1,933 research outputs found
Strongly lensed repeating Fast Radio Bursts as precision probes of the universe
Fast Radio bursts (FRBs), bright transients with millisecond durations at
GHz and typical redshifts probably , are likely to be
gravitationally lensed by intervening galaxies. Since the time delay between
images of strongly lensed FRB can be measured to extremely high precision
because of the large ratio between the typical galaxy-lensing delay
time (10 days) and the width of bursts (ms),
we propose strongly lensed FRBs as precision probes of the universe. We show
that, within the flat CDM model, the Hubble constant can be
constrained with a uncertainty from 10 such systems probably
observed with the Square Kilometer Array (SKA) in 30 years. More
importantly, the cosmic curvature can be model-independently constrained to a
precision of . This constraint can directly test the validity of the
cosmological principle and break the intractable degeneracy between the cosmic
curvature and dark energy.Comment: 8 pages, 6 figure
Self-excited Threshold Poisson Autoregression
This paper studies theory and inference of an observation-driven model for
time series of counts. It is assumed that the observations follow a Poisson
distribution conditioned on an accompanying intensity process, which is
equipped with a two-regime structure according to the magnitude of the lagged
observations. The model remedies one of the drawbacks of the Poisson
autoregression model by allowing possibly negative correlation in the
observations. Classical Markov chain theory and Lyapunov's method are utilized
to derive the conditions under which the process has a unique invariant
probability measure and to show a strong law of large numbers of the intensity
process. Moreover the asymptotic theory of the maximum likelihood estimates of
the parameters is established. A simulation study and a real data application
are considered, where the model is applied to the number of major earthquakes
in the world
Colorectal cancer screening with fecal occult blood test: A 22-year cohort study.
The aim of the present study was to investigate the efficacy of colorectal cancer (CRC) screening with a three-tier fecal occult blood test (FOBT) in the Chinese population. The study was performed between 1987 and 2008 at the Beijing Military General Hospital, in a cohort of army service males and females aged >50 years. Between 1987 and 2005, a three-tier screening program, comprising guaiac-based FOBTs (gFOBTs), followed by immunochemical FOBTs for positive guaiac test samples and then colonoscopy for positive immunochemical test subjects, was performed annually. The cohort was followed up until 2008. The cohort included 5,104 subjects, of which, 3,863 subjects participated in screening (screening group) and 1,241 did not (non-screening group). The two groups did not differ in age, gender or other major risk factors for colon cancer. Overall, 36 CRCs occurred in the screening group and 21 in the non-screening group. Compared with the non-screening group, the relative risk for the incidence and mortality of CRC was 0.51 [95% confidence interval (CI), 0.30-0.87] and 0.36 (95% CI, 0.18-0.71), respectively, in the screening group. The general sensitivity of this three-tier FOBT was 80.6% (95% CI, 65.3-91.1). Thus, annual screening using the three-tier FOBT program may reduce the CRC incidence and mortality rate
Effect of thermal exposure on the stress-rupture life and microstructure of a low Re-containing single crystal alloy
AbstractIn this paper, the stress-rupture tests of a low Re-containing single crystal alloy IC21 before and after thermal exposure at 1100°C for various periods of time were conducted under the test condition of 1100°C/137MPa, and the microstructure of the tested specimens was characterized by SEM and TEM. The experimental results showed that the stress rupture life of this alloy was over 150h after the standard heat treatment of 1320°C, 10h/AC+870, 32h/AC, however the stress rupture life decreased with the increase of exposure time due to the microstructure degradation. The TEM analysis revealed that the interface mismatch dislocation networks were well established. It was observed that these mismatch networks could form at 1100°C even after thermal exposure for 1h without the external stress, which is quite different from that in the traditional single crystal superalloys
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