980 research outputs found
A Novel Approach in Constraining Electron Spectra in Blazar Jets: The Case of Markarian 421
We report results from the observations of the well studied TeV blazar Mrk
421 with the Swift and the Suzaku satellites in December 2008. During the
observation, Mrk 421 was found in a relatively low activity state, with the
corresponding 2-10 keV flux of erg/s/cm^2. For the purpose
of robust constraining the UV-to-X-ray emission continuum we selected only the
data corresponding to truly simultaneous time intervals between Swift and
Suzaku, allowing us to obtain a good-quality, broad-band spectrum despite a
modest length (0.6 ksec) exposure. We analyzed the spectrum with the parametric
forward-fitting SYNCHROTRON model implemented in XSPEC assuming two different
representations of the underlying electron energy distribution, both well
motivated by the current particle acceleration models: a power-law distribution
above the minimum energy with an exponential cutoff at the
maximum energy , and a modified ultra-relativistic Maxwellian
with an equilibrium energy . We found that the latter implies
unlikely physical conditions within the blazar zone of Mrk 421. On the other
hand, the exponentially moderated power-law electron distribution gives two
possible sets of the model parameters: (i) flat spectrum with low minimum electron energy , and
(ii) steep spectrum with high minimum electron energy
. We discuss different interpretations of
both possibilities in the context of a diffusive acceleration of electrons at
relativistic, sub- or superluminal shocks. We also comment on how exactly the
gamma-ray data can be used to discriminate between the proposed different
scenarios.Comment: 18 pages, 2 figures; accepted for publication in the Astrophysical
Journa
Photon generation by laser-Compton scattering at the KEK-ATF
We performed a photon generation experiment by laser-Compton scattering at
the KEK-ATF, aiming to develop a Compton based polarized positron source for
linear colliders. In the experiment, laser pulses with a 357 MHz repetition
rate were accumulated and their power was enhanced by up to 250 times in the
Fabry-Perot optical resonant cavity. We succeeded in synchronizing the laser
pulses and colliding them with the 1.3 GeV electron beam in the ATF ring while
maintaining the laser pulse accumulation in the cavity. As a result, we
observed 26.0 +/- 0.1 photons per electron-laser pulse crossing, which
corresponds to a yield of 10^8 photons in a second.Comment: 3 pages, 5 figures, Preprint submitted to TIPP09 Proceedings in NIM
DNA metabarcoding unveils multiscale trophic variation in a widespread coastal opportunist
A thorough understanding of ecological networks relies on comprehensive information on trophic relationships among species. Since unpicking the diet of many organisms is unattainable using traditional morphology‐based approaches, the application of high‐throughput sequencing methods represents a rapid and powerful way forward. Here, we assessed the application of DNA metabarcoding with nearly universal primers for the mitochondrial marker cytochrome c oxidase I in defining the trophic ecology of adult brown shrimp, Crangon crangon, in six European estuaries. The exact trophic role of this abundant and widespread coastal benthic species is somewhat controversial, while information on geographical variation remains scant. Results revealed a highly opportunistic behaviour. Shrimp stomach contents contained hundreds of taxa (>1,000 molecular operational taxonomic units), of which 291 were identified as distinct species, belonging to 35 phyla. Only twenty ascertained species had a mean relative abundance of more than 0.5%. Predominant species included other abundant coastal and estuarine taxa, including the shore crab Carcinus maenas and the amphipod Corophium volutator. Jacobs’ selectivity index estimates based on DNA extracted from both shrimp stomachs and sediment samples were used to assess the shrimp's trophic niche indicating a generalist diet, dominated by crustaceans, polychaetes and fish. Spatial variation in diet composition, at regional and local scales, confirmed the highly flexible nature of this trophic opportunist. Furthermore, the detection of a prevalent, possibly endoparasitic fungus (Purpureocillium lilacinum) in the shrimp's stomach demonstrates the wide range of questions that can be addressed using metabarcoding, towards a more robust reconstruction of ecological networks
X-ray Time Lags in TeV Blazars
We use Monte Carlo/Fokker-Planck simulations to study the X-ray time lags.
Our results show that soft lags will be observed as long as the decay of the
flare is dominated by radiative cooling, even when acceleration and cooling
timescales are similar. Hard lags can be produced in presence of a competitive
achromatic particle energy loss mechanism if the acceleration process operates
on a timescale such that particles are slowly moved towards higher energy while
the flare evolves. In this type of scenario, the {\gamma} -ray/X-ray quadratic
relation is also reproduced.Comment: 4 pages, 6 figures, Proceeding of `Multiwavelength Variability of
Blazars', Guangzhou, Chin
The proton spin sum rule chiral bag prediction, an update
We reevaluate a quark model prediction using the new QCD evolution function
calculated to the 3 loop order and conclude that this model compares favorably
with the new experimental results.Comment: 10 pages, 2 figures available by request, give fax numbe
Identification of regions critical for the integrity of the TSC1-TSC2-TBC1D7 complex
The TSC1-TSC2-TBC1D7 complex is an important negative regulator of the mechanistic target of rapamycin complex 1 that controls cell growth in response to environmental cues. Inactivating TSC1 and TSC2 mutations cause tuberous sclerosis complex (TSC), an autosomal dominant disorder characterised by the occurrence of benign tumours in various organs and tissues, notably the brain, skin and kidneys. TBC1D7 mutations have not been reported in TSC patients but homozygous inactivation of TBC1D7 causes megaencephaly and intellectual disability. Here, using an exon-specific deletion strategy, we demonstrate that some regions of TSC1 are not necessary for the core function of the TSC1-TSC2 complex. Furthermore, we show that the TBC1D7 binding site is encoded by TSC1 exon 22 and identify amino acid residues involved in the TSC1-TBC1D7 interaction
Mouse models for preeclampsia: disruption of redox-regulated signaling
The concept that oxidative stress contributes to the development of human preeclampsia has never been tested in genetically-defined animal models. Homozygous deletion of catechol-Omethyl transferase (Comt-/-) in pregnant mice leads to human preeclampsia-like symptoms (high
blood pressure, albuminurea and preterm birth) resulting from extensive vasculo-endothelial pathology, primarily at the utero-fetal interface where maternal cardiac output is dramatically increased during pregnancy. Comt converts estradiol to 2-methoxyestradiol 2 (2ME2) which
counters angiogenesis by depleting hypoxia inducible factor-1 alpha (HIF-1 alpha) at late pregnancy. We propose that in wild type (Comt++) pregnant mice, 2ME2 destabilizes HIF-1 alpha by inhibiting mitochondrial superoxide dismutase (MnSOD). Thus, 2ME2 acts as a pro-oxidant, disrupting
redox-regulated signaling which blocks angiogenesis in wild type (WT) animals in physiological pregnancy. Further, we suggest that a lack of this inhibition under normoxic conditions in mutant animals (Comt-/-) stabilises HIF-1 alpha by inactivating prolyl hydroxlases (PHD). We predict that a lack of inhibition of MnSOD, leading to persistent accumulation of HIF-1 alpha, would trigger
inflammatory infiltration and endothelial damage in mutant animals. Critical tests of this hypothesis would be to recreate preeclampsia symptoms by inducing oxidative stress in WT animals or to ameliorate by treating mutant mice with Mn-SOD-catalase mimetics or activators of PHD
Quantum magneto-optics of graphite family
The optical conductivity of graphene, bilayer graphene, and graphite in
quantizing magnetic fields is studied. Both dynamical conductivities,
longitudinal and Hall's, are analytically evaluated. The conductivity peaks are
explained in terms of electron transitions. We have shown that trigonal warping
can be considered within the perturbation theory for strong magnetic fields
larger than 1 T and in the semiclassical approach for weak fields when the
Fermi energy is much larger than the cyclotron frequency. The main optical
transitions obey the selection rule with \Deltan = 1 for the Landau number n,
however the \Deltan = 2 transitions due to the trigonal warping are also
possible. The Faraday/Kerr rotation and light transmission/reflection in the
quantizing magnetic fields are calculated. Parameters of the
Slonczewski-Weiss-McClure model are used in the fit taking into account the
previous dHvA measurements and correcting some of them for the case of strong
magnetic fields.Comment: 28 pages, 12 figures. arXiv admin note: text overlap with
arXiv:1106.340
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