237 research outputs found
Anomalous sensitivity to initial conditions and entropy production in standard maps: Nonextensive approach
We perform a throughout numerical study of the average sensitivity to initial
conditions and entropy production for two symplectically coupled standard maps
focusing on the control-parameter region close to regularity. Although the
system is ultimately strongly chaotic (positive Lyapunov exponents), it first
stays lengthily in weak-chaotic regions (zero Lyapunov exponents). We argue
that the nonextensive generalization of the classical formalism is an adequate
tool in order to get nontrivial information about this complex phenomenon.
Within this context we analyze the relation between the power-law sensitivity
to initial conditions and the entropy production.Comment: 9 pages, 12 figure
Telemedicine in chronic disease management: a Public Health perspective
Introduction
In 2014, the School of Hygiene of the University of Padua carried out an evaluation of home telemonitoring (HTM) programs for the management of chronic diseases. Our aims were to verify their efficacy, and to identify a model of care that could be integrated into the current health system. Our analysis addressed both organizational and clinical matters.
Methods
Our evaluation involved 19 reviews and 53 randomized controlled trials (RCT). Main selection criteria were: papers published over the last 15 years, HTM performed through a sensor system, data sent remotely to physicians, health out-comes and monitored parameters clearly stated. Included diseases were: heart failure, hypertension, COPD, asthma and diabetes.
Results
Several critical issues were highlighted. Due to the general tendency in the scientific literature to report HTM efficacy, there is a lack of conclusive evidence whether telemedicine actually improves both clinical (e.g. decreased disease/all-cause mortality, drop in disease/all-cause hospitalization rates, improvement in biological parameters and quality of life) and organizational (decreased length of hospital stay, decreased emergency room/other service use, decreased costs) outcomes or not.
Discussion
From a Public Health perspective, discrepancies and weaknesses may affect published results, since the best method for organizing and delivering telemedicine programs has not yet been identified. There is still no consensus on the following topics: setting: which context expresses the potential of technology best? No studies were found comparing, e.g., rural with urban communities. Within urban scenarios, samples do not discriminate users by their capability to access the healthcare network (e.g. residents in peripheral areas with limited transportation resources, rather than users with reduced mobility); target: it is unclear which demographic or socioeconomic characteristics users should possess to gain most benefit from HTM; duration and frequency: there are significant differences in RCT (and HTM program) duration. It has not been established whether HTM is more effective when permanently implemented, or only in the early stages of disease (i.e. until stabilization). There is no agreement on the optimal HTM implementation frequency, nor whether the patients should also receive traditional interventions (e.g. nurse home visits);scope: it has not been determined whether measurements should be disclosed to patients as educational means to improve disease management. However, past literature does include some indications that the effectiveness of HTM programs may be attributable to care intensification (or to a perceived intensification by the patient, as per the \u201cHawthorne effect\u201d described in sociology) or to the empowerment process.
Conclusions
HTM management of chronic diseases is a promising and remarkable strategy, still flawed by the lack of evidence. Reported efficacy, although modest, probably has a multifactorial origin. Our hypothesis is that it may not result from the technology itself, but from the impact of such process on multiple components of care, emphasizing patients' involvement and autonomy, and improving monitoring intensity. Further studies are needed to clarify the role played by the different HTM components (target, setting, etc.). The application of HTM as a tool for prevention, empowerment and reduction of healthcare access remains little explored
A recent appreciation of the singular dynamics at the edge of chaos
We study the dynamics of iterates at the transition to chaos in the logistic
map and find that it is constituted by an infinite family of Mori's -phase
transitions. Starting from Feigenbaum's function for the diameters
ratio, we determine the atypical weak sensitivity to initial conditions associated to each -phase transition and find that it obeys the form
suggested by the Tsallis statistics. The specific values of the variable at
which the -phase transitions take place are identified with the specific
values for the Tsallis entropic index in the corresponding . We
describe too the bifurcation gap induced by external noise and show that its
properties exhibit the characteristic elements of glassy dynamics close to
vitrification in supercooled liquids, e.g. two-step relaxation, aging and a
relationship between relaxation time and entropy.Comment: Proceedings of: Verhulst 200 on Chaos, Brussels 16-18 September 2004,
Springer Verlag, in pres
Sensitivity to initial conditions at bifurcations in one-dimensional nonlinear maps: rigorous nonextensive solutions
Using the Feigenbaum renormalization group (RG) transformation we work out
exactly the dynamics and the sensitivity to initial conditions for unimodal
maps of nonlinearity at both their pitchfork and tangent
bifurcations. These functions have the form of -exponentials as proposed in
Tsallis' generalization of statistical mechanics. We determine the -indices
that characterize these universality classes and perform for the first time the
calculation of the -generalized Lyapunov coefficient . The
pitchfork and the left-hand side of the tangent bifurcations display weak
insensitivity to initial conditions, while the right-hand side of the tangent
bifurcations presents a `super-strong' (faster than exponential) sensitivity to
initial conditions. We corroborate our analytical results with {\em a priori}
numerical calculations.Comment: latex, 4 figures. Updated references and some general presentation
improvements. To appear published in Europhysics Letter
Possible thermodynamic structure underlying the laws of Zipf and Benford
We show that the laws of Zipf and Benford, obeyed by scores of numerical data
generated by many and diverse kinds of natural phenomena and human activity are
related to the focal expression of a generalized thermodynamic structure. This
structure is obtained from a deformed type of statistical mechanics that arises
when configurational phase space is incompletely visited in a severe way.
Specifically, the restriction is that the accessible fraction of this space has
fractal properties. The focal expression is an (incomplete) Legendre transform
between two entropy (or Massieu) potentials that when particularized to first
digits leads to a previously existing generalization of Benford's law. The
inverse functional of this expression leads to Zipf's law; but it naturally
includes the bends or tails observed in real data for small and large rank.
Remarkably, we find that the entire problem is analogous to the transition to
chaos via intermittency exhibited by low-dimensional nonlinear maps. Our
results also explain the generic form of the degree distribution of scale-free
networks.Comment: To be published in European Physical Journal
Weak chaos and metastability in a symplectic system of many long-range-coupled standard maps
We introduce, and numerically study, a system of symplectically and
globally coupled standard maps localized in a lattice array. The global
coupling is modulated through a factor , being the distance
between maps. Thus, interactions are {\it long-range} (nonintegrable) when
, and {\it short-range} (integrable) when . We
verify that the largest Lyapunov exponent scales as , where is positive when
interactions are long-range, yielding {\it weak chaos} in the thermodynamic
limit (hence ). In the short-range case,
appears to vanish, and the behaviour corresponds to {\it
strong chaos}. We show that, for certain values of the control parameters of
the system, long-lasting metastable states can be present. Their duration
scales as , where appears to be
numerically consistent with the following behavior: for , and zero for . All these results exhibit major
conjectures formulated within nonextensive statistical mechanics (NSM).
Moreover, they exhibit strong similarity between the present discrete-time
system, and the -XY Hamiltonian ferromagnetic model, also studied in
the frame of NSM.Comment: 8 pages, 5 figure
Intermittency at critical transitions and aging dynamics at edge of chaos
We recall that, at both the intermittency transitions and at the Feigenbaum
attractor in unimodal maps of non-linearity of order , the dynamics
rigorously obeys the Tsallis statistics. We account for the -indices and the
generalized Lyapunov coefficients that characterize the
universality classes of the pitchfork and tangent bifurcations. We identify the
Mori singularities in the Lyapunov spectrum at the edge of chaos with the
appearance of a special value for the entropic index . The physical area of
the Tsallis statistics is further probed by considering the dynamics near
criticality and glass formation in thermal systems. In both cases a close
connection is made with states in unimodal maps with vanishing Lyapunov
coefficients.Comment: Proceedings of: STATPHYS 2004 - 22nd IUPAP International Conference
on Statistical Physics, National Science Seminar Complex, Indian Institute of
Science, Bangalore, 4-9 July 2004. Pramana, in pres
Is depression a real risk factor for acute myocardial infarction mortality? A retrospective cohort study
Background: Depression has been associated with a higher risk of cardiovascular events and a higher mortality in patients with one or more comorbidities. This study investigated whether continuative use of antidepressants (ADs), considered as a proxy of a state of depression, prior to acute myocardial infarction (AMI) is associated with a higher mortality afterwards. The outcome to assess was mortality by AD use. Methods: A retrospective cohort study was conducted in the Veneto Region on hospital discharge records with a primary diagnosis of AMI in 2002-2015. Subsequent deaths were ascertained from mortality records. Drug purchases were used to identify AD users. A descriptive analysis was conducted on patients' demographics and clinical data. Survival after discharge was assessed with a Kaplan-Meier survival analysis and Cox's multiple regression model. Results: Among 3985 hospital discharge records considered, 349 (8.8%) patients were classified as AD users'. The mean AMI-related hospitalization rate was 164.8/100,000 population/year, and declined significantly from 204.9 in 2002 to 130.0 in 2015, but only for AD users (-40.4%). The mean overall follow-up was 4.64.1years. Overall, 523 patients (13.1%) died within 30days of their AMI. The remainder survived a mean 5.3 +/- 4.0years. After adjusting for potential confounders, use of antidepressants was independently associated with mortality (adj OR=1.75, 95% CI: 1.40-2.19). Conclusions: Our findings show that AD users hospitalized for AMI have a worse prognosis in terms of mortality. The use of routinely-available records can prove an efficient way to monitor trends in the state of health of specific subpopulations, enabling the early identification of AMI survivors with a history of antidepressant use
Boltzmann-Gibbs thermal equilibrium distribution for classical systems and Newton law: A computational discussion
We implement a general numerical calculation that allows for a direct
comparison between nonlinear Hamiltonian dynamics and the Boltzmann-Gibbs
canonical distribution in Gibbs -space. Using paradigmatic
first-neighbor models, namely, the inertial XY ferromagnet and the
Fermi-Pasta-Ulam -model, we show that at intermediate energies the
Boltzmann-Gibbs equilibrium distribution is a consequence of Newton second law
(). At higher energies we discuss partial agreement
between time and ensemble averages.Comment: New title, revision of the text. EPJ latex, 4 figure
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
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