Sulphur and sulphate reduction with acetate and propionate in an aerobic process for sulphide removal

Summary Sulphide production rates of sulphur-and sulphate-reducing bacteria up to 50 mg per biomass support particle per day were observed in an aerated sulphide-removal reactor with polyurethane (PUR) foam as carrier material. The optimal pH and temperature for the sulphide-producing bacteria were 8.0 and 30°C respectively. Raschig rings and four types of cube-shaped PUR particles were tested as carrier materials. When using PUR particles, the sulphide production rate was always between 3% and 4% of the sulphide removal rate, dependent on the dimensions and pore size of the polyurethane support particles. With the Raschig rings this ratio was only 2% and for reactors in which no carrier materials were present it was even lower (0.6%). Media containing different mixtures of acetate, propionate, sulphur and sulphate inoculated under anoxic conditions with sludge from the aerated reactor showed the presence of acetate-degrading sulphur-reducing, but not of acetate-degrading sulphate-reducing, bacteria. With propionate as sole electron donor no degradation occurred in the presence of sulphur within 2 weeks, whereas sulphate-dependent propionate oxidation started after 5–6 days incubation. Bacteria were isolated and resembled Desulfuromonas acetoxidans and Desulfobulbus propionicus morphologically and physiologically.     

Concentrations of NaCl and sucrose: equality in perceived taste intensity

Results from previous studies suggest that sucrose and NaClsolutions have an equal perceived taste intensity when the molarconcentration of sucrose is 1.5–1.75 times the molar concentrationof NaCl. However, according to other studies, sucrose and NaClsolutions taste equally strong when their molar concentrationsare about equal. This issue was further pursued using the methodof constant stimuli, where subjects matched the perceived tasteintensity of NaCl solutions to five sucrose references and viceversa. The results concur with previous findings that sucroseand NaCl solutions have equal perceived taste intensities whenthe molar concentration of sucrose is 1.5–1.75 times themolar concentration of NaCl.     

Robust emergence of small-world structure in networks of spiking neurons

Spontaneous activity in biological neural networks shows patterns of dynamic synchronization. We propose that these patterns support the formation␣of a small-world structure—network connectivity␣optimal for distributed information processing. We␣present numerical simulations with connected Hindmarsh–Rose neurons in which, starting from random connection distributions, small-world networks evolve as a result of applying an adaptive rewiring rule. The rule connects pairs of neurons that tend fire in synchrony, and disconnects ones that fail to synchronize. Repeated application of the rule leads to small-world structures. This mechanism is robustly observed for bursting and irregular firing regimes.     

A psychophysical investigation of Beidler's mixture equation

Beidler's mixture equation (1971) describes the relationshipbetween the concentration and composition of a binary mixtureand the magnitude of the neural response. Later this equationwas generalized to a psychophysical level. The purpose of thepresent study is to show that Beidler's mixture equation canbe tested appropriately with indirect psychophysical methods,without the necessity of making assumptions about the magnitudeof the maximum responses to the single compounds which constitutethe mixture. Experiments were carried out using glucose andfructose as tastants. Concentrations of fructose and three equiratiomixture types containing glucose and fructose were matched inperceived sweetness intensities to five different glucose concentrationsusing the method of constant stimuli. The results showed thatBeidler's mixture equation describes accurately the taste interactionbetween glucose and fructose at low sweetness levels. At highsweetness levels the taste system is more efficient, as couldbe expected on the basis of Beidler's mixture equation, becausethe experimentally determined mixture concentrations were lowerthan those predicted by the mixture equation. The findings suggestthat glucose and fructose share common receptors, but that eitherone or both have additional secondary binding mechanisms.