Comparison of boundaries for HF auroral backscatter and VHF scintillation

A study is described of the equatorwards boundary of high-latitude ionospheric irregularities using measurements obtained by two different experimental techniques. Auroral traces observed on backscatter ionograms from an HF radar have been used to identify the boundary of the decametre scale-size irregularities responsible for the coherent backscatter. Simultaneous observations of scintillation on the 150 MHz signals from NNSS satellites have enabled the boundary for irregularities in the sub-kilometre scale regime to be located. Comparisons of the results from the two techniques indicate that reconciliation between boundary positions can be made in only about 50% of the cases considered. In general the scintillation boundary lies on average well polewards of that identified by the HF radar, suggesting that caution should be exercised in the mapping of irregularity boundary positions.     

Incoherent scattering from the collision dominated D-region. Comparison of theories with experimental data

There has been a long standing controversy as to the introduction of the collisional term in the incoherent scattering theory. This has profound implications in interpreting the incoherent scatter spectra from the collision dominated D- and E-regions. Among the different theoretical formulations, those by Dougherty and Farley and Waldteufel have been used for the interpretation of incoherent scatter data. Waldteufel's formulation apparently improves on the theoretical model of Dougherty and Farley by allowing for momentum conservation and temperature changes during collisions.Using incoherent scatter data from D-region heights over Arecibo we show for the first time that Dougherty and Farley's formulation is the correct one. This is due to the fact that during a collision ions lose both momentum and energy to neutrals and so far as the ion gas is concerned, neither should be conserved.Once the correct formulation has been established, it can be seen that the incoherent scatter technique offers a unique advantage in inferring mesospheric parameters with very high precision. For example, the ratio of the number density to neutral temperature in the D-region over Arecibo could be measured to accuracies of a few per cent. The results of such measurements are in excellent agreement with the CIRA 1972 model and show a day-to-day variability limited to within 10–15%.     

Equatorwards limits of the southern scintillation oval

Radio signals in the VHF range were recorded and compared with ionograms over a wide range of southern latitudes during a few equinoctial months for which a large variation in the magnetic disturbance level was observed. It is evident that the equatorwards edge of the auroral scintillation oval extends well into mid-latitudes for high values of magnetic K-index. The range-spreading type of spread-F and scintillation-producing irregularities show a high degree of spatial coincidence from the polar cap to mid-latitudes. It is suggested that the inhomogeneities responsible for both ionospheric phenomena are associated with the equatorwards propagation of travelling ionospheric disturbances (T1Ds) generated in the auroral zone.     

Elongation of midlatitude scintillation irregularities

This paper reports a study of the length of the midlatitude F-region irregularities which cause scintillations. The length of scintillation irregularities is usually measured by the Full Correlation Analysis (FCA) method. If observations from a typical 3-receiver array, with small spacing, are used the length is always found to he only a few kilometers. Basic ionospheric theory indicates that the irregularities should he much longer than this. In this experiment scintillations of beacon transmissions from polar-orbiting satellites were observed on a 3-receiver array with 310 m spacing, and a fourth receiver 4.6 km away was used to check the lengths measured. Analysis of the scintillation observations from the 310 m array used the FCA method. In all cases the FCA lengths, from the small array, were much shorter than those measured by the distant receiver. Measurements using the 4.6 km receiver gave an average ratio of 44.5 and a half-length (in ionosphere) of 9.4 km. It appears that random errors in the correlation functions cause the FCA to underestimate the length of the ground pattern of irregularities when the spacing of the receivers is much less than the pattern size.     

A racial triangle: physical anthropology and race theories between Germans,Jews and Poles

The last decades of the nineteenth century saw a growing prominence of German racial sciences. This article documents how East Central European scholars responded to their potential marginalization within the scientific community due to German racial theories in the field of physical anthropology and the popularization of science. Three personalities represent a sample of this variety: Ludwik Gumplowicz, a Polish-Jewish sociologist; Mateusz Mieses, a Galician Jewish amateur anthropologist; and Jan Czekanowski, professor of anthropology and spiritus rector of the Lwów school of anthropology. All three cases illustrate the contradictions inscribed into the concept of transnationalism. To varying extents, they belonged to the German-speaking scientific community, through which they gained access to international science. Their reactions to anti-Jewish and anti-Slavic positions among the dominant racial theories of their time shines light on the tensions which were present within the academic community, as well as on the tensions that appeared between their own (semi-)professional status, self-perception and their group identities. The international communication and contacts came into conflict with the exclusionary philosophy of racial theories, thus perpetually challenging their transnational position. The responses of these actors sought to redefine spatial and methodological frameworks amid the dominant discourses. Each making attempts in their own way, they aimed at reversing what they perceived as aberrations of racial theories while persistently remaining within this discourse.     

中日两国现代化变动特征的比较

本文基于中日两国的现代化同属于传播型、后发型现代化这一史实 ,参考现代政治学、社会学等理论提出了“思想→政治→经济”这一比较中日两国现代化的分析模型。“思想”作动于“政治”是利益表达过程 ,利益表达有“内表达”和“外表达”两种形式 ;“政治”作动于“经济”是政治输出过程 ,政治输出也有“硬驱动”和“软驱动”两种形式。在两国现代化过程的不同阶段 ,两国三个子系统间 (思想、政治、经济 )的作动方向是相同的 ,但由于两国三个子系统的内外环境、作动者和受动者的性质不同 ,因而每一作动环节出现的两种作动方式在转换和结合上存在着差异 ,正是这些差异影响了作动力度和效果 ,并最终导致了两国现代化的不同结局。本文还提出了上述分析模型的现实意义 ,即不同所有制形态下的现代化模式存在相互比较和借鉴的可能性 ,同时也对建立有中国特色的内外表达的协调转换机制和软硬驱动的有机结合模式进行了探索。     

Recent results in auroral-zone scintillation studies

Nighttime data from the Defense Nuclear Agency's Wideband satellite have consistently shown a pronounced scintillation enhancement at the point where the propagation vector lies within the local L-shell. Simultaneous observations at two well-separated stations and spaced-receiver measurements have shown that this feature is caused by a latitudinally narrow, unstable F-region ionization enhancement that produces sheet-like intermediate-scale structures. A more detailed characterization of the source region has been derived from simultaneous measurements from the TRIAD satellite and the Chatanika radar.The source region is typically convecting southward, whereby the poleward gradient at its southern boundary is stable to the gradient-drift instability. Thus, Ossakow and Chaturvedi (1979) postulated the current-convective instability as a source mechanism. Birkeland currents, when sufficiently intense, can destabilize a region that is otherwise stable to the gradient-drift instability.The sheet-like anisotropy of the irregularities is perhaps the most intriguing feature of the instability. Two mechanisms have been postulated to explain it. This paper reviews the development and current status of our understanding of this recently discovered high-latitude instability.     

郑注与汉代别家《论语注》之比较

通过汉代各家《论语》异文资料的详尽比勘,在文献记载基础上,我们认为郑注是杂糅三《论》而成的,而不属于单纯的某一《论》。郑注注重经典义理的阐发,注重礼仪制度的诠释,注重交代孔子言行发生的具体背景,同其他《论语》注相比,更有助于我们再现历史的孔子形象。     

Comparison between the Seismic Performance of Integral and Jointed Concrete Bridges

This article presents a probabilistic fragility analysis for two groups of integral and jointed concrete bridges, with varying length and column height. The results show that the integral bridges perform consistently better from a seismic perspective than the jointed bridges. Comparisons are also drawn between the seismic fragility of different geometric configurations. The results show that for integral bridges, the seismic vulnerability increases with an increase in bridge length and decreases with an increase in column height. For the jointed bridge, it was found that geometric variation in column height and bridge length does not significantly affect its seismic vulnerability.     

德沃夏克《幽默曲》音乐表现形式之比较

德沃夏克是19世纪捷克民族乐派的主要代表人物,他的钢琴小品《幽默曲》因脍炙人口的旋律被广为流传。本文以《幽默曲》为例,探讨在音乐本体（乐谱）不变的情况下,音乐表现形式与表现内容之间的关联。     

石峁皇城台与美索不达米亚“塔庙”对比分析

陕西神木石峁城址近年来的考古发掘,取得了震惊世界的重大发现,颠覆了学术界对于河套地区龙山时代文明与国家起源的传统认识①。石峁城址总面积约400万平方米,内城190万平方米,外城约210万平方米。皇城台位于内城的中部偏西侧,坐落在一处独立的山峁上,顶部平坦开阔,南、西、北三面沟壑环绕,仅东南部有山体马鞍部与外界相连,封闭性与防御性显而易见。     

The accuracy of computing ionospheric radio-wave scintillation by the thin-phase-screen approximation

In the calculation of the diffraction effects produced by a thick medium containing spatial irregularities in refractive index, a commonly-used approximate method is to represent the thick medium by a thin phase-changing screen. It is sometimes assumed that this gives a poor approximation when the medium is thick enough to produce appreciable amplitude fluctuations in the emergent wave. It is shown here that under practical ionospheric conditions the thin screen method still gives results in very good agreement with those obtained from a single-scattering calculation, even at gigahertz frequencies.     

The role of acoustic gravity waves in the generation of spread-F and ionospheric scintillation

In the aggregate, acoustic gravity waves in the F-region constitute a spectrum of geophysical noise extending from the frequencies involved in diurnal variations up to the Brunt-Väisälä buoyancy frequency. They drive a roughly uniform power spectrum of travelling ionospheric disturbances (TIDs) with vertical scales of the order of the atmospheric scale height H and with horizontal scales extending from the radius of the Earth down to H. It has been known since the 1950s that this permits multiple normals onto the F-region from an ionosonde, thereby creating the multiple-trace type of spread F on ionograms. At shorter scales the spectrum of TIDs decreases in strength and, below the mean free path of the neutral atmosphere, creates a spectrum of plasma turbulence aligned along the Earth's magnetic field. Progressively shorter scales are responsible for phase scintillation, for amplitude scintillation and for blur-type spread F on ionograms. A weak extension of the spectrum to scales less than the ion gyroradius is responsible for spread F and transequatorial propagation in the VHF band. Under evening conditions in equatorial regions a band of TIDs with wavelengths of the order of 600 km can, at times, have a phase velocity that matches the drift velocity of the plasma (Röttger 1978). This band of TIDs is then amplified until it breaks (Klostermeyer 1978). The associated explosive increase in plasma turbulence creates the plume phenomenon discovered by Woodmn and La Hoz (1976).     

东下冯文化与二里头文化比较及相关问题研究

文章通过对东下冯文化与二里头文化遗存进行比较研究,并结合文献及专家学者的研究成果,得出二者之间在文化面貌上虽有较多的共同因素,但差异较大,属于不同的考古学文化。东下冯文化的形成受到了二里头文化的较大影响,但自始至终保持自身的独特文化面貌。二里头文化属于夏人文化,东下冯文化似不属于夏人的文化,可能为夏代唐人的遗存。东下冯文化与二里头文化似乎为联盟的关系。     

先秦中国和古代希腊文明起源的地理环境之比较

文明起源的地理环境可以分为整体地理环境和中心地理环境。前者指文明整体能力所及的极限地理范围,后者指文明主体的主要活动区域。从这两个角度分别进行比较,将有助于解释希腊和中国文明侧重于陆地或是海洋发展的原因。     

民航业与旅游业市场营销方式比较

民航业与旅游业存在很强的行业相关性和市场定位方式的相似性。本通过两行业在市场营销方式上的比较,对正在实施企业化经营、市场化运作改革的民航企业提供很好的借鉴。     

中俄两国早期工业化道路比较

19世纪50、60年代,在资本主义生产关系尚未占优势的情况下,俄中两国先后启动了工业化。至第一次世界大战前,俄国工业化成就斐然,成为世界五大工业强国之一,而中国工业化成效甚微,与俄国存在着巨大的差距。造成如此结局的原因也许有很多,但两国工业化道路的差异应是其中的重要因素。中国工业化以军事工业起步,俄国以纺织工业为先导;中国政府不扶植私人工业发展,对私人企业横加摧残盘剥,俄国积极扶植私人企业发展,且利用外资,官民并举;中国政府不重视铁路建设,俄国以铁路建设为龙头,带动其他各业发展;中国政治改革滞后,工业化与政治近代化脱节,俄国政治改革紧随其后,与工业化紧密相联,产生了良好的促进作用。