Effect of shadowing and diffraction on the received GNSS signal

Abstract. The characteristics of the GNSS received signal depend on the propagation medium environment. Typically, the transmitted signal interacts with several numbers of obstacles which leads to the multipath propagation to receiver end. In such cases, diffraction over the edges or wedges of the obstacles in the propagation path should be considered. The effects of diffraction and shadowing are the important elements in radio wave propagation because of their strong influence on the received signal quality. Especially, received signal strength and characteristics are very significant for GNSS applications. This master’s thesis investigates the effect of knife-edge diffraction model and shadowing environment on the received GNSS signal. Characterization of the received signal is investigated both theoretically and experimentally. In the measurement, a dual circular polarized antenna has been used to receive the multipath GPS signal in the shadow region in which antenna was placed in the zenith direction. The measurement was performed for two scenarios 1) the receiver was in the static position, and 2) in motion for the second measurement. Measurement results show that, the received signals following the Knife-edge diffraction pattern for both measurements case. In the first measurement case, knife-edge diffraction has been identified in received signal attenuation whereas the interference pattern in the LoS propagation can be observed because of multipath effect. In the deep shadow region, a linearly polarized signal has been received in both antennas because the incident RHCP signal turned into a linearly polarized signal after diffraction. For the second measurement case, knife-edge attenuation pattern is also visible. A clear agreement between the measured and theoretical aspects has been achieved in the case of knife-edge diffraction

INVESTIGATION OF THE CAUSES OF MARITIME ACCIDENTS IN THE INLAND WATERWAYS OF BANGLADESH

Water transport is the proven cheapest and safest mode of transportation but it is the agent of catastrophe in Bangladesh. The overall scenario of Bangladesh inland water transport has been studied. The form of occurrences of maritime accidents in the inland waterways of Bangladesh may be categorized based on mode of failure. Data analysis of major accidents shows that prevention of passenger vessels’ accident will drastically reduce the number of casualties in Bangladesh Inland Waterways where the two repeatedly reported causes of accidents are overloading and inclement weather. Literature review shows that analyses were carried out mostly to investigate the mechanism of capsizing due to violation of “The Inland Shipping Laws and Rules”. To enlighten the roles of professionals like Naval Architects and Law Enforcing Agencies, the reasons behind the accidents in Bangladesh Inland Waterways have been simplified and the nature of actions required for preventing the accidents have been identified from practical point of view. The effect of consideration of overloading condition and higher wind pressure in design has been studied and found that it will have adverse effect on the socio-economical condition of Bangladesh. Role of proper design and construction has been identified by dividing the accidental phenomenon into two phases, capsizing and sinking of vessels

Water quality management on the enhancement of shrimp (Penaeus monodon Fab.) production in the traditional and improved-traditional ghers of Bangladesh

On-farm research on enhancement of P. monodon production through water quality management was carried out in five ghers of Paikgacha, Khulna. Based on the prevailing condition of the ghers, lime in the form of CaCO(sub 3), urea and TSP were used as the major inputs to minimize the soil-water acidity and to ensure the availability of natural food particles in the water bodies. Exchange of water at required level also practiced for the qualitative improvement of culture water. Ghers of varying sizes showed that water quality management and fertilization have a positive impact on production performance of P. monodon (61.59% increment) that yielded an average production of 385.43 kg/ha/crop against the present traditional rate of 238.50 kg/ha/year

Sperm cryopreservation of Indian major carp, Labeo rohita: cryodiluents, sperm: cryodiluent dilution ratio and cryoprotectan t concentration

Cryogenic preservation trials of spermatozoa of Labeo rohita were carried out. Twenty four cryodiluents (extender + cryoprotectant), with the combination of six extenders such as egg-yolk citrate, urea-egg-yolk, 0.9% NaCl, Kurokura-2, Ma and Mb and four cryoprotectants viz. DMSO, glycerol, methanol and ethanol, were used to screen out the suitable cryodiluents. Sperm was preserved in 0.25ml plastic straw in programmable freezer. Two step freezing method was followed. Sperm preserved with egg-yolk citrate and urea-egg-yolk containing 10% DMSO showed best post-thaw motility (80%) followed by 0.9% NaCl (60%) and Kurokura-2(30%) solutions. Sperm with the extenders M" and Mb clotted at the time of equilibration and also after few days of preservation. Egg-yolk citrate mixed with ethanol and methanol also showed good percentage of motility (80%) but egg-yolk citrate with glycerol showed less sperm motility (>60%). To determine suitable dilution ratio of milt and cryodiluent two best extender eggyolk citrate and urea-egg-yolk with four cryoprotectants such as DMSO, glycerol, methanol and ethanol at different ratio viz 1:2,1:4,1:7,1:10,1:15 and 1:20 were used. Highest post-thaw motility (>80%) was observed when milt was preserved with egg-yolk citrate containing 10% DMSO at 1:2, 1:4, 1:7 and 1:10 dilutions. Meanwhile using glycerol as cryoprotectants provided less post thaw motility at lower dilution ratio but with the increase of its dilution showed good sperm motility compared with other cryoprotectants. Finally, evaluation on the effect of cryoprotectant concentration on post-thaw sperm motility was conducted. Egg-yolk citrate and four cryoprotectant i.e. DMSO, glycerol, methanol and ethanol with six different concentrations namely 5%,7%, 10%, 15%, 20% and 30%.were evaluated. Among the cryoprotectants DMSO, methanol and ethanol showed highest post-thaw motility (about 80%) at 7% and 10% concentrations. Although glycerol was not suitable at low concentration but its 20% and 30% concentration levels provided best post-thaw motility. No post-thaw motility was obtained with DMSO at 30% concentration. The overall analysis on cryoprotectant concentration indicated that below 5% and above 20% cryoprotectant concentrations could not be suitable for effective cryopreservation of spermatozoa

Prevalence and risk factors of gestational diabetes mellitus in Bangladesh: Findings from demographic health survey 2017–2018

Gestational diabetes mellitus (GDM) has serious consequences for both maternal and neonatal health. The growing number of noncommunicable diseases and related risk factors as well as the introduction of new World Health Organization (WHO) diagnostic criteria for GDM are likely to impact the GDM prevalence in Bangladesh. Our study aimed to assess the national prevalence and identify the risk factors using the most recent WHO criteria. We used the secondary data of 272 pregnant women (weighted for sampling strategy) from the Bangladesh Demographic and Health Survey 2017–2018. Multivariate logistic regression was performed to determine the risk factors of GDM. The overall prevalence of GDM in Bangladesh was 35% (95/272). Increased odds of GDM were observed among women living in the urban areas (adjusted odds ratio (aOR) 2.74, 95% confidence interval (CI) 1.43–5.27) compared to rural areas and those aged ≥25 years (aOR 2.03, 95% CI 1.13–3.65). GDM rates were less prevalent in the later weeks of pregnancy compared to early weeks. Our study demonstrates that the national prevalence of GDM in Bangladesh is very high, which warrants immediate attention of policy makers, health practitioners, public health researchers, and the community. Context-specific and properly tailored interventions are needed for the prevention and early diagnosis of GDM

ON THE EXPERIMENTAL STUDY OF COMPOSITE DESSICANTS FOR ENERGY EFFICIENT AIR DEHUMIDIFICATION

This paper presents the development and performance characterization of new composite desiccants. The main compositions for the composite desiccants include silica gel, lithium chloride, calcium chloride and bentonite. Different percentage compositions of these four components were tested to determine the optimal material composition for improving moisture removal capacity under varying inlet air temperature and humidity, and amount of moisture released under different regenerative temperature. For the first time, four-layered composite desiccants were developed and tested experimentally to determine their moisture removal capacity and moisture regeneration capacity at temperature of about 60oC under inlet air conditions similar to Singapore’s tropical climate. The performances of these composite desiccants were benchmarked with the performance of pure silica gel - the most commonly used desiccant in the market today. It was observed experimentally, that employing a four-layered composite desiccant, comprising silica-gel (SiO2), Bentonite, Lithium Chloride (LiCl), and Calcium Chloride (CaCl2), has enabled greater moisture removal capacity for varying inlet air temperature and humidity ranging from 25 to 35oC and 55 to 95% relative humidity (RH). The percentage improvements, in contrast to pure silica gel, are 14 to 22.5%, and 10 to 26.3% for varying inlet air temperature and varying inlet RH, respectively.   KEYWORDS: experiments; composite desiccant; dehumidification; energy efficienc

An overview of hydrogen as a vehicle fuel

As hydrogen fuel cell vehicles move from manifestation to commercialization, the users expec t safe, convenient and customer-friendly fuelling. Hydrogen quality affects fuel cell stack performance and life time, as well as other factors such as valve operation. In this paper, previous researcher’s development on hydrogen as a possible major fuel of the future has been studied thoroughly .Hydrogen is one of the energy carriers which can replace fossil fuel and can be used as fuel in an internal combustion engines and as a fuel cell in vehicles. To use hydrogen as a fuel of internal combustion engine, engine design should be considered for avoiding abnormal combustion. As a result it can improve engine efficiency, power output and reduce NOx emissions. The emission of fuel cell is low as compared to conventional vehicles but as penalty, fuel cell vehicles need additional space and weight to install the battery and storage tank, thus increases it production cost. The production of hydrogen can be ‘carbon-free’ only if it is generated by employing genuinely carbon-free renewable energy sources. The acceptability of hydrogen technology depends on the knowledge and awareness of the hydrogen benefits towards environment and human life. Recent study shows that people still do not have the sufficient information of hydrogen

Changes in soil organic matter, plant nutrients and system productivity under conservation agricultural practices in the rice-jute cropping system

Soil organic matter (SOM) is central to soil quality and nutrient cycling. In Bangladesh, depletion of soil fertility is a serious threat to sustainability of agricultural production due to high cropping intensity and agriculture practices based on conventional tillage and residue removal (Rijpma and Jahiruddin, 2004). In this situation, CA practices (minimum tillage, crop residue retention and diverse crop rotations) could be a good option for the improvement of soil quality and crop productivity in Bangladesh. However, CA practices are poorly developed for intensive rice-based cropping system and their effect on SOM, plant nutrients and system productivity have not yet been properly addressed. Hence, the present study was undertaken to monitor the changes in SOM and other plant nutrients with system productivity under CA practices in the rice-jute cropping system in the Low Ganges River Floodplain of Bangladesh