bluuebunny/crossref_metadata_2025_split huggingface dataset:
Statistical analysis of ionospheric potential patterns for isolated substorms and sawtooth events
Authors: Cai X. , Clauer C. R. , Ridley A. J. 
Published: June 2010

Abstract. We present here results which contrast isolated substorms with individual sawtooth events. Sawtooth events are defined as quasi-periodic, large-amplitude oscillations in the energetic particle flux with a periodicity of 2–4 h observed at the geosynchronous orbit. Sawtooth events have several similarities to isolated substorms leading therefore, to different opinions about whether sawtooth events are just an intense periodic form of substorms or if they deserve a category of their own. To help resolve this, we examine the ionospheric potential patterns in the northern polar region for isolated substorms and sawtooth events using the assimilative mapping of ionospheric electrodynamics (AMIE) technique. First we show a statistical analysis of isolated substorm potential patterns. In order to examine the seasonal variation, isolated substorms are identified by mid-latitude positive bay in the north-south geomagnetic perturbation in each season, respectively. Superposed epoch analysis (SEA) is applied to obtain the typical polar potential patterns for each season. By examining the time evolution of the potential patterns and cross polar cap potential (CPCP) for isolated substorms during each season, we find only subtle seasonal variations in the results obtained using the AMIE analysis. This provides a basis for comparison with sawtooth events in the next step. From the averaged potential patterns of 213 isolated substorms and those of 184 individual sawtooth events, we find the sawtooth events show signatures similar to subtorms: the DP 1 potential pattern develops and dominates the polar region after the onset. However, the DP 1 potential cell of sawtooth events encompasses a larger area than that of isolated substorms. Moreover, the CPCP of sawtooth is stronger than that of isolated substorms. It is also shown that the sawtooth events displays greater variability between individual events than isolated substorms. We conclude that in terms of ionospheric electrodynamics, the sawtoothe events have features that are similar to those of isolates substorms, though larger in spatial extent and in magnitude.
VHF signal power suppression in stratiform and convective precipitation
Authors: McDonald A. J. , Monahan K. P. , Hooper D. A. , Gaffard C. 
Published: June 2010

Abstract. Previous studies have indicated that VHF clear-air radar return strengths are reduced during periods of precipitation. This study aims to examine whether the type of precipitation, stratiform and convective precipitation types are identified, has any impact on the relationships previously observed and to examine the possible mechanisms which produce this phenomenon. This study uses a combination of UHF and VHF wind-profiler data to define periods associated with stratiform and convective precipitation. This identification is achieved using an algorithm which examines the range squared corrected signal to noise ratio of the UHF returns for a bright band signature for stratiform precipitation. Regions associated with convective rainfall have been defined by identifying regions of enhanced range corrected signal to noise ratio that do not display a bright band structure and that are relatively uniform until a region above the melting layer. This study uses a total of 68 days, which incorporated significant periods of surface rainfall, between 31 August 2000 and 28 February 2002 inclusive from Aberystwyth (52.4° N, 4.1° W). Examination suggests that both precipitation types produce similar magnitude reductions in VHF signal power on average. However, the frequency of occurrence of statistically significant reductions in VHF signal power are very different. In the altitude range 2-4 km stratiform precipitation is related to VHF signal suppression approximately 50% of the time while in convective precipitation suppression is observed only 27% of the time. This statistical result suggests that evaporation, which occurs more often in stratiform precipitation, is important in reducing the small-scale irregularities in humidity and thereby the radio refractive index. A detailed case study presented also suggests that evaporation reducing small-scale irregularities in humidity may contribute to the observed VHF signal suppression.
Model modifications in Schumann resonance intensity caused by a localized ionosphere disturbance over the earthquake epicenter
Authors: Nickolaenko A. P. , Hayakawa M. , Sekiguchi M. , Ando Y. , Ohta K. 
Published: June 2010

Abstract. This paper is a further extension of our latest observations and modeling by Hayakawa et al. (2005a), in which we discovered the anomalous behavior of Schumann resonance observed in Japan, in possible association with the Chi-chi earthquake in Taiwan. Schumann resonance intensity changes associated with a localized decrease in the lower ionospheric height over the earthquake epicenter are modeled. The knee model of the vertical conductivity profile of the ionosphere describes the regular Earth-ionosphere cavity, and the modified knee model is introduced for the disturbance. The localized ionosphere modification is of a Gaussian radial dependence; it has a 1-Mm radius, and the decrease reaches 20 km in the lower ionosphere height over the epicenter of the earthquake (Taiwan). The diffraction problem in the Earth-ionosphere cavity with a localized disturbance is resolved by using the Stratton-Chu integral equation. This solution is constructed for the case of natural resonance oscillations driven by independent random sources distributed worldwide. The data of the Optical Transient Detector (OTD) are used to introduce the source distribution. A pronounced increase in the intensity of the Schumann resonance is obtained around the fourth mode frequency (up to 20%) when thunderstorms are concentrated in Central America. The worldwide distribution of lightning strokes blurs and slightly reduces the effect (15% increase in intensity) for the observer in Japan and the localized nonuniformity positioned over Taiwan. A clear qualitative similarity is obtained in relation to the experimental data, indicating that records collected in Japan may be explained by the impact of a localized decrease in the lower ionosphere over the epicenter of the earthquake. It is admitted that the assumed conductivity decrease could only be caused by a severe change in the ionization in the middle atmosphere. It is not in the scope of this paper to discuss the possible mechanism, but rather to show that a closer and quantitative agreement with the experiment yields information about the form and size of the ionospheric modification and about the distribution of global thunderstorm activity during measurements.
Thermal, atmospheric and ionospheric anomalies around the time of the Colima M7.8 earthquake of 21 January 2003
Authors: Pulinets S. A. , Ouzounov D. , Ciraolo L. , Singh R. , Cervone G. , Leyva A. , Dunajecka M. , Karelin A. V. , Boyarchuk K. A. , Kotsarenko A. 
Published: June 2010

Abstract. The paper examines the possible relationship of anomalous variations of different atmospheric and ionospheric parameters observed around the time of a strong earthquake (Mw 7.8) which occurred in Mexico (state of Colima) on 21 January 2003. These variations are interpreted within the framework of the developed model of the Lithosphere-Atmosphere-Ionosphere coupling. The main attention is focused on the processes in the near ground layer of the atmosphere involving the ionization of air by radon, the water molecules' attachment to the formed ions, and the corresponding changes in the latent heat. Model considerations are supported by experimental measurements showing the local diminution of air humidity one week prior to the earthquake, accompanied by the anomalous thermal infrared (TIR) signals and surface latent heat flux (SLHF) and anomalous variations of the total electron content (TEC) registered over the epicenter of the impending earthquake three days prior to the main earthquake event. Statistical processing of the data of the GPS receivers network, together with various other atmospheric parameters demonstrate the possibility of an early warning of an impending strong earthquake.
A modeling study of ionospheric F2-region storm effects at low geomagnetic latitudes during 17-22 March 1990
Authors: Pavlov A. V. , Fukao S. , Kawamura S. 
Published: June 2010

Abstract. We have presented a comparison between the modeled NmF2 and hmF2, and NmF2 and hmF2, which were observed in the low-latitude ionosphere simultaneously by the Kokubunji, Yamagawa, Okinawa, Manila, Vanimo, and Darwin ionospheric sounders, by the middle and upper atmosphere (MU) radar during 17-22 March 1990, and by the Arecibo radar for the time period of 20-22 March 1990. A comparison between the electron and ion temperatures measured by the MU and Arecibo radars and those produced by the model of the ionosphere and plasmasphere is presented. The empirical zonal electric field, the meridional neutral wind taken from the HWM90 wind model, and the NRLMSISE-00 neutral temperature and densities are corrected so that the model results agree reasonably with the ionospheric sounder observations, and the MU and Arecibo radar data. It is proved that the nighttime weakening of the equatorial zonal electric field (in comparison with that produced by the empirical model of Fejer and Scherliess (1997) or Scherliess and Fejer (1999)), in combination with the corrected wind-induced plasma drift along magnetic field lines, provides the development of the nighttime enhancements in NmF2 observed over Manila during 17-22 March 1990. As a result, the new physical mechanism of the nighttime NmF2 enhancement formation close to the geomagnetic equator includes the nighttime weakening of the equatorial zonal electric field and equatorward nighttime plasma drift along magnetic field lines caused by neutral wind in the both geomagnetic hemispheres. It is found that the latitudinal positions of the crests depend on the E×B drift velocity and on the neutral wind velocity. The relative role of the main mechanisms of the equatorial anomaly suppression observed during geomagnetic storms is studied for the first time in terms of storm-time variations of the model crest-to-trough ratios of the equatorial anomaly. During most of the studied time period, a total contribution from meridional neutral winds and variations in the zonal electric field to the equatorial anomaly changes is larger than that from geomagnetic storm disturbances in the neutral temperature and densities. Vibrationally excited N2 and O2 promote the equatorial anomaly enhancement during the predominant part of the studied time period, however, the role of vibrationally excited N2 and O2 in the development of the equatorial anomaly is not significant. The asymmetries in the neutral wind and densities relative to the geomagnetic equator are responsible for the north-south asymmetry in NmF2 and hmF2, and for the asymmetry between the values of the crest-to-trough ratios of the Northern and Southern Hemispheres. The model simulations provide evidence in favor of an asymmetry in longitude of the energy input into the auroral region of the Northern Hemisphere on 21 March 1990.
Potassium: Radonuclides
Authors: Jun Taehong , Tsay Olga G. , Churchill David G. 
Published: June 2010

Abstract

There are currently 28 known nuclides of potassium (K). Three of these are naturally occurring:
39
K,
40
K, and
41
K of which potassium‐40 is the only naturally occurring radionuclide. With its long half‐life of 1.28 × 10
9
years and an abundance of 0.012%,
40
K is a discrete source of natural radiation. Thus, in potassium‐rich foods, minerals, etc., a distinct natural dose is unavoidable for humans and all living creatures on Earth. Thus, it may be quantified in soil, plants, and animals and allows for various studies. Potassium‐40 may decay to calcium‐40 (89% probability) or may undergo electron capture (EC) to give argon‐40 (11% probability). The
biological
half‐life (excretion time decay) of
40
K, however, is 30 days. As it is often found in many mineral forms, potassium‐40 is a common constituent of soil and water, but not air. There are various reports in which
40
K is tracked migrating from soil(s) into various plants. In countries such as Europe and Brazil, drinking water was also scrutinized and found to contain
abnormal
levels of
40
K. The abundance of
40
K in human diet and foods from places such as China, Pakistan, and Ukraine has also been studied.
Cesium: Radionuclide
Authors: Lima Enrique 
Published: June 2010

Abstract

Radionuclides of cesium are generated mainly from nuclear fission. Many cesium radionuclides are known, but
134
Cs and
137
Cs are of the greatest concern because of their radiological properties. Cesium is present in polluted effluents of nuclear power plants. Gas, liquid, and solid wastes contaminated with cesium can be found but aqueous effluents, where cesium is present in the cationic form, are the most common. These cations can reach agricultural fields due to their high affinity for clays. Thus, cesium radionuclides can be incorporated into the food chain, and ultimately transported to human beings.
Phosphorus: Radionuclides
Authors: Kim Kibong , Churchill David G. 
Published: June 2010

Abstract32P and33P are important radionuclides of phosphorus with half‐lives of 14.3 and 25.3 days, respectively, and which decay via β−emission. These isotopes (of 23 known) have anthropogenic sources and are prepared by the enrichment of sulfur. The radionuclides are used in tracer studies primarily as phosphate, or other common phosphate forms such as “phosphate rock” or ortho‐phosphoric acid. Various labeling and therapeutic studies have been performed in the fields of biology, botany, and in clinical medicine and are mentioned herein. Radioisotopes of phosphorus can be detected by liquid scintillation counting. There is, however, limited knowledge about remediation as32P and33P are short‐lived.
Uranium: Radionuclides
Authors: Vandenhove Hildegarde , Hurtgen Christian , Payne Timothy E. 
Published: June 2010

AbstractThis article describes the occurrence, chemistry, and bioavailability of uranium (U) in terrestrial and aquatic environments, its analysis in environmental samples, and remedial measures applicable to uranium‐contaminated water and soil. Uranium is widely distributed throughout the world. There are three main isotopes present in natural uranium, which comprises234U (0.0055%),235U (0.72%), and238U (99.27%). Uranium can occur either in its reduced state (U(IV)), which is generally highly immobile, or in its more soluble and mobile (U(VI)) state. Uranium mobility and bioavailability are governed by oxidation state, complexation by organic and inorganic ligands, pH, sorption by minerals including clays and hydroxides, and interactions with organic matter. In uncontaminated surface waters uranium content is generally low (<1 ppb). Most groundwaters are low in uranium but the concentration range is large (<0.001–2600 ppb), resulting from the interaction of groundwater with naturally occurring uranium‐bearing materials or anthropogenic contamination sources. Since groundwater is a major source for drinking water, various methods have been developed to remove uranium from potable water. Similar methods are applied in wastewater treatment. Extraction and processing of uranium ore or minerals containing natural radionuclides has resulted in the generation of waste streams. The major challenge associated with these contaminated waste streams, residues, or sites is typically the larger volumes of material and the relatively low specific activities.
Mediterranean Sea: Radionuclides
Authors: Delfanti Roberta , Papucci Carlo 
Published: June 2010

AbstractThe main sources of anthropogenic radioactivity in the Mediterranean Sea are fallout from atmospheric nuclear weapon testing and from the Chernobyl accident in 1986, while the releases from the nuclear industry are small. Consequently, the present radionuclide levels in the marine environment are of no concern from the radiological point of view. However, the Mediterranean Sea is an ideal environment to show how both coastal and open‐sea processes act to redistribute radionuclides in the different compartments of the marine environment. In fact, the Mediterranean Sea is considered a miniature ocean, where all the processes characterizing the global ocean take place on smaller space and timescales. For these reasons, in the past decades it had largely been used as a “laboratory basin” for process studies. In this framework, anthropogenic and natural radionuclides were often measured to be used as tracers of water mass dynamics, transit and renewal times, particle dynamics, sediment accumulation, etc. In this article, we first briefly describe the physical and biogeochemical characteristics of the Mediterranean Sea. After reviewing and quantifying the sources of radioactivity, we mainly focus on two radionuclides: (i)137Cs: conservative in the open sea, the most abundant anthropogenic radionuclide, and, among these, the main contributor to radioactive dose to the population, and (ii) the very long‐lived239,240Pu: nonconservative and the most abundant among transuranics. We describe their distribution and time trend in seawater, sediments, and biota, define their budgets in the basin, quantify the exchanges at the Gibraltar and Turkish Straits, and indicate future trends. We also report levels and distributions of selected natural radionuclides: (i)238U, with234Th as the main tracer for particle dynamics and whose concentration in the Mediterranean slightly differs from that in the oceans, and (ii)210Po, which is efficiently accumulated by marine organisms and is the main contributor to radioactive dose to the population. Finally, we identify topics for future research, mainly related to the application of nuclear techniques to the study of oceanographic processes.
Cesium: Global Ocean Distribution
Authors: Inomata Yayoi 
Published: June 2010

AbstractSince the 1950s Cesium‐137(137Cs) concentrations in the surface waters of the global ocean have been extensively measured in numerous studies. This article, based on the analysis of the137Cs concentrations in the HAM‐global database, summarizes the results of spatial and temporal variations in137Cs concentrations in the surface waters (0–10 m) of the global ocean for the period 1957 to 2005.137Cs in the surface waters of the North Pacific Ocean and North Atlantic Ocean has mainly originated from the nuclear weapon testing global fallout in the late 1950s and early 1960s. In the 1970s and 1980s, the discharge from the nuclear fuel reprocessing plants was the dominant source for the North Atlantic Ocean and its northeast marginal seas. The seas that were largely affected by the fallout of the Chernobyl accident in 1986 were the Baltic, the Black, and the Mediterranean Seas. In the 1990s and 2000s, the137Cs concentrations were decreasing in the global ocean. During this time, the difference in concentrations in the various seas reduced when compared with those in the 1960s and 1970s. In 2005, the most anthropogenic137Cs contaminated area of the global ocean was Baltic Sea, whereas the most undisturbed area was the Antarctic Ocean.137Cs in the surface water had an almost homogeneous distribution in the North Pacific, the equatorial region in the Pacific, and the Indian Ocean. The fact that the apparent‐half residence time (the decreasing rate of137Cs concentration) is almost equal in these regions suggests that the137Cs injected into the western North Pacific Ocean by global fallout was transported to the subtropics and tropics through oceanographic processes. Part of137Cs was recirculated in the Pacific Ocean, and the rest was transported into the Indian Ocean via the Indonesian through flow.
Perfluorinated Polymers, Polytetrafluoroethylene
Authors: Gangal Subhash V. , Brothers Paul D. 
Published: June 2010

Abstract
Polytetrafluoroethylene (PTFE) has a unique position in the plastics industry due to its chemical inertness, heat resistance, excellent electrical insulation properties, and low coefficient of friction over a wide temperature range. The white to translucent solid polymer has an extremely high molecular weight in the 106–107 range. PTFE is a highly crystalline polymer with high thermal stability derived from the strong carbon‐fluorine bond. As a result, PTFE is a very useful high temperature polymer. Commercial PTFE is manufactured by two different polymerization processes that result in two different types of chemically identical polymers. Suspension polymerization produces a granular resin and emulsion polymerization is used to produce fine powder resins (coagulated dispersion) or aqueous dispersions. Because of its high molecular weight, PTFE does not flow and can not be fabricated by conventional techniques. The suspension polymerized PTFE is usually fabricated by modified metallurgy techniques. Emulsion polymerized, coagulated PTFE is processed by a cold extrusion process while the stabilized aqueous dispersions are processed according to latex processing techniques.
Pulsed Power Applications with Conductive (Carbon‐Loaded) Composite Polymer Electrodes—Requirements and Characterization
Authors: Roodenburg Bart , de Haan Sjoerd , Malchev Plamen , Leitão Telma , Mendes Eduardo 
Published: June 2010

AbstractPulsed power (PP) is a technology where energy is released to a load in a short time. Every device using this technology needs electrodes to transfer the electric energy to the load. Recent developments in composite conductive polymers make them suitable as electrodes for new or existing PP applications, where normally metals were used. Composite polymers, consisting of conductive filler and a nonconductive matrix, can solve several specific problems in common and to be developed (PP) applications, due to their ability to conduct current or to store electrical charge, in combination with their elasticity. In general, polymer electrodes behave differently on pulsed stimuli compared to a static load and metal electrodes. An overview of many existing characterization methods and a newly developed technique suited for characterization of conductive polymers for PP applications in particular is described. For three different applications,artificial muscles, cell electroporation, andbiofouling prevention, the requirements for the polymer electrodes and specific application‐related issues are addressed with examples.
Microstructure Analysis of Acrylate‐Methacrylate Copolymers by
13
C Nuclear Magnetic Resonance Spectroscopy
Authors: Matlengiewicz Marek 
Published: June 2010

Abstract

Microstructure of acrylate‐methacrylate copolymers can be determined in detail by means of
13
C nuclear magnetic resonance (NMR) spectroscopy. Several signals in the
13
C NMR spectra of such copolymers are sensitive to compositional and conformational differences in the macromolecular chain. However, only the carbonyl and β‐CH
2
carbons from the main chain provide complete and complementary information on distribution of configurational–compositional sequences, since only these two carbons are present in all (meth)acrylate units. Carbonyl signal is the source of information on distribution of odd sequences, usually up to configurational–compositional pentads. Complementary information, on distribution of even sequences, can be derived from the signal of β‐CH
2
carbons of the main chain. Spectral simulation can verify the signal assignment to respective sequences and incremental calculations of the chemical shifts of individual sequences were found to be useful for both carbonyl and methylene signal.