1,299 research outputs found
Bayesian decision making in human collectives with binary choices
Here we focus on the description of the mechanisms behind the process of
information aggregation and decision making, a basic step to understand
emergent phenomena in society, such as trends, information spreading or the
wisdom of crowds. In many situations, agents choose between discrete options.
We analyze experimental data on binary opinion choices in humans. The data
consists of two separate experiments in which humans answer questions with a
binary response, where one is correct and the other is incorrect. The questions
are answered without and with information on the answers of some previous
participants. We find that a Bayesian approach captures the probability of
choosing one of the answers. The influence of peers is uncorrelated with the
difficulty of the question. The data is inconsistent with Weber's law, which
states that the probability of choosing an option depends on the proportion of
previous answers choosing that option and not on the total number of those
answers. Last, the present Bayesian model fits reasonably well to the data as
compared to some other previously proposed functions although the latter
sometime perform slightly better than the Bayesian model. The asset of the
present model is the simplicity and mechanistic explanation of the behavior.Comment: 8 pages, 6 figures, 1 tabl
Dissipative solitons which cannot be trapped
In this paper we study the behavior of dissipative solitons in systems with
high order nonlinear dissipation and show how they cannot survive under the
effect of trapping potentials both of rigid wall type or asymptotically
increasing ones. This provides an striking example of a soliton which cannot be
trapped and only survives to the action of a weak potential
Razonamiento inferencial informal: el caso de la prueba de significaciĂłn con estudiantes de bachillerato
El presente trabajo es un estudio exploratorio sobre el razonamiento inferencial informal (RII) llevado a cabo con estudiantes de bachillerato (15-17 anÌos). Se les aplicoÌ un problema que se refiere formalmente como prueba de hipoÌtesis sobre proporciones. Las respuestas se organizaron y analizaron con base en un marco conceptual formado por tres categoriÌas. Como resultado, se observoÌ que las respuestas de los estudiantes combinan sus conocimientos informales acerca del contexto y los datos del problema. El contexto familiar provocoÌ poca dificultad para hacer inferencias adecuadas; consecuencia de un razonamiento adecuado debido a que la mayoriÌa reconoce el modelo probabiliÌstico debido al azar y se razona apropiadamente con eÌl. Se concluye que el razonamiento en la prueba de significacioÌn es maÌs natural para los estudiantes y es una pauta para desarrollar el RII asiÌ como el uso de contextos familiares
Computation of inflationary cosmological perturbations in chaotic inflationary scenarios using the phase-integral method
The phase-integral approximation devised by Fr\"oman and Fr\"oman, is used
for computing cosmological perturbations in the quadratic chaotic inflationary
model. The phase-integral formulas for the scalar and tensor power spectra are
explicitly obtained up to fifth order of the phase-integral approximation. We
show that, the phase integral gives a very good approximation for the shape of
the power spectra associated with scalar and tensor perturbations as well as
the spectral indices. We find that the accuracy of the phase-integral
approximation compares favorably with the numerical results and those obtained
using the slow-roll and uniform approximation methods.Comment: 21 pages, RevTex, to appear in Phys. Rev
Directed transport as a mechanism for protein folding in vivo
We propose a model for protein folding in vivo based on a Brownian-ratchet
mechanism in the multidimensional energy landscape space. The device is able to
produce directed transport taking advantage of the assumed intrinsic asymmetric
properties of the proteins and employing the consumption of energy provided by
an external source. Through such a directed transport phenomenon, the
polypeptide finds the native state starting from any initial state in the
energy landscape with great efficacy and robustness, even in the presence of
different type of obstacles. This model solves Levinthal's paradox without
requiring biased transition probabilities but at the expense of opening the
system to an external field.Comment: 16 pages, 7 figure
Optimization of the Superconducting Linear Magnetic Bearing of a Maglev Vehicle
Considering the need for cost/performance prediction and optimization of
superconducting maglev vehicles, we develop and validate here a 3D finite
element model to simulate superconducting linear magnetic bearings. Then we
reduce the 3D model to a 2D model in order to decrease the computing time. This
allows us to perform in a reasonable time a stochastic optimization considering
the superconductor properties and the vehicle operation. We look for the
permanent magnet guideway geometry that minimizes the cost and maximizes the
lateral force during a displacement sequence, with a constraint on the minimum
levitation force. The displacement sequence reproduces a regular maglev vehicle
operation with both vertical and lateral movements. For the sake of comparison,
our reference is the SupraTrans prototype bearing. The results of the
optimization suggest that the bearing cost could be substantially reduced,
while keeping the same performances as the initial design. Alternatively, the
performances could be significantly improved for the same original cost
Changes on the nanostructure of cementitius calcium silicate hydrates (C-S-H) induced by aqueous carbonation
The nanostructure of the main binding phase of the hydrated cements, the calcium silicate hydrates (C-S-H), and their structural changes due to aqueous carbonation have been characterized using TEM, nitrogen physisorption, and SAXS. Synthetic C-S-H has been used for this purpose. Two different morphologies were identified, similar to the high density and low density C-S-H types. When submitting the sample to a CO 2 flux, the low density phase was completely carbonated. The carbonation by-products, calcium carbonate, and silica gel were also identified and characterized. The precipitation of the silica gel increased the specific surface area from 95 to 132 m 2/g, and its structure, formed by particles of ~5 nm typical radius, was observed by small angle X-ray scattering. In addition, the resistance of the high density C-S-H to carbonation is reported, and the passivating effect of the precipitated calcium carbonate is also discussed. Finally, the results have been compared with carbonation features observed in Portland cement carbonated experimentally at downhole conditions.
Estimation in the Birnbaum-Saunders distribution based on scale-mixture of normals and the EM-algorithm
Scale mixtures of normal (SMN) distributions are used for modeling symmetric data. Members
of this family have appealing properties such as robust estimates, easy number generation, and efficient computation of the ML estimates via the EM-algorithm. The Birnbaum-Saunders (BS) distribution is a positively skewed model that is related to the normal distribution and has received
considerable attention. We introduce a type of BS distributions based on SMN models, produce a lifetime analysis, develop the EM-algorithm for ML estimation of parameters, and illustrate the obtained results with real data showing the robustness of the estimation procedure.Peer Reviewe
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