The Cosmological Constant

This is a review of the physics and cosmology of the cosmological constant. Focusing on recent developments, I present a pedagogical overview of cosmology in the presence of a cosmological constant, observational constraints on its magnitude, and the physics of a small (and potentially nonzero) vacuum energy.Comment: 50 pages. Submitted to Living Reviews in Relativity (http://www.livingreviews.org/), December 199

Bulk viscous cosmological model with interacting dark fluids

The objective of the present work is to study a cosmological model for a spatially flat Universe whose constituents are a dark energy field and a matter field which includes baryons and dark matter. The constituents are supposed to be in interaction and irreversible processes are taken into account through the inclusion of a non-equilibrium pressure. The non-equilibrium pressure is considered to be proportional to the Hubble parameter within the framework of a first order thermodynamic theory. The dark energy and matter fields are coupled by their barotropic indexes, which are considered as functions of the ratio between their energy densities. The free parameters of the model are adjusted from the best fits of the Hubble parameter data. A comparison of the viscous model with the non-viscous one is performed. It is shown that the equality of the dark energy and matter density parameters and the decelerated-accelerated transition occur at earlier times when the irreversible processes are present. Furthermore, the density and deceleration parameters and the distance modulus have the correct behavior which is expected for a viable scenario of the present status of the Universe.Comment: 10 pages, 7 figures, to be published in Brazilian Journal of Physic

Relations between assemblages of carpological remains and modern vegetation in a shallow reservoir in southern Poland

This paper explores relations between assemblages of carpological remains and vegetation in and around a small, shallow reservoir in southern Poland. The study was conducted from 2006 to 2008. Quantity and distribution of species in the reservoir were recorded annually during the growing season. In October 2008, 40 samples of surface sediment (top 2 cm) were collected along transects at 10 m intervals. Samples of 100 cm3 were prepared for analysis of plant macroremains. Assemblages of carpological remains generally reflect local vegetation well. In some cases, however, even analysis of numerous samples failed to fully capture the species composition or reflect plant ratios in the parent phytocenosis. Reasons for this include factors that affect seed production, transport and fossilization, which differ among species. Among the best-represented macroremains were plants of the rush phytocenosis. In analysed samples, macroremains of 68.8 % of extant rushes were identified. Sixty percent of submerged and floating-leaf taxa were found in carpological samples, whereas 26.7 % of the trees and bushes were represented in sediment deposits. Species composition of phytocenoses in the reservoir and in surrounding areas was best reflected by macroremains from the nearby reed bed. Numbers of diaspores of Mentha aquatica, Hippuris vulgaris and Carex reflected well their relative abundance in phytocenoses. Chara sp., Juncus inflexus and Eupatorium cannabinum were overrepresented, whereas Typha latifolia and Sparganium minimum were poorly represented in relation to contemporary plant cover. There were no diaspores of Phragmites australis, which dominates the contemporary reed bed. Besides the shape of a reservoir, the key factor influencing diaspore numbers is distribution of plant cover. In many cases, single diaspores (Potentilla erecta, Myosotis scorpioides, Lythrum salicaria, Scutellaria galericulata), or higher concentrations (Hippuris vulgaris, Mentha aquatica, Eleocharis palustris, Schoenoplectus tabernaemontani, Chara sp.) reflected well the location of parent vegetation. The findings indicate that carpological remains in sediments can be an important source of information about plants in and around lakes. They generally reflect well local vegetation and in some cases may be used to identify taxa that dominated in the past

Shedding Light on the Galaxy Luminosity Function

From as early as the 1930s, astronomers have tried to quantify the statistical nature of the evolution and large-scale structure of galaxies by studying their luminosity distribution as a function of redshift - known as the galaxy luminosity function (LF). Accurately constructing the LF remains a popular and yet tricky pursuit in modern observational cosmology where the presence of observational selection effects due to e.g. detection thresholds in apparent magnitude, colour, surface brightness or some combination thereof can render any given galaxy survey incomplete and thus introduce bias into the LF. Over the last seventy years there have been numerous sophisticated statistical approaches devised to tackle these issues; all have advantages -- but not one is perfect. This review takes a broad historical look at the key statistical tools that have been developed over this period, discussing their relative merits and highlighting any significant extensions and modifications. In addition, the more generalised methods that have emerged within the last few years are examined. These methods propose a more rigorous statistical framework within which to determine the LF compared to some of the more traditional methods. I also look at how photometric redshift estimations are being incorporated into the LF methodology as well as considering the construction of bivariate LFs. Finally, I review the ongoing development of completeness estimators which test some of the fundamental assumptions going into LF estimators and can be powerful probes of any residual systematic effects inherent magnitude-redshift data.Comment: 95 pages, 23 figures, 3 tables. Now published in The Astronomy & Astrophysics Review. This version: bring in line with A&AR format requirements, also minor typo corrections made, additional citations and higher rez images adde

Canas-Segovia V. United States immigration and naturalization service brief amicus curiae of the office of the united nations high commissioner for refugees

In April 1990, the United States Court of Appeals for the Ninth Circuit gave judgment in Canas-Stgovia v. Immigration and Naturalization Service, a case involving applications for asylum by two brothers, both citizens of El Salvador and Jehovah's Witnesses. The Court upheld the appeal, and ruled that the appellants qualified for asylum in the United States. As it had done in three previous cases, the Office of the United Nations High Commissioner for Refugees submitted an amicus curiae brief in support of appellants. This brief examines the law and practice relating to conscientious objection, and considers how and in which circumstances those who refuse to do military service can be considered as refugees under the 1951 Convention/1967 Protocol. It shows that under the well-founded fear of persecution standard, the likelihood of punishment under a law of universal or general application does not itself rule out the possibility of persecution within the meaning of the Convention; that an 'intent to persecute' on the part of a government or other State authority is not a necessary precondition for the existence of a well-found fear of persecution; and that UNHCR has consistently adopted these positions, as shown particularly by the relevant provisions of the UNHCR Handbook on Procedurts and Crittnafor Determining Rifugtt Status. The brief also examines the international legal standing of the right to conscientious objection, considered on its own merits in the human rights context, from the perspective of State practice and that of international and regional organizations; it refers to significant developments in various United Nations fora. The brief argues that the Board of Immigration Appeals appears to have interpreted the petitioners' claims as based solely on a well-founded fear of religious persecution. But, regardless of the precise characterization of the applicant's motives, the conscientious refusal to bear arms inevitably places the individual in political opposition to his or her government, in a situation of conflicting duties that should be resolved in accordance with international standards of reasonableness and proportionality. Finally, the brief suggests a framework of standards within which the refugee status of conscientious objectors may be determined, taking account of the special value attributed to the individual's right to freedom of conscience and its relationship to competing interests of State and community. © 1990 Oxford University Press

Canas-Segovia V. United States immigration and naturalization service brief amicus curiae of the office of the united nations high commissioner for refugees

In April 1990, the United States Court of Appeals for the Ninth Circuit gave judgment in Canas-Stgovia v. Immigration and Naturalization Service, a case involving applications for asylum by two brothers, both citizens of El Salvador and Jehovah's Witnesses. The Court upheld the appeal, and ruled that the appellants qualified for asylum in the United States. As it had done in three previous cases, the Office of the United Nations High Commissioner for Refugees submitted an amicus curiae brief in support of appellants. This brief examines the law and practice relating to conscientious objection, and considers how and in which circumstances those who refuse to do military service can be considered as refugees under the 1951 Convention/1967 Protocol. It shows that under the well-founded fear of persecution standard, the likelihood of punishment under a law of universal or general application does not itself rule out the possibility of persecution within the meaning of the Convention; that an 'intent to persecute' on the part of a government or other State authority is not a necessary precondition for the existence of a well-found fear of persecution; and that UNHCR has consistently adopted these positions, as shown particularly by the relevant provisions of the UNHCR Handbook on Procedurts and Crittnafor Determining Rifugtt Status. The brief also examines the international legal standing of the right to conscientious objection, considered on its own merits in the human rights context, from the perspective of State practice and that of international and regional organizations; it refers to significant developments in various United Nations fora. The brief argues that the Board of Immigration Appeals appears to have interpreted the petitioners' claims as based solely on a well-founded fear of religious persecution. But, regardless of the precise characterization of the applicant's motives, the conscientious refusal to bear arms inevitably places the individual in political opposition to his or her government, in a situation of conflicting duties that should be resolved in accordance with international standards of reasonableness and proportionality. Finally, the brief suggests a framework of standards within which the refugee status of conscientious objectors may be determined, taking account of the special value attributed to the individual's right to freedom of conscience and its relationship to competing interests of State and community. © 1990 Oxford University Press