18 research outputs found
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
Kin discrimination and possible cryptic species in the social amoeba Polysphondylium violaceum
Abstract
Background
The genetic diversity of many protists is unknown. The differences that result from this diversity can be important in interactions among individuals. The social amoeba Polysphondylium violaceum, which is a member of the Dictyostelia, has a social stage where individual amoebae aggregate together to form a multicellular fruiting body with dead stalk cells and live spores. Individuals can either cooperate with amoebae from the same clone, or sort to form clonal fruiting bodies. In this study we look at genetic diversity in P. violaceum and at how this diversity impacts social behavior.
Results
The phylogeny of the ribosomal DNA sequence (17S to 5.8S region) shows that P. violaceum is made up of at least two groups. Mating compatibility is more common between clones from the same phylogenetic group, though matings between clones from different phylogenetic groups sometimes occurred. P. violaceum clones are more likely to form clonal fruiting bodies when they are mixed with clones from a different group than when they are mixed with a clone of the same group.
Conclusion
Both the phylogenetic and mating analyses suggest the possibility of cryptic species in P. violaceum. The level of divergence found within P. violaceum is comparable to the divergence between sibling species in other dictyostelids. Both major groups A/B and C/D/E/F show kin discrimination, which elevates relatedness within fruiting bodies but not to the level of clonality. The diminished cooperation in mixes between groups suggests that the level of genetic variation between individuals influences the extent of their cooperation
A single-center randomized, controlled trial investigating the efficacy of a mHealth ECG technology intervention to improve the detection of atrial fibrillation: the iHEART study protocol
Cell differentiation and dominant signaling pathway signatures in the molecular classification of human breast cancer cell lines
Molecular basis of reduced or absent expression of decay-accelerating factor in Cromer blood group phenotypes
Defining, Navigating, and Negotiating Success: The Experiences of Mid-Career Robert Wood Johnson Clinical Scholar Women
BACKGROUND: We studied female graduates of the Robert Wood Johnson Clinical Scholars Program (CSP, Class of 1984 to 1989) to explore and describe the complexity of creating balance in the life of mid-career academic woman physicians. METHODS: We conducted and qualitatively analyzed (κ 0.35 to 1.0 for theme identification among rater pairs) data from a semi-structured survey of 21 women and obtained their curricula vitae to quantify publications and grant support, measures of academic productivity. RESULTS: Sixteen of 21 (76%) women completed the survey. Mean age was 48 (range: 45 to 56). Three were full professors, 10 were associate professors, and 3 had left academic medicine. Eleven women had had children (mean 2.4; range: 1 to 3) and 3 worked part-time. From these data, the conceptual model expands on 3 key themes: (1) defining, navigating, and negotiating success, (2) making life work, and (3) making work work. The women who described themselves as satisfied with their careers (10/16) had clarity of values and goals and a sense of control over their time. Those less satisfied with their careers (6/16) emphasized the personal and professional costs of the struggle to balance their lives and described explicit institutional barriers to fulfillment of their potential. CONCLUSION: For this group of fellowship-prepared academic women physicians satisfaction is achieving professional and personal balance
Repair of Recoarctation and Aortic Valve Replacement with the On-X Valve in a Pediatric Patient: A Case Report
Sildenafil for pulmonary hypertension in neonates: An updated systematic review and meta‐analysis
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A pulsar-based time-scale from the international pulsar timing array
We have constructed a new time-scale, TT(IPTA16), based on observations of radio pulsars presented in the first data release from the International Pulsar Timing Array (IPTA). We used two analysis techniques with independent estimates of the noise models for the pulsar observations and different algorithms for obtaining the pulsar time-scale. The two analyses agree within the estimated uncertainties and both agree with TT(BIPM17), a post-corrected time-scale produced by the Bureau International des Poids et Mesures (BIPM). We show that both methods could detect significant errors in TT(BIPM17) if they were present. We estimate the stability of the atomic clocks from which TT(BIPM17) is derived using observations of four rubidium fountain clocks at the US Naval Observatory. Comparing the power spectrum of TT(IPTA16) with that of these fountain clocks suggests that pulsar-based time-scales are unlikely to contribute to the stability of the best time-scales over the next decade, but they will remain a valuable independent check on atomic time-scales. We also find that the stability of the pulsar-based time-scale is likely to be limited by our knowledge of solar-system dynamics, and that errors in TT(BIPM17) will not be a limiting factor for the primary goal of the IPTA, which is to search for the signatures of nano-Hertz gravitational waves
Asymmetric mass ratios for bright double neutron-star mergers
The discovery of a radioactively powered kilonova associated with the binary neutron-star merger GW170817 remains the only confirmed electromagnetic counterpart to a gravitational-wave event(1,2). Observations of the late-time electromagnetic emission, however, do not agree with the expectations from standard neutron-star merger models. Although the large measured ejecta mass(3,4 )could be explained by a progenitor system that is asymmetric in terms of the stellar component masses (that is, with a mass ratio q of 0.7 to 0.8)(5), the known Galactic population of merging double neutron-star systems (that is, those that will coalesce within billions of years or less) has until now consisted only of nearly equal-mass (q> 0.9) binaries(6). The pulsar PSR J1913+1102 is a double system in a five-hour, low-eccentricity (0.09) orbit, with an orbital separation of 1.8 solar radii(7), and the two neutron stars are predicted to coalesce in 470(-11)(+12) million years owing to gravitational-wave emission. Here we report that the masses of the pulsar and the companion neutron star, as measured by a dedicated pulsar timing campaign, are 1.62 +/- 0.03 and 1.27 +/- 0.03 solar masses, respectively. With a measured mass ratio of q= 0.78 +/- 0.03, this is the most asymmetric merging system reported so far. On the basis of this detection, our population synthesis analysis implies that such asymmetric binaries represent between 2 and 30 per cent (90 per cent confidence) of the total population of merging binaries. The coalescence of a member of this population offers a possible explanation for the anomalous properties of GW170817, including the observed kilonova emission from that event