The influence of bicarbonate supplementation on plasma levels of branched-chain amino acids in haemodialysis patients with metabolic acidosis

BACKGROUND: It has been hypothesized that correction of metabolic acidosis might improve the nutritional state of acidotic haemodialysis (HD) patients partly because of a reduced oxidation of branched-chain amino acids (BCAA). AIM: We investigated whether bicarbonate (Bic) supplementation in acidotic HD patients results in increased plasma levels of BCAA. METHODS: In a longitudinal study (run-in period, 2 months; study period, 6 months), the effect of Bic supplementation on plasma levels of BCAA was studied in 12 acidotic HD patients (7 men, 5 women, mean age 54 +/- 18 years) with a predialysis bicarbonate (Bic) concentration smaller or equal to 22 mmol/l. Bic was supplemented by increasing Bic concentration of the dialysate and by oral Bic supplementation. RESULTS: Predialysis Bic increased significantly during the study period (18.7 +/- 2.7 vs. 23.1 +/- 11.5 mmol/l). There was no change in nutritional parameters. However, plasma levels of the BCAA valine, leucine, and isoleucine increased significantly. CONCLUSIONS: In haemodialysis patients with metabolic acidosis, Bic supplementation over a 6-months period resulted in an increase in plasma levels of BCAA. Further study is needed to elucidate the mechanisms behind, and the clinical importance of the observed changes in plasma BCAA levels.     

A systematic review on parametric dependencies of transpired solar collector performance

Zero or low‐carbon buildings can be achieved through novel technology solutions and integrating renewable energy into the buildings. One method of reducing the fossil fuel dependency of buildings and limiting greenhouse gas emissions is integrating the solar thermal system into the built environment. Recently, transpired solar collector has been identified as 1 of the most efficient solar thermal conversion technologies where a very high efficiency can be achieved. The proposed review paper investigates the performance of transpired solar collectors (TSCs) and discusses the relevant case studies in this context. This paper introduces the background and concept of TSCs. It mainly focuses on the study of parametric dependency of the performance of TSCs. The paper also investigates various mathematical models, experimental study, and numerical simulations particularly CFD used for TSC performance analysis. This proposed paper concluded that wind speed and airflow rate are the most dominant factor in TSC performance but solar irradiation, hole diameter, hole geometry, and pitch size have limited effect on TSC performance; also, profile with longer pitch tends to lower the collector efficiency and heat transfer coefficient. However, profile with shorter pitch tends to reduce the wind effect.     

生物地球化学循环模型DNDC及其应用

生物地球化学模型是模拟研究化学元素动态的新兴领域,可用于陆地生态系统内植物、有机物和无机营养元素动态变化和循环。DNDC模型(DeNitrification-DeComposition Model)是美国新罕布什尔州大学陆地海洋空间研究中心开发研制的,最初是为了模拟农田生态系统固碳、氮流失和水平衡而创建,目前该模型可以模拟草地、湿地、林地等陆地生态系统碳氮动态过程。DNDC模型已经在美洲、欧洲、澳洲以及亚洲的一些地区得到了验证和运用。DNDC模型可用来分析陆地植物生长规律、土壤硝化和反硝化作用、温室气体和痕量气体排放预测研究、不同土壤类型及气候条件对森林生态系统碳氮通量变化的影响以及气候变化对生物地球化学循环的影响预测等。     

配筋钢管混凝土短柱中环向箍筋的受力机理

通过轴压试验和数值模拟手段,研究了箍筋对配筋钢管混凝土轴压短柱(R-CFST)力学性能的影响机理及承载力计算方法,旨在提出R-CFST设计方法和了解R-CFST施工时能否适当减少箍筋用量以降低成本。试验参数有平行式和螺旋式两种箍筋形式,其中平行式箍筋有三种间距,共准备4组8根R-CFST和3根钢管混凝土试件。试件在受力性能、承载力、断裂韧性、延性、套箍效应和破坏模式等方面的分析结果表明：构件在最大荷载前的受力特性和承载力与箍筋间距和形式无关,承载力计算时可不予考虑;平行式箍筋纵向间距的变化不会对构件的力学性能产生明显影响,因而推荐使用较大的箍筋间距以获得较好的经济效益;螺旋式箍筋有助于提高构件最大荷载后的受力性能,尤其是对延性的提高作用更为显著,因而推荐使用螺旋式箍筋以获得构件较好的延性和抗震性能。在试验结果的基础上,进行了数值分析研究,提出了可靠和有效的核心混凝土本构方程和此类构件的数值模拟方法,结合模拟结果进一步验证了试验结论的准确性。最后,对R-CFST的承载力计算方法展开了研究,发现美国规范给出的公式是过于保守的,充分分析后提出了与我国规范的设计习惯相匹配的R-CFST承载力计算公式,与实验结果对比分析表明提出的公式可以用于工程设计。     

Immediate recovery from acute renal insufficiency after abdominal decompression

A 61-year-old man received an aorto-iliac reconstruction after he was admitted because of a ruptured abdominal aortic aneurysm. Postoperatively, he developed cardiopulmonary insufficiency with anuria. After the intra-abdominal pressure had risen to 40 cmH2O (measured by a urinary bladder catheter), it was decided to perform a relaparotomy. Immediately after abdominal decompression--without correction of any other intra-abdominal pathology--the diuresis increased and several other cardiopulmonary parameters improved significantly. When a critically ill patient shows a rapid increase of the intra-abdominal pressure above a critical level an acute abdominal compartment syndrome may develop. This syndrome consists mainly of potentially fatal cardiopulmonary and renal insufficiency, for which (re)laparotomy with abdominal decompression is the only correct treatment.     

Explaining the experience curve: Cost reductions of Brazilian ethanol from sugarcane

Production costs of bio-ethanol from sugarcane in Brazil have declined continuously over the last three decades. The aims of this study are to determine underlying reasons behind these cost reductions, and to assess whether the experience curve concept can be used to describe the development of feedstock costs and industrial production costs. The analysis was performed using average national costs data, a number of prices (as a proxy for production costs) and data on annual Brazilian production volumes. Results show that the progress ratio (PR) for feedstock costs is 0.68 and 0.81 for industrial costs (excluding feedstock costs). The experience curve of total production costs results in a PR of 0.80. Cost breakdowns of sugarcane production show that all sub-processes contributed to the total, but that increasing yields have been the main driving force. Industrial costs mainly decreased because of increasing scales of the ethanol plants. Total production costs at present are approximately 340 US$/m_ethanol³ (16 US$/GJ). Based on the experience curves for feedstock and industrial costs, total ethanol production costs in 2020 are estimated between US$ 200 and 260/m³ (9.4–12.2 US$/GJ). We conclude that using disaggregated experience curves for feedstock and industrial processing costs provide more insights into the factors that lowered costs in the past, and allow more accurate estimations for future cost developments.     

Evaluation of attenuation corrections using Monte Carlo simulated lung SPECT

SPECT (single photon emission computed tomography) images are distorted by photon attenuation. The effect is complex in the thoracic region due to different tissue densities. This study compares the effect on the image homogeneity of two different methods of attenuation correction in lung SPECT; one pre-processing and one post-processing method. This study also investigates the impact of attenuation correction parameters such as lung contour, body contour, density of the lung tissue and effective attenuation coefficient. The Monte Carlo technique was used to simulate SPECT studies of a digital thorax phantom containing a homogeneous activity distribution in the lung. Homogeneity in reconstructed images was calculated as the coefficient of variation (CV). The isolated effect of the attenuation correction was assessed by normalizing pixel values from the attenuation corrected lung by pixel values from the lung with no attenuation effects. Results show that the CV decreased from 12.8% with no attenuation correction to 4.4% using the post-processing method and true densities in the thoracic region. The impact of variations in the definition of the body contour was found to be marginal while the corresponding effect of variations in the lung contour was substantial.     

软化学法合成正交结构LiMnO_2及其电化学性能

研究以氢氧化锂和三氧化二锰为原料,用软化学法制备具有正交结构的锂离子电池正极材料LiMnO2。用X射线衍射法确定了材料的结构,用扫描电镜考察了材料形貌和反应时间的关系,观察结果显示得到的LiMnO2的粒子尺寸在300~500nm。结合循环伏安法和交流阻抗分析研究了合成条件对材料组织结构、尺寸与电化学性能的影响。材料的电化学性能测试结果表明,合成的正交扭曲结构LiMnO2(o-LiMnO2)材料在电化学过程中初期表现了较好的电化学性能。但材料在电化学过程中逐步向尖晶石结构相LiMn2O4转变,容量产生衰减,其循环寿命有待更进一步改善。