37,385 research outputs found
Cost-efficient vaccination protocols for network epidemiology
We investigate methods to vaccinate contact networks -- i.e. removing nodes
in such a way that disease spreading is hindered as much as possible -- with
respect to their cost-efficiency. Any real implementation of such protocols
would come with costs related both to the vaccination itself, and gathering of
information about the network. Disregarding this, we argue, would lead to
erroneous evaluation of vaccination protocols. We use the
susceptible-infected-recovered model -- the generic model for diseases making
patients immune upon recovery -- as our disease-spreading scenario, and analyze
outbreaks on both empirical and model networks. For different relative costs,
different protocols dominate. For high vaccination costs and low costs of
gathering information, the so-called acquaintance vaccination is the most cost
efficient. For other parameter values, protocols designed for query-efficient
identification of the network's largest degrees are most efficient
Pulsating-campaigns of human prophylaxis driven by risk perception palliate oscillations of direct contact transmitted diseases
Human behavioral responses play an important role in the impact of disease
outbreaks and yet they are often overlooked in epidemiological models.
Understanding to what extent behavioral changes determine the outcome of
spreading epidemics is essential to design effective intervention policies.
Here we explore, analytically, the interplay between the personal decision to
protect oneself from infection and the spreading of an epidemic. We do so by
coupling a decision game based on the perceived risk of infection with a
Susceptible-Infected-Susceptible model. Interestingly, we find that the simple
decision on whether to protect oneself is enough to modify the course of the
epidemics, by generating sustained steady oscillations in the prevalence. We
deem these oscillations detrimental, and propose two intervention policies
aimed at modifying behavioral patterns to help alleviate them. Surprisingly, we
find that pulsating campaigns, compared to continuous ones, are more effective
in diminishing such oscillations.Comment: 19 pages, 6 figure
Almost exact recovery in noisy semi-supervised learning
This paper investigates noisy graph-based semi-supervised learning or
community detection. We consider the Stochastic Block Model (SBM), where, in
addition to the graph observation, an oracle gives a non-perfect information
about some nodes' cluster assignment. We derive the Maximum A Priori (MAP)
estimator, and show that a continuous relaxation of the MAP performs almost
exact recovery under non-restrictive conditions on the average degree and
amount of oracle noise. In particular, this method avoids some pitfalls of
several graph-based semi-supervised learning methods such as the flatness of
the classification functions, appearing in the problems with a very large
amount of unlabeled data
Antisymmetrized molecular dynamics of wave packets with stochastic incorporation of Vlasov equation
On the basis of the antisymmetrized molecular dynamics (AMD) of wave packets
for the quantum system, a novel model (called AMD-V) is constructed by the
stochastic incorporation of the diffusion and the deformation of wave packets
which is calculated by Vlasov equation without any restriction on the one-body
distribution. In other words, the stochastic branching process in molecular
dynamics is formulated so that the instantaneous time evolution of the averaged
one-body distribution is essentially equivalent to the solution of Vlasov
equation. Furthermore, as usual molecular dynamics, AMD-V keeps the many-body
correlation and can naturally describe the fluctuation among many channels of
the reaction. It is demonstrated that the newly introduced process of AMD-V has
drastic effects in heavy ion collisions of 40Ca + 40Ca at 35 MeV/nucleon,
especially on the fragmentation mechanism, and AMD-V reproduces the
fragmentation data very well. Discussions are given on the interrelation among
the frameworks of AMD, AMD-V and other microscopic models developed for the
nuclear dynamics.Comment: 26 pages, LaTeX with revtex and epsf, embedded postscript figure
On the effect of heterogeneity in stochastic interacting-particle systems
We study stochastic particle systems made up of heterogeneous units. We
introduce a general framework suitable to analytically study this kind of
systems and apply it to two particular models of interest in economy and
epidemiology. We show that particle heterogeneity can enhance or decrease the
collective fluctuations depending on the system, and that it is possible to
infer the degree and the form of the heterogeneity distribution in the system
by measuring only global variables and their fluctuations
Environment-Induced Decoherence and the Transition From Quantum to Classical
We study dynamics of quantum open systems, paying special attention to those
aspects of their evolution which are relevant to the transition from quantum to
classical. We begin with a discussion of the conditional dynamics of simple
systems. The resulting models are straightforward but suffice to illustrate
basic physical ideas behind quantum measurements and decoherence. To discuss
decoherence and environment-induced superselection einselection in a more
general setting, we sketch perturbative as well as exact derivations of several
master equations valid for various systems. Using these equations we study
einselection employing the general strategy of the predictability sieve.
Assumptions that are usually made in the discussion of decoherence are
critically reexamined along with the ``standard lore'' to which they lead.
Restoration of quantum-classical correspondence in systems that are classically
chaotic is discussed. The dynamical second law -it is shown- can be traced to
the same phenomena that allow for the restoration of the correspondence
principle in decohering chaotic systems (where it is otherwise lost on a very
short time-scale). Quantum error correction is discussed as an example of an
anti-decoherence strategy. Implications of decoherence and einselection for the
interpretation of quantum theory are briefly pointed out.Comment: 80 pages, 7 figures included, Lectures given by both authors at the
72nd Les Houches Summer School on "Coherent Matter Waves", July-August 199
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