167 research outputs found
OGLE-2018-BLG-0532Lb: Cold Neptune With Possible Jovian Sibling
We report the discovery of the planet OGLE-2018-BLG-0532Lb, with very obvious
signatures in the light curve that lead to an estimate of the planet-host mass
ratio . Although there are
no obvious systematic residuals to this double-lens/single-source (2L1S) fit,
we find that can be significantly improved by adding either a third
lens (3L1S, ) or second source (2L2S, ) to
the lens-source geometry. After thorough investigation, we conclude that we
cannot decisively distinguish between these two scenarios and therefore focus
on the robustly-detected planet. However, given the possible presence of a
second planet, we investigate to what degree and with what probability such
additional planets may affect seemingly single-planet light curves. Our best
estimates for the properties of the lens star and the secure planet are: a host
mass , system distance kpc and planet mass
with projected separation au.
However, there is a relatively bright (and also relatively blue) star
projected within mas of the lens, and if future high-resolution images
show that this is coincident with the lens, then it is possible that it is the
lens, in which case, the lens would be both more massive and more distant than
the best-estimated values above.Comment: 48 pages, 9 figures, 7 table
Observation of contemporaneous optical radiation from a gamma-ray burst
The origin of gamma-ray bursts (GRBs) has been enigmatic since their
discovery. The situation improved dramatically in 1997, when the rapid
availability of precise coordinates for the bursts allowed the detection of
faint optical and radio afterglows - optical spectra thus obtained have
demonstrated conclusively that the bursts occur at cosmological distances. But,
despite efforts by several groups, optical detection has not hitherto been
achieved during the brief duration of a burst. Here we report the detection of
bright optical emission from GRB990123 while the burst was still in progress.
Our observations begin 22 seconds after the onset of the burst and show an
increase in brightness by a factor of 14 during the first 25 seconds; the
brightness then declines by a factor of 100, at which point (700 seconds after
the burst onset) it falls below our detection threshold. The redshift of this
burst, approximately 1.6, implies a peak optical luminosity of 5 times 10^{49}
erg per second. Optical emission from gamma-ray bursts has been generally
thought to take place at the shock fronts generated by interaction of the
primary energy source with the surrounding medium, where the gamma-rays might
also be produced. The lack of a significant change in the gamma-ray light curve
when the optical emission develops suggests that the gamma-rays are not
produced at the shock front, but closer to the site of the original explosion.Comment: 10 pages, 2 figures. Accepted for publication in Nature. For
additional information see http://www.umich.edu/~rotse
OGLE-2019-BLG-0960 Lb: The Smallest Microlensing Planet
We report the analysis of OGLE-2019-BLG-0960, which contains the smallest mass-ratio microlensing planet found to date (q = 1.2-1.6 × 10-5 at 1s). Although there is substantial uncertainty in the satellite parallax measured by Spitzer, the measurement of the annual parallax effect combined with the finite source effect allows us to determine the mass of the host star (M L = 0.3-0.6 M o?), the mass of its planet (m p = 1.4-3.1 M ?), the projected separation between the host and planet (a ? = 1.2-2.3 au), and the distance to the lens system (D L = 0.6-1.2 kpc). The lens is plausibly the blend, which could be checked with adaptive optics observations. As the smallest planet clearly below the break in the mass-ratio function, it demonstrates that current experiments are powerful enough to robustly measure the slope of the mass-ratio function below that break. We find that the cross-section for detecting small planets is maximized for planets with separations just outside of the boundary for resonant caustics and that sensitivity to such planets can be maximized by intensively monitoring events whenever they are magnified by a factor A \u3e 5. Finally, an empirical investigation demonstrates that most planets showing a degeneracy between (s \u3e 1) and (s \u3c 1) solutions are not in the regime (log s| » 0) for which the close / wide degeneracy was derived. This investigation suggests that there is a link between the close / wide and inner/outer degeneracies and also that the symmetry in the lens equation goes much deeper than symmetries uncovered for the limiting cases
OGLE-2017-BLG-0406: <i>Spitzer</i> Microlens Parallax Reveals Saturn-mass Planet orbiting M-dwarf Host in the Inner Galactic Disk
Adjuvant chemotherapy for stage III colon cancer: Relative dose intensity and survival among veterans
Background: Given the paucity of information on dose intensity, the objective of this study is to describe the use of adjuvant chemotherapy for stage III colon cancer, focusing on relative dose intensity (RDI), overall survival (OS) and disease-free survival (DFS). Methods: Retrospective cohort of 367 patients diagnosed with stage III colon cancer in 2003-2008 and treated at 19 VA medical centers. Kaplan-Meier curves summarize 5-year OS and 3-year DFS by chemotherapy regimen and RDI, and multivariable Cox proportional hazards regression was used to model these associations. Results: 5-fluorouracil/leucovorin (FU/LV) was the most commonly initiated regimen in 2003 (94.4%) and 2004 (62.7%); in 2005-2008, a majority of patients (60%-74%) was started on an oxaliplatin-based regimen. Median RDI was 82.3%. Receipt of >70% RDI was associated with better 5-year OS (p70% RDI at the first year (HR=0.58; 95% CI=0.37-0.89) and married status (HR=0.66; 95% CI=0.45-0.97) were associated with significantly decreased risk of death, while age ≥75 (versus 55-64) (HR=2.06; 95% CI=1.25-3.40), Charlson Comorbidity Index (HR=1.17; 95% CI=1.06-1.30), T4 tumor status (versus T1/T2) (HR=5.88; 95% CI=2.69-12.9), N2 node status (HR=1.68; 95% CI=1.12-2.50) and bowel obstruction (HR=2.32, 95% CI=1.36-3.95) were associated with significantly increased risk. Similar associations were observed for DFS. Conclusion: Patients with stage III colon cancer who received >70% RDI had improved 5-year OS. The association between RDI and survival needs to be examined in studies of adjuvant chemotherapy for colon cancer outside of the VA
Bacterial Flagella: Twist and Stick, or Dodge across the Kingdoms
The flagellum organelle is an intricate multiprotein assembly best known for its rotational propulsion of bacteria. However, recent studies have expanded our knowledge of other functions in pathogenic contexts, particularly adherence and immune modulation, e.g., for Salmonella enterica, Campylobacter jejuni, Pseudomonas aeruginosa, and Escherichia coli. Flagella-mediated adherence is important in host colonisation for several plant and animal pathogens, but the specific interactions that promote flagella binding to such diverse host tissues has remained elusive. Recent work has shown that the organelles act like probes that find favourable surface topologies to initiate binding. An emerging theme is that more general properties, such as ionic charge of repetitive binding epitopes and rotational force, allow interactions with plasma membrane components. At the same time, flagellin monomers are important inducers of plant and animal innate immunity: variation in their recognition impacts the course and outcome of infections in hosts from both kingdoms. Bacteria have evolved different strategies to evade or even promote this specific recognition, with some important differences shown for phytopathogens. These studies have provided a wider appreciation of the functions of bacterial flagella in the context of both plant and animal reservoirs
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