Studies on citric acid production by Aspergillus niger in batch fermentation

Citric acid is one of the very important commercial product with constant demand in the market . Citric acid production by fungi have been reported by many workers since 1913.The present study focused on production of citric acid by Aspergillus niger  in batch fermentation. The maximum yield was found to be 1.5mg/ml

Austenite in Transformation-Induced Plasticity Steel Subjected to Multiple Isothermal Heat Treatments

The thermodynamic limit to the progress of the bainite reaction in steels containing a cementite inhibitor often leaves large quantities of thermally or mechanically unstable austenite. Such austenite is not effective in delaying the onset of plastic instabilities during the course of deformation. In such circumstances, it is useful to conduct isothermal transformation at a high temperature where the rate of reaction is relatively rapid, followed by a lower temperature step that permits more bainite to be generated. This in turn increases the stability of the refined austenite, which then transforms gently over a large range of strain during a tensile test. A significant corollary is that the two-step heat treatments are unnecessary in low-carbon steels, where the bainite reaction is able to proceed to a greater extent before reaching the thermodynamic limit. Furthermore, the two-step process can be counterproductive in low carbon steel, because the austenite content is reduced to a level below which it does not enhance the mechanical properties. Other circumstances in which multiple heat treatments are necessary are also discussed.The authors are grateful to POSCO for support through Steel Innovation Programme, and to the World Class University Programme of the National Research Foundation of Korea, Ministry of Education, Science and Technology, project number R32-2008-000-10147.This is the accepted manuscript version. The final published version is available from Springer at http://link.springer.com/article/10.1007%2Fs11661-014-2405-z

A Fatigue Crack Growth Model for Random Fiber Composites

Fatigue crack growth behavior of a randomly oriented short carbon fiber rein-forced polyether ether ketone (PEEK) composite is studied at four different load ratios. Based on the experimental data, a new fatigue crack growth model is proposed which accounts for crack growth throughout the entire fatigue cycle and not just at the maximum load. The proposed model involves a weighted averaging procedure and is found to fit the fatigue crack growth rates at all load ratios in a single power law equation. Finally, it is observed that the fatigue threshold intensity of this material decreases with increasing load ratio.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67507/2/10.1177_002199839703101804.pd