Use of venous-to-arterial carbon dioxide tension difference to guide resuscitation therapy in septic shock

The mixed venous-to-arterial carbon dioxide(CO_2)tension difference[P(v-a) CO_2]is the difference between carbon dioxide tension(PCO_2) in mixed venous blood(sampled from a pulmonary artery catheter) and the PCO_2 in arterial blood.P(v-a) CO_2 depends on the cardiac output and the global CO_2 production,and on the complex relationship between PCO_2 and CO_2 content.Experimental and clinical studies support the evidence that P(v-a) CO_2 cannot serve as an indicator of tissue hypoxia,and should be regarded as an indicator of the adequacy of venous blood to wash out the total CO_2generated by the peripheral tissues.P(v-a) CO_2 can be replaced by the central venous-to-arterial CO_2 difference(△PCO_2),which is calculated from simultaneous sampling of central venous blood from a central vein catheter and arterial blood and,therefore,more easy to obtain at the bedside.Determining the △PCO_2 during the resuscitation of septic shock patients might be useful when deciding when to continue resuscitation despite a central venous oxygen saturation(SCVO_2) > 70%associated with elevated blood lactate levels.Because high blood lactate levels is not a discriminatory factor in determining the source of that stress,an increased △PCO_2(> 6 mmHg)could be used to identify patients who still remain inadequately resuscitated.Monitoring the △PCO_2 from the beginning of the reanimation of septic shock patients might be a valuable means to evaluate the adequacy of cardiac output in tissue perfusion and,thus,guiding the therapy.In this respect,it can aid to titrate inotropes to adjust oxygen delivery to CO_2 production,or to choose between hemoglobin correction or fluid/inotrope infusion in patients with a too low ScvO_2 related to metabolic demand.The combination of P(v-a) CO_2 or △PCO_2 with oxygen-derived parameters through the calculation of the P(v-a) CO_2 or △PCO_2/arteriovenous oxygen content difference ratio can detect the presence of global anaerobic metabolism.

Effects of Second-Order Sum-and Difference-Frequency Wave Forces on the Motion Response of a Tension-Leg Platform Considering the Set-down Motion

This paper presents a study on the motion response of a tension-leg platform(TLP) under first-and second-order wave forces, including the mean-drift force, difference and sum-frequency forces. The second-order wave force is calculated using the full-field quadratic transfer function(QTF). The coupled effect of the horizontal motions, such as surge, sway and yaw motions, and the set-down motion are taken into consideration by the nonlinear restoring matrix. The time-domain analysis with 50-yr random sea state is performed. A comparison of the results of different case studies is made to assess the influence of second-order wave force on the motions of the platform. The analysis shows that the second-order wave force has a major impact on motions of the TLP. The second-order difference-frequency wave force has an obvious influence on the low-frequency motions of surge and sway, and also will induce a large set-down motion which is an important part of heave motion. Besides, the second-order sum-frequency force will induce a set of high-frequency motions of roll and pitch. However, little influence of second-order wave force is found on the yaw motion.

Regulation of the intermittent release of giant unilamellar vesicles under osmotic pressure

Osmotic pressure can break the fluid balance between intracellular and extracellular solutions.In hypo-osmotic so-lution,water molecules,which transfer into the cell and burst,are driven by the concentration difference of solute across the semi-permeable membrane.The complicated dynamic processes of intermittent bursts have been previously observed.However,the underlying physical mechanism has yet to be thoroughly explored and analyzed.Here,the intermittent re-lease of inclusion in giant unilamellar vesicles was investigated quantitatively,applying the combination of experimental and theoretical methods in the hypo-osmotic medium.Experimentally,we adopted a highly sensitive electron multiplying charge-coupled device to acquire intermittent dynamic images.Notably,the component of the vesicle phospholipids af-fected the stretch velocity,and the prepared solution of vesicles adjusted the release time.Theoretically,we chose equations and numerical simulations to quantify the dynamic process in phases and explored the influences of physical parameters such as bilayer permeability and solution viscosity on the process.It was concluded that the time taken to achieve the balance of giant unilamellar vesicles was highly dependent on the molecular structure of the lipid.The pore lifetime was strongly related to the internal solution environment of giant unilamellar vesicles.The vesicles prepared in viscous solution were able to visualize long-lived pores.Furthermore,the line tension was measured quantitatively by the release velocity of inclusion,which was of the same order of magnitude as the theoretical simulation.In all,the experimental values well matched the theoretical values.Our investigation clarified the physical regulatory mechanism of intermittent pore forma-tion and inclusion release,which provides an important reference for the development of novel technologies such as gene therapy based on transmembrane transport as well as controlled drug delivery based on liposomes.

Expansion of spherical cavity of strain-softening materials with different elastic moduli of tension and compression

An expansion theory of spherical cavities in strain-softening materials with different moduli of tension and com-pression was presented. For geomaterials,two controlling parameters were introduced to take into account the different moduli and strain-softening properties. By means of elastic theory with different moduli and stress-softening models,general solutions cal-culating Tresca and Mohr-Coulomb materials' stress and displacement fields of expansion of spherical cavity were derived. The effects caused by different elastic moduli in tensile and compression and strain-softening rates on stress and displacement fields and development of plastic zone of expansion of cavity were analyzed. The results show that the ultimate expansion pressure,stress and displacement fields and development of plastic zone vary with the different elastic moduli and strain-softening prop-erties. If classical elastic theory is adopted and strain-softening properties are neglected,rather large errors may be the result.

A形斜塔不等跨斜拉桥施工关键技术研究

毕节市倒天河某新建桥设计为半漂浮体系的A形斜塔不等跨斜拉桥,该桥为典型的市政景观桥梁。该类型桥塔在施工阶段均处于大偏心、长悬臂状态,塔底应力与塔端位移极其敏感,施工过程如何确保塔身应力不超限、线形不超标等问题为主塔施工的重难点。施工借助midas Civil有限元软件模拟计算,阐明了一次张拉成桥方案的可行性,并根据计算结果预判主梁现浇支架受力增大的情况,对施工具有指导意义。除此,仿真计算结果可获取各施工阶段的变形与应力参数,结合实时监控数据对各施工阶段进行了指导与纠偏,确保各构件的结构安全和线形要求,成桥索力与设计高度吻合,效果较好。

Pcv-aCO_(2)/Ca-cvO_(2)、外周灌注指数联合血乳酸在脓毒症休克患者预后评估中的应用价值

目的探讨中心静脉-动脉二氧化碳分压差与动脉-中心静脉氧含量差的比值(Pcv-aCO_(2)/Ca-cvO_(2))、外周灌注指数联合血乳酸(Lac)在脓毒症休克患者预后评估中的应用价值。方法选取南阳市第一人民医院急诊医学科2019年8月至2020年5月收治的65例脓毒症休克患者作为研究对象,根据患者住院28 d的预后分为存活组(52例)和死亡组(13例)。回顾性收集两组患者收治重症监护病房当天(T0)及经过复苏治疗6 h(T1)后的心率(HR)、中心静脉压(CVP)、平均动脉压(MAP)、外周灌注指数(PPI)、血乳酸(Lac)及血气分析结果,分析28 d死亡的相关影响因素,采用受试者工作特征(ROC)曲线分析Pcv-aCO_(2)/Ca-cvO_(2)、PPI、Lac及三者联合对28 d死亡的预测价值。结果死亡组患者复苏前MAP、PPI、Lac及Pcv-aCO_(2)/Ca-cvO_(2)均较存活组差(P<0.05),两组患者复苏前HR、CVP、Pcv-aCO_(2)差异无统计学意义(P>0.05);复苏6 h后,两组患者血流灌注指数、血流动力学及氧代谢参数都有所改善,但死亡组患者各参数恢复情况均较存活组差(P<0.05);多因素回归分析显示,复苏6 h后PPI、Lac、Pcv-aCO_(2)/Ca-cvO_(2)比值均与28 d病死率相关,是脓毒性休克患者28 d死亡的独立危险因素(P<0.05);ROC曲线分析显示,Pcv-aCO_(2)/Ca-cvO_(2)约登指数(0.692)最大时对应截断值为1.48,曲线下面积为0.867,预测患者28 d死亡敏感度为85.29%,特异度为83.87%;PPI约登指数(0.686)最大时对应截断值为1.71,曲线下面积为0.884,预测患者28 d死亡敏感度为91.18%,特异度为77.42%;Lac约登指数(0.627)最大时对应截断值为5.30,曲线下面积为0.859,预测患者28 d死亡敏感度为85.29%,特异度为77.42%;三者联合预测患者28 d死亡敏感度为88.24%,特异度为90.32%。结论PPI、Lac、Pcv-aCO_(2)/Ca-cvO_(2)是脓毒性休克患者28 d死亡的独立危险因素,三者联合可以更准确地评估脓毒症休克患者的预后。

A New Elasticity and Finite Element Formulation for Different Young's Modulus When Tension and Compression Loadings

This paper presents a new elasticity and finite element formulation for different Young's modulus when tension and compression loadings in anisotropy media. The case studies, such as anisotropy and isotropy, were investigated. A numerical example was shown to find out the changes of neutral axis at the pure bending beams.

Internal Force Analysis Due to the Supporting Translation in Statically (Indeterminate) Structures for Different Elastic Modulus

For statically indeterminate structure, the internal force will be changed with the translation of the supports, because the internal force is related to the absolute value of the stiffness EI. When the tension is different with the compression modulus, EI is the function of internal force and is not constant any more that is different from classic mechanics. In the other words, it is a nonlinear problem to calculate the internal force. The expression for neutral axis of the statically indeterminate structure was derived in the paper. The iterative program for nonlinear internal force was compiled. One case study was presented to illustrate the difference between the results using the different modulus theory and the single modulus theory as in classical mechanics. Finally, some reasonable suggestions were made for the different modulus structures.

基于Ansys的高压输电塔风振特性分析

在电力大范围应用的背景下,研究输电线路的振动特性对电网整体的安全性有着极其重要的意义。文中推导了三线两塔耦合系统的力学简化模型,利用Ansys软件建立了典型的500 kV交流双回路耐张塔模型,在此基础上利用Davenport风速谱对电力塔模型节点的风载荷进行了模拟,阐明了分析的有效性。利用理论方法和有限元方法分别计算了塔-线耦合体系的动力特性,结果表明理论计算与有限元结果保持一致,证明了理论的有效性。此外通过有限元的分析还能看出耦合系统出现了一部分由塔或线诱发的新振型,且同阶下耦合的振动频率要小于单塔的振动频率。

Smart Semi-active PID-ACO control strategy for tower vibration reduction in Wind Turbines with MR damper

Wind turbine technology is well known around the globe as an eco-friendly and eff ective renewable power source. However, this technology often faces reliability problems due to structural vibration. This study proposes a smart semi-active vibration control system using Magnetorheological (MR) dampers where feedback controllers are optimized with nature-inspired algorithms. Proportional integral derivative (PID) and Proportional integral (PI) controllers are designed to achieve the optimal desired force and current input for MR the damper. PID control parameters are optimized using an Ant colony optimization (ACO) algorithm. The eff ectiveness of the ACO algorithm is validated by comparing its performance with Ziegler-Nichols (Z-N) and particle swarm optimization (PSO). The placement of the MR damper on the tower is also investigated to ensure structural balance and optimal desired force from the MR damper. The simulation results show that the proposed semi-active PID-ACO control strategy can signifi cantly reduce vibration on the wind turbine tower under diff erent frequencies (i.e., 67%, 73%, 79% and 34.4% at 2 Hz, 3 Hz, 4.6 Hz and 6 Hz, respectively) and amplitudes (i.e. 50%, 58% and 67% for 50 N, 80 N, and 100 N, respectively). In this study, the simulation model is validated with an experimental study in terms of natural frequency, mode shape and uncontrolled response at the 1st mode. The proposed PID-ACO control strategy and optimal MR damper position is also implemented on a lab-scaled wind turbine tower model. The results show that the vibration reduction rate is 66% and 73% in the experimental and simulation study, respectively, at the 1st mode.

Arterial and End-Tidal Carbon Dioxide in Supine Obese Patients during General Anesthesia

Background: We investigated the differences between partial pressure of arterial carbon dioxide and end-tidal carbon dioxide (P(a-ET)CO2) with respect to the Broca-Katsura index (BKI), which is an obesity index, in obese patients during general anesthesia. Materials and Methods: From January 2003 to December 2013, we studied 601 patients aged 16 years old or over undergoing general anesthesia. Patients had American Society of Anesthesiology physical status I and II and we reviewed their anesthetic charts. The P(a-ET)CO2 with respect to the BKI divided patients into two groups: 16 to 2 values between the two groups. Results: In patients aged 16 to 2 was 2.2 ± 3.1 mmHg at BKI 2 was 3.2 ± 4.1 mmHg at BKI 2 tends to increase in obese patients during general anesthesia with increasing BKI in patients aged 16 to < 65 years old.

双柱悬索拉线塔风致倒塌易损性分析

作为风敏感结构,双柱悬索拉线塔在强风荷载作用下易遭受不同程度的损伤甚至发生倒塌破坏,因此,有必要对其进行风灾易损性分析。为此,本文提出一种双柱悬索拉线塔风致倒塌易损性分析方法。首先,考虑结构参数的不确定性,基于拉丁超立方抽样建立双柱悬索拉线塔不确定性模型,完成所有样本模型的非线性静力推覆分析;然后,利用B-R准则和对数正态分布函数拟合得到双柱悬索拉线塔倒塌易损性曲线;最后,研究风向角和拉线初张力对结构倒塌易损性曲线的影响。研究结果表明:相较于确定性倒塌分析,不确定性倒塌分析能够更好地评估双柱悬索拉线塔的抗风承载能力;风向角对双柱悬索拉线塔的倒塌易损性影响较大,结构的最不利风向角为45°,当基本风速小于56.5 m/s时,结构在任一风向角下的倒塌概率都很小;拉线初张力对结构倒塌临界风速无影响,但对立柱顶点位移易损性曲线影响较大;增大拉线初张力,左右侧立柱的顶点位移易损性曲线均向左移动,且其对背风侧立柱的影响更大。

基于拉压差异的沥青混合料强度与疲劳特性

【目的】探究沥青混合料的拉压差异力学特性。【方法】开展了典型沥青混合料直接拉伸和四点弯曲强度及疲劳试验,基于材料拉压模量差异特性推导并得到了区别于传统四点弯曲梁的真实四点弯曲强度计算公式,分析了传统四点弯曲、真实四点弯曲及直接拉伸应力状态下强度、疲劳寿命及模量衰变规律。【结果】真实四点弯曲强度约为传统四点弯曲强度的80%,在相同加载速率下,不同应力状态强度中直接拉伸强度最小,且其对加载速率的敏感性亦最低;在相同应力水平下,直接拉伸疲劳寿命最小,但在相同真实应力比下直接拉伸疲劳寿命最大,真实四点弯曲疲劳寿命约为传统四点弯曲疲劳寿命的46%;真实四点弯曲疲劳试验的模量衰变速率远小于直接拉伸模量衰变速率,且破坏时前者的模量衰减幅度更小。【结论】材料的拉压差异特性对其力学参数的测试结果及变化规律影响显著,研究成果可为考虑拉压差异的沥青路面结构设计参数取值提供参考。

大型冷却塔夏季日照筒壁温差原型实测与分布准则

中国现行规范的夏季日照筒壁温差条款源自20世纪80年代秦岭电厂的单一冷却塔(105m)实测结果,既有条款忽略了不同地域与不同尺度的温差分布影响,同时国际上现有冷却塔夏季日照温差分布准则取值存在差异,亟需开展真实大型冷却塔日照筒壁温差更普适的实测研究。鉴于此,基于预制墙板日照试验实现非接触式红外三维测温技术的有效性校订,以分布于我国“寒冷及严寒地区”的五座不同典型高度的大型冷却塔进行夏季全天候的筒壁温差实测;基于实测数据数理统计,提炼了日照筒壁温差的板内梯度分布、时域演变规律、空间分布模式和向阳内壁特性;在此基础上,量化了夏季日照筒壁温差子午向分布、环向分布、最大温差取值,提炼了囊括向阳内壁的大型冷却塔筒壁温差分布准则。研究发现,我国“寒冷及严寒地区”应考虑日照温度应力;日照筒壁温差沿厚度为三段式梯度分布,沿塔高约为恒值,沿环向为外表面非对称半圆分布,喉部以上向阳内壁具有负温差。研究结论加深了对大型冷却塔日照温差分布的理解,也为规范修订提供实测依据。

超低负荷下660MW塔式锅炉低氧工况下燃烧过程数值模拟研究

针对锅炉在超低负荷下运行时通常过量空气系数较高,导致NO_(x)浓度较高的问题,采用数值模拟的方法研究锅炉在低氧工况下不同给煤位置的燃烧特性和NO_(x)排放特性.结果表明:50%与30%汽轮机热耗率验收(THA)工况下采用相同磨煤机组合运行时,速度、烟气组分、温度分布规律类似,进粉位置上移导致主燃区上部温度升高且分布更均匀,切圆半径逐渐减小,燃尽风消旋作用使混合增强,因此有利于燃烧的稳定.2台磨煤机运行相比3台局部煤粉浓度更大,主燃区的燃烧温度更高,导致更多NO_(x)生成;30%THA工况下,当下层磨煤机运行时冷灰斗附近温度较高;低氧工况下,NO_(x)质量浓度最高值低于360mg/m^(3),当负荷从50%THA降低至30%THA,炉膛出口NO_(x)浓度降低20.8%.

钛合金室温受压蠕变损伤本构模型

为了解决工程上在评估深潜器耐压壳体安全可靠性时不考虑拉压蠕变破坏机理产生的差异,会导致较大计算误差问题,本文提出了适用于室温蠕变的蠕变损伤本构模型。通过分析钛合金材料蠕变特性,考虑了室温环境下位错堆积造成的蠕变阻力,并且位错堆积的现象与时间有关。基于微分自洽法提出了适用于室温环境下的钛合金蠕变本构模型,得到受压情况下TC4ELI的相关材料参数,并将该模型用USDFLD和CREEP子程序进行定义。研究表明:对于受压结构而言,使用通过拉伸蠕变实验得到的本构模型的计算结果会过于保守,对于含V型缺口平板受压时等效蠕变应变的相对误差为168.20%。本文所提出的模型适用于环肋耐压壳结构的蠕变损伤分析。

甲型H1N1流感病毒性肺炎患者并发ARDS的临床特征与危险因素

目的分析甲型H1N1流行性感冒(流感)病毒性肺炎并发ARDS患者的临床特征,筛选ARDS预测指标。方法收集入院时尚未发生ARDS的甲型H1N1流感病毒性肺炎患者的临床资料,以住院期间是否发生ARDS分为ARDS组(A组,34例)和非ARDS组(B组,142例),比较2组的临床资料,采用Logistic回归分析及受试者工作特征(ROC)曲线分析甲型H1N1流感病毒性肺炎患者发生ARDS的危险因素。结果A组25例(73.5%)和B组40例(28.2%)有继发感染的病原学证据。A组气促、咳嗽咳痰、3 d内肺部病变扩大≥50%、外周血中性粒细胞分类、血清IL-6水平、肺泡动脉氧分压差[P(A-a)O2]、急性生理学与慢性健康状况评分系统Ⅱ(APACHEⅡ)评分和序贯器官衰竭评估(SOFA)均高于B组,年龄、白细胞总数、流感疫苗接种率均低于B组(P均<0.05)。多因素Logistic回归分析显示血清IL-6水平(OR=1.017,P=0.034)和P(A-a)O2(OR=3.672,P=0.002)是甲型H1N1流感病毒性肺炎患者发生ARDS的危险因素。血清IL-6水平和P(A-a)O2预测ARDS的ROC曲线下面积(AUC)分别是0.843、0.977,2指标AUC比较差异有统计学意义(P<0.05),cut-off值分别为94.6 ng/L、111.7 mm Hg,灵敏度为76.5%、85.3%,特异度为79.6%、98.6%;两者联合预测ARDS的灵敏度为77.5%,特异度为98.1%,AUC 0.996,与P(A-a)O2的AUC比较差异无统计学意义(P>0.05)。结论入院时查血清IL-6、P(A-a)O2均能预测甲型H1N1流感病毒性肺炎是否会并发ARDS,其中P(A-a)O2的预测价值较好,两者联合预测ARDS并不优于P(A-a)O2,但可能有助于判断继发感染。

炼铁厂2#脱硫塔除雾器压差问题研究及处理

炼铁厂2#脱硫塔除雾器运行过程压差持续升高,烟囱出口下“石膏雨”,对烧结机系统的正常生产和周围环境造成很大影响。本文针对压差问题,从工艺参数操作、设备运行情况等方面进行研究分析,制定解决的方案措施,保证脱硫塔设备稳定顺行。

斜拉桥支座变形沉降对结构的影响分析

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