979 resultados para semi-analytic modelling


Relevância:

30.00% 30.00%

Publicador:

Resumo:

Forest management policy decisions are complex due to the multiple-use nature of goods and services from forests, difficulty in monetary valuation of ecological services and the involvement of a large number of stakeholders. Multi-attribute decision techniques can be used to synthesise stakeholder preferences related to regional forest planning because it can accommodate conflicting, multidimensional, incommensurable and incomparable objectives. The objective of this paper is to examine how the Analytical Hierarchy Process (AHP) can be used to incorporate stakeholder preferences in determining optimal forest land-use choices. The Australian Regional Forest Agreement Programme is taken as an illustrative case for the analysis. The results show that the AHP can formalise public participation in decision making and increase the transparency and the credibility of the process.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Variation in the incoming sheet material and fluctuations in the press setup is unavoidable in many stamping plants. The effect of these variations can have a large influence on the quality of the final stamping, in particular, unpredictable springback of the sheet when the tooling is removed. While stochastic simulation techniques have been developed to simulate this problem, there has been little research that connects the influence of the noise sources to springback. This paper characterises the effect of material and process variation on the robustness of springback for a semi-cylindrical channel forming operation, which shares a similar cross-section profile as many automotive structural components. The study was conducted using the specialised sheet metal forming package AutoFormTM Sigma, for which a series of stochastic simulations were performed with each of the noise sources incrementally introduced. The effective stress and effective strain scatter in a critical location of the part was examined and a response window, which indicates the respective process robustness, was defined. The incremental introduction of the noise sources allows the change in size of the stressstrain response window to be tracked. The results showed that changes to process variation parameters, such as BHP and friction coefficient, directly affect the strain component of the stressstrain response window by altering the magnitude of external work applied to forming system. Material variation, on the other hand, directly affected the stress component of the response window. A relationship between the effective stressstrain response window and the variation in springback was also established.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Numerous mathematical models have been developed to evaluate both initial and transient stage removal efficiency of deep bed filters. Microscopic models either using trajectory analysis or convective-diffusion equations were used to compute the initial removal efficiency. These models predicted the removal efficiency under favorable filtration conditions quantitatively, but failed to predict the removal efficiency under unfavorable conditions. They underestimated the removal efficiency under unfavorable conditions. Thus, semi-empirical formulations were developed to compute initial removal efficiencies under unfavorable conditions. Also, correction for the adhesion of particles onto filter grains improved the results obtained for removal efficiency from the trajectory analysis. Macroscopic models were used to predict the transient stage removal efficiency of deep bed filters. O’Melia and Ali’s model assumed that the particle removal is due to filter grains as well as the particles that are already deposited onto the filter grain. Thus, semi-empirical models were used to predict the ripening of filtration. Several modifications were made to the model developed by O’Melia and Ali to predict the deterioration of particle removal during the transient stages of filtration. Models considering the removal of particles under favorable conditions and the accumulation of charges on the filter grains during the transient stages were also developed. This paper evaluates those models and their applicability under different operating conditions of filtration.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

A laboratory-scale set-up consisting of rapid mixing device and floating medium filter was used to study the use of a downflow floating medium filter (DFF) with an in-line flocculation arrangement as a static flocculator and a prefilter. The semi-empirical mathematical model formulated incorporates flocculation within the filter, particle/floc attachment onto the filter and the detachment of flocs from the medium. The mathematical model for filtration takes into account the expansion of the filter bed. The removal efficiency of DFF and headless development were successfully simulated for different conditions of filtration velocity, filter depth and influent suspended solids (SS). The values of attachment coefficient a(p)β and headless coefficient β1 were found to be independent of filtration velocity, filter depth and influent SS concentration.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

In this work, analytical models of pure bending are developed to simulate a particular type of bend test and to determine possible errors arising from approximations used in analyzing experimental data. Analytical models proposed for steels include a theoretical solution of pure bending and a series of finite element models, based on the von Mises yield function, are subjected to different stress and strain conditions. The results show that for steel sheets the difference between measured and calculated results of the moment-curvature behaviour is small and the numerical results from the finite element models indicate that experimental results obtained from the test are acceptable in the range of the pure bending operation. Further for magnesium alloys, which exhibit unsymmetrical yielding, the algorithm of the yield function with a linear isotropic hardening model is implemented by programming a user subroutine in Abaqus for bending simulations of magnesium. The simulations using the proposed user subroutine extract better results than those using the von Mises yield function.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

The construction industry in the UK needs to improve its performance and provide clients with an improved level of satisfaction. The inefficient design and construction process is usually criticised as one of the main causes of poor performance.

A new construction process system, CONstruction Best Practice System (CONBPS), has been developed based on the use of an expert system. CONBPS is based on the traditional procurement strategy as it is probably the most popular procurement method in the UK and yet it is subject to most criticism. This model clearly identifies the roles and responsibilities of the major parties within the building team and identifies the activities and the key issues within the project cycle. The completed model reflects the full project cycle from inception to completion.

The prototype of this system has been demonstrated to the construction participants for their comments. The practitioners included architects, quantity surveyors, planning supervisors, private and public clients. The method of collecting data was through the use of semi-structured interviews.

Following feedback from practitioners, the CONBPS has been updated. This version is more robust; besides, it is more practical and user-friendly as it incorporates the comments from practitioners, who are also the potential users.

The primary aim of this paper is to discuss the development of the updated CONBPS. The improvement of the updated CONBPS includes the information for constructing the system, the computerised functions, system structure, knowledge representation structure and the system operation.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

A decision-making framework was developed and applied in regional Australia to identify adaptation issues arising in agricultural systems and rural production as a consequence of climate change. Australian agriculture is very susceptible to the adverse impacts of climate change, with major shifts in temperature and rainfall projected. An advantage of the framework is that it provides a suite of tools to aid in the formulation of strategies for sustainable regional development and adaptation. The decision-making framework uses a participatory approach that integrates land suitability analysis with uncertainty analysis and spatial optimisation to determine optimal agricultural land use (at a regional scale) for current and possible future climatic conditions. It thus provides a robust analytic approach to (i) recognise regions under threat of productivity declines, (ii) identify alternative cropping systems better adapted to likely future climatic conditions and (iii) investigate policy actions to improve the sub-optimal situations created by climate change. The decision-making framework and its methods were applied in a case study of the South West Region of Victoria.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Three trials were carried out to determine energy metabolized (EM) requirement model for starting and growing pullets from different strains, at five ambient temperatures and different percentage feather coverage. In Trial I, metabolizable energy requirements for maintenance (MEm) and efficiency of energy utilization were estimated using 64 birds of two different strains, Hy-Line W36 (HLW36) and Hy-Line Semi-heavy (HLSH), from 9 to 13 weeks of age. The effects of ambient temperature (12, 18, 24, 30 and 36ºC) and percentage feather coverage (0, 50 and 100%) on MEm were assessed in the second trial, using 48 birds per temperature per strain (HLSH and HLW36) from 9 to 13 weeks of age. Trial III evaluated ME requirements for weight gain (MEg) using 1,200 birds from two light strains (HLW36 and Hisex Light, HL) and two semi-heavy strains (HLSH and Hisex Semi-heavy, HSH) reared until 18 weeks of age. According to the prediction models, MEm changed as a function of temperature and feather coverage, whereas MEg changed as a function of age and bird strain. Thus, two models were developed for birds aged 1 to 6 weeks, one model for the light strain and one for the semi-heavy strain. Energy requirements (ER) were different among strains from 7 to 12 weeks, and therefore 4 models were elaborated. From 13 to 18 weeks, one single model was produced for semi-heavy birds, since ER between semi-heavy strains were not different, whereas two different models were elaborated for the light layers. MEg of light birds was higher than MEg of semi-heavy birds, independent of age.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Relevância:

30.00% 30.00%

Publicador:

Resumo:

In the Nilo Coelho irrigation scheme, Brazil, the natural vegetation has been replaced by irrigated agriculture, bringing importance for the quantification of the effects on the energy exchanges between the mixed vegetated surfaces and the lower atmosphere. Landsat satellite images and agro-meteorological stations from 1992 to 2011 were used together, for modelling these exchanges. Surface albedo (α0), NDVI and surface temperature (T0) were the basic remote sensing retrieving parameters necessary to calculate the latent heat flux (λE) and the surface resistance to evapotranspiration (rs) on a large scale. The daily net radiation (Rn) was obtained from α0, air temperature (Ta) and short-wave transmissivity (τsw) throughout the slob equation, allowing the quantification of the daily sensible heat flux (H) by residual in the energy balance equation. With a threshold value for rs, it was possible to separate the energy fluxes from crops and natural vegetation. The averaged fractions of Rn partitioned as H and λE, were in average 39 and 67%, respectively. It was observed an increase of the energy used for the evapotranspiration process inside irrigated areas from 51% in 1992 to 80% in 2011, with the ratio λE/Rn presenting an increase of 3 % per year. The tools and models applied in the current research, can subsidize the monitoring of the coupled climate and land use changes effects in irrigation perimeters, being valuable when aiming the sustainability of the irrigated agriculture in the future, avoiding conflicts among different water users. © 2012 SPIE.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Modelling polymers with side chains is always a challenge once the degrees of freedom are very high. In this study, we present a successful methodology to model poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene] (MEH-PPV) and poly[3-hexylthiophene] (P3HT) in solutions, taking into account the influence of side chains on the polymer conformation. Molecular dynamics and semi-empirical quantum mechanical methods were used for structure optimisation and evaluation of optical properties. The methodology allows to describe structural and optical characteristics of the polymers in a satisfactory way, as well as to evaluate some usual simplifications adopted for modelling these systems. Effective conjugation lengths of 8-14.6 and 21 monomers were obtained for MEH-PPV and P3HT, respectively, in accordance with experimental findings. In addition, anti/syn conformations of these polymers could be predicted based on intrinsic interactions of the lateral branches. © 2013 Copyright Taylor and Francis Group, LLC.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Localizar em subsuperfície a região que mais influencia nas medidas obtidas na superfície da Terra é um problema de grande relevância em qualquer área da Geofísica. Neste trabalho, é feito um estudo sobre a localização dessa região, denominada aqui zona principal, para métodos eletromagnéticos no domínio da freqüência, utilizando-se como fonte uma linha de corrente na superfície de um semi-espaço condutor. No modelo estudado, tem-se, no interior desse semi-espaço, uma heterogeneidade na forma de camada infinita, ou de prisma com seção reta quadrada e comprimento infinito, na direção da linha de corrente. A diferença entre a medida obtida sobre o semi-espaço contendo a heterogeneidade e aquela obtida sobre o semi-espaço homogêneo, depende, entre outros parâmetros, da localização da heterogeneidade em relação ao sistema transmissor-receptor. Portanto, mantidos constantes os demais parâmetros, existirá uma posição da heterogeneidade em que sua influência é máxima nas medidas obtidas. Como esta posição é dependente do contraste de condutividade, das dimensões da heterogeneidade e da freqüência da corrente no transmissor, fica caracterizada uma região e não apenas uma única posição em que a heterogeneidade produzirá a máxima influência nas medidas. Esta região foi denominada zona principal. Identificada a zona principal, torna-se possível localizar com precisão os corpos que, em subsuperfície, provocam as anomalias observadas. Trata-se geralmente de corpos condutores de interesse para algum fim determinado. A localização desses corpos na prospecção, além de facilitar a exploração, reduz os custos de produção. Para localizar a zona principal, foi definida uma função Detetabilidade (∆), capaz de medir a influência da heterogeneidade nas medidas. A função ∆ foi calculada para amplitude e fase das componentes tangencial (Hx) e normal (Hz) à superfície terrestre do campo magnético medido no receptor. Estudando os extremos da função ∆ sob variações de condutividade, tamanho e profundidade da heterogeneidade, em modelos unidimensionais e bidimensionais, foram obtidas as dimensões da zona principal, tanto lateralmente como em profundidade. Os campos eletromagnéticos em modelos unidimensionais foram obtidos de uma forma híbrida, resolvendo numericamente as integrais obtidas da formulação analítica. Para modelos bidimensionais, a solução foi obtida através da técnica de elementos finitos. Os valores máximos da função ∆, calculada para amplitude de Hx, mostraram-se os mais indicados para localizar a zona principal. A localização feita através desta grandeza apresentou-se mais estável do que através das demais, sob variação das propriedades físicas e dimensões geométricas, tanto dos modelos unidimensionais como dos bidimensionais. No caso da heterogeneidade condutora ser uma camada horizontal infinita (caso 1D), a profundidade do plano central dessa camada vem dada pela relação po = 0,17 δo, onde po é essa profundidade e δo o "skin depth" da onda plana (em um meio homogêneo de condutividade igual à do meio encaixante (σ1) e a freqüência dada pelo valor de w em que ocorre o máximo de ∆ calculada para a amplitude de Hx). No caso de uma heterogeneidade bidimensional (caso 2D), as coordenadas do eixo central da zona principal vem dadas por do = 0,77 r0 (sendo do a distância horizontal do eixo à fonte transmissora) e po = 0,36 δo (sendo po a profundidade do eixo central da zona principal), onde r0 é a distância transmissor-receptor e δo o "skin depth" da onda plana, nas mesmas condições já estipuladas no caso 1D. Conhecendo-se os valores de r0 e δo para os quais ocorre o máximo de ∆, calculado para a amplitude de Hx, pode-se determinar (do, po). Para localizar a zona principal (ou, equivalentemente, uma zona condutora anômala em subsuperfície), sugere-se um método que consiste em associar cada valor da função ∆ da amplitude de Hx a um ponto (d, p), gerado através das relações d = 0,77 r e p = 0,36 δ, para cada w, em todo o espectro de freqüências das medidas, em um dado conjunto de configurações transmissor-receptor. São, então, traçadas curvas de contorno com os isovalores de ∆ que vão convergir, na medida em que o valor de ∆ se aproxima do máximo, sobre a localização e as dimensões geométricas aproximadas da heterogeneidade (zona principal).

Relevância:

30.00% 30.00%

Publicador:

Resumo:

The competitive regime faced by individuals is fundamental to modelling the evolution of social organization. In this paper, we assess the relative importance of contest and scramble food competition on the social dynamics of a provisioned semi-free-ranging Cebus apella group (n=18). Individuals competed directly for provisioned and clumped foods. Effects of indirect competition were apparent with individuals foraging in different areas and with increased group dispersion during periods of low food abundance. We suggest that both forms of competition can act simultaneously and to some extent synergistically in their influence on social dynamics; the combination of social and ecological opportunities for competition and how those opportunities are exploited both influence the nature of the relationships within social groups of primates and underlie the evolved social structure. Copyright (c) 2008 S. Karger AG, Basel

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Camptothecin, (CPT) is a pentacyclic alkaloid isolated for the first time from the Chinese tree Camptotheca acuminata, and which has soon attracted the attention of medicinal chemists and pharmacologists due to its promising anti-cancer activity against the most aggressive histo-types. So far, most of the synthesized camptothecin analogues are A and B ring modified compounds, which have been prepared via synthetic or semi-synthetic routes. To the best of our knowledge, a very limited number of C, D, or E ring modified analogues of CPT have been reported; moreover, the few derivatives known from the literature showed a reduced or no biological activity. This dissertation presents synthetic studies on camptothecin new derivatives along with the development of a new and general semi-synthetic methodology to obtain a large variety of analogues. We report here the semi-synthesis of a new family of 5-substituted CPT's, along with their biological activity evaluation, which will be compared with reference compounds. The use of carrier-linked prodrugs has emerged as a useful strategy to overcome some of the drawbacks related with the use of the parent drug, such as low solubility, membrane permeability properties, low oral absorption, instability, toxicity, and nontargeting. Herein we report CPT-prodrugs synthesized via ring opening of the lactone moiety as 17-O-acyl camptothecin tripartate conjugates, which bear a polyamine side chain with different architectures, as the carriers. Moreover, we found that the replacement of the oxygen atom with sulphur on the piridone D-ring, dramatically improves the potency of the novel 16a-thio-camptothecin derivatives, opening new possibilities in the modelling of this class of compounds.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

The aim of this work is to put forward a statistical mechanics theory of social interaction, generalizing econometric discrete choice models. After showing the formal equivalence linking econometric multinomial logit models to equilibrium statical mechanics, a multi- population generalization of the Curie-Weiss model for ferromagnets is considered as a starting point in developing a model capable of describing sudden shifts in aggregate human behaviour. Existence of the thermodynamic limit for the model is shown by an asymptotic sub-additivity method and factorization of correlation functions is proved almost everywhere. The exact solution for the model is provided in the thermodynamical limit by nding converging upper and lower bounds for the system's pressure, and the solution is used to prove an analytic result regarding the number of possible equilibrium states of a two-population system. The work stresses the importance of linking regimes predicted by the model to real phenomena, and to this end it proposes two possible procedures to estimate the model's parameters starting from micro-level data. These are applied to three case studies based on census type data: though these studies are found to be ultimately inconclusive on an empirical level, considerations are drawn that encourage further refinements of the chosen modelling approach, to be considered in future work.