Faculty of Engineering and Technology

Non-metal Doped TiO2 Nanocomposites for the Removal of Nuclear Waste from Water

Tue, 03 Mar 2026 00:00:00 GMT

Non-metal Doped TiO2 Nanocomposites for the Removal of Nuclear Waste from Water Hassan, Md. Mehedi This study focuses on the synthesis and evaluation of non-metal doped titanium dioxide (TiO2) nanoparticles for the potential remediation of radionuclide-contaminated water. Undoped TiO2 and doped TiO2, e.g., B-doped TiO2 (B–TiO2), C-doped TiO2 (C–TiO2), N-doped TiO2 (N–TiO2) were successfully prepared by the sol-gel method. The resultant nanoparticles were thoroughly characterized by XRD, FESEM, EDX, TEM, FTIR, UV–Vis spectroscopy, DLS, zeta potential measurement, and AAS to study their structural, morphological, optical, and adsorption properties. Furthermore, batch adsorption and photocatalytic experiments using adsorbents were conducted to assess their efficiency in radionuclide removal. While attempting to extract radioactive isotopes from water, real radionuclides were not implemented due to safety, cost, and facility constraints. Instead, the nonradioactive analogs—cobalt, iodine, manganese, and zinc (which have similar radioisotopes, such as 60Co2+, 131I-, 54Mn2+, and 65Zn2+)—were employed, due to their similarity with the radioactive elements. XRD results revealed that both the doped and undoped TiO2 were crystalline anatase, and B-doping led to the formation of a small amount of the rutile phase. Both SEM and TEM images showed that the morphology and particle dimension were influenced by doping, with the smallest average particle size being reached for C–TiO2. The adsorption capacity was evaluated using iodine adsorption and the removal of metal ions. The C–TiO2 and N–TiO2 nanocomposites were found to show excellent adsorption properties among the doped samples, which may be due to a higher surface area and improved surface chemistry. The findings indicate that non-metal doping can enhance the photocatalytic and adsorption activity of TiO2. Thus, these materials are promising candidates for treating radioactive wastewater. This thesis is submitted for the degree of Master of Philosophy.

Securing Graphical Authentication Using Keystroke Dynamics

Tue, 03 Mar 2026 00:00:00 GMT

Securing Graphical Authentication Using Keystroke Dynamics Roy, Indrani Account recovery is a critical aspect of web application security, often overlooked despite its importance. Traditional account recovery methods, such as sending a password reset link or a new username to the user’s registered email, are vulnerable to impostors who may have access to the user’s email and other credentials. This vulnerability makes account recovery a potential weak point in the overall security of a web application. Recent applications of behavioral biometrics, such as keystroke dynamics, for attack detection and user authentication bear similarities to biometric authentication. Adding keystroke dynamics analysis to the account recovery process significantly increases the difficulty for an impostor to successfully recover and take over a user’s account. To enhance user authentication effectiveness and raise account recovery requirements through keystroke dynamics, this study adds one additional measure of keystroke patterns to the already-existing features. Compared to other access control systems based on biometric features like face or fingerprint, keystroke analysis has attained a respectable level of accuracy. In this aim, this study uses experimental data and statistical analysis to show how the unique keystroke measure provided may be utilized in conjunction with the current authentication mechanism to greatly improve the authentication and security of sensitive applications. It may be beneficial to recognize the intruders and expel them from the system as long as this job can accommodate their typing rhythm. In this study, generative adversarial networks (GAN) are utilized to generate keyboard dynamics data with a focus on impersonating a user at the identification step in both fixed text and fixed sentence contexts. Three distinct architectures have been devised, implemented, and validated with the aid of machine learning and deep learning: vanilla-GAN based on simple neural networks NN, LSTM-GAN based on recurrent neural networks using long short-term memories (LSTM), CNN-GAN based on convolutional neural networks. The developed Conditional Generative Adversarial Networks have shown that these architectures can successfully replicate a user’s keystroke dynamics by learning about the user’s typing style and generating keyboard dynamics data using different GANs with different architectural styles. Findings show that keystroke dynamics patterns can be efficiently produced by the GAN and utilized to trick keystroke authentication systems. This thesis is submitted for the degree of Master of Philosophy.

Isolation and Characterization of Amylase Producing Microbes and Its Sequential Strain Development for Industrial Enzyme Production

Mon, 02 Mar 2026 00:00:00 GMT

Isolation and Characterization of Amylase Producing Microbes and Its Sequential Strain Development for Industrial Enzyme Production Fuadh-Al-Kabir, Md. Amylase enzymes are essential biocatalysts with wide-ranging industrial applications, including food processing, textile desizing, detergent formulation, paper production, and pharmaceuticals, owing to their ability to hydrolyze starch into simpler sugars. Despite the rising industrial demand, Bangladesh currently lacks domestic amylase production facilities, resulting in a dependence on total imports. To address this challenge, the present study aimed to isolate potent amylase-producing bacterial strains from natural sources, followed by their characterization, strain improvement through mutagenesis, optimization of production parameters, and evaluation of their industrial applicability. The ultimate goal was to develop a sustainable and indigenous source of amylase for local utilization. Following the harvesting period, soil samples were obtained from potato-growing areas in the Munshiganj and Rangpur districts, specifically from sites where remnants of decomposing potato matter remained in the fields. A total of 128 microbial isolates comprising 69 bacterial and 59 fungal strains were obtained using nutrient agar and potato dextrose agar media. Primary screening for amylase activity was conducted via starch agar assays followed by iodine staining, and hydrolysis zone-to-colony diameter ratios were determined. Among the bacterial isolates, S-1 and S-2 showed the highest hydrolytic potential, with the zone ratios of 3.44 and 4.98, respectively. Secondary screening using the dinitro salicylic acid (DNS) method revealed that isolate S-2 exhibited the highest crude amylase activity (7.98 ± 0.26 U/mL), compared to S-1 (5.21 ± 0.21 U/mL). Based on these findings, isolate S-2 was selected for further investigation. Protein concentration estimated by the Folin–Lowry method yielded 0.981 ± 0.03 mg/mL, with a corresponding specific activity of 8.14 ± 0.25 U/mg, confirming the isolates for industrial potential. Morphological analyses (Gram staining, spore staining, colony traits) indicated that isolate S-2 belonged to the Bacillus genus. This was supported by biochemical tests including catalase, Simmons’ citrate, starch hydrolysis, nitrate reduction, Voges-Proskauer and indole tests. The bacterial isolate was conclusively identified as Bacillus subtilis based on comprehensive molecular analysis involving 16S rRNA gene amplification, nucleotide sequencing, and subsequent phylogenetic evaluation showing over 99% similarity with reference sequences from the NCBI database. Amylase production from Bacillus subtilis S-2 was significantly enhanced through systematic strain improvement using physical (UV, gamma) and chemical (EMS) mutagenesis. The wild-type strain exhibited an initial amylase activity of 7.98 ± 0.26 U/mL, ii which significantly increased following mutagenic treatment. Among the conditions tested, UV exposure at 254 nm for 15 minutes resulted in the highest enzyme activity of 15.72 ± 0.32 U/mL, representing a 96.99% enhancement compared to the wild type. Gamma irradiation (1.0 kGy) and EMS (0.5%, 60 min) also significantly boosted production (15.11 ± 0.34 and 15.22 ± 0.48 U/mL, respectively). The UV-induced mutant (S2-UV3) was selected for further optimization. To maximize enzyme production, a dual-stage optimization strategy was employed, initially utilizing the conventional one-variable-at-a-time (OVAT) technique, followed by a more refined statistical optimization through Response Surface Methodology (RSM) based on the Box–Behnken Design (BBD). OVAT revealed optimal conditions pH 7.0, temperature at 45°C, 72 hours incubation and 1.5% starch achieving 24.21 ± 0.52 U/mL activity. Peptone (1.0%) was the best nitrogen source. Both commercial soluble starch and locally sourced potato starch yielded comparable enzyme activity (~24 U/mL), indicating agro-industrial applicability. RSM optimized the process further, with a robust model (R² = 98.96%, p < 0.0001). Predicted conditions (pH 7.02, 46.06°C and 1.56% starch) yielded 26.12± 0.46 U/mL in validation trials. Scaling-up in a 5 L fermenter with 1 vvm aeration and 130 rpm agitation improved production by 19.15%, reaching at 31.12± 0.62 U/mL attributed to enhanced oxygen transfer and temperature control. These results confirm process scalability and economic viability using locally available resources. Purification of amylase from UV-mutated (S2-UV3) was performed from RSM-optimized cultures. The preliminary crude enzyme preparation demonstrated an activity level of 26.12 ± 0.46 U/mL, accompanied by a protein content of 0.98 ± 0.04 mg/mL, thereby yielding a specific enzymatic activity of 26.65 U/mg protein. Following a three-step purification protocol comprising ammonium sulfate precipitation, dialysis, and gel filtration chromatography, the enzyme was recovered with an activity of 64.22 U/mL and a significantly enhanced specific activity of 133.79 U/mg. This process resulted in a 5.02-fold purification and a yield of 74.8%, indicating the effectiveness and reliability of the purification protocol in concentrating and refining the target enzyme. For long-term application, S2-UV3 was evaluated for strain preservation. Cryopreservation at –80°C in 20% glycerol retained ~80% activity after 12 months, while 4°C storage showed notable decline after 6 months. Thus, –80°C with glycerol is the optimal condition for long-term storage. Purified enzyme stability was assessed under varied storage conditions. While 4°C was maintained >70% (47.44 U/mL) activity for 6 months, significant losses occurred. Storage at iii –20°C and –80°C retained 75–78% activity after a year. Inclusion of 0.1% sodium azide and 20% glycerol enhanced stability up to 87%, while lyophilized enzyme at 4°C preserved over 92% activity. The lyophilization and freezing with glycerol are the most effective strategies for long-term enzyme stability. SDS-PAGE of the purified enzyme showed a single band (~56 kDa), confirming molecular purity and alignment with known Bacillus α-amylases. Absence of additional bands indicated structural homogeneity, essential for consistent industrial use. The purified amylase (64.22 U/mL) showed strong industrial applicability. In textile desizing, complete starch removal from cotton fabric was confirmed via iodine staining and reducing sugar release (4.20 ± 0.11 mg/mL). In detergent-assisted cleaning, enzyme-detergent synergy yielded maximum starch stain removal (4.86 ± 0.15 mg/mL). These findings validate the enzyme's eco-friendly, effective role in textile and detergent industries. In conclusion, this study successfully established a comprehensive work for the isolation, characterization, and mutagenesis-based improvement of a potent amylase-producing Bacillus subtilis strain sourced from locally collected soil samples. The use of low-cost agricultural waste, such as potato peels, as an alternative carbon source combined with systematic optimization and multistep purification led to the development of a highly active and stable enzyme. The purified amylase exhibited excellent performance in eco-friendly industrial applications, including textile desizing and detergent-based starch stain removal. Altogether, the optimized production process and improved bacterial strain offer a valuable biotechnological resource for sustainable, indigenous enzyme production in Bangladesh and hold promising potential for future industrial scale-up and commercialization. This thesis is submitted for the degree of Doctor of Philosophy.

DEVELOPMENT AND STUDY OF THE CHARACTERISTICS AND STABILITY OF A MICROPROCESSOR BASED FEEDBACK CONTROL SYSTEM FOR A THREE PHASE INDUCTION MOTOR

Sun, 07 Sep 2025 00:00:00 GMT

DEVELOPMENT AND STUDY OF THE CHARACTERISTICS AND STABILITY OF A MICROPROCESSOR BASED FEEDBACK CONTROL SYSTEM FOR A THREE PHASE INDUCTION MOTOR A microprocessor based three phase induction motor speed control system is designed and developed. The rated value of the motor is 1390 revolution per minute(rpm) 50 Hz. But by the use of present control system the motor speed can be varied from 500 rpm to 2000 rpm at the rated torque. A six step three phase inverter is designed to drive the motor. To avoid commutation failure in a wide frequency range n-channel MOS FET is used place of SCR. One way digital delay circuit is designed to avoid high voltage dc short circuit situation due to the FET's turn off delay. A computer interface card is designed to read the speed of the motor and to write (set) the required voltage level either in digitat to analogue(D/A) converter or in Demultiplexer to set the appropriate voltage which drive the VCO for generating required motor driving frequency. This frequency is then fed in logic circuit to generate device triggering pulses for three phase inverter. A number of programs in C++ is written to perform the activities between the computer and the interfacing card. In the screen of the computer we can see several aspects of the running motor such as speed, slip, torque and deviation of all these values from the rated values. 382875 A mechanical section is developed to apply some load to the motor. Several characteristics of the motor is observed in different loaded condition and presented in a graphical form. This experimental graphs are compared with the theoretical ones. And last the performance of the present work is evaluated and proposal is made for further development of the present motor control system. This thesis is submitted for the degree of Master of Philosophy.