Modeling of Biofilm Growth on Fine Spherical Particles with the Use of Cellular Automata: The Influence of Cell Death and Lysis on the Biofilm Structure

The paper concerns the modeling of heterogeneous biofilm growth on fine spherical particles of such biofilm forms as, e.g., fluidized-bed bioreactors. Three discrete mathematical models based on cellular automata theory were proposed. The double-substrate kinetics of biomass growth, biomass displacement, internal and external mass transfer resistances, death and lysis of microbiological cells and biofilm detachment were taken into account. It was shown that there are no significant qualitative and quantitative differences between biofilm growth on flat and spherical particles of different radii. Computer simulations were compared with experimental observations. Qualitative and quantitative agreement areachieved if both cell death and lysis aretaken into consideration and a proper algorithm of biomass displacement is used. The value of the bacteria lysis rate coefficient was estimated.

Investigation of growth kinetics and partial denitrification performance in strain Acinetobacter johnsonii under different environmental conditions

A denitrifying strain ZY04 with a high nitrite-accumulating rate was isolated and purified from activated sludge in a laboratory-scale A 2 /O reactor. The strain was characterized and identified as Acinetobacter johnsonii by 16S rDNA phylogenetic analysis. The sequences of the key functional genes ( napA , nirB , nirD ) involved in partial denitrification were amplified via polymerase chain reaction, which provided a basis for exploring gene expression. The effects of different environmental factors (C/N ratio, pH and temperature) on the partial denitrification performance and transcriptional levels of the functional genes during the logarithmic growth phase were investigated by batch experiments. The results showed that the partial denitrification performance was optimal when the C/N ratio was 5, the pH value was 6–8 and the temperature was 25°C. The gene expression during the logarithmic growth phase indicated the good performance of partial denitrification under different environmental conditions. All three functional genes exhibited the highest expression levels at 25°C. The results of inhibitory kinetics analysis revealed that three biokinetic models (Aiba, Edwards and Andrews) simulated the growth pattern of strain ZY04 inhibited by a single substrate (nitrate or sodium acetate) well. In the double-substrate inhibitory model, five models of nine combinations successfully fitted the growth characteristics of the strain affected by the double substrate of nitrate and sodium acetate. The relevant semi-saturation parameters and substrate inhibition parameters were obtained, and the correlation coefficient ( R 2 ) reached 98%.

Liquid–liquid gravity displacement in a vertical fracture during drilling: Experimental study and mathematical model

Gravity displacement often occurs when drilling a vertical fractured formation, causing a downhole complexity with risk of blowout and reservoir damage, well control difficulty, drilling cycle prolongation, and increased costs. Based on an experimental device created for simulating the gravity displacement, various factors affecting the displacement quantity were quantitatively evaluated by simulating the fracture width, asphalt viscosity, drilling fluid density, and viscosity under different working conditions, and a liquid–liquid displacement law was obtained. Using the theories of rock mechanics, fluid mechanics, and seepage mechanics, based on conformal mapping, as well as a fracture-pore double substrate fluid flow model, we established a steady-state mathematical model of fractured formation liquid–liquid gravity displacement by optimizing the shape factors and using a combination of gravity displacement experiments to verify the feasibility of the mathematical model. We analyzed the influence of drilling fluid density, fracture height and length, and asphalt viscosity on displacement rate, and obtained the corresponding laws. The results show that when the oil–fluid interface is stable, the fracture width is the most important factor affecting the gravity displacement, and plugging is the most effective means of managing gravity displacement.

Advances in Discovery of PDE10A Inhibitors for CNS-Related Disorders. Part 1: Overview of the Chemical and Biological Research

Phosphodiesterase 10A (PDE10A) is a double substrate enzyme that hydrolyzes second messenger molecules such as cyclic-3’,5’-adenosine monophosphate (cAMP) and cyclic-3’,5’-guanosine monophosphate (cGMP). Through this process, PDE10A controls intracellular signaling pathways in the mammalian brain and peripheral tissues. Pharmacological, biochemical, and anatomical data suggest that disorders in the second messenger system mediated by PDE10A may contribute to impairments in the central nervous system (CNS) function, including cognitive deficits as well as disturbances of behavior, emotion processing, and movement. This review provides a detailed description of PDE10A and the recent advances in the design of selective PDE10A inhibitors. The results of preclinical studies regarding the potential utility of PDE10A inhibitors for the treatment of CNS-related disorders, such as schizophrenia as well as Huntington’s and Parkinson’s diseases are also summarized.