微波时间传递精度和时延分析

分析了引起微波时间传递系统时延变化的原因和单向及双向时间传递比对精度;分析表明,根据微波双向时间比对的长期测量数据可对搬钟实验得到的时延值进行修正,采用该修正结果可减小单向时间比对的误差。     

Oral histories in meteoritics and planetary science – XXII: John T. Wasson

In this interview, John Wasson (Fig.  1 ) describes his childhood and undergraduate years in Arkansas and his desire to pursue nuclear chemistry as a graduate student at MIT. Upon graduation, John spent time in Munich (Technische Hochschule), the Air Force Labs in Cambridge, MA, and a sabbatical at the University of Bern where he developed his interests in meteorites. Upon obtaining his faculty position at UCLA, John established a neutron activation laboratory and began a long series of projects on the bulk compositions of iron meteorites and chondrites. He developed the chemical classification scheme for iron meteorites, gathered a huge set of iron meteorite compositional data with resultant insights into their formation, and documented the refractory and moderately volatile element trends that characterize the chondrites and chondrules. He also spent several years studying field relations and compositions of layered tektites from Southeast Asia, proposing an origin by radiant heating from a mega‐Tunguska explosion. Recently, John has explored oxygen isotope patterns in meteorites and their constituents believing the oxygen isotope results to be some of the most important discoveries in cosmochemistry. John also describes the role of postdoctoral colleagues and their important work, his efforts in the reorganization and modernization of the Meteoritical Society, his contributions in reshaping the journal Meteoritics, and how, with UCLA colleagues, he organized two meetings of the society. John Wasson earned the Leonard Medal of the Meteoritical Society in 1992 and the J. Lawrence Smith Medal of the National Academy in 2003.

Figure 1 Open in figure viewer PowerPoint John T. Wasson.

DS

John, thank you for letting me document your oral history. Let us start with my normal opening question, how did you get interested in meteorites?

JW

My Ph.D. research was in nuclear chemistry at MIT. Until late in my studies I thought I could be a nuclear chemist using the classical scientific method. That is, you gather data on a topic that seems interesting, you look for patterns in the data, and you write an interpretative paper that explains the data. I had learned, though, by going to Gordon Conferences, that this was not the way nuclear chemistry was being done. Nuclear chemists measured gamma ray energies as accurately as they could, they tried to fit these into energy levels diagrams, and then the nuclear physicists took over and interpreted the data. The nuclear physicists looked for the patterns in the energy‐level diagrams and made the models. That was not what I had in mind. But while I was at MIT, I heard lectures by Harold Urey, Hans Suess, and James Arnold. These were people whose backgrounds were not that different from mine and all three extolled the virtues of working on meteorites, and how you could learn neat things about how the solar system worked. That's a strength of MIT, exposure to neat ideas, and I credit the institution for doing this. So that was it. I was hooked.

DS

You have talked to us about how you became interested in meteorites, let's go back and talk about your precollege years.

     

The Fragmentation of Asteroids – A Synopsis of Analytical Methods (Mitteilungen der Universitäts-Sternwarte Jena Nr. 119)

Basing on the author's work a review of the possibilities as well as the limits of treating the problem of the collisional history of the asteroids by analytical methods is given. Using empirical data on rock fragmentation and general principles like symmetry and mass conservation the distribution function of the fragments arising from a single collision is analytically formulated. The size distribution of asteroids adjusting when crushing collisions have taken place a sufficiently long time can be obtained as the solution of an integrodifferential equation with partial derivatives (equation of fragmentation). Quasi-stationary solutions of the equation of fragmentation are discussed for particular cases. The problem of the steady state is reduced to the solution of a transcendental equation. The results obtained show that analytical methods already offer a good theoretical understanding of the observed size distribution of the asteroids. They should be, therefore, a useful basis of carrying out numerical calculations.     

用GPS校准计算机系统时间

文章介绍了一种计算机时间校正系统,该系统利用GPS提供标准时间,采用UNIX C作为编程语言,具有良好的兼容性,可移植性,可以方便地用于计算机系统时间的校正。     

像运动法测量视宁度参数中曝光时间的重要性及其测定

大气湍流会导致天文图像的像质衰减 ,而视宁度r0 则是描述这种衰减的特征参数。在本文中 ,我们给出了像运动法测量中r0 和曝光时间之间的关系 :曝光时间必须小于大气相干时间 ,否则测量的r0 值将偏大。基于这个原因以及对仪器检测的需要 ,我们必须对视宁度测量仪的曝光时间进行准确地测量。为此我们设计了一种实验方法来测定视频CCD的曝光时间 ,实验的结果表明这种方法是可靠的     

嵌入式时间间隔计数器的研制

介绍了一种新研制的嵌入式时间间隔计数器，它可作为一种功能模块用于用户的设备或时统中，实现高精度时间测量。从基本原理、硬、软件和功能等不同角度对计数器进行了较为详细的讨论。在该计数器的研制过程中还开发了用来调试计数器和供计数器用户使用的计算机应用软件，对此也作了简要介绍。最后，给出了计数器的设计指标和一些实测数据。     

基于GNSS CV的精密时间服务系统的设计与实现

通过研究GNSS(global navigation satellite syetem,全球导航卫星系统)共视远程时间传递技术,并结合现代网络通信技术,搭建了基于GNSS CV(common-view,共视)的精密时间服务系统的硬件平台。利用中国科学院国家授时中心保持的精确时间UTC(NTSC)和GNSS共视接收机观测数据,实现了用户与国家授时中心之间的在线数据传输和比对处理,为用户时间与UTC(NTSC)之间的高精度时间同步提供了一种解决方案。     

Dantu's mineralogical properties – A view into the composition of Ceres' crust

Impact crater Dantu not only exhibits a very complex geological history but also shows an exceptional heterogeneity of its surface composition. Because of its location within a low‐lying region named Vendimia Planitia, which has been proposed to represent an ancient impact basin, Dantu possibly offers a window into the composition of Ceres’s deeper crust, which apparently is enriched in ammonia. Local concentration of carbonates within Dantu or its ejecta blanket may be either exposed or their emplacement induced by the Dantu impact event. Because carbonates can be seen along Dantu's crater walls, exposed due to recent slumping, but also as fresh spots or clusters of spots scattered across the surface, the deposition/formation of carbonates took place over a long time period. The association of several bright spots enriched in carbonates with sets of fractures on Dantu's floor might be accidental. Nevertheless, its morphological and compositional similarity to the faculae in Ceres’s prominent impact crater Occator including its hydrated state does not exclude a cryo‐volcanic origin, i.e., upwelling of carbonate‐enriched brines influenced by H₂O ice in the subsurface. Indeed, an isolated H₂O ice spot can be identified near Dantu, which shows that ice still exists in Ceres’s subsurface at midlatitudes and that it can exist on the surface for a longer period of time.     

NTSC时频基准实验室守时系统自动监测软件

为了能实时了解中国科学院国家授时中心（NTSC）时频基准实验室守时系统的运转情况,编制了本软件。本软件的功能是对系统中原子钟最近一个月的比对数据进行实时计算后,得到一个纸面的加权平均时间尺度“TA”,用它作为监测UTC（NTSC）、UTC（JATC）和原子钟运转情况的参考,给出TA-UTC（NTSC）、TA-UTC（JATC）、以及每个钟相对于TA的速率曲线。通过选用窗体上设置的各个按钮,能很方便地监测原子钟和测量设备的运行情况。位于陕西蒲城的BPL监控室可以通过远程局域网得到NTSC守时实验室的数据,实时运行本软件,并用TA作为参考,即可监测BPL监控室原子钟运行情况,并且对BPL发播工作钟时间T（PU）进行监测和频率驾驭,以实现T（Pu）同步到扩形（NTSC）。     

Pollution and eutrophication history AD 1800–2005 as recorded in sediments from five lakes in Central Chile

One of the fundamental problems to quantifying past impact of anthropogenic activities is that long series of observational data for pollutant deposition and changes in the nutrient cycling of ecosystems (eutrophication) are often not available. Lake sediments may provide suitable archives to decipher the history of local and regional pollution and eutrophication.Here we provide quantitative high-resolution data for the history of airborne pollutants and eutrophication from sediments of five lakes in Central Chile between ca. AD 1800–2005. We use spheroidal carbonaceous particles (SCPs) from fossil fuel combustion and excess atmospheric Cu deposition from mining activities as a proxy for atmospheric deposition. Organic carbon and nitrogen flux rates to the sediments and C/N ratios are used as a proxy for aquatic primary production and eutrophication.We show that the lake sediment SCP and Cu records are highly consistent and depict in great detail the local and regional history of urban, industrial and transportation history as reported in independent documentary sources and statistics. The pre-industrial and pre-1950 background concentrations (and flux rates) of the substances can be quantified. We can also show that technical measures taken in the early 1980s to trim down Cu emissions from the copper mines reduced the excess atmospheric Cu fallout to the lakes by about 50%.Eutrophication of the lakes did not start before ca. 1980. Prior to that time, warm season temperatures explain most of the variance in TOC and N flux to the sediments. The three dimictic lakes show only moderate eutrophication responses to enhanced N supply (as atmospheric fallout; enrichment factors for TOC and N 1.1–2.6), suggesting that mainly phosphorus controls aquatic primary production. The meromictic lake, where phosphorus recycling is likely, shows the largest response (enrichment factors for TOC and N between 9–20).While all five lakes show overall consistent and similar trends for the pollution history during the 19th and 20th century, there are significant differences in the details of the individual profiles. This suggests that local sources are highly important and the common regional (background) signal is relatively marginal. This is very different from Europe.     

BPSK调制信号中的幅度调制现象分析

在许多场合 ,需要找出BPSK(BinaryPhaseShiftKey ,即二进制相移键控 )调制信号的调制时刻。但实际上并不能直接发现BPSK调制信号的调制时刻 ,只能看到有明显的幅度调制现象。对这种现象产生的原因和用途作了分析 ,并通过仿真实验对这种现象进行了验证。     

A “lost” sunspot observation in 1785

The reconstruction of the solar activity during some years of the 18th century is poorly known because there are scarce sunspot observations. The aim of this short contribution is to present a “lost” sunspot observation realized by the Portuguese scientist Sanches Dorta during his observation of the solar eclipse of 1785 from Rio de Janeiro (Brazil). This record was not included in the database compiled by Hoyt and Schatten (1998). We present new estimations of the solar activity during 1785. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The crustal dichotomy of Mars

The crustal dichotomy of Mars describes the topographic division between the young plains in the northern hemisphere and the old terrain in the southern hemisphere. The highland-lowland boundary separates the younger plains from the older, high-standing terrain and consists of three geologically-distinct regions: the Tharsis Province, the chaotic terrain, and the fretted terrain (which includes gradational boundary types)-all are characterised by tensional tectonics. This paper presents new geological evidence that shows the topographic division at the fretted terrain formed in the late Noachian-early Hesperian time period: the same time period in which the Tharsis Province and chaotic terrain formed, and fracturing of a southern-hemisphere-type surface beneath the northern plains occurred. These are inherent features of the crustal dichotomy, indicating it must have also formed during the late Noachian-early Hesperian time period. An analogy is made between the northern lowlands and sedimentary basins on Earth: both are basin like and are surrounded by provinces that have been subjected to pronounced tensional tectonics. This paper uses the White and McKenzie model (1989a) to propose that a lithospheric-stretching event on Mars, in the late Noachian-early Hesperian time period, produced the crustal dichotomy; the Tharsis Province formed by uplift (over a sub-surface hotspot) and gave rise to lithospheric stretching, and the northern lowlands formed by subsidence (over normal asthenospheric temperatures). Detachment faults, operating from the Tharsis Province and around northern lowlands, allowed structural equilibrium and large lithospheric extensions to be attained during this period: they also defined the geometry of the lowlands. The proposal is supported with calculations used to estimate the amount of subsidence that can be achieved in this way.     

守时设备故障的自动诊断和报警系统设计

为了及时发现守时主系统运行中出现故障概率最高的设备,降低比对数据的出错率,提高守时精度及比对数据的可靠性和完整性,设计了一种守时设备故障的自动诊断和报警系统。该系统采用专家系统故障诊断方法,通过对守时比对系统的时间比对数据的实时监测和分析,发现比对数据异常,及时启动故障自动诊断系统,通过报警系统报告发生故障的可能设备,实现故障的及时发现和尽快排除。结果表明,该守时设备故障的自动诊断和报警系统达到了预期目标。     

E-CHONDRITES: SIGNIFICANCE OF THE PARTITION OF ELEMENTS BETWEEN ‘SILICATE’ AND ‘SULPHIDE’

Bulk chemical analyses of six E-chondrites (Daniel's kuil, Khairpur, Kota Kota, Saint-Sauveur, South Oman and St Mark's) are given, together with partial analyses of a further five (Blithfield, Hvittis, Indarch, Jajh deh Kot Lalu and Pillistfer). The distribution of some normally lithophile elements (Al, Ca, Cr, K, Mg, Na, P and Ti) between silicate and sulphide groups of minerals was determined using the selective attack by dry chlorine (350°C) on magnetically separated fractions. Subdivision of the E-chondrites into types I and II (Yavnel;, 1963; Anders, 1964) is accepted and it is shown using chemical data that St Mark's and Saint-Sauveur should be included in type I. Sulphides contribute an unexpectedly high proportion of several elements to the bulk: e.g. Ca (av. 88.5% type I, 66.3% type II); Ti(av. 77.1% type I, 84.8% type II) and P as phosphide (av. 44.4% type I, > 83.2% type II). The proportion of Ti contributed to the bulk composition by the sulphides in types I and II increases with increae in ‘thermal metamorphic effect’ (Easton, 1983b) within each type. There is marked variability in the relative abundances of metal, phosphide, silicate and sulphide among the members of each type in keeping with their aggregate nature. The chemical composition of the ‘silicate’ and ‘sulphide’ in type IE-chondrites differs from that in type II (e.g. CaO in the silicates, Mg in the bulk sulphides) which therefore precludes the isochemical evolution of all E-chondrites from a common parent material. Partition of Ti between silicate and sulphide groups of minerals indicates that types I and II E-chondrites originated in separate, chemically distinct bodies.     

综合脉冲星时的小波分析算法

由单脉冲星定义的脉冲星时受几种噪声源的影响,为削弱这些影响得到一种更稳定的时间尺度,采取将多颗脉冲星定义的单脉冲星时进行综合的分析方法得到综合脉冲星时．用两种方法:经典加权算法和小波分解算法,对PSRB1855 09和PSR B1937 21两颗脉冲星进行综合计算并做出比较,经典加权算法无法兼顾脉冲星不同频率上的稳定度,而用小波分析的方法对PSR B1855 09和PSR B1937 21两颗脉冲星进行综合,能够有效抑制不同频率上噪声的影响,达到更好的效果．     

Stochastic data in astronomy. II. Search for harmonic components of time series with very large gaps

This is an analysis of certain aspects of using the CLEAN algorithm for Fourier analysis of short segments of time series and of time series consisting of short segments of length ΔT separated by very long irregular gaps. It is assumed that the time series contain a harmonic component of amplitude A with a period longer than the length of the longest of the segments of the time series plus white noise with dispersion N². Reliability plots are constructed for determining the ranges of the parameters (ν, ϕ) for which the CLEAN procedure can be used to determine the values of ν, the frequency, and ϕ, the phase of the harmonic component, with a given accuracy. The results of this analysis are used to search for harmonic components in the variation of the Hβ line profile in spectra of the triple star δ Ori A obtained in 2004 with the BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences. __________ Translated from Astrofizika, Vol. 50, No. 2, pp. 281–297 (May 2007).     

Comment on “The origin of eucrites,diogenites, and olivine diogenites: Magma ocean crystallization and shallow magma processes on Vesta” by B. E. Mandler and L. T. Elkins‐Tanton

Mandler and Elkins‐Tanton ( 2013 ) recently proposed an upgraded magma ocean model for the differentiation history of the giant asteroid 4 Vesta. They show that a combination of both equilibrium crystallization and fractional crystallization processes can reproduce the major element compositions of eucritic melts and broadly the range of mineral compositions observed in diogenites. They assert that their model accounts for all the howardites, eucrites, and diogenites (HEDs), and use it to predict the crustal thickness and the proportions of the various lithologies. Here, we show that their model fails to explain the trace element diversity of the diogenites, contrary to their claim. The diversity of the heavy REE enrichment exhibited by the orthopyroxenes in diogenites is inconsistent with crystallization of these cumulates in either shallow magma chambers replenished by melts from a magma ocean or in a magma ocean. Thus, proportions of the various HED lithologies and the crustal thickness predicted from this model are not necessarily valid.     

Time structure of solar decametre type III radio bursts

The time structure of solar radio decametre Type III bursts occurring during the periods of enhanced emission is investigated. It is found that the time profiles can take a variety of forms of which three distinct types are the following: (1) profiles where the intensity rises to a small but steady value before the onset of the main burst, (2) the intensity of the main burst reduces to a finite level and remains steady before it decays to the base level, (3) the steady state is present during the rise as well as the decay phase of the main burst. It is shown that these profiles are not due to random superposition of bursts with varying amplitudes. They are also probably not manifestations of fundamental-harmonic pairs. Some of the observed time profiles can be due to superposition ot bursts caused by ordered electron beams ejected with a constant time delay at the base of the corona.