Optical clocks and relativity

Observers in relative motion or at different gravitational potentials measure disparate clock rates. These predictions of relativity have previously been observed with atomic clocks at high velocities and with large changes in elevation. We observed time dilation from relative speeds of less than 10 meters per second by comparing two optical atomic clocks connected by a 75-meter length of optical fiber. We can now also detect time dilation due to a change in height near Earth's surface of less than 1 meter. This technique may be extended to the field of geodesy, with applications in geophysics and hydrology as well as in space-based tests of fundamental physics.     

Calibrating duckweeds: light, clocks, metabolism, flowering

The roles of photoperiodism and related light-dependent and hormonal processes in plants are not well understood. Rapid growth, aquatic habit, and adaptability to axenic culture make the Lemnaceae, or duckweeds, excellent material for investigating these topics and others in which highly defined conditions or the presence of organic substances are crucial. As a major example among several that are described, recent work with one species suggests a relation between some features of carbon dioxide flux and the photoperiodic timing mechanism, thus providing a system in which the biochemical basis of the latter may be explored.     

Plant circadian clocks increase photosynthesis, growth, survival, and competitive advantage

Circadian clocks are believed to confer an advantage to plants, but the nature of that advantage has been unknown. We show that a substantial photosynthetic advantage is conferred by correct matching of the circadian clock period with that of the external light-dark cycle. In wild type and in long- and short-circadian period mutants of Arabidopsis thaliana, plants with a clock period matched to the environment contain more chlorophyll, fix more carbon, grow faster, and survive better than plants with circadian periods differing from their environment. This explains why plants gain advantage from circadian control.     

Trapped free radicals and electrons in organic glasses

Free radicals, hydrogen atoms, and electrons produced in rigid organic glasses at sufficiently low temperatures have lifetimes of minutes to years. They can be studied by their electron spin resonance spectra and, in the case of electrons, by their optical spectra, recombination luminescence, and electrical conductivity. The decay kinetics of these reaction intermediates serve to distinguish those trapped as geminate pairs or in spurs of high concentration from those formed with random distributions. Electron spin resonance studies of relaxation times and of the spectra of radical pairs provide further evidence on geometrical distributions. The decay rates of radicals combining with reactive geminate partners are dependent on the size and shape of the radical, the temperature, and the nature of the matrix. Decay is much slower in deuterated matrices than in protiated matrices. The factors that control the physical trapping of electrons in organic glasses are under intensive investigation. There is evidence that many electrons trapped relatively weakly during irradiations at 4 degrees K deepen their traps by orientation of dipoles when the matrix is warmed; that most electrons are trapped in the field of the geminate positive ion; that in some matrices the traps have a bound excited state to which the electron can be promoted without detrapping; and that trapped electrons can tunnel to solute molecules with a higher electron affinity than the trap depth.     

Circadian clocks in daily and seasonal control of development

The rotation of the earth results in regular changes in the light environment, and organisms have evolved a molecular oscillator that allows them to anticipate these changes. This daily molecular oscillator, known as the circadian clock, regulates a diverse array of physiologies across a wide variety of organisms. This review highlights a few of the insights we have into circadian clock regulation of development, in both plants and animals. A common thread linking plants and animals is the use of the circadian clock to sense changes in day length and to mediate a diverse number of photoperiodic responses.     

蛀干类害虫引诱剂诱虫谱及诱集的主要昆虫种群动态

为了弄清蛀干类害虫引诱剂林间诱捕马尾松蛀干类昆虫的效果,于2006—2008年每年的4—11月蛀干类昆虫活动期,在浙江省仙居县官路镇大北地溪林场应用蛀干类害虫引诱剂诱捕马尾松蛀干类昆虫。结果表明:蛀干类害虫引诱剂具有较广的诱虫谱,可以诱捕到危害马尾松枝叶和树干的昆虫16科42种,包括3种具携带松材线虫能力的昆虫,即松墨天牛、短角幽天牛和马尾松角胫象;天敌资源昆虫2科2种。天牛科、小蠹科和象甲科是马尾松蛀干害虫的优势群体,天牛科种类最多,达12种;诱捕到的优势种是立毛角胫象、松梢小蠹、短角幽天牛。蛀干类害虫引诱剂可以持续监测林间松墨天牛、短角幽天牛、马尾松角胫象、立毛角胫象和松瘤象等松树主要蛀干害虫成虫的发生时间、发生量和发生规律,连续使用还能显著降低林间蛀干类害虫的虫口密度,为监测、预报和控制松树主要蛀干害虫提供直接、客观的依据。     

Solar heating and cooling

We have adequate theory and engineering capability to design, install, and use equipment for solar space and water heating. Energy can be delivered at costs that are competitive now with such high-cost energy sources as much fuel-generated, electrical resistance heating. The technology of heating is being improved through collector developments, improved materials, and studies of new ways to carry out the heating processes. Solar cooling is still in the experimental stage. Relatively few experiments have yielded information on solar operation of absorption coolers, on use of night sky radiation in locations with clear skies, on the combination of a solar-operated Rankine engine and a compression cooler, and on open cycle, humidification-dehumidification systems. Many more possibilities for exploration exist. Solar cooling may benefit from collector developments that permit energy delivery at higher temperatures and thus solar operation of additional kinds of cycles. Improved solar cooling capability can open up new applications of solar energy, particularly for larger buildings, and can result in markets for retrofitting existing buildings. Solar energy for buildings can, in the next decade, make a significant contribution to the national energy economy and to the pocketbooks of many individual users. very large-aggregate enterprises in manufacture, sale, and installation of solar energy equipment can result, which can involve a spectrum of large and small businesses. In our view, the technology is here or will soon be at hand; thus the basic decisions as to whether the United States uses this resource will be political in nature.     

海南草地贪夜蛾高空诱虫灯诱虫动态监测与分析

草地贪夜蛾是2019年入侵海南的重大农业迁飞性害虫,严重威胁海南的粮食和南繁种业安全,为摸清其在海南的发生危害规律,在海南海口、儋州和三亚开展了草地贪夜蛾高空诱虫灯监测.结果显示:2019年8月1日至2021年5月31日监测期间(儋州监测起始时间为2019年10月1日),海口草地贪夜蛾诱虫数量峰期在2020年3—10月...     

Dominoes and clocks: the union of two views of the cell cycle

We review the recent advances in understanding transitions within the cell cycle. These have come from both genetic and biochemical approaches. We discuss the phylogenetic conservation of the mechanisms that induce mitosis and their implications for other transitions in the cell cycle.     

加快数字图书馆建设,提供更好的信息服务

新世纪图书馆业发生着巨大的变化,数字图书馆是未来图书馆的存在形式。分析了数字化图书馆的基本概念和对高校图书馆发展的意义,阐述了高校图书馆数字化应用现状及存在的问题,提出了促进高校图书馆数字化发展的一些建议。     

12种木兰科乔木固碳释氧和降温增湿能力研究

选取木兰科的落叶齐木和常绿乔木各6种,采用Li-6400XT携带型光合作用测量仪和ACCUPAR LP-80型植物冠层分析仪测定各植物的光合速率、蒸腾速率和叶面积指数,量化分析各树种单位土地面积上的固碳释氧和降温增湿能力。结果表明,单位土地面积上,常绿树种的日固碳释氧能力排序为乐昌含笑<平伐含笑<紫花含笑<毛桃木莲<观光木<木莲,日降温增湿能力排序为乐昌含笑<平伐含笑<毛桃木莲<紫花含笑<木莲<观光木;落叶树种中的日固碳释氧能力排序为厚朴<黄花玉兰<黄山木兰<紫玉兰<凹叶厚朴<鹅掌楸,日降温增湿能力排序为厚朴<黄山木兰<黄花玉兰<凹叶厚朴<紫玉兰<鹅掌楸。综合分析发现,落叶乔木的固碳释氧和降温增湿能力比常绿乔木好。     

Active optics, adaptive optics, and laser guide stars

Optical astronomy is crucial to our understanding of the universe, but the capabilities of ground-based telescopes are severely limited by the effects of telescope errors and of the atmosphere on the passage of light. Recently, it has become possible to construct inbuilt corrective devices that can compensate for both types of degradations as observations are conducted. For full use of the newly emerged class of 8-meter telescopes, such active corrective capabilities, known as active and adaptive optics, are essential. Some physical limitations in the adaptive optics field can be overcome by artificially created reference stars, called laser guide stars. These new technologies have lately been applied with success to some medium and very large telescopes.