2,237 research outputs found
An NPZ Model with State-Dependent Delay due to Size-Structure in Juvenile Zooplankton
The study of planktonic ecosystems is important as they make up the bottom
trophic levels of aquatic food webs. We study a closed
Nutrient-Phytoplankton-Zooplankton (NPZ) model that includes size structure in
the juvenile zooplankton. The closed nature of the system allows the
formulation of a conservation law of biomass that governs the system. The model
consists of a system of nonlinear ordinary differential equation coupled to a
partial differential equation. We are able to transform this system into a
system of delay differential equations where the delay is of threshold type and
is state-dependent. The system of delay differential equations can be further
transformed into one with fixed delay. Using the different forms of the model
we perform a qualitative analysis of the solutions, which includes studying
existence and uniqueness, positivity and boundedness, local and global
stability, and conditions for extinction. Key parameters that are explored are
the total biomass in the system and the maturity level at which the juvenile
zooplankton reach maturity. Numerical simulations are also performed to verify
our analytical results
Using association rule mining to enrich semantic concepts for video retrieval
In order to achieve true content-based information retrieval on video we should analyse and index video with
high-level semantic concepts in addition to using user-generated tags and structured metadata like title, date,
etc. However the range of such high-level semantic concepts, detected either manually or automatically,
usually limited compared to the richness of information content in video and the potential vocabulary of
available concepts for indexing. Even though there is work to improve the performance of individual concept
classifiers, we should strive to make the best use of whatever partial sets of semantic concept occurrences
are available to us. We describe in this paper our method for using association rule mining to automatically
enrich the representation of video content through a set of semantic concepts based on concept co-occurrence
patterns. We describe our experiments on the TRECVid 2005 video corpus annotated with the 449 concepts
of the LSCOM ontology. The evaluation of our results shows the usefulness of our approach
Quantum Metropolis Sampling
The original motivation to build a quantum computer came from Feynman who
envisaged a machine capable of simulating generic quantum mechanical systems, a
task that is believed to be intractable for classical computers. Such a machine
would have a wide range of applications in the simulation of many-body quantum
physics, including condensed matter physics, chemistry, and high energy
physics. Part of Feynman's challenge was met by Lloyd who showed how to
approximately decompose the time-evolution operator of interacting quantum
particles into a short sequence of elementary gates, suitable for operation on
a quantum computer. However, this left open the problem of how to simulate the
equilibrium and static properties of quantum systems. This requires the
preparation of ground and Gibbs states on a quantum computer. For classical
systems, this problem is solved by the ubiquitous Metropolis algorithm, a
method that basically acquired a monopoly for the simulation of interacting
particles. Here, we demonstrate how to implement a quantum version of the
Metropolis algorithm on a quantum computer. This algorithm permits to sample
directly from the eigenstates of the Hamiltonian and thus evades the sign
problem present in classical simulations. A small scale implementation of this
algorithm can already be achieved with today's technologyComment: revised versio
Practical learning method for multi-scale entangled states
We describe a method for reconstructing multi-scale entangled states from a
small number of efficiently-implementable measurements and fast
post-processing. The method only requires single particle measurements and the
total number of measurements is polynomial in the number of particles. Data
post-processing for state reconstruction uses standard tools, namely matrix
diagonalisation and conjugate gradient method, and scales polynomially with the
number of particles. Our method prevents the build-up of errors from both
numerical and experimental imperfections
Characterization of complex quantum dynamics with a scalable NMR information processor
We present experimental results on the measurement of fidelity decay under
contrasting system dynamics using a nuclear magnetic resonance quantum
information processor. The measurements were performed by implementing a
scalable circuit in the model of deterministic quantum computation with only
one quantum bit. The results show measurable differences between regular and
complex behaviour and for complex dynamics are faithful to the expected
theoretical decay rate. Moreover, we illustrate how the experimental method can
be seen as an efficient way for either extracting coarse-grained information
about the dynamics of a large system, or measuring the decoherence rate from
engineered environments.Comment: 4pages, 3 figures, revtex4, updated with version closer to that
publishe
Évaluation de l’utilisation et de la présentation des résultats d’analyses factorielles et d’analyses en composantes principales en éducation
Nous évaluons l’utilisation et la présentation des résultats d’analyses factorielles et d’analyses en composantes principales dans six périodiques canadiens en éducation publiés entre 1995 et 2005. À partir de 1089 articles, nous avons relevé 61 utilisations de ces analyses. En ayant recours à une grille de lecture, nous avons recueilli des informations sur le but de l’utilisation de l’analyse, la taille de l’échantillon, les variables, la méthode d’extraction, le critère de dimensionnalité, la méthode de rotation des axes et les résultats présentés. Nous avons identifié des lacunes, tant au niveau des pratiques que de la présentation des résultats. Enfin, nous formulons quelques recommandations quant à l’utilisation rigoureuse de ces types d’analyses.This paper presents an evaluation of the use and presentation of results of factor analysis and principal component analysis as published between 1995 and 2005 in six Canadian educational periodicals. From a corpus of 1089 articles, the authors noted 61 uses of these analyses. Using a reading grid, they noted information on the objective of the analysis, the sample size, the variables, the extraction method, the dimensionality criteria, the method for axes rotation, and the results presented. They identified deficiencies both at the level of practices and in the result presentation. Finally, the authors formulate several recommendations regarding a more rigorous use of these types of analyses.Evaluamos la utilización y la presentación de los resultados de análisis factoriales y de análisis en componentes principales dentro de seis publicaciones periódicas canadienses en educación publicadas entre 1995 et 2005. En 1089 artículos, notamos 61 utilizaciones de estos análisis. Mediante una matriz de lectura, recolectamos informaciones en cuanto al objetivo de la utilización de análisis, el tamaño de la muestra, las variables, el método de extracción, el criterio de dimensionalidad, el método de rotación de los ejes y los resultados presentados. Identificamos unas lagunas, tanto a nivel de las prácticas como de la presentación de los resultados. Por terminar, formulamos algunas recomendaciones en cuanto a la utilización rigorosa de estos tipos de análisis
Exponential speed-up with a single bit of quantum information: Testing the quantum butterfly effect
We present an efficient quantum algorithm to measure the average fidelity
decay of a quantum map under perturbation using a single bit of quantum
information. Our algorithm scales only as the complexity of the map under
investigation, so for those maps admitting an efficient gate decomposition, it
provides an exponential speed up over known classical procedures. Fidelity
decay is important in the study of complex dynamical systems, where it is
conjectured to be a signature of quantum chaos. Our result also illustrates the
role of chaos in the process of decoherence.Comment: 4 pages, 2 eps figure
Actionable Recourse in Linear Classification
Machine learning models are increasingly used to automate decisions that
affect humans - deciding who should receive a loan, a job interview, or a
social service. In such applications, a person should have the ability to
change the decision of a model. When a person is denied a loan by a credit
score, for example, they should be able to alter its input variables in a way
that guarantees approval. Otherwise, they will be denied the loan as long as
the model is deployed. More importantly, they will lack the ability to
influence a decision that affects their livelihood.
In this paper, we frame these issues in terms of recourse, which we define as
the ability of a person to change the decision of a model by altering
actionable input variables (e.g., income vs. age or marital status). We present
integer programming tools to ensure recourse in linear classification problems
without interfering in model development. We demonstrate how our tools can
inform stakeholders through experiments on credit scoring problems. Our results
show that recourse can be significantly affected by standard practices in model
development, and motivate the need to evaluate recourse in practice.Comment: Extended version. ACM Conference on Fairness, Accountability and
Transparency [FAT2019
On compatibility and improvement of different quantum state assignments
When Alice and Bob have different quantum knowledges or state assignments
(density operators) for one and the same specific individual system, then the
problems of compatibility and pooling arise. The so-called first
Brun-Finkelstein-Mermin (BFM) condition for compatibility is reobtained in
terms of possessed or sharp (i. e., probability one) properties. The second BFM
condition is shown to be generally invalid in an infinite-dimensional state
space. An argument leading to a procedure of improvement of one state
assifnment on account of the other and vice versa is presented.Comment: 8 page
Comparative parasitism of the fish plagioscion squamosissimus in native and invated river basins.
Biological invasions are considered a major threat to biodiversity around the world, but the role of parasites in this process is still little investigated. Here, we compared parasite infections of a host species in the areas where it originated and where it was introduced, and in native and introduced species in the same environment, using the endoparasites of the fish Plagioscion squamosissimus (Sciaenidae) in 3 Brazilian basins. Samples were taken in 2 rivers where the species is native, i.e., Solimões River (SO) and Tocantins River (TO), and where the species was introduced, the upper Parana´ River (PR). In addition, abundances of diplostomids and larval nematodes were compared between P. squamosissimus and 2 native competitors in the PR, Hoplias malabaricus and Raphiodon vulpinus. In total, 13 species of endoparasites were recorded, but only Austrodiplostomum sp. and cestode cysts were present in all localities. Although infracommunity richness was similar, their species composition was slightly different among localities. General linear models using the relative condition factor of fish as response variables, and abundance of the most prevalent parasites as possible predictors showed that the condition of fish is negatively correlated with parasite abundance only in the native range (TO). Abundance of diplostomid eye flukes was higher in the PR, and in the native species H. malabaricus when compared to the invader, which might present an advantage for P. squamosissimus if they compete for prey. However, although P. squamosissimus may have lost some of its native parasites during its introduction to the PR, it is now possibly acting as a host for native generalist parasites
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