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The spinning of fibers from polymer melts is sometimes limited at high takeup rates by the onset of a flow instability known as “draw resonance,” which is characterized by large amplitude fluctuations in the takeup area and the force. In this work, the onset and growth of the spinning instability is analyzed for an isothermal Newtonian liquid by examining the nonlinear dynamics of the most unstable spatial mode. At draw ratios below the critical value D R = 20·21 computed from linear theory the system is stable to finite-amplitude perturbations. At higher draw ratios all disturbances approach a stable finite-amplitude oscillation which agrees in period and magnitude with experimental observations of draw resonance.

Active transport vesicles of Escherichia coli were shown to possess low levels of energy-independent and energy-dependent nicotinamide nucleotide transhydrogenase activities. Breakage of such vesicles in a French pressure cell resulted in a fraction which had an 8-10-fold increased respiration- and ATP-driven transhydrogenase activities. Stimulation of the ATPase activity in vesicles with Triton X-100 was also paralledled by a 2-fold increase in the energy-independent transhydrogenase. Disruption of the vesicles similarly resulted in increases in the energy-independent transhydrogenase, NADH and succinate oxidase activities but a decrease in succinate supported proline uptake. In the light of these findings, the "sidedness' of the vesicle membranes is discussed.

Summary The stimulation of the energy dependent transhydrogenase (reduction of NADP by NADH) driven by oxidative energy was linear with oligomycin in the ammonia-EDTA depleted (AE) submitochondrial particle but sigmoidal in the more severely depleted ammonia-Sephadex-urea (ASU) and silicotungstate (STA) particles. The optimal activities were quite high even in the more depleted particles. The mitochondrial energy transfer factor C (Factor C) stimulated this activity of the AE particle alone and in combination with oligomycin. Oligomycin also induced substantial activity in the ASU particle in NAD reduction by succinate driven by ascorbatetetramethyl-p-phenylenediamine oxidation in the presence of antimycin. The results show that these particles are not significantly depleted in components involved in the production of the non-phosphorylated high energy intermediate from respiration.

Experimental and analytical results are reported for radiant wall to bed heat transfer in fluidized beds. The experiments were carried out by transmitting heat from a source through a transparent wall and by maintaining the wall at the bulk bed temperature. It was thus possible to achieve purely radiative heat transfer at source temperature as low as 600°K. The results were interpreted in terms of a model postulating transient radiative heat transfer from source to the particles during their finite residence time at the wall. By using the analysis an estimate was made of the operating conditions under which thermal radiation is likely to make a significant contribution to the overall heat transfer mechanism in real systems, (where radiation and convection occur simultaneously).

The aerobic and anaerobic energy linked transhydrogenase reactions have been demonstrated in membrane preparations from E. , coli . The aerobic transhydrogenase activity could be enhanced by an energy transfer factor prepared from rat-liver mitochondria. These reactions were sensitive to 4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazole, an uncoupler of oxidative phosphorylation.

The energy-linked nicotinamide adenine dinucleotide transhydrogenase from Escherichia coli can be driven by energy obtained from ATP or from respiration. E. coli grown anaerobically has the ATP-driven transhydrogenase but no respirationdriven transhydrogenase activity. The ATP-driven activity is inhibited by 50 μM N , N ′-dicyclohexylcarbodiimide (DCCD) in membrane particles prepared from both aerobically and anaerobically grown cells, but the respiration-driven transhydrogenase is not inhibited. Low levels of DCCD enhance the respiration-driven transhydrogenase activity in membrane particles prepared from aerobically grown cells. The oxidation of NADH is one-fifth as low in particles prepared from anaerobically grown cells and is less sensitive to KCN than in particles from aerobically grown cells. The results suggest that anaerobically grown E. coli can produce and utilize the nonphosphorylated high-energy intermediate from ATP. However, this membrane appears to be depleted in its ability to transduce oxidative energy to form the high-energy intermediate.

The ATP-Pi exchange activity of highly purified preparations of ‘ATP synthetase’ was inhibited by F1-antiserum, Pullman inhibitor, azide and also by avidin (See You and Hatefi, 1973) . The inhibition produced by the first three was relieved in the presence of ADP, and the avidin sensitivity was lost on pretreatment on the avidin with biotin. It is concluded that the ATP-Pi exchange resulted from the combined action of Factor A and a contaminating avidin-sensitive enzyme. The ADP necessary for the exchange reaction catalyzed by the latter was generated by the ATPase activity of Factor A.

A nitrogenase system that remains in the supernatant fluid after centrifuging for 3 hr at 180,000 × g can be extracted from Azotobacter vinelandii by osmotic lysis of the bacteria. This nitrogenase preparation is oxygen-labile and appears to be similar, though not identical, to that obtained from Clostridium pasteurianum . The particulate characteristic and oxygen stability of previously described preparations are likely due to the method of cell disruption, e.g., in the French pressure cell. The data support a nitrogenase model system in the intact cell in which oxygen-labile enzymes are protected from oxygen by the extensive internal membranous system which Azotobacter synthesize only when they fix nitrogen.