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Numerical Simulation and Investigation of System Parameters of Sonochemical Process
Sankar Chakma,Vijayanand S. Moholkar
Chinese Journal of Engineering , 2013, DOI: 10.1155/2013/362682
Abstract: This paper presents the effects of various parameters that significantly affect the cavitation. In this study, three types of liquid mediums with different physicochemical properties were considered as the cavitation medium. The effects of various operating parameters such as temperature, pressure, initial bubble radius, dissolved gas content and so forth, were investigated in detail. The simulation results of cavitation bubble dynamics model showed a very interesting link among these parameters for production of oxidizing species. The formation of ?OH radical and H2O2 is considered as the results of main effects of sonochemical process. Simulation results of radial motion of cavitation bubble dynamics revealed that bubble with small initial radius gives higher sonochemical effects. This is due to the bubble with small radius can undergo many acoustic cycles before reaching its critical radius when it collapses and produces higher temperature and pressure inside the bubble. On the other hand, due to the low surface tension and high vapor pressure, organic solvents are not suitable for sonochemical reactions. 1. Introduction The sonochemistry concept is a well-established technique, and now it is considered as one of the most popular advanced oxidation processes. In the last few decades, sonochemical process became one of the most popular techniques for synthesis of catalysts as well as different types of materials [4–7], degradation of pollutants [8–12], synthesis of biodiesel [13, 14], and so forth. Numerous literatures on sonochemistry have already been published [15–18] which reported the various beneficial effects of sonochemistry. The principal phenomenon behind all of these effects is the cavitation. Cavitation is nothing but nucleation, growth, and implosive collapse of a bubble. Cavitation occurs through the formation of bubbles or cavities present in liquid medium. Each cavitating bubble contains gas or vapor or a mixture of gas-vapor. When bubble contains only gas, the expansion of bubble is mainly by diffusion, pressure reduction, or by rise in temperature. However, there are several parameters which are directly involved in transient cavitation. Transient cavitation is nothing but the growth of bubbles extensively over time scales of the order of the acoustic cycle and then undergoes an implosive/energetic collapse resulting in either fragmentation, decaying oscillation, or a repeat performance [19]. Cavitation can also be the result of the enlargement of cavities that are already present in bulk liquid. Sometimes cavitation bubbles are
Sonochemical Synthesis of Cobalt Ferrite Nanoparticles
Partha P. Goswami,Hanif A. Choudhury,Sankar Chakma,Vijayanand S. Moholkar
International Journal of Chemical Engineering , 2013, DOI: 10.1155/2013/934234
Abstract: Cobalt ferrite being a hard magnetic material with high coercivity and moderate magnetization has found wide-spread applications. In this paper, we have reported the sonochemical synthesis of cobalt ferrite nanoparticles using metal acetate precursors. The ferrite synthesis occurs in three steps (hydrolysis of acetates, oxidation of hydroxides, and in situ microcalcination of metal oxides) that are facilitated by physical and chemical effects of cavitation bubbles. The physical and magnetic properties of the ferrite nano-particles thus synthesized have been found to be comparable with those reported in the literature using other synthesis techniques. 1. Introduction The spinel ferrite nanoparticles have exceptional electronic and magnetic properties, which are quite different from the bulk materials [1]. As a result, the magnetic ferrite nanoparticles have found wide applications in information storage systems, ferrofluids, and medical applications like magnetic drug delivery and hyperthermia for cancer treatment [2]. Among metal ferrites, zinc, nickel, and cobalt ferrites have been mostly applied. Cobalt ferrite (CoFe2O4) is a hard magnetic material that is known to have high coercivity and moderate magnetization [3]. On nanoscale, the cobalt ferrite achieves properties of high saturation magnetization, high coercivity, strong anisotropy, high mechanical hardness, and high chemical stability [4]. Conventional techniques for synthesis of metal nanoparticles (including cobalt ferrite particles) are sol-gel method [5, 6], microemulsions [7, 8], reverse micelles [9], autocombustion, [10] and coprecipitation [11]. A relatively new technique for synthesis of ferrite nanoparticles is the sonochemical route [12–16], in which the reaction mixture is exposed to ultrasound irradiation. Spectacular physical and chemical effects induced by ultrasound bring about the synthesis of metal ferrites from the metal salt precursors, usually acetates. The hydrolysis of acetates, followed by oxidation of the hydroxides to oxides and the reaction between oxides to yield ferrites is brought about by ultrasound and its secondary effect, cavitation. Cavitation is essentially nucleation, growth and transient implosive collapse of gas bubbles driven by ultrasound wave [17]. This technique has been well demonstrated for zinc ferrites. In our previous papers [15, 16], we have tried to illuminate the links between physics of ultrasound and cavitation and the chemistry of zinc ferrite nanoparticles. It was revealed in these studies that chemical species produced during transient
Hill to Plain: Causes and Impacts of Internal Migration of Indigenous Peoples in Bangladesh  [PDF]
Basu Mittra Chakma, Asma Akter Akhy
Sociology Mind (SM) , 2015, DOI: 10.4236/sm.2015.54024
Abstract: Various factors are related in internal migration of indigenous peoples from their ancestral places, that is hill, to the plain areas. This article aims to find out the pull and push factors of the indigenous migration. The study has been conducted in Chittagong Export Processing Zone at Chittagong, Bangladesh. The major finding of the study is that indigenous peoples are greatly migrated to plain places for economic reason voluntarily. It also indicates that among 14 indigenous groups living in the Chittagong Hill Tracts (CHT), mainly Chakma people have been migrated in large volume. It finds that women are clearly ahead than their counterparts in migrating to the plain areas. The migrant’s traditional culture and customs are greatly affected after their migration which is highlighted in this paper.
Classical Interpretations of Relativistic Phenomena  [PDF]
Sankar Hajra
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.32026
Abstract: Electric charges, electric & magnetic fields and electromagnetic energy possess momentum and energy which we could experience with our sense organs. Therefore, all these are real physical entities (objects). All physical objects are sub- ject to gravitation. Therefore, electromagnetic entities should similarly be subject to gravitation. In this paper, we have shown that classical physics with this simple consideration is equivalent to the theory of relativity—special & general— to explain many puzzling electrodynamic as well as gravitational phenomena.
Classical Derivation of Auxiliary Lorentz Transforms: Their Relations with Special Relativity  [PDF]
Sankar Hajra
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.310180
Abstract: In this paper we have given a direct deduction of the auxiliary Lorentz transforms from the consideration of Maxwell. In the Maxwell’s theory, if c is considered to be the speed of light in ether space, his equations should be affected on the surface of the moving earth. But curiously, all electromagnetic phenomena as measured on the surface of the moving earth are independent of the movement of this planet. To dissolve this problem, Einstein (1905) assumes that Maxwell’s equations are invariant to all measurers in steady motion which acts as the foundation of Special Relativity. This assumption of Einstein is possible when all four auxiliary Lorentz transforms are real. There is not a single proof that could properly justify Einstein’s assumption. On the contrary it is now known that classical electrodynamics could easily explain all relativistic phenomena rationally.
Chirantan S Chakma
International Research Journal of Pharmacy , 2011,
Abstract: The investigation was carried out to study the antibacterial activity of the Madhuca longifolia(Koenig) in gram positive and gram negative organism.. Antimicrobial activity of the acetone and aqueous extracts of M.longifolia were determined against various pathogenic bacteria. The extracts were tested against various bacteria like Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginos, .E.coli by disk diffusion method. Minimum Inhibitory Concentration (MIC) values of both extracts were determined. It is concluded that acetone extract exhibited significant antimicrobial activity. The study lends scientific support for it’s use in folk medicine.
Chirantan S. Chakma
International Research Journal of Pharmacy , 2011,
Abstract: The study was carried out to assess the analgesic effect of aqueous and ethanolic extracts of isolated compound from M.longifolia seeds in rats and mice model. All three animal groups were administered the aq. and alc.ext of M.longifolia at a dose of 4 mg to 64 mg/kg body weight. The standard drug diclofenac 5 mg/kg b.w is used in three screening method. The paw licking time, tail withdrawal time and chemical writhings in mice both aq. and alc. extracts of M.longifolia prevents significant dose dependent anti-nociceptive effect. Diclofenac 5 mg/kg failed to alter significantly the antinociceptive effect of 16 to 32 mg of both extracts or the effect on chemical assay.
A Feasible Way of Degrading Malathion Pesticide under Laboratory Condition Using Phosphate Solubilizing Bacteria  [PDF]
Pratyasha Chakma, Sumaiya Chowdhury, Latiful Bari, Sirajul Hoque
Journal of Geoscience and Environment Protection (GEP) , 2019, DOI: 10.4236/gep.2019.71001
Abstract: An experiment was carried out for identification and determination of malathion degrading phosphate solubilizing bacteria isolated from the agricultural fields. In this study, malathion degrading phosphate solubilizing bacteria were identified using NBRIP (National Botanical Research Institute’s phosphate growth medium) media. A number of bacterial colonies were screened from agricultural fields. From primarily screened colonies 4 isolates were identified as phosphate solubilizing bacteria through qualitative and quantitative analysis. The isolated 4 bacterial colonies were inoculated in NBRIP broth media enriched with malathion pesticides to observe degradation of malathion pesticide under incubation study at three different temperatures (25°C, 30°C and 37°C). However, all the four isolates showed capability in degrading malathion pesticide. The study clearly revealed that phosphate solubilizing bacteria can be used in bioremediation of environmental pollution caused by malathion pesticide.
Chirantan S Chakma,Manish P. Patel
International Research Journal of Pharmacy , 2012,
Abstract: The study was carried out to identified the presence of isolate compound madlongiside-A from bark parts of Madhuca longifolia by TLC, IR,NMR and chemical test. Further single compound can be screened in anti inflammatory and analgesic activity by rat model. As such no pharmacological activity can be done previously and the result shown that the identified isolated compound have dose dependent activity.
Can incubators work in Africa? Acorn Technologies and the entrepreneur-centric model
Chakma Justin,Masum Hassan,Singer Peter A
BMC International Health and Human Rights , 2010, DOI: 10.1186/1472-698x-10-s1-s7
Abstract: Background Incubators are organizations that support the growth of new and typically technology-based enterprises, by providing business support services that bring together human and financial capital. Although the traditional role of incubators has been for economic development, they may also be a useful policy lever to tackle global health, by fostering the development and delivery of local health innovation. Given its high disease burden, life sciences incubators hold particular potential for Africa. As the most industrially advanced African nation, South Africa serves as a litmus test for identifying effective incubator policies. The case study method was used to illustrate how one such publicly funded incubator founded in 2002, Acorn Technologies, helped to catalyze local health product innovation. Discussion Acorn helped to support twelve biomedical device firms. One of them, Real World Diagnostics, was founded by a trainee from Acorn’s innovative internship program (Hellfire). It developed rapid strip diagnostic tests for locally prevalent diseases including schistosomiasis and HIV, and reported $2 million (USD) in revenue in 2009. Acorn achieved this success by operating as a non-profit virtual incubator with little physical infrastructure. Employing a virtual model in combination with stringent selection criteria of capital efficiency for clients proved to be effective in reducing its own fixed costs. Acorn focused on entrepreneurship training and networking, both critical at an early stage in an environment dominated by multinational biomedical device companies. Acorn and its clients learned that employing a cross-subsidy business model allowed one to generate royalty revenue through imports to subsidize R&D for local diseases. However, funding constraints and government expectations for rapid self-sustainability forced Acorn to merge with its sister biotechnology incubator in 2009. Summary A key to Acorn’s achievements was identifying entrepreneurs with technologies with health and economic impact, and providing them with flexible support from an early stage. A virtual organizational model helped Acorn to focus on supporting entrepreneurs. Governments and funders may wish to consider incubation strategies that draw from these good practices. With the right policies and business models, incubators have the potential to generate both health and economic benefits for Africa.
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