4,897 research outputs found
A Last Look at the Microwave Haze/Bubbles with WMAP
The microwave "haze" was first discovered with the initial release of the
full sky data from the Wilkinson Microwave Anisotropy Probe. It is diffuse
emission towards the center of our Galaxy with spectral behavior that makes it
difficult to categorize as any of the previously known emission mechanisms at
those wavelengths. With now seven years of WMAP data publicly available, we
have learned much about the nature of the haze, and with the release of data
from the Fermi Gamma-Ray Space Telescope and the discovery of the gamma-ray
haze/bubbles, we have had a spectacular confirmation of its existence at other
wavelengths. As the WMAP mission winds down and the Planck mission prepares to
release data, I take a last look at what WMAP has to tell us about the origin
of this unique Galactic feature. Much like the gamma-rays, the microwave
haze/bubbles is elongated in latitude with respect to longitude by a factor of
roughly two, and at high latitudes, the microwave emission cuts off sharply
above ~35 degrees (compared to ~50 degrees in the gammas). The hard spectrum of
electrons required to generate the microwave synchrotron is consistent with
that required to generate the gamma-ray emission via inverse Compton
scattering, though it is likely that these signals result from distinct regions
of the spectrum (~10 GeV for the microwaves, ~1 TeV for the gammas). While
there is no evidence for significant haze polarization in the 7-year WMAP data,
I demonstrate explicitly that it is unlikely such a signal would be detectable
above the noise.Comment: 9 pages, 6 figures; accepted in ApJ; matches published version with
significantly enhanced figure
The ubiquitin-proteasome pathway in Huntington's disease.
The accumulation of mutant protein is a common feature of neurodegenerative disease. In Huntington's disease, a polyglutamine expansion in the huntingtin protein triggers neuronal toxicity. Accompanying neuronal death, mutant huntingtin aggregates in large macromolecular structures called inclusion bodies. The function of the machinery for intracellular protein degradation is linked to huntingtin toxicity and components of this machinery colocalize with inclusion bodies. An increasing body of evidence implicates the ubiquitin-proteasome pathway in the failure of cells to degrade mutant huntingtin. A number of potential mechanisms that link compromised ubiquitin-proteasome pathway function and neurodegeneration have been proposed and may offer opportunities for therapeutic intervention
Efficient Parallel Path Checking for Linear-Time Temporal Logic With Past and Bounds
Path checking, the special case of the model checking problem where the model
under consideration is a single path, plays an important role in monitoring,
testing, and verification. We prove that for linear-time temporal logic (LTL),
path checking can be efficiently parallelized. In addition to the core logic,
we consider the extensions of LTL with bounded-future (BLTL) and past-time
(LTL+Past) operators. Even though both extensions improve the succinctness of
the logic exponentially, path checking remains efficiently parallelizable: Our
algorithm for LTL, LTL+Past, and BLTL+Past is in AC^1(logDCFL) \subseteq NC
Lossy Channel Games under Incomplete Information
In this paper we investigate lossy channel games under incomplete
information, where two players operate on a finite set of unbounded FIFO
channels and one player, representing a system component under consideration
operates under incomplete information, while the other player, representing the
component's environment is allowed to lose messages from the channels. We argue
that these games are a suitable model for synthesis of communication protocols
where processes communicate over unreliable channels. We show that in the case
of finite message alphabets, games with safety and reachability winning
conditions are decidable and finite-state observation-based strategies for the
component can be effectively computed. Undecidability for (weak) parity
objectives follows from the undecidability of (weak) parity perfect information
games where only one player can lose messages.Comment: In Proceedings SR 2013, arXiv:1303.007
Evidence for Gamma-ray Jets in the Milky Way
Although accretion onto supermassive black holes in other galaxies is seen to
produce powerful jets in X-ray and radio, no convincing detection has ever been
made of a kpc-scale jet in the Milky Way. The recently discovered pair of 10
kpc tall gamma-ray bubbles in our Galaxy may be a sign of earlier jet activity
from the central black hole. In this paper, we identify a gamma-ray cocoon
feature in the southern bubble, a jet-like feature along the cocoon's axis of
symmetry, and another directly opposite the Galactic center in the north. Both
the cocoon and jet-like feature have a hard spectrum with spectral index ~ -2
from 1 to 100 GeV, with a cocoon luminosity of (5.5 +/- 0.45) x 10^35 erg/s and
luminosity of the jet-like feature of (1.8 +/- 0.35) x 10^35 erg/s at 1 to 100
GeV. If confirmed, these jets are the first resolved gamma-ray jets ever seen.Comment: 14 pages, 11 figures, accepted by Ap
Constraining Spinning Dust Parameters with the WMAP Five-Year Data
We characterize spinning dust emission in the warm ionized medium by
comparing templates of Galactic dust and Halpha with the 5-year maps from the
Wilkinson Microwave Anisotropy Probe. The Halpha-correlated microwave emission
deviates from the thermal bremsstrahlung (free-free) spectrum expected for
ionized gas, exhibiting an additional broad bump peaked at ~40 GHz which
provides ~20% of the peak intensity. We confirm that the bump is consistent
with a modified Draine & Lazarian (1998) spinning dust model, though the peak
frequency of the emission is somewhat lower than the 50 GHz previously claimed.
This frequency shift results from systematic errors in the large-scale modes of
the 3-year WMAP data which have been corrected in the 5-year data release. We
show that the bump is not the result of errors in the Halpha template by
analyzing regions of high free-free intensity, where the WMAP K-band map may be
used as the free-free template. We rule out a pure free-free spectrum for the
Halpha-correlated emission at high confidence: ~27sigma for the nearly full-sky
fit, even after marginalizing over the CMB cross-correlation bias. We also
extend the previous analysis by searching the parameter space of the Draine &
Lazarian model but letting the amplitude float. The best fit for reasonable
values of the characteristic electric dipole moment and density requires an
amplitude factor of ~0.3. This suggests that small PAHs in the warm ionized
medium are depleted by a factor of ~3.Comment: 17 pages, 13 figures; submitted to Ap
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