Cosmological horizon entropy and generalised second law for flat Friedmann Universe

We discuss the generalized second law (GSL) and the constraints imposed by it for two types of Friedmann universes. The first one is the Friedmann universe with radiation and a positive cosmological constant, and the second one consists of non-relativistic matter and a positive cosmological constant. The time evolution of the event horizon entropy and the entropy of the contents within the horizon are analyses in an analytical way by obtaining the Hubble parameter. It is shown that the GSL constraint the temperature of both the radiation and matter of the Friedmann universe. It is also shown that, even though the net entropy of the radiation (or matter) is decreasing at sufficiently large times as the universe expand, it exhibit an increase during the early times when universe is decelerating. That is the entropy of the radiation within the comoving volume is decreasing only when the universe has got an event horizon.Comment: 15 pages, 9 figure

A Translational Approach to Modeling Unique Aspects of Germ Cell Development During Self-Organization of the Primate Embryo

The specification of germ cells during embryonic development is vital not only for the development of an organism, but quite literally for the survival and propagation of its entire species. Recent work has demonstrated that several aspects of human primordial germ cell (hPGC) development are specific to primates, necessitating model systems and in vivo validation that is also species specific. In this work, a synthesis of in vitro and in vivo techniques is used to investigate hPGC specification within a human embryonic stem cell model of a gastrulating embryo known as a gastruloid. An hPGC transcriptomic signature that indicates migratory potential via canonical and novel mechanisms is indicated, raising several potential candidates for further investigation into the under-studied migratory phase of germ cell development. We seek to generate validation assays of hPGC function in an embryonic context by investigating migratory potential in grafts to the chick embryo, and demonstrate that despite significant differences between chick and human routes of migration in vivo, human in vitro-derived PGCs are in fact able to demonstrate migratory behavior in the chick, following chick migratory patterns and demonstrating a specific homing towards the chick mesonephros and gonad. These experiments not only provide a functional validation for in vitro-derived hPGCs that is complementary to molecular and epigenetic analysis, but also hint at the elements of hPGC development that are conserved throughout evolution. The gastruloid system is then used for further investigation into the hPGC niche. The power of this model system relies upon self-organization due to endogenous signaling in response to an exogenous BMP4 initiating signal, in a manner analogous to that found in the human embryo. We harness this power, using single cell image quantification and genetic tools including CRISPR-Cas9 to probe further into the signaling environment of the hPGC niche in the gastruloid model. We elucidate the role of each leg of the BMP4 – WNT – ACTIVIN/NODAL signaling cascade in development of this niche, which determines gastrulation events, in hPGC specification. These experiments not only demonstrate how BMP4 acts independently in addition to this cascade to directly specify hPGCs, but also how all three pathways work in harmony to generate self-organization of hPGCs within their gastruloid niche. By probing further into the ontogeny of hPGC specification, we find that upregulation of BLIMP1 alone, a canonical regulator of PGCs, is sufficient to induce later markers of hPGC fate, and surprisingly is also sufficient to downregulate SOX2 (a marker of epiblast and early ectodermal fate) and upregulate SOX17, which has been previously placed upstream of BLIMP1. Finally, we propose the marmoset as a good model of primate reproduction and embryogenesis, in an attempt to describe a non-human primate (NHP) system for validation of hPGC characteristics observed in vitro. We systematically investigate marmoset embryonic development in vivo using serial, high temporal and spatial resolution ultrasound imaging. We describe the morphological characteristics of implantation, gastrulation, neurulation, and organogenesis, as well as the curious marmoset phenotype of an elongated peri-gastrulation window, incorporating slowed embryonic growth and rapid extraembryonic development. In doing so, we generate an annotated ultrasound atlas of marmoset embryogenesis, and train models to identify developmental stages and predict fertilization ages from a single frame. In addition, we suggest that the extended peri-gastrulation window in the marmoset will provide a unique opportunity to perform in utero genetic editing, lineage tracing, and even allogenic transplantation to complement in vitro studies of hPGC development. This body of work provides a synthesis of culture techniques, genetic and molecular tools, and imaging systems that will provide a foundation for the exploration of not only human PGC development, but also hopefully a generalizable roadmap for translation between in vitro and in vivo studies early primate development

Statistical distribution of daily rainfall and its association with the coefficient of variation of rainfall series

The study focuses attention on the normalized rainfall curve (NRC) depicting the association between cumulated percentage rain amount (x) and cumulated percentage number of rain days (y) of the rainfall series. It is shown that the NRC is uniquely determined by the coefficient of variation (CV) of the rainfall series. There is no universal NRC that can represent all rainfall regimes. The equation x=y exp-b(100-y)c, where b and c are two empirical constants, gives a good analytical representation of the NRCs over a wide range of CV values of the rainfall series. This analytical equation is able to account for the occurrence of high rainfall intensities towards the upper extremity of the NRC for rainfall series with high values of CV

The onset of the southwest monsoon in 1990

statistics relating to the date of onset of the southwest monsoon over kerala for the 100 year period 1891-1990 reveal that the mean and median dates of onset for south kerala are 31 May and 1 June with standard deviation of 8.5 day

The onset of the southwest monsoon over Kerala: 1901-1980

Utilising daily mean rainfall from dense rain gauge networks, the dates of onset of the southwest monsoon over south and north Kerala have been derived on the basis of objective criteria for the years 1901 to 1980. These dates have been compared with the onset dates as per records of the India Meteorological Department. Statistics of the onset dates are presented. The mean onset date for south Kerala is found to be 30 May and for north Kerala 1 June with a standard deviation of about 9 days in both cases. The sharp increase in rainfall that heralds the onset of the monsoon is highlighted by superposed epoch analysis. The prevailing notion that rainfall from pre-monsoon thunderstorms progressively increases and merges with the monsoon rainfall is shown to be not valid