimate. Using non-parametric methods which combine weak and strong
lensing data, the projected masses within R200 can be constrained with a
precision of ~10%. De-projection of lensing masses increases the scatter around
the true masses by more than a factor of two due to cluster triaxiality. X-ray
mass measurements have much smaller scatter (about a factor of two smaller than
the lensing masses) but they are generally biased low by 5-20%. This bias is
ascribable to bulk motions in the gas of our simulated clusters. Using the
lensing and the X-ray masses as proxies for the true and the hydrostatic
equilibrium masses of the simulated clusters and averaging over the cluster
sample we are able to measure the lack of hydrostatic equilibrium in the
systems we have investigated.Comment: 27 pages, 21 figures, accepted for publication on A&A. Version with
full resolution images can be found at
http://pico.bo.astro.it/~massimo/Public/Papers/massComp.pd
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