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.     

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.     

偏心支撑框架子结构实时混合仿真试验研究

实时混合仿真是一种新兴的结构抗震试验方法.建立了一套混合仿真试验系统,其中包括基于OpenSees有限元软件的数值模拟计算机,具有时滞补偿功能的目标计算机以及终端连接的电液伺服控制系统.在MATLAB中建立Simulink数值仿真模型,并提出了一种基于位移预测的自适应前馈时滞补偿器.最后,以一个单层三跨高强钢组合偏心支撑钢框架结构为原型,取边跨带有偏心支撑的单层钢框架作为试验子结构,进行了一个缩尺比例为1/2结构模型的实时混合仿真试验.试验结果表明随着模型整体响应加速度峰值的增大,控制系统的最大时滞补偿误差、最大幅值误差均有增大趋势,但均在容差允许范围之内,同时说明了该混合仿真试验系统具备良好的稳定性和精度,能够有效地对偏心支撑框架子结构结构模型进行抗震性能试验.