13,776 research outputs found
A kpc-scale X-ray jet in the BL Lac source S5 2007+777
X-ray jets in AGN are commonly observed in FRII and FRI radio-galaxies, but
rarely in BL Lacs, most probably due to their orientation close to the line of
sight and the ensuing foreshortening effects. Only three BL Lacs are known so
far to contain a kpc-scale X-ray jet. In this paper, we present the evidence
for the existence of a fourth extended X-ray jet in the classical
radio-selected source S5 2007+777, which for its hybrid FRI/II radio morphology
has been classified as a HYMOR (HYbrid MOrphology Radio source). Our Chandra
ACIS-S observations of this source revealed an X-ray counterpart to the
19"-long radio jet. Interestingly, the X-ray properties of the kpc-scale jet in
S5 2007+777 are very similar to those observed in FRII jets. First, the X-ray
morphology closely mirrors the radio one, with the X-rays being concentrated in
the discrete radio knots. Second, the X-ray continuum of the jet/brightest knot
is described by a very hard power law, with photon index Gamma_x~1, although
the uncertainties are large. Third, the optical upper limit from archival HST
data implies a concave radio-to-X-ray SED. If the X-ray emission is attributed
to IC/CMB with equipartition, strong beaming (delta=13) is required, implying a
very large scale (Mpc) jet. The beaming requirement can be somewhat relaxed
assuming a magnetic field lower than equipartition. Alternatively, synchrotron
emission from a second population of very high-energy electrons is viable.
Comparison to other HYMOR jets detected with Chandra is discussed, as well as
general implications for the origin of the FRI/II division.Comment: Accepted for publication in ApJ, 19 pages, 3 figure
New determination of the production cross section for secondary positrons and electrons in the Galaxy
Targeting RAGE prevents muscle wasting and prolongs survival in cancer cachexia
Background: Cachexia, a multifactorial syndrome affecting more than 50% of patients with advanced cancer and responsible for ~20% of cancer-associated deaths, is still a poorly understood process without a standard cure available. Skeletal muscle atrophy caused by systemic inflammation is a major clinical feature of cachexia, leading to weight loss, dampening patients' quality of life, and reducing patients' response to anticancer therapy. RAGE (receptor for advanced glycation end-products) is a multiligand receptor of the immunoglobulin superfamily and a mediator of muscle regeneration, inflammation, and cancer. Methods: By using murine models consisting in the injection of colon 26 murine adenocarcinoma (C26-ADK) or Lewis lung carcinoma (LLC) cells in BALB/c and C57BL/6 or Ager−/− (RAGE-null) mice, respectively, we investigated the involvement of RAGE signalling in the main features of cancer cachexia, including the inflammatory state. In vitro experiments were performed using myotubes derived from C2C12 myoblasts or primary myoblasts isolated from C57BL/6 wild type and Ager−/− mice treated with the RAGE ligand, S100B (S100 calcium-binding protein B), TNF (tumor necrosis factor)α±IFN (interferon) γ, and tumour cell- or masses-conditioned media to analyse hallmarks of muscle atrophy. Finally, muscles of wild type and Ager−/− mice were injected with TNFα/IFNγ or S100B in a tumour-free environment. Results: We demonstrate that RAGE is determinant to activate signalling pathways leading to muscle protein degradation in the presence of proinflammatory cytokines and/or tumour-derived cachexia-inducing factors. We identify the RAGE ligand, S100B, as a novel factor able to induce muscle atrophy per se via a p38 MAPK (p38 mitogen-activated protein kinase)/myogenin axis and STAT3 (signal transducer and activator of transcription 3)-dependent MyoD (myoblast determination protein 1) degradation. Lastly, we found that in cancer conditions, an increase in serum levels of tumour-derived S100B and HMGB1 (high mobility group box 1) occurs leading to chronic activation/overexpression of RAGE, which induces hallmarks of cancer cachexia (i.e. muscle wasting, systemic inflammation, and release of tumour-derived pro-cachectic factors). Absence of RAGE in mice translates into reduced serum levels of cachexia-inducing factors, delayed loss of muscle mass and strength, reduced tumour progression, and increased survival. Conclusions: RAGE is a molecular determinant in inducing the hallmarks of cancer cachexia, and molecular targeting of RAGE might represent a therapeutic strategy to prevent or counteract the cachectic syndrome
On the Existence of Energy-Preserving Symplectic Integrators Based upon Gauss Collocation Formulae
We introduce a new family of symplectic integrators depending on a real
parameter. When the paramer is zero, the corresponding method in the family
becomes the classical Gauss collocation formula of order 2s, where s denotes
the number of the internal stages. For any given non-null value of the
parameter, the corresponding method remains symplectic and has order 2s-2:
hence it may be interpreted as an order 2s-2 (symplectic) perturbation of the
Gauss method. Under suitable assumptions, we show that the free parameter may
be properly tuned, at each step of the integration procedure, so as to
guarantee energy conservation in the numerical solution. The resulting
symplectic, energy conserving method shares the same order 2s as the generating
Gauss formula.Comment: 19 pages, 7 figures; Sections 1, 2, and 6 sliglthly modifie
Limitations of Radar Coordinates
The construction of a radar coordinate system about the world line of an
observer is discussed. Radar coordinates for a hyperbolic observer as well as a
uniformly rotating observer are described in detail. The utility of the notion
of radar distance and the admissibility of radar coordinates are investigated.
Our results provide a critical assessment of the physical significance of radar
coordinates.Comment: 12 pages, revtex and pictex macros, 3 pictex figures, 1 eps figure.
Expanded versio
Ordinary and Extraordinary Hadrons
Resonances and enhancements in meson-meson scattering can be divided into two
classes distinguished by their behavior as the number of colors N_c in QCD
becomes large: The first are ordinary mesons that become stable as N_c goes to
infinity. This class includes textbook q-bar q mesons as well as glueballs and
hybrids. The second class, extraordinary mesons, are enhancements that
disappear as N_c goes to infinity; they subside into the hadronic continuum.
This class includes indistinct and controversial objects that have been
classified as q-bar q-bar q q mesons or meson-meson molecules. Pelaez's study
of the N_c dependence of unitarized chiral dynamics illustrates both classes:
the p-wave pi-pi and K-pi resonances, the rho(770) and K*(892), behave as
ordinary mesons; the s-wave pi-pi and K-pi enhancements, the sigma(600) and
kappa(800), behave like extraordinary mesons. Ordinary mesons resemble Feshbach
resonances while extraordinary mesons look more like effects due to potentials
in meson-meson scattering channels. I build and explore toy models along these
lines. Finally I discuss some related dynamical issues affecting the
interpretation of extraordinary mesons.Comment: 18 pages, 10 figures, talk presented at the 2006 Yukawa International
Seminar: New Frontiers in QCD, Kyoto University, November 2006. This talk is
dedicated to the memory of R. H. Dalit
Towards the Measurement of Household Resilience to Food Insecurity: Applying a Model to Palestinian Household Data
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