The influence of ionospheric absorption on mid-latitude whistler mode signal occurrence from VLF transmitters

Whistler mode signals from VLF transmitters received at Faraday, Antarctica (65° S, 64° W) during 1986–1991 show an annual variation in the number of hours over which signals are observed, with a maximum in June and a minimum in December. The variation was larger at solar minimum than at maximum and can be understood in terms of changes in absorption of VLF signals in the D-region, where the high geographic latitude of Faraday plays an important role in producing low attenuation levels during the austral winter. In contrast, very little such variation was observed at Dunedin, New Zealand (46° S, 171° E) in 1991. Nighttime whistler mode signals have start and end time trends that are consistent with the influence of F-region absorption. Increases in whistler mode occurrence appear to be associated with periods of high geomagnetic activity at solar maximum but not during solar minimum. A possible mechanism involving decreased F-region absorption is discussed.     

Satellite observations of signals from a Soviet mid-latitude VLF transmitter in the magnetic-conjugate region

The results of the Intercosmos-19 satellite experiment which receives VLF signals arriving via a magnetospheric path have been examined. The reception zone in the magnetically conjugate region (MCR) has been shown to be centred near the L-value (2.6) of the transmitter of 15 kHZ radio waves. The received signals arrive at the MCR with wave normal angles to the geomagnetic field, ψ, far from the resonance cone. These results indicate an effective amplification of the signal in the magnetosphere by 10–15 dB and effective ducting of VLF waves across the equatorial plane of the magnetosphere.     

Doppler shift pulsations on whistler mode signals from a VLF transmitter

Whistler mode signals from the NAA transmitter (24 kHz) received at Faraday, Antarctica are processed to obtain the Doppler shift at a much higher time resolution than has previously been possible. This has allowed the observation of pulsations of about 13 mHz frequency which are believed to be associated with hydromagnetic waves in the magnetosphere. The pulsations are observed separately on signals with a number of discrete group delay features that can be interpreted as individual whistler ducts. Using the measured pulsation phase over the array of ducts the phase velocity and wave normal direction of the hydromagnetic wave in the equatorial plane are estimated. The direction of propagation is consistent with a source on the dayside magnetopause.The association between whistler mode Doppler shifts and hydromagnetic waves has been reported before but not, as far as we are aware, using an experimental technique that allows measurements on individual ducts in order to determine the direction of propagation of the hydromagnetic wave.     

VLF transmissions observed at anomalously high latitude above the ionosphere in the conjugate hemisphere

Ariel 3 and 4 satellite observations of the GBR 16 kHz and NAA 17.8 kHz transmissions above the ionosphere in the conjugate hemisphere show that their wave-fields generally show a rapid reduction in signal strength for geomagnetic latitudes greater than 55°–60°. Sometimes, however, the signal strength has been observed to be high in the invariant latitude range > 60°. At certain times during these observations, the signal showed clear evidence of amplification, whilst at other times the pattern of signal strength was displaced to higher latitude with the signal strength integrated over latitude being unchanged from that normally observed.It is shown that the plasmapause can guide both the NAA and GBR signals but that the efficiency of this guiding depends on the plasmapause position. The important condition is found that the plasmapause must be situated sufficiently equatorwards that half the equatorial electron gyrofrequency at the plasmapause position is greater than (or approximately equal to) the transmitter signal frequency. Ray-tracing calculations in a realistic magnetosphere model indicate that for the 16 kHz GBR signal, the efficiency of guiding falls off for L_pp, (the L-value of the plasmapause) > 3.0 and guiding effectively ceases for L_pp > 3.5.Guidance by the plasmapause results in a wave-field at higher latitude than for non-guided propagation. This will only occur when, following geomagnetic storms, the plasmapause position is at a sufficiently low L-value. This is in agreement with the experimental observations of anomalously high latitude signal reception following strong magnetic storms (K_p ≥ 4+).     

A new approach to the tympanum of Neuilly-en-Donjon

Romanesque sculpture can be profitably studied by trying to create the thought processes of those responsible for designing the programs. In particular, the thought pattern of associating various biblical stories which contain the same or similar words can be applied to the program of the little church of Neuilly-en-Donjon (Allier). It is clear that the various stories depicted are related to one another by sound - for example the Adoration of the Magi and the fall of Simon Magus and Mary Magdalen at the house of Simon the Pharisee. However, just as the genius of a monastic author such as Bernard of Clairvaux was the thematic unity he could use to organize these aural associations, so does the importance of the program at Neuilly derive from the sophisticated thematic unity of the program around the theological virtue of faith. From this study, we can learn not only to appreciate the genius of the designer of the program at Neuilly but also to attempt to unlock other secrets of Romanesque sculpure by applying this or other elements of contemporary thought processes to the parts of a program.     

A new approach to the tympanum of Neuilly-en-Donjon

Romanesque sculpture can be profitably studied by trying to create the thought processes of those responsible for designing the programs. In particular, the thought pattern of associating various biblical stories which contain the same or similar words can be applied to the program of the little church of Neuilly-en-Donjon (Allier). It is clear that the various stories depicted are related to one another by sound - for example the Adoration of the Magi and the fall of Simon Magus and Mary Magdalen at the house of Simon the Pharisee. However, just as the genius of a monastic author such as Bernard of Clairvaux was the thematic unity he could use to organize these aural associations, so does the importance of the program at Neuilly derive from the sophisticated thematic unity of the program around the theological virtue of faith. From this study, we can learn not only to appreciate the genius of the designer of the program at Neuilly but also to attempt to unlock other secrets of Romanesque sculpure by applying this or other elements of contemporary thought processes to the parts of a program.     

VELOX: a new VLF/ELF receiver in Antarctica for the Global Geospace Science mission

VELOX (VLF/ELF Logger Experiment), a new facility for systematically studying the characteristics of magnetospherically generated ELF/VLF radio noise received at a high-latitude ground station (Halley, Antarctica, 76°S, 26°W, L = 4.3), measures continuously at 1 s resolution the absolute power (peak, mean, and minimum), arrival azimuth, and polarisation ellipticity in 8 logarithmically spaced frequency bands ranging from 500 Hz to 9.3 kHz. All filtering etc. is done in real time using Digital Signal Processing (DSP) techniques. Key parameters (1 kHz and 3 kHz power channels only, at 1-minute intervals) for each day are extracted and regularly transferred to the Global Geospace Study Central Data Handling Facility. Data from the first year of operation (1992) show that, whilst the upper channels (6 kHz and 9.3 kHz) are dominated by thunderstorm (spheric) noise, which is strongest at night and repeatable from day to day, magnetospheric chorus and hiss emissions are more important in the 1–4 kHz range of high attenuation in the Earth-ionosphere waveguide. They are highly variable in intensity from below system noise level (15–20 dB above the reference level 10⁻³³ T² Hz⁻¹) up to a maximum of 60–70 dB. Three classes of event are usually observed during specific local time sectors: substorm-related chorus events in the midnight-dawn sector, dawn chorus, and hiss-like events in the afternoon; all may occasionally be completely absent on quiet days. The substorm chorus events are shorter (typically 10–20 minutes) and more narrow-band than dawn chorus. Both upper and lower cut-off frequencies rise rapidly (∼ 100 Hz/min), consistent with the energy dispersion of resonant electrons as they drift eastward from injection near midnight, and with the inward drift, driven by substorm-enhanced electric fields, of whistler ducts which support propagation to the ground. Afternoon emission events are often punctuated by sudden deep fading, to noise level within 1–2 minutes, usually followed by complete recovery after a few minutes. All frequencies in the emission band are affected simultaneously. The explanation for this effect is unknown, though it could be a cut-off of propagation through the ionosphere to the ground by irregularities or gradients tilting the wave-normals out of the transmission cone. A similar system to VELOX will be deployed on a network of Automatic Geophysical Observatories extending to higher latitudes, south of Halley.     

A new approach to Corystospermales based on Triassic permineralized stems from Argentina

Anatomically preserved mature stems of late Middle Triassic corystosperms from the Paramillo Formation of Argentina are described and assigned to Cuneumxylon spallettii gen. nov. et sp. nov. The silicified specimens show features of the pith, primary xylem and successive rings of secondary xylem and phloem. The most striking characteristic is the anomalous secondary growth, represented by secondary xylem bounded by arcs of secondary phloem probably derived from successive repositioned cambia. Cuneumxylon has two kinds of unusual centrifugal secondary growth. The first shows unequal activity of different portions of the cambium on the circumference of the axes; the consequent restriction of cambial activity to certain restricted areas develops wedged stems, which often split. The second produces polyxylic stems following supernumerary cambial activity. As in extant plants growing in arid regions, the included phloem and the associated parenchyma may have had functional value avoiding desiccation of the outer tissues of the stem during droughts. Anatomical features of other Corystospermaceae were used to determine systematic affinities and to establish relationships among medullosans, corystosperms and cycads.     

VLF scattering from a column of ionization in the Earth-ionosphere waveguide

Choosing a highly idealized model, we analyze the scattering of VLF radio waves from a thin vertical column of ionization within the Earth-ionosphere waveguide. It is shown that mode conversion is produced if the column is limited in height and/or if the ionization is a function of height. However, the relative higher-mode content would be small in some situations such as in the case of the ionization produced by a cloud-to-ionosphere lightning discharge.     

A new approach to sexual diagnosis in past populations. Practical adjustments from Van Vark's procedure

Determination of sex is a key aspect in the study of past populations. Bias in skeletal sexing is well known, however, and depends upon the completeness of the skeletal remains and the representativeness of reference samples. In order to correct these difficulties, the authors propose practical adjustments to Van Vark's well‐known procedure. Two fundamental aspects are considered to reduce the bias of sex allocation. First, we propose to increase the effectiveness of sexing during the first step (primary diagnosis only from the pelvic bone). Second, to improve the final step (secondary diagnosis from the extra‐pelvic skeleton), we consider posterior probabilities as essential. These two practical adjustments are successfully tested in a sample of known sex and lead to a classification with 94.5% accuracy. These results significantly improve sex determination in archaeological samples and therefore contribute to a better understanding of past populations. Copyright © 1999 John Wiley & Sons, Ltd.     

A new approach to recording and monitoring wet-preserved archaeological wood using three-dimensional laser scanning

The analysis and preservation of organic materials preserved within wetland environments represents one of the most costly parts of any post-excavation strategy. This paper outlines the application of high-resolution terrestrial laser scanning to one class of preserved material, worked archaeological wood. Scanning allowed the recording of the artefacts in three dimensions and the identification of features such as toolmarks. Features can be measured and volumetrically modelled within the digital environment, which may not always be possible for these often fragile materials using conventional techniques. Repeat scanning of the artefacts provided an opportunity to use comparative analysis software to investigate changes in the morphology of artefacts under contrasting conditions of short-term storage. The results suggest that immersion in water results in the least deterioration, whereas both freezing and air-drying caused distortion and degradation. This paper demonstrates that laser scanning provides a viable alternative post-excavation method for the recording, analysis and long-term ‘virtual archiving’ of organic archaeological materials, which may be more cost-effective in some instances than other methods of preservation.     

Giving new meaning to religious conversion: Churches,redevelopment, and secularization in Toronto

Research on secularization has increased in recent years, particularly amongst urban geographers. Yet the debate is still dominated by competing theories that generally fail to account for the many institutions that impede and facilitate religiosity on the urban landscape. This article is about the role that land use planning regulations have had on changes to the religious landscape in Toronto. The empirical focus is on former churches that have recently been converted to residential uses. The larger conceptual goal is to explore the extent to which these transitions affect the religious landscape in the city and to determine what they can tell us about broader processes of secularization.     

《诗经·唐风》新探

本文对<唐风>的探讨,主要涉及<唐风>的地域、时代、诗歌的题旨、特色及其影响等,对传统的各种说法加以辨析、清理、批判或补充,以期对<唐风>的诸多问题进行较为系统而深入的探讨.     

A geographical approach to trust in tourism

Abstract

Within tourism research, trust has largely been conceptualised from psychological perspectives, allowing insights into the mechanisms through which resident/stakeholder relations generate trust. Whilst this work is valuable in understanding dynamics of trust relations, such focus has meant less attention and has been given to the ways space influences trust in tourism contexts. Thus, a geographical approach is put forth to understanding trust in tourism. Through observation and semi-structured interviews concerned with the implementation of a community tourism project in southwest China, insights are provided illustrating how trust is inscribed in place. It is shown that in the Chinese context, cultural place-based specificities relating to pre-existing governance structures, social hierarchies, and the intersection of power, knowledge and trust influence the (in)abilities of NGOs to develop trust with specific residents. More meaningful dialogue between tourism research and geographical conceptualisations of trust is called for – as a way to attend to spatial and scalar differences in understanding of trust within tourism contexts.     

A bayesian approach to wiggle-matching

“Wiggle-matching” is a technique developed to provide calendar dates for a series of samples of known deposition rate using the now well-established high-precision radiocarbon calibration curve. In this paper we describe how the technique may be formulated within the Bayesian framework for statistical analysis and thereby permit the incorporation of uncertainties regarding the deposition rate. The methodology is illustrated by two archaeological examples.     

From wic to burh: a new approach to the question of the development of Early Medieval London

During the ninth century the focus of occupation in Saxon London shifted eastwards from the Covent Garden area back to the former Roman city of Londinium. Combining detailed case studies with the results of correspondence analysis, this paper critically compares archaeological features and assemblages at sites dated c. AD 770 to c. AD 850 in Middle Saxon Lundenwic with sites dated c. AD 850 to c. AD 950 in Late Saxon Lundenburh. Differences in the archaeology of the two settlements are discussed. These distinctions reveal specific areas of discontinuity that strongly support current models of a hiatus between the decline of Lundenwic and renewed activity in Lundenburh.     

Provenance of Iron Age iron in southern Germany: a new approach

Ores, slag, and blooms from an Early Iron Age smelting site in the Black Forest, southern Germany, were analysed in view of their possible provenance in combination with products from a modern smelting experiment. Rather than employing lead isotope ratios, like in a previous study, osmium and strontium isotope ratios are used for the discussion of provenance. The results of the smelting experiment with iron ores from the archaeological site and their comparison with original finds show the high potential of osmium as a tracer to determine provenance. Strontium may be an additional indicator but possible contaminations need to be assessed. A Celtic iron ingot has also been analysed to check the potential of osmium for further provenance studies.     

A mutual ecological approach to health in Mongolia

Herders spend much time and energy seeking pasture and nurturing their herd animals in Mongolia. In turn, herd animals are the primary food source for herders in the form of meat and dairy products, feeding and nurturing the herding family. The overall herding principle strives towards a mutual balance across different scales within the body and the ecological food chain, resulting in reciprocal health and well-being. The powerful medicinal qualities of the blue and yellow pasque flower (yargui, Pulsatilla spp.) are valued in Mongolia, sought out in early spring by multiple species, including herders, goats and wild deer. Herding knowledge of goats and deer seeking out the pasque flower for medicinal purposes to expel gut parasites is an excellent example of Mongolian herding families’ awareness of their interdependent interconnections with other species as part of a larger surrounding ecology. However, this level of integration may not last, as herding families increasingly rely on introduced medicines, such as anthelmintics, bought from local pharmacies and wholesalers within rural townships.     

Phytolith identification criteria for foxtail and broomcorn millets: a new approach to calculating crop ratios

Broomcorn and Foxtail millets were major crops in the Yellow River Valley region, Henan, China, during the Neolithic Yangshao period. Phytoliths and macro remains have been used to understand crop choices in this period. Distinguishing between phytoliths from millet crops and panicoid non cultigens can be challenging. We examine the effect of using only one or two identification criteria compared with a more stringent five or more with phytoliths from archaeological samples to examine crop ratios. We compare our results with the results from the macro remains. This demonstrates, firstly, that using more identification markers has a very definite effect on the results and secondly, phytoliths and macro remains are complementary proxies that when used together can produce more accurate results than used alone.