1,721,017 research outputs found
Numerical invariantization for morphological PDE schemes
No full textWelk, Martin; Kim, Pilwon; Olver, Peter J.. (2007). Numerical invariantization for morphological PDE schemes. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/4364
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A population-based optimization method using Newton fractal
Full text linkDepartment of Mathematical SciencesMetaheuristic is a general procedure to draw an agreement in a group based on the decision making of each individual beyond heuristic. For last decade, there have been many attempts to develop metaheuristic methods based on swarm intelligence to solve global optimization such as particle swarm optimizer, ant colony optimizer, firefly optimizer. These methods are mostly stochastic and independent on specific problems.
Since metaheuristic methods based on swarm intelligence require no central coordination (or minimal, if any), they are especially well-applicable to those problems which have distributed or parallel structures. Each individual follows few simple rules, keeping the searching cost at a decent level. Despite its simplicity, the methods often yield a fast approximation in good precision, compared to conventional methods.
Exploration and exploitation are two important features that we need to consider to find a global optimum in a high dimensional domain, especially when prior information is not given. Exploration is to investigate the unknown space without using the information from history to find undiscovered optimum. Exploitation is to trace the neighborhood of the current best to improve it using the information from history. Because these two concepts are at opposite ends of spectrum, the tradeoff significantly affects the performance at the limited cost of search.
In this work, we develop a chaos-based metaheuristic method, ???Newton Particle Optimization(NPO)???, to solve global optimization problems. The method is based on the Newton method which is a well-established mathematical root-finding procedure. It actively utilizes the chaotic nature of the Newton method to place a proper balance between exploration and exploitation. While most current population-based methods adopt stochastic effects to maximize exploration, they often suffer from weak exploitation. In addition, stochastic methods generally show poor reproducing ability and premature convergence. It has been argued that an alternative approach using chaos may mitigate such disadvantages. The unpredictability of chaos is correspondent with the randomness of stochastic methods. Chaos-based methods are deterministic and therefore easy to reproduce the results with less memory. It has been shown that chaos avoids local optimum better than stochastic methods and buffers the premature convergence issue.
Newton method is deterministic but shows chaotic movements near the roots. It is such complexity that enables the particles to search the space for global optimization. We initialize the particle???s position randomly at first and choose the ???leading particles??? to attract other particles near them. We can make a polynomial function whose roots are those leading particles, called ???a guiding function???. Then we update the positions of particles using the guiding function by Newton method. Since the roots are not updated by Newton method, the leading particles survive after update. For diverse movements of particles, we use modified newton method, which has a coefficient in the variation of movements for each particle. Efficiency in local search is closely related to the value of m which determines the convergence rate of the Newton method. We can control the balance between exploration and exploitation by choice of leading particles.
It is interesting that selection of excellent particles as leading particles not always results in the best result. Including mediocre particles in the roots of guiding function maintains the diversity of particles in position. Though diversity seems to be inefficient at first, those particles contribute to the exploration for global search finally.
We study the conditions for the convergence of NPO. NPO enjoys the well-established analysis of the Newton method. This contrasts with other ???nature-inspired??? algorithms which have often been criticized for lack of rigorous mathematical ground. We compare the results of NPO with those of two popular metaheuristic methods, particle swarm optimizer(PSO) and firefly optimizer(FO). Though it has been shown that there are no such algorithms superior to all problems by no free lunch theorem, that is why the researchers are concerned about adaptable global optimizer for specific problems. NPO shows good performance to CEC 2013 competition test problems comparing to PSO and FO.ope
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Mathematical Analysis on Spatio-Temporal Criminal Patterns
Full text linkDepartment of Mathematical SciencesMathematics has been used in many areas, and in particular to analyze numerous social phenomena in the world in great detail. Mathematical modeling has been used to model certain crimes and/or their phenomena. In addition, crime data analyses have been performed and used for crime prevention and control. In this study, we initially modeled crimes based on the concept of ???population biology.??? We cat-egorized crimes as felonies or misdemeanors and modified the changes in the population of each crime according to the characteristics of each offender, length of detention, recidivism rate, and arrest rate. We aimed to parameterize their characteristics and analyze the dynamics of the changes. In particular, we aimed to reflect the criminology theories of the ???broken window effect??? and ???crime school effect??? in our model. Through this modeling, we identified the equilibrium point and analyzed the stability of the equilibrium point when each effect was present. Then, we analyzed the phenomena according to the changes in the parameters related to the crimes and compared them with what was reflected in the real world using a bifurcation analysis. We then collected the criminal temporal and spatio-temporal data and used dynamic mode decomposition (DMD) to analyze the important factors of each data type. Furthermore, we calculated the key factors through DMD, compared the characteristics obtained from the temporal and spatio-temporal data with those from the original data, and analyzed the relationships obtained from each characteristic.
Based on the results of the crime dynamics, we concluded that misdemeanors must be considered to reduce the number of felonies from the perspective of police resources, as the aforementioned broken window effect and crime school effect are related to the dynamics of moving in and out of prison. We also analyzed the temporal and spatio-temporal criminal data using DMD. For the temporal data, we verified the predictions of the future states using DMD and the decay, growth, or oscillation of each type of crime. Moreover, we connected the DMD mode to crime hotspots and analyzed the environmental characteristics of the spatial factors.ope
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Reservoir computing based on explosive synchronization and quenched chaos
Full text linkDepartment of Mathematical SciencesSynchronous oscillations in neuronal ensembles have been proposed to provide a neural basis for the information processes in the brain. In this work, we present a reservoir computing(RC), a highly e???cient bio-inspired architecture, based on oscillator synchronization in a critical regime. The algorithm uses the high-dimensional transient dynamics perturbed by an input and translates it into proper output stream. One of the bene???ts of adopting coupled phase oscillators as neuromorphic elements is that the synchrony among oscillators can be ???nely tuned at arti???cial state. Especially near a critical state, the marginally synchronized oscillators operate with high e???ciency and maintain better computing performances. We also show that explosive synchronization that is induced from speci???c neuronal connectivity produces more improved and stable outputs. This work provides a systematic way to encode computing in a large size coupled oscillator, which may be useful in designing neuromorphic devices.
Furthermore we develop RC based on ???explosive death??? of chaos. The proposed reservoir utilizes transient dynamics of coupled chaotic oscillators in a critical regime where sudden amplitude death occurs. Explosive death not only brings the system a large criticality which provides a variety of orbits for computing, but also stabilizes them which otherwise diverge soon in chaotic units. The proposed framework shows better results in tasks for signal reconstructions than RC based on explosive synchronization of regular phase oscillators. We also show that the information capacity of the reservoirs at a critical point can be used as a predictive measure for computational capability of a reservoir.clos
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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