Analysis of retinal circulation using an image-based network model of retinal vasculature

This paper presents the results of a circulation analysis using an image based network model of a murine retinal vasculature, which closely represents the 3D vascular distribution of the retina. The uneven distribution of the red blood cells at vascular network bifurcations (i.e., plasma skimming effect), the microvascular diameter effect (i.e., Fahraeus-Lindqvist effect) and the role of endothelium surface layer (i.e., in vivo viscosity) were considered in determining the viscosity of the blood in the retinal vessel segments. The study yielded detailed distributions of the hemodynamic quantities in the arterial and venous trees shown in various anatomical based contour plots. Quantitative analysis was also carried out based on statistical distributions. The analysis shows that the distribution of the blood hematocrit (H(D)) in the retinal network is very non-uniform, with lower values at the pre-equator region (near the optic disc) and higher values in the equator region of the retina. This has significant influence on the distribution of apparent viscosity, pressure and wall shear stress (WSS) in the vasculature. The viscosity is generally higher in smaller vessels (i.e., pre-capillary vessels) but exceptions occur in some vessels where the H(D) is small. WSS is greater in smaller vessels located near the optic disc than that in the mainstream retinal vessels. The results presented can be directly useful to ophthalmologists and researchers working with retinal vasculature.

Effect of chloride concentration on nitrogen removal from landfill leachate in sequencing batch reactor after MAP pretreatment

Leachate generated from landfill is becoming a great environmental challenge to China as it contains high concentration of COD, ammonium and some other substances. Nitrogen removal through the conventional nitrification-denitrification process is hampered by the low C/N ratio especially for the old age landfill sites and the high energy consumption for aeration. In this study, the combination of magnesium ammonium phosphate (MAP) precipitation and Sequencing batch reactor (SBR) was suggested as a new process for the treatment of high strength ammonium, and the effect of high concentration of Cl⁻ after MAP precipitation because of the use of MgCl₂ was investigated on SBR performance. The practical upper limit of Cl⁻ for nitrification was found to be 12,000 mg/L, above which resulted in significant accumulation of ammonium in SBR system. It is suggested that an ammonium removal of 70% was suitable for the MAP treatment to achieve a balance between increasing the C/N ratio and avoiding detrimental effect from high concentration of Cl⁻ in the succeeding SBR system. DGGE analysis indicated that high diversity of Ammonium oxidizing bacteria (AOB) could be maintained at a Cl⁻ concentration of 12,000 mg/L.

The uplift of Qinghai-Xizang (Tibet) Plateau and the vicariance speciation of glyptosternoid fishes (Siluriformes: Sisoridae)

Based on the phylogenetic and biogeographical studies of the glyptosternoid fishes in Qinghai-Tibet area, the following hypothesis is proposed: the speciation of this group has a direct relationship with the three uplift intervals of the Qinghai-Tibet Plateau. This process was explained by the theory of vicariance of biogeography. The ancestor of this group was similar to Bagarus and/or Glyptothorax, which still have a wide distribution. At the moment when the Tethys sea closed, the Indian tectonic plate collided with the Eurasian tectonic plate, so the Glyptothorax-like and Bagarus-like ancestors entered Eurasia and gradually became widely distributed. After the Pleistocene, with the enforced colliding, the gradual uplift of the Qinghai-Tibet Plateau brought about the current water environment, and the Glyptosternoids were generated from Glyptothorax-like fish under this environment. The present Glyptosternum, distributed across the Himalayas is the ancestor of Glyptosternoids. In the three uplift intervals of the plateau, the water system of this region was separated gradually and Glyptosternum-like ancestor was isolated in different rivers and evolved into various species. All this resulted in the speciation and formation of the biogeographical pattern of glyptosternoids.

Deterministic Dynamics in Neuronal Discharge from Pallidotomy Targets

The non-linear dynamic specificity of the firing pattern discharged from neurons of the internal globus pallidus (GPi) was investigated by recording their spontaneous firing using a microelectrode during posteroventral pallidotomy in eight patients with Parkinson's disease. Raw data from the cells were processed to extract spiking events (discharges above a selected threshold) and the interspike interval was measured. Using the unstable periodic orbits extraction method, significant period-1, −2 and −3 orbits were identified in burst firing discharged from the GPi cells in all eight patients, suggesting that deterministic dynamics exist in the timing of the discharges. As well as providing a useful peri-operative technique for locating posteroventral pallidotomy targets in Parkinson's disease, this method also provides a promising basis for investigating characteristic neuronal discharges in other regions of the brain and for various other neurological disorders.