动态测量过程热电偶时间常数模型研究

根据热电偶动态测温过程实际换热情况,运用对流、辐射和传导等传热学有关知识,建立了热电偶时间常数数学模型.以制作热电偶最常用的3种金属-镍、铂和钨为例进行的动态测量过程热电偶时间常数特性分析结果表明,动态测量过程中热电偶时间常数应该在不同的介质温度区间相应地选取不同的换热比重.应用结果表明,采用动态测量过程热电偶时间常数...     

AN IMPLICIT ENTHALPY SOLUTION OF CONDUCTION-CONTROLLED PHASE CHANGE PROBLEMS

An implicit enthalpy solution is developed for analysis of one-dimensional conduction controlled phase change problems. The solution is based on separating the sensible and latent heat terms in an enthalpy formulation. By making the assumption of equal volume node-jumping,a variable time together with a fixed space grid is used to ensure that the phase boundary is always on a node point,so that the nonlinearity associated with the latent heat can be effectively dealt with via the source term. A freezing problem around a pipe with analytical solution is applied to demonstrate the effect of the present method.     

Noninvasive electrocardiographic parameters to assess interventricular dyssynchrony in dogs with bundle branch blocks

ObjectivesTo define electrocardiographic features of complete left bundle branch block (LBBB) and right bundle branch block (RBBB), and the use of R-peak time (RPT) to identify interventricular dyssynchrony in dogs with BBB.Animals, materials and methodsTwelve-lead ECG tracings of 20 dogs with RBBB, 20 with LBBB, and 60 healthy dogs were retrospectively analyzed and RPT was measured in precordial leads. Interventricular dyssynchrony index (IDI) was than calculated.ResultsIn RBBB, mean electrical axis (MEA) was −111° [−120/−100°], V₁RPT was significantly longer (61 ms [55–72 ms]) than left precordial leads RPT (V₂:25 ms [22–30 ms]; V₃:25 ms [22–29 ms]; V₄:24 ms [21–29 ms]; V₅:25 ms [22–29 ms]; V₆:25 ms [22–29 ms]) and when compared to normal dogs (P < 0.001). In LBBB, MEA was 76° [70/81°], RPT in left precordial leads was significantly longer (V₂:49 ms [34–58 ms]; V₃:49 ms [43–57 ms]; V₄:52 ms [45–62 ms]; V₅:53 ms [45–63 ms]; V₆:55 ms [45–63 ms]) than V₁RPT (17 ms [15–20 ms]) and when compared to normal dogs (P < 0.001). V₁RPT > 28 ms and V₅RPT > 36 ms were found to predict the presence of RBBB and LBBB with a sensitivity of 100% and 96.7%, and a specificity of 96.7% and 99.5%, respectively. The IDI was 23% [16–29%] in normal dogs and significantly greater in dogs with RBBB (33% [30–38%]; P < 0.001) and LBBB (32% [23–41%]; P = 0.006).ConclusionsThis study defines ECG features and RPT in dogs with BBB. Electrical interventricular dyssynchrony can be defined using IDI in dogs with BBB.