1,909 research outputs found
Removing Love waves from shallow seismic SH-wave data
No full textGeophysical exploration measurements are used to obtain an image of the geological structures of the subsurface, as detailed as possible. To this end, a wavefield is generated by a seismic source. This wavefield propagates through the subsurface, and will partly reflect on boundaries between layers with contrasting properties, and it will partly propagate further into the subsurface. De wavefields that have propagated back to the surface are measured with receivers. When this experiment is repeated several times on different locations, the measured data can be used to obtain the desired image. There are two kinds of seismic waves that can propagate through the subsurface. The ones that are generally used are the pressure waves, or P-waves, where the movement of the particles is parallel to the propagation direction of the wave. The other ones are the shear waves, or S-waves, where the movement of the particles is perpendicular to the propagation direction of the wave. When the particle movement is horizontally polarized (perpendicular to the plane of propagation), this wave type is often decoupled, or in other words, it propagates independently of other wave types. These waves are also called SH-waves. The surface of the Earth behaves as a perfect reflector for SH-waves. This means that all SH-waves that reach the surface will be completely reflected back into the subsurface. When the top layer of the subsurface is thin (smaller than the wavelength of the SH-wave), and when this top layer has a lower wave velocity than deeper layers, then the presence of the surface leads to a kind of surface waves, which were first described by A.E.H. Love, and are therefore called 'Love waves'. Love wave characteristics are: their group velocity is almost equal to the shear wave velocity; since they propagate solely along the surface, they attenuate slowly and are thus often stronger than reflected waves; and they are dispersive. The presence of Love waves deteriorates the quality of the final picture (or seismogram), because they obscure the desired reflections. Existing techniques to remove Love waves from seismic data often perform insufficient, or require certain knowledge about the subsurface. This knowledge is generally not available. Therefore, the ideal method should be one where the measured data alone is sufficient to separate the Love waves from the desired reflection information. The method we describe in this thesis uses the Betti-Rayleigh reciprocity theorem for elastic media. Reciprocity is a mathematical tool to relate two different states to each other. Here, one state is the actual situation, where the medium is bounded by a stress-free surface. The other state is an ideal situation, where there is no surface, and the top layer is extended to infinity. When there is no surface, there are also no surface waves. By applying the reciprocity theorem, we derive an integral equation, from which the Love wave free wavefield can be solved as a function of the data that do contain these surface waves. Other input parameters are the (shear-) wave velocity and the mass density of the top layer, and the source wavelet. When the data are discrete, the integral equation becomes a matrix equation. This can be solved using conventional numerical methods, such as matrix inversion. When the medium is horizontally layered (a so called 1-D medium), the kernel of the matrix equation becomes diagonal in the wave-number domain. Then the matrix equation reduces to a scalar expression. We tested the method on several synthetic datasets. In all cases, the Love waves were completely removed. Even other noise in the form of scattered Love waves was removed, in the cases where it was present. The method also had no problems when the input parameters were chosen wrongly. And when distortions were introduced into the data (distortions like random noise, or the effects of anelastic attenuation), the method still performed well. To test the method on field data, we performed a seismic experiment on the site of the Sofia tunnel (before it was drilled) near Hendrik Ido Ambacht in the Netherlands. The dataset that was the result seemed all right at first. Strong Love waves were indeed present in the data. However, we could not succeed in removing these Love waves with the method. Even worse, the method added noise to the data, to such an extent, that it completely obscured the original data. Although we searched extensively for possible reasons, we were not able to find the exact cause of the bad results. In the final chapter, we made a start to remove the surface waves from coupled P- and SV-wave systems, using the same method as we did for SH-waves. Because P- and SV-waves are coupled, the resulting equations are also coupled. This means that we need all possible source and receiver combinations to remove the surface waves. But it appeared that the equations could be solved independently with regard to the source direction. We validated the theory with an example where we removed the Rayleigh wave from the response of a homogeneousCivil Engineering and Geoscience
Electromagnetic effects in anti-Hermitian media with gain and loss
No full textFunding Information: L.F. was partly supported by DoinQTech, Jane and Aatos Erkko Foundation. L.F. and M.S.M. thank X. Wang, M. Nyman, and B. Zerulla for their invaluable help with numerical simulations. Also, L.F. wishes to acknowledge the support of Carsten Rockstuhl. Publisher Copyright: © 2024 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Incorporating both gain and loss into electromagnetic systems provides possibilities to engineer effects in unprecedented ways. Concerning electromagnetic effects in isotropic media that have concurrently electric and magnetic responses, there is, in fact, a degree of freedom to distribute the gain and loss in different effective material parameters. In this paper, we analytically scrutinize wave interactions with those media, and, most importantly, we contemplate the extreme scenario where such media are anti-Hermitian. Considering various conditions for excitation, polarization, and geometry, we uncover important effects and functionalities such as lasing into both surface waves and propagating waves, conversion of evanescent source fields to transmitted propagating waves, full absorption, and enhancing backward to forward scattering ratio. We hope that these findings explicitly show the potential of anti-Hermiticity to be used in optical physics as well as microwave engineering for creating and using unconventional wave phenomena.Peer reviewe
Evaluation of geostatistics in inventory of Tectona grandis L.f. stands
No full textEste trabalho teve por objetivos geral avaliar se as estimativas do volume de madeira obtidas a partir de técnicas geoestatísticas são mais precisas do que as obtidas a partir de técnicas da estatística clássica. O estudo foi realizado em povoamentos de Tectona grandis L.f. com a característica dendrométrica de volume mensurada em 101 parcelas lançadas ao longo de uma malha de amostragem com coordenadas UTM, distribuídas em 17 talhões, com uma área total de 391,87 ha. Com o ajuste do modelo semivariograma experimental, do índice de dependência espacial e das estatísticas da validação cruzada, foram obtidas duas estimativas do inventário florestal: uma utilizando estatística clássica e a outra, geoestatística. Na realização da estimação clássica, foi considerada a metodologia de amostragem sistemática, com a intensidade de amostragem de uma parcela para cada 4 ha. Na predição por geoestatística, foi ajustado o modelo de semivariograma, utilizado para avaliar a estrutura de dependência espacial da variável volume por ha na área de estudo. Em seguida, utilizou-se a krigagem em blocos para obter as predições do volume médio de cada talhão. A comparação das estimações dos dois métodos foi feita com base no erro de amostragem, sendo encontrado um menor erro com a geoestatística. Conclui-se, assim, o uso da geoestatística para realização de inventário florestal, quando existir estrutura de dependência espacial na região em estudo, uma vez que ela fornece predições mais precisas.The general objective of this work was to evaluate if estimates of wood volume obtained from geostatistics techniques are more accurate than those obtained from classical statistical techniques.The study was conducted in stands of Tectona grandis L.f. with the dendometric volume trait measured in 101 plots laid along a sampling spacing with UTM coordinates, distributed in 17 plots with a total area of 391.87 ha. By adjusting the experimental semivariogram model, index of spatial dependence and cross-validation statistics it was obtained two estimates of the forest inventory: one by using the classical statistics and the other by using geostatistics. Methodology of systematic sampling with intensity of sampling of one plot for every 4 ha was used in the conduction of the classical estimation. A semivariogram model, used to assess the structure of spatial dependence of the variable volume per ha in the study area was adjusted in the prediction by geostatistcs. Then, block kriging was used to obtain predictions of the average volume of each plot. Comparison of the two methods of estimation was made based on the sampling error, in which a minor error with geostatistics was found. Therefore, it is concluded geostatistics should be used for forest inventory when there is spatial dependence structure in the region under study inasmuch as it provides more accurate predictions.Coordenação de Aperfeiçoamento de Pessoal de Nível Superio
Exposé Landwinningsvraagstukken
No full textAls algemeen richtslijn is er aangegeven dat bij de opzet van landwinningswerken rekening gehouden moet worden met een tijdperk van ongeveer 40 jaren. Ten einde een nader inzicht in de voor te bereiden werkzaamheden te bekomen, werd er onderzoek verricht en gedeeltelijk in een viertal nota's vastgelegd. De onderzoeken gaan in specifiek over de 'Beplatingsmethode', waarbij slibvangen en beplanting der slikken een voorname rol spelen en de 'Bekleiingsmethode', waarbij getracht wordt sneller tot het doel te komen door inpoldering van een wadgebied en bekleiing ervan met specie uit de ondergrond. Bij het nagaan der mogelijkheden voor de eerstvolgende 40 jaar wordt gestuit op de volgende 7 hoofdvragen van landbouwkundige aard: 1. Is een proefpolder op de Wadden nodig ten einde te onderzoeken welke mening van slib en wadzand de meest wenselijke is? 2. Kan misschien met goedkopere middelen (proefbakken) worden volstaan? Hoe moeten deze worden ingericht? 3. Is het wadzand geschikt om als weidegrond te kunnen dien? Wat is dan de opbrengst per ha.? 4. Kunnen bossen op het Wadzand worden aangelegd? Welke opbrengst? 5. Wat kan met de zogenaamde woelmachine worden bereikt? Deze machine kan vruchtbare klei tot 4 meter diepte beneden maaiveld ophalen en over de oppervlakte spreiden. Kosten per laag van 4 cm dikte bedragen 300 à 400 gulden. 6. Welke resultaten zijn verkregen bij slibbemseting in Westerwolde en Drente? Een ter plaatse gehouden navraag wees uit dat een laag slib van eenige milimeter dikte na 30 jaar nog steeds opmerkelijk resultaten gaf. 7. Welk kavelgrootte is het meest wenselijk? De viertal nota's betreffen: - Verslag werkzaamheden in 1942 op Hollandsch Diep en Maartensgat (door opzichter Molendijk) - Verslag werkzaamheden in 1942 op de Hellegatplaten (door opzcihter Van Eyk) - Programma van onderzoek betreffende plantenonderzoek (door Dr. L.F. Kamps) - Verslag werkzaamheden proefvelden en plantenonderzoek in 1942 (door assisten Van Eerde)Landwinningswerken 194
Desempenho da teca (Tectonia grandis L.f) e do milho em sistemas de integração lavoura-pecuária-floresta na Amazônia Oriental.
No full textA região amazônica demanda a produção agropecuária em harmonia com o meio ambiente devido à grande extensão de áreas de pastagens degradadas, e os sistemas de Integração Lavoura-Pecuária-Floresta (iLPF) aparecem como uma alternativa para recuperar essas áreas. Um sistema iLPF foi implantado em 2009 no Campo Experimental da Embrapa Amazônia Oriental em Terra Alta, Pará, tendo como espécie florestal a Teca (Tectonia grandis L.f) e como componente agrícola o milho. A produção do milho e o desempenho em altura e sobrevivência da Teca foram mensurados. Três ciclos de cultivo de milho consorciado com a Teca foram avaliados. Nessa fase inicial de estabelecimento do sistema a Teca apresentou bom desempenho em altura e sobrevivência e o milho uma boa produção de grão.Editores técnicos: Roberto Porro, Milton Kanashiro, Maria do Socorro Gonçalves Ferreira, Leila Sobral Sampaio e Gladys Ferreira de Sousa
"CRESCIMENTO DE Tectona grandis L.f. EM PLANTIO COMERCIAL EM URUTAÍ, GOIÁS"
No full text"A teca (Tectona grandis L.f.) é uma das madeiras tropicais mais valorizadas, o que se torna conveniente analisar as condições climáticas e edáficas dos locais onde se origina e dos locais onde tem sido introduzida para que se possam estabelecer condições ideais de solo e clima para implantação e crescimento. É importante saber quando se realiza o primeiro desbaste, sendo que o fechamento do dossel é um bom indicador para isto, e a idade de aplicação do primeiro desbaste vai depender da qualidade de sítio. O objetivo deste estudo foi avaliar o crescimento de um povoamento de teca e seu respectivo desbaste. Os dados para a realização deste trabalho foram obtidos da Fazenda Paulo Uchoa e, a partir deles, foram feitos gráficos mostrando a evolução da circunferência florestal em cada talhão, a análise do potencial produtivo e do efeito da época de plantio no desenvolvimento da floresta, além da importância dos desbastes realizados. Os sítios com melhor desenvolvimento (classes de circunferência, diâmetro médio e área basal) foram aqueles plantados no início da época chuvosa, além da realização de desbaste para favorecer o crescimento das árvores remanescentes. Os outros apresentaram pior desempenho devido ao plantio no final das chuvas e por um deles ter sido plantado um após os demais, além da matocompetição ter sido mais intensa.
Social Perspectives And Symbolic Domination: Women's Political Presence, In Iris Marion Young And Pierre Bourdieu [perspectivas Sociais E Dominação Simbólica: A Presença Política Das Mulheres Entre Iris Marion Young E Pierre Bourdieu]
No full textThis article looks at women's political participation and presence within political power. In this regard, we discuss the tension between the emancipatory potential offered by incorporation of multiple perspectives into political debate and the reproductive action of the field. Starting from a look at causes that, in our view, may be responsible for the relative absence of women in decision-making circles and for their alleged "lack of interest" in politics, we discuss perspectives that are, in one way or another, geared toward solving (improving) this situation. The article is organized into three sections. In the first, we defend the position that a more promising way to justify the need for women's presence is offered by understanding that spaces of deliberation should house a plurality of relevant social perspectives - a concept that can be most clearly associated with the work of the U.S. political theoretician, Iris Marion Young. In the second section, we discuss some of the problems contained within this concept, most particularly, a certain naiveté present in the ideal that derives from it: the creation of a pluralist discussion and decision-making spaces resulting from electoral quotas. We use the notion of "field", taken from Pierre Bourdieu's work, in order to cleanse Young's ideas of such naiveté. Within the third section, we introduce an additional element: Nancy Fraser's distinction between "affirmative" and "transforming" policies. As preliminary conclusions, we end with an evaluation of the limitations and potentials of a politics based on the defense of increased presence of "social perspectives".18362549Araújo, C., As cotas por sexo para a competição legislativa: O caso brasileiro em comparação com experiências internacionais (2001) Dados, 44 (1), pp. 155-194. , http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0011-52582001000100006&lng=pt&nrm=iso&tlng=pt, Rio de Janeiro, Acesso em: 3.maio.2010Araújo, C., Alves, J.E.D., Impacto de indicadores sociais e do sistema eleitoral sobre as chances das mulheres nas eleições e suas interações com as cotas (2007) Dados, 50 (3), pp. 535-577. , http://www.scielo.br/pdf/dados/v50n3/04.pdf, Rio de Janeiro, Acesso em: 3.maio.2010Beauvoir, S., (2009) O segundo sexo, , Rio de Janeiro: Nova FronteiraBickford, S., (1996) The Dissonance of Democracy: Listening, Conflict, and Citizenship, , Ithaca: Cornell UniversityBolaño, R., (2009), p. 2666. , Barcelona: AnagramaBourdieu, P., (1979) La distinction: Critique sociale du jugement, , Paris: MinuitBourdieu, P., A representação política. Elementos para uma teoria do campo político (1989) O poder simbólico, , Bourdieu, P. Lisboa: DifelBourdieu, P., (1997) Méditations pascaliennes, , Paris: SeuilBourdieu, P., (1998) La domination masculine, , Paris: SeuilBourdieu, P., (1998) Le règles de l'art: Genèse et structure du champ littéraire, , Paris: SeuilBourdieu, P., (2000) Propos sur le champ politique, , Lyon: Université de LyonBourdieu, P., Passeron, J.-C., (1970) La reproduction: éléments pour une théorie du système d'enseignement, , Paris: MinuitCorrêa, M., O sexo da dominação (1999) Novos Estudos, (54), pp. 43-53. , São PauloDalcastagnè, R., Uma voz ao sol: Re-presentação e legitimidade na narrativa brasileira contemporânea (2003) Estudos de Literatura Brasileira Contemporânea, 20, pp. 33-77. , BrasíliaDalcastagnè, R., A personagem do romance brasileiro contemporâneo: 1990-2004 (2005) Estudos de Literatura Brasileira Contemporânea, 26, pp. 13-71. , BrasíliaDalcastagnè, R., Imagens da mulher na narrativa brasileira (2007) O Eixo e a Roda, (15), pp. 127-135. , Belo HorizonteDalcastagnè, R., Quando o preconceito se faz silêncio: Relações raciais na literatura brasileira contemporânea (2008) Gragoatá, (24), pp. 203-219. , NiteróiDelphy, C., Feminismo e reconstrução da esquerda (1994) Revista Estudos Feministas, 2 (1), pp. 187-199. , Rio de JaneiroElshtain, J.B., (1981) Public Man, Private Woman: Women in Social and Political Thought, , Princeton: Princeton UniversityFox, R.L., Lawless, J.L., Entering the Arena? Gender and the Decision to Run for Office (2004) American Journal of Political Science, 48 (2), pp. 264-280. , AustinFraser, N., Rethinking the Public Sphere: A Contribution to the Critique of Actually Existing Democracy (1992) Habermas and the Public Sphere, , Calhoun, C. (ed.). Cambridge, Mass.: MITFraser, N., (1997) Justice Interruptus: Critical Reflections on the "Postsocialist", Condition, , New York: RoutledgeFraser, N., Social Justice in the Age of Identity Politics: Redistribution, Recognition, and Participation (2003) Redistribution or Recognition?, , Fraser, N. & Honneth. A. A Political-Philosophical Exchange. London: VersoGorz, A., (1988) Métamorphoses du travail: Quête du sens, , Critique de la raison économique. Paris: GaliléeGorz, A., (1991) Capitalisme, socialisme, écologie: Désorientations, orientations, , Paris: GaliléeHabermas, J., (1997) Direito e democracia: Entre facticidade e validade, , 2 V. Rio de Janeiro: Tempo BrasileiroHobbes, T., (1997) Leviatã, , São Paulo: Nova CulturalJesus, C.M., (1983) Quarto de despejo: Diário de uma favelada, , Rio de Janeiro: F. AlvesJesus, C.M., (1996) Meu estranho diário, , São Paulo: XamãLins, P., (1997) Cidade de Deus, , São Paulo: Companhia das LetrasMarx, K., (1983) Contribuição à crítica da Economia Política, , São Paulo: M. FontesMiguel, L.F., Teoria política feminista e liberalismo: O caso das cotas de representação (2000) Revista Brasileira de Ciências Sociais, (44), pp. 91-102. , http://www.scielo.br/pdf/rbcsoc/v15n44/4149.pdf, São Paulo, Acesso em: 3.maio.2010Miguel, L.F., Política de interesses, política do desvelo: Representação e "singularidade feminina" (2001) Revista Estudos Feministas, 9 (1), pp. 253-267. , http://redalyc.uaemex.mx/redalyc/pdf/381/38109115.pdf, Florianópolis, Acesso em Acesso em: 3.maio.2010Miguel, L.F., As duas lógicas da ação comunicativa: Democracia e deliberação no debate contemporâneo (2002) Teoria & Sociedade, (10), pp. 104-143. , Belo HorizonteMiguel, L.F., Representação política em 3-D: Elementos para uma teoria ampliada da representação política (2003) Revista Brasileira de Ciências Sociais, (51), pp. 123-140. , http://www.scielo.br/pdf/rbcsoc/v18n51/15989.pdf, São Paulo. Acesso em: 3.maio.3010Miguel, L.F., Impasses da accountability: Dilemas e alternativas da representação política (2005) Revista de Sociologia e Política, (25), pp. 165-178. , http://www.scielo.br/pdf/rsocp/n25/31109.pdf, Curitiba, nov. Acesso em: 3.maio.2010Miguel, L.F., Utopias do póssocialismo: Esboços e projetos de reorganização radical da sociedade (2006) Revista Brasileira de Ciências Sociais, (61), pp. 91-114. , http://www.scielo.br/pdf/rbcsoc/v21n61/a05v2161.pdf, São Paulo, Acesso em: 3.maio.2010Miguel, L.F., Political Representation and Gender in Brazil: Quotas for Women and Their Impact (2008) Bulletin of Latin American Research, 27 (2), pp. 197-214. , LiverpoolMiguel, L.F., Democracia, representação e comunidade (2009) Teoria política latinoamericana, , Araújo, C. & Amadeo, J. (orgs.). São Paulo: HucitecMiguel, L.F., Biroli, F., Gênero e política no jornalismo brasileiro (2008) Revista Famecos, (36), pp. 24-39. , http://revcom.portcom.intercom.org.br/index.php/famecos/article/viewFile/5468/4966, Porto Alegre, ago. Acesso em: 3.maio.2010Miguel, L.F., A produção da imparcialidade: A construção do discurso universal a partir da perspectiva jornalística (2009) Anais, , Encontro anual da associação nacional de pós-graduação e pesquisa em comunicação social, 18., Belo Horizonte, 2-5.jun. Belo Horizonte: Associação Nacional de Pós-Graduação e Pesquisa em Comunicação SocialMiguel, L.F., Feitosa, F., O gênero do discurso parlamentar: Mulheres e homens na tribuna da Câmara dos Deputados (2009) Dados, 52 (1), pp. 201-221. , http://www.scielo.br/pdf/dados/v52n1/v52n1a06.pdf, Rio de Janeiro, Acesso em: 3.maio.2010Moi, T., (1999) What is a Woman?, , Oxford: Oxford UniversityOates, J.C., (2008) A filha do coveiro, , Rio de Janeiro: AlfaguaraOkin, S.M., (1989) Justice, Gender, and the Family, , New York: BasicPhillips, A., (1991) Engendering Democracy, , Cambridge: PolityPhillips, A., (1993) Democracy and Difference, , University Park: Pennsylvania State UniversityPhillips, A., (1995) The Politics of Presence, , Oxford: Oxford UniversityPhillips, A., (1999) Which Equalities Matter?, , Cambridge: PolityPinheiro, L.S., (2007) Vozes femininas na política: Uma análise sobre mulheres parlamentares no pós-Constituinte, , Brasília: Secretaria Especial de Políticas para as MulheresPitkin, H.F., (1967) The Concept of Representation, , Berkeley: University of CaliforniaPrzeworski, A., (1985) Capitalismo e social-democracia, , São Paulo: Companhia das LetrasRawls, J., (1997) Uma teoria da Justiça, , São Paulo: M. FontesRawls, J., (2000) O liberalismo político, , São Paulo: ÁticaRosanvallon, P., (1998) Le peuple introuvable: Histoire de la représentation démocratique en France, , Paris: GallimardRousseau, J.-J., Du contract social (1964) Œuvres complètes, , Rousseau, J.-J. T. III. Paris: GallimardRuddick, S., (1989) Maternal Thinking: Toward A Politics of Peace, , Boston: BeaconSandel, M., (1998) Liberalism and the Limits of Justice, , Cambridge: Cambridge UniversitySpivak, G.C., Can the Subaltern Speak? (1998) Marxism and the Interpretation of Culture, , Nelson, C. & Grossberg, L. (eds.). Urbana: University of IllinoisSustein, C.R., Preferências e política (2009) Revista Brasileira de Ciência Política, (1), pp. 219-254. , http://rbcp.unb.br/artigos/rbcp-n1-10.pdf, Brasília, Acesso em, Acesso em: 9.maio.2010Urbinati, N., Representation as Advocacy: A Study of Democratic Deliberation (2000) Political Theory, 28 (6), pp. 758-786. , Thousand OaksUrbinati, N., (2006) Representative Democracy: Principles and Genealogy, , Chicago: University of ChicagoVan Parijs, P., Basic Income Capitalism (1992) Ethics, 102 (3), pp. 465-484. , ChicagoVan Der Veen, R.J., Van Parijs, F., A Capitalist Road to Communism (1987) Theory and Society, 15 (5), pp. 635-655. , DordrechtWilliams, M.S., (1998) Voice, Trust, and Memory: Marginalized Groups and the Failings of Liberal Representation, , Princeton: Princeton UniversityYoung, I.M., (1990) Justice and the Politics of Difference, , Princeton: Princeton UniversityYoung, I.M., (1990) Throwing Like a Girl and Other Essays in the Feminist Philosophy and Social Theory, , Bloomington: Indiana UniversityYoung, I.M., (1997) Intersecting Voices: Dilemmas of Gender, Political Philosophy, and Policy, , Princeton: Princeton UniversityYoung, I.M., (2000) Inclusion and Democracy, , Oxford: Oxford UniversityYoung, I.M., Activist Challenges to Deliberative Democracy (2001) Political Theory, 29 (5), pp. 670-690. , Thousand OaksYoung, I.M., (2005) On Female Body Experience: "Throwing Like a Girl", and Other Essays, , Oxford: Oxford University(2006) Veja, (1966), p. 45. , http://veja.abril.com.br/acervodigital/home.aspx?edicao=1966&pg=06, Política é coisa de homem?, São Paulo, 26.jul, Acesso em: 9.maio.201
Crescimento de tectona grandis l.f. em plantio comercial em urutaí, goiás
No full textA teca (Tectona grandis L.f.) é uma das madeiras tropicais mais valorizadas, o que se torna conveniente analisar as condições climáticas e edáficas dos locais onde se origina e dos locais onde tem sido introduzida para que se possam estabelecer condições ideais de solo e clima para implantação e crescimento. É importante saber quando se realiza o primeiro desbaste, sendo que o fechamento do dossel é um bom indicador para isto, e a idade de aplicação do primeiro desbaste vai depender da qualidade de sítio. O objetivo deste estudo foi avaliar o crescimento de um povoamento de teca e seu respectivo desbaste. Os dados para a realização deste trabalho foram obtidos da Fazenda Paulo Uchoa e, a partir deles, foram feitos gráficos mostrando a evolução da circunferência florestal em cada talhão, a análise do potencial produtivo e do efeito da época de plantio no desenvolvimento da floresta, além da importância dos desbastes realizados. Os sítios com melhor desenvolvimento (classes de circunferência, diâmetro médio e área basal) foram aqueles plantados no início da época chuvosa, além da realização de desbaste para favorecer o crescimento das árvores remanescentes. Os outros apresentaram pior desempenho devido ao plantio no final das chuvas e por um deles ter sido plantado um após os demais, além da matocompetição ter sido mais intensa
Author contributions: L.F
No full textIt is well-known that financial asset returns exhibit fat-tailed distributions and long-term memory. These empirical features are the main objectives of modeling efforts using (i) stochastic processes to quantitatively reproduce these features and (ii) agent-based simulations to understand the underlying microscopic interactions. After reviewing selected empirical and theoretical evidence documenting the behavior of traders, we construct an agent-based model to quantitatively demonstrate that "fat" tails in return distributions arise when traders share similar technical trading strategies and decisions. Extending our behavioral model to a stochastic model, we derive and explain a set of quantitative scaling relations of long-term memory from the empirical behavior of individual market participants. Our analysis provides a behavioral interpretation of the long-term memory of absolute and squared price returns: They are directly linked to the way investors evaluate their investments by applying technical strategies at different investment horizons, and this quantitative relationship is in agreement with empirical findings. Our approach provides a possible behavioral explanation for stochastic models for financial systems in general and provides a method to parameterize such models from market data rather than from statistical fitting. complex systems | power law | scaling laws M odeling price returns has become a central topic in the study of financial markets due to its key role in financial theory and its practical utility. Following models by Engle and Bollerslev (1, 2), many stochastic models have been proposed based on statistical studies of financial data to accurately reproduce price dynamics. In contrast to this stochastic approach, economists and physicists using the tools of statistical mechanics have adopted a bottom-up approach to simulate the same macroscopic regularity of price changes, with a focus on the behavior of individual market participants (3-10). Although the second socalled agent-based approach has provided a qualitative understanding of price mechanisms, it has not yet achieved sufficient quantitative accuracy to be widely accepted by practitioners. Here, we combine the agent-based approach with the stochastic process approach and propose a model based on the empirically proven behavior of individual market participants that quantitatively reproduces fat-tailed return distributions and long-term memory properties (11-14). Empirical and Theoretical Market Behaviors We start by arguing that technical traders (usually agents seeking arbitrage opportunities and make their trading decisions based on price patterns) contribute much more to the dynamics of daily stock prices S t (or log price s t ≡ lnðS t Þ) than fundamentalists (who attempt to determine the fundamental values of stocks). Although fundamentalists hold a majority of the stocks, they trade infrequently (see SI Appendix, Market surveys (16-18) also provide clear evidence of the prevalence of technical analysis. We consider here only technical traders, assuming that fundamentalists contribute only to market noise. Our study is of the empirical data recorded prior to 2006 and ignores the effect of high frequency trading (HFT) that has become significant only in the past 5 y. We propose a behavioral agent-based model that is in agreement with the following empirical evidence: i. Random trading decisions made by agents on a daily basis. n 0 technical traders use different trading strategies, hence their decisions to buy, sell, or hold a position appear to be random. A trading decision is made daily because empirical studies report the lack of intraday trading persistence in empirical trading data (19). Market survey (16) also shows that fund managers put very little emphasis on intraday tradings. We estimate the probability p of having daily trade empirically from trading volumes. ii. Price returns. The price return r t ≡ s t − s t−1 is controlled by the imbalance d t between the demand and the supply of stocks-the difference in the number of buy and sell trades each day. The excess in total demand or supply moves the price up or down, where the largest r t occurs when all traders act in unison, when they all either buy or sell their stocks. We assume this relationship between price change r t and d t to be linear each day, as supported by empirical findings (20, 21). iii. Centralized interaction mechanism of returns on technical strategies. For technical traders, an important input parameter in their strategies is past price movement (22, 23). Consequently, prices and orders reflect a main interaction mechanism between agents. In many agent-based models, the interaction strength between agents need to be adjusted with agent population size (5, 24, 25) or interaction structure (26) to sustain "fat" tails in return distributions. Here we propose a centralized interaction mechanism (price change) among agents so that the strength of interaction grows with agent population and is unaffected by interaction structure. iv. Opinion convergence due to price changes. This is the unique mechanism that distinguishes our model from other models. It specifies the collective behavior of technical traders. Duffy et al. (27) found that agents learn from each other and tend to adopt the strategy that gives the most payoff. Given the price patterns at any point in time, a few most profitable technical strategies dominate the market because every technical trade
In Search of Lost Meaning. Review of the Monograph by Kharayeva L.F., Kuchukova Z.A. “Gender and Ethnogender (on the Material of Kabardian Women’s Prose)”
No full textThe review offered to our readers is devoted to the study of the phenomenon of Kabardian women’s prose, presented in the monograph “Gender and Ethnogender” by L.F. Kharaeva and Z.A. Kuchukova. The author analyzes the monograph from the point of view of its structure, sequence of presentation, relevance to the topic and corpus of chosen literary texts. The undoubted value of the monograph recognizes its theoretical and practical significance, as well as an indisputable novelty. The author recommends this scientific research to be read by all who are interested in issues of gender and its ethnospecificity, gender literature, and the latest Kabardian literature
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