bluuebunny/crossref_metadata_2025 huggingface dataset:
Atmospheric carbon dioxide and the long-term control of the Earth's climate
Authors: Carver J. H. , Vardavas I. M.
Published: July 2005

Abstract. A CO2-weathering model has been used to explore the possible evolution of the Earth's climate as the Sun steadily brightened throughout geologic time. The results of the model calculations can be described in terms of three, qualitatively different, "Megaclimates". Mega-climate 1 resulted from a period of rapid outgassing in the early Archean, with high, but declining, temperatures caused by the small weathering rates on a largely water-covered planet. Mega-climate 2 began about 3 Gyear ago as major continental land masses developed, increasing the weathering rate in the early Proterozoic and thereby depleting the atmospheric CO2 concentration. This process produced the first Precambrian glaciations about 2.3 Gyear ago. During Mega-climate 2, evolutionary biological processes increased the surface weatherability in incremental steps and plate tectonics modulated the CO2 outgassing rate with an estimated period of 150 Myear (approximately one-half the period for the formation and breakup of super continents). Throughout Mega-climate 2 the surface temperature was controlled by variations in the atmospheric CO2 level allowing transitions between glacial and non-glacial conditions. The results of the model for Mega-climate 2 are in agreement with the occurrence (and absence) of glaciations in the geologic record. Extending the model to the future suggests that CO2 control of the Earth's temperature will no longer be able to compensate for a solar flux that continues to increase. The present level of atmospheric CO2 is so small that further reduction in CO2 cannot prevent the Earth from experiencing Mega-climate 3 with steadily increasing surface temperatures caused by the continued brightening of the Sun. During Mega-climate 3, the main danger to the biosphere would come not from an increasing temperature but from a decreasing (rather than an increasing) CO2 level which could, in time, fall below 0.5 PAL, causing serious damage to the biosphere. Fortunately, the rates of change due to solar brightening are slow enough that Mega-climate 3 appears to pose no threat to the biosphere for the next 0.5-2 Gyear.
On recent developments in E-region irregularity simulationsand a summary of related theory
Authors: Janhunen P.
Published: July 2005

Abstract. Theoretical and simulation approaches to E-region irregularities (gradient drift and Farley-Buneman instabilities) are reviewed, and an account is given of some relevant observations. A new hybrid linear dispersion relation is also derived and presented. The most important problem that cannot be explained by more straightforward theories is the saturation of the phase velocity to the ion acoustic speed (Cs saturation). This phenomenon is well-known from equatorial electrojet radar observations. Recent particle simulations have yielded an interesting new explanation for the (Cs saturation, which has been named flow angle stabilization: the phase velocity is not actually (Cs saturated, but the flow angle distribution of the spatial power spectrum is highly asymmetric. The asymmetry is such that the most intense waves propagate at the k·E < 0 edge of the linearly unstable sector, and thus the phase velocity of the most intense waves is close to (Cs. Depending on the level of larger scale turbulence, the radar observes varying degrees of (Cs saturation. If the larger scale turbulence level is high (equatorial electrojet case), the local flow angle fluctuates, and there are always sub-regions within the scattering volume with local flow angles favourable for the detection of the most intense waves. Under these conditions, the spectra show (Cs saturation. If the larger scale turbulence level is lower, there will not always be enough mixing of the flow angle for even the most intense waves to be observed. In these cases, the mean Doppler shift will be proportional to the electric field, i.e. it will obey the linear theory.
External gravity oscillations in Lake Onega
Authors: Rudnev S. F. , Salvadè G. , Hutter K. , Zamboni F.
Published: July 2005

Abstract. Lake Onega is located in the southern part of Karelia, in the north-west of Russia. We report data taken by various limnigraphs and current meters and isolate, by spectral analysis, the most conspicuous barotropic periods of these signals. The analysis that follows is based on the linearized shallow-water equations, that are solved for the free oscillations and thus identify the eigenperiods and corresponding mode structures for this lake. Computational results are presented for a finite difference representation for these surface-seiche equations applied to the entire Lake Onega including its bays. The grid consists of quadratic elements of 1000 m side length corresponding to 9344 active cells. The emerging matrix eigenvalue problem exceeds the storage and compuational capacity of standard PCs or workstations and thus requires use of the approximate Lanczos procedure to isolate the first ten eigenperiods and corresponding mode structures of the barotropic seiches, lying between 12.1 and 2.2 h. Comparison of computational results and inferences from the water level and current-meter records, disclose satisfactory agreement between theory and observation.
A first numerical simulation of the development and structure of the sea breeze on the Island of Mallorca
Authors: Ramis C. , Romero R.
Published: July 2005

Abstract. A numerical study of the development and structure of the sea breeze in Mallorca is presented using a meso- numerical model. The model includes a detailed representation of the soil and vegetation processes. The study covers a diurnal cycle. The results show that the model reproduces the main known features of the circulation and new ones appear, which seem to have an appreciable effect on the circulation during the decay of the sea breeze. The orography and soil dryness have been identified as the main factors determining the structure of the breeze. Three more experiments have been performed in order to isolate the effect of each factor.
Observations of the upper ocean response to storm forcing in the South Atlantic Roaring Forties
Authors: Marsh R.
Published: July 2005

Abstract. In the austral summer of 1992–1993 the passage of a storm system drove a strong upper ocean response at 45°S in the mid-South Atlantic. Good in situ observations were obtained. CTD casts revealed that the mixed layer deepened by ~40 m over 4 days. Wind stirring dominated over buoyancy flux-driven mixing during the onset of high winds. Doppler shear currents further reveal this to be intimately related to inertial dynamics. The penetration depth of inertial currents, which are confined to the mixed layer, increases with time after a wind event, matched by a downward propagation of low values of the Richardson number. This suggests that inertial current shear is instrumental in producing turbulence at the base of the mixed layer. Evolution of inertial transport is simulated using a time series of ship-observed wind stress. Simulated transport is only 30–50% of the observed transport, suggesting that much of the observed inertial motion was forced by an earlier (possibly remote) storm. Close proximity of the subtropical front further complicates the upper ocean response to the storm. A simple heat balance for the upper 100 m reveals that surface cooling and mixing (during the storm) can account for only a small fraction of an apparent ~1 °C mixed layer cooling.
Surface heat fluxes in the Western Equatorial Pacific Ocean
Authors: Wells N. C.
Published: July 2005

Abstract. Estimates of the components of the surface heat flux in the Western Equatorial Pacific Ocean are presented for a 22-day period, together with a critical analysis of the errors. It is shown that the errors in latent heat, and solar and longwave radiation fluxes, dominate the net heat flux for this period. It is found that the net heat flux into the ocean over the 22-day period is not significantly different from zero. It is also demonstrated that because of the variability in daily averaged values of solar radiation and the latent heat of evaporation, a large number of independent flux measurements will be required to determine with confidence the climatological net heat flux in this region. The variability of latent fluxes over the 22-day period suggest that climatological estimates based on monthly mean observations may lead to a significant underestimate of the latent heat flux.
Anomalous enhancement in daytime 40-kHz signal amplitude accompanied by geomagnetic storms, earthquakes and meteor showers
Authors: De B. K. , Sarkar S. K.
Published: July 2005

Abstract. Anomalous propagational characteristics, daytime signal levels greater than night-time, were observed. The amplitude records of a 40-kHz signal propagated over a distance of 5100 km from Sanwa, Japan to Calcutta along a low-latitude path show higher signal strength at midday compared to the midnight level on days preceded by principal geomagnetic storms, earthquakes and major meteor showers. This is explained by the increased ionization in the D-region following geophysical events. The storm after-effects only have a duration of a single day in this low-latitude path.
The role of upstream ULF waves in the generation of quasi-periodic ELF-VLF emissions
Authors: Morrison K. , Freeman M. P.
Published: July 2005

Abstract. Recent work suggests that the quasi-periodic (QP) modulation ~10–50 s of naturally occurring ELF-VLF radio emissions (~0.5–5 kHz) is produced by the compressional action of Pc3 magnetic pulsations on the source of the emissions. Whilst it is generally accepted that these magnetic pulsations have an exogenic source, it is not clear what the mechanism of their generation is. A study of QP emissions observed during 1988 at Halley, Antarctica, in conjunction with IMP-8 satellite solar wind data, shows that the occurrence and modulation frequency of the emissions are strongly dependent upon the direction and strength of the IMF, respectively. The observed relationships are very similar to those previously reported for Pc3 pulsations associated with upstream ion-cyclotron resonance, involving proton beams reflected at the bowshock. In comparing the observed QP modulation frequencies with upstream wave theory, agreement was found by considering wave excitation exclusively associated with a proton beam reflected from a position on the bowshock at which the shock normal is parallel to the ambient IMF direction. Other geometries were found to be either impropitious or uncertain. The work indicates the useful diagnostic role QP emissions could play in the study of compressional ULF waves in the upstream solar wind and in monitoring the IMF conditions responsible for their generation.
Observations of the E-region horizontal winds in the auroral zone and at mid-latitudes by a ground-based interferometer
Authors: Fauliot V. , Thuillier G. , Hersé M.
Published: July 2005

Abstract. The MICADO instrument, consisting of a Michelson interferometer, has observed winds and temperatures during three winter campaigns in the auroral zone, and during 2 years at the Observatoire de Haute-Provence. The instrument observed the O(1S) oxygen emission line. Emission from this line originates from both the E- and F-regions. A method to separate the contribution from these two regions is presented for cases when the thermospheric component is comparable to that for the mesosphere. For the auroral latitudes, a mean model of the meridional and zonal neutral wind components as a function of magnetic activity and time is presented and compared to predictions from recent empirical models. For the mid-latitudes, several properties of the semi-diurnal tides are shown and compared to radar observations and predictions from recent theoretical models.
Temporal associations of life with solar and geophysical activity
Authors: Breus T. K. , Cornélissen G. , Halberg F. , Levitin A. E.
Published: July 2005

Abstract. In biology, circadian rhythms with a period of one cycle in 20–28 h are known to be ubiquitous and partly endogenous. Rhythms with a frequency lower than one cycle per day are called 'infradian rhythms'. Among them are components with one cycle in about 3.5, 7, 14 and 28 days, the multiseptans, which, like the circadians, must be regarded as a general characteristic of life: they characterize unicells as well as much more differentiated organisms. We hypothesize that heliogeophysical factors other than the solar visible light, held responsible for the evolution of circadian periodicity, underlie the infradian rhythms of biosystems. The periodicities in the solar wind and variations in the interplanetary magnetic field (IMF) which are associated with the solar rotation are very similar in length to the biological periodicities. We investigate the temporal relations of variations in solar activity and in biological systems to test associations between events in the IMF, in geomagnetic disturbance, in myocardial infarction and in physiology. By cross-spectral analysis, we also find relations at certain frequencies between changes in human physiology on the one hand, and (1) the vertical component of the induction vector of the IMF, Bz, and (2) a global index of geomagnetic disturbance, Kp, on the other hand. We wish to stimulate interest in these periodicities of both biological systems and geophysical endpoints among physicists and biologists alike, so that problems relevant to clinicians and other biologists, including evolutionists, are eventually solved by their cooperation with the geophysical community.
The use of various interplanetary scintillation indices within geomagnetic forecasts
Authors: Lucek E. A. , Clark T. D. G. , Moore V.
Published: July 2005

Abstract. Interplanetary scintillation (IPS), the twinkling of small angular diameter radio sources, is caused by the interaction of the signal with small-scale plasma irregularities in the solar wind. The technique may be used to sense remotely the near-Earth heliosphere and observations of a sufficiently large number of sources may be used to track large-scale disturbances as they propagate from close to the Sun to the Earth. Therefore, such observations have potential for use within geomagnetic forecasts. We use daily data from the Mullard Radio Astronomy Observatory, made available through the World Data Centre, to test the success of geomagnetic forecasts based on IPS observations. The approach discussed here was based on the reduction of the information in a map to a single number or series of numbers. The advantages of an index of this nature are that it may be produced routinely and that it could ideally forecast both the occurrence and intensity of geomagnetic activity. We start from an index that has already been described in the literature, INDEX35. On the basis of visual examination of the data in a full skymap format modifications were made to the way in which the index was calculated. It was hoped that these would lead to an improvement in its forecasting ability. Here we assess the forecasting potential of the index using the value of the correlation coefficient between daily Ap and the IPS index, with IPS leading by 1 day. We also compare the forecast based on the IPS index with forecasts of Ap currently released by the Space Environment Services Center (SESC). Although we find that the maximum improvement achieved is small, and does not represent a significant advance in forecasting ability, the IPS forecasts at this phase of the solar cycle are of a similar quality to those made by SESC.
Nonlinear interaction between acoustic gravity waves
Authors: Axelsson P. , Larsson J. , Stenflo L.
Published: July 2005

Abstract. The resonant interaction between three acoustic gravity waves is considered. We improve on the results of previous authors and write the new coupling coefficients in a symmetric form. Particular attention is paid to the low-frequency limit.
A numerical study of the transport and diffusion of coastal pollutants during the breeze cycle in the Island of Mallorca
Authors: Romero R. , Ramis C.
Published: July 2005

Abstract. An Eulerian study of the distribution over the Island of Mallorca of a non-reactive pollutant (SO2) emitted from an electric power plant operating at present on the north coast is performed using a meso-β numerical model, paying particular attention to the diffusive physical mechanisms. The study is applied to the conditions of sea-land breeze development. This is a local circulation that dominates the flow during the summer and favours transporting pollutants from the coast toward the centre of the island. Results indicate that values of the ground-level concentration higher than 5 μ g/m3 are restricted over a limited and mountainous region during the whole diurnal cycle. However, when the simulation is carried out with the inclusion of a twin electric plant which may be built on the south coast, the affected area becomes larger, especially early in the morning, when air over the island is sinking as a consequence of the land breeze development. The inclusion of dry deposition in the simulations does not produce important changes in the spatial and temporal evolution of the ground-level concentration.
The instability of an electron beam with a finite radius in a boundless plasma
Authors: Lizunov G. V. , Volokitin A. S. , Skidanov D. B.
Published: July 2005

Abstract. Within the framework of a linear theory, the instability of an electron beam with a finite radius in a cold magnetised boundless plasma is considered. It is shown that a finite beam dimension influences the generation of quasi-potential waves in two aspects: the perpendicular wave number is quantised so that the frequencies of the waves are subjected to strong selection; a new kind of instability appears due to wave energy losses by emission into surrounding space. Growth rate dependence of wave numbers and frequencies is investigated for typical parameters of experiments with electron beams in space.
HF radar observations of equatorial spread-F over West Africa
Authors: Cécile J.-F. , Vila P. , Blanc E.
Published: July 2005

Abstract. New experimental data depicting equatorial spread-F were taken during an HF radar sounding campaign in Korhogo (Ivory Coast, 9°24N, 5°37W, dip 4°S). Range-time-intensity maps of the radar echoes have been analyzed to identify the signatures of density depletions and bottomside spread-F. Density depletions are well known features of equatorial spread-F, and are believed to emerge after the development of a Rayleigh-Taylor instability on the bottomside F-layer. A simple model is developed and used to simulate the flow of density depletions over the radar field of view. The simulation permits an interpretation of the data that yields the zonal flow velocity as a function of local time. Comparisons with previous measurements are undertaken to assess the consistency of the computational results, and qualitative arguments are presented to identify bottomside spread-F. Using the computational results as reference, a morphological study of ionograms showing spread-F is undertaken which reveals the specific signature of bottomside spread-F on ionograms recorded just after sunset.
Dispersion of passive tracers in model flows: effects of the parametrization of small-scale processes
Authors: Lacorata G. , Purini R. , Vulpiani A. , Zambianchi E.
Published: July 2005

Abstract. A set of numerical experiments is presented, in which we study the dynamics of passive particles advected by given two-dimensional velocity fields and perturbed by a non-white noise with a characteristic time τ. Data and model results have shown that this kind of random perturbation is able to represent subgridscale processes for upper ocean mesoscale turbulence for regions of the world ocean where turbulence can be assumed to be homogeneous. Extensive computations in different fields characterized by cell-like structure, both stationary and time-dependent, representing very idealized geophysical flow situations, show that the presence of a finite correlation time scale does lead to enhanced or arrested dispersion, depending on the considered flow; however, it does not seem to affect the gross qualitative behaviour of the dispersion processes, which is primarily affected by the large-scale velocity field.
Determination of interstellar pickup ion distributions in the solar wind with SOHO and Cluster
Authors: Möbius E. , Rucinski D. , Isenberg P. A. , Lee M. A.
Published: July 2005

Abstract. Over the last 10 years, the experimental basis for the study of the local interstellar medium has been substantially enhanced by the direct detection of interstellar pickup ions and of interstellar neutral helium within the heliosphere. Pickup ions can be studied for a wide range of interstellar species. However, currently the accuracy of the method to determine the parameters of the interstellar medium, namely neutral density, temperature and relative velocity, is hampered by two problems: (1) In most cases the crucial ionization rates are not available from simultaneous measurements and (2) the transport of the pickup ions in the interplanetary medium substantially modifies the measured spatial distribution of the ions. In this study we will discuss how the enhanced capabilities of the instrumentation on SOHO and Cluster in combination with ongoing efforts to model the pickup ion distributions will lead to a significant improvement over the coming years.
Heterogeneous loss of OH on NaCl and NH4NO3 at tropospheric temperatures
Authors: Ivanov A. V. , Gershenzon Y. M. , Gratpanche F. , Devolder P. , Sawerysyn J.-P.
Published: July 2005

Abstract. The uptake coefficients (Γ) for OH radicals on some dry salts of tropospheric interest (NaCl and NH4NO3) have been investigated as a function of temperature using the flow tube technique combined with an EPR spectrometer as a detection method. The temperature dependence of Γ-values measured over the temperature range 245–340 K can be expressed in Arrhenius form: ΓOHNaCl=(1.2±0.7)×10–5exp[(1750±200)/T] and ΓOHNH4NO3=(1.4±0.5)×10–4exp[(1000±100)/T]. These Arrhenius expressions lead to very similar Γ-values (~4×10–3) for both salts studied at 300 K. It is shown that the heterogeneous OH sinks on solids aerosol play a very minor role in tropospheric chemistry in comparison with the homogeneous sinks.
Equatorial ionospheric response to the 10.7 cm radio flux over two sunspot cycles (1969−1991)
Authors: Hajkowicz L. A.
Published: July 2005

Abstract. It is evident that fluctuations in a standard ionospheric parameter, the minimum (virtual) height (h´F) of the equatorial F-region in the African (Ouagadougou), Asian (Manila) and American (Huancayo) longitudinal sectors, closely resemble changes in solar activity as deduced from the 10.7 cm solar flux index (S), over two solar cycles (1969–91). The monthly median hourly value of h´F, particularly in the post-sunset period (18–20 LT), are positively correlated with the monthly average S. The value of h´F can be deduced from an empirical formula: h´F=0.68S+218.3, with the correlation coefficient (r) between h´F and S being 0.78. The diurnal distribution of r during daytime (06–14 LT) was radically different for the African and Asian longitudinal sectors during 1980-1991, with the most pronounced difference in the post-noon period (12–14 LT) when the correlation coefficients r for the Asian and African sectors are 0.8 and 0.2, respectively. Thus, the daytime F-region in the African sector responded far less to changes in solar activity than the Asian F-region during this cycle. This longitudinal anomaly was however absent in the preceding cycle (1969–1979) when the African and Asian sectors were both characterised by low daytime and pronounced post-sunset correlation coefficient r. The American sector appears to have a high correlation coefficient r in daytime increasing to a small maximum in the post-sunset interval. The post-sunset enhancement in r is a characteristic feature for equatorial stations only (corrected geomagnetic latitude <10°).
Disturbed vertical E×B plasma drifts in the equatorial F2 region at solar minimum deduced from observed NmF2 and hmF2 variations
Authors: Mikhailov A. V. , Förster M. , Leschinskaya T. Y.
Published: July 2005

Abstract. Ground-based ionosonde and magnetic-field observations on the equatorial station Huancayo, ESRO4 neutral-composition measurements, and theoretical model calculations were used to analyze disturbed E×B vertical plasma drift during the phase of solar minimum in 1973. Vertical drifts calculated for disturbed days do not show the systematic decrease often mentioned in publications, and demonstrate strong dependence on IMF-Bz changes. It is confirmed with the help of our drift calculations that Bz turnings to a northward direction result in a decrease (up to reversal) of normal Sq (eastward during daytime and westward at nighttime) in the zonal component of electric field. Southward Bz excursions enhance normal Ey both in daytime and nighttime hours. Model predictions of Ey\\'s reaction to IMF-Bz changes are discussed.
Variations in the polar cap area during intervals of substorm activity on 20-21 March 1990 deduced from AMIE convection patterns
Authors: Taylor J. R. , Yeoman T. K. , Lester M. , Emery B. A. , Knipp D. J.
Published: July 2005

Abstract. The dynamic behaviour of the northern polar cap area is studied employing Northern Hemisphere electric potential patterns derived by the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure. The rate of change in area of the polar cap, which can be defined as the region of magnetospheric field lines open to the interplanetary magnetic field (IMF), has been calculated during two intervals when the IMF had an approximately constant southward component (1100–2200 UT, 20 March 1990 and 1300–2100 UT, 21 March 1990). The estimates of the polar cap area are based on the approximation of the polar cap boundary by the flow reversal boundary. The change in the polar cap area is then compared to the predicted expansion rate based on a simple application of Faraday\\'s Law. Furthermore, timings of magnetospheric substorms are also related to changes in the polar cap area. Once the convection electric field reconfigures following a southward turning of the IMF, the growth rate of the observed polar cap boundary is consistent with that predicted by Faraday\\'s Law. A delay of typically 20 min to 50 min is observed between a substorm expansion phase onset and a reduction in the polar cap area. Such a delay is consistent with a synthesis between the near Earth neutral line and current disruption models of magnetospheric substorms in which the dipolarisation in the magnetotail may act as a trigger for reconnection. These delays may represent a propagation time between near geosynchronous orbit dipolarisation and subsequent reconnection further down tail. We estimate, from these delays, that the neutral X line occurs between ~35RE and ~75RE downstream in the tail.
Fractals and magnetic storm
Authors: Wang Tan-Wen
Published: July 2005

Abstract. Fractal theory is applied in a quantitative analysis of geomagnetic storms. Fractal dimensions (D) of the attractor for storm data from the Beijing observatory (40.0°N, 116.2°E) using several time intervals are calculated. A maximum value of 1.4 has been obtained for a geomagnetic storm; on quite days the dimension is only slightly larger than 0.5. Data from two storms are analyzed here. Results show that a combination of both D and the magnetic index, k, can perhaps describe the degree of solar disturbance better than the single parameter k.
On long-term evolution of seasonal precipitation in southwestern Europe
Authors: Valero F. , Doblas F. J. , González J. F.
Published: July 2005

Abstract. Annual cycles in long time series of precipitation from sixteen southwest European observatories have been analysed using complex demodulation. The stations have been clustered into two distinct regions and a hybrid one. They are referred to as the southwestern Europe precipitation Atlantic regime (SEPAR) and the southwestern Europe precipitation Mediterranean regime (SEPMER), with the hybrid regime referred to in terms of the mean amplitude ratios between semiannual and annual rainfall components. Some evidence of linking between seasonal cycle harmonic amplitudes and the zonal circulation has been found for SEPAR stations and a more obscured relationship for the SEPMER region. Within the SEPAR region the strength of the relationship is diminished towards the north. A trend analysis of the amplitudes against time since 1920 has also been carried out and the results reveal a divergent pattern in trends between annual and semiannual component amplitudes for the SEPAR region. In fact, both an increasing annual-amplitude trend and a decreasing semiannual-amplitude trend are observed, in each case statistically significant. The fact that the seasonal cycle variability of rainfall in southwestern Europe becomes more sensitive southwards to changes in atmospheric zonal circulation over the North Atlantic might, in our opinion, be related to the swing of the circumpolar vortex.
BRINGING IN THE WILD: THE COMMODIFICATION OF WILD ANIMALS IN THE CAPE COLONY/PROVINCE c. 1850–1950
Authors: VAN SITTERT LANCE
Published: July 2005

The history of the imperial/colonial elite's preoccupation with saving a handful of specific ‘game’ species in reserves has come to stand for the relationship of all classes with all wild animals in both South Africa and the wider world of the British empire. The result is a narrative of process and periodization flawed in general and false in the specific case of the Cape Colony/Province, where economics rather than ideology was both the primary motor of game conservation and the mediating factor in human relationships with wild animal species. Here the general trend across the century from 1850 to 1950 was, contra MacKenzian orthodoxy, towards private not public ownership of game propelled by a rural rather than an urban elite. Public ownership was instead restricted to ‘vermin’ species in which the state created a market in which it became the chief consumer. The Cape's great tradition was refracted through its customary permissive legislation to yield a myriad of small traditions at the regional or local level. Rather than an argument for Cape exceptionalism, its wild animal history is a caution against glib generalizations from the elite archive and an indication of the need to broaden prevailing ‘game reserve history’ to include the full range of human and animal inhabitants as agents rather than as residual analytical categories in any narrative.
‘Payback time’: community volunteering among older adults as a transformative mechanism
Authors: NARUSHIMA MIYA
Published: June 2005

This qualitative study explores the conditions and experiences of older adults' ‘formal’ volunteering through non-profit organisations (NPOs) in Toronto from both organisational and individual perspectives. In spite of the ageing population and the need for NPOs to expand their services, the participation of Canadian seniors in community volunteering has been stagnant for 15 years. What organisational and structural supports might encourage the expansion of volunteering among this group? How do current administrative conditions impact upon senior volunteers? What do older adults expect to gain from community volunteering? The qualitative data collected through interviews, documents and participant observation are analysed using an inter-disciplinary framework that combines theories of the moral economy of ageing, adult development and transformative learning. The results include a socio-demographic profile of senior volunteers in 12 Toronto NPOs, and the administrative characteristics of the six organisations that engage the majority. It is argued that the self-help and transformative mechanisms embedded in community volunteering provide opportunities for retirees to sustain their self-esteem and sense of wellbeing, while cultivating ‘generativity’ in late adulthood. Promoting transformative learning enables community volunteering to provide meaningful roles for seniors, and promotes citizenship participation and the social economy in an ageing society.
Seroprevalence of hepatitis E virus (HEV) antibody and the possible association with chronic liver disease: a case-control study in Albania
Authors: KONDILI L. A. , CHIONNE P. , PORCARO A. , MADONNA E. , TAFFON S. , RESULI B. , TALIANI G. , RAPICETTA M.
Published: June 2005

A case-control study involving 109 in-patients with chronic liver disease and 190 in-patients with no apparent liver disease was conducted to evaluate the seroprevalence of anti-HEV antibodies and the possible association with chronic liver disease. Among cases, the anti-HEV prevalence was 36·6% which increased significantly by age; among controls, the prevalence was 12·1% (P<0·05) and was similar among age groups <60 years. Among cases, aged >50 years (OR 4·0, 95% CI 1·4–11) and the presence of end stage liver disease (ESLD) (OR 4·3, 95% CI 1·4–12·8) were associated independently with anti-HEV positivity. The mean optical density, determined by anti-HEV immunoenzymatic test, was significantly higher among patients with ESLD, compared to the other patients. These results indicate that there is a high seroprevalence of anti-HEV in patients with chronic liver disease and a possible association between HEV infection and/or anti-HEV production and advanced stage chronic liver disease.
Un modèle psycholinguistique informatique de la reconnaissance des mots dans la chaîne parlée du français
Authors: LÉWY NICOLAS , GROSJEAN FRANÇOIS , GROSJEAN LYSIANE , RACINE ISABELLE , YERSIN CAROLE
Published: July 2005

Nous proposons un nouveau modèle psycholinguistique informatique du français. Le modèle, intitulé FN5, porte sur la reconnaissance de mots parlés, présentés en isolé (déterminant, adjectif antéposé, substantif) ou en suites de deux mots (déterminant et substantif, adjectif antéposé et substantif). Grâce à un lexique de plus de 17 000 mots, à une architecture connexionniste localiste, et à des mécanismes développés spécifiquement (processeur de position, groupements de connexions, et point d'isolation), le modèle peut simuler, de manière séquentielle ou simultanée, certains effets propres au mot isolé (fréquence, longueur, homophonie) ou à une suite de mots (coupure lexicale, enchaînement, liaison, effacement du schwa). De plus, le modèle tient compte de certaines différences qui existent entre le français standard et le français de Suisse romande (nombre de voyelles, durée vocalique en fin de mot, et statut du schwa). Nous décrivons ce modèle, présentons son interface graphique, et l'illustrons avec des exemples de simulation.
Summer regional rainfall over southern Ontario and its associations with outgoing longwave radiation and moisture convergence
Authors: Bao Zhenhao , Ye Hengchun , Taylor Peter A.
Published: July 2005

Daily rainfall records at 50 sites across southern Ontario are used to investigate the association of summer regional rainfall with outgoing longwave radiation (OLR) and moisture convergence, from 1991 to 2000. The results suggest that OLR values correspond well to heavy rainfall amounts when rain occurs over more than 90% of the study region. The average regional daily precipitation of 12.1 mm/day corresponds to 213.0 W/m2 of OLR values in the study region. Also, OLR is more significantly associated with the regional daily rainfall amount than moisture convergence in the atmospheric layers between 1000 hPa and 300 hPa although both are associated with precipitation. The study suggests that when a low OLR departure centres over Ontario, the region tends to have extremely heavy rainfall and flooding. The results of this study indicate that OLR is a useful tool for satellite detection of extremely heavy rainfall and possible flash flooding during the summer season over southern Ontario. Copyright © 2005 Royal Meteorological Society
Modelling precipitation trends in England and Wales
Authors: Mills Terence C.
Published: July 2005

Using a variety of trend extraction techniques applied to monthly observations from 1766 to 2002 on the EWP dataset, this study confirms that there is evidence of a trend towards wetter winters (November to March), particularly in December and January, and drier summers, although this feature appears to be concentrated in June and July. Trend precipitation in autumn (August to November) is more difficult to pin down, with alternative methods producing quite different trend patterns, thus highlighting how difficult it can be to extract trends from noisy data. In general, the results appear to be reasonably consistent with those of Alexander & Jones (2001) using rather different techniques, thus lending weight to the views expressed by them. Copyright © 2005 Royal Meteorological Society
A CHR-based implementation of known arc-consistency
Authors: ALBERTI MARCO , GAVANELLI MARCO , LAMMA EVELINA , MELLO PAOLA , MILANO MICHELA
Published: July 2005

In classical CLP(FD) systems, domains of variables are completely known at the beginning of the constraint propagation process. However, in systems interacting with an external environment, acquiring the whole domains of variables before the beginning of constraint propagation may cause waste of computation time, or even obsolescence of the acquired data at the time of use. For such cases, the Interactive Constraint Satisfaction Problem (ICSP) model has been proposed (Cucchiara et al. 1999a) as an extension of the CSP model, to make it possible to start constraint propagation even when domains are not fully known, performing acquisition of domain elements only when necessary, and without the need for restarting the propagation after every acquisition. In this paper, we show how a solver for the two sorted CLP language, defined in previous work (Gavanelli et al. 2005) to express ICSPs, has been implemented in the Constraint Handling Rules (CHR) language, a declarative language particularly suitable for high level implementation of constraint solvers.
Effect of nanosize modulation of granular La0.67Sr0.33MnO3 manganites on temperature-dependent low-field spin-polarized tunneling magnetoresistance
Authors: Dey P. , Nath T. K. , Kumar Uday , Mukhopadhyay P. K.
Published: July 2005

We have investigated magnetotransport behaviors of a series of single-phase, nanocrystalline La0.67Sr0.33MnO3 (LSMO) samples having grain sizes in the nanometric regime (14, 22, and 26 nm), all synthesized through chemical route “pyrophoric reaction process.” The motivation behind the present investigation is to study the effects of nanometric grain size on magnetoresistance (MR), specially its temperature and magnetic-field dependences. Magnetoresistance measurements show that in all samples there is a large negative MR at very low fields (LFMR), followed by a slower varying negative MR at comparatively high fields (HFMR), in the ferromagnetic regime. Surprisingly, we observed that at both low- and high-field regimes, the magnitude of MR remains constant up to sufficiently high temperature and then drops sharply with temperature. This temperature-dependent MR behavior gets enhanced with the decrease in particle size. Most interestingly, we found a considerable low-field MR (14%) persisting even at 200 K, which is an appreciable improvement on the results of previous workers. In order to explore the basic physics behind this unusual temperature dependence of MR, we analyzed our data in the light of a phenomenological model [P. Raychaudhuri et al., J. Appl. Phys. 84, 2048 (1998)], based on spin-polarized transport of conduction electrons at the grain boundaries, with major attention being paid to the gradual slippage of domain walls across the grain-boundary pinning centers in an applied magnetic field. Finally, we have attributed this feature of LFMR to the surface magnetization of our nanosize granular LSMO samples, which is crucial for nanodimensional systems.
Annealing effects on the temperature dependence of photoluminescence characteristics of GaAsSbN single-quantum wells
Authors: Li J. , Iyer S. , Bharatan S. , Wu L. , Nunna K. , Collis W. , Bajaj K. K. , Matney K.
Published: July 2005

In this work we investigate the effects of ex situ annealing in N ambient and in situ annealing in As ambient on the temperature dependence of photoluminescence (PL) spectral characteristics of GaAsSbN∕GaAs single-quantum-well heterostructures. The focus of this work is on three representative nitride samples grown by molecular-beam epitaxy. The widths of the quantum wells (QWs) varied from 8 to 9 nm and the concentrations of nitrogen and antimony as determined from high-resolution x-ray diffraction and secondary-ion-mass spectroscopy were in the range of 0.8%–1.4% and 26%–33%, respectively. One sample was ex situ annealed in N ambient at 700 °C for 10 min. Two other samples were in situ annealed in As ambient at 650 and 700 °C, respectively, also for 10 min. Excitonic transitions in the QWs exhibit the well-known “S-curve” behavior in the temperature dependence of the PL peak energy. In addition, the variation of the full width at half maximum with temperature exhibits an “inverted S-curve” behavior. These are well-known signatures of localized excitons. The PL characteristics such as total integrated intensity and full width at half maximum as well as their temperature dependence, and the quality x-ray rocking curves clearly indicate that in situ annealing is more effective in reducing the densities of the localized states and of nonradiative recombination centers leading to better quality quantum well structures.
Robust TaNx diffusion barrier for Cu-interconnect technology with subnanometer thickness by metal-organic plasma-enhanced atomic layer deposition
Authors: Kim H. , Detavenier C. , van der Straten O. , Rossnagel S. M. , Kellock A. J. , Park D.-G.
Published: July 2005

Ta N x diffusion barriers with good barrier properties at subnanometer thickness were deposited by plasma-enhanced atomic layer deposition (PE-ALD) from pentakis(dimethylamino)Ta. Hydrogen and/or nitrogen plasma was used as reactants to produce TaNx thin films with a different nitrogen content. The film properties including the carbon and oxygen impurity content were affected by the nitrogen flow during the process. The deposited film has nanocrystalline grains with hydrogen-only plasma, while the amorphous structure was obtained for nitrogen plasma. The diffusion barrier properties of deposited TaN films for Cu interconnects have been studied by thermal stress test based on synchrotron x-ray diffraction. The results indicate that the PE-ALD TaN films are good diffusion barriers even at a small thickness as 0.6nm. Better diffusion barrier properties were obtained for higher nitrogen content. Based on a diffusion kinetics analysis, the nanocrystalline microstructure of the films was responsible for the better diffusion barrier properties compared to polycrystalline PE-ALD TaN films deposited from TaCl5.
Effects of nonparabolic bands in quantum wires
Authors: Godoy Andrés , Yang Zhicheng , Ravaioli Umberto , Gámiz Francisco
Published: July 2005

A nonparabolic band model has been implemented for a one-dimensional electron gas, using a modified Schrödinger equation which takes into account size quantization in the transverse cross section of a silicon quantum wire. The quantized states and the corresponding one-dimensional density of states have been analyzed when the nonparabolicity is present, to quantify the importance of the effect of realistic bands at higher energies.
Production of a MeV proton with 30 mJ laser energy by optimizing the focusing spot using a deformable mirror
Authors: Nayuki Takuya , Fujii Takashi , Oishi Yuji , Takano Kei , Wang Xiaofang , Andreev Alexander Alekseevitch , Nemoto Koshichi , Ueda Ken-ichi
Published: July 2005

The production of energetic protons using a polyimide tape of 7.5μm thickness was carried out with laser pulses of 30 mJ energy and 80 fs duration. A deformable mirror system with a genetic algorithm (GA) was developed to optimize the laser-focusing spot. The fitness values used in the GA were measured from the focusing intensities under the low-gain condition of the power amplifier, or from x-ray in situ signals emitted from the target. Although we obtained a diffraction-limited size of 2μm (full width at half maximum) using the former value, a precise compensation using the latter value was essential to accelerate protons whose flux was 106/MeV/shot to a maximum energy of 1.1±0.3MeV with laser pulses of only 30 mJ energy since a laser spot that is too tight may be sensitive to wave-front distortion caused by residual thermal lenses of the power amplifier.
Simultaneous determination of density and viscosity of liquids based on quartz-crystal resonators covered with nanoporous alumina
Authors: Goubaidoulline Ilchat , Reuber Johanna , Merz Friederike , Johannsmann Diethelm
Published: July 2005

Quartz-crystal resonators were coated with a layer of alumina nanopores in order to allow for simultaneous measurement of density and viscosity of a liquid. Whereas the motion of the liquid contained in the pores is locked to the movement of the crystal, the liquid located above the surface experiences internal shear. The latter portion of the liquid dissipates energy, thereby increasing the bandwidth of the resonance. Based on the increase in bandwidth, viscous loading and mass loading can be distinguished, allowing for an independent determination of the density and the viscosity of Newtonian liquids.
Effect of magnetic dilution in Zn1−xMnxGa2Se4 (0<x<0.5)
Authors: Morón M. C. , Hull S.
Published: July 2005

The profound effect of magnetic dilution in Zn1−xMnxGa2Se4 with 0<x<0. 5 is demonstrated by the analysis of neutron powder diffraction and magnetic susceptibility data. All the members of the series show a defective stannite crystal structure and a random distribution of the Mn ions. The magnetic archetype system of Zn1−xMnxGa2Se4 with 0<x<0. 5 is not found to be MnGa2Se4 (the magnetic end member of the series with I4¯ symmetry) but, instead, a hypothetical compound with I4¯2m symmetry. The distance between the Mn ions along the various magnetic superexchange pathways is not seriously affected by the degree of dilution. However, the global magnetic interaction between manganese ions is found to be significantly higher than that expected for the classical magnetic dilution of the parent MnGa2Se4. A generally applicable method for the calculation of the correct Weiss temperature θ in diluted magnetic semiconductors is provided.
Constructing dynamical systems with specified symbolic dynamics
Authors: Hirata Yoshito , Judd Kevin
Published: July 2005

In this paper we demonstrate how to construct signals (time series) of continuous-time dynamical systems that exhibit a given symbolic dynamics. This is achieved without construction of the ordinary differential equations that generate the flow. This construction is of theoretical interest and is useful as a source of dynamical data that can be used to test various data analysis algorithms.
A multichannel, high-resolution, UV spectrometer for laser-fusion applications
Authors: Donaldson W. R. , Millecchia M. , Keck R.
Published: July 2005

A 63-channel, ultraviolet (UV) spectrometer has been designed and tested. With an input energy of 1μJ per channel, 63 spectra can be acquired simultaneously on a single, multibeam laser shot. The spectrometer has a dispersion at the detector plane of 8.6×10−2pm∕μm and a spectral window of 2.4 nm at λ=351nm. The wavelength resolution varies from 2.5 pm at the center of the field of view to 6 pm at the edge.
Mobile high-temperature superconductor dc superconducting quantum interference device cooled by a pulse-tube cooler
Authors: He D. F. , Yoshizawa M. , Nakamura M.
Published: July 2005

We developed a mobile high-temperature superconductor dc superconducting quantum interference device (SQUID) magnetometer cooled by a pulse-tube cooler, which could be kept locked when moving in the Earth's field without shielding. A temperature controlling method was used in this system to stabilize the operation temperature of the pulse-tube cooler. Using the mobile SQUID magnetometer as a magnetic field sensor, we performed some eddy-current nondestructive evaluation experiments and successfully detected the defect in ferromagnetic materials.