Determination of the critical absolute blood volume for intradialytic morbid events

The reduction of blood volume below a critical threshold is assumed to trigger intradialytic morbid events (IME). Recently, we presented a simple method to determine the absolute blood volume during routine hemodialysis (HD) carried out without blood sampling and without injection of dyes or radiolabeled markers. Such information could be used to detect excessive volume reduction during HD and to prevent IME. Therefore, we performed a pilot study in IME‐prone patients to identify the absolute blood volume at which they developed clinical symptoms. A volume of 240 mL of ultrapure dialysate was automatically infused into the extracorporeal circulation using the bolus function of a commercial online hemodiafiltration machine incorporating a blood volume monitor (BVM). The increase in relative blood volume (RBV) caused by the infusion was measured and used to determine the absolute blood volume at that time. The blood volume per kilogram body mass at the time of symptomatic IME was also determined. All IME‐prone patients of a single‐dialysis center were included in the study. Ten out of 12 patients became symptomatic at a specific blood volume between 65 and 56 mL/kg (mean 62 mL/kg) whereas RBV showed a wide scatter (82–97%). A specific blood volume of 65 mL/kg seems to represent the threshold for IME by this method. The technique could be completely automated without altering the hardware of the dialysis device. Present feedback systems for automated blood volume‐controlled ultrafiltration could be adapted to maintain absolute blood volume above this critical volume to safely prevent volume‐dependent IME.     

关于大连地区集中空调的几点思考

结合大连地区的气候特点,根据本人在设计过程中的总结,对集中空调系统做了几点具体的分析,其中包括对常见集中空调的方案比较,水系统一次泵变流量系统,二次泵变流量系统以及变风量风系统。     

小孔流道内容积交变空化流场特性分析

目的 基于容积交变空化原理,研究小孔流道内容积交变空化流场的演变规律,以及容积交变频率和容积变化量等关键工艺参数对流场特性的影响,为容积交变空化抛光小孔内表面提供指导。方法 首先,建立小孔流道内容积交变空化流场的三维瞬态仿真模型。其次,采用标准k-epsilon模型、Zwart-Gerber-Belamri模型模拟不同容积交变频率和容积变化量下容积交变空化流场含气率和湍流强度,并与高速摄像结果进行比较分析。最后,对机械加工的Al 1060和T2 Cu小孔内表面进行抛光,验证容积交变空化抛光小孔内表面的可行性。结果 在一个周期内,当容积变化量为20 mm,容积交变频率分别为90、100、110、120 Hz时,小孔流道内容积交变空化流场含气率和湍流强度均随容积交变频率的增大而增大,含气率最高可达0.664 8;当容积交变频率为120 Hz,容积变化量分别为10、15、20、25 mm时,小孔流道内容积交变空化流场含气率和湍流强度均随容积变化量的增大而增大,含气率最高可达0.706 8。随着活塞的拉伸和压缩,湍流强度也由两边强、中间弱逐渐转变为两边弱、中间强,并在周期末达到最大。实验研究表明,经过容积交变空化抛光后,Al 1060小孔内表面的粗糙度由0.704 4 μm降低到0.324 7 μm,T2 Cu小孔内表面的粗糙度由0.721 4 μm降低到0.357 3 μm,小孔内表面粗糙度明显降低。结论 容积交变空化抛光小孔内表面具有可行性。可通过提高容积交变频率和容积变化量来提高小孔流道内容积交变空化流场含气率和湍流强度,进而提高容积交变空化抛光小孔内表面的抛光效率。     

Morphology and quantitative characteristics of ceramic phase in Ti-HA composites with ? 20vol% HA

This paper studied Ti-HA composites with low volume fractions of hydroxyapatite (HA), which are usually used as internal layers of functionally graded materials to withstand heavy load. Optical microscopy (OM), X-ray diffractometry (XRD), and scanning electron microscopy (SEM) were used to analyze the microstructure of cold-pressed composites after sintering at 1,100°C. Quantitative analysis of volume fractions and mean particle volumes of the ceramic phase was adopted to further discuss the reaction between Ti and HA. CaO and Ti _x P _y were produced in the Ti-HA reaction. With the increase of HA volume fraction, the Ti-HA reaction could be divided into three stages including stable initiation, stimulating term and re-stabilization according to the quantitative characteristics of the ceramic phase.     

一种新的驾驭式可视化方法

驾驭式的可视化方法通过在数据场内不断地改变观察位置,以便交互地对数据场进行考察。与已有的驾驭式方法不同,本文提出的新方法只在驾驭的过程中抽取物质分界面,采取投影成像的方法,加快绘制过程。另外,新方法还提供局部操作的机制,以便对感兴趣的局部特征进行细致的研究,实验结果表明,本方法对于大规模数据场的可视化是一种有效的途径。     

Automatic feedback control of relative blood volume changes during hemodialysis improves blood pressure stability during and after dialysis

Automatic feedback systems have been designed to control relative blood volume changes during hemodialysis (HD) as hypovolemia plays a major role in the development of dialysis hypotension. Of these systems, one is based on the concept of blood volume tracking (BVT). BVT has been shown to improve intra-HD hemodynamic stability. We first questioned whether BVT also improves post-HD blood pressure stability in hypotension-prone patients and second, whether BVT is effective in reducing the post-HD weight as many hypotension-prone patients are overhydrated because of an inability to reach dry weight. After a 3-week period on standard HD, 12 hypotension-prone patients were treated with two consecutive BVT treatment protocols. During the first BVT period of 3 weeks, the post-HD target weight was kept identical compared with the standard HD period (BVT-constant weight; BVT-cw). During the second BVT period of 6 weeks, we gradually tried to lower the post-HD target weight (BVT-reduced weight; BVT-rw). In the last week of each period, we studied intra-HD and 24 hr post-HD blood pressure behavior by ambulatory blood pressure measurement (ABPM). Pre- and post-HD weight did not differ between standard HD and either BVT-cw or BVT-rw. Heart size on a standing pre-dialysis chest X-ray did not change significantly throughout the study. There were less episodes of dialysis hypotension during BVT compared with standard HD (both BVT periods: p<0.01). ABPM data were complete in 10 patients. During the first 16 hr post-HD, systolic blood pressure was significantly higher with BVT in comparison with standard HD (both BVT periods: p<0.05). The use of BVT in hypotension-prone patients is associated with higher systolic blood pressures for as long as 16 hr post-HD. BVT was not effective in reducing the post-HD target weight in this patient group.     

实验室标准传声器前腔体积的测量方法研究

实验室标准传声器的前腔体积(包括等效体积)是耦合腔互易校准声压灵敏度的主要不确定度分量.为了控制前腔体积与等效体积引入的不确定度分量,应用声学方法测量实验室标准传声器的前腔体积,分别利用有源耦合腔结合系列哑头空腔的方法和多个平面波耦合腔的方法对LS1P和LS2P传声器的前腔体积与等效体积之和进行测量.实验结果表明,有源耦合腔法和多个平面波耦合腔法均能有效测量实验室标准传声器的前腔体积,且测量结果具有较好的一致性.前腔体积的精确测量实现了实验室标准传声器声压灵敏度的高精度校准.     

Material spatial randomness: From statistical to representative volume element

The material spatial randomness forces one to re-examine various basic concepts of continuum solid mechanics. In this paper we focus on the Representative Volume Element (RVE) that is commonly taken for granted in most of deterministic as well as in stochastic solid mechanics, although in the latter case it is called the Statistical Volume Element (SVE). The key issue is the scale over which homogenization is being carried out—it is called the mesoscale, separating the microscale (level of microheterogeneities) from the macroscale (level of RVE). As the mesoscale grows, the SVE tends to become the RVE. This occurs in terms of two hierarchies of bounds stemming from Dirichlet and Neumann boundary value problems on the mesoscale, respectively. Since generally there is no periodicity in real random media, the RVE can only be approached approximately on finite scales. We review results on this subject in the settings of linear elasticity, finite elasticity, plasticity, viscoelasticity, thermoelasticity, and permeability.     

Radioisotope blood volume measurement in hemodialysis patients

Accurate assessment of blood volume (BV) may be helpful for prescribing hemodialysis (HD) and for reducing complications related to hypovolemia and volume overload. Monitoring changes in relative BV (RBV) using hematocrit, e.g., Crit‐Line Monitor (CLM‐III), an indirect method, cannot be used to determine absolute BV. We report the first study of BV measurement for assessing volume status in HD patients using the indicator dilutional method. Ten adult HD patients were enrolled in this prospective observational study. BV measurement was performed before and after HD using BV analysis (BVA)‐100 (Daxor Corporation, New York, NY, USA). BVA‐100 calculates BV using radiolabeled albumin (Iodine‐131) followed by serial measures of the radioisotope. Fluid loss from the extravascular space was calculated by subtracting the change in BV from total weight loss. Intradialytic changes in RBV were measured by CLM‐III. Eight out of 10 cases had significant hypervolemia, two cases were normovolemic. The range of BV variation from predicted normal was 156 to 1990 mL. Significant inter‐individual differences in extravascular space fluid loss ranged from 54% to 99% of total weight loss. Spearman correlation showed a good correlation in the measurement of RBV by BVA‐100 and CLM‐III in 8 out of 10 patients (r² = 0.64). BV measurement using BVA‐100 is useful to determine absolute BV as well as changes in BV and correlates reasonably well with CLM‐III measurements. Individual refilling ability can be determined as well. This may prove useful in prescribing and monitoring ultrafiltration rates, establishment of optimal BV in HD patients and reducing morbidity and mortality associated with chronic HD.     

Node‐based uniform strain elements for three‐node triangular and four‐node tetrahedral meshes

Node‐based uniform strain elements for three‐node triangular and four‐node tetrahedral meshes are presented. The elements use the linear interpolation functions of the original mesh, but each element is associated with a single node. As a result, a favourable constraint ratio for the volumetric response is obtained for problems in solid mechanics. The uniform strain elements do not require the introduction of additional degrees of freedom and their performance is shown to be significantly better than that of three‐node triangular or four‐node tetrahedral elements. In addition, nodes inside the boundary of the mesh are observed to exhibit superconvergent behaviour for a set of example problems. Published in 2000 by John Wiley & Sons, Ltd.     

无油线性压缩机变容量制冷性能实验研究

无油线性压缩机具有结构简单紧凑、效率高和寿命长等优点,在航空航天热控领域具有巨大的发展潜力。针对实验室研制的无油线性压缩机进行变容量制冷性能研究,分析行程和余隙容积变化对压缩机的制冷性能受的影响。实验结果表明,在冷凝温度为48℃,蒸发温度为10℃,热沉温度维持15℃,行程从6.5 mm增加到8.9 mm时,压缩机的制冷量会随行程的增大而增大。在行程为8.9 mm时,最大制冷量为180 W;系统的COP和压缩效率会随着行程的增大先增大后减小,在行程为7.9 mm时,具有最高COP和压缩效率,分别为1.78%和30.6%。在冷凝温度为55℃,蒸发温度为10℃,热沉温度稳定在15℃,系统的余隙长度从0.1 mm增加到1.1 mm时,随着余隙长度的增加,压缩机的制冷量、COP和压缩效率会逐渐降低。电机效率会随着余隙容积的增加先升高后降低,在余隙长度为0.9 mm时,电机效率为78.4%。     

通风系统风量分配器性能的数值模拟

在许多通风系统中,常采用风量分配器来保证在各送风支路风量发生变化时系统风量的平衡。本文采用计算流体力学的方法,模拟了风量分配器的进风管和出风管道截面尺寸、进风口风速等因素与风量分配器风量分配特性间的关系,并分析了上述因素对风量分配特性的影响作用。     

Thermodynamic properties of R 22 + R 114 mixtures in the high-density region for temperatures from 310 to 370 K

The densities for mixtures of R 22 and R 114 have been measured with the variable-volume method using a metal bellows as a function of temperature and pressure. The results for three different compositions (75, 50, and 25 mol% R 22) cover the high-density region along seven isotherms between 310 and 370 K at 15 pressures from 1.0 to 10 MPa. Based on the present density measurements, the values of the excess molar volume, the volume expansion coefficient, and the isothermal compressibility have been calculated. The excess molar volumes for each mixture below 340 K are positive, whereas those above 350 K decrease with decreasing pressure and become negative at low pressures. The behavior of the volume expansion coefficient and the isothermal compressibility for the equimolar mixture are closer to that for R 114 than the average of those for both pure components.     

Simulation of rafting type and stress distribution in nickel-based superalloys with different volume fractions of γ′ phase

A representative volume element is introduced to represent the microstructure of γ/γ′ morphology with periodic boundary conditions to formulate the full mode of the micromechanical analysis. [0 0 1]-oriented alloys with γ′ volume fractions from 60 to 70% are simulated under tensile loading. A raft criterion is implemented into the user subroutine to predict the rafting type. The misfit stress is considered by different thermal expansion coefficients of the two phases. It is very high in γ phase and slightly decreases with the increasing of γ′ volume fraction. The stress distributions in the two phases change during creep deformation. The creep crack initiation time slightly increases with the increase of γ′ volume fraction. The stress components decrease with the increasing of γ′ volume fraction at the beginning and change due to the stress redistribution during creep loading.     

基于多分辨率裁剪纹理的体裁剪技术

为解决单分辨率裁剪纹理的数据规模过大的问题,该文提出了一种具有INDEX-DATA二级结构的多分辨率裁剪纹理。文章主要介绍了多分辨率裁剪纹理的定义和结构,并讨论多分辨率纹理的构建方法和基于多分辨率纹理的体裁剪方法,最后对实验结果进行了分析讨论。该文方法已在自主知识产权可视化软件SVIP中得到应用,取得了令人满意的结果。     

生物安全实验室压力波动的原因和控制措施的探讨

对生物安全实验室负压形成机理进行了分析,总结了生物安全实验室压力控制的特点;对影响生物安全实验室压力波动的因素进行了阐述,并给出了相应的控制措施。     

A new hybrid method for optimal circuit design using semi-definite programming

In this article a new method for yield optimization (design centring) is introduced. The method has a statistical-geometrical nature, hence it is called hybrid. The method exploits the semi-definite programming applications in approximating the feasible region with two bounding ellipsoids. These ellipsoids are obtained using a two phase algorithm. In the first phase, the minimum volume ellipsoid enclosing the feasible region is obtained. The largest ellipsoid that can be inscribed inside the feasible region is obtained in the second phase. The centres of these bounding ellipsoids are used as design centres. In the second phase, an additional polytopic region approximation is constructed. A comparison between the obtained region approximations is given. Saving in the number of circuit simulations needed for yield optimization is also considered. Practical examples are given to show the effectiveness of the new method.