Multiterminal high-voltage dc (HVdc) grid has huge potential in long-distance bulk power transmission. Such HVdc structures have reached greater heights due to the concept of hybrid interconnections ...in HVdc by promoting power-sharing between different technologies of HVdc terminals. Modular multilevel converter (MMC) technology has further paved its way to act as a high-power HVdc transformer, which has encouraged the invention of many dc-dc MMC topologies. This article furthers the operation of an existing modular dc-dc converter for hybrid interconnection by proposing philosophies that establish its operation when one of the poles of an HVdc terminal is removed while the other terminal is bipolar. Moreover, hybrid arms, comprising of both full-bridge and half-bridge submodules are used in the converter, instead of only the full-bridge, to optimize the number of devices. The effectiveness of the proposed philosophies is demonstrated in multiterminal operation by simulation in the MATLAB/Simulink platform. The performance of these philosophies is also verified in a down-scaled laboratory prototype.
In this article, a modular multilevel dc-dc converter philosophy is proposed which can form an effective interlink to exchange power between line commutated converter (LCC) based high voltage direct ...current (HVdc) link and voltage source converter-based HVdc grid of same or different voltage levels. The converter exhibits symmetric four quadrant operation irrespective of the voltage polarity in the LCC-based HVdc link. In the event of reversal of power flow by reversing the voltage polarity in the LCC-based HVdc link, the power flow direction/magnitude through the interlink can be made to remain unchanged without the need of any extra switching arrangement. The working principle is explained analytically and its operation is validated by simulation as well as experimental results.
also known as water spinach, is an aquatic non-conventional leafy vegetable and is considered a healthy and seasonal delicacy in ethnic food culture. The study revealed the presence of rich chemical ...and biochemical composition in
and antioxidant activities. Moreover, the plant extracts demonstrated significant DNA damage prevention activity against UV/H
O
-induced oxidative damage. High-resolution mass spectrometric analysis by UPLC-qTOF-MS/MS resulted in the identification of over 65 different compounds and 36 important secondary metabolites. Most of the compounds identified represented polyphenolic compounds,
polyphenol glycosides and phenolic acids, followed by alkaloids and terpenoids. A UPLC-DAD method was developed and quantified for 10 different polyphenolic compounds. Out of all the metabolites examined, a significant number of compounds were reported to have various bioactive properties, including antibacterial, antiviral, antitumor, hepatoprotection, and anti-depressant effects. The plant extracts were found to contain various compounds, including euphornin, lucidenic acid, and myricitin glycosides, which possess significant medicinal value. Metabolite analysis utilizing GC-MS revealed the presence of various fatty acids, amino acids, sugars, and organic acids. The analysis revealed the presence of essential unsaturated fatty acids such as α-linolenic acid as well as beneficial substances such as squalene., The evaluation of glycemic control activity was carried out by comprehending the inhibitory potential of α-amylase and α-glucosidase, outlining the kinetics of the inhibition process. The inhibitory activities were compared to those of acarbose and revealed stronger inhibition of α-glucosidase as compared to α-amylase. Furthermore, the mechanism of inhibition was determined using
analysis, which involved molecular docking and molecular dynamic simulation of the identified IA phytochemicals complexed with the hydrolase enzymes. The study generates convincing evidence that dietary intake of
provides a positive influence on glycemic control along with various health-protective and health-promoting benefits.
The northeastern depressed region of Bangladesh is highly susceptible to recurrent flash flooding due to excessive rainfall over these areas and in the upstream hilly regions. Two such severe ...pre-monsoon flash flood events occurred in 2016 and 2017. This research attempts to forecast both flash flood events using a coupled atmospheric-hydrological numerical weather prediction (NWP) model, namely the weather research and forecasting (WRF) model. The ARW (Advanced Research WRF) model is able to predict the rainfall over these areas with a lead time of 91 h. However, the discharge and water level are overestimated by the WRF-Hydro model. The model predicts a flash flood with a lag of approximately 12 h with respect to the highest amount of rainfall. The overall performances of the models were satisfactory. The two parameters, rainfall and subsequent discharge, which are required for delineation of lag time, were almost precisely simulated. Simulated values also had fewer errors, justified by the root mean squared error (RMSE) and mean absolute error values. The Nash–Sutcliffe efficiency criterion scores for model-derived discharge were close to 1.0, and the RMSE-observation standard deviation ratio scores were less than 0.5. This finding proves that the NWP models could be considered for forecasting flash flood events over selected areas of Bangladesh.
One important characteristic of modular multilevel converter (MMC) is the existence of circulating current, which consists of a dc component and a series of undesirable even-order (predominantly ...second-order) harmonics. However, only the dc part of the circulating current is required for power balance, the ac harmonics are unwanted. These undesirable harmonics should be suppressed to reduce device stress and power losses. Most state-of-the-art circulating current suppression techniques employ separate controllers to generate the arm reference voltage for circulating current suppression. This paper proposes an alternate approach, eliminating the need of any additional control loop. Generation of undesirable circulating current is prevented inherently in the modulation stage. Reduced switching frequency sorting algorithm based modulation framework is employed to ensure reduced switching loss. Suitability of the proposed method is validated by experiments performed on a three-phase laboratory prototype of MMC. Steady state and transient operation of the MMC in grid-connected condition is studied.
The present work deals with the design and performance analysis of high frequency resonant inverter based Induction Heating (IH) System employing Boost Power Factor Correction (PFC) technique to ...overcome the problems due to EMI and RFI. Most of the existing techniques use passive filters for harmonics attenuation that fails to meet the present day requirement because of drawbacks like considerably high THD, poor dynamic performance, etc. This paper presents a new control approach for boost PFC based on inner and outer loops to eliminate the problems due to harmonics in the IH system. The equivalent circuit parameter model of the IH system has been used to analyze the presence of harmonics and the incorporation of boost PFC at the input of the system shows its elimination as per the stringent EMI-RFI regulations. Moreover, attention has been paid off to the design algorithm of the boost PFC and a detailed mathematical analysis has been done to outline an approach for its parameter selection. A comparative analysis of the IH system with and without the incorporation of the boost PFC has been done in terms of the THD in the input current waveform. The findings of the present work show that the incorporation of Boost PFC eliminates the harmonics in the IH system in a better manner than the existing techniques. Doi: 10.28991/HIJ-2021-02-02-05 Full Text: PDF
This study aimed at analysing the effects of coconut (Cocos nucifera L.) kernel extract (CKE) on oxidative stress, C-MYC proto-oncogene, and tumour formation in a skin cancer model. Tumorigenesis was ...induced by dimethylbenzaanthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA). In vitro antioxidant activity of CKE was assessed using 2, 2-diphenyl-1-picrylhydrazyl (DPPH), hydrogen peroxide (H2O2), total phenolic and flavonoid content assays. CKE showed a higher antioxidant activity then ascorbic acid (*P < 0.05, ***P < 0.0001). HPLC and NMR study of the CKE revealed the presence of lauric acid (LA). Following the characterization of CKE, mice were randomly assigned to receive DMBA/TPA Induction and CKE treatment at different doses (50, 100, and 200 mg/kg) of body weight. LA 100 mg/kg of body weight used as standard. Significantly, the CKE200 and control groups' mice did not develop tumors; however, the CKE100 and CKE50 treated groups did develop tumors less frequently than the DMBA/TPA-treated mice. Histopathological analysis revealed that the epidermal layer in DMBA-induced mice was thicker and had squamous pearls along with a hyperplasia/dysplasia lesion, indicating skin squamous cell carcinoma (SCC), whereas the epidermal layers in CKE200-treated and control mice were normal. Additionally, the CKE treatment demonstrated a significant stimulatory effect on the activities of reactive oxygen species (ROS), glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD), as well as an inhibitory effect on lipid peroxidase (*P < 0.05, **P < 0.01, ***P < 0.001, ***P < 0.0001) and c-MYC protein expression (*P < 0.05, **P < 0.01, ***P < 0.001, ***P < 0.0001). In conclusion, CKE prevents the growth of tumors on mouse skin by reducing oxidative stress and suppressing c-MYC overexpression brought on by DMBA/TPA induction. This makes it an effective dietary antioxidant with anti-tumor properties.
•Coconut kernel extract reduces oxidative stress, C-MYC expression, and tumor formation in skin cancer model.•Lauric Acid is present in CKE. Compared to ascorbic acid, CKE has a higher potential for antioxidants.•CKE treatment inhibits tumor development by reducing c-MYC overexpression and enhancing antioxidant activities.•CKE's antioxidant property delays or inhibits skin cancer in mice revealing its potent anticancer properties.
High voltage dc (HVdc) transmission has gradually gained its popularity in long distance transmission of power. The possibility of multi-terminal HVdc network has further projected HVDC as a ...potential mode of power trading across geographical boundaries. The emergence of modular multilevel converter (MMC)-based dc-dc converters has led to the interconnection of HVdc networks across voltage levels, converter technologies and line topologies. This paper puts forward a topological modification in an existing MMC-based dc-dc converter topology, acting as a hybrid interconnect between different converter technologies, for interface of an asymmetric monopolar voltage source converter (VSC) and a bipolar line commutated converter (LCC)-based HVdc links. The proposed operation of the topology is validated experimentally in a down-scaled laboratory prototype. The proposed topology is further investigated for short-circuit fault conditions in any of the poles of HVdc bus and appropriate fault mitigation strategies are adopted for short-cicuit fault in both LCC and VSC bus. The fault mitigation strategies are validated by simulation in Matlab/Simulink platform.
A modular dc-dc converter topology is discussed in this paper which provides an economic solution on existing modular multilevel converter (MMC) based dc-dc converters for forming a hybrid interlink ...in high voltage dc (HVdc) network. The number of semiconductor devices is optimized by using hybrid MMC to minimize losses and at the same time ensure dc fault clearance capability. The topology is demonstrated for three modes of operation of the dc-dc converter such as bipolar VSC to bipolar LCC, bipolar VSC to monopolar LCC and monopolar VSC to bipolar LCC dc buses with the help of simulation results in Matlab/Simulink.
Introduction
The safety and quality of many medicinally important herbs are compromised since farmers and small organizations are involved in the cultivation, aggregation, and primary processing of ...these herbs. Such organizations often lack adequate quality control facilities. To improve the safety and quality of herbal products, simple, rapid, and affordable quality control systems are required.
Objectives
The aim of this study was to assess the suitability of microwave oven‐drying for moisture content (MC) determination and sample preparation of herbs in small organizations.
Methods
Microwave oven‐drying (720 W) and convective oven‐drying at 105°C for MC determination were compared. The effects of three different drying methods (microwave oven‐drying, low‐temperature convective drying, and freeze‐drying) on in vitro antioxidant and polyphenol oxidase (PPO) activity were determined, similarity analysis was conducted using HPLC signature spectra, and validation was performed with LC‐MS focusing on one herb.
Results
Microwave oven‐drying at 720 W significantly reduced the drying time (from hours to minutes), whereas the spatial variation of temperature in convective ovens set at 105°C can cause about 10% underestimation of MC. Microwave oven‐drying showed similar macro‐properties like freeze‐drying and higher extractability (10%–20%) and in vitro antioxidant capacity (33%–66%) and lower PPO activity compared to low‐temperature convective drying. HPLC signature spectra revealed strong similarity of soluble components between freeze‐dried and microwave oven‐dried herbs. LC‐MS analysis demonstrated more common compounds between freeze‐dried and microwave oven‐dried Centella asiatica extracts, whereas convective tray‐dried samples had fewer compounds common with samples obtained by freeze‐drying or microwave oven‐drying.
Conclusions
Microwave oven‐drying is rapid (tens of min) and shows small batch‐to‐batch variation compared to oven‐drying at 105°C. The in vitro antioxidant assays and signature spectra can be used for assessing the source and purity or quality of a specific herb variety.
The research explores the suitability of microwave oven‐drying for moisture content determination and sample preparation for quality control of herbal materials. Results indicate that microwave oven‐drying significantly reduces drying time, exhibits properties similar to freeze‐drying, and enhances extractability and antioxidant capacity. HPLC and LC‐MS analyses reveal that microwave oven‐drying can protect many of the target bioactive in herbs. In conclusion, microwave oven‐drying offers a rapid and reliable alternative to traditional oven‐drying methods for ensuring herb safety and quality in small‐scale production.
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