Progenitor delay-time distribution of short gamma-ray bursts: Constraints from observations

Context. The progenitors of short gamma-ray bursts (SGRBs) have not yet been well identified. The most popular model is the merger of compact object binaries (NS-NS/NS-BH). However, other progenitor models cannot be ruled out. The delay-time distribution of SGRB progenitors, which is an important property to constrain progenitor models, is still poorly understood. Aims. We aim to better constrain the luminosity function of SGRBs and the delay-time distribution of their progenitors with newly discovered SGRBs. Methods. We present a low-contamination sample of 16 Swift SGRBs that is better defined by a duration shorter than 0.8 s. By using this robust sample and by combining a self-consistent star formation model with various models for the distribution of time delays, the redshift distribution of SGRBs is calculated and then compared to the observational data. Results. We find that the power-law delay distribution model is disfavored and that only the lognormal delay distribution model with the typical delay tau >= 3 Gyr is consistent with the data. Comparing Swift SGRBs with T90 > 0.8 s to our robust sample (T90 < 0.8 s), we find a significant difference in the time delays between these two samples. Conclusions. Our results show that the progenitors of SGRBs are dominated by relatively long-lived systems (tau >= 3 Gyr), which contrasts the results found for Type Ia supernovae. We therefore conclude that primordial NS-NS systems are not favored as the dominant SGRB progenitors. Alternatively, dynamically formed NS-NS/BH and primordial NS-BH systems with average delays longer than 5 Gyr may contribute a significant fraction to the overall SGRB progenitors.Comment: 8 pages, 6 figures, Astron. Astrophys. in pres

Identification of Novel Host Genes Required for Antiviral Immunity and Viral Genome Replication in C. Elegans

RNA interference (RNAi) is a wide-spread gene silencing mechanism that control diverse biological functions and triggered by small interfering RNAs (siRNAs) processed from the viral genome or its replication intermediates. Mechanistic studies of antiviral RNAi in Caenorhabditis elegans has led to the identification of several critical factors involved in the process. As a result, whether antiviral RNAi requires additional novel genes remains to be an open question. Viruses are intracellular parasites that rely on host products for reproduction. Disrupting their interaction with host factors can significantly compromise their replication and keep them under control. Thus, identification of host genes involved in viral genome replication will facilitate the development of antiviral drugs. In this dissertation, I present how I designed and conducted genome-wide genetic screens to look for novel worm genes required for antiviral immunity and viral genome replication. To identify novel factors required for antiviral RNAi but not for classical RNAi, a reporter worm strain containing four transgenes corresponding to known antiviral RNAi gene was developed for a biased genetic screen. It was expected that any loss-of-function alleles derived from these four known genes will be automatically rejected during the screen. Altogether 25 candidate alleles were identified and assigned to 2 known antiviral RNAi genes and 11 novel genes. Specifically, rsd-6 was confirmed as one of the candidate genes through mapping-by-sequencing strategy and 2 candidate genes as key requirement of antiviral RNAi but dispensable for classical RNAi. I believe that these 2 candidate genes are novel antiviral RNAi genes since drh-1 is so far the only one that falls into this category and has been excluded during the screen. To look for worm genes required for Orsay virus genome replication I used a triple mutant that carries the FR1gfp replicon transgene as reporter for loss of viral genome replication. The transgene-mediated viral genome replication also ensures that no false positive mutants will be picked up because of failure in virus genome replication initiation. Altogether 16 candidate alleles were identified and assigned to 12 novel genes. Most importantly, I found that most of these 12 candidate genes also play essential role in directing the genome replication of Orsay virus, which naturally infects C. elegans. To my knowledge, this is the first work that has successfully led to the identification of critical worm factors required for viral genome replication

International Political Practice of Austro-Marxism

In the political practice of Austro-Marxism, the Austrian Social Democratic leaders stood in the intermediate position between “the Second International” and “the Third International”, and in the international communist movement, they even used centrist political thinking patterns to lead the “Second and Half International.” We can say that, in international affairs, with the upgrading of the prestige of Austrian Social Democratic Party and the prevalence of the Marxist theory in Austria, the Austro-Marxism centrist road is no longer confined to the domestic political arena and they take advantage of the Social Democratic Party of Austria to exert a major influence on international communist movements