25,494 research outputs found
Photometric monitoring of the blazar 3C 345 for the period 1996 - 2006
We present the results of the blazar 3C 345 monitoring in Johnson-Cousins
BVRI bands for the period 1996 - 2006. We have collected 29 V and 43 R data
points for this period; the BI light curves contain a few measurements only.
The accuracy of our photometry is not better than 0.03 mag in the VR bands. The
total amplitude of the variability obtained from our data is 2.06 mag in the V
band and 2.25 mag in the R one. 3C 345 showed periods of flaring activity
during 1998/99 and 2001: a maximum of the blazar brightness was detected in
2001 February - 15.345 mag in the V band and 14.944 mag in the R one. We
confirm that during brighter stages 3C 345 becomes redder; for higher fluxes
the colour index seems to be less dependent on the magnitude. The intra-night
monitoring of 3C 345 in three consecutive nights in 2001 August revealed no
significant intra-night variability; 3C 345 did not show evident flux changes
over timescales of weeks around the period of the intra-night monitoring. This
result supports the existing facts that intra-night variability is correlated
with rapid flux changes rather than with specific flux levels
Scaling limits of loop-erased random walks and uniform spanning trees
The uniform spanning tree (UST) and the loop-erased random walk (LERW) are
related probabilistic processes. We consider the limits of these models on a
fine grid in the plane, as the mesh goes to zero. Although the existence of
scaling limits is still unproven, subsequential scaling limits can be defined
in various ways, and do exist. We establish some basic a.s. properties of the
subsequential scaling limits in the plane. It is proved that any LERW
subsequential scaling limit is a simple path, and that the trunk of any UST
subsequential scaling limit is a topological tree, which is dense in the plane.
The scaling limits of these processes are conjectured to be conformally
invariant in 2 dimensions. We make a precise statement of the conformal
invariance conjecture for the LERW, and show that this conjecture implies an
explicit construction of the scaling limit, as follows. Consider the Loewner
differential equation
with boundary values , in the range z\in\U=\{w\in\C\st |w|<1\},
. We choose \zeta(t):= \B(-2t), where \B(t) is Brownian motion on
\partial \U starting at a random-uniform point in \partial \U. Assuming the
conformal invariance of the LERW scaling limit in the plane, we prove that the
scaling limit of LERW from 0 to \partial\U has the same law as that of the
path . We believe that a variation of this process gives the
scaling limit of the boundary of macroscopic critical percolation clusters.Comment: (for V2) inserted another figure and two more reference
Exotic Nuclei and Matter in a Chirally Effective Approach
A relativistic approach to describe nuclear and in general strongly
interacting matter is introduced and discussed. Here, not only the nuclear
forces but also the masses of the nucleons are generated through meson fields.
Within this framework it is possible to calculate properties of finite nuclei
at a level of accuracy similar to dedicated relativistic nuclear structure
models. Due to the more general approach, a wider range of properties of
hadronic states can be investigated. A number of results for heavy and
neutron-rich nuclei toward the drip line are presented.Comment: Contribution to the Proceedings of the VII International Symposium on
EXOtic Nuclei (EXON-2014) in St. Petersburg, Russi
Nuclear physics and cosmology
Nuclear physics has provided one of two critical observational tests of all Big Bang cosmology, namely Big Bang Nucleosynthesis. Furthermore, this same nuclear physics input enables a prediction to be made about one of the most fundamental physics questions of all, the number of elementary particle families. The standard Big Bang Nucleosynthesis arguments are reviewed. The primordial He abundance is inferred from He-C and He-N and He-O correlations. The strengthened Li constraint as well as D-2 plus He-3 are used to limit the baryon density. This limit is the key argument behind the need for non-baryonic dark matter. The allowed number of neutrino families, N(nu), is delineated using the new neutron lifetime value of tau(n) = 890 + or - 4s (tau(1/2) = 10.3 min). The formal statistical result is N(nu) = 2.6 + or - 0.3 (1 sigma), providing a reasonable fit (1.3 sigma) to three families but making a fourth light (m(nu) less than or equal to 10 MeV) neutrino family exceedly unlikely (approx. greater than 4.7 sigma). It is also shown that uncertainties induced by postulating a first-order quark-baryon phase transition do not seriously affect the conclusions
Nuclear constraints on the age of the universe
A review is made of how one can use nuclear physics to put rather stringent limits on the age of the universe and thus the cosmic distance scale. The age can be estimated to a fair degree of accuracy. No single measurement of the time since the Big Bang gives a specific, unambiguous age. There are several methods that together fix the age with surprising precision. In particular, there are three totally independent techniques for estimating an age and a fourth technique which involves finding consistency of the other three in the framework of the standard Big Bang cosmological model. The three independent methods are: cosmological dynamics, the age of the oldest stars, and radioactive dating. This paper concentrates on the third of the three methods, and the consistency technique
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