11,336 research outputs found
Sousa School
No full textTwo male and two female students eating their school lunch.
Sousa School, possibly Washington, DC.
Day of month is an estimate.https://egrove.olemiss.edu/rosa_1900-1959/1039/thumbnail.jp
A novel topology of modular multilevel bidirectional non-isolated dc-dc converter
No full textThe paradigm of smart grids has been continuously
addressing new challenges in terms of power electronics
converters, for instance, to deal with technologies like
renewables, electric mobility, energy storage, and hybrid power
grids. Allied with this context, a novel topology of modular
multilevel bidirectional (MMB) non-isolated dc-dc converter is
proposed in this paper. Taking into consideration the nature of
the proposed MMB dc-dc converter, it is appropriated to operate
as back-end converter linked to front-end ac-dc converters based
on cascade structures, i.e., with more than one dc-link. As
distinctive features, the proposed MMB dc-dc converter can
operate with five-voltage levels, allowing to reduce the voltage
stress in each semiconductor, and it is controlled based on the
interleaved principle of operation, although it is not an
interleaved converter. A dedicated pulse-width modulation, as
well as voltage and current control strategies, are proposed and
clearly explained along the paper. The claimed distinctive
features of the proposed MMB dc-dc converter are supported by
analytic description and by computer simulation validation,
considering steady-state and transient-state operations in
relevant conditions of the dc interfaces.This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project newERA4GRIDs PTDC/EEI-EEE/30283/2017, and by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by FCT
Common Mode Currents in DC Power Routers
No full textThe grid reinforcement and energy redirection needs have led to the emergence of Back-To-Back Voltage Source Converter (BTB-VSC) based dc power routers. This paper investigates the low frequency Common Mode Currents (CMCs) that arise in the system if the employed BTB-VSCs have an un-isolated ac path connected in parallel to their output ports. Simulation results are presented to show a sensitivity analysis of lower order harmonics in CMC with respect to the operating active and reactive power of the dc router, dc link voltage, link resistance, modulation method and pole capacitance. Experimental results are shared to show existance of lower order CMC in 3-wire ac link operating in parallel with the dc power router and these are mitigated using zero sequence controller
Uterine NK cells are critical in shaping DC immunogenic functions compatible with pregnancy progression.
No full textDendritic cell (DC) and natural killer (NK) cell interactions are important for the regulation of innate and adaptive immunity, but their relevance during early pregnancy remains elusive. Using two different strategies to manipulate the frequency of NK cells and DC during gestation, we investigated their relative impact on the decidualization process and on angiogenic responses that characterize murine implantation. Manipulation of the frequency of NK cells, DC or both lead to a defective decidual response characterized by decreased proliferation and differentiation of stromal cells. Whereas no detrimental effects were evident upon expansion of DC, NK cell ablation in such expanded DC mice severely compromised decidual development and led to early pregnancy loss. Pregnancy failure in these mice was associated with an unbalanced production of anti-angiogenic signals and most notably, with increased expression of genes related to inflammation and immunogenic activation of DC. Thus, NK cells appear to play an important role counteracting potential anomalies raised by DC expansion and overactivity in the decidua, becoming critical for normal pregnancy progression
Modeling, Control, and Operation of an M-DAB DC-DC Converter for Interconnection of HVDC Grids
No full textFuture high-voltage direct-current (HVDC) networks based on voltage source converters (VSCs) will have different structures (asymmetric monopolar, bipolar, or symmetric monopolar), voltage levels, control, and protection schemes. Therefore, dc-dc converters are needed to interconnect those VSC-HVDC grids and several technical issues on their control and operational systems must be adequately addressed. A dc-dc converter based on a modular-dual active bridge (M-DAB) converter is suggested to reach a desirable interconnection of the HVDC grids and regulate power flow (PF) between them. A dynamic averaged model is proposed for the M-DAB converter and its stability is analyzed using the Lyapunov function. Moreover, a new local controller based on nonlinear control theory is proposed for the M-DAB. The new M-DAB local controller is integrated with the energy management system (EMS), by updating the PF equations, to create a complete control structure. Considering the CIGRE DCS3 HVDC test system and the studied M-DAB, static, dynamic simulation, and experimental studies are conducted and the dc-dc converter and the performance of the designed controllers and the EMS are examined and validated.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Intelligent Electrical Power Grid
Restructuring the existing medium voltage distribution grids using DC systems
No full textGreen Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag
Cold cracking in DC-cast high strength aluminum alloy ingots: An intrinsic problem intensified by casting process parameters
No full textFor almost half a century the catastrophic failure of direct chill (DC) cast high strength aluminum alloys has been challenging the production of sound ingots. To overcome this problem, a criterion is required that can assist the researchers in predicting the critical conditions which facilitate the catastrophic failure of the ingots. This could be achieved at first glance by application of computer simulations to assess the level and distribution of residual thermal stresses. However, the simulation results are only able to show the critical locations and conditions where and when high stresses may appear in the ingots. The prediction of critical void/crack size requires simultaneous application of fracture mechanics. In this paper, we present the thermo-mechanical simulation results that indicate the critical crack size distribution in several DC-cast billets cast at various casting conditions. The simulation results were validated upon experimental DC-casting trials and revealed that the existence of voids/cracks with a considerable size is required for cold cracking to occur.Materials Science & EngineeringMechanical, Maritime and Materials Engineerin
A Dynamically Reconfigurable Recursive Switched-Capacitor DC-DC Converter with Adaptive Load Ability Enhancement
No full textMultiple voltage conversion ratio (VCR) recursive switched-capacitor (SC) dc-dc converters, based on several basic 2:1 converters, are widely used for on-chip power supplies due to their flexible VCRs for higher energy efficiency. However, conventional multiple VCR SC converters usually have one or more 2:1 converters unused for some VCRs, which results in lower power density and chip area wastage. This article presents a new recursive dc-dc converter system, which can dynamically reconfigure the connection of all on-chip 2:1 converter cells so that the unused converters in the conventional designs can be reused in this new architecture for increasing the load-driving capacity, power density, and power efficiency. To validate the design, a 4-bit-input 15-ratio system was designed and fabricated in a 180-nm BCD process, which can support a maximum load current of \text{0.71}\,\text{mA} and achieves a peak power efficiency of 93.1% with 105.3\,\mu \text{A/mm} {2} chip power density from a 2-V input power supply. The measurement results show that the load-driving capacity can become 6.826×, 2.236×, and 2.175× larger than the conventional topology when the VCR is 1/2, 1/4, and 3/4, respectively. In addition, the power efficiency under these specific VCRs can also be improved considerably.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Instrumentatio
A proposed bidirectional three-level DC-DC power converter for applications in smart grids: an experimental validation
No full textThe integration of renewable energy sources (RES), energy storage systems (ESS), and electric mobility into smart grids requires the use of DC-DC back-end power converters for adjusting voltage levels. Although a DC-DC converter applied for RES only operates in unidirectional mode, when applied to ESS or EM, the bidirectional mode is a fundamental requisite for exchanging power with the electrical power grid. In this context, this paper presents an experimental validation of a proposed bidirectional three-level DC-DC converter considering its application for smart grids. Traditionally, the DC-DC power converters of such applications are two-level converters. However, by employing a three-level topology, it is possible to improve the quality of the variables controlled by the power converter. Moreover, since the proposed DC-DC converter is controlled to produce a controlled current, the proposed current control and modulation strategies are introduced and described. A complete analysis of the operation principle of the proposed bidirectional three-level DC-DC power converter is presented, supported by experimental validation, employing a laboratory prototype.This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2019. This work has been supported by FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017, and by the FCT Project newERA4GRIDs PTDC/EEI-EEE/30283/2017. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by FCT
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Toll-like receptor expression in murine DC subsets: lack of TLR7 expression by CD8α+ DC correlates with unresponsiveness to imidazoquinolines
No full textToll-like receptors (TLR) recognize microbial and viral patterns and activate dendritic cells (DC). TLR distribution among human DC subsets is heterogeneous: plasmacytoid DC (PDC) express TLR1, 7 and 9, while other DC types do not express TLR9 but express other TLR. Here, we report that mRNA for most TLR is expressed at similar levels by murine splenic DC sub-types, including PDC, but that TLR3 is preferentially expressed by CD8α+ DC while TLR5 and TLR7 are selectively absent from the same subset. Consistent with the latter, TLR7 ligand activates CD8α– DC and PDC, but not CD8α+ DC as measured by survival ex vivo, up-regulation of surface markers and production of IL-12p40. These data suggest that the dichotomy in TLR expression between plasmacytoid and non-plasmacytoid DC is not conserved between species. However, lack of TLR7 expression could restrict the involvement of CD8α+ DC in recognition of certain mouse pathogens
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