Production of fumaric acid by immobilized rhizopus using rotary biofilm contactor

Rotary biofilm contactor (RBC) is a reactor consisting of plastic discs that act as supports for micro-organisms. The discs are mounted on a horizontal shaft and placed in a medium-containing vessel. During nitrogen-rich growth phase, mycelia ofRhizopus oryzae ATCC 20344 grew on and around the discs and formed the “biofilm” of self-immobilized cells on the surface of the plastic discs. During the fermentation phase, the discs are slowly rotated, and the biofilms are exposed to the medium and the air space, alternately. With RBC, in the presence of CaCO₃,Rhizopus biofilm consumes glucose and produces fumaric acid with a volumetric productivity of 3.78 g/L/h within 24 h. The volumetric productivity is about threefolds higher with RBC than with a stirred-tank fermenter with CaCO₃. Furthermore, the duration of fermentation is one-third of the stirred-tank system. The immobilized biofilm is active for over a 2-wk period with repetitive use without loss of activity.

     

A lower estimate for the modified Steiner functional

We prove inequality (1) for the modified Steiner functionalA(M), which extends the notion of the integral of mean curvature for convex surfaces. For the proof, we also establish an expression forA(M) in terms of an integral over all hyperplanes intersecting the polyhedral surfaceM.     

On Gilmore-Gomory's open question for the bottleneck TSP

Consider the traveling salesman problem where the distance between two cities A and B is an integrable function of the y-coordinate of A and the x-coordinate of B. This problem finds important applications in operations management and combinatorial optimization. Gilmore and Gomory (Oper. Res. 12 (1964) 655) gave a polynomial time algorithm for this problem. In the bottleneck variant of this problem (BP), we seek a tour that minimizes the maximum distance between any two consecutive cities. For BP, Gilmore and Gomory state that they “do not yet know how to solve the problem for general integrable functions”. We show that BP is strongly NP-complete. Also, we use this reduction to provide a method for proving NP-completeness of other combinatorial problems.     

Governing equations, experiments, and the experimentalist

It is argued that the most important test of the understanding of any experiment is whether or not the results are consistent with the equations and boundary conditions believed to govern the flow. If they are not, then either the measurements are incorrect, the equations or boundary conditions are wrong, or the experiment performed was not the one believed to have been done. It is suggested that many apparently contradictory experimental results are, in fact, the result of the latter and have not been recognized as such because of a failure to apply the governing equations to the data. The arguments are supported by examples from turbulent shear flow experiments.     

Conformations of isolated ampholytic dendrimers in solutions

We study the conformations of isolated trifunctional ampholytic dendrimers in solutions. For the previously homo-dendrimer case studied in the literature, we discuss the issues of density profiles, the existence of a cavity, backfolding, bond stretching and scaling laws for the dendrimer size across the good-to-poor solvent transition. We then consider the effect of introducing monomer charges in the outermost generation opposite to those in the interior generations in an electrically neutral overall ampholytic co-dendrimer.     

Operational characteristics of dual gain single cavity Nd:YVO4 laser

Operational characteristics of a dual gain single cavity Nd:YVO₄ laser have been investigated. With semiconductor diode laser pump power of 2 W, 800 mW output was obtained with a slope efficiency of 49%. Further, by changing the relative orientation of the two crystals the polarization characteristics of the output could be varied. In particular by keeping the two Nd:YVO₄ crystals with their c-axes orthogonal to each other and adjusting the gain of the crystals so that both operate at approximately the same power level, completely unpolarized beams could be obtained.