Phase and amplitude scintillations due to electrojet irregularities

Features of the power spectra of weak amplitude and phase scintillations on a VHF signal, transmitted from a geostationary satellite and recorded at an equatorial station, are found to be in good agreement with theory. Irregularity drift speeds transverse to the signal path were extracted from the first few pronounced Fresnel minima in the power spectra. For some data intervals, a low frequency peak, associated with an irregularity wavelength greater than the Fresnel dimension, could be identified in the phase spectrum. The dominant wavelength of the large scale waves is found to be ≳ 1.5km.     

spread-F ionospheric irregularities and their relationship to stable auroral red arcs at magnetic mid-latitudes

The signature of the stable auroral red arc (SAR arc) as it appears on ionograms is described. The key features are a very significant increase in the amount of spread-F and a reduction in the maximum plasma density compared with regions just equatorward and poleward of the SAR arc Identification of the SAR arc signature is made by using complementary data from the global auroral imaging instrument on board the Dynamics Explorer-1 satellite.At sunspot minimum there is a positive correlation between the occurrence of spread-F on ionograms from Argentine Islands, Antarctica (65°S, 64°W; L = 2.3) and magnetic activity. In contrast, at sunspot maximum there is a weak negative correlation when the K magnetic index is less than 6. but a significant increase in spread-F occurrence at K ⩾ 6. Detailed study of ionograms shows that there are two distinct regions where considerable spread-F is observed. These are the region where SAR arcs occur and the poleward edge of the mid-latitude ionospheric trough. They are separated by a region associated with the trough minimum, where comparatively little spread-F is seen. It is suggested that the movement of these features to lower latitudes with increasing magnetic and solar activity can explain the lack of correspondence between variations of spread-F occurrence as a function of magnetic activity at sunspot maximum compared with that at sunspot minimum at Argentine Islands.     

Observations of random and quasi-periodic scintillations at southern mid-latitudes over a solar cycle

An extended period (1973–1985) of recording of random and Fresnel type quasi-periodic (QP) scintillations in southern mid-latitudes, using satellite beacon transmissions at a frequency of 150 MHz, has provided some new information on the morphology of scintillation-producing irregularities.It has become evident that a pronounced daytime increase of the random type of scintillations in the southern winter (at 1200–1600 LT) occurs throughout the solar cycle and becomes a distinct daytime maximum during the years of sunspot minimum. Scintillations are most intense in the pre-midnight period in the southern summer (2000–2400 LT). There is a gradual decline in scintillation activity by about 40% from the period of sunspot maximum to the period of sunspot minimum. It appears that a specific type of sporadic-E, so-called constant height Es (Esc), is responsible for daytime scintillation activity in winter. Night-time scintillations are strongly correlated with the presence of the range-spread type of spread-F, but not so with the frequency-spread type.There are two peaks in the occurrence of QP scintillations, predominantly in the southern summer: in the late morning (0800–1000 LT) and in the pre-midnight period (2000–2200 LT). The daytime QP scintillations occur mainly polewards of the station, whereas the night-time scintillations are recorded predominantly equatorwards. There is a distinct increase in the occurrence number of QP scintillations with a decrease in the sunspot number.     

Generation of stationary irregularities due to heating of the high-latitude ionospheric E-region

The nonlinear equations describing the generation of artificial irregularities in the E-region of the high-latitude ionosphere due to Joule electron heating under the action of high-power radio waves are derived, including the low-frequency nonlinearities, and investigated in the three-wave approximation. Expressions for the stationary spectra of the short wavelength two-stream and long wavelength gradient-drift and current-convective irregularities are presented. The typical saturation amplitudes of the density fluctuations are obtained.     

Large-scale irregularities of electron concentration in the southern magnetic anomaly area according to Intercosmos 19 satellite data

Using Intercosmos 19 satellite topside sounding data, a type of complex ionogram for which the lowest frequency of the radio-wave which has passed through the ionosphere is smaller than the greatest frequency of the radio-wave reflected from the ionosphere is considered. (Under normal conditions these frequencies are identically equal.) A mechanism is suggested by which radio-waves transmitted by the satellite propagate over 3000 km in the topside ionosphere in the presence of inclined large-scale plasma structures, which can explain the main features of such ionograms.The space-time distribution of this phenomenon on a global scale is analysed. It is shown that it manifests itself mainly in the local winter, in the daytime and in the Southern Hemisphere. It is hypothesized that these large-scale irregularities are formed in the vicinity of the South Atlantic magnetic anomaly and then move westward.     

The effects of neutral winds on the propagation of medium-scale atmospheric gravity waves at mid-latitudes

The influence of neutral winds on the propagation of medium-scale atmospheric gravity waves at mid-latitudes is investigated. A 3-dimensional neutral wind model is developed and used together with an atmospheric model in a gravity-wave ray-tracing analysis. It is demonstrated that the thermospheric wind can act as a filter for waves travelling at unfavorable angles to the mean flow, via the mechanisms of reflection and critical coupling. This wind filtering action rotates clockwise diurnally through 360° in the northern hemisphere. Observational evidence is presented which supports these predictions. Extensive modelling indicates that (a) faster and longer period waves are least affected by the neutral winds and (b) fixed-height (e.g. HF Doppler) observations of medium scale gravity waves is only likely to be possible for waves generated locally (within 500–1000 km). Waves generated at greater distances are probably dissipated before reaching the observation region.     

Experimental investigation of carbon dioxide trapping due to capillary retention in saline aquifers

Capillary trapping is a physical mechanism by which carbon dioxide (CO₂) is naturally immobilized in the pore spaces of aquifer rocks during geologic carbon sequestration operations, and thus a key aspect of estimating geologic storage potential. Here, we studied capillary trapping of supercritical carbon dioxide (scCO₂), and the effect of initial scCO₂ saturation and flow rate on the storage/trapping potential of Berea sandstone. We performed two‐phase, scCO₂‐brine displacements in two samples, each subject to four sequential drainage–imbibition core‐flooding cycles to quantify end‐point saturations of scCO₂ with the aid of micro‐ and macro‐computed tomography imaging. From these experiments, we found that between 51% and 75% of the initial CO₂ injected can be left behind after the brine injection. We also observed that the initial scCO₂ saturation influenced the residual scCO₂ saturation to a greater extent than the rate of brine injection under the experimental conditions examined. In spite of differences in the experimental conditions tested, as well as those reported in the literature, initial and residual saturations were found to follow a consistent relationship.     

Ion-cyclotron noise excitation in the topside ionosphere according to observations at the Intercosmos-14 satellite

A band-limited ELF emission having very distinct upper as well as lower cutoff frequencies, most probably determined by local parameters of the plasma, were discovered by the VLF experiment on board the Intercosmos-14 satellite (apogee height 1707 km, perigee 345 km; inclination 74°). This type of noise was observed in the day-time, at middle and low latitudes, at altitudes 600 km< h < 1400 km. The very clear case observed on March 5, 1976 is discussed in detail and arguments are listed that this ELF emission is locally generated ion-cyclotron noise. Calculations of the growth of the proton cyclotron resonance instability show that the growth may be positive if the loss cone angle of the energetic protons is sufficiently great. This condition is fulfilled at low altitudes near the mirror points. Depending on the width of the distribution function of energetic protons the growth of the Instability may be positive in the whole frequency band of the proton branch of ion-cyclotron waves or only in certain parts of that frequency band.     

Application of Landsat satellite imagery to monitor land‐cover changes at the Athabasca Oil Sands,Alberta, Canada

A major advantage of satellite remote sensing is that the imagery acquired provides a synoptic view of the landscape. Thus, repeat coverage by the satellite on a regular basis permits the detection of changes in land‐cover over time. This study demonstrates the application of remote sensing technology to the monitoring of mining activities at the Athabasca Oil Sands region of Alberta, Canada. First, we describe the techniques used to match a time sequence of Landsat imagery, both spatially and spectrally, to ensure that the spectral changes through time are due to land‐cover variations. A series of spectral trajectories were then extracted to assess changes in land‐cover through time. Secondly, a land‐cover classification was produced from the baseline 1984 imagery and, using historic and future mine extents, the classification was analyzed to determine the proportion of each land‐cover type affected through development. Results of the analysis indicate that since 1984 there has been a larger reduction in mixedwood dense and broadleaf vegetation classes than mixedwood sparse or dense conifer stands in the area. Based on the delineations of mine‐site activity, the area of woodland and wetland habitat subject to development has increased from approximately 2,520 hectare (ha) in 1984 to 32,930 ha in 2005.     

New datings of Amudian layers at Qesem Cave (Israel): results of TL applied to burnt flints and ESR/U-series to teeth

Because only a few radiometric data are actually available, the chronology of the Amudian – a blade-dominated industry of the Acheulo-Yabrudian Cultural Complex (AYCC) of the late Lower Paleolithic in the Levant – is still not well constrained. Qesem Cave offers the opportunity to enhance our knowledge of the chronological position of this industry which is unique to the Levant. The Qesem Amudian bearing layers yielded also human remains showing affinities with those of modern populations recovered in the Middle Paleolithic sites of Skhul and Qafzeh. The results presented here are the first attempt to apply the TL and ESR/U-series dating methods at this site and these methods yielded results which are generally in agreement. They support a time interval of hominid-bearing occupation of the areas of the cave where Amudian lithic artifacts were recovered during MIS 8 and likely 9 for the Deep Pit Area, and during MIS 8 and possibly 7 for the Upper part of the sequence (Square K/10 and the Eastern Microfauna-Bearing Area). An older occupation of the cave is also conceivable on the base of two dating results (MIS 11).     

元末"青巾军"入蜀考——兼释重庆《玄宫之碑》

元朝末年,当西系红巾军明玉珍部从湖北举兵入川,占领重庆不久,东系红巾军的一支余部,也在李喜喜的带领下进入蜀境,史称“青巾军”,或“青军”。本文依据历史文献和明玉珍陵墓中发现的《玄宫之碑》,考证出青巾军入蜀的时间,不是旧籍所载的至正十八年,而是十七年;明玉珍在至正十八年、十九年出兵攻打的对象,不是元朝官军,而是青巾军。弄清青巾军入蜀后的踪迹及表现,有助于揭开明玉珍据蜀称帝前一段鲜为人知的经历,澄清长期混沌的元末四川政治军事格局。     

Experimental Study on Damage Behavior of Reinforced Concrete Shear Walls Subjected to Cyclic Loads

Previous experimental research on shear walls has mainly focused on load carrying capacity, deformation, or hysteretic characteristics, with relatively little attention paid to individual damage states and their corresponding responses during the entire loading process until failure. The damage behavior of seven reinforced concrete shear wall specimens subjected to cyclic loading is presented in this study. The effects of the axial load ratio, transverse reinforcement ratio of confining boundary elements, and cross-section shape on damage characteristics, ductility, shear deformation, and crack width of the specimens were analyzed comprehensively.     

On the effect of a beam of energetic electrons on the whistler-mode growth rate due to gyroresonant interactions

The dispersion relation for whistler-mode waves in the presence of an idealised beam of energetic electrons that is moving either parallel or antiparallel to the gyroresonant electrons is analysed. The dependence of the real part of the dispersion relation on the velocity of the beam is shown to be responsible for an additional growth rate, for the beam antiparallel to the gyroresonant electrons, or for a reduced growth rate for the parallel condition. The effect could be important in explaining some features of VLF emissions such as hiss which propagate through the magnetosphere in the opposite direction to the gyroresonant electrons.     

从武穴主和到五原誓师——试述孙中山对冯玉祥的影响

孙中山是伟大的革命先行。他推翻了封建帝制,催生了中华民国,使民主共和的思想深入人心。他创立的以“民族、民权、民生”为核心的三民主义理论及“联俄、联共、扶助农工”三大政策,引导、影响了整整几代人投身民族复兴、献身国民革命。冯玉祥即是其中的一员。本试图通过对冯玉祥在“武穴主和”至五原誓师这一段经历、思想的剖析,说明冯玉祥的每一步革命行动,都是在孙中先生人格魅力的感召下产生的,都是在三民主义理论的影响下进行的,是孙中先生引导冯玉祥脱离了北洋军阀的阵营,投身于国民节命。     

利用X-CT和数字图像相关法对遗址反复干湿导致的劣化机制进行基础研究

此研究是以石材和土壤所构成的考古遗址为主要研究对象。在确定石材和土壤的渗透性下,通过数字体积相关法(DVC)和数字图像相关法(DIC)对干湿劣化的环境条件进行定量的评估,并提出控制这种劣化发生的环境调整方法。 为了收集基本数据,通过DIC及X射线成像技术分析从湿润到干燥的过程中丰浦硅砂的位移量实验,并在实验中,使用DIC计算样品在收缩应力下的变形分布。此外,本次实验以铁粉作为示踪剂添加至样品中,并以铁粉作为参考点计算丰浦硅砂特定范围的移动量,借此评估铁粉作为示踪剂的适用性及精确性。结果表明,通过拍摄干燥前后样品的X射线图像,并用DIC进行分析可以计算出干燥前后的变形分布。在样品中添加示踪剂也被发现有助于分析样品局部区域的移动方向及移动量。因此通过此基本数据的检验,相信将来通过X射线计算机断层扫描(X-CT)及数字体积相关法(DVC)的应用,可以用来阐明反复干湿风化的劣化机制。     

Case Shot: An Interim Report on Experimental firing and Analysis to Interpret Early Modern Battlefield Assemblages

Abstract

This article reports on the first stage of a programme of ongoing experimental research to reproduce the firing of artillery case shot of the 17th century, to recover the distribution of the bullets fired, and to analyse their character, to assist in interpretation of case shot distributions from surveys of 17th century battlefields.     

清代中俄恰克图边境贸易研究的新收获

清代中俄关系的研究 ,由于边界问题的争执 ,一直受到两国政界与学界的重视 ,中国在上世纪特别是七八十年代就对中俄关系有过相当深入的研究 ,比起清代中国与其他国家关系的研究来说 ,中俄关系是研究最为深入的领域之一。不过就清代中俄关系来说 ,边界问题与政治关系探讨较多 ,相对来说贸易与经济的往来研究较为薄弱。清代中俄贸易主要是在恰克图 ,中俄恰克图贸易事关清代经济贸易、外交政策以及满蒙关系等问题 ,相当重要。学术界就此进行了一些探讨 ,尚需要更深入、全面的研究。南开大学历史学院米镇波先生的新著《清代中俄恰克图边境贸易》…