Dissolution, Formation, and Transformation of the Lead Corrosion Product PbO\u3csub\u3e2\u3c/sub\u3e: Rates and Mechanisms of Reactions that Control Lead Release in Drinking Water Distribution Systems

As one of the major lead corrosion products in lead service lines, lead(IV) oxide: PbO2) can react with water through reductive dissolution, resulting in elevated lead concentrations in tap water. Limited data are available on the rates and mechanisms of PbO2 dissolution. Information regarding the impact of water chemistry on the rates and mechanisms of PbO2 dissolution can provide potential strategies to control the release of lead from corrosion products to drinking water. The present study investigated effects of water chemistry on the rates and mechanisms of PbO2 dissolution, the equilibrium solubility of PbO2, and the rates of lead release from lead pipes with corrosion scales. The dissolution rate of pure plattnerite: β-PbO2) was investigated as a function of pH and the concentrations of carbonate, orthophosphate, free chlorine, and monochloramine in continuously stirred tank reactors: CSTR). Complementary batch experiments were conducted to compare the effects of water chemistry on the PbO2 dissolution rate for different solid-water contact times. The equilibrium solubility of plattnerite in the presence of free chlorine was then investigated. Lead release from pipe scales was determined under different water chemistry conditions at flow or no-flow conditions to optimize the water chemistry for mitigating lead release. For these experiments new lead pipes were conditioned in the presence of free chlorine and carbonate to form corrosion scales. Dissolution experiments provided direct evidence that the PbO2 dissolution rate increases when the disinfectant is switched from free chlorine to monochloramine, which is consistent with the high lead concentrations observed in Washington D.C. from 2001 to 2004 following such a switch. Lower pH and the presence of carbonate accelerated PbO2 dissolution. Addition of orthophosphate as a potential corrosion inhibitor had multiple effects on PbO2 dissolution rates. A detailed mechanism and rate model were proposed for PbO2 reductive dissolution. Batch experiments showed that the residence time also played an important role in controlling dissolved lead concentrations. Pipe scales developed under drinking water conditions contained PbO2 and hydrocerussite: Pb2(CO3)2(OH)2). In experiments with these pipe scales, when compared with stagnant conditions water flow significantly accelerated the release of both dissolved and total lead from pipe scales. Among various water chemistry conditions, the dissolved lead was lowest from corrosion scales in contact with solutions containing orthophosphate. Two models were proposed to predict lead release from pipe scales

Iterative Assembly of Two Separate Polyketide Chains by the Same Single-module Bacterial Polyketide Synthase in the Biosynthesis of HSAF

HSAF (1) was isolated from the biocontrol agent Lysobacter enzymogenes (Figure 1).[1-4] This bacterial metabolite belongs to polycyclic tetramate macrolactams (PTM) that are emerging as a new class of natural products with distinct structural features. [5, 6] HSAF exhibits a potent antifungal activity and shows a novel mode of action.[1-4] The HSAF biosynthetic gene cluster contains only a single-module hybrid polyketide synthasenonribosomal peptide synthetase (PKS-NRPS), although the PTM scaffold is apparently derived from two separate hexaketide chains and an ornithine residue.[1-4] This suggests that the same PKS module would act not only iteratively, but also separately, in order to link the two hexaketide chains with the NRPS-activated ornithine to form the characteristic PTM scaffold. Recently, the Gulder group reported heterologous expression of the ikarugamycin (4) biosynthetic gene cluster in E. coli,[7] and the Zhang group reported the enzymatic mechanism for formation of the inner 5-memebered ring and demonstrated the polyketide origin of the ikarugamycin skeleton.[8] Ikarugamycin is a Streptomyces-derived PTM which has a 5,6,5-tricyclic system (Figure 1). Both the Gulder and Zhang groups showed that a three-gene cluster is sufficient for ikarugamycin biosynthesis. Despite the progress, this iterative polyketide biosynthetic mechanism had not been demonstrated using purified PKS and NRPS. In addition, HSAF has a 5,5,6-tricyclic system, and its gene cluster contains at least six genes.[3] Finally, unlike most PTM compounds, HSAF is produced by a Gramnegative bacterium, L. enzymogenes. Here, we report the heterologous production of HSAF analogs in Gram-positive Streptomyces hosts, in which the native PKS have been deleted. We also obtained evidence for the formation of the polyene tetramate intermediate in Streptomyces when only the single-module hybrid PKS-NRPS gene was expressed. Finally, we showed the in vitro production of the polyene tetramate using the individually purified PKS and NRPS. The results provide direct evidence for this iterative polyketide biosynthetic mechanism that is likely general for the PTM-type hybrid polyketide-peptides

The ratio of CRP to prealbumin levels predict mortality in patients with hospital-acquired acute kidney injury

<p>Abstract</p> <p>Background</p> <p>Animal and human studies suggest that inflammation and malnutrition are common in acute kidney injury (AKI) patients. However, only a few studies reported CRP, a marker of inflammation, albumin, prealbumin and cholesterol, markers of nutritional status were associated with the prognosis of AKI patients. No study examined whether the combination of inflammatory and nutritional markers could predict the mortality of AKI patients.</p> <p>Methods</p> <p>155 patients with hospital-acquired AKI were recruited to this prospective cohort study according to RIFLE (Risk, Injury, Failure, Lost or End Stage Kidney) criteria. C-reactive protein (CRP), and the nutritional markers (albumin, prealbumin and cholesterol) measured at nephrology consultation were analyzed in relation to all cause mortality of these patients. In addition, CRP and prealbumin were also measured in healthy controls (n = 45), maintenance hemodialysis (n = 70) and peritoneal dialysis patients (n = 50) and then compared with AKI patients.</p> <p>Results</p> <p>Compared with healthy controls and end-stage renal disease patients on maintenance hemodialysis or peritoneal dialysis, patients with AKI had significantly higher levels of CRP/prealbumin (<it>p </it>< 0.001). Higher level of serum CRP and lower levels of albumin, prealbumin and cholesterol were found to be significant in the patients with AKI who died within 28 days than those who survived >28 days. Similarly, the combined factors including the ratio of CRP to albumin (CRP/albumin), CRP/prealbumin and CRP/cholesterol were also significantly higher in the former group (<it>p </it>< 0.001 for all). Multivariate analysis (Cox regression) revealed that CRP/prealbumin was independently associated with mortality after adjustment for age, gender, sepsis and sequential organ failure assessment (SOFA, <it>p </it>= 0.027) while the others (CRP, albumin, prealbumin, cholesterol, CRP/albumin and CRP/cholesterol) became non-significantly associated. The hazard ratio was 1.00 (reference), 1.85, 2.25 and 3.89 for CRP/prealbumin increasing according to quartiles (<it>p </it>= 0.01 for the trend).</p> <p>Conclusions</p> <p>Inflammation and malnutrition were common in patients with AKI. Higher level of the ratio of CRP to prealbumin was associated with mortality of AKI patients independent of the severity of illness and it may be a valuable addition to SOFA score to independent of the severity of illness and it may be a valuable addition to SOFA score to predict the prognosis of AKI patients.</p

Investigation on two abnormal phenomena about thermal conductivity enhancement of BN/EG nanofluids

The thermal conductivity of boron nitride/ethylene glycol (BN/EG) nanofluids was investigated by transient hot-wire method and two abnormal phenomena was reported. One is the abnormal higher thermal conductivity enhancement for BN/EG nanofluids at very low-volume fraction of particles, and the other is the thermal conductivity enhancement of BN/EG nanofluids synthesized with large BN nanoparticles (140 nm) which is higher than that synthesized with small BN nanoparticles (70 nm). The chain-like loose aggregation of nanoparticles is responsible for the abnormal increment of thermal conductivity enhancement for the BN/EG nanofluids at very low particles volume fraction. And the difference in specific surface area and aspect ratio of BN nanoparticles may be the main reasons for the abnormal difference between thermal conductivity enhancements for BN/EG nanofluids prepared with 140- and 70-nm BN nanoparticles, respectively

Characterization of Cross-Linking in Guar Gum Hydrogels via the Analysis of Thermal Decomposition Behavior and Water Uptake Kinetics

This study aimed to explore a test method for evaluating the effective cross-linking density of hydrogels. A guar gum–epichlorohydrin hydrogel (GEH) was prepared using guar gum (GG) as the raw material and epichlorohydrin (ECH) as the cross-linking agent. The thermal and mechanical properties, equilibrium swelling rate (ESR), water uptake (WU), and mass cross-linking degree of the hydrogels were assessed. Furthermore, the diffusion behavior of water molecules in the freeze-dried GEH was investigated. The experimental results showed the significance of the initial decomposition temperature (Ti) and final decomposition temperature (Tf) of the freeze-dried GEHs in determining the effective cross-linking density. The water uptake kinetics of the freeze-dried GEH was consistent with the linear fitting of the pseudo-second-order kinetic model and nonlinear fitting of the Fickian diffusion model, suggesting that chemisorption dominated the water absorption process in the GEH. Therefore, the effective cross-linking density of the hydrogels could be determined from the thermodynamic analysis and the diffusive behavior of water molecules in the gels. The thermal stability and water diffusion kinetics of the hydrogels were closely linked to the effective cross-linking density and pendant modification

Jointly Learning the Discriminative Dictionary and Projection for Face Recognition

Recently, dictionary learning has become an active topic. However, the majority of dictionary learning methods directly employs original or predefined handcrafted features to describe the data, which ignores the intrinsic relationship between the dictionary and features. In this study, we present a method called jointly learning the discriminative dictionary and projection (JLDDP) that can simultaneously learn the discriminative dictionary and projection for both image-based and video-based face recognition. The dictionary can realize a tight correspondence between atoms and class labels. Simultaneously, the projection matrix can extract discriminative information from the original samples. Through adopting the Fisher discrimination criterion, the proposed framework enables a better fit between the learned dictionary and projection. With the representation error and coding coefficients, the classification scheme further improves the discriminative ability of our method. An iterative optimization algorithm is proposed, and the convergence is proved mathematically. Extensive experimental results on seven image-based and video-based face databases demonstrate the validity of JLDDP

Clinical features of patients with pituitary stalk thickening: a review of 159 cases from one medical center

Abstract Background Pituitary stalk thickening (PST) used as an imaging diagnosis plays a major role in diagnosis and treatment of the hypothalamus and pituitary disease at an early stage. Up until now, several lines of systematic investigations have been conducted among adolescents, and the results indicated that PST is possibly one of the principal early manifestations of sellar region tumor. To characterize the major clinical features of PST and to identify the most effective treatments we conducted this study. Methods This was a retrospective review of patients with PST evaluated at Huashan Hospital over an eight-year period between 2007 and 2014. One hundred fifty nine patients who were diagnosed PST were included. The data including demographics, clinical presentations, imaging examinations, laboratory results and surgery were thoroughly reviewed and carefully analyzed. According to their clinical presentations and examinations, relevant treatments were adopted and different prognosis were observed. Results Of the 159 patients, 57 were males and 102 were females (median age was 29 and 43.4% were under the age of 21 years). And of the patients in the age group between 30 and 35 years, 84% were females. “Polydipsia and polyuria” was the most common clinical manifestation observed in 90 cases (>50%). 49.5% of the patients were diagnosed to have at least one anterior pituitary dysfunction. The sellar region MRI (SR-MRI) data showed that patients who had different clinical presentations or pituitary function showed different SR-MRI appearance. Over 60% patients who performed follow-up MRI showed shrunken PST. Fourteen cases who received radiotherapy appeared to be improved as shown by MRI. Conclusions PST is most commonly seen in the teenagers and the women of reproductive age. Distinct etiology may be identified based on the clinical manifestations, age and SR-MRI, which would help to make the final decision for treatments. Radiotherapy and immuno-suppressed therapy are effective in alleviating clinical symptoms and shrinking the stalk thickening

Is the serum vitamin D level at the time of hospital-acquired acute kidney injury diagnosis associated with prognosis?

Low circulating vitamin D levels have been suggested to potentially contribute to acute complications in critically ill patients. However, in patients with acute kidney injury (AKI), whether vitamin D deficiency occurs and is a potential contributor to worse early outcomes at the time of AKI diagnosis remains unclear.Two hundred patients with AKI were enrolled in our study. Healthy subjects and critically ill patients without AKI served as controls. Serum vitamin D concentrations were measured in the three groups. The patients with AKI were followed up for 90 days and grouped according to median serum vitamin D concentrations. In addition, vitamin D receptor polymorphisms (BsmI and FokI) were measured in these patients; they were also followed up for 90 days and grouped according to vitamin D receptor gene mutations. Low serum 1,25-dihydroxyvitamin D levels (59.56±53.00 pmol/L) were detected in patients with AKI and decreased with increasing severity of AKI. There were no significant findings with respect to 25-hydroxyvitamin D. The 90-day survival curves of individuals with high vitamin D concentrations showed no significant differences compared with the curves of individuals with low concentrations. The survival curves of patients with BB/Bb or FF/Ff genotypes also showed no significant differences compared with patients with bb or ff genotypes. In Cox regression analysis, the vitamin D status in patients with AKI was not an independent prognostic factor as adjusted by age, sex, Sequential Organ Failure Assessment score, or vitamin D receptor polymorphisms.Patients with AKI manifested a marked decrease in the 1,25-dihydroxyvitamin D level at the time of AKI diagnosis, and the degree of 1,25-dihydroxyvitamin D deficiency increased with the severity of AKI. No association between the serum vitamin D level at the time of AKI diagnosis and 90-day all-cause mortality was found in patients with AKI