7,037 research outputs found
Shadows and photon spheres with spherical accretions in the four-dimensional Gauss-Bonnet black hole
We investigate the shadows and photon spheres of the four-dimensional
Gauss-Bonnet black hole with the static and infalling spherical accretions. We
show that for both cases, the shadow and photon sphere are always present. The
radii of the shadow and photon sphere are independent of the profiles of
accretion for a fixed Gauss-Bonnet constant, implying that the shadow is a
signature of the spacetime geometry and it is hardly influenced by accretion in
this case. Because of the Doppler effect, the shadow of the infalling accretion
is found to be darker than that of the static one. We also investigate the
effect of the Gauss-Bonnet constant on the shadow and photon sphere, and find
that the larger the Gauss-Bonnet constant is, the smaller the radii of the
shadow and photon sphere will be. In particular, the observed specific
intensity increases with the increasing of the Gauss-Bonnet constant.Comment: published versio
Analysis of Down syndrome failed to be diagnosed after prenatal screening: A multicenter study.
To analyze the characters of Down syndrome (DS) who failed to be diagnosed after prenatal screening and hope to be able to improve the programs of prenatal screening and reduce the missed diagnosis of DS. In this multicenter study, we collected the missed cases from 3 prenatal diagnosis centers and analyzed their characters. A total of 126 DS babies failed to be diagnosed after prenatal screening. Their mothers accepted the prenatal screening in second trimester. We collected the mothers' blood and detected the levels of alpha-fetoprotein (AFP) and the free beta subunit of human chorionic gonadotropin (fβhCG) by time-resolved fluoroimmunoassay. The values were also presented as multiples of the median (MoM) and determined the risk of carrying a fetus with DS by Wallace LifeCycle Elipse analysis software. Compared with normal control group, the level of fβhCG and hCG MoM were dramatically increased, while AFP and AFP MoM were decreased. The area under the receiver-operating-characteristic curve of trisomy 21 was 0.8387 for hCG-MoM and AFP-MoM testing. The sensitivity, specificity, positive predictive value, and negative predictive value were 84.6%, 74.8%, 75.4%, and 83.6%, respectively. Meanwhile, the prediction mode was "0.39957 + 1.90897HCG-MOM -3.32713AFP-MOM". It was worthwhile noting that the risk of 65.9% DS missed diagnosis group were higher than 1/1000, 92.9% higher than 1/3000. However, 72.5% cases in normal control group were lower than 1/3000. Only 9.2% mothers would be higher than the value of risk in 1/1000. The prediction mode of hCG MoM and AFP MoM might be able to help us reduce the missed diagnosis. It is also necessary to adjust more reasonable range of noninvasive prenatal testing with further clinical researches
Coexistence of Localized and Extended States in Disordered Systems
It is commonly believed that Anderson localized states and extended states do
not coexist at the same energy. Here we propose a simple mechanism to achieve
the coexistence of localized and extended states in a band in a class of
disordered quasi-1D and quasi-2D systems. The systems are partially disordered
in a way that a band of extended states always exists, not affected by the
randomness, whereas the states in all other bands become localized. The
extended states can overlap with the localized states both in energy and in
space, achieving the aforementioned coexistence. We demonstrate such
coexistence in disordered multi-chain and multi-layer systems.Comment: 5 pages, 3 figure
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