Comparative analysis of metazoan chromatin organization

Genome function is dynamically regulated in part by chromatin, which consists of the histones, non-histone proteins and RNA molecules that package DNA. Studies in Caenorhabditis elegans and Drosoph ..

The US Program in Ground-Based Gravitational Wave Science: Contribution from the LIGO Laboratory

Recent gravitational-wave observations from the LIGO and Virgo observatories have brought a sense of great excitement to scientists and citizens the world over. Since September 2015,10 binary black hole coalescences and one binary neutron star coalescence have been observed. They have provided remarkable, revolutionary insight into the "gravitational Universe" and have greatly extended the field of multi-messenger astronomy. At present, Advanced LIGO can see binary black hole coalescences out to redshift 0.6 and binary neutron star coalescences to redshift 0.05. This probes only a very small fraction of the volume of the observable Universe. However, current technologies can be extended to construct "3rd Generation" (3G) gravitational-wave observatories that would extend our reach to the very edge of the observable Universe. The event rates over such a large volume would be in the hundreds of thousands per year (i.e. tens per hour). Such 3G detectors would have a 10-fold improvement in strain sensitivity over the current generation of instruments, yielding signal-to-noise ratios of 1000 for events like those already seen. Several concepts are being studied for which engineering studies and reliable cost estimates will be developed in the next 5 years

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

The architecture of Permian glossopterid ovuliferous reproductive organs

A historical account of research on glossopterid ovuliferous reproductive structures reveals starkly contrasting interpretations of their architecture and homologies from the earliest investigations. The diversity of interpretations has led to the establishment of a multitude of genera for these fossil organs, many of the taxa being synonymous. We identify a need for taxonomic revision of these genera to clearly demarcate taxa before they can be used effectively as palaeobiogeographic or biostratigraphic indices. Our assessment of fructification features based on extensive studies of adpression and permineralized fossils reveals that many of the character states for glossopterids used in previous phylogenetic analyses are erroneous. We interpret glossopterid fertiligers to have been borne in loose strobili in which individual polysperms represent fertile cladodes of diverse morphologies subtended by a vegetative leaf or bract. Polysperms within the group are variously branched or condensed with ovule placement ranging from marginal to abaxial, in some cases occurring on recurved branchlets or in cupule-like structures. Glossopterid polysperms of all types are fringed by one or two ranks of wing-like structures that may represent the remnants of megasporophylls that were, ancestrally, developed on the fertile axillary shoot. Glossopterid fertiligers have similarities to the condensed bract/ovuliferous scale complexes of conifer cones, but comparisons with Mesozoic seed-ferns are hindered by insufficient data on the arrangement and homologies of the ovulebearing organs of the latter group. Nevertheless, glossopterid polysperms differ from the ovuliferous organs of Mesozoic seed-ferns by longitudinal versus transverse folding, respectively.Also funded by the National Science Foundation [project #1636625]; University of the Witwatersrand; Rhodes University; the DST-NRF Centre of Excellence in Palaeosciences and the NRF African Origins Platform [UID: 98822]</p

Search for gravitational waves from Scorpius X-1 in the first Advanced LIGO observing run with a hidden Markov model

Results are presented from a semicoherent search for continuous gravitational waves from the brightest low-mass X-ray binary, Scorpius X-1, using data collected during the first Advanced LIGO observing run. The search combines a frequency domain matched filter (Bessel-weighted F-statistic) with a hidden Markov model to track wandering of the neutron star spin frequency. No evidence of gravitational waves is found in the frequency range 60–650 Hz. Frequentist 95% confidence strain upper limits, h095%=4.0×10-25, 8.3×10-25, and 3.0×10-25 for electromagnetically restricted source orientation, unknown polarization, and circular polarization, respectively, are reported at 106 Hz. They are ≤10 times higher than the theoretical torque-balance limit at 106 Hz