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Search Results: 1 - 10 of 16206 matches for " Mohammad Obaidur Rahman "
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Effect of Bismuth Addition on Structure and Mechanical Properties of Tin-9Zinc Soldering Alloy  [PDF]
Muhommad Abdul Wadud, M. A. Gafur, Md. Rakibul Qadir, Mohammad Obaidur Rahman
Materials Sciences and Applications (MSA) , 2015, DOI: 10.4236/msa.2015.69081
Abstract: Sn-Zn based solder is a possible replacement of Pb solder because of its better mechanical properties. The alloys need to be studied and explored to get a usable solder alloy having better properties. In this work eutectic Sn-9Zn and three Tin-Zinc-Bismuth ternary alloys were prepared and investigated their microhardness and mechanical properties. Microhardness, tensile strength and elastic modulus increase with Bi addition while ductility decreases with Bi addition.
Thermal Behavior and Magnetic Properties of Nd-Fe-B Based Exchange Spring Nanocomposites Nd4-xTbxFe83.5Co5Cu0.5Nb1B6 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1) Melt-Spun Ribbons  [PDF]
Palash Chandra Karmaker, Mohammad Obaidur Rahman, Nguyen Huy Dan, Samia Islam Liba, Per Nordblad, Dilip Kumar Saha, Sheikh Manjura Hoque
Advances in Materials Physics and Chemistry (AMPC) , 2017, DOI: 10.4236/ampc.2017.76018
Abstract: Co-rich Nd-Fe-B nanocomposite ribbons with Tb substituted have been fabricated by single roller melt spinning technique of Nd4-xTbxFe83.5Co5Cu0.5Nb1B6 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1) alloys in an argon (Ar) atmosphere at a circumferential speed of 40 m/s. According to the differential scanning calorimeter (DSC) traces the nanocomposite samples have been annealed at different temperatures like 675°C, 687°C, 700°C, 712°C and 725°C for 10 min. Crystallization behavior was studied by X-ray diffraction in which it was found that the XRD patterns are characterized by broad diffused pattern which demonstrate the amorphous state of materials. The ribbon samples were also characterized by vibration sample magnetometer (VSM) and Mössbauer spectroscopy at as-cast and annealed condition. Co-rich and Tb substitution has significantly enhanced the value of coercivity (Hc) and maximum energy product (BH)max. Highest value of Hc and (BH)max has been obtained as 2.36 kOe and 6.11 MGOe for the sample annealed at 700°C for 10 min with higher concentration of Tb. The M-H hysteresis loops show extremely soft natures which do not possess any area. We have found reduced remanent ratio (Mr/Ms) up to 0.49 at optimal annealing temperature 700°C. However, with the annealing of the samples in the above mentioned temperature, evolution of large coercivity was observed due to the formation of exchange couple hard and soft nanocrystal composites. We have investigated the variation of Curie temperature (Tc) with annealing temperature of the melt spun ribbon samples. Mossbauer spectroscopy was carried out to study the hyperfine parameters such as hyperfine field, hyperfine field distribution for full width half maximum (FWHM) and isomer shift of Fe species of these two phases.
Design of an Efficient MAC Protocol for Opportunistic Cognitive Radio Networks
Mahfuzulhoq Chowdhury,Asaduzzaman,Mohammad Obaidur Rahman,Md. Fazlul Kader
International Journal of Computer Science & Information Technology , 2012,
Abstract: Cognitive radio technology has been developed in recent years to make efficient use of the wirelessspectrum especially for opportunistic spectrum access. Cognitive radio technology enables the secondary(cognitive) users to use the unused licensed spectrum of the primary users. Medium Access Control (MAC)protocol plays a vital role in spectrum utilization, primary user’s (PU) interference management andsecondary user’s coordination in cognitive radio (CR) networks. Here, we propose a new MAC protocolwhere control transceiver attached with sensor improves the accuracy of spectrum sensing result as well asprotects the primary user from interference. In our proposed MAC protocol, each secondary user (SU) isequipped with two radios, solves the multichannel hidden terminal problem (MHTP). Our proposed MACprotocol considers collision avoidance among SU’s and between SU’s and PU’s. We develop an analyticalmodel validated by simulation. Our scheme improves the network throughput in presence of sensing error.
Socio Demographic and Health Related Determinants of Over Weighted Diabetic Patients in Bangladesh
Obaidur Rahman,Rafiqul Islam
Current Research Journal of Biological Sciences , 2012,
Abstract: The purpose for this study is to assess the socio-demographic and health related determinants of over weighted diabetic patients in Bangladesh. To fulfill this objective, chi square and logistic regression analysis have been performed using the data extracted from 300 diabetic patients attending Rajshahi Diabetes Association, Rajshahi, Bangladesh. The assessment of this study shows that 29.7% of all diabetic patients have over weight of which female diabetic patients (19.0%) are more over weighted than male diabetic patients (10.7%). Also, peoples have a higher risk to develop abdominal obesity and diabetes with increasing their age especially older age. The majority of over weighted diabetic patients (15.3%) is sleeping more than normal hours (>6 h) and 10.7% have over weight with high blood pressure. Poor control of diabetes is one of the main reasons to develop over weight. It has been found that age, sex, controlling diabetic through exercise, increasing diabetes because of food habit, low blood pressure and high blood pressure are significantly associated with the over weight of diabetic patients. Also, it is identified that age, sex, education, duration of sleeping, controlling diabetic through exercise, increasing diabetes because of food habit, low blood pressure, normal blood pressure and high blood pressure have significant effect on over weight.
Association between Fasting of Ramadan and Risk Factors of Diabetes: A Study from Rajshahi City in Bangladesh
Obaidur Rahman,Md. Rafiqul Islam
Advance Journal of Food Science and Technology , 2011,
Abstract: The purpose of the study is to identify the association between fasting of Ramadan and risk factors of diabetes through χ2-test using the data of 297 Muslim diabetic patients collected from Rajshahi Diabetes Association, Rajshahi, Bangladesh. It is seen that 61.3 and 38.7% respondents perform religious activities regularly and irregularly respectively. But 86.2% respondents perform Ramadan fasting in which 57.6% and 28.6% respondents perform fasting in Ramadan regularly and irregularly respectively. The majority of respondents (79.5%) are belonged to >40 years of age where 68.7% perform fasting in Ramadan. Most of the respondents with performing Ramadan fasting (52.5%) are in middle (41-60 years) age group and they have a greater risk of diabetes with increasing their age especially after age 40 years. Again, 55.6 and 56.2% patients with fasting in Ramadan have normal blood pressure and normal weight respectively. So, fasting of Ramadan helps to keep blood pressure normal and to control weight of body which is very important for diabetic patients. During Ramadan fasting, there are 56.5% patients whose diabetic situation is decreasing or stable, 62% patients whose gastric have been decreasing and 48.1% patients whose weight of the body have been losing. Again, only 11.8% patients with fasting in Ramadan have a habit of smoking at present and the rest of them are not smoking at present. Also, it is found that respondent’s age, occupation, living house, blood pressure, perform religious activities, diabetic situation during performing Ramadan, gastric decreasing during performing Ramadan, losing weight during performing Ramadan and smoking habit are significantly associated with fasting in Ramadan. So, Ramadan fasting can play an important role for controlling blood pressure, weight of the body, gastric, diabetes and for avoiding habit of smoking which is very essential for healthy life.
Determinants of HIV/AIDS Awareness among Garments Workers in Dhaka City, Bangladesh  [PDF]
Nazrul Islam Mondal, Rafiqul Islam, Obaidur Rahman, Shafiur Rahman, Nazrul Hoque
World Journal of AIDS (WJA) , 2012, DOI: 10.4236/wja.2012.24042
Abstract: The main purpose of this study is to find the awareness level as well as the determinants of awareness on HIV/AIDS among the garments workers in Dhaka City, Bangladesh. To do so, 200 garments workers were interviewed through a structured questionnaire using purposive sampling technique. As the statistical tools, univariate analysis was completed to figure out frequency distribution and the binary logistic regression model was used to predict the probability occurrence of the events by fitting data. The results revealed that the majority of the garments workers (63.5%) are very young (18 - 27 years), almost all (97.5%) are literate and most of them (57.0%) used contraceptives. Importantly, most of the respondents (64.0%) had not participated in any type of seminar or workshop related to HIV/AIDS, though almost all the respondents (84.5%) know HIV is a dangerous and life threatening disease. The logistic regression model identified that respondents' education, contraceptive usage, mass media and HIV workshops have statistically significant positive effects on HIV/AIDS awareness. Various media campaigns are strongly suggested to be increased knowledge and awareness to control the spread of HIV as well as STDs among garments workers in Bangladesh.
Germanium Based Two-Dimensional Photonic Crystals: The Hexagonal and Honeycomb Lattices  [PDF]
Fairuz Aniqa Salwa, Muhammad Mominur Rahman, Muhammad Obaidur Rahman, Muhammad Abdul Mannan Chowdhury
Optics and Photonics Journal (OPJ) , 2019, DOI: 10.4236/opj.2019.93004
Abstract: The properties of two-dimensional (2D) photonic crystals (PCs) composed of germanium (Ge) are discussed. We investigate polarization-dependent photonic band diagrams (transverse electric and transverse magnetic polarizations), gap maps, surface plots, contour maps, etc. for 2D PCs with Ge rods in air and vice versa for two different lattices geometries, namely hexagonal and honeycomb lattices. The obtained graphs for the four possible combinations are presented in this paper. All the graphs depict clear photonic band gaps. The conditions for the largest TE and TM band gaps are described. The honeycomb lattice of Ge rods in air background offers a large complete photonic band gap Δω/ωm greater than 8% (for rod radius of r = 0.2 μm). Using these data, new Ge based photonic devices can be fabricated to confine, control and manipulate light in a more useful way.
Maternity Benefit Practices at NGOs in Bangladesh: Laws and Implementation  [PDF]
Omar Faroque, Md. Rafiqul Islam, Md. Obaidur Rahman, Md. Mominul Islam
Beijing Law Review (BLR) , 2013, DOI: 10.4236/blr.2013.44021

Maternity leave is an important benefit to the female employees and it plays important role to increase organizational loyalty, efficiency and job satisfaction, particularly in the Non-Government Organizations (NGOs). The objective of the study is to assess the laws and implementation of the maternity benefits at the diverse NGOs on different working echelon inBangladesh. Descriptive statistics and zero order correlation method have been performed using the data haul out from one hundred female employees experiencing at least one child at the different NGOs inKurigram District,Bangladesh. Among all female employees, salary structure and the managerial position are not satisfactory at NGOs in Bangladesh, although higher education of females plays an important role to get the job. In case of maternity benefits, all of them have got three or four months as maternity leave period and a significant number have not got any types of payment during maternity leave (27%), have not enjoyed maternity leave properly (24%), and have been terminated, sent away or expelled etc. due to maternity leave (19%). In addition, an inverse relation of duration of maternity leave with age (26.4%) and length of service (34.1%) has also been identified i.e., duration of maternity leave decreases with increasing employees’ age and length of services. In our study, evidently there are no NGO practices laws of maternity benefit properly in Bangladesh. Therefore, every NGO should administer and implement the Laws of maternity benefit properly.

Isolation of Bulk Amount of Piperine as Active Pharmaceutical Ingredient (API) from Black Pepper and White Pepper (Piper nigrum L.)  [PDF]
Zihan Rahman Khan, Fatema Moni, Suriya Sharmin, Muhammad Abdullah Al-Mansur, Abdul Gafur, Obaidur Rahman, Farhana Afroz
Pharmacology & Pharmacy (PP) , 2017, DOI: 10.4236/pp.2017.87018
In the pharmaceutical world the majority of the active pharmaceutical ingredients (API) have been obtained from the natural products. Piperine is such naturally occurring alkaloid which can be considered as major bioactive phytochemical having broad spectrum of pharmacological activities. It is obtained from the most valuable ethnomedicinal spices peppercorns i.e. black pepper and white pepper, which are the fruits of the Asian vine Piper nigrum L. Because of the widespread traditional uses of this medicinal compound, present article reveals a simple and effective isolation method of bulk piperine. The novelty of this investigation is to provide an idea for utilizing such natural method of large scale commercial piperine production as API drug in spite of chemical synthesis. Piperine was isolated in a pure crystal form and characterized by its melting point, X-Ray diffraction (XRD) studies and spectral data, including two-dimensional nuclear magnetic resonance (2D-NMR) spectroscopy. Chromatographic techniques like Thin Layer Chromatography (TLC) and High Performance Liquid Chromatography (HPLC) were applied to determine the purity of the yielded piperine. It was found that piperine yield from black pepper was within 2.5% - 3.0% and from white pepper within 4.0% - 4.5% and the purity of the yielded piperine was found to be up to 98.5% for black pepper and 98.2% for white pepper. Considering this yield value and purity it is indicated that, such effective isolation method can be successfully utilized for industrial large-scale production commercially. According to the result, it can be claimed that, as a natural product the isolated piperine can also be utilized as API drug like other expensive chemically synthesized piperine in different drug formulation.
Status of Selective Emitters for p-Type c-Si Solar Cells  [PDF]
Mohammad Ziaur Rahman
Optics and Photonics Journal (OPJ) , 2012, DOI: 10.4236/opj.2012.22018
Abstract: Crystalline silicon (c-Si) solar cells have the lion share in world PV market. Solar cells made from crystalline silicon have lower conversion efficiency, hence optimization of each process steps are very important. Achieving low-cost photovoltaic energy in the coming years will depend on the development of third-generation solar cells. Given the trend towards these Si materials, the most promising selective emitter methods are identified to date. Current industrial monocrystalline Cz Si solar cells based on screen-printing technology for contact formation and homogeneous emitter have an efficiency potential of around 18.4%. Limitations at the rear side by the fully covering Al-BSF can be changed by selective emitter designs allowing a decoupling and separate optimization of the metallised and non-metallised areas. Several selective emitter concepts that are already in industrial mass production or close to it are presented, and their specialties and status concerning cell performance are demonstrated. Key issues that are considered here are the cost-effectiveness, added complexity, additional benefits, reliability and efficiency potential of each selective emitter tech- niques.
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