773 research outputs found
A Chandra X-ray detection of the L dwarf binary Kelu-1: Simultaneous Chandra and Very Large Array observations
Magnetic activity in ultracool dwarfs, as measured in X-rays and H,
shows a steep decline after spectral type M7-M8. So far, no L dwarf has been
detected in X-rays. In contrast, L dwarfs may have higher radio activity than M
dwarfs. We observe L and T dwarfs simultaneously in X-rays and radio to
determine their level of magnetic activity in the context of the general
decline of magnetic activity with cooler effective temperatures. The field L
dwarf binary Kelu-1 was observed simultaneously with Chandra and the Very Large
Array. Kelu-1AB was detected in X-rays with erg/s, while it remained undetected in the radio down to a limit of erg/s/Hz. We argue that,
whereas the X-ray and H emissions decline in ultracool dwarfs with
decreasing effective temperature, the radio luminosity stays (more or less)
constant across M and early-L dwarfs. The radio surface flux or the luminosity
may better trace magnetic activity in ultracool dwarfs than the ratio of the
luminosity to the bolometric luminosity. Deeper radio observations (and at
short frequencies) are required to determine if and when the cut-off in radio
activity occurs in L and T dwarfs, and what kind of emission mechanism takes
place in ultracool dwarfs.Comment: Accepted for publication as a Letter in Astronomy & Astrophysic
Cytochrome c activation of CPP32-like proteolysis plays a critical role in a Xenopus cell-free apoptosis system
The -cleus experiment: A gram-scale fiducial-volume cryogenic detector for the first detection of coherent neutrino-nucleus scattering
We discuss a small-scale experiment, called -cleus, for the first
detection of coherent neutrino-nucleus scattering by probing nuclear-recoil
energies down to the 10 eV-regime. The detector consists of low-threshold
CaWO and AlO calorimeter arrays with a total mass of about 10 g and
several cryogenic veto detectors operated at millikelvin temperatures.
Realizing a fiducial volume and a multi-element target, the detector enables
active discrimination of , neutron and surface backgrounds. A first
prototype AlO device, operated above ground in a setup without
shielding, has achieved an energy threshold of eV and further
improvements are in reach. A sensitivity study for the detection of coherent
neutrino scattering at nuclear power plants shows a unique discovery potential
(5) within a measuring time of weeks. Furthermore, a site
at a thermal research reactor and the use of a radioactive neutrino source are
investigated. With this technology, real-time monitoring of nuclear power
plants is feasible.Comment: 14 pages, 19 figure
Preservation of Mitochondrial Structure and Function after Bid- or Bax-Mediated Cytochrome c Release
Proapoptotic members of the Bcl-2 protein family, including Bid and Bax, can activate apoptosis by directly interacting with mitochondria to cause cytochrome c translocation from the intermembrane space into the cytoplasm, thereby triggering Apaf-1–mediated caspase activation. Under some circumstances, when caspase activation is blocked, cells can recover from cytochrome c translocation; this suggests that apoptotic mitochondria may not always suffer catastrophic damage arising from the process of cytochrome c release. We now show that recombinant Bid and Bax cause complete cytochrome c loss from isolated mitochondria in vitro, but preserve the ultrastructure and protein import function of mitochondria, which depend on inner membrane polarization. We also demonstrate that, if caspases are inhibited, mitochondrial protein import function is retained in UV-irradiated or staurosporine-treated cells, despite the complete translocation of cytochrome c. Thus, Bid and Bax act only on the outer membrane, and lesions in the inner membrane occurring during apoptosis are shown to be secondary caspase-dependent events
Black hole masses and starbursts in X-shaped radio sources
It has been suggested that the X-shaped morphology observed in some radio
sources can reflect either a recent merger of two supermassive black holes
(SMBHs) or the presence of a second active black hole in the galactic nucleus.
These scenarios are tested by studying the relationship between the black hole
mass, radio and optical luminosity, starburst history, and dynamic age of radio
lobes in a sample of 29 X-shaped radio galaxies drawn from a list of 100
X-shaped radio source candidates identified from the FIRST survey. The same
relationships are also studied in a control sample consisting of 36 radio-loud
active nuclei with similar redshifts and optical and radio luminosities. The
X-shaped objects are found to have statistically higher black hole masses and
older starburst activity compared to the objects from the control sample.
Implications of these findings are discussed for the black hole merger scenario
and for the potential presence of active secondary black holes in post-merger
galaxies.Comment: 11 pages, 8 figure
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