In vitro evaluation of commercially available theophylline sustained release tablets in Pakistan

The dissolution behavior of five commercially available brands of sustained release theophylline tablets was studied in phosphate buffer solutions of pH 1.2, 4.5, 5.5, 6.0 and 7.5 at 37 °C using the USP dissolution apparatus II (paddle method). Drug concentration in the samples was determined spectrophotometrically at 272 nm. For predicting the release characteristics of theophylline from selected commercially available tablets the data obtained in the dissolution studies was fitted into various mathematic models defining kinetic parameters of drug release like zero-order rate equation, first-order rate equation, Hixen-crowell cube root law, Higuchi equation and Korsemeyer-Peppas model. Tablets were subjected to weight variation test, hardness, drug content and in vitro release studies. The present study revealed that drug release increases with the increase of pH of the dissolution medium and also varies from brand to brand. Among the five selected brands, B1 and B4 showed better pH dependency and drug release behaviour. It has been suggested that possible reasons for difference in dissolution or drug release behaviour are the difference in the manufacturing techniques and the quantity of hydrophobic excepients used by different manufacturers, which retard the penetration of dissolution medium and ultimately decreases availability of drug in the solution.Colegio de Farmacéuticos de la Provincia de Buenos Aire

In vitro evaluation of commercially available theophylline sustained release tablets in Pakistan

The dissolution behavior of five commercially available brands of sustained release theophylline tablets was studied in phosphate buffer solutions of pH 1.2, 4.5, 5.5, 6.0 and 7.5 at 37 °C using the USP dissolution apparatus II (paddle method). Drug concentration in the samples was determined spectrophotometrically at 272 nm. For predicting the release characteristics of theophylline from selected commercially available tablets the data obtained in the dissolution studies was fitted into various mathematic models defining kinetic parameters of drug release like zero-order rate equation, first-order rate equation, Hixen-crowell cube root law, Higuchi equation and Korsemeyer-Peppas model. Tablets were subjected to weight variation test, hardness, drug content and in vitro release studies. The present study revealed that drug release increases with the increase of pH of the dissolution medium and also varies from brand to brand. Among the five selected brands, B1 and B4 showed better pH dependency and drug release behaviour. It has been suggested that possible reasons for difference in dissolution or drug release behaviour are the difference in the manufacturing techniques and the quantity of hydrophobic excepients used by different manufacturers, which retard the penetration of dissolution medium and ultimately decreases availability of drug in the solution.Colegio de Farmacéuticos de la Provincia de Buenos Aire

Red shifting of absorption maxima of phenothiazine based dyes by incorporating electron-deficient thiadiazole derivatives as π-spacer

AbstractThis study was carried out to design phenothiazine based dyes by incorporating electron-deficient thiadiazole derivatives as π-spacer. Density functional theory and time-dependent density functional theory calculations of the geometries, electronic structures and absorption spectra of the dyes before and after binding to titanium oxide were carried out. Effects of the electron-deficient units on the spectra and electrochemical properties have been investigated. Compared with the reference compound CS1A, Dyes 1–4 display remarkably enhanced spectral responses in the red portion of the solar spectrum. The newly designed dyes demonstrate desirable energetic and spectroscopic parameters, and may lead to efficient metal-free organic dye sensitizers for DSSCs

Control and Protection of MMC-Based HVDC Systems: A Review

The voltage source converter (VSC) based HVDC (high voltage direct current system) offers the possibility to integrate other renewable energy sources (RES) into the electrical grid, and allows power flow reversal capability. These appealing features of VSC technology led to the further development of multi-terminal direct current (MTDC) systems. MTDC grids provide the possibility of interconnection between conventional power systems and other large-scale offshore sources like wind and solar systems. The modular multilevel converter (MMC) has become a popular technology in the development of the VSC-MTDC system due to its salient features such as modularity and scalability. Although, the employment of MMC converter in the MTDC system improves the overall system performance. However, there are some technical challenges related to its operation, control, modeling and protection that need to be addressed. This paper mainly provides a comprehensive review and investigation of the control and protection of the MMC-based MTDC system. In addition, the issues and challenges associated with the development of the MMC-MTDC system have been discussed in this paper. It majorly covers the control schemes that provide the AC system support and state-of-the-art relaying algorithm/ dc fault detection and location algorithms. Different types of dc fault detection and location algorithms presented in the literature have been reviewed, such as local measurement-based, communication-based, traveling wave-based and artificial intelligence-based. Characteristics of the protection techniques are compared and analyzed in terms of various scenarios such as implementation in CBs, system configuration, selectivity, and robustness. Finally, future challenges and issues regarding the development of the MTDC system have been discussed in detail

Design of an integrated sub-6 GHz and mmWave MIMO antenna for 5G handheld devices

The authors appreciate financial support from Universidad Carlos III de Madrid and the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant Agreement No 801538. As well as, this work was partially supported by the Antenna and Wireless Propagation Group (https://sites.google.com/view/awpgrp/home accessed on 16 June 2021) and from the Researchers Supporting Project number (RSP-2021/58), King Saud University, Riyadh, Saudi Arabia

Comparative Performance Study of Dissolved Gas Analysis (DGA) Methods for Identification of Faults in Power Transformer

© 2023 Abdul Wajid et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/The power transformer is an essential component of the electrical network that can be used to step up and step down voltage. Dissolved gas analysis (DGA) is the most reliable method for the identification of incipient faults in power transformers. Various DGA methods are used to observe the generated key gases after oil decomposition. The main gases included are hydrogen (H2), ethylene (C2H4), acetylene (C2H2), methane (CH4), and ethane (C2H6). There is a lack of research that can compare the performance of various DGA methods in identification of faults in power transformer. In addition, it is also not clear which DGA method is optimal for identification of faults in power transformer. In this paper, the comparative performance study of seven DGA methods such as Roger’s ratio, key gas, IEC ratio, the Doernenburg ratio, the Duval triangle, three-ratio method, and the relative percentage of four gases is carried out in order to identify the optimal technique for fault identification in transformer. The data of various power transformers installed in “RAWAT” NTDC grid station, Islamabad, and “UCH-II” power station, Balochistan, are considered for the comparative analysis. This analysis shows that the three-ratio method provides better performance than other DGA methods in accurately identifying the faults in power transformers. The three-ratio method has 90% accuracy in identifying the faults in power transformer.Peer reviewe

Quantification of carbon dioxide released from effervescent granules as a predictor of formulation quality using modified Chittick apparatus

Purpose: To develop a method for the measurement of carbon dioxide (CO2) released from effervescent formulations. Methods: Effervescent granules were prepared using sodium bicarbonate and citric acid by fusion and solvent-assisted granulation methods. The amount of CO2 released was determined from the maximum pressure of gas release, time profile of pressure gradient using modified Chittick apparatus and gravimetric changes following effervescence. Results: The amount of CO2 released from effervescent granules prepared by fusion method was 8.125, 8.763 and 7.98 mM/g measured by ideal gas equation, pressure gradient and gravimetric method, respectively. The formulation prepared by solvent-assisted granulation showed 5.525, 5.475 5.36 mM/g of carbon dioxide measured by the above three methods, respectively. The effervescent granules prepared by fusion method showed approximately 2 % loss in effervescence. However, approximately 39 % loss in effervescence was observed for the formulation prepared by solventassisted granulation. The commercial products showed a loss in effervescence in the range of 5 - 15%. Conclusion: Modified Chittick’s apparatus is a useful analytical tool for monitoring of the CO2 from effervescent granules as a function of method of preparation

Molekularna filogenija i genetička raznolikost domaćih jakova (Bos grunniens) u Pakistanu na temelju mitohondrijskih i mikrosatelitskih markera

The complete Cytchrome b gene and partial mtDNA control region were sequenced for the Pakistani domestic yak (Bos grunniens) within the Bovidae family. A total of 300 samples were genotyped using 27 bovine microsatellite markers from the Gilgit-Baltistan and Skardu regions of Pakistan. We identified a total of 35 mutations and 9 haplotypes based on D-loop sequences, with a haplotype and nucleotide diversity of 0.9640±0.051 and 0.02172±0.00224, respectively. For the Cyt b gene, a total of 23 variable sites and six different haplotypes were observed with 0.885±0.067 haplotype and 0.00989±0.003 nucleotide diversity. Phylogenetic analysis of D-loop and Cyt b gene suggested that domestic yak sequences cluster into two highly divergent maternal lineages (lineages I and II), while three haplogroups A, C, and D were identified of the six previously known haplogroups. Haplogroups A and C were dominant and widely distributed among all investigated yak samples. All microsatellites were polymorphic and a total of 138 alleles were observed, with average polymorphic information content (PIC) of 0.56 indicating their effectiveness. The average heterozygosity was observed at 0.6071 with allele diversity of 5.1111 and gene diversity of 0.4830. The implications of these findings can be applied for yak conservation.Za pakistanskog domaćeg jaka (Bos grunniens) iz obitelji šupljorožaca (Bovidae), sekvenciran je cjelokupni citokromni b gen i djelomice kontrolna regija mtDNK. Genoti¬pizirano je tri stotine uzoraka uporabom 27 goveđih mikrosatelitskih markera pasmine Gilgit-Baltistan i Skardu iz Pakistana. Identifi¬cirali smo ukupno 35 mutacija i 9 haplotipova na temelju sekvencija D-petlje uz haplotipsku i nukleotidnu raznolikost od 0,9640±0,051, od¬nosno 0,02172±0,00224. Za citokromni b gen, ukupno 23 varijabilne lokacije i šest različi¬tih haplotipova zamijećeno je s 0,885±0,067 haplotipskom i 0,00989±0,003 nukleotidnom raznolikošću. Filogenetska analiza D-petlje i citokromnog b gena ukazala je da se sekven¬ce domaćih jakova grupiraju u dvije vrlo di¬vergentne loze po majci (loza I i II), dok su identificirane tri haplogrupe A, C i D od ranije poznatih šest haplogrupa. Haplogrupe A i C bile su dominantne i široko rasprostranjene među svim istraženim uzorcima jakova. Svi mikrosateliti bili su polimorfni te je zamijeće¬no ukupno 138 alela, s prosječnim sadržajem polimorfne informacije (PIC) od 0,56 ukazu¬jući na njihovu učinkovitost. Zamijećena je prosječna heterozigotnost od 0,6071 s alelnom raznolikošću 5,1111 i genetskom raznolikošću 0,4830. Implikacije ovih nalaza mogu se rabiti za očuvanje populacije jakova

Estimation of multi-infeed HVDC inter converter direct current interaction in close electric proximity

This paper aims at investigating the direct current interaction between various converters of High Voltage Direct Current (HVDC) system, which lie in close electric proximity within the multi-infeed configuration. The interaction between converters in multi-infeed DC system are highly possible events which need to be evaluated in order to avoid the adverse operational results. The various indices such as multi-infeed interaction factor (MIIF) considering AC busbar voltages, local and concurrent commutation failures (CF) in converter stations under different AC disturbances, influence of AC system’s strength on fault recovery time (FRT), transient over-voltage (TOV) under permanent DC faults, voltage and power stability of multi-infeed DC system are comprehensively illustrated in literatures. However, there is lack of literature regarding the investigation of current interaction in multi-infeed DC system. Therefore, in this paper, a power flow approach is adopted to estimate the inter converter direct current interaction. An index, multi-infeed current interaction factor (MICIF) is proposed that can effectively depicts the interaction between converters. The MICIF index is verified through electromagnetic transient simulations of dual infeed HVDC system developed in PSCAD/EMTDC. The results show that MICIF index can accurately assess the interaction between different converter stations of HVDC system under steady and transient states