More and more satellites are populating the sky nowadays in the Low Earth orbits (LEO). Most of the targeted applications are related to broadband and narrowband communications, Earth observation, synthetic aperture radar, and internet-of-Things (IoT) connectivity. In addition to these targeted applications, there is yet-to-be-harnessed potential for LEO and positioning, navigation, and timing (PNT) systems, or what is nowadays referred to as LEO-PNT. No commercial LEO-PNT solutions currently exist and there is no unified research on LEO-PNT concepts. Our survey aims to fill the gaps in knowledge regarding what a LEO-PNT system entails, its technical design steps and challenges, what physical layer parameters are viable solutions, what tools can be used for a LEO-PNT design (e.g., optimisation steps, hardware and software simulators, etc.), the existing models of wireless channels for satellite-toground and ground-to-satellite propagation, and the commercial prospects of a future LEO-PNT system. A comprehensive and multidisciplinary survey is provided by a team of authors with complementary expertise in wireless communications, signal processing, navigation and tracking, physics, machine learning, Earth observation, remote sensing, digital economy, and business models.
Aquaculture medicines, drugs, and chemicals or simply AMDC, are critical in protecting aquaculture farmers from disease in farmed animals and economic losses. The AMDC is now a well-established industry in Bangladesh, and each year, new products that benefit farmers are launched. This review examined published research information on AMDC over the last decade (2011-2020) and discovered that 41 research publications from various parts of Bangladesh were published, citing the names of 1484 AMDC products. It was discovered that 19 generic antibiotics are well established and widely used in different regions' aquaculture, including shrimp aquaculture. Although some researchers expressed concern about the use of antibiotics in aquaculture, they believe that with proper withdrawal periods and the application of small doses, farmers may avoid economic losses. However, the pathway of the antibiotic introduction in aquaculture setup in Bangladesh was unknown to the researchers, through this review, we revealed the pathway of antibiotics introduction in aquaculture. Additionally, this review revealed that various AMDC products, including oxygen suppliers, growth promoter supplements, disinfectants, raw chemicals, probiotics, pond preparation and management AMDC, and toxic gas removal AMDC, are readily available in various markets throughout Bangladesh. The observation implied that research on the efficacy of various AMDC products in Bangladesh's agro-ecological zones could be conducted, which would aid researchers in deciphering the true nature of AMDC in sub-tropical climates. Asian J. Med. Biol. Res. 2021, 7 (2), 90-106
The coastal embankment system has been gradually built during the last 40 years. The embankments were originally designed to increase agricultural production by preventing salt water intrusion not to protect against cyclonic storms. The alignment of the embankments did not consider the changing conditions in bathymetry of the sea and thalweg migration of the rivers and therefore many embankments are located under tidal water level and have severe toe and slope erosion problems during the monsoon season. The crest level and embankment cross sections have not optimized the protection of hinterland and the embankment itself and therefore the embankments typically only provide protection for the cyclones with 5-12 year return periods and the designed crest level of the sea facing coastal polder equal to the sum of normal maximum recorded water stage plus 1.50m. In this study to estimate the design crest level and side slope for sea facing embankment have been established based on maximum storm surge level, wave run-up for cyclonic wave, freeboard allowing 5 l/m/s overtopping ,potential climate change impact and land subsidence. Statistical analysis of surge level and wave run-up is carried out using Extreme Value Analysis (EVA) in MIKE Zero.
Today, a substantial portion of global trade is carried by sea. Consequently, the reliance on Global Navigation Satellite System (GNSS)-based navigation in the oceans and inland waterways has been rapidly growing. GNSS is vulnerable to various radio frequency interference. The objective of this research is to propose a resilient Multi-Frequency, Multi-Constellation (MFMC) receiver in the context of maritime navigation to identify any GNSS signal jamming incident and switch to a jamming-free signal immediately. With that goal in mind, the authors implemented a jamming event detector that can identify the start, end, and total duration of the detected jamming event on any of the impacted GNSS signal(s). By utilizing a jamming event detector, the proposed resilient MFMC receiver indeed provides a seamless positioning solution in the event of single-frequency jamming on either the lower or upper L-band. In addition, this manuscript also contains positioning performance analysis of GPS-L5-only, Galileo-E5a-only, and Galileo-E5b-only signals and their multi-GNSS combinations in a maritime operational environment in the Gulf of Finland. The positioning performance of lower L-band GNSS signals in a maritime environment has not been thoroughly investigated as per the authors’ knowledge.
A broad variety of aquaculture-related medications, drugs, and chemicals (AMDC) are extensively used in the aquaculture industry in South-Eastern Bangladesh. Fish farmers are worried about the quality of their final product, and disease outbreaks must be stopped at all costs. Farmers are sometimes one ahead of the curve when it comes to producing healthy final products by including probiotics, vitamins, and minerals into their aquaculture setups to promote early and disease-free output. However, the current study was carried out in south eastern Bangladesh, specifically in the highly dense aquaculture regions of Chandpur, Cumilla, and Feni district (17 upazilas), from November 2016 to January 2018. Questions were asked through interviews and a Focus Group Discussion (FGD) was held to gather primary data. The major target groups were aquaculture farmers, AMDC shops, pharmaceutical company employees, and hatchery owners. In this three-county area, according to the findings from the thorough research, there are a total of 33 companies that advertise 330 generics brand products via their own distributional channels. Among the available AMDC products in the study area, growth promoters were mostly abundant products among all categories while other products such as predator removal products, insecticides and ectoparasiticides, water quality and pond management, plankton producer, plankton bloom cleaner, disinfectant and disease treatment, toxic gas reducer, pH controller, oxygen supply, stress reducer, growth promoter, probiotics and antibiotics were most selling products to the farmers. The present study revealed 19 generic of antibiotics were available and prescribed by the AMDC vendors or aquaculture disease consultants (ADC) around the regions. Additionally, the research also included the dosages of AMDC and the method of administration in the aquaculture pond, which will assist both the farmers and the ADC in selecting and suggesting the appropriate medications or treatments that may be beneficial to the farmers in the long run. Asian Australas. J. Biosci. Biotechnol. 2021, 6 (2), 103-127
Microcystin-LR (MC-LR) is one of the most frequent and most lethal toxicants and a vital environmental pollutant due to its toxicity and persistence. It is hepatotoxins and have been shown to be potent tumor-promoters which pose a serious threat to human health in the form of chronic exposure through drinking water. In this study, a novel electrochemical method for the determination of MC-LR has been developed using protein phosphatase 2A (PP2A) enzyme inhibition. The rapid and simple determination of PP2A activity was accomplished by means of hydrodynamic voltammetry in a 50 µL micro-droplet with a rotating disk electrode (RDE). The chronoamperometric response were obtained from the electrochemical oxidation of p-aminophenol (PAP) following the enzymatic conversion of p-aminophenyl phosphate (PAPP) as a substrate. PP2A activity estimated by using PAPP substrate is affected by MC-LR, and this phenomenon decreases the current signal of PAP. The IC 50 value was calculated as 0.08 µg/L which is well below the World Health Organization (WHO) provisional guideline value for total MC-LR of 1 µg/L in drinking water. The enzymatic reaction using RDE is possible to perform using fewer chemicals in a rapid manner. Therefore, the method can be very attractive for MC contaminated drinking water routine assessment.
An experiment was conducted for 60 d in a recirculatory system consisting of 20 glass aquariums (each of size 41 × 41 × 46 cm) to evaluate meat and bone meal (MBM) as partial replacement for fish meal (FM) in Macrobrachium rosenbergii postlarvae (PLs) with a view to develop an inexpensive nursery diet. Three nursery diets were formulated to contain 32% protein and to be as isoenergetic as possible. FM in these diets was progressively replaced with MBM (Diet 1 contained 25% FM and 14% MBM, Diet 2 contained 20% FM and 20% MBM, and Diet 3 contained 15% FM and 26% MBM). Inclusion levels of mustard oilcake and sesame meal in diets were kept fixed at 10%. A commercial shrimp nursery diet (30% protein) from Saudi Bangla Fish Feed Ltd., Mymensingh, was used as the reference diet (Diet 4). Each treatment had three replicates. PLs of M. rosenbergii (26 ± 0.02 mg) were stocked at the rate of 60 PLs (1 PL/L) in each aquarium. At the beginning, PLs were fed three times daily at a rate of 20% of the body weight and it was gradually reduced to 10% at Day 30. The ranges of water quality parameters in the system were as follows: temperature, 27–29 C; dissolved oxygen, 6.5–8.4 mg/L; pH, 6.8–8.3; and total ammonia, 0.01–0.15 mg/L. The result of the study showed that there was no significant difference (P > 0.05) between the weight gains of PLs fed Diet 1 (containing 14% MBM) and Diet 4 (reference diet) but was significantly higher than other dietary groups containing higher levels of MBM. Diets 1 and 4 showed significantly lower (P < 0.05) apparent food conversion ratios (1.74 and 1.73, respectively). The survival (%) of PLs ranged between 62 and 76% with PLs fed Diets 1 and 4 showing significantly higher (P < 0.05) survival. The result of the study demonstrated that the MBM could be included at 14% level in a nursery diet, and a diet containing 25% FM, 14% MBM, 10% sesame meal, and 10% mustard oilcake may be recommended for profitable production of PLs of M. rosenbergii.
: -The Meghna Estuary region of Bangladesh is a unique environment where the constant process of land formation and erosion takes place due to the complex interactions between large river discharge, enormous sediment load, strong tidal forces, wind actions, wave, salinity & cyclonic storm surge and estuarine circulation. These hydrodynamic factors and their interactions shape the morphology of the Meghna Estuary. During dry season upland fresh water flow into the Bay through the estuary is very much lower than that of monsoon season. Tidal action becomes stronger and dominates water flow pattern in the Meghna estuary. The distribution of flow and water level in the different channels of the Meghna estuary are governed by river discharge, the tide and the wind speed. Velocity is higher during ebb tide than that of flood tide due to combined effect of upstream flow and downward tidal current. Velocity in monsoon is much higher compare to dry period because upstream discharge is higher in monsoon. Most of the accretion and erosion mainly occurs during monsoon and post monsoon period. In pre-monsoon and post monsoon, wave height is less compared to monsoon as wind speed is less during these periods. Along the left Bank of this estuary, significant wave is considerable. As a result, tremendous whirl action due to tidal effects and whirl action due to enormous drainage flow during monsoon, wave action, tidal surge of the lower Meghna causes breaching of the major parts of the embankments of polder 59/2 and adjacent area. The main purpose of this research paper is to understand the hydrodynamic features of the Meghna estuary.
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