Simulation Analysis and Comparison of Point of Care Testing and Central Laboratory Testing.

Background. In response to demand for fast and efficient clinical testing, the use of point-of-care testing (POCT) has become increasingly common in the United States. However, studies of POCT implementation have found that adopting POCT may not always be advantageous relative to centralized laboratory testing. Methods. We construct a simulation model of patient flow in an outpatient care setting to evaluate tradeoffs involved in POCT implementation across multiple dimensions, comparing measures of patient outcomes in varying clinical scenarios, testing regimes, and patient conditions. Results. We find that POCT can significantly reduce clinical time for patients, as compared to traditional testing regimes, in settings where clinic and central testing areas are far apart. However, as distance from clinic to central testing area decreased, POCT advantage over central laboratory testing also decreased, in terms of time in the clinical system and estimated subsequent productivity loss. For example, testing for pneumonia resulted in an estimated average of 27.80 (central lab) versus 15.50 (POCT) total lost productive hours in a rural scenario, and an average of 14.92 (central lab) versus 15.50 (POCT) hours in a hospital-based scenario. Conclusions. Our results show that POCT can effectively reduce the average time a patient spends in the system for varying condition profiles and clinical scenarios. However, the number of total lost productive hours, a more holistic measure, is greatly affected by testing quality, where POCT often is at a disadvantage. Thus, it is important to consider factors such as clinical setting, target condition, testing costs, and test quality when selecting appropriate testing regime.

[Fractal structure and physicochemical characteristics analysis of aerobic sludge floc in A2/O process].

Image analysis method, free settling test were performed to determine the morphology, particle size distribution, free setting velocity, effective density, porosity and fractal dimensions in different topological spaces of aerobic sludge flocs in A2/O process. Then the physicochemical indices, corresponding to the sludge properties such as: settleability, compressibility, dewaterability and stability, were measured. Besides these, the extra-cellular polymeric substances (EPS) were extracted from sludge and classified as different components. The results showed that the sludge floc with irregular morphology was high porous. The effective densities of these sludge flocs generally increased with the increase of their size, but the porosities within the flocs and their free settling velocities decreased accordingly. The median diameters of the sludge flocs at two different sampling times were 248.81 microm, 332.86 microm, respectively. Their corresponding average effective densities were 0.0040, 0.0072 g x cm(-3), and average free settling velocities were 2.67 mm x s(-1), 4.79 mm x s(-1), and giving the average porosities of0.94, 0.89. The dimensional analysis methods, based on power law correlations between floc perimeter, projected area and maximum length, were used to determine the one- and two-dimensional fractal dimensions (D1 and D2 ) of sludge flocs, giving D1 = 1.03 or 1.19, D2 = 1.64 or 1.84. The mass fractal dimensions (D(f)) of these sludge flocs were determined by the bi-logarithm relations of effective density (based on Logan empirical equation)-maximum diameter which equaled to 1.74 or 2.29. The above results demonstrated that the second sample of sludge flocs was larger and more compact, but smoother than the first sample. Moreover, the results also showed that the sludge flocs in A2/O process with high flocculating ability or high negative surface charge had high values of sludge volume index (SVI) and zone setting velocity (ZSV), and low values of fractal dimensions in 2-D or 3-D spaces of sludge flocs correlated to high shear sensitivity and low floc strength, indicating low sludge stability. The high quantity of extra-cellular substances (EPS) in the sludge was related to poor dewaterability. As same as the conclusion of literature, the protein component in EPS could improve the negative surface charge of sludge flocs.

[Impact of hydraulic retention time (HRT) in ABR on its operation performance and granular sludge characteristics when treating low-strength wastewater].

The impact of hydraulic retention time (HRT) in an anaerobic baffled reactor (ABR) on its operation performance and granular sludge characteristics was investigated through both testing its operation and analyzing the particle size distribution (PSD) and fractal dimensions of these sludge granules when treating low-strength wastewater. As HRT was gradually reduced from 24 h to 5 h, ABR had good performance on the organics removal and could reach about 90% for the COD removal, the VFA contents in ABR effluent and their pH values showed opposite trends. Most COD in wastewater was removed in the first two compartments of ABR during the running period of HRT from 24 h to 12 h, after that, the middle three compartments in ABR performed the most removal work. The MISS in latter compartments of ABR increased and the tendency of MLVSS/MISS ratios in the former three compartments were higher than that in the latter two ones appeared more and more remarkable along with the decrease of HRT. At HRT 24 h and 18 h, the granules grew bigger than before start-up,whose one-dimensional fractal dimension (D) decreased and two-dimensional fractal dimension (D2) increased, implying the smoother surface and more compact structure. As the HRT changed to 12 h and 8 h, the increasing D1 and decreasing D2 of granular sludge indicated its rougher surface and looser structure, and the bigger granules were formed with holes in their center. At HRT 5 h, smoother and more compact granules formed with smaller number median diameters of 0.72-0.82 mm than that at HRT 8 h. The looser granules were broken-up and some granules were discharged from ABR under the hydraulic disturbance and screening effect, at the same time, the growth of microorganism and their EPS (extracellular polymer substance) secretion could smooth the surface of the fragmentized granules. The fractal dimensions of granular sludge in the one-dimensional and two-dimensional topological spaces behaved inversely in each compartment of ABR at the same HRT, that is to say, the granular sludge along the ABR sequences became smoother on the surface meanwhile more compact structurally.