61 research outputs found
A numerical study of the development of bulk scale-free structures upon growth of self-affine aggregates
During the last decade, self-affine geometrical properties of many growing
aggregates, originated in a wide variety of processes, have been well
characterized. However, little progress has been achieved in the search of a
unified description of the underlying dynamics. Extensive numerical evidence
has been given showing that the bulk of aggregates formed upon ballistic
aggregation and random deposition with surface relaxation processes can be
broken down into a set of infinite scale invariant structures called "trees".
These two types of aggregates have been selected because it has been
established that they belong to different universality classes: those of
Kardar-Parisi-Zhang and Edward-Wilkinson, respectively. Exponents describing
the spatial and temporal scale invariance of the trees can be related to the
classical exponents describing the self-affine nature of the growing interface.
Furthermore, those exponents allows us to distinguish either the compact or
non-compact nature of the growing trees. Therefore, the measurement of the
statistic of the process of growing trees may become a useful experimental
technique for the evaluation of the self-affine properties of some aggregates.Comment: 19 pages, 5 figures, accepted for publication in Phys.Rev.
Interface roughening with nonlinear surface tension
Using stability arguments, this Brief Report suggests that a term that
enhances the surface tension in the presence of large height fluctuations
should be included in the Kardar-Parisi-Zhang equation. A one-loop
renormalization group analysis then shows for interface dimensions larger than
an unstable strong-coupling fixed point that enters the system
from infinity. The relevance of these results to the roughening transition is
discussed.Comment: 4 pages RevTeX, 1 figur
High dimensional behavior of the Kardar-Parisi-Zhang growth dynamics
We investigate analytically the large dimensional behavior of the
Kardar-Parisi-Zhang (KPZ) dynamics of surface growth using a recently proposed
non-perturbative renormalization for self-affine surface dynamics. Within this
framework, we show that the roughness exponent decays not faster than
for large . This implies the absence of a finite upper
critical dimension.Comment: RevTeX, 4 pages, 2 figures. To appear in Phys. Rev.
Directed polymers in high dimensions
We study directed polymers subject to a quenched random potential in d
transversal dimensions. This system is closely related to the
Kardar-Parisi-Zhang equation of nonlinear stochastic growth. By a careful
analysis of the perturbation theory we show that physical quantities develop
singular behavior for d to 4. For example, the universal finite size amplitude
of the free energy at the roughening transition is proportional to (4-d)^(1/2).
This shows that the dimension d=4 plays a special role for this system and
points towards d=4 as the upper critical dimension of the Kardar-Parisi-Zhang
problem.Comment: 37 pages REVTEX including 4 PostScript figure
Recent results on multiplicative noise
Recent developments in the analysis of Langevin equations with multiplicative
noise (MN) are reported. In particular, we:
(i) present numerical simulations in three dimensions showing that the MN
equation exhibits, like the Kardar-Parisi-Zhang (KPZ) equation both a weak
coupling fixed point and a strong coupling phase, supporting the proposed
relation between MN and KPZ;
(ii) present dimensional, and mean field analysis of the MN equation to
compute critical exponents;
(iii) show that the phenomenon of the noise induced ordering transition
associated with the MN equation appears only in the Stratonovich representation
and not in the Ito one, and
(iv) report the presence of a new first-order like phase transition at zero
spatial coupling, supporting the fact that this is the minimum model for noise
induced ordering transitions.Comment: Some improvements respect to the first versio
Renormalization group study of one-dimensional systems with roughening transitions
A recently introduced real space renormalization group technique, developed
for the analysis of processes in the Kardar-Parisi-Zhang universality class, is
generalized and tested by applying it to a different family of surface growth
processes.
In particular, we consider a growth model exhibiting a rich phenomenology
even in one dimension. It has four different phases and a directed percolation
related roughening transition. The renormalization method reproduces extremely
well all the phase diagram, the roughness exponents in all the phases and the
separatrix among them. This proves the versatility of the method and elucidates
interesting physical mechanisms.Comment: Submitted to Phys. Rev.
Critical behavior of a one-dimensional fixed-energy stochastic sandpile
We study a one-dimensional fixed-energy version (that is, with no input or
loss of particles), of Manna's stochastic sandpile model. The system has a
continuous transition to an absorbing state at a critical value of
the particle density. Critical exponents are obtained from extensive
simulations, which treat both stationary and transient properties. In contrast
with other one-dimensional sandpiles, the model appears to exhibit finite-size
scaling, though anomalies exist in the scaling of relaxation times and in the
approach to the stationary state. The latter appear to depend strongly on the
nature of the initial configuration. The critical exponents differ from those
expected at a linear interface depinning transition in a medium with point
disorder, and from those of directed percolation.Comment: 15 pages, 11 figure
Ecological Invasion, Roughened Fronts, and a Competitor's Extreme Advance: Integrating Stochastic Spatial-Growth Models
Both community ecology and conservation biology seek further understanding of
factors governing the advance of an invasive species. We model biological
invasion as an individual-based, stochastic process on a two-dimensional
landscape. An ecologically superior invader and a resident species compete for
space preemptively. Our general model includes the basic contact process and a
variant of the Eden model as special cases. We employ the concept of a
"roughened" front to quantify effects of discreteness and stochasticity on
invasion; we emphasize the probability distribution of the front-runner's
relative position. That is, we analyze the location of the most advanced
invader as the extreme deviation about the front's mean position. We find that
a class of models with different assumptions about neighborhood interactions
exhibit universal characteristics. That is, key features of the invasion
dynamics span a class of models, independently of locally detailed demographic
rules. Our results integrate theories of invasive spatial growth and generate
novel hypotheses linking habitat or landscape size (length of the invading
front) to invasion velocity, and to the relative position of the most advanced
invader.Comment: The original publication is available at
www.springerlink.com/content/8528v8563r7u2742
Avalanche Dynamics in Evolution, Growth, and Depinning Models
The dynamics of complex systems in nature often occurs in terms of
punctuations, or avalanches, rather than following a smooth, gradual path. A
comprehensive theory of avalanche dynamics in models of growth, interface
depinning, and evolution is presented. Specifically, we include the Bak-Sneppen
evolution model, the Sneppen interface depinning model, the Zaitsev flux creep
model, invasion percolation, and several other depinning models into a unified
treatment encompassing a large class of far from equilibrium processes. The
formation of fractal structures, the appearance of noise, diffusion with
anomalous Hurst exponents, Levy flights, and punctuated equilibria can all be
related to the same underlying avalanche dynamics. This dynamics can be
represented as a fractal in spatial plus one temporal dimension. We develop
a scaling theory that relates many of the critical exponents in this broad
category of extremal models, representing different universality classes, to
two basic exponents characterizing the fractal attractor. The exact equations
and the derived set of scaling relations are consistent with numerical
simulations of the above mentioned models.Comment: 27 pages in revtex, no figures included. Figures or hard copy of the
manuscript supplied on reques
Risk profiles and one-year outcomes of patients with newly diagnosed atrial fibrillation in India: Insights from the GARFIELD-AF Registry.
BACKGROUND: The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) is an ongoing prospective noninterventional registry, which is providing important information on the baseline characteristics, treatment patterns, and 1-year outcomes in patients with newly diagnosed non-valvular atrial fibrillation (NVAF). This report describes data from Indian patients recruited in this registry. METHODS AND RESULTS: A total of 52,014 patients with newly diagnosed AF were enrolled globally; of these, 1388 patients were recruited from 26 sites within India (2012-2016). In India, the mean age was 65.8 years at diagnosis of NVAF. Hypertension was the most prevalent risk factor for AF, present in 68.5% of patients from India and in 76.3% of patients globally (P < 0.001). Diabetes and coronary artery disease (CAD) were prevalent in 36.2% and 28.1% of patients as compared with global prevalence of 22.2% and 21.6%, respectively (P < 0.001 for both). Antiplatelet therapy was the most common antithrombotic treatment in India. With increasing stroke risk, however, patients were more likely to receive oral anticoagulant therapy [mainly vitamin K antagonist (VKA)], but average international normalized ratio (INR) was lower among Indian patients [median INR value 1.6 (interquartile range {IQR}: 1.3-2.3) versus 2.3 (IQR 1.8-2.8) (P < 0.001)]. Compared with other countries, patients from India had markedly higher rates of all-cause mortality [7.68 per 100 person-years (95% confidence interval 6.32-9.35) vs 4.34 (4.16-4.53), P < 0.0001], while rates of stroke/systemic embolism and major bleeding were lower after 1 year of follow-up. CONCLUSION: Compared to previously published registries from India, the GARFIELD-AF registry describes clinical profiles and outcomes in Indian patients with AF of a different etiology. The registry data show that compared to the rest of the world, Indian AF patients are younger in age and have more diabetes and CAD. Patients with a higher stroke risk are more likely to receive anticoagulation therapy with VKA but are underdosed compared with the global average in the GARFIELD-AF. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01090362
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