752 research outputs found
The electromagnetic dipole operator effect on B -> Xs gamma at O(alpha_s^2)
The flavor-changing electromagnetic dipole operator O_7 gives the dominant
contribution to the B -> Xs gamma decay rate. We calculate two-loop QCD
corrections to its matrix element together with the corresponding
bremsstrahlung contributions. The optical theorem is applied, and the relevant
imaginary parts of three-loop diagrams are computed following the lines of our
recent t -> Xb W calculation. The complete result allows us to test the
validity of the naive non-abelianization (NNA) approximation that has been
previously applied to estimate the NNLO QCD correction to Gamma(B -> Xs
gamma)/Gamma(B -> Xu e nu). When both decay widths are normalized to m^5_{b,R}
in the same renormalization scheme R, the calculated O(alpha_s^2) correction is
sizeable (~ 6%), and the NNA estimate is about 1/3 too large. On the other
hand, when the ratio of the decay widths is written as
S*(m_b(m_b)/m_{b,pole})^2, the calculated O(alpha_s^2) correction to S is at
the level of 1% for both the complete and the NNA results.Comment: Corrected pi^2 terms in the description of intermediate steps in
Section II. Final results unchange
Discovery of extended radio emission in the young cluster Wd1
We present 10 micron, ISO-SWS and Australia Telescope Compact Array
observations of the region in the cluster Wd1 in Ara centred on the B[e] star
Ara C. An ISO-SWS spectrum reveals emission from highly ionised species in the
vicinity of the star, suggesting a secondary source of excitation in the
region. We find strong radio emission at both 3.5cm and 6.3cm, with a total
spatial extent of over 20 arcsec. The emission is found to be concentrated in
two discrete structures, separated by 14''. The westerly source is resolved,
with a spectral index indicative of thermal emission. The easterly source is
clearly extended and nonthermal (synchrotron) in nature. Positionally, the B[e]
star is found to coincide with the more compact radio source, while the
southerly lobe of the extended source is coincident with Ara A, an M2 I star.
Observation of the region at 10micron reveals strong emission with an almost
identical spatial distribution to the radio emission. Ara C is found to have an
extreme radio luminosity in comparison to prior radio observations of hot stars
such as O and B supergiants and Wolf-Rayet stars, given the estimated distance
to the cluster. An origin in a detatched shell of material around the central
star is therefore suggested; however given the spatial extent of the emission,
such a shell must be relatively young (10^3 yrs). The extended non thermal
emission associated with the M star Ara A is unexpected; to the best of our
knowledge this is a unique phenomenon. SAX (2-10keV) observations show no
evidence of X-ray emission, which might be expected if a compact companion were
present.Comment: 5 pages including encapsulated figures, figure 3 separate. Accepted
for MNRAS pink page
Early warning signals for predicting cryptomarket vendor success using dark net forum networks
In this work we focus on identifying key players in dark net cryptomarkets.
Law enforcement aims to disrupt criminal activity conducted through these
markets by targeting key players vital to the market's existence and success.
We particularly focus on detecting successful vendors responsible for the
majority of illegal trade. Our methodology aims to uncover whether the task of
key player identification should center around plainly measuring user and forum
activity, or that it requires leveraging specific patterns of user
communication. We focus on a large-scale dataset from the Evolution
cryptomarket, which we model as an evolving communication network. While user
and forum activity measures are useful for identifying the most successful
vendors, we find that betweenness centrality additionally identifies those with
lesser activity. But more importantly, analyzing the forum data over time, we
find evidence that attaining a high betweenness score comes before vendor
success. This suggests that the proposed network-driven approach of modelling
user communication might prove useful as an early warning signal for key player
identification
Possible overlapping time frames of acquisition and consolidation phases in object memory processes: a pharmacological approach
In previous studies, we have shown that acetylcholinesterase inhibitors and phosphodiesterase inhibitors (PDE-Is) are able to improve object memory by enhancing acquisition processes. On the other hand, only PDE-Is improve consolidation processes. Here we show that the cholinesterase inhibitor donepezil also improves memory performance when administered within 2 min after the acquisition trial. Likewise, both PDE5-I and PDE4-I reversed the scopolamine deficit model when administered within 2 min after the learning trial. PDE5-I was effective up to 45 min after the acquisition trial and PDE4-I was effective when administered between 3 and 5.5 h after the acquisition trial. Taken together, our study suggests that acetylcholine, cGMP, and cAMP are all involved in acquisition processes and that cGMP and cAMP are also involved in early and late consolidation processes, respectively. Most important, these pharmacological studies suggest that acquisition processes continue for some time after the learning trial where they share a short common time frame with early consolidation processes. Additional brain concentration measurements of the drugs suggest that these acquisition processes can continue up to 4–6 min after learning
HIF-1 alpha-independent hypoxia-induced rapid PTK6 stabilization is associated with increased motility and invasion
© 2014 Landes Bioscience. PTK6/Brk is a non-receptor tyrosine kinase overexpressed in cancer. Here we demonstrate that cytosolic PTK6 is rapidly and robustly induced in response to hypoxic conditions in a HIF-1-independent manner. Furthermore, a proportion of hypoxic PTK6 subsequently re-localized to the cell membrane. We observed that the rapid stabilization of PTK6 is associated with a decrease in PTK6 ubiquitylation and we have identified c-Cbl as a putative PTK6 E3 ligase in normoxia. The consequences of hypoxia-induced PTK6 stabilization and subcellular re-localization to the plasma membrane include increased cell motility and invasion, suggesting PTK6 targeting as a therapeutic approach to reduce hypoxia-regulated metastatic potential. This could have particular significance for breast cancer patients with triple negative disease
Pion pole contribution to hadronic light-by-light scattering and muon anomalous magnetic moment
We derive an analytic result for the pion pole contribution to the
light-by-light scattering correction to the anomalous magnetic moment of the
muon, . Using the vector meson dominance model (VMD) for
the pion transition form factor, we obtain .Comment: 4 pages, revte
Hadronic Light-by-Light Contribution to Muon g-2 in Chiral Perturbation Theory
We compute the hadronic light-by-light scattering contributions to the muon
anomalous magnetic moment, \amulbl, in chiral perturbation theory that are
enhanced by large logarithms and a factor of . They depend on a low-energy
constant entering pseudoscalar meson decay into a charged lepton pair. The
uncertainty introduced by this constant is , which is
comparable in magnitude to the present uncertainty entering the leading-order
vacuum polarization contributions to the anomalous moment. It may be reduced to
some extent through an improved measurement of the branching
ratio. However, the dependence of \amulbl on non-logarithmically enhanced
effects cannot be constrained except through the measurement of the anomalous
moment itself. The extraction of information on new physics would require a
future experimental value for the anomalous moment differing significantly from
the 2001 result reported by the E821 collaboration.Comment: 7 pages, 2 figure
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