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This paper presents a statistical and numerical investigation that examines the optimization and sensitivity analysis of the unsteady laminar natural convective heat transfer flow of Fe3O4-water nanofluid in a hexagonal cavity considering the impacts of a sloping magnetic field in one-component nanofluid model. The inclined walls of the cavity are maintained at a constantly low temperature, while the bottom wall is uniformly heated. The upper wall, however, is regarded as adiabatic. The nanofluid thermal conductivity model incorporates the impact of Brownian motion. The Galerkin weighted residual finite element method has been employed to solve the governing dimensionless equations. The results are provided regarding the average Nu, streamlines, and isotherms. The study uses response surface methodology to analyze the sensitivity of parameters such as the Ha, Ra, and nanoparticle volume percentage. Using a response surface policy allows for optimizing the process and identifying the most favorable circumstances to achieve the maximum thermal transfer rate. The flow pattern of the nanofluid is significantly affected by the magnetic field and its alignment. The numerical results indicate a significant rise in the average Nu as the nanoparticle volume percentage, magnetic field inclination angle, nanoparticle type factor, and Ra increase. Conversely, the Hartmann number and the nanoparticle's diameter have contrasting effects. When considering Brownian motion, the average Nu grows by 225.89 % for Ra = 106 with ϕ = 0.03 and 25.28 % for the other case. The optimal condition for heat transfer occurs when Ra = 106, Ha = 4, and ϕ =0.03 while keeping the other parameters constant.

This study seeks to examine quantitatively the two-dimensional unsteady free convective heat transfer enhancement of Al2O3-Cu/H2O hybrid nanofluid within a rectotrapezoidal-shaped structure. The lower wall is both uniformly and non-uniformly heated with different thermal boundary conditions, the top horizontal wall is adiabatic, and the vertical and inclined walls are assumed chilly. The enclosure is penetrated by a periodic magnetic field. A set of variable transformations is used to render the governing equations dimensionless, which makes it possible to identify the model parameters that control it. The finite element method is then used to numerically solve these equations. To verify the code's numerical precision, comparisons with formerly available works are performed and, a high level of agreement is obtained among the results. The generated outcomes are shown for the principal parameters that control the flow in the context of streamlines, heat lines, isotherms, average Nusselt number, friction factor, and thermal efficiency index. The findings demonstrated that the efficiency index, friction factor, and heat transmission are all considerably influenced by the Rayleigh number (Ra). The lowest Ra yields the maximum thermal efficiency. The results also revealed that the hybrid nanoparticle volume fraction and period of the magnetic field amplified the heat transfer rate and efficiency index due to the increased pumping force. It is observed that when the percentage of the mixing ratios for Cu nanoparticles rises from 0% to 100%, the heat transport in Al2O3-Cu/H2O hybrid nanofluid increases for a fixed volume fraction of hybrid nanoparticles. As compared to parabolic and sinusoidal boundary conditions, the uniform temperature boundary setting for Ra = 105 exhibits the highest average rate of heat transport of 10.04. The average Nusselt number increases by 25.12% at Ra = 103 with a 3% volume fraction of hybrid nanofluid as compared to pure water and the mixing ratios of Al2O3:Cu = 0:300 gives the highest increased rate of 16.30%. The results further illustrate that Al2O3-Cu/H2O hybrid nanofluid has the highest heat transfer rate compared to the pure water and Al2O3– H2O nanofluid.

Radon is a naturally occurring carcinogenic agent, poses a serious health hazard when inhaled or ingested in significant amounts. The water of the Padma river will be used as a tertiary coolant for the soon-to-be-commissioned ‘Rooppur Nuclear Power Plant’. Hence, it is important to assess the radiological status of the river prior to the commission of this power plant. Therefore, for the first time, 25 samples of water were collected from various locations of the Padma River and analyzed for radon concentration using the RAD H2O (DURRIDGE) radon monitoring device. The radon concentrations were found in the range from 0.077 ± 0.036 to 0.494 ± 0.211 Bq/L with a mean of 0.250 ± 0.093 Bq/L. All the concentrations were found to be below the recommended limits of WHO (100 Bq/L) and USEPA (11.1 Bq/L). The mean annual effective dose due to the radon exposure via inhalation and ingestion pathways were 0.638 μSv/y and 0.629 μSv/y, respectively, which were all well below the annual effective dose recommended by WHO (0.1 mSv/y). Since Bangladesh lacks a national safety limit of radon in water, this pioneering study provides baseline data on radon levels for the environment around Rooppur Nuclear Power Plant.

In a first-of-its-kind study, terrestrial radionuclide concentrations were measured in 35 topsoil samples from the outskirts of Dhaka using HPGe gamma-ray spectrometry to assess the radiological consequences of such a vast number of brick kilns on the plant workers, general as well as dwelling environment. The range of activity concentrations of 226Ra, 232Th, and 40K is found at 19 ± 3.04 to 38 ± 4.94, 39 ± 5.85 to 57 ± 7.41, and (430 ± 51.60 to 570 ± 68.40) Bq/kg, respectively. 232Th and 40K concentrations were higher than the global averages. Bottom ash deposition in lowlands, fly ash buildup in soils, and the fallout of micro-particles are all probable causes of the elevated radioactivity levels. 137Cs was found in the sample, which indicates the migration of 137Cs from nuclear accidents or nuclear fallout, or the contamination of feed coal. Although the effective dose received by the general public was below the recommended dose limit but, most estimates of hazard parameters surpass their respective population weighted global averages, indicating that brick kiln workers and nearby residents are not safe due to prolonged exposures to terrestrial radiation. In addition, the soil around sampling sites is found to be unsuitable for agricultural purposes.

Background: Dietary exposure is the main source of bioaccumulation of trace elements through contaminated fruits and vegetables, which are rich sources of vitamins and minerals, but also toxic elements, which harm our health and well-being. Objectives: This study focused on human health nutrition and risks associated with the cancer-causing and non-cancerous trace elements in commonly available winter fruits and vegetables collected from Mymensingh divisional city markets. Methods: Six locally available fruits (viz. pineapple, guava, hog plum, water chestnut, banana, Indian olive) and six seasonal vegetables (viz. red amaranth, radish leaves, brinjal, bottle gourd, radish, and carrot) were collected. The atomic absorption spectrophotometer was used to determine the contents of Zn, Fe, Mn, Cu, Pb, Cr, and Cd. Target Hazard Quotient (THQ), Hazard Index (HI), and Cumulative Incremental Lifetime Cancer Risk (∑ILCR) were calculated to estimate non-cancer and cancer health risks. Results: All trace element contents were higher in vegetables than in fruits except Cu. Chromium contents were below the detectable limit for all fruits and vegetables. The highest amounts of Zn (10.54 µg g−1 fresh wt.), Fe (68.75 µg g−1 fresh wt.) and Mn (55.65 µg g−1 fresh wt.) were found in radish leaves. On the other hand, the maximum amounts of Pb (0.388 µg g−1 fresh wt.) and Cd (0.180 µg g−1 fresh wt.) were found in red amaranth, while the highest content of Cu (5.67 µg g−1 fresh wt.) was determined from banana. The calculated HI was

Nonlinear damped forced oscillators are very importance in the fields of mechanical, electrical and other dynamical systems. Small oscillations are being investigated by classical perturbations. Earlier Cheung et al. presented a modified Lindstedt–Poincare method for large amplitude of oscillation; but its mathematical manipulation is tremendously difficult. Moreover, it fails to determine the solutions when linear restoring force vanishes. In this article, a modification of the same method is made which greatly reduces mathematical calculations. On the other hand, it provides more accurate results and is used whether linear restoring force is present or not.

A 10-week indoor culture study was done to evaluate the effects of varying C/N ratios on growth performance, body composition, immunity, and haematology of stinging catfish Heteropneustes fossilis cultured in zero-water exchange culture tanks. Biofloc-based tanks with four levels of C/N ratio (12, 15, 18, 21) via the addition of carbohydrate referred to as ‘CN12′, ‘CN15', 'CN18' and 'CN21', and freshwater tanks operated with the facility of water exchange and without the addition of carbohydrate referred to as 'Control' (CN10). Fish (average weight 0.60 g) were stocked in 15 experimental tanks with 300 L water capacity and fed a commercial diet containing 30 % crude protein. The water quality parameters (pH, temperature, total ammonia nitrogen, nitrite nitrogen, dissolved oxygen, total suspended solids, and total dissolved solids) were monitored throughout the experiment. There was no significant (P > 0.05) difference among the treatments in the case of DO and temperature. The pH, total ammonia nitrogen, and nitrite nitrogen contents decreased with increasing C/N ratio, whereas the total dissolved solids and total suspended solids increased with gradually increasing the C/N ratio. Compared to the control, the treatment CN15 resulted in a 72 % and 34.4 % higher percent weight gain and specific growth rate, respectively. CN15 treatment resulted in improved feed utilization, as measured by feed conversion ratio (1.32 ± 0.07) and protein efficiency ratio (1.36 ± 0.10), which were 36.2 % lower and 54.5 % higher, respectively, than control. However, there were no differences in growth performance and feed utilization data between CN15 to CN21. Increasing the C/N ratio increased the body protein and ash contents and decreased the moisture and lipid contents compared to control. In the serum lysozyme test, the lysozyme value increased with a gradually increasing C/N ratio, and a better result was found in the CN15-CN21 treatments (15.58–15.74 µg ml−1) compared to the control (12.45 µg ml−1). At the end of the rearing period, fish were subjected to a challenge test with Aeromonas hydrophilla to determine the mortality rate where mortality was the lowest in CN15 treatment. Furthermore, increasing the C/N ratio from 15 to 21:1 showed better results for haemoglobin, white blood cells, red blood cells and hematocrit values. Overall, the manipulation of the C/N ratio from 15 to 21:1 revealed suitable for the feed utilization, growth performance, body composition, and immunity of stinging catfish. Therefore, maintaining a C/N ratio of 15:1 can be recommended for the culture of stinging catfish in the biofloc system.

This study investigated the effective utilization of black cumin (Nigella sativa) extract as natural antioxidant source in cooked beef patties at refrigeration storage for 15 days and its efficacy was figured out against synthetic antioxidant butylated hydroxyl anisole (BHA). For this purpose, beef patties were formulated having five treatments namely control group (T0), 0.1% BHA (T1), 0.1%, 0.2% and 0.3% black cumin extract as (T2), (T3) and (T4) respectively. Day's intervals of this study were on 0, 5th, 10th, and 15th day. Black cumin extract revealed an excellent antioxidant activity over BHA in terms of sensory (color, flavor, tenderness, juiciness, and overall acceptability) and physicochemical (pH, free fatty acids (FFA), peroxide value (POV) and thiobarbituric acid reactive substance (TBARS)) qualities in patties. Sensory attributes and pH value were decreased significantly (p

The modified Lindstedt-Poincare method has been generalized for solving strongly nonlinear oscillators. The original formula (presented by Cheung et al.) covers a class of nonlinear problems. So, it requires another formula to cover the remaining class. Usually two solutions can be found for all nonlinear oscillators (utilizing the original and proposed formulae), but one of them is suitable only. The new formula has been derived in a similar way of Cheung et al. However, using two simple conversion formulae such approximate solutions can be found easily from the classical Lindstedt-Poincare solution. For some rare nonlinear oscillators it requires their combination. In lack of linear restoring force the original formula (of Cheung et al.) fails. The generalized method also covers it. Keywords: Nonlinear oscillation, Perturbation method, Modified Lindstedt-Poincare method

Recently, an approximate solution of the quadratic nonlinear oscillator has been presented based on the harmonic balance method. According to this method a set of nonlinear algebraic equations appear among the unknown coefficients of the several harmonic terms. Moreover, all these algebraic equations have no analytic solutions and sometimes no real solution can be found. In this article, a simple form of harmonic balance solution is obtained where algebraic complexity is partially reduced and all the related nonlinear algebraic equations are solved analytically.

In this paper, a new analytical approach based on harmonic balance method (HBM) is presented to obtain the approximate periods and the corresponding periodic solutions of quadratic nonlinear oscillators. The result obtained in new approach has been compared with that obtained by other existing method. The present method gives not only better result than other existing result but also gives very close to the corresponding numerical result (considered to be the exact result). Moreover, the method is simple and straightforward. Keywords: Quadratic nonlinear oscillator, Harmonic balance method, Periodic solution

A modified energy balance method (EBM) has been presented to obtain higher-order approximate periodic solutions from the integral expression (i.e., first order differential equation) of some nonlinear oscillators. It has been shown that the method is more effective than the classical EBM as well as some recently developed approaches such as homotopy perturbation method, harmonic balance method and iterative method. Keywords: Energy balance method, Perturbation method, Nonlinear oscillators, Constant force oscillator

This paper investigates thermophoretic deposition of micron sized particles on unsteady forced convective heat and mass transfer flow due to a rotating disk. Using similarity transformations the governing nonlinear partial differential equations are transformed into a system of ordinary differential equations that are then solved numerically by applying Nachtsheim–Swigert shooting iteration technique along with sixth-order Runge–Kutta integration scheme. The effects of the pertinent parameters on the radial, tangential and axial velocities, temperature and concentration distributions, and axial thermophoretic velocity together with the local skin-friction coefficient, and local Nusselt number are displayed graphically. The inward axial thermophoretic deposition velocity (local Stanton number) is also tabulated. The obtained results show that axial thermophoretic velocity is increased with the increasing values of the thermophoretic coefficient, thermophoresis parameter, rotational parameter as well as unsteadiness parameter. The results also show that inward axial thermophoretic particle deposition velocity decreases with the increase of the Lewis number.

In this paper, an analytical approximate technique based on harmonic balance method (HBM) is presented to obtain the approximate frequencies and the corresponding periodic solutions of a conservative oscillator having inertia and static non-linearity. The results of the present paper are valid for small and large amplitudes of oscillation. In previous articles, the first and second approximations were determined for the same oscillator; but the results were not close to the exact result. On the contrary, the new results of this paper are very close to the exact result. Keywords: Harmonic balance method, Non-linear oscillation, Large amplitude

The molecular marker is a useful tool for assessing genetic variations and resolving cultivar identities. Information on genetic diversity and relationships among rice landraces from Bangladesh is currently very limited. Thirty-five rice genotypes including 33 landraces and 01 HYV of Bangladesh and 1 Indian landrace of particular interest to breeding programs were evaluated by means of random amplified polymorphic DNA (RAPD) technique. For molecular characterization, RAPD markers viz., OPC 03, OPC 04 and OPA 01 gave reproducible and distinct polymorphic amplified products. A total of 20 RAPD bands were scored of which 15 polymorphic amplification products were obtained by using these arbitrary primers. The size of amplified fragments were ranged from 550 to 1775 bp. Based on analysis performed on a similarity matrix using UPGMA, 35 genotypes were grouped into 2 main clusters. Landrace Sylhet balam and Mota aman was totally different from other genotypes. The information will facilitate selection of genotypes to serve as parents for effective rice breeding programs in Bangladesh.

In this paper, a design method for optimal cancer chemotherapy schedules via genetic algorithm (GA) is presented. The design targets the key objective of chemotherapy to minimize the size of cancer tumor after a predefined time with keeping toxic side effects in limit. This is a difficult target to achieve using conventional clinical methods due to poor therapeutic indices of existing anti-cancer drugs. Moreover, there are clinical limitations in treatment administration to maintain continuous treatment. Besides, carefully decided rest periods are recommended to for patient’s comfort. Three intermittent drug scheduling schemes are presented in this paper where GA is used to optimize the dose quantities and timings by satisfying several treatment constraints. All three schemes are found to be effective in total elimination of cancer tumor after an agreed treatment length. The number of cancer cells is found zero at the end of the treatment for all three cases with tolerable toxicity. Finally, two of the schemes, “Fixed interval variable dose (FIVD) and “Periodic dose” that are periodic in characteristic have been emphasized due to their additional simplicity in administration along with friendliness to patients. responses to the designed treatment schedules. Therefore the proposed design method is capable of planning effective, simple, patient friendly and acceptable chemotherapy schedules.

In this paper, a design method for optimal cancer chemotherapy schedules via genetic algorithm (GA) is presented. The design targets the key objective of chemotherapy to minimize the size of cancer tumor after a predefined time with keeping toxic side effects in limit. This is a difficult target to achieve using conventional clinical methods due to poor therapeutic indices of existing anti-cancer drugs. Moreover, there are clinical limitations in treatment administration to maintain continuous treatment. Besides, carefully decided rest periods are recommended to for patient’s comfort. Three intermittent drug scheduling schemes are presented in this paper where GA is used to optimize the dose quantities and timings by satisfying several treatment constraints. All three schemes are found to be effective in total elimination of cancer tumor after an agreed treatment length. The number of cancer cells is found zero at the end of the treatment for all three cases with tolerable toxicity. Finally, two of the schemes, “Fixed interval variable dose (FIVD) and “Periodic dose” that are periodic in characteristic have been emphasized due to their additional simplicity in administration along with friendliness to patients. responses to the designed treatment schedules. Therefore the proposed design method is capable of planning effective, simple, patient friendly and acceptable chemotherapy schedules.

The modified solutions of some nonlinear oscillators have been obtained based on the classical iteration procedure. In this article we have used the Fourier series and utilized all of its terms (sometimes approximately) in each iterative step. The third and fourth approximate frequencies of different nonlinear problems show good agreement with the exact values.

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Diploma in Youth Development Work (DYDW) imparted through distance mode which was introduced at Bangladesh Open University (BOU) in 1999 aiming at accessible and flexible learning opportunities to the young men and women involved in youth development activities and prepare the participating youth towards performing active and constructive role in the regeneration of their fellow youth to become effective partners in socio-economic development. The program feature and success and failure of the enrolled students have been discussed. Rural and urban, male and female, government and non-government, and gender issues were considered in the study for the enrolled students. Up to 2006, three cycles of the program have been completed and 25%, 27% and 16% of the students respectively of 1st, 2nd and 3rd cycle could successfully complete. The dropout rate of the 1st, 2nd and 3rd cycle were 51%, 41% and 67% respectively. The drop out rate is very high and increasing day by day. The reasons of high dropout rate might be due to language difficulty, lack of proper recommendation in high competitive job opportunities, lack of service incentives, financial support, scholarship/fellowship and recognition as cadre service by the Government. Service incentives to the diploma graduates have been suggested to reduce the attrition rate. (Contains 2 figures.)