795 research outputs found
Intersections of quadrics, moment-angle manifolds, and Hamiltonian-minimal Lagrangian embeddings
We study the topology of Hamiltonian-minimal Lagrangian submanifolds N in C^m
constructed from intersections of real quadrics in a work of the first author.
This construction is linked via an embedding criterion to the well-known
Delzant construction of Hamiltonian toric manifolds. We establish the following
topological properties of N: every N embeds as a submanifold in the
corresponding moment-angle manifold Z, and every N is the total space of two
different fibrations, one over the torus T^{m-n} with fibre a real moment-angle
manifold R, and another over a quotient of R by a finite group with fibre a
torus. These properties are used to produce new examples of Hamiltonian-minimal
Lagrangian submanifolds with quite complicated topology.Comment: 14 pages, published version (minor changes
Energy dependence of Ti/Fe ratio in the Galactic cosmic rays measured by the ATIC-2 experiment
Titanium is a rare, secondary nucleus among Galactic cosmic rays. Using the
Silicon matrix in the ATIC experiment, Titanium has been separated. The energy
dependence of the Ti to Fe flux ratio in the energy region from 5 GeV per
nucleon to about 500 GeV per nucleon is presented.Comment: 8 pages, 4 figures, accepted for publication in Astronomy Letter
Contribution of the magnetic resonance to the third harmonic generation from a fishnet metamaterial
We investigate experimentally and theoretically the third harmonic generated
by a double-layer fishnet metamaterial. To unambiguously disclose most notably
the influence of the magnetic resonance, the generated third harmonic was
measured as a function of the angle of incidence. It is shown experimentally
and numerically that when the magnetic resonance is excited by pump beam, the
angular dependence of the third harmonic signal has a local maximum at an
incidence angle of {\theta} \simeq 20{\deg}. This maximum is shown to be a
fingerprint of the antisymmetric distribution of currents in the gold layers.
An analytical model based on the nonlinear dynamics of the electrons inside the
gold shows excellent agreement with experimental and numerical results. This
clearly indicates the difference in the third harmonic angular pattern at
electric and magnetic resonances of the metamaterial.Comment: 7 pages, 5 figure
Calculations of fission rates for r-process nucleosynthesis
Fission plays an important role in the r-process which is responsible not
only for the yields of transuranium isotopes, but may have a strong influence
on the formation of the majority of heavy nuclei due to fission recycling. We
present calculations of beta-delayed and neutron-induced fission rates, taking
into account different fission barriers predictions and mass formulae.
It is shown that an increase of fission barriers results naturally in a
reduction of fission rates, but that nevertheless fission leads to the
termination of the r-process. Furthermore, it is discussed that the probability
of triple fission could be high for and have an effect on the formation
of the abundances of heavy nuclei. Fission after beta-delayed neutron emission
is discussed as well as different aspects of the influence of fission upon
r-process calculations.Comment: 28 pages, 10 figures, to be published in Nuclear Physics
A theory of -dissipative solvers for scalar conservation laws with discontinuous flux
We propose a general framework for the study of contractive semigroups
of solutions to conservation laws with discontinuous flux. Developing the ideas
of a number of preceding works we claim that the whole admissibility issue is
reduced to the selection of a family of "elementary solutions", which are
certain piecewise constant stationary weak solutions. We refer to such a family
as a "germ". It is well known that (CL) admits many different contractive
semigroups, some of which reflects different physical applications. We revisit
a number of the existing admissibility (or entropy) conditions and identify the
germs that underly these conditions. We devote specific attention to the
anishing viscosity" germ, which is a way to express the "-condition" of
Diehl. For any given germ, we formulate "germ-based" admissibility conditions
in the form of a trace condition on the flux discontinuity line (in the
spirit of Vol'pert) and in the form of a family of global entropy inequalities
(following Kruzhkov and Carrillo). We characterize those germs that lead to the
-contraction property for the associated admissible solutions. Our
approach offers a streamlined and unifying perspective on many of the known
entropy conditions, making it possible to recover earlier uniqueness results
under weaker conditions than before, and to provide new results for other less
studied problems. Several strategies for proving the existence of admissible
solutions are discussed, and existence results are given for fluxes satisfying
some additional conditions. These are based on convergence results either for
the vanishing viscosity method (with standard viscosity or with specific
viscosities "adapted" to the choice of a germ), or for specific germ-adapted
finite volume schemes
Possible structure in the cosmic ray electron spectrum measured by the ATIC-2 and ATIC-4 experiments
A strong excess in a form of a wide peak in the energy range of 300-800 GeV
was discovered in the first measurements of the electron spectrum in the energy
range from 20 GeV to 3 TeV by the balloon-borne experiment ATIC (J. Chang et
al. Nature, 2008). The experimental data processing and analysis of the
electron spectrum with different criteria for selection of electrons,
completely independent of the results reported in (J. Chang et al. Nature,
2008) is employed in the present paper. The new independent analysis generally
confirms the results of (J. Chang et al. Nature, 2008), but shows that the
spectrum in the region of the excess is represented by a number of narrow
peaks. The measured spectrum is compared to the spectrum of (J. Chang et al.
Nature, 2008) and to the spectrum of the Fermi/LAT experiment.Comment: LaTeX2e, 10 pages, 4 figures, a paper for ECRS 2010 (Turku, Finland);
http://www.astrophys-space-sci-trans.net/7/119/2011
Non-thermal high-energy emission from colliding winds of massive stars
Colliding winds of massive star binary systems are considered as potential
sites of non-thermal high-energy photon production. This is motivated merely by
the detection of synchrotron radio emission from the expected colliding wind
location. Here we investigate the properties of high-energy photon production
in colliding winds of long-period WR+OB-systems. We found that in the
dominating leptonic radiation process anisotropy and Klein-Nishina effects may
yield spectral and variability signatures in the gamma-ray domain at or above
the sensitivity of current or upcoming gamma-ray telescopes. Analytical
formulae for the steady-state particle spectra are derived assuming diffusive
particle acceleration out of a pool of thermal wind particles, and taking into
account adiabatic and all relevant radiative losses. For the first time we
include their advection/convection in the wind collision zone, and distinguish
two regions within this extended region: the acceleration region where spatial
diffusion is superior to convective/advective motion, and the convection region
defined by the convection time shorter than the diffusion time scale. The
calculation of the Inverse Compton radiation uses the full Klein-Nishina cross
section, and takes into account the anisotropic nature of the scattering
process. This leads to orbital flux variations by up to several orders of
magnitude which may, however, be blurred by the geometry of the system. The
calculations are applied to the typical WR+OB-systems WR 140 and WR 147 to
yield predictions of their expected spectral and temporal characteristica and
to evaluate chances to detect high-energy emission with the current and
upcoming gamma-ray experiments. (abridged)Comment: 67 pages, 24 figures, submitted to Ap
Upturn observed in heavy nuclei to iron ratios by the ATIC-2 experiment
The ratios of fluxes of heavy nuclei from sulfur (Z=16) to chromium (Z=24) to
the flux of iron were measured by the ATIC-2 experiment. The ratios are
decreasing functions of energy from 5 GeV/n to approximately 80 GeV/n, as
expected. However, an unexpected sharp upturn in the ratios are observed for
energies above 100 GeV/n for all elements from Z=16 to Z=24. Similar upturn but
with lower amplitude was also discovered in the ATIC-2 data for the ratio of
fluxes of abundant even nuclei (C, O, Ne, Mg, Si) to the flux of iron.
Therefore the spectrum of iron is significantly different from the spectra of
other abundant even nuclei.Comment: 4 pages, LaTeX2e, a paper for 23rd European Cosmic Ray Symposium
(2012
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