Fission track ages and ages of deposition of deep-sea microtektites

The Australasian and Ivory Coast deep-sea microtektites have fission track ages of 0.71 and 1.09 million years, respectively. These ages are in good agreement with the ages of deposition of the microtektites determined from paleomagnetic data. Both the fission track ages and ages of deposition of the microtektites agree with the potassium/ argon and fission track ages of tektites from the respective tektite strewn fields.     

Gekkonid lizards: average ages derived from tail-loss data

Information on the rate of tail loss by autotomy, obtained from mark and recapture data, was used to estimate the average ages of adult individuals of the geckos Gehyra variegata and Heteronota binoei; the ages calculated were 4.4 and 1.9 years, respectively.     

New ages for the last Australian megafauna: continent-wide extinction about 46,000 years ago

All Australian land mammals, reptiles, and birds weighing more than 100 kilograms, and six of the seven genera with a body mass of 45 to 100 kilograms, perished in the late Quaternary. The timing and causes of these extinctions remain uncertain. We report burial ages for megafauna from 28 sites and infer extinction across the continent around 46,400 years ago (95% confidence interval, 51,200 to 39,800 years ago). Our results rule out extreme aridity at the Last Glacial Maximum as the cause of extinction, but not other climatic impacts; a "blitzkrieg" model of human-induced extinction; or an extended period of anthropogenic ecosystem disruption.     

论信息时代图书馆员的权利

在迈入信息时代的今天，人们普遍重视的是读者的权利，强调“以人为本”；却往往忽视图书馆员的权利，馆员的人格尊严、信息知情、继续教育、工作发展等方面权利经常遭到侵犯，图书馆员应该享有的权利为何屡遭侵犯？由此引发了笔者作为一名老图书馆员对图书馆员权利的思考与审视。     

不同年龄牦牛肝中挥发性物质的测定及分析

研究分别选取犊牦牛(6月龄)和成年牦牛(36月龄)肝,采用顶空固相微萃取(HS-SPME)和气相色谱质谱联用(GC-MS)对其挥发性化合物进行检测,分析了不同年龄牦牛肝中挥发性化合物的差异.结果表明:相比成年牦牛肝,犊牦牛肝中的醛类物质高出43.81%,酮类高出11.52%,而烃类低44.94%.芳香族化合物,成年牦牛肝中的含量是犊牦牛的17倍.此外,苯甲醛、壬醛、己醛、庚醛等与脂肪氧化有关的挥发性化合物,在犊牦牛肝中的相对含量明显高于成年牦牛.     

Human cerebral hemispheres develop at different rates and ages

The development of the cerebral hemispheres was assessed by using measures of electroencephalographic coherence and phase in 577 children ranging in age from 2 months to early adulthood. Two categories of age-dependent change in electroencephalographic coherence and phase were noted: continuous growth processes that were described best by an exponential growth function, and discrete growth spurts that appeared in specific anatomical locations at specific postnatal periods. The left and right hemispheres developed at different rates and with different postnatal onset times with the timing of growth spurts overlapping the timing of the major developmental stages described by Piaget.     

不同竹龄毛竹材燃烧性能的研究

利用锥形量热仪,在50 kW·m-2的热辐射功率下,对1～6年生的毛竹Phyllostachys pubescens人工林竹材的燃烧性能指标进行了测定.结果表明:随着竹龄的增加,毛竹材的点燃时间、释烟总量和比消光面积均有所增大,质量损失率和第一释热峰有所下降,第二释热峰与竹龄无显著相关,但出现的时间延迟;4年生以上的毛竹材各项燃烧性能指标趋于稳定.图3表2参8     

U-Pb ages from the neoproterozoic Doushantuo Formation, China

U-Pb zircon dates from volcanic ash beds within the Doushantuo Formation (China) indicate that its deposition occurred between 635 and 551 million years ago. The base records termination of the global-scale Marinoan glaciation and is coeval with similar dated rocks from Namibia, indicating synchronous deglaciation. Carbon isotopic and sequence-stratigraphic data imply that the spectacular animal fossils of the Doushantuo Formation are for the most part younger than 580 million years old. The uppermost Doushantuo Formation contains a pronounced negative carbonate carbon isotopic excursion, which we interpret as a global event at circa 551 million years ago.     

不同龄期柠条茎秆的拉剪强度试验与分析

[目的]为优化柠条联合收获机切割过程中的平茬参数,本文研究了不同平茬位置与不同生长年限柠条茎秆的生物力学性质。[方法]采用完全随机区组设计方法,分别对柠条茎秆样本进行拉伸与剪切试验。[结果]试验测得柠条茎秆的抗拉强度均值为138N·mm~(-2),柠条茎秆的抗剪强度均值为35N·mm~(-2);柠条茎秆的拉伸断裂强度与平茬位置和生长年龄都密切相关,且生长年龄对其试验指标的影响比平茬位置对其的影响要大,随生长年龄的增加,柠条茎秆抗拉强度升高;柠条茎秆的抗剪强度与生长年龄相关,而与柠条的平茬位置关系不大。[结论]在柠条联合收获机平茬作业时,应当首先考虑柠条的生长年龄,其次考虑平茬位置。本研究为柠条联合收获机的设计与作业条件的选择提供理论依据。     

不同日龄混合柄瘤蚜茧蜂对寄主虫龄的选择及子代蜂发育表现

对同一头混合柄瘤蚜茧蜂雌蜂连续观察5 d,比较其对蚕豆蚜若蚜和成蚜的选择,并观察了子代蜂的发育特性。结果表明:5日龄蜂对不同虫龄蚜虫的寄生率无显著差异,子代蜂羽化率和雌性比亦无显著差异,但寄生2、3龄若蚜的子代雌蜂体型显著大于寄生其他蚜虫的子代雌蜂,寄生3龄若蚜的子代雄蜂显著大于寄生成蚜的子代雄蜂。在其他日龄(1～4)蜂中,1、4日龄蜂对不同龄若蚜的寄生率无显著差异,但均高于对成蚜的寄生,2、3日龄蜂对2龄若蚜的寄生偏好显著高于对更高虫龄的寄生;3日龄蜂的子代蜂羽化率在各虫龄蚜虫之间无显著差异,其他日龄蜂寄生低龄若蚜的子代羽化率高于寄生较高虫龄蚜虫;寄生中间龄期若蚜(3、4龄)的子代蜂雌性比显著高于寄生1龄或成蚜的子代蜂;1日龄蜂子代雌蜂体型在不同虫龄蚜虫间无显著差异,但2～4日龄蜂寄生2、3龄若蚜的子代雌性体型大于寄生1龄、4龄或成蚜的子代雌蜂;1、2日龄蜂的子代雄蜂体型在各虫龄蚜虫间无显著差异,3、4日龄蜂寄生中间龄期若蚜的子代雄性体型大于寄生1龄若蚜或成蚜。根据本研究结果推测,与低龄蜂相比高龄蜂对寄主品质要求更高,其幼虫对寄主的调节能力更强。     

浅谈信息时代的农业科研管理

本文论述了信息化对农业科研管理工作的重要性,就目前农业科研管理工作的现状,提出信息时代农业科研管理工作的建议.     

Radiometric ages of kodiak seamount and giacomini guyot, gulf of alaska: implications for circum-pacific tectonics

Kodiak Seamount and Giacomini Guyot have been dated at 22.6 +/- 1.1 and 19.9 +/- 1.0 [2sigma (standard deviation)] x 10(6) years, respectively. Concordant whole-rock and plagioclase potassium-argon dates and fission-track apatite ages demonstrate that significant quantities of excess radiogenic (40)Ar are not present in the dated samples. These seamounts are the northwesternmost edifices of the Pratt-Welker chain, which cuts obliquely across magnetic anomaly patterns in an older northeastern Pacific sea floor. The older of the two dated seamounts is in the Aleutian Trench, apparently about to be subducted. If one assumes that seamounts are generated by plate motion over a fixed hot spot in the mantle, a Pacific-plate motion of 6.6 centimeters per year during early Miocene time may be calculated.     

不同年龄马尾松人工林生物量结构特征

对三明市尤溪县不同年龄马尾松人工林生物量结构特征进行了研究,结果表明:不同年龄马尾松林生长差异较大,但32、33、34和41年生马尾松林分平均胸径和平均树高变化不大;不同年龄马尾松人工林在单株、林分和根系生物量及净生物量上均表现出较大差异,其中34年生马尾松成熟林树干生物量所占百分比最高,可达到80.80%,此时的经济效益最高,可进行适当的采伐,在保证马尾松正常更新的同时,将获得更好的经济效益.     

藏绵羊羔羊睾丸leydig细胞增龄性变化特征

为了比较分析不同月龄藏绵羊羔羊睾丸leydig细胞发育特征,探索其发育特征与生精功能的关系.应用组织化学方法及电子显微镜技术,研究了1~6月龄羔羊睾丸leydig细胞增龄性变化特征.光镜观察结果表明:leydig细胞及其周围间质组织结构随月龄增龄性变化明显.1,2月龄羔羊睾丸间质内毛细血管分布较少,管壁内皮细胞较圆,发育不完善,周围有散在的纺锤形或星形的幼稚成纤维细胞,结缔组织分布较少;3,4月龄羔羊睾丸间质内血管内皮细胞发育完善,巨噬细胞位于间质血管周围,细胞较大,形态不规则,结缔组织有所增加;5,6月龄羔羊睾丸间质内毛细血管数量增多,管壁内皮细胞包围成形,成纤维细胞呈长索状,轮廓清楚,核仁大而明显,结缔组织明显增加.电镜下观察结果表明,3月龄之前睾丸leydig细胞以幼稚型为主,核较圆,异染色质较多,胞体近卵圆形;3月龄的羔羊睾丸leydig细胞体积明显增大,可见少量粗面内质网,胞浆内有少量分泌性颗粒出现.4月龄及以后的羔羊leydig细胞体积大,胞核多不规则,核仁明显,胞浆内空泡及分泌性颗粒明显增多;间质成纤维细胞呈长索状,血管壁内皮细胞包围成形.因此,3月龄之前,藏绵羊羔羊leydig细胞处于胚胎型向成熟型过渡时期;4月龄以后逐渐发育成熟,为leydig细胞的局部分泌调节提供结构支持,对生精小管的进一步发育以及后期精子发生具有重要意义.     

Rapid kimberlite ascent and the significance of Ar-Ar ages in xenolith phlogopites

Kimberlite eruptions bring exotic rock fragments and minerals, including diamonds, from deep within the mantle up to the surface. Such fragments are rapidly absorbed into the kimberlite magma so their appearance at the surface implies rapid transport from depth. High spatial resolution Ar-Ar age data on phlogopite grains in xenoliths from Malaita in the Solomon Islands, southwest Pacific, and Elovy Island in the Kola Peninsula, Russia, indicate transport times of hours to days depending upon the magma temperature. In addition, the data show that the phlogopite grains preserve Ar-Ar ages recorded at high temperature in the mantle, 700 degrees C above the conventional closure temperature.