Long base line interferometry: a new technique

The technique of using magnetic-tape recorders and atomic frequency standards to operate two widely separated radio telescopes as a phase-coherent interferometer when the stations have no radio-frequency connecting link has been successfully tested at the National Research Council of Canada's Algonquin Radio Observatory.     

Emerging coherence in a population of chemical oscillators

Coherence of interacting oscillating entities has importance in biological, chemical, and physical systems. We report experiments on populations of chemical oscillators and verify a 25-year-old theory of Kuramoto that predicts that global coupling in a set of smooth limit-cycle oscillators with different frequencies produces a phase transition in which some of the elements synchronize. Both the critical point and the predicted dependence of order on coupling are seen in the experiments. We extend the studies both to relaxation and to chaotic oscillators and characterize the quantitative similarities and differences among the types of systems.     

Real-time, very-long-baseline interferometry based on the use of a communications satellite

The Hermes satellite, a joint Canadian-American program, has been used to provide a communication channel between radio telescopes in West Virginia and Ontario, for very-long-baseline interferometry (VLBI). This system makes possible instantaneous correlation of the data as well as a sensitivity substantially better than that of earlier VLBI systems, by virtue of a broader observational bandwidth. With the use of a geostationary communications satellite it is possible to eliminate the tape recorders and the most troublesome part of the postobservational data processing. A further possibility is the development of a phase-coherent interferometer.     

An intercontinental array--a next-generation radio telescope

It is difficult to estimate accurately the cost of constructing a large scientific instrument that involves many techniques. On the other hand, most of the component parts of the VLBA consist of antennas and electronic systems that already exist or are being fabricated. The kind of 25-m antennas being constructed for the VLA will cost about $900,000 each and will work at wavelengths as short as 1 cm. A multifrequency radiometer, hydrogen maser frequency standard, small control computer, control building, and wide-band instrumentation recorder bring the cost to about $1.5 million per element, or $15 million for a ten-element array using tape recorders. A multistation playback facility, with ten recorders and enough correlators to handle all interferometer pairs simultaneously, together with the necessary computers to control the processor and reduce the data, may add $5 million. The total cost is thus about $20 million at current prices, including an adequate supply of magnetic tape. This is comparable to the cost of existing large radio telescopes and arrays. An array that used a geostationary communication satellite to transmit the data to a real-time correlator would cost $30 million to $50 million more, but this is still within the price range of other space astronomy projects. It is thus feasible to construct at reasonable cost an intercontinental very long baseline array which has sub-milliarcsecond resolution. This would complement the Very Large Array now being constructed (4), which is much more sensitive to objects of low surface brightness. This next step would permit the study of the universe with unprecedented angular resolution.     

The very long baseline array

The Very Long Baseline Array is a high-resolution synthesis radio telescope consisting of ten antennas, each 25 meters in diameter, located throughout the United States from Puerto Rico to Hawaii. Each antenna will be equipped with low-noise receivers spaced throughout the frequency range from 330 megahertz to 43 gigahertz, a hydrogen-maser frequency standard for time and frequency reference, and broadband digital tape recorders. Tapes recorded at each antenna will be simultaneously replayed and correlated in a specially built digital correlator, and the correlator output will, by Fourier transformation, be used to construct images of celestial radio sources with an angular resolution better than one thousandth of an arc second.     

加快数字农业建设 为农业农村现代化增添新动能

［目的］贯彻落实党的十九大报告提出的乡村振兴战略以及习近平总书记最近提出的实施大数据战略要求。［方法］文章认为数字农业是实现这两大战略融合发展的必然要求和根本途径。数字农业将沿着数字技术产业化和农业产业数字化两条主线发展。［结果］数字技术产业化是用信息把小农户和大市场连接起来、用网络把乡村和城市连接起来开展全产业链条的信息服务,将形成市场主导的新型农业服务体系。产业数字化是把农业全过程数字化,提升农业生产的空间应变能力和生产要素的匹配使用能力,改善农业生产方式向精准农业和智慧农业方式发展,将形成政府推动的新型农业生产方式。两条主线融合到现代农业当中,必然形成数字农业经济体系,成为现代农业的实现途径和表现形式,成为数字中国和数字经济的重要组成部分。［结论］该文认为数字农业或者现代农业是必须同时包含数字和土地这两个核心要素的产业体系,论证了数字技术和现代农业的辩证关系。根据国内外实践和经验总结,初步提出了我国建设数字农业的基本思路、重点任务和工作措施。     

Experimental realization of Wheeler's delayed-choice gedanken experiment

Wave-particle duality is strikingly illustrated by Wheeler's delayed-choice gedanken experiment, where the configuration of a two-path interferometer is chosen after a single-photon pulse has entered it: Either the interferometer is closed (that is, the two paths are recombined) and the interference is observed, or the interferometer remains open and the path followed by the photon is measured. We report an almost ideal realization of that gedanken experiment with single photons allowing unambiguous which-way measurements. The choice between open and closed configurations, made by a quantum random number generator, is relativistically separated from the entry of the photon into the interferometer.     

数字人文“二手证据”循证范式研究：以敦煌汉简为例

[目的/意义]随着数字人文研究范式的兴起,为研究者基于二手资源开展循证研究提供了契机。[方法/过程]本文首先梳理了数字人文“二手证据”循证范式相关的理论基础,并以敦煌汉简为例对数字人文“二手证据”循证范式进行了实证分析。通过来自CNKI的287篇敦煌汉简相关研究文献的编码分析,检验了信度和效度,并对类目体系展开了综合分析。[结果/结论]本文提出了循证数字人文基于“二手证据”展开循证研究的包括文献检索、类目编制、“二手证据”要素的综合分析3个阶段,以及证据检索、信度检验环节、效度检验环节和类目构建、证据要素综合5个环节构成的“三阶段五环节”范式。本研究所构建的范式,对循证数字人文学科、学术和话语体系建设具有一定的理论参照和实践指引价值。     

Engineering complex dynamical structures: sequential patterns and desynchronization

We used phase models to describe and tune complex dynamic structures to desired states; weak, nondestructive signals are used to alter interactions among nonlinear rhythmic elements. Experiments on electrochemical reactions on electrode arrays were used to demonstrate the power of mild model-engineered feedback to achieve a desired response. Applications are made to the generation of sequentially visited dynamic cluster patterns similar to reproducible sequences seen in biological systems and to the design of a nonlinear antipacemaker for the destruction of pathological synchronization of a population of interacting oscillators.     

浅谈网络图书馆、数字图书馆、虚拟图书馆的概念

结合多位专家学者对网络图书馆、数字图书馆、虚拟图书馆概念的认识，利用哲学中的认识论浅谈三者的概念。三概念间有着千丝万缕的联系，但是由于认识角度不同三者有细微差异。网络图书馆、数字图书馆、虚拟图书馆分别强调现代图书馆信息资源共享的网络化传播方式、数字化加工过程、虚拟化组织形式。三者是对同一事物从不同侧面进行的描述。     

Multiple circadian oscillators regulate the timing of behavioral and endocrine rhythms in female golden hamsters

A single daily "surge" in pituitary luteinizing hormone release was observed in ovariectomized-estrogen-treated hamsters expressing an intact circadian rhythm of locomotor activity. In contrast, two luteinizing hormone surges occurred within a single 24-hour period in hamsters whose activity rhythm had dissociated or "split" into two distinct components. These observations indicate that both behavioral and endocrine circadian rhythms are regulated by the same multioscillator system, which seems to be composed of at least two distinct circadian oscillators.     

Entrainment of a population of synthetic genetic oscillators

Biological clocks are self-sustained oscillators that adjust their phase to the daily environmental cycles in a process known as entrainment. Molecular dissection and mathematical modeling of biological oscillators have progressed quite far, but quantitative insights on the entrainment of clocks are relatively sparse. We simultaneously tracked the phases of hundreds of synthetic genetic oscillators relative to a common external stimulus to map the entrainment regions predicted by a detailed model of the clock. Synthetic oscillators were frequency-locked in wide intervals of the external period and showed higher-order resonance. Computational simulations indicated that natural oscillators may contain a positive-feedback loop to robustly adapt to environmental cycles.     

基于组态分析的数字直播活动效果提升路径研究

[目的/意义]数字直播是企业开展网络活动的重要方式。通过发现能够使企业数字直播活动创造更大价值的要素或要素组合，并采取多途径增强这些要素，从而达到企业数字直播活动效果提升的目的，这对企业发展有创新指导意义。[方法/过程]选取4个与数字直播活动相关的影响因素作为条件变量，采用活动效果作为结果变量，并结合清晰集定性比较分析与线性判别降维对烟草领域数字直播活动的数据进行组态分析。[结果/结论]研究发现，单个因素并不构成提升数字直播活动效果的必要条件，应考虑不同条件因素的组合；存在游戏辅助型和话题支撑型两条组态路径能改善数字直播活动的效果；这两条路径适用不同的数字直播形式，企业应根据自身需求进行选择并在实践中细化路径。     

数字管道中的工艺与自动化系统设计

数字管道的建设就是各种数据库和图形库的建设,而数字管道建设中的一些技术给管道工艺和自动化设计带来了一定的变化。通过利用数字管道建设的一些成果,设计人员能够使管道设计与未来的管理有机地结合,在设计阶段就对未来油气管道的运行控制和完整性管理奠定坚实的基础。通过数字管道建设要素的分析,阐述了数字管道中对工艺与自动化系统设计的要求,说明了管道工艺和自动化设计应满足数字管道的数据平台及数据模型,达到提高管道建设与运营管理的质量、效率、安全等综合管理水平的目的。     

一种基于标准白板的颜色校正方法

本研究提出了一种基于标准白板的颜色校正方法。首先制作一块标准白板。在标准色温下拍摄附带标准白板的景物,得到标准图像,通过程序统计出图像中白板区域的RGB三色的各自均值,作为颜色校正的基准值。同样,得到在非标准色温下白板区域的RGB三色的各自均值。两组值相比较,得到非标准图像RGB三色各自的校正系数,然后按此系数对整个图像的每个象素进行校正。试验结果表明,校正图像与标准图像不仅在视觉上可达到一致,并且在数值上也能达到基本一致,该方法通过计算机编程来实现简单实用,快速准确。     

Antiphase oscillation of the left and right suprachiasmatic nuclei

An unusual property of the circadian timekeeping systems of animals is rhythm "splitting," in which a single daily period of physical activity (usually measured as wheel running) dissociates into two stably coupled components about 12 hours apart; this behavior has been ascribed to a clock composed of two circadian oscillators cycling in antiphase. We analyzed gene expression in the hypothalamic circadian clock, the suprachiasmatic nucleus (SCN), of behaviorally "split" hamsters housed in constant light. The results show that the two oscillators underlying the split condition correspond to the left and right sides of the bilaterally paired SCN.     

浅谈网络图书馆、数字图书馆、虚拟图书馆的概念

结合多位专家学者对网络图书馆、数字图书馆、虚拟图书馆概念的认识，利用哲学中的认识论浅谈三者的慨念。三概念间有着千丝万缕的联系，但是由于认识角度不同三者有细微差异。网络图书馆、数字图书馆、虚拟图书馆分别强调现代图书馆信息资源共享的网络化传播方式、数字化加工过程、虚拟化组织形式。三者是对同一事物从不同侧面进行的描述。     

Testosterone induces "splitting" of circadian locomotor activity rhythms in birds

Under the influence of testosterone, the free-running circadian rhythm of locomotor activity of the starling, Sturnus vulgaris, tends to "split" into two components which temporarily run with different circadian frequencies: "splitting" occurred in intact birds whose testes grew, and in castrated birds that were injected with testosterone. Since "splitting" most probably reflects the temporal separation of two (or two groups of) circadian oscillators, these results suggest that testosterone affects the mutual coupling of circadian oscillators controlling locomotor activity.     

Very-Long-Baseline Radio Interferometry: The Mark III System for Geodesy, Astrometry, and Aperture Synthesis

The Mark III very-long-baseline interferometry (VLBI) system allows recording and later processing of up to 112 megabits per second from each radio telescope of an interferometer array. For astrometric and geodetic measurements, signals from two radio-frequency bands (2.2 to 2.3 and 8.2 to 8.6 gigahertz) are sampled and recorded simultaneously at all antenna sites. From these dual-band recordings the relative group delays of signals arriving at each pair of sites can be corrected for the contributions due to the ionosphere. For many radio sources for which the signals are sufficiently intense, these group delays can be determined with uncertainties under 50 picoseconds. Relative positions of widely separated antennas and celestial coordinates of radio sources have been determined from such measurements with 1 standard deviation uncertainties of about 5 centimeters and 3 milliseconds of arc, respectively. Sample results are given for the lengths of baselines between three antennas in the United States and three in Europe as well as for the arc lengths between the positions of six extragalactic radio sources. There is no significant evidence of change in any of these quantities. For mapping the brightness distribution of such compact radio sources, signals of a given polarization, or of pairs of orthogonal polarizations, can be recorded in up to 28 contiguous bands each nearly 2 megahertz wide. The ability to record large bandwidths and to link together many large radio telescopes allows detection and study of compact sources with flux densities under 1 millijansky.     

Effects of Irrigation Water Quality and Drip Tape Arrangement on Soil Salinity,Soil Moisture Distribution,and Cotton Yield (Gossypium hirsutum L.) Under Mulched Drip Irrigation in Xinjiang,China

More and more attention is being focused on saline water utilization in irrigation due to the shortage of fresh water to agriculture in many regions. For purpose of reducing the risks of using of saline water for irrigation, the mechanism of soil moisture and salinity distribution and transport should be well understood for developing optimum management strategies. In this paper, field experiments were carried out at Junggar Basin, China, to study the effects of drip irrigation water quality and drip tape arrangement on distribution of soil salinity and soil moisture. Six treatments were designed, including two drip tape arrangement modes and three irrigation water concentration levels (0.24, 4.68, and 7.42 dS m-1). Results showed that, soil moisture content (SMC) directly beneath the drip tape in all treatments kept a relatively high value about 18% before boll opening stage; the SMC in the narrow strip in single tape arrangement (Ms) plot was obviously lower than that in the double tapes arrangement (Md) plot, indicating that less sufficient water was supplied under the same condition of irrigation depth, but there was no significant reduction in yield. Mulching had not significant influence on salt accumulation but the drip tape arrangement, under the same condition of irrigation water depth and quality, compared with Md, Ms reduced salt accumulation in root zone and brought about relatively high cotton yield.