Bidirectional dual-bridge dc/dc converter with high frequency isolation is gaining more attentions in renewable energy system due to small size and high-power density. In this paper, a dual-bridge ...series resonant dc/dc converter is analyzed with two simple modified ac equivalent circuit analysis methods for both voltage source load and resistive load. In both methods, only fundamental components of voltages and currents are considered. All the switches may work in either zero-voltage-switching or zero-current-switching for a wide variation of voltage gain, which is important in renewable energy generation. It is also shown in the second method that the load side circuit could be represented with an equivalent impedance. The polarity of cosine value of this equivalent impedance angle reveals the power flow direction. The analysis is verified with computer simulation results. Experimental data based on a 200 W prototype circuit is included for validation purpose.
A wide range zero-voltage switching (ZVS) active-clamped L-L type current-fed isolated dc-dc converter is proposed for fuel cells to utility interface application. The proposed converter maintains ...ZVS of all switches from full load down to very light load condition for wide input voltage variation. Detailed operation, analysis, design, simulation and experimental results for the proposed converter are presented. The auxiliary active clamping circuit absorbs the turn-off voltage spike and also assists in achieving ZVS of main switches. The ZVS of auxiliary switches and main switches is achieved by the energy stored in the boost inductors and series inductor (aided by parallel inductor), respectively. Rectifier diodes operate with zero-current switching. An experimental converter rated at 200 W has been designed, built and tested in the laboratory to verify the analysis, design and performance of the proposed converter for wide variations in input voltage and load.
Due to wide soft-switching operation range, high-frequency isolated resonant converters are featured with low switching losses. Therefore, it is meaningful to minimize the resonant tank current in an ...isolated resonant converter in order to enhance the overall system efficiency. In this work, a bidirectional series-resonant converter under phase-shifted modulation combined with a modified pulsewidth modulation gating scheme is addressed. The modified pulsewidth modulation gating scheme is helpful to keep more switches operating in zero-voltage switching (ZVS) at light load. According to the steady-state analysis with the fundamental harmonic approximation approach, a specified control strategy with minimum rms tank current based on three control dimensions is proposed in closed form. The validity of the proposed control strategy is verified through experimental tests. The pulsewidth of modulated voltage using the modified gating scheme is larger than that of the conventional pulsewidth modulation voltage, which compensates for the effects of more high-order harmonics on rms current. Therefore, compared with existing control strategies for minimum current operation, the proposed control strategy demonstrates comparable performance in depressing conduction loss and wider soft-switching range in high load range. And it is able to achieve higher efficiency at light load, thanks to more switches working in ZVS.
An electrolyzer is part of a renewable energy system and generates hydrogen from water electrolysis that is used in fuel cells. A dc-to-dc converter is required to couple the electrolyzer to the ...system dc bus. This paper presents the design of three soft-switched high-frequency transformer isolated dc-to-dc converters for this application based on the given specifications. It is shown that LCL-type series resonant converter (SRC) with capacitive output filter is suitable for this application. Detailed theoretical and simulation results are presented. Due to the wide variation in input voltage and load current, no converter can maintain zero-voltage switching (ZVS) for the complete operating range. Therefore, a two-stage converter (ZVT boost converter followed by LCL SRC with capacitive output filter) is found suitable for this application. Experimental results are presented for the two-stage approach which shows ZVS for the entire line and load range.
Deformation response of ferrite and martensite in a commercially produced dual-phase sheet steel with a nominal composition of 0.15% C–1.45% Mn–0.30% Si (wt.%) was characterized by nanoindentation ...and uniaxial compression of focused ion beam-milled cylindrical micropillars (1–2μm diameter). These experiments were conducted on as-received and pre-strained specimens. The average nanoindentation hardness of ferrite was found to increase from ∼2GPa in the as-received condition to ∼3.5GPa in the specimen that had been pre-strained to 7% plastic tensile strain. Hardness of ferrite in the as-received condition was inhomogeneous: ferrite adjacent to ferrite/martensite interface was ∼20% harder than that in the interior, a feature also captured by micropillar compression experiments. Hardness variation in ferrite was reversed in samples pre-strained to 7% strain. Martensite in the as-received condition and after 5% pre-strain exhibited large scatter in nanoindentation hardness; however, micropillar compression results on the as-received and previously deformed steel specimens demonstrated that the martensite phase in this steel was amenable to plastic deformation and rapid work hardening in the early stages of deformation. The observed microscopic deformation characteristics of the constituent phases are used to explain the macroscopic tensile deformation response of the dual-phase steel.
The present study was conducted with an objective of isolation, in vitro expansion, growth kinetics, molecular characterization and in vitro differentiation of fetal adnexa derived caprine ...mesenchymal stem cells. Mid-gestation gravid caprine uteri (2-3 months) were collected from abattoir to derive mesenchymal stem cells (MSCs) from fetal adnexa {amniotic fluid (cAF), amniotic sac (cAS), Wharton's jelly (cWJ) and cord blood (cCB)} and expanded in vitro. These cultured MSCs were used at the 3rd passage (P3) to study growth kinetics, localization as well as molecular expression of specific surface antigens, pluripotency markers and mesenchymal tri-lineage differentiation. In comparison to cAF and cAS MSCs, cWJ and cCB MSCs showed significantly (P<0.05) higher clonogenic potency, faster growth rate and low population doubling (PDT) time. All the four types of MSCs were positive for alkaline phosphatase (AP) and differentiated into chondrogenic, osteogenic, and adipogenic lineages. These stem cells expressed MSC surface antigens (CD73, CD90 and CD105) and pluripotency markers (Oct4, Sox2, Nanog, KLF, cMyc, FoxD3) but did not express CD34, a hematopoietic stem cell marker (HSC) as confirmed by RT-PCR, immunocytochemistry and flow cytometric analysis. The relative mRNA expression of MSC surface antigens (CD73, CD90 and CD105) was significantly (P<0.05) higher in cWJ MSCs compared to the other cell lines. The mRNA expression of Oct4 was significantly (P<0.05) higher in cWJ, whereas mRNA expression of KLF and cMyc was significantly (P<0.05) higher in cWJ and cAF than that of cAS and cCB. The comparative assessment revealed that cWJ MSCs outperformed MSCs from other sources of fetal adnexa in terms of growth kinetics, relative mRNA expression of surface antigens, pluripotency markers and tri-lineage differentiation potential, hence, these MSCs could be used as a preferred source for regenerative medicine.
An integrated single-phase single-stage high-frequency transformer isolated dual-tank LCL-type series resonant ac-dc converter with fixed-frequency phase-shift control strategy is presented. The ...circuit configuration combines a diode rectifier, a boost converter, and two identical half-bridge dc-dc LCL resonant converters. A high power factor and a low total harmonic distortion are achieved by discontinuous current mode operation of the front-end power factor correction circuit. The output voltage is regulated by the fixed-frequency phase-shift between two identical half-bridge LCL resonant converters. Soft-switching operation is achieved for all of the switches. The operation of intervals and steady-state analysis are presented briefly. A design example of a 100-W proposed converter is given, together with its simulated and experimental results for different input voltages.
, commonly known as job's tear, is a tall grain-bearing tropical plant of the family
. The ethanolic root extract (ERE) of the plant was investigated for the first time for anti-venom activity ...against Indian cobra
venom.
studies were conducted to determine neutralization of phospholipase A
(PLA
) activity of the
venom by the ERE. ERE showed significant inhibition of PLA
activity, which was further confirmed from effective neutralization of human red blood cells (HRBC) lysis induced by the venom. In addition, venom-induced proteolysis, fibrinogenolysis, DNase activity were also neutralized by the ERE, which contained carbohydrates, glycolides, resins and tannins. Oral administration of ERE at doses levels 100, 200 and 400 mg/kg effectively inhibited
venom-induced lethality in mice. Myotoxicity induced by
venom, measured by creatine kinase activity in rats was significantly neutralized by the ERE at a dose of 200 mg/kg. Stigmasterol, as one of the component isolated from the ERE, was found to have venom phospholipase A
inhibition potential, which was confirmed by molecular docking studies with PLA
. In summary, these studies indicate the ability of ERE of
to effectively neutralize the toxic effects of the venom is, in part, contributed by the inhibition of PLA
activity among other venom-derived factors.
This study used a set of different bacteriophages to control contaminations of
Salmonella
spp., a major food pathogen. A cocktail of four phages designated based on host range and in vitro lytic ...assay showed a lower bacteriophage insensitive mutant frequency and considerable stability at 4 °C and 28 °C up to 60 days. The work evaluated the effectiveness of cocktail of four phages in reducing
Salmonella
spp. in four different food matrices (liquid egg, eggshell, milk, lettuce). A maximum of 1.7 log reduction in
Salmonella
spp
.
was achieved upon treatment of liquid eggs with phage cocktail for 72 h at 4 °C. In milk, the application of phage cocktail reduced recoverable
Salmonella
spp. by 1.9 log and 1.8 log at 28ºC (6 h) and 4ºC (72 h), respectively. A significant 2.9 log reduction of
Salmonella
spp. was obtained in eggshell after a 6 h incubation and
Salmonella
spp. was beyond detection level after 24 h at 28ºC. The application of cocktail also reduced
Salmonella
spp. beyond the detectable level in lettuce after 8 h at 28 °C. Our results indicated considerable stability of phages in different food matrices. Taken together, our findings establish the potential effectiveness of the bacteriophage cocktail as a biocontrol agent for
Salmonella
spp. in different food matrices.
Zinc oxide and multiwall carbon nanotubes ZnO/(MWCNT) composites were synthesised using wet chemical method and annealed at 400 °C for 1 h. They were studied for their microstructure, morphology, ...optical, electrical and gas sensing properties. SEM analysis showed uniform hexagonal disc like structure of ZnO within the fibers of MWCNT. XRD pattern indicated that the crystalline nature of the sample with hexagonal wurtzite phase. The crystallite size was reduced due to the increased MWCNT concentration. Optical band gap was determined using Tauc's plot. It was decreased from 3.12eV to 2.97eV with increasing MWCNT concentration. FTIR spectra confirmed the Zn–O stretching and carboxylic group in the ZnO composite samples. I–V curve showed the ohmic nature of sample. 1-butanol sensing properties were studied at the room temperature of 27 °C in static mode. Experiment results indicated a highest sensitivity with ZnO at 500 ppm. Whereas ZnO/MWCNT composite sensor showed faster response and recovery times.
•Synthesised particles are studied for their microstructure, morphology, optical and electrical characteristics.•A uniform hexagonal disc like ZnO structure is obtained with few pores due to annealing at high temperature (4000C). The MWCNT fibers surrounding the ZnO provides a path for electron conduction.•Gas sensing study at room temperature (270 C) towards the target gas (1-butanol) at various ppm levels (50ppm -500 ppm) showed a better sensitivity (5.1) for pure ZnO as compared to ZnO/MWCNT nano composites. But ZnO/MWCNT nano composites showed faster response and recovery time (∼10 sec and 18 sec) at 100 ppm.
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