On perfect fluid models in non-comoving observational spherical coordinates

We use null spherical (observational) coordinates to describe a class of inhomogeneous cosmological models. The proposed cosmological construction is based on the observer past null cone. A known difficulty in using inhomogeneous models is that the null geodesic equation is not integrable in general. Our choice of null coordinates solves the radial ingoing null geodesic by construction. Furthermore, we use an approach where the velocity field is uniquely calculated from the metric rather than put in by hand. Conveniently, this allows us to explore models in a non-comoving frame of reference. In this frame, we find that the velocity field has shear, acceleration and expansion rate in general. We show that a comoving frame is not compatible with expanding perfect fluid models in the coordinates proposed and dust models are simply not possible. We describe the models in a non-comoving frame. We use the dust models in a non-comoving frame to outline a fitting procedure.Comment: 8 pages, 1 figure. To appear in Phys.Rev.

The genome of the stable fly, Stomoxys calcitrans, reveals potential mechanisms underlying reproduction, host interactions, and novel targets for pest control.

The stable fly, Stomoxys calcitrans, is a major blood-feeding pest of livestock that has near worldwide distribution, causing an annual cost of over $2 billion for control and product loss in the USA alone. Control of these flies has been limited to increased sanitary management practices and insecticide application for suppressing larval stages. Few genetic and molecular resources are available to help in developing novel methods for controlling stable flies. This study examines stable fly biology by utilizing a combination of high-quality genome sequencing and RNA-Seq analyses targeting multiple developmental stages and tissues. In conjunction, 1600 genes were manually curated to characterize genetic features related to stable fly reproduction, vector host interactions, host-microbe dynamics, and putative targets for control. Most notable was characterization of genes associated with reproduction and identification of expanded gene families with functional associations to vision, chemosensation, immunity, and metabolic detoxification pathways. The combined sequencing, assembly, and curation of the male stable fly genome followed by RNA-Seq and downstream analyses provide insights necessary to understand the biology of this important pest. These resources and new data will provide the groundwork for expanding the tools available to control stable fly infestations. The close relationship of Stomoxys to other blood-feeding (horn flies and Glossina) and non-blood-feeding flies (house flies, medflies, Drosophila) will facilitate understanding of the evolutionary processes associated with development of blood feeding among the Cyclorrhapha

Looking to peripheral river islands in Brazil to develop an urban island water metabolism perspective.

Across Brazil, including the water rich Amazon region, access to safe drinking water remains a challenge and rainwater harvesting has gained credibility as a technological solution. Complementing a more techno-centric approach, this practice paper analyses initial findings from an 'immersion' that was undertaken in August 2017 on Paquetá and surrounding islands located on the periphery of Belém (Schiffer and Swan, 2018), through the proposed urban island water metabolism framework. As such, the research draws on the 'urban metabolism' concept which can be described as socio-technical, socio-economic, socio-political and socio-ecological flows including water resources, people and information in, out and within the urban environment (Currie and Musango, 2016; Kennedy, Cuddihy and Engel-Yan, 2007). Here this has been adapted to 'urban island water metabolisms'. The research highlights the value of more holistic and situated understanding of water systems in urban island contexts including: the role of intra-island networks that operate beyond municipal borders; accessibility in the contexts of ever changing water levels; and seasonal dimensions. The paper recommends longer-term and comparative research to further the understanding of the specific needs and challenges for water management in these peripheral contexts and to strengthen the urban island water metabolism concept