LOCAL DIGITAL CONTROL OF POWER ELECTRONIC CONVERTERS IN A DC MICROGRID BASED ON A-PRIORI DERIVATION OF SWITCHING SURFACES

In power electronic basedmicrogrids, the computational requirements needed to implement an optimized online control strategy can be prohibitive. The work presented in this dissertation proposes a generalized method of derivation of geometric manifolds in a dc microgrid that is based on the a-priori computation of the optimal reactions and trajectories for classes of events in a dc microgrid. The proposed states are the stored energies in all the energy storage elements of the dc microgrid and power flowing into them. It is anticipated that calculating a large enough set of dissimilar transient scenarios will also span many scenarios not specifically used to develop the surface. These geometric manifolds will then be used as reference surfaces in any type of controller, such as a sliding mode hysteretic controller. The presence of switched power converters in microgrids involve different control actions for different system events. The control of the switch states of the converters is essential for steady state and transient operations. A digital memory look-up based controller that uses a hysteretic sliding mode control strategy is an effective technique to generate the proper switch states for the converters. An example dcmicrogrid with three dc-dc boost converters and resistive loads is considered for this work. The geometric manifolds are successfully generated for transient events, such as step changes in the loads and the sources. The surfaces corresponding to a specific case of step change in the loads are then used as reference surfaces in an EEPROM for experimentally validating the control strategy. The required switch states corresponding to this specific transient scenario are programmed in the EEPROM as a memory table. This controls the switching of the dc-dc boost converters and drives the system states to the reference manifold. In this work, it is shown that this strategy effectively controls the system for a transient condition such as step changes in the loads for the example case.

Demographic effects on the use of vertical sources of guidance by managers in widely differing cultural contexts

Data provided by 7380 middle managers from 60 nations are used to determine whether demographic variables are correlated with managers’ reliance on vertical sources of guidance in different nations and whether these correlations differ depending on national culture characteristics. Significant effects of Hofstede’s national culture scores, age, gender, organization ownership and department function are found. After these main effects have been discounted, significant although weak interactions are found, indicating that demographic effects are stronger in individualist, low power distance nations than elsewhere. Significant non-predicted interaction effects of uncertainty avoidance and masculinity-femininity are also obtained. The implications for theory and practice of the use of demographic attributes in understanding effective management procedures in various parts of the world are discussed.

Message passing for distributed optimisation of power allocation with renewable resources

The increase in renewable energy generators introduced into the electricity grid is putting pressure on its stability and management as predictions of renewable energy sources cannot be accurate or fully controlled. This, with the additional pressure of fluctuations in demand, presents a problem more complex than the current methods of controlling electricity distribution were designed for. A global approximate and distributed optimisation method for power allocation that accommodates uncertainties and volatility is suggested and analysed. It is based on a probabilistic method known as message passing [1], which has deep links to statistical physics methodology. This principled method of optimisation is based on local calculations and inherently accommodates uncertainties; it is of modest computational complexity and provides good approximate solutions.We consider uncertainty and fluctuations drawn from a Gaussian distribution and incorporate them into the message-passing algorithm. We see the effect that increasing uncertainty has on the transmission cost and how the placement of volatile nodes within a grid, such as renewable generators or consumers, effects it.

School desegregation in Broward County, Florida, 1970--1998: A historical study of power

This is a historical case study on school desegregation and power in Broward County, Florida from 1970 to 1998. The purpose of this study is to describe, explain and analyze types of power used by the School Board of Broward County, Florida and community activists, in their efforts to influence desegregation decisions from 1970 to 1998. In addition, this study explains who benefited and who won from the School Board's desegregation decisions and who governed those decisions? ^ A historical case study approach was used as the method for conducting this study. Data sources included 11 interviews of individuals who were involved in school desegregation issues as either School Board officials or community activists and 10 archival data sources. ^ The theoretical models of Russell, Galbraith, Wartenberg and Domhoff were used to determine the different types of power techniques used by School Board officials and community activists and to answer the questions: who benefited and who won from the School Board's desegregation decisions and who governed those policies and practices? ^ The primary beneficiaries of school desegregation policies and practices in Broward County were: white, affluent communities and the builders, developers, realtors and other businesses in the western suburban communities. All of the data sources indicated that the black community did not benefit from the School Board's desegregation policies. ^ The primary power techniques used by School Board officials to influence desegregation policies and practices was “power over opinions” and compensation. These power techniques were manifested by the School Board publicly disputing the allegations raised by community activists and by compensating those who supported and promoted the School Board's desegregation policies and practices. ^ The power techniques primarily used by community activists were coercive force and “power over opinions.” They effectively used these power techniques to change the School Board's policies and practices they felt were detrimental to black children and the black community. ^ Based on the analysis of the qualitative data, it can be concluded that black children did not benefit from school desegregation in Broward County, Florida and the community continues to suffer residual effects from past desegregation policies and practices. ^

School desegregation in Broward County, Florida 1970-1998 : a historical study of power

This is a historical case study on school desegregation and power in Broward County, Florida from 1970 to 1998. The purpose of this study is to describe, explain and analyze types of power used by the School Board of Broward County, Florida and community activists, in their efforts to influence desegregation decisions from 1970 to 1998. In addition, this study explains who benefited and who won from the School Board's desegregation decisions and who governed those decisions? A historical case study approach was used as the method for conducting this study. Data sources included 11 interviews of individuals who were involved in school desegregation issues as either School Board officials or community activists and 10 archival data sources. The theoretical models of Russell, Galbraith, Wartenberg and Domhoff were used to determine the different types of power techniques used by School Board officials and community activists and to answer the questions: who benefited and who won from the School Board's desegregation decisions and who governed those policies and practices? The primary beneficiaries of school desegregation policies and practices in Broward County were: white, affluent communities and the builders, developers, realtors and other businesses in the western suburban communities. All of the data sources indicated that the black community did not benefit from the School Board's desegregation policies. The primary power techniques used by School Board officials to influence desegregation policies and practices was "power over opinions" and compensation. These power techniques were manifested by the School Board publicly disputing the allegations raised by community activists and by compensating those who supported and promoted the School Board's desegregation policies and practices. The power techniques primarily used by community activists were coercive force and "power over opinions." They effectively used these power techniques to change the School Board's policies and practices they felt were detrimental to black children and the black community. Based on the analysis of the qualitative data, it can be concluded that black children did not benefit from school desegregation in Broward County, Florida and the community continues to suffer residual effects from past desegregation policies and practices.

The World Heritage vs. Local Comnuty : identifying the sources of conflicts

The presented work is an essay rather than a scientific dissertation. The author wants to put an impact on the source of conflicts regarding the complex subject of heritage management and conservation in comparison with the local needs and the given context. The paper attempts to show the role of local communities and their cooperation with authorities as well as the effects of such cooperation. The area of research comprises the problems arising in the field of implementing external rules on the local field, challenges appearing regarding the needs of local communities and the efforts of official authorities trying to implement the principles of the conventions. The problems arise when local communities display the lack of understanding and do not share the common idea of heritage conservation. This is caused mainly by the decreasing possibilities of comfortable life. The author tries to identify the main and wrongful approaches as ‘Gone with the Wind’, ‘The Prince and The Pauper’, ‘Heart of Darkness’ or ‘Scarlet letter’. The focus will be put to explain what the areas are where a mutual misunderstanding arise and why all parts to the problem present different points of view. What creates a value? Is it a heritage object or maybe the other values need a stronger protection? When the general duty and the need to protect the heritage is regarded as a controversy and when it is considered as a value within a given community? The international public interest in heritage protection is often regarded as an attempt to diminish the sovereign power of the community and provokes severe controversies and tensions. The major problem envisaged today seems to be the massive and increasing urbanisation and the destruction of the vestiges still existing of traditional cultures, when we consider century urban post-industrial districts of Upper Silesia in Poland, the medieval cities in Western Europe, the traditional nomad Masaya villages in Kenya or the remains of vanished cultures in various regions of Asia. The preferred platform of cooperation between the parts of the conflict includes divergent needs, beliefs and practices of communities and the possible fields of reconciling the abovementioned. Chosen examples of the best practices considering mutual cooperation will be underlined.

Wild mushrooms and their mycelia as sources of bioactive compounds: antioxidant, anti-inflammatory and cytotoxic properties

Mushrooms are an important source of natural compounds with acknowledged bioactivity. Pleurotus eryngii (DC.) Quél., in particular, is widely recognized for its organoleptic quality and favorable health effects, being commercially produced in great extent. On the other hand, Suillus bellinii (Inzenga) Watling is an ectomycorrhizal symbiont, whose main properties were only reported in a scarce number of publications. Some current trends point toward using the mycelia and the culture media as potential sources of bioactive compounds, in addition to the fruiting bodies. Accordingly, P. eryngii and S. bellinii were studied for their composition in phenolic acids and sterols, antioxidant capacity (scavenging DPPH radicals, reducing power, β-carotene bleaching inhibition and TBARS formation inhibition), anti-inflammatory effect (by down-regulating LPS-stimulated NO in RAW264.7 cells) and anti-proliferative activity (using MCF-7, NCI-H460, HeLa, HepG2 and PLP2 cell lines). Overall, S. bellinii mycelia showed higher contents of ergosterol and phenolic compounds (which were also detected in higher quantity in its fruiting body) and stronger antioxidant activity than P. eryngii. On the other hand, P. eryngii mycelia showed anti-inflammatory (absent in S. bellinii mycelia) and a cytotoxicity similar (sometimes superior) to its fruiting bodies, in opposition to S. bellinii, whose mycelia presented a decreased anti-proliferative activity. Furthermore, the assayed species showed differences in the growth rate and yielded biomass of their mycelia, which should also be considered in further applications.

Sources of variation of energy and nutrient intake among adolescents in São Paulo, Brazil

The aim of the current study was to describe the sources of variation of energy and nutrient intake and to calculate the number of repetitions of diet measurements to estimate usual intake in adolescents from São Paulo, Brazil. Data was collected using 24-hour dietary recalls (24hR) in 273 adolescents between 2007 and 2008. Individuals completed a repeat 24hR around two months later. The sources of variation were estimated using the random effect model. Variance ratios (within-person to between-person variance ratio) and the number of repetitions of 24hR to estimate usual intake were calculated. The principal source of variation was due to within-person variance. The contribution of day of week and month of year was less than 8%. Variations ranged from 1.15 for calcium to 7.31 for vitamin E. The number of 24hR repeats required to estimate usual intake varied according to nutrient and gender, numbering 15 for males and 8 for females.

Pollen sources of the orchid bee Euglossa annectans Dressler 1982 (Hymenoptera: Apidae, Euglossini) analyzed from larval provisions

In order to analyze the pollen resources used by the orchid bee Euglossa annectans, samples of larval provisions from cells under construction were taken from 12 different trap nests (wooden boxes) on Santa Catarina Island, southern Brazil. The 43 samples collected between 2002 and 2005 represented all months except December. Overall, 74 pollen types from 24 families were distinguished. Among the 26 pollen types that reached more than 10% in monthly means, the families Melastomataceae, Bromeliaceae, Ochnaceae, Fabaceae, and Myrtaceae were most frequently represented. The Shannon-Weaver diversity index H' for the 43 brood cells varied from 0.10-1.65 and the annual diversity was 0.98. Similarity indices ranged from 0 to 0.87 and were highest during spring and summer. The results characterize E. annectans as a polylectic species. Based on these data, we can conclude that Euglossa females may act as pollinators of many forest species.

A Lagrangian Identification of the Main Sources of Moisture Affecting Northeastern Brazil during Its Pre-Rainy and Rainy Seasons

This work examines the sources of moisture affecting the semi-arid Brazilian Northeast (NEB) during its pre-rainy and rainy season (JFMAM) through a Lagrangian diagnosis method. The FLEXPART model identifies the humidity contributions to the moisture budget over a region through the continuous computation of changes in the specific humidity along back or forward trajectories up to 10 days period. The numerical experiments were done for the period that spans between 2000 and 2004 and results were aggregated on a monthly basis. Results show that besides a minor local recycling component, the vast majority of moisture reaching NEB area is originated in the south Atlantic basin and that the nearby wet Amazon basin bears almost no impact. Moreover, although the maximum precipitation in the ""Poligono das Secas'' region (PS) occurs in March and the maximum precipitation associated with air parcels emanating from the South Atlantic towards PS is observed along January to March, the highest moisture contribution from this oceanic region occurs slightly later (April). A dynamical analysis suggests that the maximum precipitation observed in the PS sector does not coincide with the maximum moisture supply probably due to the combined effect of the Walker and Hadley cells in inhibiting the rising motions over the region in the months following April.

Sources of carbonaceous aerosol in the Amazon basin

The quantification of sources of carbonaceous aerosol is important to understand their atmospheric concentrations and regulating processes and to study possible effects on climate and air quality, in addition to develop mitigation strategies. In the framework of the European Integrated Project on Aerosol Cloud Climate Interactions (EUCAARI) fine (D(p) < 2.5 mu m) and coarse (2.5 mu m < Dp < 10 mu m) aerosol particles were sampled from February to June (wet season) and from August to September (dry season) 2008 in the central Amazon basin. The mass of fine particles averaged 2.4 mu g m(-3) during the wet season and 4.2 mu g m(-3) during the dry season. The average coarse aerosol mass concentration during wet and dry periods was 7.9 and 7.6 mu g m(-3), respectively. The overall chemical composition of fine and coarse mass did not show any seasonality with the largest fraction of fine and coarse aerosol mass explained by organic carbon (OC); the average OC to mass ratio was 0.4 and 0.6 in fine and coarse aerosol modes, respectively. The mass absorbing cross section of soot was determined by comparison of elemental carbon and light absorption coefficient measurements and it was equal to 4.7 m(2) g(-1) at 637 nm. Carbon aerosol sources were identified by Positive Matrix Factorization (PMF) analysis of thermograms: 44% of fine total carbon mass was assigned to biomass burning, 43% to secondary organic aerosol (SOA), and 13% to volatile species that are difficult to apportion. In the coarse mode, primary biogenic aerosol particles (PBAP) dominated the carbonaceous aerosol mass. The results confirmed the importance of PBAP in forested areas. The source apportionment results were employed to evaluate the ability of global chemistry transport models to simulate carbonaceous aerosol sources in a regional tropical background site. The comparison showed an overestimation of elemental carbon (EC) by the TM5 model during the dry season and OC both during the dry and wet periods. The overestimation was likely due to the overestimation of biomass burning emission inventories and SOA production over tropical areas.

Sources of particulate matter: emission profile of biomass burning

Biomass burning is an important source of atmospheric Particulate Matter (PM) in Brazil: the burning of forests in the northwest and of sugar cane plantations in the southeast are important examples. The objective of this work is the measurement of the PM emission profile of burning of sugar cane and other characteristic vegetative burning in the region of Sao Carlos-SP/Brazil. Samples of PM(10) and PM(2.5) were collected in different conditions, including small laboratory controlled burnings and real ones. The samples were analysed by X-Ray Fluorescence (XRF) and 14 chemical elements quantified. t-Student tests were performed to compare the obtained profiles, using as a reference a vegetative burn profile taken from the USEPA data bank SPECIATE. All measured profiles presented significant amounts of Cl and K, which are confirmed as tracers of sugar cane foliage burning.

An algorithm for computerized automatic tuning of power system stabilizers

The main objective of this paper is to relieve the power system engineers from the burden of the complex and time-consuming process of power system stabilizer (PSS) tuning. To achieve this goal, the paper proposes an automatic process for computerized tuning of PSSs, which is based on an iterative process that uses a linear matrix inequality (LMI) solver to find the PSS parameters. It is shown in the paper that PSS tuning can be written as a search problem over a non-convex feasible set. The proposed algorithm solves this feasibility problem using an iterative LMI approach and a suitable initial condition, corresponding to a PSS designed for nominal operating conditions only (which is a quite simple task, since the required phase compensation is uniquely defined). Some knowledge about the PSS tuning is also incorporated in the algorithm through the specification of bounds defining the allowable PSS parameters. The application of the proposed algorithm to a benchmark test system and the nonlinear simulation of the resulting closed-loop models demonstrate the efficiency of this algorithm. (C) 2009 Elsevier Ltd. All rights reserved.

Sources of Variations When Comparing Concrete Carbonation Results

Carbonation is one of the main concerns for concrete service life in tropical countries. The mechanism and materials that produce it have been widely studied as well as natural and accelerated methods to report and analyze it. In spite of reported investigations, there is a need for information that could allow an adequate interpretation of the results of the standardization process. This lack of information can produce variations not only in the interpretation but also in the predictions of service life. The purpose of this paper is to analyze and discuss variables that could be sources of error, especially when performing accelerated tests. As a result, a methodologies to minimize variations when interpreting and comparing results is proposed, such as specimen geometry and preconditioning, spacing, relative humidity, and CO(2) concentration.

Expert system for the assessment of power transformer insulation condition based on type-2 fuzzy logic systems

An efficient expert system for the power transformer condition assessment is presented in this paper. Through the application of Duval`s triangle and the method of the gas ratios a first assessment of the transformer condition is obtained in the form of a dissolved gas analysis (DGA) diagnosis according IEC 60599. As a second step, a knowledge mining procedure is performed, by conducting surveys whose results are fed into a first Type-2 Fuzzy Logic System (T2-FLS), in order to initially evaluate the condition of the equipment taking only the results of dissolved gas analysis into account. The output of this first T2-FLS is used as the input of a second T2-FLS, which additionally weighs up the condition of the paper-oil system. The output of this last T2-FLS is given in terms of words easily understandable by the maintenance personnel. The proposed assessing methodology has been validated for several cases of transformers in service. (C) 2010 Elsevier Ltd. All rights reserved.