7,474 research outputs found
Multi-alternative decision-making with non-stationary inputs
One of the most widely implemented models for multialternative
decision-making is the multihypothesis sequential
probability ratio test (MSPRT). It is asymptotically optimal,
straightforward to implement, and has found application in
modelling biological decision-making. However, the MSPRT
is limited in application to discrete (‘trial-based’), non-timevarying
scenarios. By contrast, real world situations will
be continuous and entail stimulus non-stationarity. In these
circumstances, decision-making mechanisms (like the MSPRT)
which work by accumulating evidence, must be able to discard
outdated evidence which becomes progressively irrelevant. To
address this issue, we introduce a new decision mechanism
by augmenting the MSPRT with a rectangular integration
window and a transparent decision boundary. This allows
selection and de-selection of options as their evidence changes
dynamically. Performance was enhanced by adapting the
window size to problem difficulty. Further, we present an
alternative windowing method which exponentially decays
evidence and does not significantly degrade performance,
while greatly reducing the memory resources necessary. The
methods presented have proven successful at allowing for the
MSPRT algorithm to function in a non-stationary environment
Scaling Behavior of Driven Interfaces Above the Depinning Transition
We study the depinning transition for models representative of each of the
two universality classes of interface roughening with quenched disorder. For
one of the universality classes, the roughness exponent changes value at the
transition, while the dynamical exponent remains unchanged. We also find that
the prefactor of the width scales with the driving force. We propose several
scaling relations connecting the values of the exponents on both sides of the
transition, and discuss some experimental results in light of these findings.Comment: Revtex 3.0, 4 pages in PRL format + 5 figures (available at
ftp://jhilad.bu.edu/pub/abbhhss/ma-figures.tar.Z ) submitted to Phys Rev Let
“Cities go smart!”: A system dynamics-based approach to smart city conceptualization
The world’s population has grown rapidly. Thus, new challenges have arisen in terms of people’s quality of life, natural resources renewal, and urban environment sustainability. The smart city concept was developed to deal with these challenges by incorporating new technologies in order to find solutions that preserve cities’ environment while promoting their residents’ wellbeing. However, for cities to be truly “smart”, they should be evaluated, and, to that end, determinants that facilitate their creation need to be identified. This study thus sought to combine cognitive mapping and the system dynamics approach to find which factors foster smart city success, as well as the cause-and-effect relationships among these determinants. In two groupwork sessions, a panel of experts identified a wide range of smart city determinants and analyzed the dynamics of their relationships. The results were validated by the panel members and senior representatives of Cascais and Évora City Councils, Portugal, who confirmed that the analysis system developed provides a deeper understanding of this research context. The advantages and limitations of the proposed framework are also discussed.info:eu-repo/semantics/publishedVersio
All-optical high speed NOR gate based on two photon absorption in silicon wire waveguides
We demonstrate for the first time an all-optical logic NOR gate in submicron size silicon wire waveguides. High speed operation at equivalent 80Gbps data rate was achieved using pump induced non-degenerate two-photon absorption inside the waveguides. The device requires low pulse energy (few pJ) for logic gate operation. (C) 2005 Optical Society of America
Temperature effects on dislocation core energies in silicon and germanium
Temperature effects on the energetics of the 90-degree partial dislocation in
silicon and germanium are investigated, using non-equilibrium methods to
estimate free energies, coupled with Monte Carlo simulations. Atomic
interactions are described by Tersoff and EDIP interatomic potentials. Our
results indicate that the vibrational entropy has the effect of increasing the
difference in free energy between the two possible reconstructions of the
90-degree partial, namely, the single-period and the double-period geometries.
This effect further increases the energetic stability of the double-period
reconstruction at high temperatures. The results also indicate that anharmonic
effects may play an important role in determining the structural properties of
these defects in the high-temperature regime.Comment: 8 pages in two-column physical-review format with six figure
Study of Radiographic Linear Indications and Subsequent Microstructural Features in Gas Tungsten Arc Welds of Inconel 718
This study presents examples and considerations for differentiating linear radiographic indications produced by gas tungsten arc welds in a 0.05-in-thick sheet of Inconel 718. A series of welds with different structural features, including the enigma indications and other defect indications such as lack of fusion and penetration, were produced, radiographed, and examined metallographically. The enigma indications were produced by a large columnar grain running along the center of the weld nugget occurring when the weld speed was reduced sufficiently below nominal. Examples of respective indications, including the effect of changing the x-ray source location, are presented as an aid to differentiation. Enigma, nominal, and hot-weld specimens were tensile tested to demonstrate the harmlessness of the enigma indication. Statistical analysis showed that there is no difference between the strengths of these three weld conditions
Adsorptividade de solos da microbacia do Córrego do Espraiado, Ribeirão Preto: riboflavina como modelo de adsorção.
Em area onde foram desenvolvidos estudos sobre os efeitos dos herbicidas atrazina e 2,4-D sobre a populacao microbiana dos solos da microbacia do Espraiado, Ribeirao Preto-SP, foi tambem pesquisado o uso de riboflavina, composto organico facilmente detectavel por espectrofotometria a baixas concentracoes, como modelo de estudos de adsorcao de solos. Os solos empregados neste trabalho foram provenientes de 9 pontos selecionados da microbacia para estudos microbiologicos e se agruparam em argilosos e arenosos, com teores de materia organica de 0,15 a 3,50%. Os resultados de adsorcao mostraram que a riboflavina foi adsorvida pelos diferentes solos, em proporcoes variadas dependente do solo. As isotermas de adsorcao revelaram isotermas do tipo L, como as observadas para os herbicidas triazinicos, como a atrazina. Os valores experimentais, para amostras coletadas de 0-20 cm aplicados a equacao de Freundlich, mostraram correlacao variando de 0.93 a 0,99, e valores de K de 0,47 a 63,43 e 1/n de 0,42 a 1,42. Os valores de Kd para riboflavina em diferentes amostras variaram de 0,61 +- 0,26 (amostra de solo arenoso) a 56,1 +- 13,7 (amostra de solo argiloso) enquanto o Koc variou de 230 +- 32 (solo arenoso) a 4671 +- 780 (solo argiloso). Amostras de solos argilosos coletadas a 80-90 cm, com menor teor de materia organica, tiveram valores de Koc maiores, enquanto em solo arenoso foram semelhantes. Valores de Kd, Koc e constantes da equacao e Freundlich encontrados para riboflavina sao comparaveis aqueles de uma gama de herbicidas puplicados na literatura, tornando riboflavina um modelo pratico e conveniente para o estudo de adsorptividade de herbicidas em solos
Stochastic Feedback and the Regulation of Biological Rhythms
We propose a general approach to the question of how biological rhythms
spontaneously self-regulate, based on the concept of ``stochastic feedback''.
We illustrate this approach by considering the neuroautonomic regulation of the
heart rate. The model generates complex dynamics and successfully accounts for
key characteristics of cardiac variability, including the power spectrum,
the functional form and scaling of the distribution of variations, and
correlations in the Fourier phases. Our results suggest that in healthy systems
the control mechanisms operate to drive the system away from extreme values
while not allowing it to settle down to a constant output.Comment: 15 pages, latex2e using rotate and epsf, with 4 ps figures. Submitted
to PR
Slave boson model for two-dimensional trapped Bose-Einstein condensate
A system of N bosons in a two-dimensional harmonic trap is considered. The
system is treated in term of the slave boson representation for hard-core
bosons which is valid in the arbitrary density regimes. I discuss the
consequences of higher order interactions on the density profiles by mapping
the slave boson equation to the known Kohn-Sham type equation within the
density functional scheme.Comment: 12 pages, 3 figures. Submitted to J. Phys. B : At. mol. opt. phy
- …