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Saccharomyces cerevisiae is the cheapest strain available for the conversion of biomass substrate. In the present study, it is used for bio-ethanol production from sugar molasses. The influencing parameters that affect the production of bio-ethanol from sugar molasses are optimized. The optimal values of the parameters such as temperature, pH, substrate concentration, enzyme concentration and fermentation period are found to be 35°C, 4.0, 300 gm/l, 2 gm/l and 72 h respectively. Under this optimum operating condition the maximum of 53% bio-ethanol yield is achieved. The rate of formation of bio-ethanol is found to be well fitted with Michael-Menten equation and the rate constants such as V_max and K_m are found to be 0.71 mol/l sec and 81.63 mol/l respectively. 

In this paper, a method of stability analysis for the general milling process is given. The milling operation is described by a linear differential-difference equation with periodic coefficients. An algorithm which can be used in conjunction with the digital computer is developed as a means of analytically determining the stability of this equation. This algorithm will permit the determination of the stability boundaries in the space of controllable parameters associated with a cutting operation and allows more realistic models for milling to be studied than have been attempted up to the present time. The technique is used to predict the stability in an example of a milling operation.

In the cutting process, forces are induced at each of the cutter teeth in contact with the workpiece, and these forces in turn excite the machine tool structure. Due to the inherent feedback which exists between the cutting forces and the structure deflection, there are conditions under which this system becomes unstable. When this occurs, a condition of self-excited chatter exists. In the theory of self-excited chatter for single point tools wherein the tool is continuously in contact with the workpiece, the system can be described by a time-invariant equation, and has been rather fully developed. However, the milling process cannot be described in this manner. It is characterized by a multitooth cutter, and the cutting process itself is interrupted. Also, the direction of the cutting forces generated by each tooth does not remain constant with respect to the machine tool structure as for turning operations, but changes direction as a function of cutter position. In this paper, more complete description of the milling process is formulated. The resulting equation is a general nth order vector-matrix linear equation with periodic coefficients and a transport lag. Or equally, it is a linear differential-difference equation with time-varying coefficients. This equation is then expressed as n-first order equations (state variable form), consistent with current literature and in a form compatible for digital computer analysis.

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