Role of Synthetic Slag Treatment on the Morphology of Non-Metallic Inclusions and Subsequent Cold Drawability of the High Carbon Wire Rod Steel

Alok Srivastava,Ashok Kamaraj,Durbadal Mandal,K. Mondal,Gopi K. Mandal 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.7

The present work discusses the evolution of microstructure and non-metallic inclusions during wire drawing process in asynthetic slag-treated 5.5 mm diameter high carbon wire rod steel. It has been observed that failure of the as-received wirerod (without synthetic slag treatment) takes place at different stages of deformation during wire drawing operation. However,in case of the synthetic slag-treated wire rods (TW specimen), failure takes place consistently at ~ 95% reduction in thecross-sectional area of the wire. In a quest to understand the failure mechanisms during wire drawing process, a systematicstudy has been carried out by analyzing the microstructures and non-metallic inclusions in the steel wires drawn at variousstages of deformation. The improved drawability of the treated wire specimens is attributed to the decrease in the amountof unfavourable non-deformable inclusions in the steel matrix, and this stems from the synthetic slag treatment of the liquidsteel. Microstructural investigation also confirms the complete realignment of pearlite colonies along the wire drawingdirection followed by thinning and disintegration of cementite lamellae at higher deformation, particularly in case of thesynthetic slag-treated wire rod steel.

Production of Azadirachtin from Plant Tissue Culture: State of the Art and Future Prospects

Ashok K. Srivastava,Gunjan Prakash,Sant S. Bhojwani 한국생물공학회 2002 Biotechnology and Bioprocess Engineering Vol.7 No.4

With increasing awareness towards environment-friendly and non-toxic pesticide azadirachtin obtained from neem tree (Azadirachta indica) is gaining more and more importance. Its broad-spectrum activity, peculiar mode of action. eco-friendly and non-toxic action towards beneficial organisms has offered many advantages over chemical pesticides. All currently use commercial formulations based on azadirachtin contains azadirachtin extracted from seeds of naturally grown whole plants which is labour intensive process depending upon many uncontrollable geographical and climatic factors. Plant tissue culture can be a potential process for the production, offering consistent, stable and controlled supply of this bioactive compound, However the research on tissue culture aspects of production are in preliminary stage and requires culture and process optimization for the development of a commercially viable process. This review states the present status and future challenges of plant tissue culture for azadirachtin production.

Bioprocess Strategies and Recovery Processes in Gibberellic Acid Fermentation

Ashok K. Srivastava,Ruchi Shukla,Subhash Chand 한국생물공학회 2003 Biotechnology and Bioprocess Engineering Vol.8 No.5

Gibberellic acid (GA3) is a commercially important plant growth hormone, which is gaining much more attention all over the world due to its effective use in agriculture and brewing industry. Industrially it is produced by submerged fermentation technique using Ascomycetous fungus Gibberella fujikuroi. Solid state and immobilized cell fermentation techniques had also been developed as an alternative to obtain higher yield of GA3. This review summarizes the problems of GA3 fermentation such as production of co-secondary metabolites along with GA3, substrate inhibition and degradation of GA3 to biologically inert compound gibberellenic acid, which limits the yield of GA3 in the fermentation medium. These problems can be overcome by various bioprocessing strategies e.g. two - stage and fed batch cultivation processes. Further research on bioreactor operation strategies such as continuous and / or extractive fermentation with or without cell recycle / retention system need to be investigated for improvement in yield and productivity. Down stream processing for GA3 isolation is also a challenge and procedures available for the same have been critically evaluated.

Variability of Azadirachtin in Azadirachta indica (neem) and Batch Kinetics Studies of Cell Suspension Culture

Ashok K. Srivastava,Gunjan Prakash,C. J. S. K. Emmannuel 한국생물공학회 2005 Biotechnology and Bioprocess Engineering Vol.10 No.3

Seeds of neem were collected from different parts of India and analyzed for their azadirachtin content by High Performance Liquid Chromatography (HPLC). In order to assess the effects of genotypic and geographical variation on azadirachtin content in cell cultures, callus development was attempted in the seeds containing high and low concentration of azadirachtin. The concentration of azadirachtin in callus cultures was significantly affected by the explant source. Seed kernels with higher azadirachtin content produced higher azadirachtin content in callus cultures and lower azadirachtin content was seen in callus cultures produced from seed kernels with low azadirachtin content. The protocol for development of elite stock culture of Azadirachta indica was established with the objective of selecting a high azadirachtin-producing cell line. The highest azadirachtin-producing cell line was selected and the effects of different media and illumination conditions on growth and azadirachtin production were studied in shake flask suspension culture. Detailed batch growth kinetics was also established. These studies provided elite starter culture and associated protocols for cultivation of A. indica plant cell culture in the bioreactor.

Bioprocess Strategies and Recovery Processes in Gibberellic Acid Fermentation

Shukla, Ruchi,Srivastava, Ashok K.,Chand, Subhash The Korean Society for Biotechnology and Bioengine 2003 Biotechnology and Bioprocess Engineering Vol.8 No.5

Gibberellic acid (GA$_3$) is a commercially important plant growth hormone, which is gaining much more attention all over the world due to its effective use in agriculture and brewing industry. Industrially it is produced by submerged fermentation technique using Ascomycetous fungus Gibberella fujikuroi. Solid state and immobilized cell fermentation techniques had also been developed as an alternative to obtain higher yield of GA$_3$. This review summarizes the problems of GA$_3$ fermentation such as production of co-secondary metabolites along with GA$_3$, substrate inhibition and degradation of GA$_3$ to biologically inert compound gibberellenic acid, which limits the yield of GA$_3$ in the fermentation medium. These problems can be overcome by various bioprocessing strategies e.g. two - stage and fed batch cultivation processes. Further research on bioreactor operation strategies such as continuous and / or extractive fermentation with or without cell recycle / retention system need to be investigated for improvement in yield and productivity. Down stream processing for GA$_3$ isolation is also a challenge and procedures available for the same have been critically evaluated.

Impact of Non-Reactive Ceria Nanoparticles on the Wettability and Reaction Kinetics Between Lead-Free Sn–58Bi and Cu Pad

Ashutosh Sharma,Ashok K. Srivastava,Kwan Lee,Byungmin Ahn 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.4

Lead-free Sn–58Bi– x CeO 2 ( x in wt% = 0, 0.3, 0.6 and 0.9) composite solder was prepared via mechanical blending andmelting route. The ceria nanoparticles (CeO 2 ) were prepared from chemical precipitation method. Further, the variationin microstructure and phase composition, melting point, wetting and mechanical properties were studied through scanningelectron microscopy, energy dispersive spectroscopy, transmission electron microscopy, diff erential scanning calorimetry,spreading ratio, contact angle and tensile testing, respectively. It was shown that Sn–58Bi– x CeO 2 composite solders show16.66 and 32.05% increase in spread ratio and wetting angle, respectively, due to the enhanced melt fl uidity up to x = 0.6. The fraction of hard Bi-phase was also refi ned simultaneously. The tensile results showed a slight decrease in ultimatetensile strength and enhancement in ductility up to x = 0.3 and 0.6 except at x = 0.9. High temperature aging also demonstrateda reduced intermetallic compounds thickness when fraction of ceria nanoparticles in the matrix was up to x = 0.6. Itis suggested that for optimum set of soldering properties, the concentration of the nanoparticles should be at 0.6 wt% in themonolithic Sn–58Bi alloy.

Influence of Inhibitors on the Corrosion of Al and Al-composites in Chloride-containing Solutions - A Review

Neeraj Kumar,Ashok K. Srivastava,Prabhat Gautam,M. K. Manoj 한국재료학회 2022 한국재료학회지 Vol.32 No.5

Corrosion is a natural, inevitable process, and is one of the world's most serious problems. Losses incurred due to corrosion are extremely expensive for society. Several technological strategies have been explored and implemented to address these losses. The use of inhibitors to prevent corrosion is a common and efficient method to reduce corrosion losses. This review covers Al and Al-composite corrosion inhibitors in chloride-containing solutions, because of their popularity in a broad array of industrial applications. A vast number of studies in the literature detail the common tendency of Al and Al-composites with reinforcements to deteriorate. Accordingly, it is worthwhile to employ inhibitors to protect them, as discussed in the present work. The emphasis is on selecting the smartest corrosion inhibitor and evaluating its performance. According to the study, the most commonly used corrosion inhibitors are 1,4-naphthoquinone (NQ), 1,5-naphthalene diol, 3-amino-1,2,4-triazole-5-thiol (ATAT), ammonium tetrathiotungstate, clotrimazole, amoxicillin, antimicrobial and antifungal drugs. Electrochemical impedance spectroscopy (EIS), potentiodynamic (PDP), and weight loss were among the most commonly used modern electrochemical technologies to test inhibitors’ efficacy under environmental conditions.

Continuous Propionic Acid Production from Cheese Whey Using In Situ Spin Filter

Gupta, Achin,Srivastava, Ashok K. The Korean Society for Biotechnology and Bioengine 2001 Biotechnology and Bioprocess Engineering Vol.6 No.1

The potential use of spin filter device to retain Propionibacterium acidipropionici in the bioreactor under continuous mode of fermentation, and improve acid productivity, was examined. The yield of propionic acid based on lactose concentration was 51% in batch and 54% in continuous (dilution rate = 0.05 h(sup)-1) operation. The yield in continuous fermentation with cell retention using spin filter of 10 micron size (dilution rate = 0.05 h(sup)-1) was even higher at 70% (w/w). The volumetric productivity under batch and continuous mode of operation were 0.312g L(sup)-1 h(sup)-1 and 0.718g L(sup)-1 h(sup)-1 respectively. Continuous fermentation with cell retention demonstrated even higher volumetric productivities at 0.98g L(sup)-1 h(sup)-1 with out clogging problems. It could be used for utilization of cheese whey to produce propionic acid at higher yield and productivities.

THRESHOLD AND SATURATION VOLTAGES MODELING OF CARBON NANOTUBE FIELD EFFECT TRANSISTORS (CNT-FETS)

JOSE M. MARULANDA,ASHOK SRIVASTAVA,ASHWANI K. SHARMA 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2008 NANO Vol.3 No.3

We present analytical model equations for threshold voltage (Vth) and saturation voltage (Vds,sat) characterizing CNT-FETs. These model equations have been obtained from the charge and potential distributions between the gate and substrate in a CNT-FET. It is shown that both Vth and Vds,sat are strongly dependent on chiral vectors of CNTs. The results show close agreement between theoretical and graphical modeling techniques. It is also shown that the calculated Vth of a CNT-FET with chiral vector (3,1) is in close agreement with the corresponding published work.

Bioprocess Considerations for Production of Secondary Metabolites by Plant Cell Suspension Cultures

Chattopadhyay, Saurabh,Farkya, Sunita,Srivastava, Ashok K.,Bisaria, Virendra The Korean Society for Biotechnology and Bioengine 2002 Biotechnology and Bioprocess Engineering Vol.7 No.3

Plant cell culture provides a viable alternative over whole plant cultivation for the production of secondary metabolites. In order to successfully cultivate the plant cells at large scale, several engineering parameters such as, cell aggregation, mixing, aeration, and shear sensitivity are taken into account for selection of a suitable bioreactor. The media ingredients, their concentrations and the environmental factors are optimized for maximal synthesis of a desired metabolite. Increased productivity in a bioreactor can be achieved by selection of a proper cultivation strategy (batch, fed-batch, two-stage etc.), feeding of metabolic precursors and extraction of intracellular metabolites. Proper understanding and rigorous analysis of these parameters would pave the way towards the successful commercialization of plant cell bioprocesses.