409 research outputs found
CONTRACTING OVER PERSISTENT INFORMATION
We consider a dynamic principal-agent problem, where the sole instrument the
principal has to incentivize the agent is the disclosure of information. The principal aims at maximizing the (discounted) number of times the agent chooses the
principalâs preferred action. We show that there exists an optimal policy, where
the principal recommends its most preferred action and discloses information as
a reward in the next period, until either this action becomes statically optimal for
the agent or the agent perfectly learns the state
Giant dispersion of critical currents in superconductor with fractal clusters of a normal phase
The influence of fractal clusters of a normal phase on the dynamics of a
magnetic flux trapped in a percolative superconductor is considered. The
critical current distribution and the current-voltage characteristics of
fractal superconducting structures in the resistive state are obtained for an
arbitrary fractal dimension of the cluster boundaries. The range of fractal
dimensions, where the dispersion of critical currents becomes infinite, is
found. It is revealed that the fractality of clusters depresses of the electric
field caused by the magnetic flux motion thus increasing the critical current
value. It is expected that the maximum current-carrying capability of a
superconductor can be achieved in the region of giant dispersion of critical
currents.Comment: 7 pages with 3 figure
Comparison of regeneration capacity and Agrobacterium-mediated cell transformation efficiency of different cultivars and rootstocks of Vitis spp. via organogenesis.
The success of in vitro plant regeneration and the competence of genetic transformation greatly depends on the genotype of the species of interest. In previous work, we developed a method for the efficient Agrobacterium-mediated genetic transformation via organogenesis of V. vinifera cultivar Thompson Seedless, by using meristematic bulk (MB) as starting tissue. In this study, we applied this method for the regeneration and transformation of MBs obtained from the Italian cultivar Ciliegiolo and two of the commonly used Vitis rootstocks, 110 Richter and Kober 5BB, in comparison with Thompson Seedless. The A. tumefaciens strain EHA105, harbouring pK7WG2 binary vector, was used for the transformation trials, which allowed selection through the enhanced-green fluorescent protein (eGFP) and the neomycin phosphotransferase (nptII) gene. Putative transformed tissues and/or shoots were identified by either a screening based on the eGFP expression alone or its use in combination with kanamycin in the medium. MBs obtained from Thompson Seedless showed the highest regeneration and transformation cell competence, which subsequently allowed the recovery of stably transformed plants. Ciliegiolo, 110 Richter, and Kober 5BB, produced actively growing transgenic calli showing eGFP fluorescence, more consistently on selective media, but had no regenerative competence
AMBIENTE, ENERGIA, ALIMENTAZIONE. MODELLI GIURIDICI COMPARATI PER LO SVILUPPO SOSTENIBILE. ENVIRONMENT, ENERGY, FOOD. COMPARATIVE LEGAL MODELS FOR SUSTAINABLE DEVELOPMENT. Vol. I, Tomo II
AMBIENTE, ENERGIA,ALIMENTAZIONE. MODELLI GIURIDICI COMPARATI PER LO SVILUPPO SOSTENIBILE.. ENVIRONMENT, ENERGY, FOOD. COMPARATIVE LEGAL MODELS FOR SUSTAINABLE DEVELOPMENT . Volume I, Tomo I
The rotational broadening and the mass of the donor star of GRS 1915+105
The binary parameters of the microquasar GRS 1915+105 have been determined by
the detection of Doppler-shifted 12CO and 13CO lines in its K-band spectrum
(Greiner et al., 2001, Nature, 414, 522). Here, we present further analysis of
the same K-band VLT spectra and we derive a rotational broadening of the donor
star of V sin i=26+-3 km/s from the 12CO/13CO lines. Assuming that the K-type
star is tidally locked to the black hole and is filling its Roche-lobe surface,
then the implied mass ratio is q = M_d/M_x = 0.058+-0.033. This result,
combined with (P, K, i)=(33.5 d, 140 km/s, 66 deg) gives a more refined mass
estimate for the black hole, , than previously
estimated, using an inclination of i=66+-2 deg (Fender et al. 1999) as derived
from the orientation of the radio jets and a more accurate distance. The mass
for the early K-type giant star is , consistent with
a more evolved stripped-giant donor star in GRS 1915+105 than, for example, the
donor star of the prototype black-hole X-ray transient, V404 Cyg which has the
longest binary period after GRS 1915+105.Comment: 4 pages, 1 figure, A&A Lette
Clustering of loose groups and galaxies from the Perseus--Pisces Survey
We investigate the clustering properties of loose groups in the
Perseus--Pisces redshift Survey (PPS). Previous analyses based on CfA and SSRS
surveys led to apparently contradictory results. We investigate the source of
such discrepancies, finding satisfactory explanations for them. Furthermore, we
find a definite signal of group clustering, whose amplitude exceeds the
amplitude of galaxy clustering (,
for the most significant case; distances are
measured in \hMpc). Groups are identified with the adaptive
Friends--Of--Friends (FOF) algorithms HG (Huchra \& Geller 1982) and NW
(Nolthenius \& White 1987), systematically varying all search parameters.
Correlation strenght is especially sensitive to the sky--link (increasing
for stricter normalization ), and to the (depth \mlim of the) galaxy
data. It is only moderately dependent on the galaxy luminosity function
, while it is almost insensitive to the redshift--link (both to
the normalization and to the scaling recipes HG or NW).Comment: 28 pages (LaTeX aasms4 style) + 5 Postscript figures ; ApJ submitted
on May 4th, 1996; group catalogs available upon request
([email protected]
New Optical Insights into the Mass Discrepancy of Galaxy Clusters: The Cases of A1689 and A2218
We analyze the internal structures of clusters A1689 and A2218 by applying a
recent development of the method of wavelet analysis, which uses the complete
information obtained from optical data, i.e. galaxy positions and redshifts. We
find that both clusters show the presence of structures superimposed along the
line of sight with different mean redshifts and smaller velocity dispersions
than that of the system as a whole, suggesting that the clusters could be cases
of the on-going merging of clumps. In the case of A2218 we find an acceptable
agreement between our estimate of optical virial mass and X-ray and
gravitational lensing masses. On the contrary, in the case of A1689 we find
that our mass estimates are smaller than X-ray and gravitational lensing ones
at both small and large radii. In any case, at variance with earlier claims,
there is no evidence that X-ray mass estimates are underestimated.Comment: 8 pages, 2 eps figures, Use LaTeX2e, accepted by Astrophysical
Journal, in press November 1997, Vol.49
Effectiveness of the âecological beachâ model: Beneficial management of posidonia beach casts and banquette
Observational Mass-to-Light Ratio of Galaxy Systems: from Poor Groups to Rich Clusters
We study the mass-to-light ratio of galaxy systems from poor groups to rich
clusters, and present for the first time a large database for useful
comparisons with theoretical predictions. We extend a previous work, where B_j
band luminosities and optical virial masses were analyzed for a sample of 89
clusters. Here we also consider a sample of 52 more clusters, 36 poor clusters,
7 rich groups, and two catalogs, of about 500 groups each, recently identified
in the Nearby Optical Galaxy sample by using two different algorithms. We
obtain the blue luminosity and virial mass for all systems considered. We
devote a large effort to establishing the homogeneity of the resulting values,
as well as to considering comparable physical regions, i.e. those included
within the virial radius. By analyzing a fiducial, combined sample of 294
systems we find that the mass increases faster than the luminosity: the linear
fit gives M\propto L_B^{1.34 \pm 0.03}, with a tendency for a steeper increase
in the low--mass range. In agreement with the previous work, our present
results are superior owing to the much higher statistical significance and the
wider dynamical range covered (about 10^{12}-10^{15} M_solar). We present a
comparison between our results and the theoretical predictions on the relation
between M/L_B and halo mass, obtained by combining cosmological numerical
simulations and semianalytic modeling of galaxy formation.Comment: 25 pages, 12 eps figures, accepted for publication in Ap
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