Eddy current effects in plain and hollow cylinders spinning inside homogeneous magnetic fields: Application to magnetic resonance

International audienceWe present a thorough analysis of eddy currents that develop in a rectangular cross section toroid rotating in a uniform magnetic field. The slow rotation regime is assumed. Compact expressions for the current density, the total dissipated power, and the braking torque are given. Examination of the topology of current lines reveals that depending upon the relative dimensions of the side and length of the toroid two different regimes exist. The conditions of existence of the two regimes are analytically established. In view of nuclear magnetic resonance (NMR) applications, we derive the angular variation of the magnetic field created by eddy currents and lay down the formalism necessary for calculating the effect of this field on the NMR spectra of the conductor itself or of a sample co-rotating with the conductor, a situation encountered when dealing with rotating detectors. Examples of calculations for cases of practical interest are presented. The theory is confronted with available data, and we give guidelines for the design of optimized rotating micro-coils

Remote sensing techniques in the search for ancient shipwrecks: how to distinguish a wreck from a rock in geophysical recordings

Η εργασία παρουσιάζει τον τρόπο με τον οποίο οι μέθοδοι θαλάσσιας γεωφυσικής μπορούν να χρησιμοποιηθούν με αποτελεσματικότητα για αρχαιολογικές έρευνες βαθέων υδάτων. Σημαντικός παράγοντας για τη σωστή ερμηνεία των γεωφυσικών καταγραφών είναι η συμμόρφωση με τις αρχές της ωκεανογραφίας και της θαλάσσιας γεωλογίας. Ο συνδυασμός δεδομένων από τον τομογράφο υποστρώματος παρέχει πολύτιμα στοιχεία για τη δομή του, η γνώση της οποίας συμβάλει στην γεωλογικά σωστή ερμηνεία των καταγραφών του ηχοβολιστή πλευρικής σάρωσηςThis paper presents the way conventional marine geophysical methods may be used with the highest efficiency for deep-water archaeological research, especially for the detection of ancient shipwrecks. Their use becomes all the more effective, when the principles of oceanography and marine geology are being followed during the interpretation of the geophysical recordings. The integration of sub-bottom profiling data provides valuable information on the geological structure of the seafloor 's shallow substrate, which are an almost absolute prerequisite for a geologically reasonable interpretation of the side scan sonar images. Otherwise, interpretation of the sonar recordings may be erroneous or may be in direct discrepancy with the shallow sub-seafloor geological structure. Limitations of the efficiency of the geophysical methods in the case of targets of biogenic or anthropogenic origin or in shallow water environments are also being discusse

An Introduced Methodology for Estimating Landslide Hazard for Seismic andRainfall Induced Landslides in a Geographical Information System Environment

The demand for estimating landslide hazard has evolved during the last decade. Landslides are characterised among the most severe natural hazards, which can cause casualties, fatalities, harm or detriment in natural and man-made environment. In the first part of this paper the results of the research conducted on slope deformation due to seismic loading are presented. According to field observations deformation and displacement of natural and man-made slopes in strong earthquakes are common phenomena, even though they are associated to moderate magnitude seismic events. These permanent displacements are due to seismic loading, and are produced because the material, through which acceleration pulses have to travel before reaching the ground surface, has a finite strength, and stresses induced by strong earthquakes may overcome this strength limit and bring about failure. Many methods were developed in order to assess the earthquake induced ground displacements due to seismic energy flow. We applied the simplified Newmark’s model, in order to study the problem of slope stability estimation and induced permanent deformations. In the current paper, the outcome of the studies attached to slope stability estimation under static and dynamic conditions considering the factors controlling safety conditions is introduced. These principal factors were first introduced to an artificial neural network and the estimated factor of safety and displacement were subsequently implemented in a geographical information system. A software tool was developed in order to produce landslide hazard maps due to static and dynamic loading, implementing failure criteria. In the second part, the results of the investigation of slope hydrology conditions in slope stability are presented. In these cases the factor of safety decreases due to prolonged precipitation and eventually the slope may fail. A parametric study of the effect of suction zone in slope stability of unsaturated soils is examined. This study focuses on slope behaviour under rainfall conditions

Low-cost, pseudo-Halbach dipole magnets for NMR

We present designs for compact, inexpensive and strong dipole permanent magnets aimed primarily at magnetic resonance applications where prepolarization and detection occur at different locations. Low-homogeneity magnets with a 7.5 mm bore size and field up to nearly 2 T are constructed using low-cost starting materials, standard workshop tools and only few hours of labor – an achievable project for a student or postdoc with spare time. As an application example we show how our magnet was used to polarize the nuclear spins in approximately 1 mL of pure [$^{13}$C]-methanol prior to detection of its high-resolution NMR spectrum at zero field (measurement field below 10$^{-10}$ T), where signals appear at multiples of the carbon-hydrogen spin-spin coupling frequency $^{1}$J$_{CH}$=140.7(1) Hz.This work has received support from the European Research Council (author DS, grant agreement FP7-205119 R-EvolutioN-MR) and from the European Commission’s Seventh Framework Program (author MCDT under the Marie Curie International Outgoing Fellowship Programme, grant agreement FP7-625054 ODMR-CHEM; author DS, 2007–2013)

Low-cost, pseudo-Halbach dipole magnets for NMR

We present designs for compact, inexpensive and strong dipole permanent magnets aimed primarily at magnetic resonance applications where prepolarization and detection occur at different locations. Low-homogeneity magnets with a 7.5 mm bore size and field up to nearly 2 T are constructed using low-cost starting materials, standard workshop tools and only few hours of labor – an achievable project for a student or postdoc with spare time. As an application example we show how our magnet was used to polarize the nuclear spins in approximately 1 mL of pure [$^{13}$C]-methanol prior to detection of its high-resolution NMR spectrum at zero field (measurement field below 10$^{-10}$ T), where signals appear at multiples of the carbon-hydrogen spin-spin coupling frequency $^{1}$J$_{CH}$=140.7(1) Hz.This work has received support from the European Research Council (author DS, grant agreement FP7-205119 R-EvolutioN-MR) and from the European Commission’s Seventh Framework Program (author MCDT under the Marie Curie International Outgoing Fellowship Programme, grant agreement FP7-625054 ODMR-CHEM; author DS, 2007–2013)