特定制动工况下肌肉主动力对颈部损伤的影响

为研究特定制动工况下颈部肌肉主动力对人体颈部损伤的影响,建立了一个包含颈部详细几何结构并且具有肌肉主被动响应能力的混合假人有限元模型. 以特定制动工况加速度作为输入,研究当假人颈部肌肉分别处于放松和预先紧张状态下并佩戴某头盔时,颈部的运动学以及生物力学响应. 结果表明：在制动开始前,预先紧张颈部肌肉使头部质心水平加速度、头部相对T1胸椎水平位移以及转角3个运动学参数的峰值下降20%以上,导致颈部在整个运动过程中表现出了更好的稳定性. 从生物力学的角度来说,预先紧张颈部肌肉使得椎骨以及椎间盘最大米塞斯应力分别降低了36.95%和48.20%;颈部损伤评价指标Nij值降低25.06%,降低了乘员在该制动工况下颈部受伤的风险.     

高钙粉煤灰制备低导热高强度陶瓷材料及其表征

从泰国Mae Moh发电厂收集的高钙粉煤灰（HCFA）被用作陶瓷生产的原料。X射线荧光表征下HCFA主要成分为28.55wt% SiO₂、16.06wt% Al₂O₃、23.40wt% CaO和17.03wt% Fe₂O₃。由于钙质和铁质含量比例较高,使用HCFA替代钾长石,用量为10wt%–40wt%。研究了替代高钙粉煤灰（0–40wt%）和烧结温度（1000–1200°C）对陶瓷基材料的物理、机械和热性能的影响。结果表明,加入适量的HCFA可以提高陶瓷样品的致密化程度和强度,降低陶瓷样品的导热系数。粉煤灰中高比例的钙质和铁质成分促进了陶瓷样品的玻璃化行为。研究结果说明,在最佳粉煤灰含量和烧结温度下,液相的形成促进了致密化。此外,这些组分还促进了更丰富的莫来石形成,从而提高了陶瓷样品的弯曲强度。在1150–1200°C烧结温度下,添加10wt%–30wt%的粉煤灰,可获得最佳陶瓷性能。在 1200°C、 吸水率几乎为零（0.03%）时,添加粉煤灰10wt%–30wt%（PSW-FA(10)–(30)）的FA陶瓷样品的最大弯曲强度在92.25–94.71 MPa范围内。就隔热材料而言,粉煤灰添加量的增加对热导率有积极的影响,这是因为陶瓷FA样品内部无机分解反应产生的气体产生了更高的孔隙度。在1150°C烧结的陶瓷样品中添加20wt%–40wt%的高钙粉煤灰可将热导率降低14.78%–49.25%,同时保持可接受的弯曲强度值（~45.67–87.62 MPa）。基于其表现出良好的机械和热性能,利用这种高钙粉煤灰作为粘土成分的替代原料制造瓷砖是可行的。     

编者按:《氢冶金专刊》

双碳战略正在推动传统冶金行业进行转型升级,冶金行业的高质量和低碳化改革势在必行。氢气作为21世纪的清洁能源,其具有从源头上实现低碳冶金的潜力,目前全球冶金工业已经将“氢冶金”作为未来发展的目标。近年来,以钢铁为代表的传统冶金工艺在富氢冶炼以及氢冶金新工艺方面均得到了快速发展,标志着冶金工业在低碳转型的道路上正在飞速前进。为庆祝北京科技大学成立70周年和加快冶金行业在低碳发展方向的脚步,《矿物冶金与材料学报（英文版）》期刊特此出版“氢冶金”专刊。来自包括德国马普所、日本九州大学在内的世界顶尖大学或研究院所的专家学者受邀分享了他们在“氢冶金”研究方面的进展和展望。专刊共收录了12篇论文,包括1篇等离子氢冶金综述及11篇研究论文。所有论文主要围绕传统炼铁流程富氢冶炼、氢基直接还原炼铁以及等离子氢冶金三个方向。其中,包括高炉富氢冶炼后铁矿石和焦炭的行为变化研究、流化床富氢冶炼物理化学研究、富氢直接还原过程球团矿的还原机理研究以及等离子氢冶金新工艺在铁冶炼中的应用。专刊收录论文覆盖范围全面,从传统冶金工艺的创新到富氢冶金新工艺的开发,涉及了目前氢冶金方面较为热点的研究方向。本专刊客座主编希望通过本期论文,为从事“氢冶金”研究方向的学者们提供一个全面交流的机会,以促进“氢冶金”工艺及技术的发展,早日完成碳中和的伟大目标。我们衷心感谢所有作者和审稿人对本期专刊的奉献和大力支持。     

益肾方对db/db糖尿病小鼠肾保护作用的疗效观察

目的:探讨益肾方对db/db糖尿病小鼠肾保护作用的效果.方法:60只db/db糖尿病小鼠随机分为模型组、益肾方低剂量组、益肾方高剂量组和洛汀新组,15只同背景db/m小鼠为正常对照组,分别灌胃12周,检测肾功能相关生化指标,并对肾组织进行HE、PAS染色.结果:与对照组相比,模型组、益肾方低剂量组、益肾方高剂量组和洛汀...     

可对角化矩阵特征值分解扰动问题的快速求解方法

针对特征值扰动计算的传统方法收敛速度慢的问题,提出了一种求解特征值扰动问题的快速迭代算法.首先,通过矩阵变换将初始矩阵的特征值扰动问题转化为对角矩阵的特征值扰动问题.然后,提出了一种快速迭代算法求解扰动参数,同时对算法的收敛性进行分析,并将其与基于摄动级数展开法导出的方法进行对比. 再次,采用逐一求解特征值并进行矩阵降阶的策略,有效降低运算量.最后,通过2个算例分别展示算法的计算过程及其在结构模态参数追踪方面的应用效果.     

Conservation status of the threatened, insular San Jose brush rabbit ( Sylvilagus mansuetus )

The conservation status and distribution of the insular endemic San Jose brush rabbit ( Sylvilagus mansuetus ), as well as threats to its population viability, were determined through surveys undertaken since 1995 on San José Island in the Gulf of California, Mexico. Sylvilagus mansuetus is restricted to a specific desert habitat found in the southwestern coastal plains of the island. Vegetation in this habitat is composed primarily of 7 plant species. The extent of rabbit occurrence is only 20 km 2 , and the population density estimate in the most optimal habitat is 25–35 individuals · km –2 . To our knowledge, the San Jose brush rabbit possesses the smallest distribution among all lagomorph species. Sylvilagus mansuetus is threatened by a population of feral cats and by human activities, including illegal hunting, development of a tourist area, and a salt mine. Human activities, even over a short time frame, could severely impact this restricted area and endanger the survival of this species. Recommended management includes removing cats and conducting additional research on the rabbit’s life history and ecology. Se determinó el estado de conservación y la distribución del conejo de San José ( Sylvilagus mansuetus ), una especie insular endémica, mediante muestreos que se han llevado a cabo desde 1995 en la isla de San José en el Mar de Cortés, México. Sylvilagus mansuetus quedó restringido a un tipo específico de hábitat desértico en la llanura costera suroccidental de la isla, donde predominan 7 especies de plantas. La extensión de la especie es de sólo 20 km 2 , y la densidad de la población en el hábitat óptimo se estimó entre 25 y 35 individuos · km –2 . Hasta donde conocemos, el conejo de San José tiene el área de distribución más pequeña de todas las especies de lagomorfos. Sylvilagus mansuetus se ve amenazado por una población de gatos ferales y por actividades humanas tales como la caza ilegal, el turismo y la operación de una mina de sal. Las actividades humanas podrían tener un impacto severo en esta área restringida y podrían poner en peligro la supervivencia de esta especie dentro de poco tiempo. Algunas acciones recomendables para el manejo de la especie incluyen el eliminar los gatos y llevar a cabo estudios adicionales para obtener más detalles sobre la biología y ecología del conejo a fin de mejorar su conservación.     

Status of an invading mainland jackrabbit on Cerralvo island, Gulf of California

We report the first observations of the black-tailed jackrabbit ( Lepus californicus ) on Cerralvo Island, Baja California Sur, Mexico. Evidence suggests a self-sustaining population. Analysis of available records indicates no previous record of Lepus on the island. Introduction of the jackrabbit to the island appears to have occurred between 1960 and 1991.     

New bisexual form of Cavernocypris subterranea (Wolf, 1920) (Crustacea, Ostracoda) from Idaho

Males of Cavernocypris subterranea were found for the first time in an Idaho spring. The bisexual form is described on soft body parts and valves. The genus Cavernocypris now includes 2 bisexual and 1 parthenogenteic species.     

Growth and demography of one population of the lizard Sceloporus mucronatus mucronatus

We report on growth and demography of Sceloporus mucronatus mucronatus , a lizard subspecies endemic to central Mexico. We characterize the life history of this subspecies, provide quantitative information relevant to conservation, and add to the growing literature on the diversity of life histories in the genus Sceloporus . We calculated body growth rates and fitted them to the Von Bertalanffy, the logistic-by-length, and the logistic-by-weight growth models. The Von Bertalanffy model provided the best fit, and we used it to analyze the growth pattern. Growth rates were similar during the 1st year of life in both sexes, but after that point males grew faster and reached maturity earlier (20 months) than females (31 months). We used a population projection matrix to model population dynamics during 2003–2004 and found a positive population growth rate (λ = 1.769). However, based on the projected stable size-class vector ( w ), this population does not appear to have reached stability, and it might be currently experiencing considerable interannual fluctuations. Elasticity values showed that the transition from the juvenile stage to the 1st adult stage was the vital rate that contributes the most to population growth rate, followed by fecundity and stasis of the 1st reproductive category. While total elasticities for demographic processes were similar, elasticities per size class showed the relatively high importance of small adults in comparison to juveniles and large adults. The restriction of this endemic subspecies to central Mexico, where human activities and consequent habitat destruction are increasing, demands further quantitative evaluation and monitoring of populations, even though our results indicate a potential for population growth.     

恐龙刺客

地铁车厢里很闷热.我的霸王龙身躯比其他每个人都来得大,这成了个问题.拥有一种与众不同的体色也有益处,因为大多数人都缩起身子避开我.这就是我成为一头缩小版霸王龙的原因.它帮助我免受大家的注意,因为乘客们纷纷移开了视线.