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Cognitive abilities, sociocultural background and academic achievement

Diniz, António; Pocinho, Margarida Maria Ferreira Diogo Dias; Almeida, Leandro Silva
Fonte: Psicothema Publicador: Psicothema
Tipo: Artigo de Revista Científica
Publicado em //2011 ENG
Relevância na Pesquisa
36.05%
The infl uence of students’ sociocultural background on academic achievement is a well established fact. Research also points out that sociocultural background is related to students’ cognitive abilities and these have an effect on their academic achievement. However, the mediator role of cognitive abilities on the relationship between sociocultural background and academic achievement is less well known. A structural equation model that represents these relationships was tested in a sample (N= 728) of Portuguese junior high school students. Multigroup analysis of the model showed the importance of the cognitive ability mediation effect between sociocultural background and academic achievement in the 7th and 9th grades, but not in the 8th grade. This difference may be the result of the academic transition experienced in the 7th and 9th grades in the Portuguese educational system, which requires parents’ higher involvement in school.

Separating the wheat from the chaff: unbiased filtering of background tandem mass spectra improves protein identification

JUNQUEIRA, Magno; SPIRIN, Victor; BALBUENA, Tiago Santana; WARIDEL, Patrice; SURENDRANATH, Vineeth; KRYUKOV, Grigoriy; ADZHUBEI, Ivan; THOMAS, Henrik; SUNYAEV, Shamil; SHEVCHENKO, Andrej
Fonte: AMER CHEMICAL SOC Publicador: AMER CHEMICAL SOC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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Only a small fraction of spectra acquired in LC-MS/MS runs matches peptides from target proteins upon database searches. The remaining, operationally termed background, spectra originate from a variety of poorly controlled sources and affect the throughput and confidence of database searches. Here, we report an algorithm and its software implementation that rapidly removes background spectra, regardless of their precise origin. The method estimates the dissimilarity distance between screened MS/MS spectra and unannotated spectra from a partially redundant background library compiled from several control and blank runs. Filtering MS/MS queries enhanced the protein identification capacity when searches lacked spectrum to sequence matching specificity. In sequence-similarity searches it reduced by, on average, 30-fold the number of orphan hits, which were not explicitly related to background protein contaminants and required manual validation. Removing high quality background MS/MS spectra, while preserving in the data set the genuine spectra from target proteins, decreased the false positive rate of stringent database searches and improved the identification of low-abundance proteins.

Novos métodos de estimação de ruído de fundo de céu aplicados à missão CoRoT.; New methods for estimating sky background noise applied to the CoRoT mission.

Coelho, Luciana Guidon
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 11/04/2012 PT
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O satélite franco-europeu com participação brasileira, CoRoT (Convention, Rotation and planetary Transits), faz parte de uma missão espacial dedicada à sismologia estelar e à busca por exoplanetas. Para a descoberta de exoplanetas, o objetivo é detectar a ocultação temporária da estrela ao redor da qual orbita o planeta em questão, ou seja, detectar um trânsito planetário que pode ser traduzido por uma diminuição tênue do fluxo de fótons estelar coletado pelos CCDs do fotômetro. Existem alguns ruídos e diversas fontes de luz que atingem os CCDs e que não são provenientes das estrelas em estudo. Tais ruídos e fontes de luz geram uma iluminação chamada de fundo de céu nos CCDs que é não homogênea e que precisa ser corrigida antes do início da exploração científica dos dados obtidos nas observações do satélite. A correção de fundo de céu é um procedimento padrão na redução de dados fotométricos, e consiste na subtração do nível médio de fundo de céu das medições fotométricas de uma estrela. Para a determinação do fundo de céu o CoRoT utiliza um conjunto de janelas de fundo de céu. Este trabalho propõem métodos alternativos para a alocação destas janelas de fundo de céu e estimação do ruído de fundo de céu para o canal de exoplanetas do satélite CoRoT. São apresentados dois novos métodos de alocação de janelas e são testados diversos métodos de estimação de ruído de fundo de céu. Os testes realizados neste trabalho sugerem fortemente a utilização do método chamado k-min para a alocação de janelas e do método mediana e 5 vizinhos para a estimação de ruído de fundo de céu. O método k-min procura alocar as janelas de maneira homogênea e em locais de mínimo de uma imagem do céu observado pelo satélite e o método mediana e 5 vizinhos estima o ruído de fundo de céu a partir da mediana de todas as janelas de fundo de céu com nível DC corrigido pela mediana das cinco janelas vizinhas mais próximas.; The French-European satellite with Brazilian participation...

O curso de educação fisica : a questão da formação academica na visão de seus agentes; Physical education course: the issue of academic background according to the oppinion of its agents

Patricia Mano Trindade
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 26/02/2007 PT
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Este trabalho visa à análise sobre a atual perspectiva na formação acadêmica na área de Educação Física. Para tanto, parte-se de uma pesquisa bibliográfica referente à história da universidade ocidental, seguida da universidade no Brasil, como contextualização à história da Educação Física na universidade brasileira. Pretende-se, nesta tese, uma reflexão que contribua para a compreensão dos aspectos relevantes na formação profissional nesta área. Como aporte teórico ao trabalho, foram pesquisados os movimentos ocorridos na área da Educação Física, associados às concepções teóricas e ao contexto, tidos como determinantes nos processos de mudança. A investigação empírica foi desenvolvida com o estudo de caso do curso de Educação Física da Faculdade de Jaguariúna - FAJ e teve como objetivo conhecer quais as expectativas em relação à formação acadêmica que manifestam os diretores, docentes e discentes inseridos num contexto de conflitantes demandas. A análise dos dados nos permite conhecer esses conflitos em relação às tendências dos enfoques da Formação Geral, Básica e Profissional; This study aims at analyzing the current perspective as regards the academic background in Physical Education. Thus...

Valores de background geoquímico e suas implicações em estudos ambientais

Rodrigues,Aline Sueli de Lima; Nalini Júnior,Hermínio Arias
Fonte: Escola de Minas Publicador: Escola de Minas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2009 PT
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O estabelecimento de valores de background geoquímico como medida relativa para distinguir concentrações naturais de um elemento (geogênica e/ou biogênica) e a influência das atividades antrópicas nestas concentrações representa um dos assuntos mais importantes das ciências ambientais recentes. A relação entre as alterações naturais e as proporcionadas pela ação antrópica nas espécies químicas é uma questão que envolve implicações importantes nas áreas da geologia, toxicologia e biologia, entre outros campos do conhecimento. Isto é especialmente importante, quando interpretações geoquímicas de elementos tóxicos são requeridas. Assim, o objetivo principal desse artigo é apresentar e discutir as razões pelas quais o estabelecimento de valores de background geoquímico tem implicações nos estudos ambientais. Ao longo desse artigo, são apresentados alguns conceitos de background geoquímico e os principais métodos utilizados para avaliar a concentração background de elementos químicos (métodos direto e indireto). Além disso, são destacados alguns exemplos de estudos desenvolvidos no Brasil. Estudos envolvendo o estabelecimento de valores de background geoquímico são importantes porque permitem avaliar riscos potenciais de contaminação e identificar concentrações naturais de elementos-traço de uma determinada área.

Improved estimate of the policy-relevant background ozone in the United States using the GEOS-Chem global model with 1/2° × 2/3° horizontal resolution over North America

Zhang, Lin; Jacob, Daniel James; Downey, Nicole V.; Wood, Dana A.; Blewitt, Doug; Carouge, Claire C.; van Donkelaar, Aaron; Jones, Dylan B.A.; Murray, Lee; Wang, Yuxuan
Fonte: Elsevier BV Publicador: Elsevier BV
Tipo: Artigo de Revista Científica
EN_US
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The policy-relevant background (PRB) ozone is defined by the US Environmental Protection Agency (EPA) as the surface ozone concentration that would be present over the US in the absence of North American anthropogenic emissions. It is intended to provide a baseline for risk and exposure assessments used in setting the National Ambient Air Quality Standard (NAAQS). We present here three-year statistics (2006–2008) of PRB ozone over the US calculated using the GEOS-Chem global 3-D model of atmospheric composition with 1/2° × 2/3° horizontal resolution over North America and adjacent oceans (2° × 2.5° for the rest of the world). We also provide estimates of the US background (no anthropogenic US emissions) and natural background (no anthropogenic emissions worldwide and pre-industrial methane). Our work improves on previous GEOS-Chem PRB estimates through the use of higher model resolution, 3-year statistics, better representation of stratospheric influence, and updated emissions. PRB is particularly high in the intermountain West due to high elevation, arid terrain, and large-scale subsidence. We present for this region a detailed model evaluation showing that the model is successful in reproducing ozone exceedances up to 70 ppbv. However...

Variability in surface ozone background over the United States: Implications for air quality policy

Fiore, A.; Jacob, Daniel James; Liu, H.; Yantosca, Robert M.; Fairlie, T. D.; Li, Q.
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica
EN_US
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The U.S. Environmental Protection Agency (EPA) presently uses a 40 ppbv background O3 level as a baseline in its O3 risk assessments. This background is defined as those concentrations that would exist in the absence of North American emissions. Lefohn et al. [2001] have argued that frequent occurrences of O3 concentrations above 50–60 ppbv at remote northern U.S. sites in spring are of stratospheric origin, challenging the EPA background estimate and implying that the current O3 standard (84 ppbv, 8-hour average) may be unattainable. We show that a 3-D global model of tropospheric chemistry reproduces much of the observed variability in U.S. surface O3 concentrations, including the springtime high-O3 events, with only a minor stratospheric contribution (always <20 ppbv). We conclude that the previous interpretations of a stratospheric source for these events underestimated the role of regional and hemispheric pollution. While stratospheric intrusions might occasionally elevate surface O3 at high-altitude sites, our results indicate that these events are rare and would not compromise the O3 air quality standard. We find that the O3 background is generally 15–35 ppbv, with some incidences of 40–50 ppbv in the west in spring at high-elevation sites (>2 km). It declines from spring to summer and further decreases during O3 pollution episodes. The 40 ppbv background assumed by EPA thus actually underestimates the risk associated with O3 during polluted conditions. A better definition would represent background as a function of season...

Background ozone over the United States in summer: Origin, trend, and contribution to pollution episodes

Fiore, Arlene M.; Jacob, Daniel James; Bey, Isabelle; Yantosca, Robert M.; Field, Brendan; Fusco, Andrew; Wilkinson, James
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica
EN_US
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Observations indicate that ozone (O3) concentrations in surface air over the United States in summer contain a 20–45 ppbv background contribution, presumably reflecting transport from outside the North American boundary layer. We use a three-dimensional global model of tropospheric chemistry driven by assimilated meteorological observations to investigate the origin of this background and to quantify its contribution to total surface O3 on both average and highly polluted summer days. The model simulation is evaluated with a suite of surface and aircraft observations over the United States from the summer of 1995. The model reproduces the principal features in the observed distributions of O3 and its precursors, including frequency distributions of O3 concentrations and the development of regional high-O3 episodes in the eastern United States. Comparison of simulations with 1995 versus 1980 global fossil fuel emissions indicates that the model captures the previously observed decrease in the high end of the O3 probability distribution in surface air over the United States (reflecting reduction of domestic hydrocarbon emissions) and the increase in the low end (reflecting, at least in the model, rising Asian emissions). In the model...

Desempenho e background familiar: um estudo no acesso a uma instituição de ensino técnico federal no Brasil; The infuence of Family background in the access to Federal Technical Education in Brazil

Assunção, Marcus Vinicius Dantas de
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Administração; Políticas e Gestão Públicas; Gestão Organizacional Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Administração; Políticas e Gestão Públicas; Gestão Organizacional
Tipo: Dissertação Formato: application/pdf
POR
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This paper comprises an investigation on the influence of the variable family backgrounds (father school level, mother school level and family income) over the pupil s performance in admissions examination (entrance test or PROITEC) at Instituto Federal de Educação, Ciência e Tecnologia do Rio Grande do Norte (IFRN). From that point of view, the main goal of this research is to analyze the influence of the family background as a determiner of the pupil´s performance in the access to Technical and Professional education at IFRN. Secondary data were used from two databases (entrance test and PROITEC) adding up to 19.226 observations to the vacancies offered in the year of 2013. Aiming at achieving the proposed goal, a conceptual model composed of three hypothesis was developed. The results were presented in four stages: stage I presentation of the descriptive statistical results of the two databases; stage II separation of the campi in clusters; stage III analysis of multiple regressions; stage IV analysis of the logistics regressions. Two statistical tests were used to validate the hypothesis: T-test and Wald test. Hypothesis 1 and 2 were confirmed and H3 was refused. The results presented favorable causal connections to the family income and the father school level variables (with bigger effect for fathers with a higher education degree). The mother school level variable did not provide statistical significance for this research. Based on this result...

Background Traffic Modeling for Large-Scale Network Simulation

Li, Ting
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
36.1%
Network simulation is an indispensable tool for studying Internet-scale networks due to the heterogeneous structure, immense size and changing properties. It is crucial for network simulators to generate representative traffic, which is necessary for effectively evaluating next-generation network protocols and applications. With network simulation, we can make a distinction between foreground traffic, which is generated by the target applications the researchers intend to study and therefore must be simulated with high fidelity, and background traffic, which represents the network traffic that is generated by other applications and does not require significant accuracy. The background traffic has a significant impact on the foreground traffic, since it competes with the foreground traffic for network resources and therefore can drastically affect the behavior of the applications that produce the foreground traffic. This dissertation aims to provide a solution to meaningfully generate background traffic in three aspects. First is realism. Realistic traffic characterization plays an important role in determining the correct outcome of the simulation studies. This work starts from enhancing an existing fluid background traffic model by removing its two unrealistic assumptions. The improved model can correctly reflect the network conditions in the reverse direction of the data traffic and can reproduce the traffic burstiness observed from measurements. Second is scalability. The trade-off between accuracy and scalability is a constant theme in background traffic modeling. This work presents a fast rate-based TCP (RTCP) traffic model...

Elterliche Hausaufgabenhilfe unter dem Blickwinkel sozialer Disparitäten: Eine Untersuchung pädagogisch-psychologischer Prozesse; Parental Homework Involvement and Family Background: A Process Analysis

Dumont, Hanna
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
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Das Verstehen der Entstehung sozialer Disparitäten des Kompetenzerwerbs im deutschen Schulsystem ist sowohl für die empirische Bildungsforschung als auch für die Öffentlichkeit von zentraler Bedeutung. Diesbezüglich herrscht mittlerweile Einigkeit darüber, dass die im Elternhaus stattfindenden Prozesse und Mechanismen identifiziert werden müssen, die zu unterschiedlichen Kompetenzen und Lernvoraussetzungen von Kindern und Jugendlichen führen. Vor diesem Hintergrund geht die Arbeit der Frage nach, ob die Entstehung der sozialen Disparitäten im deutschen Schulsystem zu einem Teil auf Unterschiede in der elterlichen Hausaufgabenhilfe zwischen sozial privilegierten und benachteiligten Familien zurückgeführt werden kann. Diesbezüglich wurden drei Fragestellungen aufgestellt: (1) Gibt es einen Zusammenhang zwischen Merkmalen des sozialen Hintergrunds und elterlicher Hausaufgabenhilfe? (2) Gibt es einen Zusammenhang zwischen elterlicher Hausaufgabenhilfe und dem Schulerfolg von Kindern und Jugendlichen? (3) Fungiert die elterliche Hausaufgabenhilfe als Mediator zwischen sozialem Hintergrund und Schulerfolg von Kindern und Jugendlichen? Zur Untersuchung dieser Fragestellungen wurden vier Teilstudien, in denen Schülerinnen und Schüler der 5. bis 8. Jahrgangsstufe über die Qualität der Hausaufgabenhilfe ihrer Eltern befragt wurden...

The impact of background resolution on Target Acquisitions Weapons Software (TAWS) sensor performance

Pearcy, Charles M.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado Formato: xiv, 51 p. : ill. (some col.), map
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Approved for public release, distribution is unlimited; This study evaluated the sensitivity of TAWS detection range calculations to the spatial resolution of scenario backgrounds. Sixteen independent sites were analyzed to determine TAWS background. Multispectral satellite data were processed to different spatial resolutions from 1m to 8km. The resultant imagery was further processed to determine TAWS background type. The TAWS background type was refined to include soil moisture characteristics. Soil moisture analyses were obtained using in situ measurements, the Air Force's Agricultural-Meteorological (AGRMET) model and the Army's Fast All-seasons Soil Strength (FASST) model. The analyzed imagery was compared to the current default 1o latitude by 1o of longitude database in TAWS. The use of the current default TAWS background database was shown to result in TAWS ranges differing from the 1m standard range by 18-23%. The uncertainty was reduced to 5% when background resolution was improved to 8km in rural areas. By contrast, in urban regions the uncertainty was reduced to 14% when spatial resolution was reduced to 30m. These results suggest that the rural and urban designations are important to the definition of a background database.; First Lieutenant...

Neutron Background Simulation for the CRESST - II Experiment; Simulation des Neutronenuntergrundes für das CRESST - II Experiment

Scholl, Stephan Michael
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: Dissertation; info:eu-repo/semantics/doctoralThesis
DE_DE
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In dieser Arbeit wird die Simulation des durch Neutronen induzierten Untergrunds für das CRESST-II Experiment zum direkten Nachweis dunkler Materie behandelt. Der von Neutronen induzierte Untergrund stellt einen fundamentalen, irreduziblen Untergrund für alle Experimente dar, die Dunkle Materie über die Messung der Rückstoßenergie eines streuenden Kerns nachweisen wollen. In dieser Arbeit geht es insbesondere um die Fragestellung, inwiefern die vom CRESST - II Experiment beobachteten Ereignisse durch Neutronenstreuung erklärbar sind. Die astrophysikalische Motivation zur Suche nach dunkeler Materie} ist in dem heutigen kosmologische Standardmodell LambdaCDM gegeben, welches die Existenz dunkler Materie postuliert, welche weder elektromagentisch noch stark wechselwirken darf. Desweiteren muss die dunkele Materie kalt sein, denn Teilchen mit relativistischen Energien sind mit der beobachteten Strukturbildung im Universum nicht vereinbar. Sowohl supersymmetrische Modelle als auch Theorien mit zusätzlichen Dimensionen erlauben stabile Teilchen mit Massen zwischen 50 GeV und einigen TeV, diese als WIMPs (Weakly Interacting Massive Particle) bezeichneten Teilchen sind grundsätzlich auch experimentell beobachtbar. Das CRESST -- II Experiment versucht den direkten Nachweis der schwache Wechselwirkung der WIMPs durch die Detektion des gestreuten Kerns. Das Experiment zeichnet sich durch eine hervorragende Diskriminierung des elektromagnetischen Untergrunds von Kernrückstössen aus. Ein nichtdiskriminierbarer Untergrund ist durch neutroneninduzierte Kernrückstösse gegeben. Die Analyse der Wechselwirkung der Neutronen mit dem Aufbau des Experimentes und insbesondere die Energiedeposition in den verwendeten Detektoren erfordert den Einsatz von Monte - Carlo Simulationen. Hierbei wird das in der Teilchenpysik weit verbreitete GEANT4 Programmpaket verwendet. Die Implementierung der Neutronenstreuung innerhalb von GEANT4 wird getestet und die notwendige Verbesserung des Programmcodes für die inelastische Neutronenstreuung in GEANT4 vorgestellt. Der getestete und verbesserte Code wird dann zur Simulation der bekannten Neutronenquellen für den CRESST - II Aufbau verwendet: - Neutronen...

The structure of the background errors in a global wave model.

Greenslade, Diana J. M.
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2004
Relevância na Pesquisa
36.16%
One of the main limitations to current wave data assimilation systems is the lack of an accurate representation of the structure of the background errors. For example, the current operational wave data assimilation system at the Australian Bureau of Meteorology (BoM) prescribes globally uniform background error correlations of Gaussian shape with a length scale of 300 km and the error variance of both the background and observation errors is defined to be 0.25 m². This thesis describes an investigation into the determination of the background errors in a global wave model. There are two methods that are commonly used to determine background errors: the observational method and the 'NMC method'. The observational method is the main tool used in this thesis, although the 'NMC method' is considered also. The observational method considers correlations of the differences between observations and the background, in this case, the modelled Significant Wave Height (SWH) field. The observations used are satellite altimter estimates of SWH. Before applying the method, the effect of the irregular satellite sampling pattern is examined. This is achieved by constructing a set of anomaly correlations from modelled wave fields. The modelled wave fields are then sampled at the locations of the altimeter observations and the anomaly correlations are recalculated from the simulated altimeter data. The results are compared to the original anomaly correlations. It is found that in general...

Background errors in a global wave model determined from altimeter data

Greenslade, Diana J. M.; Young, Ian R.
Fonte: American Geophysical Union (AGU) Publicador: American Geophysical Union (AGU)
Tipo: Artigo de Revista Científica Formato: 24 pages
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One of the main limitations to current wave data assimilation systems is the lack of an accurate representation of the structure of the background errors. One method that may be used to determine background errors is the observational method of Hollingsworth and Lönnberg [1986] . This method considers correlations of the differences between observations and the background. For the case of Significant Wave Height (SWH), potential observations come from satellite altimeters. In this paper, correlations of the differences between modeled SWH and bias-corrected ERS-2 data are calculated. The irregular sampling pattern of the altimeter is accounted for by adjusting the correlation length scales according to latitude and the calculated length scale. The results show that the length scale of the background errors varies significantly over the globe, with the largest scales at low latitudes and shortest scales at high latitudes. Very little seasonal or year-to-year variability in the correlation length scales is detected. Conversely, the magnitude of the background error variance is found to have considerable seasonal and year-to-year variability. By separating the altimeter ground tracks into ascending and descending tracks, it is possible to examine...

Background Initialization with A New Robust Statistical Approach

Wang, H.; Suter, D.
Fonte: IEEE; Online Publicador: IEEE; Online
Tipo: Conference paper
Publicado em //2005 EN
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Initializing a background model requires robust statistical methods as the task should be robust against random occurrences of foreground objects, as well as against general image noise. The median has been employed for the problem of background initialization. However, the median has only a breakdown point of 50%. In this paper, we propose a new robust method which can tolerate more than 50% of noise and foreground pixels in the background initialization process. We compare our new method with five others and give quantitative evaluations on background initialization. Experiments show that the proposed method achieves very promising results in background initialization.; Hanzi Wang and D. Suter; © 2005 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases...

A Novel interest-point-based background subtraction algorithm

Dehghani, Alireza; Sutherland, Alistair
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em //2014 ENG
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Current Background Subtraction (BGS) algorithms are mostly pixel-based methods. We propose an Interest-Point(IP)-based BGS algorithm applicable in IP-based Computer Vision applications. Based on a block-wise processing strategy, the frames are divided into blocks of the same size. IPs inside each block are together Events. Throughout the frame sequence, the algorithm stores the Events in each block as well as the numbers of their occurrences (Repetition Index (RI)) in a Binary Tree. The RI is used to classify Events as either background or foreground. The background Events appear significantly more often than foreground Events. Events with an RI greater than a certain threshold are classified as background, the rest as foreground. This Event classification is used to label IPs of frames into the foreground and background IPs. Experimental results quantitatively show that the proposed algorithm delivers a good subtraction rate in comparison with other BGS approaches. Moreover, it creates a map of the background usable for further processing, it is robust to changes in illumination and can keep itself updated to changes in the background.

Matched filter stochastic background characterization for hyperspectral target detection

West, Jason
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado Formato: 19334 bytes; 6661951 bytes; 320441 bytes; 1 bytes; 2061 bytes; 698 bytes; 5624 bytes; 49 bytes; 19334 bytes; 6661951 bytes; application/pdf; application/pdf; text/plain; text/plain; text/plain; application/octet-stream; application/octet-stream; applicati
EN_US
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Algorithms exploiting hyperspectral imagery for target detection have continually evolved to provide improved detection results. Adaptive matched filters, which may be derived in many different scientific fields, can be used to locate spectral targets by modeling scene background as either structured geometric) with a set of endmembers (basis vectors) or as unstructured stochastic) with a covariance matrix. In unstructured background research, various methods of calculating the background covariance matrix have been developed, each involving either the removal of target signatures from the background model or the segmenting of image data into spatial or spectral subsets. The objective of these methods is to derive a background which matches the source of mixture interference for the detection of sub pixel targets, or matches the source of false alarms in the scene for the detection of fully resolved targets. In addition, these techniques increase the multivariate normality of the data from which the background is characterized, thus increasing adherence to the normality assumption inherent in the matched filter and ultimately improving target detection results. Such techniques for improved background characterization are widely practiced but not well documented or compared. This thesis will establish a strong theoretical foundation...

Matched filter stochastic background characterization for hyperspectral target detection

West, Jason
Fonte: International Society for Optical Engineering (SPIE) Publicador: International Society for Optical Engineering (SPIE)
Tipo: Proceedings Formato: 1264494 bytes; application/pdf
EN_US
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Algorithms exploiting hyperspectral imagery for target detection have continually evolved to provide improved detection results. Adaptive matched filters can be used to locate spectral targets by modeling scene background as either structured (geometric) with a set of endmembers (basis vectors) or as unstructured (stochastic) with a covariance or correlation matrix. These matrices are often calculated using all available pixels in a data set. In unstructured background research, various techniques for improving upon scene-wide methods have been developed, each involving either the removal of target signatures from the background model or the segmentation of image data into spatial or spectral subsets. Each of these methods increase the detection signal-to-background ratio (SBR) and the multivariate normality (MVN) of the data from which background statistics are calculated, thus increasing separation between target and non-target species in the detection statistic and ultimately improving thresholded target detection results. Such techniques for improved background characterization are widely practiced but not well documented or compared. This paper provides a review and comparison of methods in target exclusion, spatial subsetting and spectral pre-clustering...

Video Background Subtraction in Complex Environments

Santoyo-Morales,Juana E.; Hasimoto-Beltrán,Rogelio
Fonte: UNAM, Centro de Ciencias Aplicadas y Desarrollo Tecnológico Publicador: UNAM, Centro de Ciencias Aplicadas y Desarrollo Tecnológico
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2014 EN
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Background subtraction models based on mixture of Gaussians have been extensively used for detecting objects in motion in a wide variety of computer vision applications. However, background subtraction modeling is still an open problem particularly in video scenes with drastic illumination changes and dynamic backgrounds (complex backgrounds). The purpose of the present work is focused on increasing the robustness of background subtraction models to complex environments. For this, we proposed the following enhancements: a) redefine the model distribution parameters involved in the detection of moving objects (distribution weight, mean and variance), b) improve pixel classification (background/foreground) and variable update mechanism by a new time-space dependent learning-rate parameter, and c) replace the pixel-based modeling currently used in the literature by a new space-time region-based model that eliminates the noise effect caused by drastic changes in illumination. Our proposed scheme can be implemented on any state of the art background subtraction scheme based on mixture of Gaussians to improve its resilient to complex backgrounds. Experimental results show excellent noise removal and object motion detection properties under complex environments.