9,398 research outputs found
Spin Filtering of Stored (Anti)Protons: from FILTEX to COSY to AD to FAIR
We review the theory of spin filtering of stored (anti)protons by multiple
passage through the polarized internal target (PIT). Implications for the
antiproton polarization buildup in the proposed PAX experiment at FAIR GSI are
discussed.Comment: 4 pages, 1 figure, Presented at the 17th Intl. Spin Physics
Symposium, SPIN2006, Kyoto, Japan, October 2-7, 200
Quantum nature of cyclotron harmonics in thermal spectra of neutron stars
Some isolated neutron stars show harmonically spaced absorption features in
their thermal soft X-ray spectra. The interpretation of the features as a
cyclotron line and its harmonics has been suggested, but the usual explanation
of the harmonics as caused by relativistic effects fails because the
relativistic corrections are extremely small in this case. We suggest that the
features correspond to the peaks in the energy dependence of the free-free
opacity in a quantizing magnetic field, known as quantum oscillations. The
peaks arise when the transitions to new Landau levels become allowed with
increasing the photon energy; they are strongly enhanced by the square-root
singularities in the phase-space density of quantum states in the case when the
free (non-quantized) motion is effectively one-dimensional. To explore
observable properties of these quantum oscillations, we calculate models of
hydrogen neutron star atmospheres with B \sim 10^{10} - 10^{11} G (i.e.,
electron cyclotron energy E_{c,e} = 0.1 - 1 keV) and T_{eff} = 1 - 3 MK. Such
conditions are thought to be typical for the so-called central compact objects
in supernova remnants, such as 1E 1207.4-5209 in PKS 1209-51/52. We show that
observable features at the electron cyclotron harmonics form at moderately
large values of the quantization parameter, b_{eff} = E_{c,e}/kT_{eff} = 0.5 -
20. The equivalent widths of the features can reach 100 - 200 eV; they grow
with increasing b_{eff} and are lower for higher harmonics.Comment: 6 pages; shortened, references updated; published in Ap
On the bi-Hamiltonian Geometry of WDVV Equations
We consider the WDVV associativity equations in the four dimensional case.
These nonlinear equations of third order can be written as a pair of six
component commuting two-dimensional non-diagonalizable hydrodynamic type
systems. We prove that these systems possess a compatible pair of local
homogeneous Hamiltonian structures of Dubrovin--Novikov type (of first and
third order, respectively).Comment: 21 pages, revised published version; exposition substantially
improve
Mediation, arbitration and negotiation
We compare three common dispute resolution processes { negotiation, mediation, and arbitration { in the framework of Crawford and Sobel (1982). Under negotiation, the two parties engage in (possibly arbitrarily long) face-to-face cheap talk. Under mediation, the parties communicate with a neutral third party who makes a non-binding recommendation. Under arbitration, the two parties commit
to conform to the third party recommendation. We characterize and compare the optimal mediation and arbitration procedures. Both mediators and arbitrators should optimally filter information, but mediators should also add noise to it. We find that unmediated negotiation performs as well as mediation if and only if the degree of
conflict between the parties is low
Hard Extended X-ray Source in the IC 443 SNR Resolved by Chandra: A Fast Ejecta Fragment or a New Pulsar Wind Nebula?
A Chandra observation of the isolated hard X-ray source XMMU
J061804.3+222732, located in the region of apparent interaction of the
supernova remnant IC 443 with a molecular cloud, resolved the complex structure
of the source in a few bright clumps embedded in an extended emission of a ~ 30
arcsec size. The X-ray spectra of the clumps and the extended emission are
dominated by a hard power-law component with a photon index of 1.2--1.4. In
addition, we see some indications of an optically thin thermal plasma of a ~
0.3 keV temperature. The observed X-ray morphology and spectra are consistent
with those expected for an isolated supernova ejecta fragment interacting with
a dense ambient medium. A possible alternative interpretation is a pulsar wind
nebula associated with either IC 443 or another SNR, G189.6+3.3.Comment: Accepted for publication in The Astrophysical Journal Letters High
resolution Images of Fig.1 are appende
High energy processes in the vicinity of the Kerr's black hole horizon
Two particle collisions close to the horizon of the rotating nonextremal
black hole are analyzed. It is shown that high energy of the order of the Grand
Unification scale in the centre of mass of colliding particles can be obtained
when there is a multiple collision - the particle from the accretion disc gets
the critical momentum in first collision with the other particle close to the
horizon and then there is a second collision of the critical particle with the
ordinary one. High energy occurs due to a great relative velocity of two
particles and a large Lorentz factor. The dependence of the relative velocity
on the distance to horizon is analyzed, the time of movement from the point in
the accretion disc to the point of scattering with large energy as well as the
time of back movement to the Earth are calculated. It is shown that they have
reasonable order.Comment: 13 pages, 2 figures, added some formulas and one referenc
Systems of conservation laws with third-order Hamiltonian structures
We investigate -component systems of conservation laws that possess
third-order Hamiltonian structures of differential-geometric type. The
classification of such systems is reduced to the projective classification of
linear congruences of lines in satisfying additional
geometric constraints. Algebraically, the problem can be reformulated as
follows: for a vector space of dimension , classify -tuples of
skew-symmetric 2-forms such that for some non-degenerate symmetric
.Comment: 31 page
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