4,949 research outputs found
Decay of Nuclear Giant Resonances: Quantum Self-similar Fragmentation
Scaling analysis of nuclear giant resonance transition probabilities with
increasing level of complexity in the background states is performed. It is
found that the background characteristics, typical for chaotic systems lead to
nontrivial multifractal scaling properties.Comment: 4 pages, LaTeX format, pc96.sty + 2 eps figures, accepted as: talk at
the 8th Joint EPS-APS International Conference on Physics Computing (PC'96,
17-21. Sept. 1996), to appear in the Proceeding
Different fractal properties of positive and negative returns
We perform an analysis of fractal properties of the positive and the negative
changes of the German DAX30 index separately using Multifractal Detrended
Fluctuation Analysis (MFDFA). By calculating the singularity spectra
we show that returns of both signs reveal multiscaling. Curiously,
these spectra display a significant difference in the scaling properties of
returns with opposite sign. The negative price changes are ruled by stronger
temporal correlations than the positive ones, what is manifested by larger
values of the corresponding H\"{o}lder exponents. As regards the properties of
dominant trends, a bear market is more persistent than the bull market
irrespective of the sign of fluctuations.Comment: presented at FENS2007 conference, 8 pages, 4 Fig
Foreground separation using a flexible maximum-entropy algorithm: an application to COBE data
A flexible maximum-entropy component separation algorithm is presented that
accommodates anisotropic noise, incomplete sky-coverage and uncertainties in
the spectral parameters of foregrounds. The capabilities of the method are
determined by first applying it to simulated spherical microwave data sets
emulating the COBE-DMR, COBE-DIRBE and Haslam surveys. Using these simulations
we find that is very difficult to determine unambiguously the spectral
parameters of the galactic components for this data set due to their high level
of noise. Nevertheless, we show that is possible to find a robust CMB
reconstruction, especially at the high galactic latitude. The method is then
applied to these real data sets to obtain reconstructions of the CMB component
and galactic foreground emission over the whole sky. The best reconstructions
are found for values of the spectral parameters: T_d=19 K, alpha_d=2,
beta_ff=-0.19 and beta_syn=-0.8. The CMB map has been recovered with an
estimated statistical error of \sim 22 muK on an angular scale of 7 degrees
outside the galactic cut whereas the low galactic latitude region presents
contamination from the foreground emissions.Comment: 29 pages, 25 figures, version accepted for publication in MNRAS. One
subsection and 6 figures added. Main results unchange
The joint large-scale foreground-CMB posteriors of the 3-year WMAP data
Using a Gibbs sampling algorithm for joint CMB estimation and component
separation, we compute the large-scale CMB and foreground posteriors of the
3-yr WMAP temperature data. Our parametric data model includes the cosmological
CMB signal and instrumental noise, a single power law foreground component with
free amplitude and spectral index for each pixel, a thermal dust template with
a single free overall amplitude, and free monopoles and dipoles at each
frequency. This simple model yields a surprisingly good fit to the data over
the full frequency range from 23 to 94 GHz. We obtain a new estimate of the CMB
sky signal and power spectrum, and a new foreground model, including a
measurement of the effective spectral index over the high-latitude sky. A
particularly significant result is the detection of a common spurious offset in
all frequency bands of ~ -13muK, as well as a dipole in the V-band data.
Correcting for these is essential when determining the effective spectral index
of the foregrounds. We find that our new foreground model is in good agreement
with template-based model presented by the WMAP team, but not with their MEM
reconstruction. We believe the latter may be at least partially compromised by
the residual offsets and dipoles in the data. Fortunately, the CMB power
spectrum is not significantly affected by these issues, as our new spectrum is
in excellent agreement with that published by the WMAP team. The corresponding
cosmological parameters are also virtually unchanged.Comment: 5 pages, 4 figures, submitted to ApJL. Background data are available
at http://www.astro.uio.no/~hke under the Research ta
Flat Dark Matter Dominated Models with Hybrid Adiabatic Plus Isocurvature Initial Conditions
We investigate the consequences of flat, dark-matter dominated cosmogonies
with hybrid isocurvature and adiabatic initial perturbations and with
Harrison-Zel'dovich primordial spectrum normalised to the -DMR two-year
measurements. We show that whilst the -DMR data alone shows no preference
for a specific admixture of these modes, acceptable combinations are strongly
constrained by other observational data. Nevertheless, in some cases a suitable
mixture of these modes still may be used in an attempt to avoid some of the
observed problems of purely adiabatic models. Specifically, we consider
critical density, cold dark matter (CDM) and mixed dark matter (MDM) models.Comment: Two uuencoded compressed Postscript files containing (1) 19 pages
manuscript, (2) four figures (tarred together). Submitted to The
Astrophysical Journa
COBE-DMR-normalisation for inflationary flat dark matter models
The two-year COBE-DMR 53 and 90 GHz sky maps, in both galactic and ecliptic
coordinates, are used to determine the normalisation of inflationary universe
models with a flat global geometry and adiabatic density perturbations. The
appropriately normalised cold and mixed dark matter models and cosmological
constant dominated, cold dark matter models, computed for a range of values of
Omega_b and h, are then compared to various measures of structure in the
universe. Critical density CDM models appear to be irreconcilable with
observations on both large and small scales simultaneously, whereas MDM models
provide a somewhat better fit to the data. Although the COBE-DMR data alone
prefer a nearly critical value for the total density, low-density cosmological
constant models with Omega_0 greater than or equal to 0.15 can not be rejected
at a confidence level exceeding 95%. Such models may also provide a
significantly better fit to the matter distribution data than critical density
CDM.Comment: uuencoded postscript file (complete text and figures). Accepted for
publication in MNRA
Stochastic Opinion Formation in Scale-Free Networks
The dynamics of opinion formation in large groups of people is a complex
non-linear phenomenon whose investigation is just at the beginning. Both
collective behaviour and personal view play an important role in this
mechanism. In the present work we mimic the dynamics of opinion formation of a
group of agents, represented by two state , as a stochastic response of
each of them to the opinion of his/her neighbours in the social network and to
feedback from the average opinion of the whole. In the light of recent studies,
a scale-free Barab\'asi-Albert network has been selected to simulate the
topology of the interactions. A turbulent-like dynamics, characterized by an
intermittent behaviour, is observed for a certain range of the model
parameters. The problem of uncertainty in decision taking is also addressed
both from a topological point of view, using random and targeted removal of
agents from the network, and by implementing a three state model, where the
third state, zero, is related to the information available to each agent.
Finally, the results of the model are tested against the best known network of
social interactions: the stock market. A time series of daily closures of the
Dow Jones index has been used as an indicator of the possible applicability of
our model in the financial context. Good qualitative agreement is found.Comment: 24 pages and 13 figures, Physical Review E, in pres
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