基于Oyane准则的金属板材渐进成形破裂预测

针对渐进成形中的破裂缺陷,将Oyane准则引入数值模拟中,有效预测了渐进成形中金属板料的成形极限.首先,针对DC56D+Z钢板,基于获取的Oyane准则材料参数,通过试验与数值模拟确定了破裂积分值I=4为破裂的临界条件.然后,基于响应面法建立了工艺参数与I积分值之间的非线性模型,且通过方差分析验证了该模型的有效性.研究得出:该数值模型可以有效预测最大破裂积分I值,I值随着成形角α、层间距Δz和工具头直径d的增大而增大,3个工艺参数的影响作用逐渐减弱,且αΔz、αd两种组合的交互作用影响较大.     

中间相沥青基泡沫炭发泡过程及其动力学研究

以AR中间相沥青为原料,结合TG、黏度分析、MS及IR等表征方法研究了中间相沥青基泡沫炭的发泡过程及其动力学特征.结果表明:中间相沥青在发泡过程中主要发生脂肪碳链的热解反应并释放出H2、CH4、H2O和CO等气体,导致熔融沥青中的分子组成产生变化,进而引起其黏度变化.在此基础上采用TG分析模拟不同升温速率及发泡温度下中间相沥青的失重过程,并通过拟合中间相沥青恒温阶段的TG曲线,发现中间相沥青的恒温失重率Δw与发泡时间tb成较好的线性关系,结合Arrhenius方程计算得到不同升温速率下恒温发泡过程的动力学参数.此研究工作对于中间相沥青基泡沫炭的可控制备具有较好的理论指导作用.     

外星人 隐藏在众目睽睽之下吗?

2020年7月,全球启动了三项非载人航天任务,均发射前往火星.这三项任务分别是:中国的天问一号、美国宇航局(NASA)的毅力号和阿拉伯联合酋长国的希望号.中国和美国的航天任务都设计了探测器,这些探测器将寻找火星上当前或过去的生命迹象.此外,NASA还计划发射"欧罗巴快艇"(Europa Clipper)探测器去勘探木卫...     

在实验室中寻找量子黑洞

正在物理学中,我们通过猜测来发现一个新的规律,然后将猜测的结果与实验结果进行比较。正如理查德·费曼所说:"你的猜测有多美没有用,你有多聪明也没什么用……如果与实验不符,那它就错了。"这就是物理和数学的本质区别。数学家也会猜测,其真理的最终裁决者是严格的证据。物理学家可以使用甚至发明复杂的数学工具,但他们的目标不同:解释宇宙的真实面貌。     

跨越女性独立执行空间任务的门槛

正克里斯蒂娜·科赫重返地球,她完成了三次无男性参与的太空行走,也创造了在太空中停留的时间记录,但你应该知道的远不止这些。不查谷歌和维基的话,你能说出多少宇航员的名字?说出尼尔·阿姆斯特朗和巴兹·奥尔德林的名字并不难。他们是首次登上月球的那两个宇航员。你应该也很可能还记得为他俩驾驶指令舱的宇航员迈克尔·柯林斯。不过,因为他并非是第一批在月球上行走的宇航员,所以你对他的名字可能没有那么熟悉。     

Distribution and ecology of freshwater Ostracoda (Crustacea) collected from springs of Nevada, Idaho, and Oregon: a preliminary study

Fourteen freshwater ostracod species collected from 24 springs in Nevada, Idaho, and Oregon between 1991 and 1994 were classified. Their ecology, based on major water parameters (i.e., temperature, dissolved oxygen, pH, conductivity), and biogeographical distribution in North America were studied. Among these 14 species, 9 ( Ilyocypris bradyi , I. gibba , Darwinula stevensoni , Candona candida , Heterocypris incongruens , Herpetocypris reptans , H. chevreuxi , Prionocypris canadensis , P. longiforma ) are new records for Nevadas ostracod fauna, while 3 ( H. reptans , P. canadensis , and Cypria turneri ) are new species for Oregon. H. reptans , P. canadensis , and Heterocypris salina are also recorded as new for the ostracod literature of Idaho. Scottia pseudobrowniana , collected from Nevada, is a new ostracod species for the United States. The occurrence of 5 Holarctic species in the northern Great Basin area may suggest a possible historical relationship with the European ostracod fauna.     

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.     

Correlation,entropy, and information transfer in black hole radiation

Since the discovery of Hawking radiation, its consistency with quantum theory has been widely questioned. In the widely described picture, irrespective of what initial state a black hole starts with before collapsing, it eventually evolves into a thermal state of Hawking radiations after the black hole is exhausted. This scenario violates the principle of unitarity as required for quantum mechanics and leads to the acclaimed ‘‘information loss paradox'. This paradox has become an obstacle or a reversed touchstone for any possible theory to unify the gravity and quantum mechanics. Based on the results from Hawking radiation as tunneling, we recently show that Hawking radiations can carry off all information about the collapsed matter in a black hole. After discovering the existence of information-carrying correlation, we show in great detail that entropy is conserved for Hawking radiation based on standard probability theory and statistics. We claim that information previously considered lost remains hidden inside Hawking radiation. More specifically, it is encoded into correlations between Hawking radiations. Our study thus establishes harmony between Hawking radiation and the unitarity of quantum mechanics, which establishes the basis for a significant milestone toward resolving the long-standing information loss paradox. The paper provides a brief review of the exciting development on Hawking radiation. In addition to summarize our own work on this subject, we compare and address other related studies.     

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.