Quantitative assessment of collateral time on perfusion computed tomography in acute ischemic stroke patients

Background and aimGood collateral circulation is recognized to maintain perfusion and contribute to favorable clinical outcomes in acute ischemic stroke. This study aimed to derive and validate an optimal collateral time measurement on perfusion computed tomography imaging for patients with acute ischemic stroke.MethodsThis study included 106 acute ischemic stroke patients with complete large vessel occlusions. In deriving cohort of 23 patients, the parasagittal region of the ischemic hemisphere was divided into six pial arterial zones according to pial branches of the middle cerebral artery. Within the 85 arterial zones with collateral vessels, the receiver operating characteristic analysis was performed to derive the optimal collateral time threshold for fast collateral flow on perfusion computed tomography. The reference for fast collateral flow was the peak contrast delay on the collateral vessels within each ischemic arterial zone compared to its contralateral normal arterial zone on dynamic computed tomography angiography. The optimal perfusion collateral time threshold was then tested in predicting poor clinical outcomes (modified Rankin score of 5–6) and final infarct volume in the validation cohort of 83 patients.ResultsFor the derivation cohort of 85 arterial zones, the optimal collateral time threshold for fast collateral flow on perfusion computed tomography was a delay time of 4.04 s [area under the curve = 0.78 (0.67, 0.89), sensitivity = 73%, and specificity = 77%]. Therefore, the delay time of 4 s was used to define the perfusion collateral time. In the validation cohort, the perfusion collateral time showed a slightly higher predicting power than dynamic computed tomography angiography collateral time in poor clinical outcomes (area under the curve = 0.72 vs. 0.67; P < 0.001). Compared to dynamic computed tomography angiography collateral time, the perfusion collateral time also had better performance in predicting final infarct volume (R-squared values = 0.55 vs. 0.23; P < 0.001).ConclusionOur results indicate that perfusion computed tomography can accurately quantify the collateral time after acute ischemic stroke

Weapon-Target Assignment Problem by Multiobjective Evolutionary Algorithm Based on Decomposition

The weapon-target assignment (WTA) problem is a key issue in Command & Control (C2). Asset-based multiobjective static WTA (MOSWTA) problem is known as one of the notable issues of WTA. Since this is an NP-complete problem, multiobjective evolutionary algorithms (MOEAs) can be used to solve it effectively. The multiobjective evolutionary algorithm based on decomposition (MOEA/D) is a practical and promising multiobjective optimization technique. However, MOEA/D is originally designed for continuous multiobjective optimization which loses its efficiency to discrete contexts. In this study, an improved MOEA/D is proposed to solve the asset-based MOSWTA problem. The defining characteristics of this problem are summarized and analyzed. According to these characteristics, an improved MOEA/D framework is introduced. A novel decomposition mechanism is designed. The mating restriction and selection operation are reformulated. Furthermore, a problem-specific population initialization method is presented to improve the efficiency of the proposed algorithm, and a novel nondominated solution-selection method is put forward to handle the constraints of Pareto front. Appropriate extensions of four MOEA variants are developed in comparison with the proposed algorithm on some generated scenarios. Extensive experiments demonstrate that the proposed method is effective and promising

Hyper-Pseudo-Viscoelastic Model and Parameter Identification for Describing Tensile Recovery Stress–Strain Responses of Rubber Components in TBR

Tires are often in service under dynamic conditions. Realizing the high-precision prediction of the mechanical response of rubber materials under cyclic loading can provide guidance for the design of high-performance tires. In this work, the tensile recovery stress-strain responses of rubber materials in nine different components of a truck and bus radial (TBR) tire were obtained through experiments. Before fitting, an experimental data processing method was proposed to facilitate the parameter identification for a hyper-pseudo-viscoelastic model, that is, the raw experimental data were changed to the adjusted test data. The HyperFit software was used to fit the adjusted test data based on the Yeoh hyperelastic model and the Ogden-Roxburgh pseudoelastic model to obtain the initial material parameters for the two models. In order to describe the permanent set, the Prony series viscoelastic model was introduced. The Isight software was adopted to optimize the parameters. The results showed that the hyper-pseudo-viscoelastic model (i.e., the combination of Yeoh, Ogden-Roxburgh and Prony series models) can describe the tensile recovery mechanical responses (loading curve, unloading curve and permanent set) of nine different rubber components in TBRs. The fitting results are in good agreement with the adjusted data, and all the coefficients of determination (R2) exceed 0.975. Finally, the cyclic deformation simulation of a dumbbell rubber specimen was carried out based on the above constitutive model and fitted parameters. R2 was used to describe the simulation accuracy and its value reached 0.968

The microstructures and mechanical properties of low-cost Ti particles reinforced AZ81 composites

Compared to conventional ceramic particle-reinforced Mg composites, incorporating Ti particles into the Mg molten melt poses greater difficulty due to their significantly higher density compared to Mg. To develop a feasible and effective method for incorporating Ti particles, the water flow visualization experiment was used to reveal the optimum parameters of the stirring velocity, the height of the stirrer, and the angle of the stirrer to the horizon. Based on the results, the Ti/AZ81 composite was successfully fabricated at a variable speed (100–950 rpm/min) and height (4–10 cm) with an angle of 75° via nearly semi-solid stirring casting and followed by hot extrusion. The distribution of Ti particles in the Mg matrix was more homogenous, exhibiting fewer flaws and a higher recovery rate. The tensile results indicated that the Ti/AZ81 composite exhibited excellent comprehensive mechanical properties with an ultimate strength (UTS), yield strength (YS), and elongation of 374.5 MPa, 263.5 MPa, and 11.5%, respectively, which were superior to other Ti particle-reinforced AZ alloys. The characterizations revealed that the interfacial product AlTi phase was additionally formed and the Ti/Mg interface showed a strong bonding strength. The dynamic recrystallization (DRX) was significantly promoted due to the particle-stimulated nucleation (PSN) and Ti particles weakened the precipitation of Mg17Al12. Based on the quantitative calculations, the increased strength was mainly attributed to grain refinement, the mismatch coefficient of thermal expansion (CTE), and the heterogeneous microstructures of Ti/AZ81 composite, in which heterogeneous deformation-induced (HDI) strengthening is dominant

HIV/AIDS Knowledge, Attitudes and Behaviors Assessment of Chinese Students: A Questionnaire Study

The objective of this study was to assess students' knowledge, attitudes and practices on HIV and AIDS. A questionnaire was administered to a cross section of 259 Chinese undergraduates. Respondents were asked to provide information about knowledge and attitudes about HIV/AIDS. Study results indicated that the majority of undergraduates had a moderate level of HIV and AIDS knowledge, acceptance and attitudes towards people with HIV and AIDS. Boys had more acceptance and positive attitudes towards people with HIV and AIDS than girls. Students majoring in medicine performed better (more knowledgeable and accepting) than non-medical students. Differences between students with various monthly expenditures were found-- 6.2% of students had 3-5 sexual partners which has rarely been found in Chinese students; most students did not know HIV VCT centers and most students did not show their confidence for controlling of HIV and AIDS in China. In conclusion, students’ knowledge about HIV/AIDS was uneven. A peer educational program to talk about self esteem, healthy sexual attitudes, being human-accepting and loving should be developed in the near future