18,306 research outputs found
The structure of N(1535) in the aspect of chiral symmetry
The structure of N(1535) is discussed in dynamical and symmetry aspects based
on chiral symmetry. We find that the N(1535) in chiral unitary model has
implicitly some components other than meson-baryon one. We also discuss the
N(1535) in the chiral doublet picture.Comment: 4 pages, no figure, talk given at Workshop on Chiral Symmetry in
Hadron and Nuclear Physics: Chiral07, Osaka, Japan, 13-16 Nov 200
Electromagnetic transitions in an effective chiral Lagrangian with the eta-prime and light vector mesons
We consider the chiral Lagrangian with a nonet of Goldstone bosons and a
nonet of light vector mesons. The mixing between the pseudoscalar mesons eta
and eta-prime is taken into account. A novel counting scheme is suggested that
is based on hadrogenesis, which conjectures a mass gap in the meson spectrum of
QCD in the limit of a large number of colors. Such a mass gap would justify to
consider the vector mesons and the eta-prime meson as light degrees of freedom.
The complete leading order Lagrangian is constructed and discussed. As a first
application it is tested against electromagnetic transitions of light vector
mesons to pseudoscalar mesons. Our parameters are determined by the
experimental data on photon decays of the omega, phi and eta-prime meson. In
terms of such parameters we predict the corresponding decays into virtual
photons with either dielectrons or dimuons in the final state.Comment: 17 pages, extended discussion on mixin
Irreversibility and the arrow of time in a quenched quantum system
Irreversibility is one of the most intriguing concepts in physics. While
microscopic physical laws are perfectly reversible, macroscopic average
behavior has a preferred direction of time. According to the second law of
thermodynamics, this arrow of time is associated with a positive mean entropy
production. Using a nuclear magnetic resonance setup, we measure the
nonequilibrium entropy produced in an isolated spin-1/2 system following fast
quenches of an external magnetic field and experimentally demonstrate that it
is equal to the entropic distance, expressed by the Kullback-Leibler
divergence, between a microscopic process and its time-reverse. Our result
addresses the concept of irreversibility from a microscopic quantum standpoint.Comment: 8 pages, 7 figures, RevTeX4-1; Accepted for publication Phys. Rev.
Let
Genotoxic mixtures and dissimilar action: Concepts for prediction and assessment
This article has been made available through the Brunel Open Access Publishing Fund. This article is distributed under the terms of the
creative commons Attribution license which permits any use, distribution, and reproduction in any medium, provided the original author(s)and the source are credited.Combinations of genotoxic agents have frequently been assessed without clear assumptions regarding their expected (additive) mixture effects, often leading to claims of synergisms that might in fact be compatible with additivity. We have shown earlier that the combined effects of chemicals, which induce micronuclei (MN) in the cytokinesis-block micronucleus assay in Chinese hamster ovary-K1 cells by a similar mechanism, were additive according to the concept of concentration addition (CA). Here, we extended these studies and investigated for the first time whether valid additivity expectations can be formulated for MN-inducing chemicals that operate through a variety of mechanisms, including aneugens and clastogens (DNA cross-linkers, topoisomerase II inhibitors, minor groove binders). We expected that their effects should follow the additivity principles of independent action (IA). With two mixtures, one composed of various aneugens (colchicine, flubendazole, vinblastine sulphate, griseofulvin, paclitaxel), and another composed of aneugens and clastogens (flubendazole, doxorubicin, etoposide, melphalan and mitomycin C), we observed mixture effects that fell between the additivity predictions derived from CA and IA. We achieved better agreement between observation and prediction by grouping the chemicals into common assessment groups and using hybrid CA/IA prediction models. The combined effects of four dissimilarly acting compounds (flubendazole, paclitaxel, doxorubicin and melphalan) also fell within CA and IA. Two binary mixtures (flubendazole/paclitaxel and flubendazole/doxorubicin) showed effects in reasonable agreement with IA additivity. Our studies provide a systematic basis for the investigation of mixtures that affect endpoints of relevance to genotoxicity and show that their effects are largely additive.UK Food Standards Agenc
Is the ground state of Yang-Mills theory Coulombic?
We study trial states modelling the heavy quark-antiquark ground state in
SU(2) Yang-Mills theory. A state describing the flux tube between quarks as a
thin string of glue is found to be a poor description of the continuum ground
state; the infinitesimal thickness of the string leads to UV artifacts which
suppress the overlap with the ground state. Contrastingly, a state which
surrounds the quarks with non-abelian Coulomb fields is found to have a good
overlap with the ground state for all charge separations. In fact, the overlap
increases as the lattice regulator is removed. This opens up the possibility
that the Coulomb state is the true ground state in the continuum limit.Comment: 10 pages, 9 .eps figure
Optical Versus Mid-Infrared Spectroscopic Classification of Ultraluminous Infrared Galaxies
The origin of huge infrared luminosities of ultraluminous infrared galaxies
(ULIGs) is still in question. Recently, Genzel et al. made mid-infrared (MIR)
spectroscopy of a large number of ULIGs and found that the major energy source
in them is massive stars formed in the recent starburst activity; i.e.,
70% -- 80% of the sample are predominantly powered by the starburst. However,
it is known that previous optical spectroscopic observations showed that the
majority of ULIGs are classified as Seyferts or LINERs (low-ionization nuclear
emission-line regions). In order to reconcile this difference, we compare types
of emission-line activity for a sample of ULIGs which have been observed in
both optical and MIR. We confirm the results of previous studies that the
majority of ULIGs classified as LINERs based on the optical emission-line
diagnostics turn to be starburst-dominated galaxies based on the MIR ones.
Since the MIR spectroscopy can probe more heavily-reddened, inner parts of the
ULIGs, it is quite unlikely that the inner parts are powered by the starburst
while the outer parts are powered by non-stellar ionization sources. The most
probable resolution of this dilemma is that the optical emission-line nebulae
with the LINER properties are powered predominantly by shock heating driven by
the superwind activity; i.e., a blast wave driven by a collective effect of a
large number of supernovae in the central region of galaxy mergers.Comment: 15 pages, 2 tables, and 3 eps figures. The Astrophysical Journal
(Part 1), in pres
Dielectronic Resonance Method for Measuring Isotope Shifts
Longstanding problems in the comparison of very accurate hyperfine-shift
measurements to theory were partly overcome by precise measurements on
few-electron highly-charged ions. Still the agreement between theory and
experiment is unsatisfactory. In this paper, we present a radically new way of
precisely measuring hyperfine shifts, and demonstrate its effectiveness in the
case of the hyperfine shift of and in
. It is based on the precise detection of dielectronic
resonances that occur in electron-ion recombination at very low energy. This
allows us to determine the hyperfine constant to around 0.6 meV accuracy which
is on the order of 10%
XMM-Newton Spectroscopy of the Starburst Dominated Ultra Luminous Infrared Galaxy NGC 6240
We present new XMM-Newton observation of the Ultra Luminous Infrared Galaxy
(ULIRG) NGC 6240. We analyze the reflecting grating spectrometer (RGS) data,
and data from the other instruments, and find a starburst dominated 0.5-3 keV
spectrum with global properties resembling those observed in M82 but with a
much higher luminosity. We show that the starburst region can be divided into
an outer zone, beyond a radius of about 2.1 kpc, with a gas temperature of
about 10^7 K and a central region with temperatures in the range (2-6) x 10^7
K. The gas in the outer region emits most of the observed Oviii Lyman-alpha
line and the gas in the inner region the emission lines of higher ionization
ions, including a strong Fexxv line. We also identify a small inner part, very
close to the active nuclei, with typical Seyfert 2 properties including a large
amount of photoionized gas producing a strong Fe K-alpha 6.4 keV line. The
combined abundance, temperature and emission measure analysis indicates super
solar Ne/O, Mg/O, Si/O, S/O and possibly also Fe/O. The analysis suggests
densities in the range of (0.07-0.28) x epsilon^(-1/2) cm^(-3) and a total
thermal gas mass of about 4 x 10^8 x epsilon^(1/2) solar masses, where epsilon
is the volume filling factor. We used a simple model to argue that a massive
starburst with an age of about 2 x 10^7 years can explain most of the observed
properties of the source. NGC 6240 is perhaps the clearest case of an X-ray
bright luminous AGN, in a merger, whose soft X-ray spectrum is dominated by a
powerful starburst.Comment: 10 pages, 6 diagrams, accepted by ApJ, added a few minor change
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