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Main Field (main + field)
Selected AbstractsA comprehensive model of the quiet-time, near-Earth magnetic field: phase 3GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2002Terence J. Sabaka Summary The near-Earth magnetic field is caused by sources in the Earth's core, ionosphere, magnetosphere, lithosphere and from coupling currents between the ionosphere and the magnetosphere, and between hemispheres. Traditionally, the main field (low degree internal field) and magnetospheric field have been modelled simultaneously, with fields from other sources being modelled separately. Such a scheme, however, can introduce spurious features, especially when the spatial and temporal scales of the fields overlap. A new model, designated CM3 (Comprehensive Model: phase 3), is the third in a series of efforts to coestimate fields from all of these sources. This model has been derived from quiet-time Magsat and POGO satellite and observatory hourly means measurements for the period 1960,1985. It represents a significant advance in the treatment of the aforementioned field sources over previous attempts, and includes an accounting for main field influences on the magnetosphere, main field and solar activity influences on the ionosphere, seasonal influences on the coupling currents, a priori characterization of the influence of the ionosphere and the magnetosphere on Earth-induced fields, and an explicit parametrization and estimation of the lithospheric field. The result is a model that describes well the 591 432 data with 16 594 parameters, implying a data-to-parameter ratio of 36, which is larger than several popular field models. [source] Earth's magnetic field: ocean current contributions to vertical profiles in deep oceansGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2001F. E. M. (Ted) Lilley SUMMARY The Earth's main magnetic field, arising in the core, should, in the ocean, have a well-defined uniform gradient with depth. Superimposed upon this uniform gradient may be magnetic signals due to a variety of sources. These include crustal magnetization, the transient fluctuations arising external to the Earth and causing secondary induced fields within it; and, the focus of the present paper, magnetic signals arising from the motional induction of seawater moving in the steady main magnetic field of Earth. There are circumstances where theory predicts such motionally-induced magnetic fields to be of order 102 nT, and to vary with depth in a way which is directly related to the velocity profile. Exploratory soundings of the magnetic field with depth have been made in the oceans around Australia, both to test these predictions, and to investigate the practicability of measuring such profiles. The magnetic field parameter observed has been that of the ,total field', which should sense the component of the ocean velocity which lies in the magnetic meridian. The magnetometer has been lowered by cable from a ship and also operated free-fall to the seafloor (and return). The observations appear both to confirm the theoretical gradient of the main field where there is no ocean current and, where ocean currents exist, to give evidence of their profiles resolved in the direction of magnetic north. In particular, observations taken in an eddy of the East Australian Current show the correct contrast in sign for north and south flowing streams. [source] Assessment of regional geomagnetic field modelling methods using a standard data set: spherical cap harmonic analysisGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2000Z. Düzgit Various methods that take account of the potential nature of the field have been proposed for modelling geomagnetic data on a regional scale. Several of these have been applied to a standard data set based on annual mean values from observatories in Europe. Here, we examine some of the properties of spherical cap harmonic analysis when applied to this data set, and compare the quality of fit with that of the other models. It is found that, for this data set, rectangular polynomial analysis provides a compact fit to main field data, but that in most other cases, for both main field and anomaly data, spherical cap harmonic analysis provides the better fit. Although relatively insensitive to chosen cap size, spherical cap harmonic analysis deteriorates more rapidly than the other methods when the number of coefficients is reduced. [source] Removal of DC power-line magnetic-field effects from airborne total magnetic-field measurementsGEOPHYSICAL PROSPECTING, Issue 3 2000Mehran Gharibi Power lines carrying DC current can strongly affect total magnetic-field measurements. A simple algorithm using Biot,Savart's law was made to remove magnetic-field components due to a DC power line from airborne total magnetic-field measurements in the Gävle area, Sweden. The power-line location was estimated from observed data and then split into short line segments. The magnetic-field components due to each segment were calculated and summed together to give the total magnetic effect due to the power line at each observation point. The corrected total magnetic field was calculated by subtracting the power-line magnetic-field vector, projected on to the direction of the main field, from the measured total field. The results show a successful removal of the power-line magnetic effect from the total magnetic-field measurements. However, an error in the estimation of the power-line location can result in a magnetic-field residual after correction. A non-linear median filtering was used to remove this residual when needed. [source] Nitric oxide in plants: the history is just beginningPLANT CELL & ENVIRONMENT, Issue 3 2001M. V. Beligni ABSTRACT Nitric oxide (NO) is a bioactive molecule that exerts a number of diverse activities in phylogenetically distant species, as well as opposing effects in related biological systems. It was firstly described in mammals as a major messenger in the cardiovascular, immune and nervous system, in which it plays regulatory, signalling, cytoprotective and cytotoxic effects (Ignarro, Annual Review of Pharmacology and Toxicology 30, 535,560, 1990; Anbar, Experientia 51, 545,550, 1995). This versatility is mainly achieved through interactions with targets via either a redox or an additive chemistry (Stamler, Cell 78, 931,936, 1994). For this reason, metal- and thiol-containing proteins serve as major target sites for NO: these include signalling proteins, receptors, enzymes, transcription factors and DNA, among others. Furthermore, NO is a small, highly diffusible molecule. It rapidly crosses biological membranes and triggers various different processes in a short period of time. In this context, NO can co-ordinate and regulate cellular functions of microsomes and organelles such as mitochondria. The ubiquity of NO reactions, as well as the finding that the biochemical and molecular mechanisms underlying many physiological processes are well conserved between diverse species, have opened the exploration of NO chemistry in different organisms. Among these, plants were not the exception. The research in plants has been focused on three main fields: (i) the search for NO or any source of NO generation; (ii) the examination of the effects of NO upon exogenous treatments; and (iii) the search for the same molecules involved in NO-sensitive transduction pathways as in animals (e.g. cGMP, Ca2+, calmodulin). As it is evident from this review, recent progress on NO functionality in plants has been impressive. With the use of biochemistry, molecular genetics and structural biology, together with classical physiological approaches, an explosion of new discoveries will surely begin. It is certainly a good time for plant biologists. [source] Der Viadukt über das Tarntal bei Millau , Von den ersten Entwurfsgedanken bis zur FertigstellungBAUTECHNIK, Issue 2 2006Michel Virlogeux Prof. Dr.-Ing. Der Bau des Viadukts über das Tarntal bei Millau in Mittelfrankreich begann im Oktober 2001 und war im Dezember 2004 vollendet. Der Viadukt mit einer Gesamtlänge von 2460 m umfaßt sechs 342 m lange Hauptfelder, die an sieben Pylonen verankert sind und stellt einen bedeutenden Fortschritt im Entwurf von Schrägseilbrücken dar. Die Autobahn verläuft 270 m über dem Fluß, zwei ihrer Pfeiler sind höher als 230 m. Mit den 87 m hohen Pylonen über der Fahrbahn überragen sie den Eiffelturm. Ausgearbeitet wurden zwei Lösungen, eine in Spannbeton und eine in Stahlbauweise. The viaduct over the Tarn valley near Millau , from early design to completion. The erection of the viaduct over the Tarn valley near Millau in central France began in October 2001 and was completed in December 2004. The viaduct with an overall length of 2460 m covers six 342 m long main fields, those at seven suspension towers is embodied and represents an important progress in design of cable-stayed bridges. The motorway runs in 270 m height over the river, two of their columns are more highly than 230 m. Together with the 87 m high pylons over the roadway towers are higher then the Eiffel tower in Paris. Two solutions were prepared, one in prestressed concrete and one in steel construction method. [source] | ||||||||||