Term Sheet Research Articles

Multi-objective optimization of composite sandwich structures using Artificial Neural Networks and Genetic Algorithm

Sandwich structures offer significant opportunities to improve the performance of many industrial applications such as aerospace, automotive, and marine. The design of a composite sandwich structure is often challenging because it is driven by the balance between the weight and cost of these structures. In this paper, a multi-objective optimization model using a Genetic Algorithm (GA) and an Artificial Neural Network (ANN) is presented to evaluate a new optimization approach in terms of weight and cost minimization for the composite sandwich structures. Classical lamination and beam bending theories were used, along with Monte Carlo simulation, to generate the design data for the proposed composite sandwich structure, which is applied as a floor panel for a high-speed train. Multilayer feedforward neural networks were used for predicting safety factors, cost, and weight of the designed structure based on the following inputs: core density, core thickness, face sheet materials’ combinations, and applied load. The trained Neural Network model was able to predict the considered results with a good performance metric, namely the coefficient of determination (R2 = 0.99) and the Mean Square Error (MSE = 1.3·10−5).Multi-objective optimization for cost and weight minimization was performed with a Genetic Algorithm using the derived ANN model. The obtained Pareto front provided several non-dominated optimal points leading to insights on the optimization process. The Finite Element Method (FEM) was used to model the key points of the optimal designs (i.e. the design with the lowest cost, weight, and Pareto optimal points). The FEM and optimization results had a maximum deviation of about 8.9%, indicating a good agreement between the two techniques.The newly elaborated methodology demonstrates a new approach for obtaining the optimum design of the investigated composite sandwich structure constructed from honeycomb core and laminated face sheets in terms the cost and weight. The study concluded that the use of Carbon Fiber-Reinforced Plastic (CFRP) or Fiber-Metal Laminate (FML) face sheets results in significant weight savings of about 59.5% and 48.6%, respectively, compared to an all-aluminum sandwich structure.

Milkbasket takeover by Reliance Retail Venture Limited: the ethical dilemma

Learning outcomes After completion of the case study, the students would be able to comprehend the crisis at hand for Milkbasket, why did it resist Reliance’s takeover in the first place, then to evaluate the pros-cons and future prospects for the organization post-acquisition; to evaluate from an ethical standpoint the process of mergers and acquisitions using ethical frameworks to understand how, when, to whom and through what processes do mergers and acquisitions qualify the test of being ethical; and to analyse different hostile takeovers, especially through tender offers, proxy contests and toehold bidding strategy in this case. Case overview/synopsis Founded in 2015, Milkbasket was a micro-delivery start-up based in Gurugram (near New Delhi), India. Milkbasket would let its subscribers order till midnight and deliver groceries, milk and other everyday essentials to its subscribers before 7 a.m. next day. It had burnt a lot of cash and was facing difficulty in getting investors; as such they were engaged in discussions with many companies. Two of them – Reliance Retail Venture Limited and BigBasket – were not accepting the proposed valuation, but Milkbasket got term sheets from other two companies. Complexity academic level This case study can be used for graduate courses on strategic management, business ethics and corporate governance. This case study can also be used in corporate finance course to highlight the importance of making ethical/responsible judgements to protect stakeholder interests. Supplementary materials Teaching notes are available for educators only. Subject code CSS 3: Entrepreneurship.

Asistensi: raising capital for innovation in health insurance, migrants and remittances

Learning outcomes After completion of this case study, students will be able to describe the funding path for start-ups, including the amounts and profiles of the usual investors or sources of funds, according to the moment in their life cycle and the characteristics of the initiative; highlight the challenges faced by start-up founders in weak entrepreneurial ecosystems and risky institutional environments; and argue in favor of or against different modes and typical instruments of venture capital (VC) investments in the early stages of new businesses, each of them different regarding dilutions, valuation potential, depth of negotiations and term sheets. Case overview/synopsis Asistensi, a technology and telemedicine start-up founded in 2020 in Venezuela by three entrepreneurs (Andrés Simón González-Silén, Luis Enrique Velásquez and Armando Baquero), raised US$3m in less than a year in a seed round in which it attracted the attention of professional VC funds such as Mountain Nazca, Alma Mundi Ventures and 468 Capital. Everything was set for launching operations in Mexico and the Dominican Republic in April 2021. However, a series of difficulties led to higher expenditure than planned, prompting the entrepreneurs to seek additional capital. The decision on the financial instrument to be associated with the potential valuation and shareholder dilution figures has been posed as a dilemma. Complexity academic level The case study focuses on understanding the start-up financing process. It can be used effectively in management- and finance-related subjects for graduate students taking introductory topics in entrepreneurship and entrepreneurial finance, as well as introductory executive education courses in entrepreneurship, entrepreneurial finance and VC. Supplementary materials Teaching notes are available for educators only. Subject code CSS3: Entrepreneurship

History Students’ Readiness in Using QR Code Based E-Job Sheet

The research objective is to identify primary history students' readiness to use QR code-based e-job sheets in terms of knowledge, experience, and supporting facilities. The research material consists of digital technology devices, smartphones, internet networks, electronic worksheets, QR Code applications, and an assessment of historical learning. This research applied a quantitative approach. Research respondents included significant history students at the Faculty of Social Sciences Universitas Negeri Padang from 2018 to 2022, including 140 students. Data were collected through a Google Form application questionnaire and shared with the students via WhatsApp. The data were analyzed quantitatively by using percentages and averages. General findings showed that many students were ready to use QR code-based e-job sheets, but others still needed them. The particular findings included: 1) more than half of respondents knew what the e-job sheet was, but two-thirds of them had no experience using the e-job sheet, 2) related to QR codes, it was found that half of the respondents knew what QR code was, but a part of them had no experience using QR codes, and 3) two-thirds of the respondents stated that supporting facilities such campus internet and their smartphone were unable to support the use of QR codes-based e-job sheets. QR code-based e-job sheets have become essential in optimizing digital technology in learning activities. Further research is needed to measure the effectiveness of using QR code-based e-job sheets as an alternative strategy and instrument for assessing learning outcomes in the digital era.

History Students’ Readiness in Using QR Code Based E-Job Sheet

The research objective is to identify primary history students' readiness to use QR code-based e-job sheets in terms of knowledge, experience, and supporting facilities. The research material consists of digital technology devices, smartphones, internet networks, electronic worksheets, QR Code applications, and an assessment of historical learning. This research applied a quantitative approach. Research respondents included significant history students at the Faculty of Social Sciences Universitas Negeri Padang from 2018 to 2022, including 140 students. Data were collected through a Google Form application questionnaire and shared with the students via WhatsApp. The data were analyzed quantitatively by using percentages and averages. General findings showed that many students were ready to use QR code-based e-job sheets, but others still needed them. The particular findings included: 1) more than half of respondents knew what the e-job sheet was, but two-thirds of them had no experience using the e-job sheet, 2) related to QR codes, it was found that half of the respondents knew what QR code was, but a part of them had no experience using QR codes, and 3) two-thirds of the respondents stated that supporting facilities such campus internet and their smartphone were unable to support the use of QR codes-based e-job sheets. QR code-based e-job sheets have become essential in optimizing digital technology in learning activities. Further research is needed to measure the effectiveness of using QR code-based e-job sheets as an alternative strategy and instrument for assessing learning outcomes in the digital era.

An innovative prestressing system of prestressed carbon fiber sheets for strengthening RC beams under flexure

An innovative prestressing system was developed in this study, which can effectively anchor the prestressed carbon fiber sheets as well as conveniently apply prestress to the carbon fiber sheets. Tensioning tests of the carbon fiber sheet-anchor assemblies were first conducted to verify the anchorage behavior of anchors. Then this prestressing system was used for strengthening reinforced concrete (RC) beams to further verify its feasibility and investigate the effect of the impregnation and curing conditions of the carbon fiber sheets on the flexural strengthening efficiency. The results indicated that the tested ultimate capacity of the carbon fiber sheet-anchor assembly reached 72.1∼97.9% of the theoretical ultimate capacity of the carbon fiber sheet based on different impregnation and curing conditions. The concrete crushing failure and rupture failure of prestressed carbon fiber sheets occurred in the strengthened RC beams. The cracking and yielding loads of the RC beams with prestressed sheets were increased by 56.7∼68.5% and 21.7∼30%, respectively, while those with non-prestressed sheets were increased by 27.3% and 13.7%, respectively. The ultimate load was significantly affected by the impregnation and curing conditions. The prestressed carbon fiber sheets with the uncured full impregnation condition were not superior to the non-prestressed sheets in terms of the ultimate load, whereas the cured full impregnation and partial impregnation conditions were more effective than the uncured full impregnation condition. Finally, theoretical equations were used to calculate the cracking, yielding, and ultimate moments of RC beams strengthened with prestressed carbon fiber sheets.

Функціонування банківської системи України під час війни

The purpose of this article is to outline the financial situation of Ukraine during the ongoing war with Russia and to show the actions of the National Bank of Ukraine to preserve and ensure financial stability in emergency conditions. The article indicates the impact of the war on the financial state of the economy and the banking sector. The state of the Ukrainian economy, as well as the banking sector, as the basis of the financial system, is characterized. Threats and challenges, risks inherent in the activities of financial service providers – banks are indicated, attention is focused on credit risk. Changes in bank balance sheets in terms of assets and liabilities in foreign currency in recent years (2018–2022) were considered, the main reasons for the deterioration of the quality of the loan portfolio and the reasons for the reduction of the loan portfolio were noted. An analysis of non-performing assets of banks and the reasons for their increase was carried out. The reports of the National Bank of Ukraine and the State Statistics Service of Ukraine were used for the analysis. The following priority directions of NBU activity for 2023 have been identified: credit risk and liquidity risk management; capital; maintaining business models and internal management, including ensuring the continuity of operation of bank branches under martial law. The need for global efforts to restore the economy and financial system of Ukraine after the end of the war is substantiated.

Carbon Nanotube-Polyurethane Composite Sheets for Flexible Thermoelectric Materials.

Integration of single-wall carbon nanotubes (SWCNTs) in the form of fabriclike sheets or other preformed assemblies (films, fibers, etc.) simplifies their handling and allows for composites with higher nanotube contents, which is needed to better exploit their outstanding properties and achieve multifunctional materials with improved performance. Here, we show the development of p-type SWCNT-thermoplastic polyurethane (TPU) fabric materials with a wide range of SWCNT contents (from 5 to 90 wt %) by employing a one-step filtration method using a suspension of SWCNTs in a TPU solvent/nonsolvent mixture. The mechanical and thermoelectric (TE) properties of these SWCNT-TPU nanocomposites were tailored by varying the SWCNT/TPU wt % ratio, achieving significant advantages relative to the pristine SWCNT buckypaper (BP) sheets in terms of strength and stretchability. In particular, the SWCNT-TPU nanocomposite with a 50/50 wt % ratio composition (equivalent to 15 vol % of SWCNTs) shows a power factor (PF) of 57 μW m-1 K-2, slightly higher compared to the PF of the SWCNT BP prepared under the same conditions (54 μW m-1 K-2), while its mechanical properties significantly increased (e.g., ∼7-, 25-, and 250-fold improvements in stiffness, strength, and tensile toughness, respectively). These results represent a significant step toward the development of easy-to-process self-supporting and stretchable materials with robust mechanical properties for flexible thermoelectric devices.

POGIL (Process Oriented Guided Inquiry Learning) e-Worksheet to Improve Critical Thinking Skills on Reaction Rate Material

The aims of this research were to obtain the eligibility of the POGIL e-worksheet to improve students' critical thinking skills on reaction rate material in terms of validity, practicality, and effectiveness criteria. The type of research was research and development using the ADDIE development model with three stages, Analyze, Design, and Development. The research was obtain validity from the validation sheet in terms of the eligibility of content, presentation, language, and design getting mode ≥ 3 so it was declared valid. Practicality was obtained from a response questionnaire supported by a student activity observation sheet. Overall practicality of the response questionnaire has 89.09% (very practical), while the learner activity observation sheet getting mode = 1. Effectiveness was obtained from the pretest and posttest of critical thinking skills supported by student learning results. The result of the critical thinking skills test got N-gain, 0.929 Interpretation, 0.722 Analysis, 0.694 Evaluation, 0.556 Inference, and 0.933 Explanation and obtained a significance value of 0 in the paired sample t-test so it was concluded there was an increase in students' critical thinking skills in reaction rate material after using POGIL e-worksheet. The learning outcomes test data were analyzed using the Wilcoxon signed rank test has 0 probability value, then it can be concluded there is an increase in student learning outcomes in reaction rate material after using the POGIL e-worksheet. Based on the results of validity, practicality, and effectiveness, the development of the POGIL e-worksheet is feasible.

Effect of Bioabsorbable Poly (dl-Lactide ε-Caprolactone) on Healing of Experimentally Injured Acute Traumatic Middle Ear Mucosa Damage.

Postoperative adhesion is an important complication after middle-ear surgeries. Although many materials have been tried to prevent this complication, the use of Poly (dl-lactide ε-caprolactone) as an anti-adhesive material after middle-ear surgery has not yet been reported. The aim of this study was to evaluate the anti-adhesive effect of poly (dl-lactide ε-caprolactone) on the ears of rats with middle-ear mucosa damage. In our study, 14 Wistar albino rats and 28 ears in total were used. The rats were randomly divided into 4 groups. Middle ear mucosa damage was performed in all groups with a transcanal approach under otomicroscopy in sterile conditions. The effects of poly (dl-lactide ε-caprolactone), silicone sheet, and absorbable gelatin sponge were compared histologically with the secondary healing group. In addition, hearing evaluation was performed before the procedure and on the 28th postoperative day. No significant difference was observed in transient otoacoustic emission and distortion product otoacoustic emissions tests performed before and after the surgical procedure when the groups were compared. While adhesion was observed in the tympanic membrane in the absorbable gelatin sponge group, no adhesion was observed in the other groups. In the absorbable gelatin sponge group, increased fibroblastic activity, inflammation, and neovascularization were observed in the middle-ear mucosa. No significant difference was observed in silicone sheet, poly (dl-lactide ε-caprolactone), and control groups in terms of fibroblastic activity, inflammation, and neovascularization. It can be concluded that absorbable poly (dl-lactide ε-caprolactone) is nonototoxic and biocompatible with the rat's middle ear cavity by short-term evaluation.

Studying Corrosion Resistance of Different Roofing Sheets in Ghana

Background: The request for housing in Ghana is great and as a result the selection of durable roofing sheets have become very significant as roofing plays a vital role in building construction. The goal of the investigation was to see how corrosive compounds affected the most predominant roofing sheets on the Ghanaian market. One-star galvanized Japan [G1*Jap], Galvanized Coated [GC], Aluzinc three star galvanized [AlZn3*], One Star Galvanized Indi [G1*Ind], and Aluminium [Al] were the most common on the market and were therefore used. The corrosion experiments were carried out by putting the various samples in five jars containing various chemicals for varying amounts of time. A computer interfaced Optical Microscope (Leica DM 2500M) was employed to study the surface microstructures of the corroded surfaces, with the corrosion rates per day being determined. Results: Average corrosion rates for One-star Galvanized Japan [G1*Jap] roofing sheets were observed to be the most corrosive resistant whiles [AlZn3*] roofing sheets were the least resistant to corrosion. Generally, G1*Jap roofing sheet stood out as the best roofing sheet in terms of resistance to corrosion. Conclusion: These numbers lead to the conclusion that when compared to the other roofing sheets, G1*Jap roofing sheets were shown to be the most corrosion resistant. The most corroded roofing sheets were found to be Aluzinc three star galvanized [AlZn3*] roofing sheets.

Application possibilities of scanning acoustic microscopy in the assessment of explosive welding

Abstract The last two decades have brought stable and impressive development accompanied by the industry acceptance of the use of high energy techniques based on energy obtained from explosive detonation energy. Such manufacturing processes are not only commercially viable, but also allow complex product shapes and unique combinations of metal sheets in terms of materials to be obtained; they enable the creation of composites which cannot be obtained by other conventional methods. Plated sheets are composed of a base material and a thinner plating material layer. An essential aspect in the validation of explosive welding is the quality control of joints made using this technology. The basic control methods are destructive tests – mainly metallographic, which reveal the microstructure at the connection boundary. Non-destructive tests, used in industrial practice, are classical, normalised ultrasonic tests of welding joints, conducted in accordance with ISO 17640:2017 and ISO 11666:2018 standards. Due to the relatively low thickness of the explosion-tested layers (2 mm and 3 mm single layers), which is the object of this study, assessing them using widely available ultrasonic techniques is limited. According to current scientific studies, the application of the scanning acoustic microscopy (SAM) is a prospective non-destructive method allowing for the qualitative and quantitative assessment of the continuity of the metallic connection on the contact surface of two materials. This paper presents the results of research on the quality of clads, welded explosively using a non-destructive research technique, namely SAM, verified with metallographic tests.

Thin-film Maxwell hybrid nanofluid flow over an unsteady inclined stretching sheet in terms of nonlinear mixed convection

Maxwell fluid and stretching sheets are used in many industries. The vision of this research is to explore the properties of thin-film Maxwell hybrid nanofluid on an inclined stretching sheet. Silver (Ag) and titanium dioxide (TiO2) are used as nanomaterials. Maxwell fluid is utilized as a base fluid in the preparation of nanofluid by blending nanocomponents into the base fluid. The comparative analysis has been done for the (Ag) nanofluid and (Ag + TiO2) hybrid nanofluid. The proposed flow model has been solved analytically using the homotopy analysis method. In this article, we also consider Brownian motion and thermophoresis, and its effects are studied simultaneously via the Buongiorno model. This study also analyzes the boundary layer of velocity, temperature, and concentration profiles. The proposed model has been converted into highly nonlinear differential equations by means of similarity transformation. The numerical results of velocity, temperature, and concentration profiles are also displayed graphically. The solution of the model involved key parameters such as thermophoretic parameter, magnetic parameter, and Brownian motion. The outputs of the embedding parameters are analyzed and discussed. The percentage wise enhancement in the heat transfer rate between the nanofluids and hybrid nanofluids has been calculated and displayed.

VALIDATION OF LEARNING ACTIVITY SHEETS AND LEARNERS PERFORMANCE IN ARALING PANLIPUNAN

Expert opinion was taken for the validity of the Learning Activity Sheets depending on four characteristics: Utilization, Runtime, Appeal, and Comprehensiveness. Learning Activity Sheets. Learners' performance will be recorded in a monitoring tool whether they completed every task in their Learning Activity Sheets. Thus, the data will be validated through a questionnaire on the characteristics of Learning Activity Sheets. The Learning Activity Sheets are an advantage for the teachers who can?t decide on activities most suitable for learners. Teachers may be aware of the appeal of learning activity sheets in delivering the lessons and activities to the learner?s comprehension. This paper analyzes the significant difference between the Learning Activity Sheets and Performance Task components. Specifically, it ought to determine the significant effect of the learning activity sheet on the performance in Araling Panlipunan, the mean performance of grade 8 learners based on the result of Pre-Test and Post Test, significant difference in the mean performance of grade 8 learners based on the result of the pre-test and post-test, the level of Validity of the Learning Activity Sheets in Araling Panlipunan in terms of their characteristics as to: Utilization, Runtime, Appeal and Comprehensiveness, the level of validation of the Learning Activity Sheets in Araling Panlipunan in terms of content as to: Content, Organization and Language, Illustrations/Image and Design and Layout. With activity sheets created by the teachers, the researcher aims to determine the Academic Performance of Learners. The level of validity of learning activity sheets in terms of components and characteristics is significant to the learners' learning. The components of Learning Activity Sheets significantly affect the learners learning outcomes using the pre-test and posttest in Araling Panlipunan. There is a significant difference in the mean of grade 8 learners based on their pre-test and post-test results. In conclusion, teachers may be aware of the appeal of learning activity sheets in delivering the lessons and activities to the learner?s comprehension. It is suggested that the Curriculum Developers and Writers may examine every aspect of the learning material to ensure the correctness and accurate information for students to establish prior knowledge of the lesson.

Design parameters for Airy beams in light-sheet microscopy.

We derive analytical expressions for the length, thickness, and curvature of an Airy light sheet in terms of basic parameters of the cubic phase and the paraxially defined focusing optics that form the beam. The length and thickness are defined analogously to the Rayleigh range and beam waist of a Gaussian beam, hence providing a direct and quantitative comparison between the two beam types. The analytical results are confirmed via numerical Fresnel propagation simulations and discussed within the context of light-sheet microscopy, providing a comprehensive guide for the design of the illumination unit.

Connecting theory of plasmoid-modulated reconnection to observations of solar flares

Abstract The short timescale of the solar flare reconnection process has long proved to be a puzzle. Recent studies suggest the importance of the formation of plasmoids in the reconnecting current sheet, with quantifying the aspect ratio of the width to length of the current sheet in terms of a negative power $ \alpha $ of the Lundquist number, that is, $ {S}^{-\alpha } $ , being key to understanding the onset of plasmoids formation. In this paper, we make the first application of theoretical scalings for this aspect ratio to observed flares to evaluate how plasmoid formation may connect with observations. For three different flares that show plasmoids we find a range of $ \alpha $ values of $ \alpha =0.26 $ to $ 0.31 $ . The values in this small range implies that plasmoids may be forming before the theoretically predicted critical aspect ratio ( $ \alpha =1/3 $ ) has been reached, potentially presenting a challenge for the theoretical models.

Collagen Dressing Versus Conventional Vaseline Gauze Dressing in Reducing Pain and Infection at the Donor Area for Skin Grafting: A Prospective Interventional Study

Introduction: The harvest of a split thickness skin graft causes a partial thickness injury and an outflow of blood and protein rich exudate from the donor site wound. Conventionally, closed dressings are employed using petroleum jelly impregnated gauge which are permeable to bacteria and wound exudate soaks through. This may lead to pain and infection of the donor site. Biological dressings create the most physiological interface between the wound surfaces and the environment and also dressings are natural, non immunogenic, non pyrogenic and hypo allergenic. Collagen sheet is one such dressing material used. Aim: To compare the conventional dressing using petroleum jelly impregnated gauze versus biological dressing with collagen sheets in terms of pain, infection and healing at skin graft site. Materials and Methods: It was a prospective interventional study conducted in Department of Surgery, SSG Hospital and Medical College, Baroda, Gujarat, India over a period of November 2012 to November 2017 on 220 participants. Randomisation was done by choosing an envelope containing cards marked ‘A’ or ‘B’. The group A (110) was a study group with collagen sheet dressing while group B (110) was the control group with conventional vaseline gauze dressing. Both group patients were examined at six hours postoperatively and then two times a day at 8:00 am and 8:00 pm daily. They were evaluated for pain with Visual Analogue Scale (VAS) score, infection, haematoma formation, healing at donor site and allergic reaction to collagen. Results: Mean VAS score for pain showed that it decreased over a period of time in both the groups. The group with collagen sheet dressing shows decreasing means VAS score from 4.34 on 1st day to 0.29 on 3rd day (p<0.0001). Similarly, the vaseline gauze dressing shows decreasing mean VAS score from 5.64 on 1st day to 1.39 on 3rd day (p<0.0001). Conclusion: Collagen sheet dressing are easy to apply, with advantage of less pain at donor site and lower infection rate. Also healing time required is less than the vaseline gauze dressing. collagen sheet dressing is clinically more efficient overall.

Preliminary study on the use of 3D printed biodegradable polymeric sheet for the manufacturing of medical prostheses by SPIF

Incremental Sheet Forming (ISF) and Fused Deposition Modelling (FDM) of polymers have both an edge over conventional manufacturing by their ability to directly get complex structures without the need of a mold or a die. Obtaining biocompatible polymer blanks for ISF is not always as easy as it could be expected. Concerning nowadays FDM offers a good opportunity to print biocompatible polymer sheets as blanks to next be formed by ISF. Exploring the combination of FDM and ISF for two biodegradable polymers (Polylactic acid (PLA) and Polycaprolactone (PCL)) is the objective of this work.An analysis of the initial printed sheets in terms of thickness uniformity and surface roughness was carried out. Truncated cone shape with fixed slope angle geometries in a CNC machine were formed. The ISF process parameters modified were the traditional: step down, feed rate and spindle speed. As saved outputs there are: Forming Forces, Maximum Temperature, Surface Integrity, Surface Roughness and Shape Accuracy. After this first approach, a good feasibility process window was established for being used on prosthesis manufacturing of PCL. On the contrary, the feasibility window for PLA is limited because of its low formability. The first results of the combination of both additive manufacturing processes are interesting and deserve further studies to evaluate more in depth the behaviors and the forming mechanism of these materials.

Electro-Thermal Model-Based Design of Bidirectional On-Board Chargers in Hybrid and Full Electric Vehicles

In this paper, a model-based approach for the design of a bidirectional onboard charger (OBC) device for modern hybrid and fully electrified vehicles is proposed. The main objective and contribution of our study is to incorporate in the same simulation environment both modelling of electrical and thermal behaviour of switching devices. This is because most (if not all) of the studies in the literature present analyses of thermal behaviour based on the use of FEM (Finite Element Method) SWs, which in fact require the definition of complicated models based on partial derivative equations. The simulation of such accurate models is computationally expensive and, therefore, cannot be incorporated into the same virtual environment in which the circuit equations are solved. This requires long waiting times and also means that electrical and thermal models do not interact with each other, limiting the completeness of the analysis in the design phase. As a case study, we take as reference the architecture of a modular bidirectional single-phase OBC, consisting of a Totem Pole-type AC/DC converter with Power Factor Correction (PFC) followed by a Dual Active Bridge (DAB) type DC/DC converter. Specifically, we consider a 7 kW OBC, for which its modules consist of switching devices made with modern 900 V GaN (Gallium Nitrade) and 1200 V SiC (Silicon Carbide) technologies, to achieve maximum performance and efficiency. We present a procedure for sizing and selecting electronic devices based on the analysis of behaviour through circuit models of the Totem Pole PFC and DAB converter in order to perform validation by using simulations that are as realistic as possible. The developed models are tested under various operating conditions of practical interest in order to validate the robustness of the implemented control algorithms under varying operating conditions. The validation of the models and control loops is also enhanced by an exhaustive robustness analysis of the parametric variations of the model with respect to the nominal case. All simulations obtained respect the operating limits of the selected devices and components, for which its characteristics are reported in data sheets both in terms of electrical and thermal behaviour.

Laparoscopic cholecystectomy during COVID-19 pandemic- Retrospective analysis of tertiary care centre

INTRODUCTION: Laparoscopic cholecystectomy is the most commonly performed general surgical procedure. During the COVID-19 pandemic, general recommendation worldwide is to postpone elective surgeries as far as possible to decrease the resource utilization and also aerosol-related transmission among hospital staff and patients. We conducted this study to see the burden of gallbladder disease, their management and outcomes of all patients who presented to our centre during first wave of COVID-19 pandemic.
 METHODS: We conducted a retrospective analysis of all patients who underwent laparoscopic cholecystectomy at the Hospital for Advanced Medicine and Surgery (HAMS) after the commencement of strict lockdown in the first wave of the COVID-19 pandemic. Ethical approval for the study was taken from Nepal Health Research Council. All the surgeries were performed as per HAMS interim policy for infection prevention and control during the COVID-19 pandemic. Data were extracted from the discharge sheet and outcomes in terms of duration of hospitalization, morbidity, mortality, and COVID -19 infection among patient and operating team staff after surgery were assessed.
 RESULTS: Out of 110 cases operated for gallbladder disease, 90 patients were included in the study with complete data. The most common presentations were dyspepsia (28) and biliary colic (22). Patients were managed with laparoscopic cholecystectomy (79), percutaneous cholecystostomy (4), laparoscopic subtotal cholecystectomy (5), open cholecystectomy (1). The median duration of hospitalization 22 hours. There was no COVID-19 transmission among staff and patients.
 CONCLUSIONS: Laparoscopic cholecystectomies are feasible during COVID-19 pandemic and safely performed following infection prevention guidelines. It can be still be performed in day case basis to decrease the bed occupancy and avoiding crowd in hospitals.