2,230 research outputs found
Anomalous scaling due to correlations: Limit theorems and self-similar processes
We derive theorems which outline explicit mechanisms by which anomalous
scaling for the probability density function of the sum of many correlated
random variables asymptotically prevails. The results characterize general
anomalous scaling forms, justify their universal character, and specify
universality domains in the spaces of joint probability density functions of
the summand variables. These density functions are assumed to be invariant
under arbitrary permutations of their arguments. Examples from the theory of
critical phenomena are discussed. The novel notion of stability implied by the
limit theorems also allows us to define sequences of random variables whose sum
satisfies anomalous scaling for any finite number of summands. If regarded as
developing in time, the stochastic processes described by these variables are
non-Markovian generalizations of Gaussian processes with uncorrelated
increments, and provide, e.g., explicit realizations of a recently proposed
model of index evolution in finance.Comment: Through text revision. 15 pages, 3 figure
Branching Processes and Evolution at the Ends of a Food Chain
In a critically self--organized model of punctuated equilibrium, boundaries
determine peculiar scaling of the size distribution of evolutionary avalanches.
This is derived by an inhomogeneous generalization of standard branching
processes, extending previous mean field descriptions and yielding
together with , as distribution exponent of avalanches starting from
species at the ends of a food chain. For the nearest neighbor chain one obtains
numerically , and for the
first return times of activity, again distinct from bulk exponents.Comment: REVTex file, 12 pages, 2 figures in eps-files uuencoded, psfig.st
Adsorption-like Collapse of Diblock Copolymers
A linear copolymer made of two reciprocally attracting N-monomer blocks
collapses to a compact phase through a novel transition, whose exponents are
determined with extensive MC simulations in two and three dimensions. In the
former case, an identification with the statistical geometry of suitable
percolation paths allows to predict that the number of contacts between the
blocks grows like . In the compact phase the blocks are mixed and, in
two dimensions, also zipped, in such a way to form a spiral, double chain
structure.Comment: 4 pages, 5 Postscript figure
Direct and Regioselective Di-alpha-fucosylation on the Secondary Rim of beta-Cyclodextrin
A straightforward glycosylation method is described to regio- and stereoselectively introduce two alpha-L-fucose moieties directly to the secondary rim of beta-cyclodextrin. Using NMR and MS fragmentation studies, the nonasaccharide structure was determined, which was also visualized using molecular dynamics simulations. The reported glycosylation method proved to be robust on gram-scale, and may be generally applied to directly glycosylate beta-cyclodextrins to make well-defined multivalent glycoclusters.</p
Young pre-Low-Mass X-ray Binaries in propeller phase : Nature of the 6.7-hour periodic X-ray source 1E 161348-5055 in RCW 103
Discovery of the 6.7-hour periodicity in the X-ray source 1E 161348-5055 in
RCW 103 has led to investigations of the nature of this periodicity. We explore
a model for 1E 161348-5055, wherein a fast-spinning neutron star with a
magnetic field G in a young pre-Low-Mass X-ray Binary (pre-LMXB)
with an eccentric orbit of period 6.7 hr operates in the "propeller" phase. The
6.7-hr light curve of 1E 161348-5055 can be quantitatively accounted by a model
of orbitally-modulated mass transfer through a viscous accretion disk and
subsequent propeller emission (both Illarionov-Sunyaev type and
Romanova-Lovelace et al type), and spectral and other properties are also in
agreement. Formation and evolution of model systems are shown to be in
accordance both with standard theories.Comment: 11 pages, 4 figures, accepted for publication in Astronomy and
Astrophysics on 23/08/200
Classical and Quantum Solutions and the Problem of Time in Cosmology
We have studied various classical solutions in cosmology. Especially we
have obtained general classical solutions in pure \ cosmology. Even in the
quantum theory, we can solve the Wheeler-DeWitt equation in pure \
cosmology exactly. Comparing these classical and quantum solutions in \
cosmology, we have studied the problem of time in general relativity.Comment: 17 pages, latex, no figure, one reference is correcte
The 2008 October Swift detection of X-ray bursts/outburst from the transient SGR-like AXP 1E 1547.0-5408
We report on the detailed study of the 2008 October outburst from the
anomalous X-ray pulsar (AXP) 1E 1547.0-5408 discovered through the Swift/Burst
Alert Telescope (BAT) detection of SGR-like short X-ray bursts on 2008 October
3. The Swift/X-ray Telescope (XRT) started observing the source after less than
100 s since the BAT trigger, when the flux (about 6E-11 erg/cm^2/s in the 2-10
keV range) was >50 times higher than its quiescent level. Swift monitored the
outbursting activity of 1E 1547.0-5408 on a daily basis for approximately three
weeks. This strategy allowed us to find a phase-coherent solution for the
source pulsations after the burst, which, besides period and period derivative,
requires a positive Period second derivative term (spin-down increase). The
time evolution of the pulse shape is complex and variable, with the pulsed
fraction increasing from 20% to 50% within the Swift observational window. The
XRT spectra can be fitted well by means of a single component, either a
power-law (PL) or a blackbody (BB). During the very initial phases of the
outburst the spectrum is hard, with a PL photon index about 2 (or kT about 1.4
keV) which steepens to about 4 (or kT about 0.8 keV) within one day from the
BAT trigger, though the two components are likely present simultaneously during
the first day spectra. An INTEGRAL observation carried out five days after the
trigger provided an upper limit of about 2E-11 erg/cm^2/s to the emission of 1E
1547.0-5408 in the 18-60 keV band.Comment: 10 pages, 2 tables, 6 figures; accepted for publication in MNRA
Boundary effects in a random neighbor model of earthquakes
We introduce spatial inhomogeneities (boundaries) in a random neighbor
version of the Olami, Feder and Christensen model [Phys. Rev. Lett. 68, 1244
(1992)] and study the distributions of avalanches starting both from the bulk
and from the boundaries of the system. Because of their clear geophysical
interpretation, two different boundary conditions have been considered (named
free and open, respectively). In both cases the bulk distribution is described
by the exponent . Boundary distributions are instead
characterized by two different exponents and , for free and open boundary conditions, respectively. These
exponents indicate that the mean-field behavior of this model is correctly
described by a recently proposed inhomogeneous form of critical branching
process.Comment: 6 pages, 2 figures ; to appear on PR
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