Dynamický model dvou synchronních generátorů propojených dlouhou přenosovou linkou

Due to the large desire to utilize transmission networks for more flexible power interchange transactions, the high requirement for power system dynamic analysis has grown significantly in recent years. While dynamics and stability have been studied for years in a long term planning and design environment, there is a recognized need to perform this analysis in a weekly or even daily operation environment. The dynamic performance of power systems is important to both the system organizations, from an economic viewpoint, and society in general, from a reliability viewpoint. The analysis of power system dynamics and stability is increasing daily in terms of number and frequency of studies, as well as in complexity and size. Dynamic phenomena have been discussed according to basic function, time-scale properties, and problem size. In a realistic system, electric power system consist of the interconnection of large numbers of synchronous generators operating in parallel. These generators are connected together by transmission lines. In the operation process, the rotor angles of generators swing relatively to another one during transients. Under disturbances the synchronism of machines in system is achieved when maintaining equilibrium between electromagnetic and mechanical torques. In other words, a system is unstable if the angle difference between two interconnected generators is not sufficiently damped in the evaluation time. The instability typically occurs as increasingly swings angle generators leading to some loss of synchronism with other generators. One of the constraints for long distance AC transmission is the large phase angular difference which is required to transmit a given amount of power. Therefore, in order to gain dynamic behavior characteristics of system when subject to disturbances, this work will focus on modeling two synchronous generators linked by long AC transmission line. Within the content of this work, for the analysis of system modes, the system is computed based on a detailed model of synchronous machines, transformers, loads and the long transmission line including voltage dynamics and frequency response. The system power equilibrium equations are derived and linearized for the small disturbance stability analysis and some transient disturbances. These results can serve to define stability margin of a power system. This stability limit would play important role in improving designs of the different system connection conditions.V posledních dynamických letech významně vzrostly nároky na pružnost výměny elektrické energie, což klade zvýšené nároky na dynamickou analýzu energetických systémů. Zatím co dynamika a stabilita sítí je dlouhodobě studována při dlouhodobém plánování, je nyní zapotřebí k zamezení nežádoucích výpadků přenosu energie tuto analýze provádět daleko rychleji on-line s okamžitými on-line naměřenými daty. Dynamicky stabilní výkon přenášený v energetických systémech je důležitý jak z organizačních důvodů, tak z ekonomického hlediska spolu s hlediskem spolehlivosti. Analýzou dynamiky a stability energetických systémů se v současnosti zabývá velké množství aktuální odborné literatury. Literární studie se liší podle detailnosti popisu systému a jeho velikosti. Dynamické jevy byly diskutovány podle základní funkce, podle vlastností, podle časového měřítka atd. V reálném systému se elektrická energetická soustava skládá z propojení velkého počtu synchronních generátorů pracujících paralelně. Tyto generátory jsou propojeny přenosovými linkami. Při provozním procesu se úhly rotorů generátorů v průběhu přechodových otáček relativně otáčejí jiným. Při poruchách dochází k synchronizaci strojů v systému při zachování rovnováhy mezi elektromagnetickými a mechanickými momenty. Jinými slovy, systém je nestabilní, pokud úhlový rozdíl mezi dvěma propojenými generátory není dostatečně tlumen. Nestabilita se zpravidla vede ke ztrátě synchronizace s ostatními generátory a k rozpadu okrsku sítě vypnutím proudových, napěťových a výkonových ochran. Jedním z omezení stability přináší pro dálkový přenos dlouhým vedením. Dlouhé metalické vedení zvyšuje fázový úhlový rozdíl, který je nutný k přenosu daného výkonu střídavým proudem. Proto se za účelem získání popisu dynamického chování systému při poruchách soustředí tato práce na modelování dvou synchronních generátorů propojených dlouhým AC přenosovým vedením. V rámci této práce je pro analýzu systémových režimů systém vypočítán na základě podrobného modelu synchronních strojů, transformátorů, zátěží a dlouhé přenosové linky včetně dynamiky napětí a frekvenční odezvy

PRELIMINARY PHYTOCHEMICAL ANALYSIS OF LEAF EXTRACTS OFTHUJA ORIENTALIS (L.) ENDL

Abstract The objective of the present study was to investigate the presence of various phytochemicals from the methanolic, ethanolic, aqueous and ethyl acetate extracts of leaf extracts ofThujaorientalis (L.) Endl.Preliminary phytochemical screening of the extracts revealed the presence of alkaloids, flavonoids, terpenoids,tannins, phenols, anthraquinone, glycosides,oils and fats, and carbohydrates. The present study provides evidence that solvent extracts of Thujaorientalis (L.) Endlcontains medicinally important bioactive compounds and this justifies the use of plant species as traditional medicine for treatment of various diseases

Carrot hairy roots (Daucus carota L.) characterisation and optimisation for high β‐carotene extraction

Hairy roots are widely known as a biological system for the production of highly diverse biomolecules. β‐carotene – a precursor for vitamin A – is known to be an anti‐oxidant and anti‐gastric cancer and protection agent against cardiovascular disease, heart disease and stroke. β‐carotene has been chemically synthesised and consumed by humans. However, the chemical process often produces a by‐product that may be harmful to human health. Therefore, this study established a protocol to induce hairy roots (HRs) from a Vietnamese carrot variety and produce natural β‐carotene. The Rhizobium rhizogenes ATCC15834 harbouring Ri plasmid and a Vietnamese carrot variety were used as materials for genetic transformation and HR induction studies. The result showed that approximately 50 HR lines were obtained. Culture medium supplemented with 30 mg/L of sucrose that gave the highest biomass of HR was shown in carrot HR line 30, which had a doubling time of 6.5 days. The highest content of β‐carotene extraction, at 128 mg/100g hairy roots, was achieved with a ratio volume (v/v) of 2‐propanol and plant samples of 20:1, followed by two hours’ incubation with 2‐propanol at 60 °C. Our study reveals a highly efficient protocol for Vietnamese carrot hairy root establishment and multiplication. A very efficient protocol for β‐carotene extraction from the hairy root was established to produce natural β‐carotene that achieves the same β‐carotene quantity as that produced by normal roots. This study provides new insight into the production of high‐content and natural β‐carotene for therapeutic application

Para-Social Interaction and Trust in Live-Streaming Sellers

Live streaming is one of the modern methods that allows sellers to create, transmit, or broadcast some content on the internet in real-time, and it has been used by many small individual merchants. Understanding how live streaming contributes to online consumption is becoming increasingly important in social commerce as the live-streaming industry has grown more and more popular. However, the number of studies on live streaming is still quite limited in Vietnam. Therefore, this research will look at the mechanism that enables live streaming to boost customer trust in streamers. Using PLS-SEM on a sample of 360 respondents who viewed selling live streams on social network sites in Vietnam, we discovered that other members' endorsement, value similarity, hedonic value, and utilitarian value contribute to good para-social interaction. Next, utilitarian and hedonic values, streamer product expertise, and para-social interaction all positively affect trust in the streamers. The findings could help live-streaming sellers better understand their social interactions with viewers, resulting in increased customer trust. Doi: 10.28991/ESJ-2023-07-03-06 Full Text: PD

Sintering behavior and physical properties of Bi0.5(Na1–xKx)0.5SnO3 lead-free ceramics

In this study, Bi0.5(Na1–xKx)0.5SnO3 (BNKS) ceramics (x = 0, 0.1, 0.2, 0.3, and 0.4) were fabricated via ultrasound wave before milling. The time of ball milling decreased from 20 to 1 h. The X-ray diffraction patterns show that the BNKS has a single-phase structure. When the potassium content increases, the phase structure of the ceramics changes from rhombohedral to tetragonal. When sintered at 1100 °C and x = 0.2, the ceramics’ physical properties are the best with the mass density of 5.59 g/cm3, the electromechanical coupling constants kp of 0,31 and kt of 0.27, the remanent polarization of      11.9 µC/cm; the dielectric constant εr of 1131, and the highest dielectric constant emax of 4800

TÀI NGUYÊN VỊ THẾ ĐẢO CỒN CỎ

Being a basaltic volcano, Con Co island is an isometric hill 2.3 km2 wide and 63 m high, located far 24 km from the mainland, and guards the entrance to the Gulf of Tonkin. It is isolated, but unique in location, and relatively closed to mainland. Despite its small size, the characteristics of morphology and spatial structures, geological composition, area, height, ecological landscape, dynamics and stability of the island... create great values of geo-natural position resources and favorable environment for island residents. Regarding geo - economic position resources, the island is a district under the Quang Tri province, a priority location for development of the country’s marine and island economy, and the economic centre at the entrance of the Gulf of Tonkin. This is also a convenient site for the development of marine economic sectors such as fishery, natural conservation, services - tourism and some others. In terms of geo-political position resources, the island has tremendous advantages for the sovereignty, sovereign rights and national interests at sea. As an outpost at the highly sensitive geo-political area, the Con Co island has the great value of defense, as a solid military base in the entrance of the Gulf of Tonkin and the most important link in the line of defense from coastal islands in the North Centre. It possesses many valuable cultural heritages, especially the heroic relics during the war against the US.Đảo Cồn Cỏ nguồn gốc núi lửa bazan, dạng đồi đẳng thước rộng 2,3 km2, cao 63 m, nằm cách xa bờ 24 km. Đảo có vị trí lẻ loi ở cửa vịnh Bắc Bộ và khá gần bờ Việt Nam. Mặc dù diện tích đảo nhỏ, nhưng các đặc điểm về hình thể và cấu trúc không gian, cấu tạo địa chất; diện tích, độ cao và cảnh quan sinh thái; động lực và tính ổn định... đã tạo ra giá trị lớn cho đảo về tài nguyên địa - tự nhiên và môi trường sinh cư thuận lợi cho các loài sinh vật và con người. Về giá trị vị thế địa - kinh tế, Cồn Cỏ thuộc đơn vị hành chính cấp huyện thuộc tỉnh Quảng Trị, là vị trí ưu tiên đối với phát triển kinh tế biển - đảo của đất nước; là vị trí trung tâm của không gian kinh tế khu cửa vịnh Bắc Bộ. Đây là một địa bàn thuận lợi cho phát triển các lĩnh vực kinh tế biển như thủy sản, bảo tồn biển, dịch vụ - du lịch cùng với các loại hình dịch vụ khác. Về giá trị vị thế địa - chính trị, đảo Cồn Cỏ có giá trị to lớn đối với việc bảo vệ các quyền và lợi ích quốc gia của Việt Nam trên biển. Là đảo tiền tiêu nằm trong vùng địa - chính trị nhạy cảm cao, đảo có giá trị lớn về phòng thủ, là một cứ điểm quân sự vững chắc ở vùng cửa vịnh Bắc Bộ và mắt xích quan trọng nhất trong phòng tuyến các đảo ven bờ Bắc Trung Bộ. Cồn Cỏ có các giá trị di sản văn hoá biển đảo, đặc biệt là những chiến tích anh hùng trong thời chiến tranh chống Mỹ

TỔNG HỢP VẬT LIỆU Ni/UiO-66 THEO PHƯƠNG PHÁP TRỰC TIẾP VÀ GIÁN TIẾP

An archetypal metal-organic framework, UiO-6,6, synthesized with the solvo-thermal method, has a large specific surface area of 1071 m2·g–1. This material was modified with NiCl2 in the direct (Nix(tt)/UiO-66) and indirect (Nix(gt)/UiO-66) methods. The two modified materials were characterized by using powder X-ray diffraction, scanning electron microscopy, and infrared spectroscopy. Their crystalline and chemical structure is not much different. However, the thermal and porous properties differ from each other.UiO-66 là họ vật liệu khung hữu cơ kim loại tổng hợp bằng phương pháp nhiệt dung môi có diện tích bề mặt riêng lớn (1071 m2·g–1). Vật liệu UiO-66 này được biến tính bằng NiCl2 theo phương pháp trực tiếp (Nix(tt)/UiO-66) và gián tiếp (Niy(gt)/UiO-66). Kết quả đặc trưng hai vật liệu biến tính này bằng nhiễu xạ tia X, hiển vi điện tử quét và phổ hồng ngoại khác nhau không đáng kể. Tuy nhiên, phân tích nhiệt trọng lượng và đẳng nhiệt hấp phụ – khử hấp phụ N2 cho thấy có sự khác nhau giữa các phương pháp tổng hợp

NGHIÊN CỨU KHẢO SÁT VÀ ĐÁNH GIÁ CÁC ĐIỀU KIỆN ẢNH HƯỞNG XỈ THÉP HẤP PHỤ VÀ LOẠI BỎ ARSEN TRONG NƯỚC

This paper presents the results of this research which utilizes solid waste resources in the environment, namely steel slag, to adsorp and remove arsenic in water. The study conducted empirical processes based on the processes in the experimental conditions affecting arsenic adsorption and removal by steel slag in contaminated water: concentration, steel slag size, steel slag weight, pollution concentration, temperature, symbiotic ions. The research results show: The lower initial solution concentration is, the more easily adsorption equilibrium can achieve, the higher initial concentration is, the longer it takes to reach adsorption equilibrium; the smaller steel slag particle is, the more easily adsorption equilibrium can reach; the larger particle size, the longer the time to reach adsorption equilibrium; the more increasing the number of steel slag particles, the greater the pollutant adsorption, the higher the removal efficiency; initial pH concentration affects As adsorption of steel slag (III); influence of temperature on As adsorption of steel slag (III) is not clear; different ions (NO3-, Cl‑, F-, SO42- and PO43-) intervene in As adsorption of steel slag (III) in solution. Thus, the choice of steel slag as the material to adsorb and remove arsenic in water is the optimal method, bringing economic efficiency, environmental protection and practical application.Bài báo trình bày kết quả nghiên cứu này là tận dụng nguồn chất thải rắn trong môi trường là xỉ thép đưa vào hấp phụ và loại bỏ arsen trong nước. Việc nghiên cứu thực hiện các quy trình thực nghiệm theo các quy trình thực nghiệm ở các điều kiện ảnh hưởng đến tính năng xỉ thép hấp phụ và loại bỏ arsen trong nước ô nhiễm: nồng độ, kích cỡ, khối lượng hạt xỉ thép cần thiết, nồng độ ô nhiễm, nhiệt độ, các ion cộng sinh. Kết quả nghiên cứu cho thấy: nồng độ dung dịch ban đầu càng thấp cân bằng hấp phụ càng dễ đạt được, nồng độ dung dịch ban đầu càng cao thì phải mất thời gian dài mới đạt cân bằng hấp phụ; kích thước hạt xỉ thép càng nhỏ cân bằng hấp phụ càng dễ đạt đến, kích thước hạt lớn thì thời gian đạt cân bằng hấp phụ sẽ kéo dài; lượng hạt xỉ thép gia tăng càng cao thì hấp phụ lượng chất ô nhiễm càng lớn, hiệu quả loại bỏ càng nhiều; nồng độ pH ban đầu ảnh hưởng đến tính năng xỉ thép hấp phụ As (III); ảnh hưởng của nhiệt độ đến tính năng xỉ thép hấp phụ As (III) không rõ ràng; các ion khác nhau (NO3-, Cl-, F-, SO42- và PO43-) can thiệp đến tính năng xỉ thép hấp phụ As (III) trong dung dịch. Như vậy, lựa chọn xỉ thép làm vật liệu hấp phụ và loại bỏ arsen trong nước là phương thức tối ưu, mang lại hiệu quả kinh tế, bảo vệ môi trường và tính ứng dụng cao có thể đưa vào áp dụng thực tiễn

RMDM: A Multilabel Fakenews Dataset for Vietnamese Evidence Verification

In this study, we present a novel and challenging multilabel Vietnamese dataset (RMDM) designed to assess the performance of large language models (LLMs), in verifying electronic information related to legal contexts, focusing on fake news as potential input for electronic evidence. The RMDM dataset comprises four labels: real, mis, dis, and mal, representing real information, misinformation, disinformation, and mal-information, respectively. By including these diverse labels, RMDM captures the complexities of differing fake news categories and offers insights into the abilities of different language models to handle various types of information that could be part of electronic evidence. The dataset consists of a total of 1,556 samples, with 389 samples for each label. Preliminary tests on the dataset using GPT-based and BERT-based models reveal variations in the models' performance across different labels, indicating that the dataset effectively challenges the ability of various language models to verify the authenticity of such information. Our findings suggest that verifying electronic information related to legal contexts, including fake news, remains a difficult problem for language models, warranting further attention from the research community to advance toward more reliable AI models for potential legal applications.Comment: ISAILD@KSE 202

In vitro antioxidant activity and bioactive compounds from Calocybe indica

Nowadays, the use of mushrooms in medicine is ubiquitous and has achieved particular success. The antioxidants in mushrooms can deactivate free radicals. This study assesses the antioxidant potential of mushroom Calocybe indica with the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging methods and the total antioxidant capacity. The mushroom’s ethanol extract exhibits acceptable activity with a low IC50 value (240.11 μg/mL), approximately 2.9 times lower than that of the mushroom Ophiocordyceps sobolifera extract. The ABTS scavenging rate of the extract is around 60% at 500 µg/mL, and the total antioxidant capacity is equivalent to 64.94 ± 1.03 mg of GA/g or 77.42 ± 0.42 μmol of AS/g.  The total phenolics, flavonoids, polysaccharides, and triterpenoids are equivalent to 29.33 ± 0.16 mg of GAE/g, 17.84 ± 0.11 mg of QUE/g (5.04 ± 0.04%), and 4.96 ± 0.04 mg of oleanolic acid/g, respectively. Specifically, the total triterpenoid content has been reported for the first time. The mushroom can have potential biomedical applications