5,100 research outputs found
A Multi-Armed Bandit to Smartly Select a Training Set from Big Medical Data
With the availability of big medical image data, the selection of an adequate
training set is becoming more important to address the heterogeneity of
different datasets. Simply including all the data does not only incur high
processing costs but can even harm the prediction. We formulate the smart and
efficient selection of a training dataset from big medical image data as a
multi-armed bandit problem, solved by Thompson sampling. Our method assumes
that image features are not available at the time of the selection of the
samples, and therefore relies only on meta information associated with the
images. Our strategy simultaneously exploits data sources with high chances of
yielding useful samples and explores new data regions. For our evaluation, we
focus on the application of estimating the age from a brain MRI. Our results on
7,250 subjects from 10 datasets show that our approach leads to higher accuracy
while only requiring a fraction of the training data.Comment: MICCAI 2017 Proceeding
The Halo Occupation Distribution of Black Holes: Dependence on Mass
We investigate the halo occupation distribution (HOD) of black holes within a
hydrodynamic cosmological simulation that directly follows black hole growth.
Similar to the HOD of galaxies/subhalos, we find that the black hole occupation
number can be described by the form N_BH proportional to 1+ (M_Host)^alpha
where alpha evolves mildly with redshift indicating that a given mass halo
(M_Host) at low redshift tends to host fewer BHs than at high redshift (as
expected as a result of galaxy and BH mergers). We further divide the
occupation number into contributions from black holes residing in central and
satellite galaxies within a halo. The distribution of M_BH within halos tends
to consist of a single massive BH (distributed about a peak mass strongly
correlated with M_Host), and a collection of relatively low-mass secondary BHs,
with weaker correlation with M_Host. We also examine the spatial distribution
of BHs within their host halos, and find they typically follow a power-law
radial distribution (i.e. much more centrally concentrated than the subhalo
distribution). Finally, we characterize the host mass for which BH growth is
feedback dominated (e.g. star formation quenched). We show that halos with
M_Host > 3 * 10^12 M_sun have primary BHs that are feedback dominated by z~3
with lower mass halos becoming increasingly more affected at lower redshift.Comment: 10 pages, 7 figures, submitted to MNRA
CELL DEATH AND AUTOPHAGY: CYTOKINES, DRUGS, AND NUTRITIONAL FACTORS
Cellsmay use multiple pathways to commit suicide. In certain contexts, dying cells generate large amounts
of autophagic vacuoles and clear large proportions of their cytoplasm, before they finally die, as exemplified
by the treatment of human mammary carcinoma cells with the anti-estrogen tamoxifen (TAM,
â€1 M). Protein analysis during autophagic cell death revealed distinct proteins of the nuclear fraction
including GST- and some proteasomal subunit constituents to be affected during autophagic cell death.
Depending on the functional status of caspase-3, MCF-7 cells may switch between autophagic and apoptotic
features of cell death [Fazi, B., Bursch,W., Fimia, G.M., Nardacci R., Piacentini, M., Di Sano, F., Piredda,
L., 2008. Fenretinide induces autophagic cell death in caspase-defective breast cancer cells. Autophagy
4(4), 435â441]. Furthermore, the self-destruction of MCF-7 cells was found to be completed by phagocytosis
of cell residues [Petrovski, G., Zahuczky, G., Katona, K., Vereb, G., Martinet,W., Nemes, Z., Bursch,W.,
FĂ©suÌs, L., 2007. Clearance of dying autophagic cells of different origin by professional and non-professional
phagocytes. Cell Death Diff. 14 (6), 1117â1128].
Autophagy also constitutes a cellâs strategy of defense upon cell damage by eliminating damaged bulk
proteins/organelles. This biological condition may be exemplified by the treatment of MCF-7 cells with
a necrogenic TAM-dose (10 M), resulting in the lysis of almost all cells within 24 h. However, a transient
(1 h) challenge of MCF-7 cells with the same dose allowed the recovery of cells involving autophagy.
Enrichment of chaperones in the insoluble cytoplasmic protein fraction indicated the formation of aggresomes,
a potential trigger for autophagy. In a further experimental model HL60 cells were treated with
TAM, causing dose-dependent distinct responses: 1â5 MTAM, autophagy predominant; 7â9 M, apoptosis
predominant; 15 M, necrosis. These phenomena might be attributed to the degree of cell damage
caused by tamoxifen, either by generating ROS, increasing membrane fluidity or forming DNA-adducts.
Finally, autophagy constitutes a cellâs major adaptive (survival) strategy in response to metabolic challenges
such as glucose or amino acid deprivation, or starvation in general. Notably, the role of autophagy
appears not to be restricted to nutrient recycling in order to maintain energy supply of cells and to adapt
cell(organ) size to given physiological needs. For instance, using a newly established hepatoma cell line
HCC-1.2, amino acid and glucose deprivation revealed a pro-apoptotic activity, additive to TGF- 1. The proapoptotic
action of glucose deprivation was antagonized by 2-deoxyglucose, possibly by stabilizing the
mitochondrial membrane involving the action of hexokinase II. These observations suggest that signaling
cascades steering autophagy appear to provide links to those regulating cell number.
Taken together, our data exemplify that a given cell may flexibly respond to type and degree of
(micro)environmental changes or cell death stimuli; a cellâs response may shift gradually from the elimination
of damaged proteins by autophagy and the recovery to autophagic or apoptotic pathways of cell
death, the failure of which eventually may result in necrosis
KASCADE-Grande Limits on the Isotropic Diffuse Gamma-Ray Flux between 100 TeV and 1 EeV
KASCADE and KASCADE-Grande were multi-detector installations to measure
individual air showers of cosmic rays at ultra-high energy. Based on data sets
measured by KASCADE and KASCADE-Grande, 90% C.L. upper limits to the flux of
gamma-rays in the primary cosmic ray flux are determined in an energy range of
eV. The analysis is performed by selecting air showers
with a low muon content as expected for gamma-ray-induced showers compared to
air showers induced by energetic nuclei. The best upper limit of the fraction
of gamma-rays to the total cosmic ray flux is obtained at eV with . Translated to an absolute gamma-ray
flux this sets constraints on some fundamental astrophysical models, such as
the distance of sources for at least one of the IceCube neutrino excess models.Comment: Published in The Astrophysical Journal, Volume 848, Number 1. Posted
on: October 5, 201
First Experimental Characterization of Microwave Emission from Cosmic Ray Air Showers
We report the first direct measurement of the overall characteristics of
microwave radio emission from extensive air showers. Using a trigger provided
by the KASCADE-Grande air shower array, the signals of the microwave antennas
of the CROME (Cosmic-Ray Observation via Microwave Emission) experiment have
been read out and searched for signatures of radio emission by high-energy air
showers in the GHz frequency range. Microwave signals have been detected for
more than 30 showers with energies above 3*10^16 eV. The observations presented
in this Letter are consistent with a mainly forward-directed and polarised
emission process in the GHz frequency range. The measurements show that
microwave radiation offers a new means of studying air showers at energies
above 10^17 eV.Comment: Accepted for publication in PR
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