Structure of tangential discontinuities at the magnetopause: the nose of the magnetopause

Observations show that the magnetopause can sometimes be represented as a tangential discontinuity in the magnetic field. In this paper, we use a theoretical model of steady-state tangential discontinuities to analyze the microscale structure of the nose of the magnetopause. The boundary layer is described in terms of a kinetic theory based on the Vlasov-Maxwell equations for the charged particles and electromagnetic fields. The general model represents the magnetosheath and magnetospheric sides as distinct regions with anisotropic displaced Maxwellian equilibrium states and allows the presence of a multi-component plasma whose ionic species have different concentrations, temperatures, anisotropies, etc. For the nose region, we assume for simplicity an isotropic Maxwellian Hydrogen plasma. Transition profiles for the magnetic field, electric potential, electric field, charge separation and density are illustrated. The variations of the magnetic field direction in the discontinuity plane show a great variety of rotational structures in accordance with recent observations. The electric potential difference is seen to control the thickness of the magnetopause. The classical Ferraro boundary layer where the ion current is neglected is recovered when the ion distribution function is a Maxwellian everywhere in the transition. When there is no electric potential difference across the sheath we find again an ‘electron-dominated’ boundary layer where the electric current is mainly carried by the electrons. However, computations of drift and thermal velocities indicate that a two-stream instability occurs in the centre of these sheaths. The result will be a broadening of the layer by wave-particle interactions leading to an ‘ion-dominated’ transition.     

Recent techniques of observations and results from the magnetopause regions

The problems encountered in making measurements in the magnetopause regions are caused mainly by the variability of the phenomena and the space/time ambiguity of most satellite observations. The physical quantities of interest for magnetopause studies are listed, together with the range of values observed. As an example of a satellite equipped for magnetopause observations the HEOS-2 payload is described. Data mainly from this and from the OGO-5 spacecraft are used to bring out characteristic features of the magnetopause and show how the experimental problems are attacked.     

Night-time ionospheric scintillations at the magnetic equator

The nocturnal and seasonal variations of equatorial ionospheric scintillations are presented. Scintillations are classified into two classes, namely, class I and class II depending on their fading rates and association with bottomside spread-F. Power spectra and frequency indices for class I and class II scintillations are presented and their theoretical implications are discussed.     

Ionospheric absorption at the magnetic equator using the A1 technique

A₁ absorption data on four operating frequencies, 1.8, 2.0, 2.2 and 2.5 MHz over a period of two years (1972–74) at Trivandrum (dip 0.6°S, geograph. lat. 8.6°N, long. 76.9°E) has been analysed to study its diurnal, day to day, long term and frequency variations. An empirical relation has been established between noon absorption and solar X-ray and 10.7 cm fluxes. Using this relation, the seasonal cosχ index has been evaluated. The deviation of the estimated absorption using this empirical relation from the observed absorption is found to be less than 10%.     

Vertical plasma drifts in the post-sunset F-region at the magnetic equator

HF doppler observations of vertical plasma drifts in the post-sunset equatorial F-region at Trivandrum (dip 0.9°S), conducted over a range of solar and geomagnetic conditions, are presented. The observations show that under magnetically quiet conditions, the characteristic post-sunset enhancement in the vertical plasma drift is quite sensitive to solar activity; the peak velocity drops by about a factor of 3 as the solar flux index (S_10.7) changes from about 125 to 70. It is found that the drift velocity enhancement has strong magnetic activity dependence only during high solar activity; the drift velocity drops by more than a factor of 2 from quiet to moderate activity, but builds back to the quiet day level for high magnetic activity. The occurrence of equatorial spread-F (ESF) is seen to be closely linked to the post-sunset enhancement in the vertical drift velocity, both showing essentially the same dependence on solar and magnetic activities. A comparison with Jicamarca observations shows that while the gross characteristics of the drift velocity pattern are about the same for the two stations, there are significant differences in the detailed variations, particularly for magnetically disturbed conditions.     

河南平粮台和郝家台遗址龙山文化的颅骨形态学分析

平粮台、郝家台龙山文化遗址是近年来豫东、豫南地区重要的考古发现,本文对两处遗址出土的龙山文化颅骨标本进行了人种学研究.平粮台组颅骨形态与先秦时期的古中原类型居民一致,而郝家台组与古中原类型、古华北类型和古西北类型均有较多相似之处.人骨的碳氮同位素分析显示,相对于平粮台遗址单一的粟作农业,郝家台粟作与稻作农业的并存揭示了郝家台龙山遗址可能存在人群的文化交流,这与郝家台组颅骨多种体质类型的混合特征相吻合.     

Scintillation at high latitudes during winter magnetic storms

Scintillation observations are described which were made at Kiruna in northern Sweden during three magnetic storm periods in the winter of 1984–1985. The results were obtained using transmissions from the multisatellite NNSS system, so that it has been possible to chart the development of scintillation activity over some 20° of geomagnetic latitude as a function of time for several days throughout each storm. A region of strong scintillation at the highest latitudes near magnetic noon is a common feature on all but the quietest days. This feature, probably associated with soft particle precipitation into the cusp, shows an abrupt boundary which moves equatorwards as the disturbance develops. In the magnetic midnight sector two latitudinally separate zones of scintillation are found, patchy at high latitudes although more sustained in the auroral zone. An absence of auroral scintillations around midnight UT can be followed by prolonged intense scintillation activity at auroral latitudes during the early morning hours on some disturbed days.     

Post-sunset F-region vertical velocity variations at magnetic equator

The vertical drift velocity of the F-region in the post-sunset period at the magnetic equatorial station Trivandrum has been studied using a HF phase path sounder. The study revealed the presence of quasi-periodic fluctuations with periods in the range 4 30 min superposed on a steady vertical motion as a regular feature of the equatorial F-region in the post-sunset period. The fluctuations in the vertical velocity arc attributed to the east west electric field fluctuations generated by internal atmospheric gravity waves. The vertical velocity fluctuations can provide the necessary seed perturbations for the growth of equatorial spread-F irregularities.     

The diffusion of the plasma column inclined at an angle to the magnetic field

Using a two-dimensional model a study is made of the dynamics of plasma irregularities, embedded in a weakly covered plasma, containing an electric field transverse to the magnetic field. The analysis shows that due to field aligned and Hall plasma drift, the irregularities are divided into two parts, one of which is stretched along the magnetic field.     

文化形态史学析论

文化形态史学对 1 9世纪的“科学”史学展开了深刻的批判 ,同时也对2 0世纪的史学有开启之功 ,具体表现在四个方面 :从显在的欧洲中心史观到隐蔽的欧洲中心史观、从局域主义到整体主义、从“脱魅”到“复魅”、从单线时间观到多元时间观     

Simultaneous observations of E and F region electric field fluctuations at the magnetic equator

Simultaneous daytime observations of E region horizontal irregularity drift velocities in the equatorial electrojet and F region vertical plasma drifts were made on a few magnetically quiet days at the magnetic equatorial station of Trivandrum (dip 0.5°N). Measurements of the electrojet irregularity velocities by VHF backscatter radar and the F region vertical plasma drifts by HF Doppier radar are used to deduce the daytime East-West electric fields in the E and F regions, respectively. The fluctuating components of the electric fields are separated and subjected to power spectral analysis. The E and F region electric field fluctuations are found to be well correlated; the estimated correlation coefficient is in the range of 0.52–0.8. The fluctuation amplitudes are of the order of 15% over the background for the E region and 25% for the F region. The spectral analysis reveals dominant components in the range of 30–90 min with F region components stronger than those of the E region by a factor of about 1.5 on the average. The F region electric fields during daytime being coupled from the low latitude E region, the good correlation observed between the E and F region perturbations suggests that the electric fields in the E region at low and equatorial latitudes are coherent for the temporal scales of the order of few tens of minutes. The spectral characteristics are such that the commonly occurring medium scale gravity waves could possibly be the source for the observed fluctuations in the E and F region electric fields.     

苏家村遗址烧土样品的过火温度研究

烧土制品作为最早的人工建筑材料,使人类的居住环境得到了根本性的改善。然而,学界关于烧土建筑的成因存在人为烘烤处理、缘自火焚、废弃习俗等多种观点。通过科技手段研究烧土制品的过火温度,有助于科学分析烧土建筑的成因,探讨与之相关的建筑工艺,丰富史前建筑史研究。磁学研究表明,考古遗址中的土壤及其他沉积物在受热后新生成了磁铁矿、磁赤铁矿等强磁性矿物导致磁性显著增强,且矿物成分和磁性几乎不会再发生变化;但当重烧的温度接近或大于原始烧成温度时,样品中原始矿物的破坏或新矿物的生成,会引起矿物磁性的改变。基于这一原理,实验室内分析受热黏土的磁化率随再加热温度的变化特征,可反映烧土制品的过火温度。苏家村遗址是大汶口文化晚期至龙山文化中期早段一处重要的聚落遗址,遗址中第5层为厚约20～40 cm的红烧土层且覆盖整个遗址,推测为房屋倒塌造成的建筑垃圾堆积层或人为堆积层,出土大量烧土块。本研究利用X射线衍射分析法、X射线荧光光谱分析法和磁化率法等对苏家村遗址出土的烧土样品开展了组成及构造特征和样品的过火温度的综合分析。结果表明,苏家村遗址烧土样品中的白灰层中人为地添加了白色陶土原料,土层中有意地添加了植物残骸作...     

青海羌人的迁徙与后来多民族的融合

我省的民族史表明,"从古到今各个民族的形成几乎都是多源多流的,源流之间又有着复杂的交错联系,有些是同源异流,有些是异源合流,有些则又是源流交叉。要孤立地搞清一个民族的族源及其发展历史,几乎是不可能的"。     

The effect of induced currents in the sea on magnetic bays observed at a coastal observatory

It is widely accepted that return currents from the auroral electrojet are responsible for the magnetic bays in the D component. The different directions of the return currents, at either end of the electrojet, means that the sign of the D bay should change as the station moves from east to west of the central meridian of the electrojet. However, there is confusion as to whether this change occurs, giving rise to different models for the substorm current system. The possible effect of induced currents on magnetic bays is shown to be significant and should be examined for each observatory before using their magnetic bays to infer substorm current systems.An analysis of magnetic bays at Halley Bay (75°S, 27°W), a coastal site in Antarctica, shows that a change in the sign of D bays does not occur. It is shown that induced currents flowing in the sea, parallel to the coast, would have an effect that is consistent with the observations.     

A rock magnetic record of Pleistocene rainfall variations at the Palaeolithic site of Attirampakkam,Southeastern India

Attirampakkam, an open-air stratified Palaeolithic site in southeastern India is the focus of ongoing studies to investigate the nature of Lower and Middle Palaeolithic occupation in relation to changing Pleistocene environments. The paucity of faunal or palaeobotanical remains at the site required the use of rock magnetic properties (χ_lf, χ_fd, χ_fd %, χ_ARM, SIRM, χ_ARM/SIRM, SIRM/χ_lf, χ_ARM/χ_lf, χ_ARM/χ_fd, S-ratio, HIRM and HIRM/IRM_300mT) as proxies for deciphering the palaeoenvironments and palaeoclimates of the region. Rock magnetic data from stratified deposits within excavated trenches show that the bulk of the sedimentation was intermittent with no subaerial exposure of sediments for long periods, and points to fluctuating wetter and drier climates associated with the Acheulian to Late Middle Palaeolithic levels. There is a general trend towards a wetter climate from Layer 5 upwards. Layer 7 offers evidence of bacterial magnetite (χ_ARM/χ_lf > 40 and χ_ARM/χ_fd > 1000), suggesting the onset of micro-anaerobic environments as a result of floods. Greigite is indicated in Layer 5 (SIRM/χ_lf > 30 × 10³ A m^?1), which indicates a reducing environment. Layer 2 represents an arid climate (higher proportion of haematite and a coarser magnetic grain size). Layer 1a again is indicative of an arid climate (presence of calcrete, magnetically “hard” minerals and coarser magnetic grain size). Results indicate that the southeast coast of India experienced a mostly dry tropical climate during the Pleistocene. The detected occurrence of a few notably more arid intervals did not disrupt occupation of the site by successive groups of hominins.     

Some peculiarities of altitudinal distribution of atomic oxygen at low latitudes during magnetic storms

Several storms were examined during the period of the ESRO-4 mission to study the altitudinal behaviour of atomic oxygen and molecular nitrogen at low latitudes. A special method of data reduction was applied to distinguish composition changes due to thermal expansion and those which resulted from some non-thermal process. It was shown that in the majority of cases studied there exists some latitudinal interval where changes of the N₂/O ratio from quiet to storm days are small compared with that observed in the purely thermal case. This latitudinal interval was found to be displaced to the winter hemisphere (not always across the equator) during solstice cases and the corresponding altitudinal interval was sometimes equal to the whole height range covered by the satellite. The effective temperature of atomic oxygen turned out to be greater than that deduced from the altitudinal distribution of N₂. This implies that there exists a non-thermal component of the [O] increase on a storm day at low latitudes and thus [O] is distributed in a non-barometric way. A possible mechanism responsible for this behaviour is downwelling due to the disturbed global thermospheric circulation.     

青铜器锈蚀结构组成及形态的比较研究

采用X射线衍射(XRD)、扫描电镜(SEM)、X射线电子能谱(EDS)和金相显微镜(OM)等方法,分析比较了染有“粉状锈”与未染“粉状锈”的典型青铜残片的锈蚀产物的矿物组成、腐蚀层分层结构及金相组织。结果发现,未染有“粉状锈”的青铜样品腐蚀层一般分为二层,外层是二价铜化合物,合金组织中未见α (α δ)组织,锈蚀产物中不含碱式氯化铜;而染有“粉状锈”的青铜样品都含有碱式氯化铜,其断面腐蚀层分三至四层,且每层锈体的结构和元素组成各不相同,在靠近合金基体层的锈层中发现了大量的CuCl存在。结果表明,青铜文物表面锈蚀覆盖层的致密性、空气中的湿度及锈层中CuCl层状分布的存在,是青铜器表面“粉状锈”形成和发展的根本原因。     

Mr. Dithers Comes to Dinner: Telework and the merging of women's work and home domains in Canada

Studies of home-based telework by women yield mixed results regarding the usefulness of telework in facilitating work–life balance. Most research on the social impacts of home-based telework focuses on workers—employees or self-employed—who deliberately choose that alternative work arrangement. Labour force analysts, however, predict an increase in employer-initiated teleworking. As a case study of the workforce of one large, financial-sector firm in Canada, this article considers the conditions of employment of involuntary teleworkers, those required by their employer to work full-time from a home office. In-depth interviews were co nducted with a sample of 18 female teleworkers working for the case study firm in a professional occupation. Study participants described the advantages and disadvantages of working from home, particularly with regard to spatial and social aspects of locating work in a home setting. The gendered nature of their jobs, and the caring and supportive functions they provide both through their employment and their household responsibilities are seen to support the relocation of their jobs from office to their homes. In many jurisdictions, telework is promoted as a means of giving women more flexibility to balance their paid work with their household responsibilities; the article highlights some of the contradictions involved in moving the workplace into women's homes.     

The influence of sunspot number and magnetic activity on the diurnal variation of the geomagnetic field at mid to high latitudes

The variations of the diurnal range of the geomagnetic field with sunspot number and with magnetic activity was studied at mid and high latitude stations in the northern hemisphere at different seasons. The effect of increasing sunspot number is small at lower latitudes and increases with geomagnetic latitude, while the effect of increasing magnetic activity is to increase the range at all latitudes, very greatly at the higher geomagnetic latitudes.