Experimental results on satellite scintillations due to field-aligned irregularities at mid-latitudes

Experiments using multi-station networks receiving signals from the VHF beacon of a geostationary satellite have been carried out in order to clarify the geometrical factor involved in ionospheric intensity scintillations due to field-aligned irregularities. The characteristics of scintillation observed in the daytime agree with the theoretical value expected for weak diffractive scattering by ionospheric irregularities with an elongation of 10 along the geomagnetic field. However, those in the night-time show much marked enhancement along the field-line due to strong refractive scattering by irregularities having the same elongation. Finally, it is shown that the geometrical factor in scintillation at mid-latitudes can be expressed as a function of the propagation angle between the radio path and the geomagnetic field in the ionosphere. The maximum values of the geometrical factor are respectively about 5 in the daytime and 14 at night.     

Plasma convection and auroral precipitation processes associated with the main ionospheric trough at high latitudes

Intervals of F-region electron density depletions associated with the main (mid-latitude) ionospheric trough have been studied using latitude scanning experiments with the EISCAT UHF radar. From 450 h of measurements over a one year period at solar minimum (April 1986–April 1987) the local time of appearance of the trough at a given latitude is observed to vary by up to about 8 h. No seasonal dependence of location is apparent, but troughs are absent in the data from summertime experiments. A weak dependence of trough location on K_p is found, and an empirical model predicting the latitude of the trough is proposed. The model is shown to be more appropriate than other available quantitative models for the latitudes covered by EISCAT. Detailed studies of four individual days show no relationship between local magnetic activity and time of observation of the trough. On all four of these days, however, the edge of the auroral oval, evidenced by enhanced electron densities in the E-region, is found to be approximately co-located with, or up to 1° poleward of, the F-region density minimum. Simultaneous ion drift velocity measurements show that the main trough is a region of strong (> several hundred metres per second) westward flow, with its boundary located approximately 1°–2° equatorward of the density minimum. Within the accuracy of the observations this relationship between the convection boundary, the trough minimum and the precipitation boundary is independent of local time and latitude. The relevance of these results is discussed in relation to theoretical models of the F-reregion at high latitudes.     

Pi(c) magnetic pulsations: their relation to ionospheric currents

The association of the phase of the H and D components of the Pi(c) pulsations with the phase of the broadscale H component magnetic bays confirms that Pi(c) pulsations result from auroral electron precipitation induced conductivity enhancements of existing current systems. Statistically determined relationships between the time delays and phases of the H and D components of magnetic Pi(c) pulsations with respect to the optical pulsations are used to infer a delay between the E-region Hall and Pedersen current fluctuations associated with the pulsating electron fluxes. Theoretical modelling of an auroral pulsation patch, as per Oguti and Hayashi, is used to show that the polarization of the Pi(c) pulsations is controlled principally by the delay between the Hall and Pedersen currents and the direction of the background E-region electric field.     

Electrodynamic structural features of the auroral zone as deduced using data from a meridional chain of ionospheric and magnetic stations

This study has used ionospheric and magnetic observational data obtained at a meridional chain of stations during the high latitude geophysical experiment ‘Taimir-82’ in the winter of 1982–1983. Mean statistical latitude-time distributions of the occurrence probability of various types of E_s, their blanketing frequency and of the amplitude of geomagnetic field H-variations have been constructed. Based on these distributions and taking the E_s properties into account, an analysis is made of the mutual correspondence of large-scale structures of the auroral ionosphere and ionospheric currents.Ionospheric currents flow mainly in the region of high E-layer ionization. With increasing magnetic activity, the zone of currents and the zone of ionization expand simultaneously toward lower latitudes. The evening eastward electrojet and the morning westward electrojet are localized inside the zone of diffuse auroral precipitation which is responsible for the formation of E_s type r. The equatorial part of the midnight westward electrojet is also located in the zone of diffuse precipitation which coincides also with the region of maximum ionization of the E-layer. The polar part of this electrojet, which extends far into the dusk sector, is located in the zone of discrete auroral precipitation (a type E_s). Whereas there exists in the meridional cross-section quite a definite relationship between the Harang discontinuity and ionospheric parameters, such a relationship is not manifested in the zonal cross-section of the Harang discontinuity.     

Dayside high latitude magnetic impulsive events: their characteristics and relationship to sudden impulses

On 17 December 1990 a series magnetic impulsive events (MIEs) were observed at high latitudes near local noon. EISCAT, situated some 5 hours of MLT away from the noon sector, detected simultaneous impulsive electron density enhancements at heights between 90 and 120 km. The MIEs at noon were also associated with riometer absorption spikes. The correlated EISCAT and riometer observations indicate that there was an elongated electron precipitation region some 3000 km wide stretching from local noon to morning. In close association with the impulsive electron precipitation, VLF emissions were observed by groundbased stations in the morning side. We interpret the large scale electron precipitation and VLF emissions as signatures of a global compression of the Earth's magnetosphere. This is confirmed by the specific type of magnetic variations simultaneously recorded at the worldwide network of magnetometers. We conclude that the small scale MIEs with their drifting ionospheric current vortex structures can (but do not necessarily have to) occur in conjunction with large scale SIs. Moreover, MIEs and SIs have a common origin: the interaction of solar wind inhomogeneities with the Earth's magnetosphere. They do, however, represent different effects of the same primary agent.     

Calcium isotopes in archaeological bones and their relationship to dairy consumption

The calcium isotope ratios (δ^44/42Ca) of bones from humans and fauna from three archaeological sites, Taforalt, Abu Hureyra, and Danebury, are evaluated in order to assess whether calcium isotope ratios of bones can be used to detect dairy consumption by adult humans. At each site the fauna δ^44/42Ca is the same regardless of species, while the humans have lower δ^44/42Ca than the local animals by 0.24–0.41‰ (site means). However we cannot ascribe this difference to dairy consumption, given this human–faunal difference also occurs in Epipalaeolithic and Mesolithic adult humans, where dairy consumption is unlikely. Rather, this difference appears to be a result of differences in metabolic processes or other aspects of diet between humans and fauna. Minimal isotopic change in sequential acid leaches of bone powders and consideration of the high calcium concentration in bone suggest that bone calcium isotope ratios are not substantially affected by diagenetic change.     

Planetary waves in the strato- and mesosphere during the Western European Winter Anomaly Campaign 1975/76 and their relation to ionospheric absorption

The planetary-scale circulation features have been analysed for the period 28 December 1975 to 11 February 1976 by means of radiosonde, rocketsonde, and satellite data (infrared radiances). Geostrophic horizontal winds, vertical motions, and amplitudes and phases of the planetary waves are provided from the stratosphere to the mesosphere (from 20 to 80 km). The development in time and space of the planetary-scale waves is discussed and it is shown how the ionospheric absorption over Spain and Germany during the Winter Anomaly Campaign is connected with these waves which can be traced from the stratosphere through the whole mesosphere.     

An alternative interpretation of auroral precipitation and luminosity observations from the DE,DMSP, AUREOL,and Viking satellites in terms of their mapping to the nightside magnetosphere

We present an interpretation, which differs from that commonly accepted, of several published case studies of the patterns of auroral electron precipitation into the high-latitude upper atmosphere in the near-midnight sector based on their mapping to the nightside magnetosphere. In our scheme bright discrete auroral structures of the oval and respective precipitation are considered to be on the field lines of the Central, or Main, Plasma Sheet at distances from 5–10 to 30–50 R_E, depending on activity. This auroral electron precipitation pattern was discussed in detail by Feldstein and Galperin [(1985) Rev. Geophys.23, 217] and Galperin and Feldstein [(1991) Auroral Physics, p. 207. Cambridge University Press. It is applied and shown to be consistent with the results of case studies based on selected transpolar passes of the DE, DMSP, AUREOL-3 and Viking satellites.A diagram summarising the polar precipitation regions and their mapping from the magnetospheric plasma domains is presented. It can be considered as a modification of the Lyons and Nishida (1988) scheme which characterizes the relationship between the gross magnetospheric structure and regions of nightside auroral precipitation. The modification takes into account non-adiabatic ion motions in the tail neutral sheet, so that the ion beams characteristic of the Boundary Plasma Sheet (BPS) originate on closed field lines of the distant Central Plasma Sheet (say, at distances more than ~30 R_E).     

Postclassic Maya slips and paints and their relationship to socio-political groups in El Petén,Guatemala

LA-ICP-MS analysis of the chemical composition of the exterior slips and red and black pigments used for painted decoration of the three Postclassic Maya slipped ceramic wares suggests that the Itzá and Kowoj used different pigments for exterior slips and decorative motifs. Additionally, different slips and paints were used depending on vessel form and decorative program (red, black, or red-and-black painting or incising). When examined with previous ceramic paste chemical analyses, the data aid in better understanding the changing socio-political alliances and dominance relations in central Petén at the eve of Spanish contact.     

白鹤梁题刻保护问题及其与水域环境的关系

白鹤梁题刻是三峡库区唯一的国家级文物保护单位,受三峡水库淹没影响。在简单介绍和评价白鹤题刻现有保护方案的基础上,本文旨在探讨白鹤梁题刻及其与水域环境的相互关系,提出在进行白鹤梁题刻保护时,除了应注意保护白鹤梁题刻本身,还应恢复白鹤梁题刻赖以生存的水域环境及其所形成的独特的人文景观。     

Black sisterhood: The situation of urban aboriginal women and their relationship to the white women's movement 1

The article argues that Aboriginal women in urban aboriginal society experience very different oppressions than do white women in urban white society. Aboriginal women believe that their greatest oppression is racism not sexism. When their objective conditions are examined it becomes obvious that this is indeed so. In fact Aboriginal women are statistically better educated and better employed than are Aboriginal men. Other economic and societal factors combine to produce a situation whereby a black woman's status within her own society is very different to that of her white sisters. Black women are more likely to be heads of household; more likely to be political leaders and less likely to be child‐burdened than their white counterparts. Consequently women's movement demands such as abortion, child‐care, the right to work and sexual liberation are not given high priority by the Aboriginal women's movement. Aboriginal women's demands stem from the politics of poverty and discrimination. These are caused by racism not sexism.     

The red line over European colonialism: comparison of the Macao museum and Hong Kong museum of history after their return to China

Hong Kong and Macao were once European colonies. A unique, hybrid culture of East and West now flourishes in these two Special Administrative Regions (SARs) of China. Both cities opened new history museums in 1998, but they adopted remarkably different approaches in their representation of their complicated and politically sensitive history. The Hong Kong Museum of History (HKMH) represents history by closely following the orientation of traditional Chinese nationalism. The postcolonial characteristics adopted by the Macao Museum to reproduce history, in contrast, are likely amongst the richest of all history museums in China. What are the reasons behind the different historical representations by Hong Kong and Macao, which were both promised a ‘One country, Two systems’ policy by the Chinese central authority? This paper argues that both museums reveal two faces of a rising China; the one in Hong Kong emphasises national dignity, and the people’s identification with and loyalty to the nation when it is engaged in state building. The one in Macao emphasises the multiple roles in finding a balanced position to coexist with superpowers, forging friendships with developing countries and building an idealised image of a (re-)rising nation through historical construction. The difference between these two museums indicates the exceptional flexibility of China’s postcommunist regime in engaging in soft power diplomacy.     

Temporary consolidation and packaging of fragile cultural relics at underwater archaeological sites to maintain their original state during extraction

The flexible sponge/epoxy composite can wrap underwater artefacts in any shape and forms a protective shell after curing, thus effectively wrapping and reinforcing the artefacts. However, the hydroscopicity of the sponge itself limits the underwater application of the sponge/epoxy composite. In this study, a novel polyurethane sponge was prepared by modified with super-hydrophobic multi-wall carbon nanotubes (SH-MWCNTs@PU sponge). Compared with the pristine PU sponge, the water-contact angle on the surface of SH-MWCNTs@PU sponges increased from 103.3 ± 1.82 to 152.6 ± 1.54^o, and oily epoxy resin was able to cover the surface completely. The study shows that when SH-MWCNTs@PU sponges/epoxy resin composite material is used underwater, it prevents both water from entering the sponge and also the inside epoxy resin from overflowing into the water. Moreover, the composite materials have excellent toughness after reinforcement under water (flexural strength = 3.56 MPa) and the soft sponges can be moulded to wrap any type of underwater artefacts. In the laboratory, when taking a broken, three-dimensional blue-and-white porcelain pot as a research subject, the entire retrieval process—temporary stabilization, packaging, extraction and reinforcement material removal—was simulated to evaluate systematically all the technological aspects of safely excavating fragile underwater relics.     

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.     

Non‐specific indicators of stress and their association with age at death in Medieval York: Using stature and vertebral neural canal size to examine the effects of stress occurring during different periods of development

Selective mortality can occur towards individuals who survive episodes of physiological stress, such as disease and malnutrition, during development. The skeletal elements affected depend on the timing of these stressful episodes. Studying multiple non‐specific indicators of stress can show which periods of development were affected and whether certain periods can be linked with selective mortality. To examine this method a preliminary study of 61 adult individuals from the Medieval population of Fishergate House, York was undertaken to examine small vertebral neural canal size and reduced adult stature. Previous studies have shown that selective mortality occurs towards individuals who display these non‐specific indicators of stress. Statistical analysis showed that small transverse neural canal diameter was significantly associated with early adult mortality for males and females and there was evidence of selective mortality towards females with reduced stature. This suggests that individuals who died in early adulthood experienced health insults during late childhood which stunted VNC growth but males in particular were not significantly affected by health insults after this age as they achieved a normal adult stature. Therefore it appears that health insults which occurred during late childhood had a greater influence on adult health in the Fishergate House population. This method could be expanded to provide more detailed information by using a greater variety of non‐specific indicators of stress which will allow more specific periods of development to be investigated. Copyright © 2010 John Wiley & Sons, Ltd.