4,856 research outputs found
Thoracic Disease Identification and Localization with Limited Supervision
Accurate identification and localization of abnormalities from radiology
images play an integral part in clinical diagnosis and treatment planning.
Building a highly accurate prediction model for these tasks usually requires a
large number of images manually annotated with labels and finding sites of
abnormalities. In reality, however, such annotated data are expensive to
acquire, especially the ones with location annotations. We need methods that
can work well with only a small amount of location annotations. To address this
challenge, we present a unified approach that simultaneously performs disease
identification and localization through the same underlying model for all
images. We demonstrate that our approach can effectively leverage both class
information as well as limited location annotation, and significantly
outperforms the comparative reference baseline in both classification and
localization tasks.Comment: Conference on Computer Vision and Pattern Recognition 2018 (CVPR
2018). V1: CVPR submission; V2: +supplementary; V3: CVPR camera-ready; V4:
correction, update reference baseline results according to their latest post;
V5: minor correction; V6: Identification results using NIH data splits and
various image model
Observe matter falling into a black hole
It has been well known that in the point of view of a distant observer, all
in-falling matter to a black hole (BH) will be eventually stalled and "frozen"
just outside the event horizon of the BH, although an in-falling observer will
see the matter falling straight through the event horizon. Thus in this "frozen
star" scenario, as distant observers, we could never observe matter falling
into a BH, neither could we see any "real" BH other than primordial ones, since
all other BHs are believed to be formed by matter falling towards singularity.
Here we first obtain the exact solution for a pressureless mass shell around a
pre-existing BH. The metrics inside and interior to the shell are all different
from the Schwarzschild metric of the enclosed mass. The metric interior to the
shell can be transformed to the Schwarzschild metric for a slower clock which
is dependent of the location and mass of the shell. Another result is that
there does not exist a singularity nor event horizon in the shell. Therefore
the "frozen star" scenario is incorrect. We also show that for all practical
astrophysical settings the in-falling time recorded by an external observer is
sufficiently short that future astrophysical instruments may be able to follow
the whole process of matter falling into BHs. The distant observer could not
distinguish between a "real" BH and a "frozen star", until two such objects
merge together. It has been proposed that electromagnetic waves will be
produced when two "frozen stars" merge together, but not true when two "real"
bare BHs merge together. However gravitational waves will be produced in both
cases. Thus our solution is testable by future high sensitivity astronomical
observations.Comment: 7 pages, 2 figures. Proceeding of the conference "Astrophysics of
Compact Objects", 1-7 July, Huangshan, China. Abridged abstrac
Phenomenology of Gamma-Ray Jets
We discuss some phenomenological aspects of -ray emitting jets. In
particular, we present calculations of the -sphere and -sphere for
various target photon fields, and employ them to demonstrate how -ray
observations at very high energies can be used to constraint the Doppler factor
of the emitting plasma and the production of VHE neutrinos. We also consider
the implications of the rapid TeV variability observed in M87 and the TeV
blazars, and propose a model for the very rapid TeV flares observed with HESS
and MAGIC in some blazars,that accommodates the relatively small Doppler
factors inferred from radio observations. Finally, we briefly discuss the
prospects for detecting VHE neutrinos from relativistic jets.Comment: Proceedings, Huangshan meeting on "Astrophysics of Compact Objects
Dynamics of Magnetized Spherical Accretion Flows
Transonic accretion flow with self-consistent treatment of random magnetic
field is presented.Comment: in proceedings to "Astrophysics of Compact Objects", Huangshan,
China, 200
Possible evidence that pulsars are quark stars
It is a pity that the real state of matter in pulsar-like stars is still not
determined confidently because of the uncertainty about cold matter at
supranuclear density, even 40 years after the discovery of pulsar. Nuclear
matter (related to neutron stars) is one of the speculations for the inner
constitution of pulsars even from the Landau's time more than 70 years ago, but
quark matter (related to quark stars) is an alternative due to the fact of
asymptotic freedom of interaction between quarks as the standard model of
particle physics develops since 1960s. Therefore, one has to focus on
astrophysical observations in order to answer what the nature of pulsars is. In
this presentation, I would like to summarize possible observational
evidence/hints that pulsar-like stars could be quark stars, and to address
achievable clear evidence for quark stars in the future experiments.Comment: 6 pages, 2 figures; a talk at the international conference
"Astrophysics of Compact Objects" (July 1-7, 2007; Huangshan, China);
http://vega.bac.pku.edu.cn/rxxu/publications/index_C.htm. A mistake in Fig.1
is corrected; Correction of typo
"Black Star" or Astrophysical Black Hole?
Recently wide publicity has been given to a claim by T. Vachaspati that
"black holes do not exist", that the objects known as black holes in
astrophysics should rather be called "black stars" and they not only do not
have event horizons but actually can be the source of spectacular gamma ray
bursts. In this short essay (no flimsier than the original preprint where these
extravagant claims appeared) I demonstrate that these ill-considered claims are
clearly wrong. Yet they present a good occasion to reflect on some well known
but little discussed conceptual difficulties which arise when applying
relativistic terminology in an astrophysical context.Comment: Poster presented at "Compact Objects" meeting in Hunagshan, China,
2-7 July 2007. To be published in the AIP Conference Proceeding serie
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