Estimation of the Longitudinal Dispersion Coefficient Using the Velocity Profile in Natural Streams

In this study, a theoretical method for predicting the longitudinal dispersion coefficient is developed based on the transverse velocity distribution in natural streams. Equations of the transverse velocity profile for irregular cross sections of the natural streams are analyzed. Among the velocity profile equations tested in this study, the beta distribution equation, which is a probability density function, is considered to be the most appropriate model for explaining the complex behavior of the transverse velocity structure of irregular natural streams. The new equation for the longitudinal dispersion coefficient that is based on the beta function for the transverse velocity profile is developed. A comparison of the proposed equation with existing equations and the observed longitudinal dispersion coefficient reveals that the proposed equation shows better agreement with the observed data compared to other existing equations.     

Nonlinear protein binding and enzyme heterogeneity: effects on hepatic drug removal

The kinetics of substrate removal by the liver and the resulting nonlinear changes in unbound fraction along the flow path at varying input drug concentrations were examined by a model simulation study. Specifically, we varied the binding association constant, KA, and the Michaelis-Menten constants (Km and Vmax) to examine the steady state drug removal (expressed as hepatic extraction ratio E) and changes in drug binding for (i) unienzyme systems and (ii) simple, parallel metabolic pathways; zonal metabolic heterogeneity was also added as a variable. At low KA, E declined with increasing input drug concentration, due primarily to saturation of enzymes; only small differences in binding were present across the liver. At high KA, a parabolic profile for E with concentration was observed; changes in unbound fraction between the inlet and the outlet of the liver followed in parallel fashion. Protein binding was the rate-determining step at low input drug concentrations, whereas enzyme saturation was the rate-controlling factor at high input drug concentration. Heterogeneous enzymic distribution modulated changes in unbound fraction within the liver and at the outlet. Despite marked changes in unbound fraction occurring within the liver for different enzymic distributions, the overall transhepatic differences were relatively small. We then investigated the logarithmic average unbound concentration and the length averaged concentration as estimates of substrate concentration in liver in the presence of nonlinear drug binding. Fitting of simulated data, with and without assigned random error (10%), to the Michaelis-Menten equation was performed; fitting was repeated for simulated data obtained with presence of a specific inhibitor of the high-affinity, anteriorly distributed pathway. Results were similar for both concentration terms: accurate estimates were obtained for anterior, high affinity pathways; an overestimation of parameters was observed for the lower affinity posteriorly distributed pathways. Improved estimations were found for posteriorly distributed pathways upon inhibition with specific inhibitors; with added random error, however, the improvement was much decreased. We applied the method for fitting of several sets of metabolic data obtained from rat liver perfusion studies performed with salicylamide (SAM) (i) without and (ii) with the presence of 2,6-dichloro-4-nitrophenol (DCNP), a SAM sulfation inhibitor. The fitted results showed that SAM sulfation was a high-affinity high-capacity pathway; SAM glucuronidation was of lower affinity but comparable capacity as the sulfation pathway, whereas SAM hydroxylation was of lower affinity and lower capacity.     

The effect of topical corticosteroids on refractive outcome and corneal haze after photorefractive keratectomy

BACKGROUND: The effect of topical corticosteroids after excimer laser photorefractive keratectomy (PRK) remains a matter of some controversy. Refractive effects may be different according to the amount of myopia and timing of instillation. METHODS: Two groups of patients were studied: Study A consisted of 215 eyes (128 patients) with PRK (mean baseline myopia, -6.53 +/- 2.22 D) that received no corticosteroids (No Corticosteroid Group) unless significant regression or corneal haze appeared (Delayed Corticosteroid Group), and in Study B, we randomly assigned eyes to the Initial Corticosteroid Group (mean baseline myopia, -6.39 +/- 1.84 D) or the No/delayed Corticosteroid Group (mean baseline myopia -5.78 +/- 2.02 D). Clinical results after PRK for low-to-moderate and high myopia were compared. RESULTS: In the first group, 70.9% (73 eyes) of moderately myopic eyes (mean, -4.56 +/- 1.10 D) belonged to the No Corticosteroid Group that had a mean refraction of -5.39 +/- 1.77 D. Delayed Corticosteroid Group eyes were more myopic (mean, -7.52 +/- 2.10 D), and showed more severe haze than those in the No Corticosteroid Group. In study B, only in high myopes with more than -6.00 D (mean, -7.76 +/- 1.15 D) did refraction and corneal haze outcomes show significant difference between the Initial Corticosteroid Group and the No/delayed Corticosteroid Group. CONCLUSIONS: The effects of topical corticosteroids after PRK were less in moderate myopes compared to high myopes. Delayed instillation of corticosteroids did not reverse the regression or haze whereas initial instillation showed a beneficial effect on high myopes but not on moderate myopes.     

Multi-antenna scheme for high capacity transmission in the digital audio broadcasting

In this paper, we apply multi-antenna scheme to DAB system for high-rate transmission. In the MIMO-DAB system with a number of transmitting and receiving antennas increases the transmission rate efficiently with low multiplication operations. For channel estimation in the MIMO-DAB system, we propose a new PRS structure and evaluate the channel estimation performance. The proposed PRS structure can estimate multi-channel information based on the semi-blind processing. The performance of proposed PRS is compared with that of conventional training sequence employing Tarokh's transmission matrix. And also we investigate the performance limitation due to the imperfect channel estimation in a MIMO-DAB receiver. It has been shown that the MIMO-DAB system with multi-antennas can achieve the high-rate transmission for multimedia broadcasting and the performance of MIMO-DAB system is impaired by imperfect channel information.     

Preparation of glucose oxidase immobilized in different carriers using radiation polymerization

Glucose oxidase (EC 1.1.3.4) was immobilized on different polymeric materials using different immobilization techniques (entrapping by γ‐irradiation, and covalent binding using epichlorohydrin). Studies were carried out to increase the thermal stability of glucose oxidase (GOD) for different applications. The activity and stability of the resulting biopolymers have been compared with those of free GOD. The effect of different polyvinyl alcohol/polyacrylamide (PVA/PAAm) compositions of the copolymer carrier on the enzymatic activity of the immobilized GOD was studied. The maximum enzymatic activity was obtained with the composition ratio of PVA/PAAm of 60:40. The behaviour of the free and immobilized enzyme was analysed as a function of pH. A broadening in the pH profile (5.5–8) was observed for immobilized preparations. The activity and stability of the resulting biopolymers produced by immobilization of GOD onto different carriers have been compared, in both aqueous and organic media, with those of the free GOD. The enzyme's tolerance toward both heat and organic solvent was enhanced by immobilization onto polymers. The addition of different concentrations of organic solvents (10–50%, v/v) to the enzyme at higher temperature (60 °C) was found to stabilize the enzyme molecule. The strongest stabilizing effect on the enzymatic activity was achieved at a concentration of 10%. Copyright © 2005 Society of Chemical Industry     

High-dose busulfan, melphalan, thiotepa and peripheral blood stem cell infusion for the treatment of metastatic breast cancer

The purpose of this study was to determine the outcome of patients with metastatic breast cancer treated with high-dose busulfan (Bu), melphalan (Mel) and thiotepa (TT) followed by peripheral blood stem cell (PBSC) infusion. Fifty-one patients with chemotherapy refractory (n = 32) or responsive (n = 19) metastatic breast cancer received Bu (12 mg/kg), Mel (100 mg/m2) and TT (500 mg/m2) followed by PBSC collected after chemotherapy and growth factor (n = 43) or growth factor alone (n = 8). The 100 day treatment-related mortality was 8% including one death from cytomegalovirus pneumonia, one from aspiration pneumonia and two from regimen-related toxicity (RRT). Seven of 28 refractory (25%) and 5/7 (71%) responsive patients with evaluable disease achieved a complete response of all measurable disease or all soft tissue disease with at least improvement in bone lesions (PR*). Fifteen of 51 patients (29%) are alive and progression-free a median of 423 days (range 353-934) after treatment, 5/32 (16%) with refractory disease and 10/19 (53%) with responsive disease. The probabilities of progression-free survival (PFS) at 1.5 years for the patients with refractory (n = 32) and responsive (n = 19) disease were 0.24 and 0.53, respectively. These preliminary data suggest that high-dose Bu/Mel/TT has significant activity in patients with advanced breast cancer and may be superior to some previously published regimens.     

Selective phosphorylation of adult tau isoforms in mature hippocampal neurons exposed to fibrillar A beta

How senile plaques and neurofibrillary tangles are linked represents a major gap in our understanding of the pathophysiology of Alzheimer's disease. We characterized a hippocampal neuronal culture system in which tau undergoes maturation in vivo; rat neurons maintained in culture for more than 3 weeks replicated the splicing and phosphorylation changes that tau undergoes upon maturation in situ. Using this model system, we induced an Alzheimer-like neuritic dystrophy following the application of fibrillar beta-amyloid. The dystrophy consisted of focal distortions and swellings within the neurites and an altered phosphorylation of the adult tau isoforms. Fibrillar beta-amyloid induced the concomitant activation of MAP kinase and GSK3 beta. The aberrant activation of several signaling pathways may lead to the abnormal phosphorylation of tau and neuritic degeneration.     

Acidogenic fermentation of blended food‐waste in combination with primary sludge for the production of volatile fatty acids

The performance of a laboratory‐scale anaerobic acidogenic fermenter fed with a mixture of blended kitchen food‐waste and primary sludge from a sewage treatment plant was investigated for the production of volatile fatty acids (VFA). The operating variables for acidogenic fermentation were kitchen food‐waste content (10 and 25 wt %), hydraulic retention time (HRT: 1, 3 and 5 days), temperature (ambient: 18 ± 2 °C, and mesophilic: 35 ± 2 °C) and pH (varied from 5.2 to 6.7). The experimental results indicated that effluent VFA concentrations and VFA production rates were higher at ambient temperature than at mesophilic conditions. The net amount of VFA with 10 wt % food‐waste increased up to 920 mg dm^?3 with an increase of HRT, but contrasting results (a decrease of 2610 mg dm^?3) were found due to the conversion of VFA into biogas in the case of 25 wt % food‐waste, which increased significantly at HRT of 3–5 days. In terms of biogas composition (CO₂ and CH₄), the organic matter was converted into CO₂ through the oxidative pathway by facultative species at low temperature while mesophilic temperature and optimum pH (6.3–7.8) played a pivotal role in increasing rate of conversion of VFA into biogas by methanogenesis. Rates of VFA production and their conversion are dependent on the food‐waste content in the mixture. Yet, the higher concentration of food‐waste (25% compared with 10%) did not produce VFA proportionally due to the increased rate of conversion of VFA into gaseous products. The maximum VFA production rate (0.318 g VFA_produced g^?1 VS_fed day^?1) was achieved in the 10 wt % food‐waste at ambient temperature and at a 5‐day HRT. Copyright © 2005 Society of Chemical Industry