This paper presents a novel single-phase high power factor PWM boost rectifier, featuring soft commutation of the active switches at zero-current (ZCS). It incorporates the most desirable properties of the conventional PWM and the soft-switching resonant techniques. The input current shaping is achieved with average current mode control, and continuous inductor current mode. This new PWM converter provides ZCS turn-on and turn-off of the active switches, and it is suitable for high power applications employing IGBTs. Principle of operation, theoretical analysis, a design example, and experimental results from a laboratory prototype rated at 1600 W with 400 Vdc output voltage are presented. The measured efficiency and power factor were 96.2% and 0.99 respectively, with an input current THD equal to 3.94%, for an input voltage THD equal to 3.8%, at rated load.
A new family of direct current (DC) to DC converters based on a zero current switching pulse width modulated (ZCS-PWM) soft commutation cell is presented. This ZCS-PWM cell is consists of two transistors, two diodes, two inductors and one capacitor; and provides zero voltage turn-on to the diodes, a zero-current turn-on and a zero-current zero-voltage turn-off to the transistors. In addition, a new commutation cell in a new ZCS-PWM boost rectifier is developed, obtaining a structure with power factor near the unity, high efficiency at wide load range and low total harmonic distortion in the input current.
This paper deals with results of a research and development (R&D) project in cooperation with Electric Power Distribution Company in São Paulo (Brazil) regarding the development and experimental analysis of a new concept of power drive system suitable for application in traction systems of electrical vehicles pulled by electrical motors, which can be powered by urban DC or AC distribution networks. The proposed front-end structure is composed by five boost power cells in interleaving connection, operating in discontinuous conduction mode as AC-DC converter, or as DC-DC converter, in order to provide the proper DC output voltage range required by DC or AC adjustable speed drivers. Therefore, when supplied by single-phase AC distribution networks, and operating as AC-DC converter, it is capable to provide high power factor, reduced harmonic distortion in the input current, complying with the restrictions imposed by the IEC 61000-3-4 standards resulting in significant improvements for the trolleybuses systems efficiency and for the urban distribution network costs. Considering the compliance with input current restrictions imposed by IEC 61000-3-4 standards, two digital control strategies were evaluated. The digital controller has been implemented using a low cost FPGA (XC3S200) and developed totally using a hardware description language VHDL and fixed point arithmetic. Experimental results from a 15 kW low power scale prototype operating in DC and AC conditions are presented...
Dissertação (Mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico.; Estudo de inversores ressonantes meia-ponte auto-oscilantes com pré-regulador Buck-Boost integrados em uma única topologia com a finalidade de alimentar lâmpadas fluorescentes. Realiza-se uma análise teórica e desenvolve-se uma metodologia de projeto. São realizadas simulações e implementação de protótipos. Todos estudos envolvem o atendimento às prescrições de desempenho e segurança da nova norma da ABNT.
Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica.; Neste trabalho é apresentada uma metodologia de modelagem do retificador boost com alto fator de potência baseado na teoria clássica de controle. Ela permite explicar o funcionamento e as diferenças existentes entre as principais técnicas de controle, onde é mostrado que a tensão de entrada deve ser incluída no modelo linear da malha de corrente. Verifica-se que é possível empregar a tensão de entrada como um sinal de controle e não como perturbação.
Segundo a metodologia apresentada existem dois tipos de controle para a malha de corrente, os quais são: controle por realimentação com referência e controle por realimentação direta (sem referência), esta última denominada como one cycle control segundo . Quando é aplicada, a realimentação direta faz com que o retificador seja visto como uma carga linear pela fonte de entrada, sendo esta uma resistência equivalente. Finalmente é proposta uma técnica de controle, para a malha externa de tensão baseada no multiplicador como meio para variar a resistência apresentada à rede.
ABELEV, B. I.; AGGARWAL, M. M.; AHAMMED, Z.; ALAKHVERDYANTS, A. V.; ALEKSEEV, I.; ANDERSON, B. D.; ARKHIPKIN, D.; AVERICHEV, G. S.; BALEWSKI, J.; BARNBY, L. S.; BAUMGART, S.; BEAVIS, D. R.; BELLWIED, R.; BETANCOURT, M. J.; BETTS, R. R.; BHASIN, A.; BHATI,
We present measurements of the charge balance function, from the charged particles, for diverse pseudorapidity and transverse momentum ranges in Au + Au collisions at root S(NN) = 200 GeV using the STAR detector at RHIC. We observe that the balance function is boost-invariant within the pseudorapidity coverage vertical bar-1.3, 1.3 vertical bar. The balance function properly scaled by the width of the observed pseudorapidity window does not depend on the position or size of the pseudorapidity window. This scaling property also holds for particles in different transverse momentum ranges. In addition, we find that the width of the balance function decreases monotonically with increasing transverse momentum for all centrality classes. (c) 2010 Elsevier B.V. All rights reserved.; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Neste trabalho foi desenvolvido um controlador electrónico de potência capaz de actuar
sobre a janela inteligente por forma a permitir a transição do estado opaco para o estado
O controlador foi desenhado com o propósito de ser o único elemento necessário para o
funcionamento das janelas inteligentes, evitando assim a utilização de uma parafernália de
equipamentos isolados, ligados entre si, para executarem o mesmo propósito.
A topologia utilizada para criar este controlador baseou-se num módulo rectificador
AC/DC, seguido por um módulo Buck e terminado por um inversor do tipo Boost. Esta
topologia permitiu que se alcançasse uma grande amplitude de tensões á saída, as quais
variam entre os 0V e os 600V, necessárias para o desenvolvimento das janelas inteligentes.
Esta solução foi pensada por forma a permitir, no futuro, o desenvolvimento de um
controlador capaz de fazer a transição do estado transparente para opaco e a ligação ao
software laboratorial LabView para recolha de dados e interpretação dos mesmos.
We calculate two-pion correlation functions at finite rapidities based on a hydrodynamical model which does not assume explicit boost invariance along the collision axis. Extracting the HBT radii through chi2 fits in both Cartesian and Yano-Koonin-Podgoretski parametrizations, we compare them with experimental results from the PHOBOS collaboration. Based on the results, we discuss longitudinal expansion dynamics.
In the beginning of the 19th century, discussions about malaria by some physicians and authorities who had acted in many Atlantic regions showed the idea that deforestation would impact positively on sanitation in Brazil. This was related to a boost - unknown until then - toward the agrarian frontiers at the expense of traditional forests and strongly marked by the rural endemics. It all happened in a time marked by the growth of the Brazilian free population, by the internalization of sugarcane farms - especially in São Paulo - by the coffee expansion, by the increase of agrarian frontier as a survival strategy for poverty, by the suppression of regulations for the settlements on vacant slots in 1822, and by the Atlantic recession in the second quarter of the 19th century. The dissemination of this conception can be evaluated based on data about migration to the agrarian frontier and the impact of malaria among free people.
Producing a prophylactic vaccine for human immunodeficiency virus (HIV) has proven to be a challenge. Most biological isolates of HIV are difficult to neutralize, so that conventional subunit-based antibody-inducing vaccines are unlikely to be very effective. In the rhesus macaque model, some protection was afforded by DNA/recombinant viral vector vaccines. However, these studies used as the challenge virus SHIV-89.6P, which is neutralizable, making it difficult to determine whether the observed protection was due to cellular immunity, humoral immunity, or a combination of both. In this study, we used a DNA prime/modified vaccinia virus Ankara boost regimen to immunize rhesus macaques against nearly all simian immunodeficiency virus (SIV) proteins. These animals were challenged intrarectally with pathogenic molecularly cloned SIVmac239, which is resistant to neutralization. The immunization regimen resulted in the induction of virus-specific CD8+ and CD4+ responses in all vaccinees. Although anamnestic neutralizing antibody responses against laboratory-adapted SIVmac251 developed after the challenge, no neutralizing antibodies against SIVmac239 were detectable. Vaccinated animals had significantly reduced peak viremia compared with controls (P < 0.01). However...
We investigated long-term memory and recall cellular immune responses to human immunodeficiency virus type 1 (HIV-1) Env and Gag proteins elicited by recombinant vesicular stomatitis viruses (VSVs) expressing Env and Gag. More than 7 months after a single vaccination with VSV-Env, ∼6% of CD8+ splenocytes stained with major histocompatibility complex class I tetramers containing the Env p18-I10 immunodominant peptide and showed a memory phenotype (CD44Hi). The level of tetramer-positive cells in memory was about 14% of the peak primary response. Recall responses elicited in these mice 5 days after boosting with a heterologous recombinant vaccinia virus expressing HIV-1 Env showed that 40 to 45% of CD8+ splenocytes were tetramer positive and activated (CD62LLo), and these cells produced gamma interferon after stimulation with Env peptide, indicating that they were functional. Five months after the boost, the long-term memory cell population (tetramer positive, CD44Hi) constituted 30% of the CD8+ splenocytes. Recall responses to HIV-1 Gag were examined in mice primed with VSV recombinants expressing HIV-1 Gag protein and boosted with a vaccinia virus recombinant expressing Gag. Using this protocol, we found that ∼40% of CD8+ splenocytes were activated (CD62LLo) and specific for a Gag immunodominant peptide (tetramer positive). The high-level Gag recall response elicited by the vaccinia virus-Gag was greater than that obtained by boosting with a VSV-Gag vector with a different VSV glycoprotein. The corresponding levels of CD44Hi memory cells were also higher long after boosting with vaccinia virus-Gag than after boosting with a glycoprotein exchange VSV-Gag. Our results show that VSV vectors elicit high-level memory CTL responses and that these can be amplified as much as six- to sevenfold using a heterologous boosting vector.
High level transient gene expression in lymphoid cells has always been challenging because of the difficulty to efficiently transfect such cells. This has precluded any attempt to clone cDNA encoding proteins by means of their specific biological function in lymphoid cells. We have developed a very efficient transient eukaryotic expression system analogous to the well-known expression system in COS cells. Firefly luciferase and human CD2 genes were used as reporter genes and cloned into the eukaryotic shuttle vector pCDM8 which contains the strong cytomegalovirus promoter and the SV40 origin of replication for autonomous plasmid replication in permissive host cells that express the large SV40 T Antigen. Co-transfection of the reporter plasmids together with an SV40 T Ag expressing plasmid resulted in the several fold amplification of either the Luc activity or the cell surface expression of the CD2 marker in a transient assay. The level of amplification was dependent on the strength of the promoter used to drive the SV40 T Ag expression and was correlated with the extent of autonomous replication of the reporter plasmid in transfected cells. This highly efficient transient gene expression by SV40 T Ag boost was suitable to several human cell lines...
We have recently shown that a single injection of mature, antigen-pulsed, human dendritic cells (DCs) rapidly elicits CD4+ and CD8+ T-cell immunity in vivo. The DCs were pulsed with 2 foreign proteins, keyhole limpet hemocyanin (KLH) and tetanus toxoid (TT), as well as an HLA A2.1-restricted influenza matrix peptide (MP). Responses to all 3 antigens peaked at 30–90 days after immunization and declined thereafter. To determine if the foreign helper proteins (TT and KLH) were essential for CD8+ T-cell responses to the viral peptide, we reinjected 3 of the HLA-2.1 subjects with mature DCs pulsed with MP alone. All 3 volunteers showed a rapid boost in MP-specific immunity, and freshly sampled blood from 1 contained cytolytic T cells. In all 3 subjects, CD8+ T-cell responses to booster DCs were faster and of greater magnitude than the responses to the first DC injection. Importantly, the T cells that proliferated after booster DC treatment secreted interferon-γ upon challenge with much lower doses of viral peptide than those elicited after the first injection, indicating a higher functional avidity for the ligand. These data begin to outline the kinetics of T-cell immunity in response to DCs and demonstrate that booster injections of mature DCs enhance both qualitative and quantitative aspects of CD8+ T-cell function in humans.
Most species of recombinant leukocyte interferons (IFN-alpha A, -alpha B, -alpha C, -alpha D, -alpha F, -alpha I, and -alpha K) were capable of boosting human natural killer (NK) activity after a 2-hr treatment of cells at a concentration of 1-80 units/ml. In contrast, recombinant human IFN-alpha J was found to be incapable of augmenting NK activity after exposure of cells for 2 hr to concentrations as high as 10,000 units/ml. This inability of IFN-alpha J to boost NK activity was not complete because, after exposure of cells to a high concentration of IFN-alpha J (10,000 units/ml) for 18 hr, boosting of cytolysis was observed. IFN-alpha J appeared to interact with receptors for IFN on NK cells since it was found to interfere with the boosting of NK activity by other species of IFN-alpha. In contrast to its deficient ability to augment NK activity, IFN-alpha J has potent antiviral and antiproliferative activities. Such extensive dissociation of these biological activities has not been observed previously with any other natural or recombinant IFN species. Thus, this IFN species may be useful for evaluating the relative importance of various biological activities on the therapeutic effects of IFN, for understanding structure-function relationships...