On the origin of UHF atmospherics

Assuming lightning discharge as a plasma it is shown that Bremsstrahlung is a possible source of UHF emissions. The computed power gives a flat frequency response with a magnitude of about 10⁻¹⁵ W m⁻² Hz⁻¹ at a distance of 1 km from the base of the channel. While partially ionized channels like stepped leader, dart leader and K-changes are the strong source of UHF emissions, the radiation from the return stroke is negligible. Our theoretical results are in excellent agreement with the experimental observations of Book and Kitagawa (1964) and Kosarevet al. (1969, 1970).     

The equatorial electrojet and the day-to-day variability of Sq

The day-to-day variability of Sq(H) at equatorial stations has been studied, using the correlation between daily ranges for the IQSY at a large number of pairs of stations. It is found that the daily ranges at stations under the equatorial electrojet are significantly less well correlated with those at other equatorial stations than is the case for pairs of equatorial stations not involving an electrojet station, for comparable distances of separation of the pairs of stations.     

内战以后美国南部的“农业阶梯”问题

农业阶梯理论以土地所有权的有无和程度为衡量标准 ,意在揭示人们从租佃农向自耕农的奋斗历程。本文在考察了内战以后美国南部种植园地区租佃农经济地位的变动状况之后得出结论 :南部不但不存在“农业阶梯” ,反而存在一种“反阶梯”趋势 ,这种趋势根源于南部自身的社会经济 ,而其根本推动力是大西洋经济圈资本主义经济的发展。     

The nocturnal intermediate layer over South Georgia

Detailed analyses of ionograms from South Georgia (54°S, 37°W; L = 1.9) show that a nocturnal intermediate layer is frequently seen between the E- and F-regions in the height range 130–180 km. The occurrence of the intermediate layer is almost totally restricted to the winter months and between the local hours of 1930 and 2300. The intermediate layer event is characterized by a prior downward movement of the F-layer, followed by the formation of the intermediate layer and its subsequent drift downwards to about 140 km. Initially, the layer is thick (~ 10–20 km), but gradually thins as it evolves. The occurrence of the intermediate layer appears to be independent of the level of magnetic activity. Observations of intermediate layers from other localities, which are briefly reviewed, are compared with those made at South Georgia. Some similarities and differences are identified.Mechanisms which account for the formation of the intermediate layer at South Georgia are considered, It is shown that the main features of the diurnal and seasonal variations of occurrence can be adequately explained by the theory of convergence of ionization driven by the solar semi-diurnal tidal winds. Some limitations of this theory are discussed, as it cannot account for all the features seen at this southern midlatitude observatory.     

美国史学界有关奴隶制起源的争论

美国的历史学在有关美国奴隶制的起源问题上的争论断断续续地已经进行了一个多世纪。争论的主要问题包括英属北美殖民地黑人奴隶制确立的时间、黑人奴隶制确立的原因以及奴隶制与种族主义的关系。鉴于这个问题涉及问题的广泛性,澄清美国奴隶制的起源,对于理解美国殖民地初期的种族关系乃至当代美国的种族问题具有重要的学术价值和现实意义。本的主要目的在于,对争论各方的主要观点进行梳理和比较,将百年来美国学围绕这一问题的争论概况介绍给国内的学界,以期促进中国学对这一问题更为深入的研究。     

The Canadian Rebellion,the American South,and Slavery

ABSTRACT

In the past few decades, thanks in large part to the work of several historians that appears in my edited collection, Revolutions Across Borders: Jacksonian America and the Canadian Rebellion (2019), there is a growing trend to consider the Canadian Rebellion within an American historical and historiographical context. Despite this exciting new research, most studies on the Rebellion and the United States continue to focus on the northern borderland. However, the Canadian Rebellion was a significant event that gained attention all over the United States, including the American South. Similar to the North, the American South was also invested in the outcome of the Rebellion. This was due to one reason: slavery. By specifically focusing on the American South and, more importantly, its influence on American foreign policy during the period, I want to encourage historians to take a more definitive stance; that slavery—just like the Panic of 1837, the Anglo-American rapprochement of thepost-War-of-1812 period, or the fear of British retaliation—played a major role in the United States Government’s official opposition to the Rebellion.     

The day-to-day variability of Sq in geomagnetically conjugate areas

The correlation of daily ranges of Sq(H) has been found to be slightly but significantly greater for pairs of stations which are approximately at magnetically conjugate locations than for other, non-conjugate pairs of similar distance of separation. It is suggested that the effect is due to field-aligned currents.     

The vernal-autumnal asymmetry in the seasonal variation of geomagnetic activity

In intervals in which the polarity of the main solar dipole field is stabilized, a 12 month wave occurs in geomagnetic activity (indices aa, Ap, Dst) with its maximum in one of the equinoctial periods. Whether the vernal or the autumnal maximum is greater depends on the polarity of the main solar dipole; the existence of the wave may be explained by the north-south asymmetry in the main solar dipole field. The results favour the southward component of the interplanetary magnetic field as the decisive factor for geomagnetic activity.     

新南方起源时期美国南方城市的发展和城市生活的变迁

新南方起源时期南方城市有显著发展,数量明显增加并初步完成城市功能的转换和城市设施的更新,为以后新南方综合性大都市的出现打下基础。但与同时期的北方城市相比,南方城市规模小,对农作物,工业原料和铁路的依赖严重,乡土气息浓厚。城市社会形态特征表现为种族隔离加剧,城市成为种族冲突的温床,一个自主自立的黑人社区形成;新老城市社会氛围差异大,老城市的相对静态与新兴城市的动态形成鲜明对照,南方社会重心不仅从农村移到城市,而且从老城市移到新兴城市。新兴城市逐渐成为南方城市发展的亮点和方向。