997 resultados para Semi-active controllers
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To manage foreign operations, companies must often send their employees on international assignments. Repatriating these expatriates can be difficult because they have been forgotten during their posting, and their new experiences are not utilised. In addition to the possible difficulties in organisational repatriation, the returnee can suffer from readjustment problems after a lengthy stay abroad has changed their habits and even identity. This thesis examines the repatriation experience of Finnish assignees returning from Russia. The purpose of the study is to understand how the repatriation experience influences their readjustment to work in Finland. This experience is influenced by many factors including personal and situational changes, the repatriation process, job and organisational factors, and individual’s motives. The theoretical background of the study is founded on two models of repatriation adjustment. A refined, holistic theoretical framework for the study is created. It describes the formation of the repatriation experience and its importance for readjustment to work and retention. The qualitative research approach is suitable for the thesis which examines the returnees’ personal experiences and feelings: a qualitative case study aims to explain the phenomenon in-depth and comprehensively. The data was collected in summer 2013 through semi-standardised interviews with eight Finnish repatriates. They had returned from Russia within the last two years. The data was analysed by structuring the interview transcripts using template analysis. The results supported earlier literature and suggest that the re-entry remains a challenging phase for both the individual and the company. For some, adjusting to a new job was difficult for various reasons. The repatriates underwent personal change and development and felt it was for the better. Many repatriates criticised the company’s repatriation process upon return. Finding a suitable return job was not clear. Instead, the returnees had to be active in finding a new position. Many assignees had only modest career-related motives regarding the assignment and they had realistic expectations about the return. Therefore they were not extremely surprised or dissatisfied when they were not actively offered positions or support by the company. The significance of motives stood out even more than the theory predicted. As predicted, they are linked to the expectations of employees. Moreover, if the employees are motivated to remain in the company, they can tolerate partly a negative repatriation experience. Despite the complexity of the return and readjustment, the assignment as a whole was seen as a rewarding experience by all participants.
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The objectives of this work were to evaluate the floristic composition and dry biomass of weeds under the canopy of seven perennial species adapted to the Semi-Arid region of Brazil, and correlate these characteristics with growth traits of the perennial species. The following perennial species were evaluated in two experiments (E1 and E2): mesquite (Prosopis juliflora), jucá (Caesalpinia ferrea), white popinac (Leucaena leucocephala), mofumbo (Combretum leprosum), neem (Azadirachata indica), sabiá (Mimosa caesalpiniaefolia) and tamarind (Tamarindus indica). In E1, the seven species were evaluated in a random block design with four replicates and nine plants per plot. In E2, evaluation comprised four species (mesquite, jucá, white popinac, and tamarind) in a random block design with eight replicates and nine plants per plot. A circle with an area of 1.77 m² was established around the trunk of each plant, two years after they were transplanted to the permanent location. The weeds collected within this circle were cut even with the ground, classified and weighed. At this time, plant height, and crown and stem diameters were evaluated in all trees of each plot. In E1 there were no differences between tree species as to weed frequency under their canopies; however, weed growth was smaller under the canopy of sabiá trees. Mesquite and sabiá had the greatest plant height and crown diameter means, but only sabiá had the greatest stem diameter. In E2, the perennial species were not different with regard to weed frequency and growth under their canopies, but mesquite had the greatest growth, as measured by plant height (with significant results for jucá as well) and crown and stem diameter.
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This doctoral thesis introduces an improved control principle for active du/dt output filtering in variable-speed AC drives, together with performance comparisons with previous filtering methods. The effects of power semiconductor nonlinearities on the output filtering performance are investigated. The nonlinearities include the timing deviation and the voltage pulse waveform distortion in the variable-speed AC drive output bridge. Active du/dt output filtering (ADUDT) is a method to mitigate motor overvoltages in variable-speed AC drives with long motor cables. It is a quite recent addition to the du/dt reduction methods available. This thesis improves on the existing control method for the filter, and concentrates on the lowvoltage (below 1 kV AC) two-level voltage-source inverter implementation of the method. The ADUDT uses narrow voltage pulses having a duration in the order of a microsecond from an IGBT (insulated gate bipolar transistor) inverter to control the output voltage of a tuned LC filter circuit. The filter output voltage has thus increased slope transition times at the rising and falling edges, with an opportunity of no overshoot. The effect of the longer slope transition times is a reduction in the du/dt of the voltage fed to the motor cable. Lower du/dt values result in a reduction in the overvoltage effects on the motor terminals. Compared with traditional output filtering methods to accomplish this task, the active du/dt filtering provides lower inductance values and a smaller physical size of the filter itself. The filter circuit weight can also be reduced. However, the power semiconductor nonlinearities skew the filter control pulse pattern, resulting in control deviation. This deviation introduces unwanted overshoot and resonance in the filter. The controlmethod proposed in this thesis is able to directly compensate for the dead time-induced zero-current clamping (ZCC) effect in the pulse pattern. It gives more flexibility to the pattern structure, which could help in the timing deviation compensation design. Previous studies have shown that when a motor load current flows in the filter circuit and the inverter, the phase leg blanking times distort the voltage pulse sequence fed to the filter input. These blanking times are caused by excessively large dead time values between the IGBT control pulses. Moreover, the various switching timing distortions, present in realworld electronics when operating with a microsecond timescale, bring additional skew to the control. Left uncompensated, this results in distortion of the filter input voltage and a filter self-induced overvoltage in the form of an overshoot. This overshoot adds to the voltage appearing at the motor terminals, thus increasing the transient voltage amplitude at the motor. This doctoral thesis investigates the magnitude of such timing deviation effects. If the motor load current is left uncompensated in the control, the filter output voltage can overshoot up to double the input voltage amplitude. IGBT nonlinearities were observed to cause a smaller overshoot, in the order of 30%. This thesis introduces an improved ADUDT control method that is able to compensate for phase leg blanking times, giving flexibility to the pulse pattern structure and dead times. The control method is still sensitive to timing deviations, and their effect is investigated. A simple approach of using a fixed delay compensation value was tried in the test setup measurements. The ADUDT method with the new control algorithm was found to work in an actual motor drive application. Judging by the simulation results, with the delay compensation, the method should ultimately enable an output voltage performance and a du/dt reduction that are free from residual overshoot effects. The proposed control algorithm is not strictly required for successful ADUDT operation: It is possible to precalculate the pulse patterns by iteration and then for instance store them into a look-up table inside the control electronics. Rather, the newly developed control method is a mathematical tool for solving the ADUDT control pulses. It does not contain the timing deviation compensation (from the logic-level command to the phase leg output voltage), and as such is not able to remove the timing deviation effects that cause error and overshoot in the filter. When the timing deviation compensation has to be tuned-in in the control pattern, the precalculated iteration method could prove simpler and equally good (or even better) compared with the mathematical solution with a separate timing compensation module. One of the key findings in this thesis is the conclusion that the correctness of the pulse pattern structure, in the sense of ZCC and predicted pulse timings, cannot be separated from the timing deviations. The usefulness of the correctly calculated pattern is reduced by the voltage edge timing errors. The doctoral thesis provides an introductory background chapter on variable-speed AC drives and the problem of motor overvoltages and takes a look at traditional solutions for overvoltage mitigation. Previous results related to the active du/dt filtering are discussed. The basic operation principle and design of the filter have been studied previously. The effect of load current in the filter and the basic idea of compensation have been presented in the past. However, there was no direct way of including the dead time in the control (except for solving the pulse pattern manually by iteration), and the magnitude of nonlinearity effects had not been investigated. The enhanced control principle with the dead time handling capability and a case study of the test setup timing deviations are the main contributions of this doctoral thesis. The simulation and experimental setup results show that the proposed control method can be used in an actual drive. Loss measurements and a comparison of active du/dt output filtering with traditional output filtering methods are also presented in the work. Two different ADUDT filter designs are included, with ferrite core and air core inductors. Other filters included in the tests were a passive du/dtfilter and a passive sine filter. The loss measurements incorporated a silicon carbide diode-equipped IGBT module, and the results show lower losses with these new device technologies. The new control principle was measured in a 43 A load current motor drive system and was able to bring the filter output peak voltage from 980 V (the previous control principle) down to 680 V in a 540 V average DC link voltage variable-speed drive. A 200 m motor cable was used, and the filter losses for the active du/dt methods were 111W–126 W versus 184 W for the passive du/dt. In terms of inverter and filter losses, the active du/dt filtering method had a 1.82-fold increase in losses compared with an all-passive traditional du/dt output filter. The filter mass with the active du/dt method was 17% (2.4 kg, air-core inductors) compared with 14 kg of the passive du/dt method filter. Silicon carbide freewheeling diodes were found to reduce the inverter losses in the active du/dt filtering by 18% compared with the same IGBT module with silicon diodes. For a 200 m cable length, the average peak voltage at the motor terminals was 1050 V with no filter, 960 V for the all-passive du/dt filter, and 700 V for the active du/dt filtering applying the new control principle.
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The aim of the present thesis was to explore possible promotional actions to support the emergence of eco-industrial business networks in Finland. The main objectives were to investigate what kind of factors affect in the development of eco-industrial networks and further make suggestions in what kinds of actions this could be supported. In addition, since the active facilitation was discovered as one potential promoting activity, further investigation about facilitation process in Finnish context was conducted and also main characteristics of nationwide facilitation programme were identified. This thesis contains literature review of network orchestration and eco-industrial networks. The latter consists of green supply chain management and industrial symbiosis, although the main focus of the study leans on the concept of industrial symbiosis. The empirical data of the study was obtained from semi-structured expert interviews. These interviews were analyzed using qualitative content analysis. The study identified four main promotional activities for eco-industrial networks: 1) building awareness, 2) incentives, 3) dismantling of legislative barriers and 4) active facilitation. In addition, a framework for facilitation activities in Finnish context was built and main characteristics of nationwide facilitation programme were identified.
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Presentation at Open Repositories 2014, Helsinki, Finland, June 9-13, 2014
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Studies of plant community dynamics are essential in understanding the demographic patterns of species since changes in demographic rates can affect the floristic composition and future structure. The purpose of the present study was to analyze the changes in the community structure and floristic composition of woody plants in a tropical semi-deciduous forest in Uberlândia in central Brazil, during a 10-years period. The data were collected in 1989 and in 2000 in 50 quadrats (10 m x 10 m) where all trees with a minimum circumference at breast height of 10 cm were sampled. In 1989, 93 species and 1103 individuals were registered. Over a period of 10 years, seven new species were added to the community, although eight disappeared. The main change that occurred during this period in the floristic composition was the replacement of savannah species occurring in forest gaps by those from the forest understory.
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Tässä työssä on tutkittu modulaarisen aktiivimagneettilaakeroidun koelaitteen mekaanista suunnittelua ja analysointia. Suurnopeusroottorin suunnittelun teoria on esitelty. Lisäksi monia analyyttisiä mallinnusmenetelmiä mekaanisten kuormitusten mallintamiseksi on esitelty. Koska kyseessä on suurnopeussähkökone, roottoridynamiikka ja sen soveltuvuus suunnittelussa on esitelty. Magneettilaakerien rakenteeseen ja toimintaan on tutustuttu osana tätä työtä. Kirjallisuuskatsaus nykyisistä koelaitteista esimerkiksi komponenttien ominaisuuksien tunnistamiseen ja roottoridynamiikan tutkimuksiin on esitelty. Työn rajauksena on konseptisuunnittelu muunneltavalle magneettilaakeroidulle (AMB) koelaitteelle ja suunnitteluprosessin dokumentointi. Muunneltavuuteen päädyttiin, koska se mahdollistaa erilaisten komponenttiasetteluiden testaamisen erilaisille magneettilaakerikokoonpanoille ja roottoreille. Pääpaino tässä työssä on suurnopeus induktiokoneen roottorin suunnittelussa ja mallintamisessa. Modulaaristen toimilaitteiden kuten magneettilaakerien ja induktiosähkömoottorin rakenne on esitelty ja modulaarisen rakenteen käytettävyyden hyödyistä koelaitekäytössä on dokumentoitu. Analyyttisiä ja elementtimenetelmään perustuvia tutkimusmenetelmiä on käytetty tutkittaessa suunniteltua suurnopeusroottoria. Suunnittelun ja analysoinnin tulokset on esitelty ja verrattu keskenään eri mallinnusmenetelmien välillä. Lisäksi johtopäätökset sähkömagneettisten osien liittämisen monimutkaisuudesta ja vaatimuksista roottoriin ja toimilaitteisiin sekä mekaanisten että sähkömagneettisten ominaisuuksien optimoimiseksi on dokumentoitu.
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O comportamento fenológico vegetativo e reprodutivo de Jatropha mollissima (Pohl) Baill., Jatropha mutabilis (Pohl) Baill. e Jatropha ribifolia (Pohl) Baill. foi comparado em uma área de caatinga hiperxerófila arbustiva-arbórea do nordeste brasileiro, no período de julho de 2005 a junho de 2007. Adicionalmente, investigou-se a correlação entre as fenofases e as variáveis abióticas (temperatura, umidade relativa, precipitação e fotoperíodo), a capacidade de armazenamento de água e o padrão de distribuição espacial. Todas as espécies apresentaram alta capacidade de armazenamento de água e comportamento fenológico contínuo e irregular com ausência de flores, frutos, queda foliar e brotamento nos meses mais frios e úmidos do ano. Apenas a floração de J. ribifolia apresentou correlação significativa com a precipitação. As três espécies apresentaram populações com distribuição agregada, favorecida principalmente devido ao processo de dispersão de sementes por autocoria. Os resultados obtidos indicam que a alta capacidade de armazenamento de água pelas espécies garante a ocorrência dos eventos fenológicos mesmo na ausência de chuvas.
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(The genus Stachybotrys (anamorphic fungi) in the semi-arid region of Brazil). Stachybotrys is characterized by macronematous, mononematous, unbranched or branched conidiophores, with discrete terminal and phialidic conidiogenous cells, and aseptate, reniform, ellipsoidal to spherical, smooth or verrucose conidia, which are produced in a slimy mass. Eight species have been reported from Brazil, occurring in the soil, air and leaf litter. During investigation of conidial fungi on decaying leaf litter in semi-arid areas of Brazil nine species were found: S. bisbyi (Sriniv.) G.L. Barron, S. chartarum (Ehrenb.) S. Hughes, S. globosa P. C. Misra & S. K. Srivast., S. kampalensis Hansf., S. longispora Matsush., S. nephrospora Hansf., S. nilagirica Subram., Stachybotrys parvispora S. Hughes and S. verrucispora Matsush. Stachybotrys nilagirica is a new record from Brazil. Descriptions, comments, geographic distribution and illustrations are presented for above mentioned species. A key for all species recorded in semi-arid region of Brazil is presented.
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Leaf CO2 assimilation (A) as a function of photosynthetic photon flux density (Q) or intercellular CO2 concentration (Ci) and chlorophyll fluorescence measurements were carried out on four tropical woody species growing in forest gap and understorey (Bauhinia forficata Link. and Guazuma ulmifolia Lam. as pioneers, and Hymenaea courbaril L. and Esenbeckia leiocarpa Engl. as non-pioneers). Chlorophyll fluorescence indicated similar acclimation capacities of photochemical apparatus to contrasting light environments irrespective to plant species. Maximum CO2 assimilation and quantum yield derived from A/Q curves indicated higher photosynthetic capacity in pioneer than in non-pioneer species in forest gap. However, the differences among species did not show a straightforward relation with their successional status regarding data derived from A/Q curves under understorey conditions. Both successional groups are able to sustain positive carbon balance under contrasting natural light availabilities, modifying photochemical and biochemical photosynthetic traits with similar phenotypic plasticity capacity.
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Floristic composition and structure of vegetation were studied in two rocky outcrop areas in the semi-arid region of northeastern Brazil. From April 2007 to September 2008, 18 monthly field trips were carried out. Vascular plants were randomly collected throughout the outcrop areas. For structural analysis, 30 plots of 1 × 1 m were set in the vegetation islands. The checklist presented combines 211 species (69 families and 168 genera), although only 56 species were collected in the plots. Fabaceae (18 spp.; 8.5%), Asteraceae (17 spp.; 8%), Orchidaceae (13 spp.; 6.1%), Euphorbiaceae (13 spp.; 6.1%), Bromeliaceae (10 spp.; 4.7%), and Poaceae (eight spp.; 3.8%) are the richest families. Overall, 1,792 shrub and herbaceous specimens were counted in the plots. The Shannon-Wiener (H) diversity index values were 2.572 and 2.547 nats individual-1. The species that presented the highest absolute abundance values (number of plants) had low frequencies in the plots and vice-versa. The biological spectrum had a high proportion of phanerophytes and therophytes, followed by cryptophytes, chamaephytes, and hemicryptophytes. The studied flora shares floristic components similar to other rocky outcrop areas of the semi-arid region in northeastern Brazil, including in relation to dominant groups in the vegetation structure.
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São apresentados a biologia floral, a dinâmica de produção de néctar, visitantes florais e sistemas reprodutivos de Jatropha ribifolia (Pohl) Baill. (Euphorbiaceae) e uma comparação dos dados obtidos para J. mollissima (Pohl) Baill. e J. mutabilis (Pohl) Baill. O estudo foi desenvolvido em uma área de caatinga hiperxerófila, na Estação Biológica de Canudos, Bahia, Brasil, de maio de 2005 a junho de 2007. As flores das três espécies estão organizadas em dicásios protogínicos. Em J. ribifolia as flores estaminadas e pistiladas duram cerca de 48 horas e a abertura é diurna, enquanto em J. mollissima e J. mutabilis as estaminadas duram entre 12 e 15 horas e as pistiladas entre 36 e 48 horas e a abertura é crepuscular. A produção de néctar, a viabilidade polínica e a receptividade estigmática iniciaram-se logo após a abertura total das flores e se sobrepuseram até sua senescência. A produção de néctar variou ao longo do dia e as flores pistiladas produziram maiores volumes que as estaminadas. A viabilidade polínica e a receptividade estigmática foram observadas nas três espécies durante toda a vida da flor. Houve diferença significativa entre os tratamentos dos sistemas reprodutivos para J. mollissima (KW = 59,796), J. mutabilis (KW = 59,058) e J. ribifolia (KW = 63,660). As três espécies produziram frutos por geitonogamia manual e xenogamia manual e apenas J. ribifolia produziu frutos por geitonogamia espontânea. As abelhas Apis mellifera, Xylocopa frontalis e X. grisescens e os beija-flores Chlorostilbon lucidus e Anopetia gounellei são os polinizadores potenciais de J. mollissima e J. mutabilis. Já para J. ribifolia, os potenciais polinizadores são A. mellifera e X. grisescens. A utilização de uma gama variada de vetores de pólen permite o fluxo polínico e a formação de frutos nas três espécies. Por sua vez, o sequenciamento no período da floração e diferenças nas dimensões das flores e nos horários da antese ajudam a manter o isolamento reprodutivo das três espécies e evitam a perda de pólen interespecífico, que poderia ser alta devido à partilha de alguns dos polinizadores.
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The selective recruitment of eosinophils in tissue is a striking feature of allergic diseases. Recently, a family of chemoattractant molecules, namely chemokines, has been described which potently activates eosinophil function in vitro. We have developed a murine model of eosinophil recruitment to compare the relative potency and efficacy of chemokines in vivo. Of the chemokines tested, only eotaxin and MIP-1a induced significant accumulation of eosinophils in vivo, but eotaxin was more effective than MIP-1a. Chemokines, especially eotaxin acting via the CCR-3 receptor, may have a fundamental role in determining selective eosinophil recruitment in vivo
Virtual Testing of Active Magnetic Bearing Systems based on Design Guidelines given by the Standards
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Active Magnetic Bearings offer many advantages that have brought new applications to the industry. However, similarly to all new technology, active magnetic bearings also have downsides and one of those is the low standardization level. This thesis is studying mainly the ISO 14839 standard and more specifically the system verification methods. These verifying methods are conducted using a practical test with an existing active magnetic bearing system. The system is simulated with Matlab using rotor-bearing dynamics toolbox, but this study does not include the exact simulation code or a direct algebra calculation. However, this study provides the proof that standardized simulation methods can be applied in practical problems.
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Alpha-Hemolysin is synthesized as a 1024-amino acid polypeptide, then intracellularly activated by specific fatty acylation. A second activation step takes place in the extracellular medium through binding of Ca2+ ions. Even in the absence of fatty acids and Ca2+ HlyA is an amphipathic protein, with a tendency to self-aggregation. However, Ca2+-binding appears to expose hydrophobic patches on the protein surface, facilitating both self-aggregation and irreversible insertion into membranes. The protein may somehow bind membranes in the absence of divalent cations, but only when Ca2+ (or Sr2+, or Ba2+) is bound to the toxin in aqueous suspensions, i.e., prior to its interaction with bilayers, can a-hemolysin bind irreversibly model or cell membranes in such a way that the integrity of the membrane barrier is lost, and cell or vesicle leakage ensues. Leakage is not due to the formation of proteinaceous pores, but rather to the transient disruption of the bilayer, due to the protein insertion into the outer membrane monolayer, and subsequent perturbations in the bilayer lateral tension. Protein or glycoprotein receptors for a-hemolysin may exist on the cell surface, but the toxin is also active on pure lipid bilayers.