Molecular-Dynamics Study on the Impact Energy Release Characteristics of Fe–Al Energetic Jets

Fe–Al energetic material releases a large amount of energy under impact loading; therefore, it can replace traditional materials and be used in new weapons. This paper introduces the macroscopic experiment and microscopic molecular-dynamics simulation research on the energy release characteristics of Fe–Al energetic jets under impact loading. A macroscopic dynamic energy acquisition test system was established to quantitatively obtain the composition of Fe–Al energetic jet reaction products. A momentum mirror impacting the Fe–Al particle molecular model was established and the microstructure evolution and impact thermodynamic response of Fe–Al particles under impact loading were analyzed. The mechanism of multi-scale shock-induced chemical reaction of Fe–Al energetic jets is discussed. The results show that the difference in velocity between Fe and Al atoms at the shock wave fronts is the cause of the shock-induced reaction; when the impact strength is low, the Al particles are disordered and amorphous, while the Fe particles remain in their original state and only the oxidation reaction of Al and a small amount intermetallic compound reaction occur. With the increase of impact strength, Al particles and Fe particles are completely disordered and amorphized in a high-temperature and high-pressure environment, fully mixed and penetrated. The temperature of the system rises rapidly, due to a violent thermite reaction, and the energy released by the jet shows an increasing trend; there is an impact intensity threshold, so that the jet release energy reaches the upper limit.     

Phase‐contrast magnetic resonance imaging measurements in intracranial aneurysms in vivo of flow patterns,velocity fields,and wall shear stress: Comparison with computational fluid dynamics

Evolution of intracranial aneurysms is known to be related to hemodynamic forces such as wall shear stress (WSS) and maximum shear stress (MSS). Estimation of these parameters can be performed using numerical simulations with computational fluid dynamics (CFD), but can also be directly measured with magnetic resonance imaging (MRI) using a time‐dependent 3D phase‐contrast sequence with encoding of each of the three components of the velocity vectors (7D‐MRV). To study the accuracy of 7D‐MRV in estimating these parameters in vivo, in comparison with CFD, 7D‐MRV and patient‐specific CFD modeling was performed for 3 patients who had intracranial aneurysms. Visual and quantitative analyses of the flow pattern and distribution of velocities, MSS, and WSS were performed using the two techniques. Spearman's coefficients of correlation between the two techniques were 0.56 for the velocity field, 0.48 for MSS, and 0.59 for WSS. Visual analysis and Bland–Altman plots showed good agreement for flow pattern and velocities but large discrepancies for MSS and WSS. These results indicate that 7D‐MRV can be used in vivo to measure velocity flow fields and for estimating MSS and WSS. Currently, however, this method cannot accurately quantify the latter two parameters. Magn Reson Med 61:409–417, 2009. © 2009 Wiley‐Liss, Inc.     

Determination of respiratory phase during acquisition of airway cine MR images

Subjects were imaged on a 1.5-T Signa MRI system using the head-neck vascular coil. An axial fast gradient echo cine, at the base of the second cervical vertebra, was obtained. A total of 128 images were acquired with a rapid image acquisition (one per second) over several respiratory cycles. The analog signal from the MR scanner (RF unblank) was utilized to determine the duration of the cine MR sequence. The phase of respiration was determined by analyzing the nasal air flow connected via pressure tubing to a pressure transducer outside the MR scanner room. We were thus able to determine the phase of respiration during acquisition of individual airway cine MR images. There was a wide range of airway volume measurements over the respiratory cycle with the lowest volume at end expiration and the highest at peak inspiration.     

Modelling the effectiveness of chlamydia screening in England

BACKGROUND: Several developed countries have initiated chlamydia screening programmes. Screening for a sexually transmitted infection has both direct individual and indirect population-wide effects. Mathematical models can incorporate these non-linear effects and estimate the likely impact of different screening programmes and identify areas where more data are needed. METHODS: A stochastic, individual based dynamic network model, parameterised from UK screening studies and data on sexual behaviour and chlamydia epidemiology, was used to investigate the likely impact of opportunistic screening on chlamydia prevalence. Three main strategies were considered for <25 year olds: (1) annual offer to women; (2) annual offer to women or if changed partner within last 6 months; (3) annual offer to men and women. Sensitivity analyses were performed for key screening parameters including uptake rate, targeted age range, percentage of partners notified, and screening interval. RESULTS: Under strategy 1, continuous opportunistic screening of women <25 years of age is expected to reduce the population prevalence by over 50% after 5 years. Prevalence is also expected to decrease in unscreened older women and in men. For all three strategies screening those aged over 25 results in small additional reductions in prevalence. Including men led to a faster and greater reduction in overall prevalence, but involved approximately twice as many tests as strategy 1 and 10% more than strategy 2. The frequency of attendance at healthcare sites limits the number of opportunities to screen and the effect of changing the screening interval. CONCLUSIONS: The model suggests that continuous opportunistic screening at high uptake rates could significantly reduced chlamydia prevalence within a few years. Opportunistic programmes depend on regular attendance at healthcare providers, but there is a lack of high quality data on patterns of attendance. Inequalities in coverage may result in a less efficient and less equitable outcome.     

组织工程软骨生物反应器的设计

目的 根据流体力学原理优化反应器内腔结构,并设计一套组织工程软骨生物反应器.方法 采用计算机仿真的方法对反应器内腔流场进行仿真计算,通过流场分析确定内腔结构,最终构建一套完整的生物反应器系统.结果 确定了生物反应器的内腔结构,生物反应器由控制系统和细胞培养室两部分构成,能置于培养箱中对软骨细胞材料复合物进行动态培养.结论 反应器内腔的结构是合理的.整个生物反应器系统运行可靠.     

Shear‐induced unfolding activates von Willebrand factor A2 domain for proteolysis

Summary. Background: To avoid pathological platelet aggregation by von Willebrand factor (VWF), VWF multimers are regulated in size and reactivity for adhesion by ADAMTS13‐mediated proteolysis in a shear flow dependent manner. Objective and methods: We examined whether tensile stress in VWF under shear flow activates the VWF A2 domain for cleavage by ADAMTS13 using molecular dynamics simulations. We generated a full length mutant VWF featuring a homologous disulfide bond in A2 (N1493C and C1670S), in an attempt to lock A2 against unfolding. Results: We indeed observed stepwise unfolding of A2 and exposure of its deeply buried ADAMTS13 cleavage site. Interestingly, disulfide bonds in the adjacent and highly homologous VWF A1 and A3 domains obstruct their mechanical unfolding. We find this mutant A2 (N1493C and C1670S) to feature ADAMTS13‐resistant behavior in vitro. Conclusions: Our results yield molecular‐detail evidence for the force‐sensing function of VWF A2, by revealing how tension in VWF due to shear flow selectively exposes the A2 proteolysis site to ADAMTS13 for cleavage while keeping the folded remainder of A2 intact and functional. We find the unconventional ‘knotted’ Rossmann fold of A2 to be the key to this mechanical response, tailored for regulating VWF size and activity. Based on our model we discuss the pathomechanism of some natural mutations in the VWF A2 domain that significantly increase the cleavage by ADAMTS13 without shearing or chemical denaturation, and provide with the cleavage‐activated A2 conformation a structural basis for the design of inhibitors for VWF type 2 diseases.     

低流量七氟醚靶控吸入与丙泊酚TCI的临床对比研究

目的：观察七氟醚靶控用于低流量吸入麻醉维持的临床规律及血流动力学变化,寻求靶控下的药物量化指标。方法：选择60例20～60岁手术患者,随机分2组每组30例：P组（丙泊酚）常规实施全凭静脉TCI靶控麻醉;S组（七氟醚）,实施低流量七氟醚靶控吸入麻醉（BIS值40）。分别记录诱导前（T1）,插管后5（T2）、15（T3）、30（T4）45（T5）、60（T6）、90（T7）、120（T8）min时的、MBP、HR、;Sev组患者加记各个时点的七氟醚IT、ET的MAc值。结果：T2点两组均比T1降低（P〈0．05）,S组高于P组（P〈0．05）,两组比较T3至T7无显著性差异（P〉0．05）;S组T3至T7各点ET值无统计学差异,ET％：2．46,约1．4MAc。结论：（1）七氟醚诱导较静脉麻醉诱导患者血流动力学稳定,（2）低流量七氟醚靶控吸入麻醉维持平稳,调控简便,效果良好。     

Isthmic uterine fibroids: the dynamics of growth

The isthmus of uterus is different from the rest of uterus and cervix in anatomic as well as functional aspects. The tumors arising from it may be subjected to a different set of forces which may predispose to growth in a tangential or horizontal direction. A young woman who underwent myomectomy for a large isthmic myoma is presented and the growth dynamics are discussed.     

Daily tympanometry for high-resolution measurement of the time between onset of cold-like illness and middle ear effusion

Background: Tympanometry is a simple method to assess middle ear pressure (MEP) and the presence of middle ear effusion (MEE), a marker of otitis media (OM). Objectives: To determine whether daily parental tympanometry and illness sign recording in their children can be used to define the time between onsets of cold‐like illness (CLI) and MEE at high resolution. Study Design: Prospective, longitudinal, 7 month, daily follow‐up on 169 children aged 1 through 8.6 years. Methods: Tympanograms and illness were recorded daily by a parent. Tympanograms were examined, rejected if artifactual, and MEP data were entered into a database, with “flat tympanograms” coded as ?400 mm H₂O = MEE. The incidence and burden of CLIs (>2 days) were calculated, and for each CLI, the presence/absence of concurrent MEE (>2 days) was determined. For each child, the average MEP for CLI and nonCLI days was calculated. Paired CLI and tympanometric results were aligned and the days between event onsets determined. Stepwise regression was used to assign risk predictors for the measured outcomes. Results: A total of 566 CLIs were recorded, and the average CLI burden/child was 16%. Age was a significant predictor of CLI incidence/child, and age, history of colds, and daily environment were predictors of CLI‐burden/child. Of the 433 evaluable CLI episodes, MEE was a complication in 37%, and MEE with a CLI was predicted by age, OM history, and environment. MEP was significantly more negative during CLI episodes, and the magnitude was predicted by age, race, and OM history. The average difference in MEE‐CLI onsets was 1.2 ± 4.0 days; approximately 32% of MEEs occurred prior to CLI onset and 17% on the same day as CLI onset. Conclusions: CLIs adversely affect the middle ear‐ambient pressure balance and are frequently associated with MEE episodes. The distribution in onsets between those events suggests that chemoprophylaxis of a child with a newly identified CLI to prevent MEE would have a low expected efficiency.     

顶端动脉瘤的血流动力学数值模拟切应力分析

目的:探讨顶端动脉瘤的血流动力学特点,分析动脉瘤的生长、破裂的可能机制。方法:采用计算流体力学（CFD）软件结合顶端动脉瘤的医学影像,对动脉瘤内血液流动数值模拟切应力进行分析。 结果:0~0.22 T时,血管内血流速度急剧上升到最大值;0.22~0.55 T时,从最大值急剧下降到初始值。切应力随血流速度变化,在0.22 T时动脉瘤颈部切应力值最大,0.55 T时最小,而在这两时刻,动脉瘤壁不存在切应力。 结论:切应力由血流冲击造成,其大小与血流速度变化一致。CFD数值模拟是一种反映动脉瘤血流动力学较好的方法,为动脉瘤的病理生理机制和临床治疗提供较好的帮助。