8,953 research outputs found
Pairs of Bubbles in Planetary Nebulae and Clusters of Galaxies
I point to an interesting similarity in the morphology and some
non-dimensional quantities between pairs of X-ray-deficient bubbles in clusters
of galaxies and pairs of optical-deficient bubbles in planetary nebulae (PNs).
This similarity leads me to postulate a similar formation mechanism. This
postulate is used to strengthen models for PN shaping by jets (or collimated
fast winds: CFW). The presence of dense material in the equatorial plane
observed in the two classes of bubbles constrains the jets and CFW activity in
PNs to occur while the AGB star still blows its dense wind, or very shortly
after. I argue that only a stellar companion can account for such jets and CFW.Comment: PASP, in pres
Superconductivity in Pseudo-Binary Silicide SrNixSi2-x with AlB2-Type Structure
We demonstrate the emergence of superconductivity in pseudo-binary silicide
SrNixSi2-x. The compound exhibits a structural phase transition from the cubic
SrSi2-type structure (P4132) to the hexagonal AlB2-type structure (P6/mmm) upon
substituting Ni for Si at approximately x = 0.1. The hexagonal structure is
stabilized in the range of 0.1 < x < 0.7. The superconducting phase appears in
the vicinity of the structural phase boundary. Ni acts as a nonmagnetic dopant,
as confirmed by the Pauli paramagnetic behavior.Comment: 12 pages, 5 figure
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Dynamic Costly State Verification with Repeated Loans: a two-period analysis
We derive the optimal contract in a two period costly state verification model with repeated loans, where in each period, the borrower invests in an identical project. We allow the borrower to switch lenders at the end of the first period. We show that while the second period optimal contract continues to be a standard debt contract, the optimal contract for the first project need not be. Regardless of the form of the first period contract, there is less monitoring in the first period and total monitoring costs are strictly lower, relative to a sequence of short term contracts. We illustrate our results assuming a uniform distribution for firm revenue and fixed monitoring costs. In particular, we show that either there is no monitoring in the first period or maximum possible amount consistent with the outside option is collected in the second period
RadioAstron probes the ultra-fine spatial structure in the HO maser emission in the star forming region W49N
HO maser emission associated with the massive star formation region W49N
were observed with the Space-VLBI mission RadioAstron. The procedure for
processing of the maser spectral line data obtained in the RadioAstron
observations is described. Ultra-fine spatial structures in the maser emission
were detected on space-ground baselines of up to 9.6 Earth diameters. The
correlated flux densities of these features range from 0.1% to 0.6% of the
total flux density. These low values of correlated flux density are probably
due to turbulence either in the maser itself or in the interstellar medium.Comment: Accepted for publication in Advances in Space Researc
Intra-Landau level polarization effect for a striped Hall gas
We calculate the polarization function including only intra-Landau level
correlation effects of striped Hall gas. Using the polarization function, the
dielectric function, the dispersion of the plasmon and the correlation energy
are computed in a random phase approximation (RPA) and generalized random phase
approximation (GRPA). The plasmon becomes anisotropic and gapless owing to the
anisotropy of the striped Hall gas and two dimensionality of the quantum Hall
system. The plasmon approximately agrees with the phonon derived before by the
single mode approximation. The (G)RPA correlation energy is compared with other
numerical calculations.Comment: 15 pages,15 figures, revtex4, published versio
H-Dihyperon in Quark Cluster Model
The H dihyperon (DH) is studied in the framework of the SU(3) chiral quark
model. It is shown that except the chiral field, the overall effect of
the other SU(3) chiral fields is destructive in forming a stable DH. The
resultant mass of DH in a three coupled channel calculation is ranged from 2225
to 2234 .Comment: 9 pages, emte
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