Very Low Frequency Electromagnetics

Analysis of heart rate variability (HRV) is a valuable, non-invasive method for quantifying autonomic cardiac control in humans. Frequency-domain analysis of HRV involving myocardial ischaemic episodes should take into account its non-stationary behaviour. The wavelet transform is an alternative tool for the analysis of non-stationary signals. Fourteen patients have been analysed, ranging from 40 to 64 years old and selected from the European Electrocardiographic ST-T Database (ESDB).

A conductivity relaxation experiment has been conducted on an SrFeCo0.5Ox sample by abruptly changing the oxygen partial pressure in the atmosphere and monitoring the change of conductivity as a function of time. The re-equilibrium process obeys Fick's second law. By fitting the relaxation data to the solution of the diffusion equation with appropriate boundary conditions, we could determine the oxygen chemical diffusion coefficient and the activation energy. The oxygen diffusion coefficient is 8.9 × 10−7 cm2/s at 900 °C and it increases with increase in temperature. Measured activation energy is 0.92 eV, which is slightly lower than that of other oxides in the system SrFe1 − xCoxOy.

The VLF-E.M. (Very Low Frequency-Electro Magnetics) method was first used for geophysical surveying in 1964. Since then many hundreds of surveys have been carried out; several variations on the original design have been introduced; and the method has become airborne.The VLF instrument is a directional radio receiver, which can be tuned to distant radio transmitters in the 15–25 kHz band. The first VLF instrument and the one most widely used to date measures the vertical real and imaginary components of the magnetic field vector.The imaginary component has been found useful in distinguishing between conductors lying at different depths below ground. Ground conductivity is also interpretable. Relative conductivity-thickness of a buried conductor affects the VLF response but is harder to interpret.The VLF-E.M. method has established its usefulness in geophysical surveying for massive sulphides and for geological mapping. Field results suggest that it may also play a useful role in exploring for the more disseminated ores, where suitable conductivity contrasts at these frequencies exist.

Early embryonic development is characterized by dramatic modifications in chromatin organization. These contribute to the formation of the totipotent cells that will differentiate into the embryonic and extra-embryonic lineages. However, some groups of genes are not affected by these global changes. Amongst these, are the genes controlled by genomic imprinting, an epigenetic mechanism that makes the maternal and the paternal genomes functionally non-equivalent in development. Somatic cell nuclear transfer (SCNT), used to clone animals, mimics the chromatin reprogramming that occurs in the post-fertilization embryo. However, SNCT leads to aberrant development, particularly of the extra-embryonic tissues. As a consequence, live-born animals are obtained at very low frequency. Here, we review how different steps in the SCNT procedure may give rise to aberrant development. Imprinted genes are amongst the frequently affected genes, and their perturbed expression explains in part the abnormal developmental phenotypes. The future challenge will be to modify currently used cloning procedures, in order to increase the efficiency of nuclear reprogramming, without affecting the gene loci at which chromatin is normally not altered during development.

Low frequency noise measurements are among the most sensitive tools for the investigation of the quality and of the reliability of semiconductor devices. The sensitivity that can be obtained depends on the background noise of the low noise preamplifier coupled to the device under test (DUT) that, at very low frequencies, is dominated by flicker noise. The low frequency noise produced by the DUT, on the other end, is very often the most interesting signal to be detected and analyzed. In this work we propose a very simple topology for the realization of a general purpose low noise preamplifier whose noise performances, at very low frequencies (below 10 Hz), are significantly better than those that can be obtained by the most popular commercial instrumentation. Indeed, a gain of 80 dB with a pass band extending from a few tens of mHz up to a few kHz with an equivalent input voltage noise as low as 14 nV/square root(Hz) (100 mHz), 1.4 nV/square root(Hz) (1 Hz), 1.0 nV/square root(Hz) (10 Hz), and 0.8 nV/square root(Hz) (1 kHz) are consistently obtained by using quite standard electronic components and with no need for trimming and/or calibration steps. Moreover, the junction field-effect transistor input stage of the amplifier is characterized by an equivalent input current noise below 4 fA/square root(Hz) in the entire bandwidth, resulting in negligible background noise degradation for DUT impedances in excess of 100 kohms.

ABSTRACT This paper investigates the benefits of a multisensor fusion methodology for underwater navigation using location-dependent signatures, or geotags. The proposed coordinate-free system uses both natural and man-made signals, as well as transient events to extract location-dependent signatures for navigation and guidance. Natural signals include the geomagnetic field, gravity field, bathymetric features, and naturally-occurring very low frequency radio signals. Man-made acoustic sources of opportunity include drainage outlets and pump stations in littoral zones and particularly in harbors, which can be explored to serve as underwater beacons for navigation. This paper models a multisensor coordinate-free system, characterizes various signals for underwater navigation, and evaluates the Multisensor Underwater Signature-based Navigation (MUSNav) system in terms of accuracy, availability, and continuity of the navigation solution.

A simple filter is developed which transforms VLF-EM real magnetic field transfer functions into apparent resistivities. It is based on the relationship between the horizontal derivative of the surface electric field and the vertical magnetic field at the surface of a two-dimensional earth model. The performance of this simple autoregressive filter is tested for modelled and real survey data. The technique yields profiles of apparent resistivity very similar, both in magnitude and in wavelength, to those which would have been obtained using VLF-EM resistivity measurements or d.c. resistivity profiling. This low-pass filter has the advantage of reducing high-wavenumber noise in the data; therefore only the major features of the VLF-EM profile are displayed.

Abstrak-Kelongsoran sering terjadi pada tanah yang memiliki topografi curam. Salah satunya adalah yang terjadi di Desa Jombok, Kecamatan Ngantang, Kabupaten Malang, Jawa Timur. Pada areal seluas satu hektar dijumpai penurunan permukaan tanah (longsor). Daerah longsoran ini diteliti dengan menggunakan salah satu metoda Geofisika, yaitu Very Low Frequency-Electromagnetic (VLF-EM). Data lapangan yang didapatkan dari hasil pengukuran metode VLF-EM biasanya tercampur dengan noise dan outlier. Pada penelitian ini digunakan filter NA-MEMD untuk menghilangkan noise dan outlier. Digunakan Filter Karous-Hjelt untuk menganalisa data secara kualitatif. Sedangkan analisa secara kuantitatif diperoleh dengan melakukan pemodelan inversi menggunakan INV2DVLF. Hasil analisis VLF-EM dengan menggunakan filter NA-MEMD mampu mereduksi noise dan outlier dari data pengukuran. Sedangkan hasil inversi 2D menunjukkan bahwa terdapat zona anomali yang menunjukkan zona lemah atau rawan longsor di area penelitian.
Abstract-Landslide often occurs in a steep topography ground. One of them is happened in the Jombok village, Ngantang, Malang, East Java. Land subsidence (landslides) often occur in this area. The landslide area investigated using one of the Geophysics methods, the Very Low Frequency-Electromagnetic (VLF-EM). The field datas obtained from measurement results of VLF-EM method are usually mixed with noise and outliers. In this research, NA-MEMD filter.is used to eliminate the noise and outliers. Karous-Hjelt (K-Hjelt) filter is udes to qualitative analyze of the data. While quantitative analysis is obtained by performing inversion modeling using INV2DVLF. VLF-EM analysis results using the NA-MEMD filter is able to reduce the noise and outliers of measurement data. While the 2D inversion results indicate that there is an anomalous zone which indicates weak or landslide-prone zones in the study area.

The seismic hazard presented by slow subduction zones is not well known. While there is a widely accepted apparent relation between “fast-young plate” subduction and great earthquake generation (e.g., Chile, 1960), the seismic record indicates that slow subduction zones are also capable of generating mega-thrust earthquakes (M > 8.2). Available data on the recurrence interval for slow subduction margins, suggests that repeat times are longer than for more rapid convergence margins (on the order of several hundred to a few thousand years). For several of these margins, however, no shallow dipping thrust earthquake focal mechanisms are observed and no mega-thrust earthquakes known either. Slow subduction zones (v ≥ 4 cm/year) are typically characterized by thick sedimentary sections on the incoming plate (2–6 km) and by a broad accretionary wedge (100–250 km). The “taper” of these accretionary wedges is mechanically related to the basal and internal friction and ranges from about 2̆ to 12̆. Some wedges have extremely shallow mean surface and basal slopes (about 1–2̆ each, taper <4̆) indicating a very weak decollement layer. These include: Barbados Ridge, Makran, Hikurangi, Mediterranean Ridge, Calabria, Gibraltar/Cadiz, and Cascadia/Washington. Nankai, Sumatra and E. Alaska have slightly higher tapers of about 5–7̆. Most of these low-taper wedges have very slow to slow convergence rates (0.5–4 cm/year). The presence of these wide accretionary wedges strongly affects the type and amount of deformation above the “up-dip limit” of the seismogenic zone. The thermally insulating effect of a wide and thick wedge of sediment produces a wide, shallow transition zone (between the 100̆C and 150̆C isotherms) as well as a substantial (up to 80 km wide) region between this and the front of the wedge, where the amount and timing of deformation is poorly understood. Indeed, recent seismological data from Nankai indicate “very-low-frequency” shallow-thrust earthquakes beneath the accretionary wedge, long considered to be “aseismic,” underscoring the unusual mechanical behavior in the transition zone. As the rigidity of the high-porosity wedge sediments is low, for an earthquake of a given seismic moment, more co-seismic slip will occur and for a longer duration, than for a deeper earthquake in more consolidated units. Thus shallow earthquakes in the wedge are more effi cient at generating a strong tsunami. Many of the margins with very broad accretionary wedges have produced extremely strong earthquakes (M9) in the past, as well as giant tsunamis.

Erosion of rock cliffs has been considered to be relatively unpredictable. This perceived stochastic nature of the erosional processes often occurs through collapses along fractures in the rock-mass. The prediction of catastrophic cliff failures and collapses remains very difficult. For advancing in this field, it is important to understand the processes through which a crack is initiated, how it develops and propagates until the final failure. This paper examines the micro-seismic signals recorded 15 h prior to a rock-fall located at Mesnil-Val, France. The results lead to the hypothesis that several phases of failure mechanisms contribute to rock-fall occurrence. The most important phases were associated with micro-seismic event families identified by multiplet selection. Each event family contained one specific frequency spectrum showing a progressive decrease of the frequencies as the rock approached failure suggesting the following phases: 1) the micro-seismic events recorded 15 h before the rock-fall were characterised by the highest frequencies in a large spectrum-band, between ~100 and 1000 Hz (family 1), suggesting a crack initiation mechanism or the opening of existing fractures; 2) the micro-seismic events recorded several minutes before the rock-fall were associated with a clear decrease in the highest frequency components (family 2) suggesting that the mechanism was related to the growing and development (or coalesce) of existing micro-cracks into larger fractures; 3) micro-seismic events recorded just before the rock-fall were associated with a lower frequency spectrum than families 1 and 2, the highest frequency components were absent (family 3), the frequency emission source mechanism could be related to the shearing or opening of the existing large fractures permitting the complete detachment of the blocky rock-mass; 4) finally, micro-seismic events with a very low frequency spectrum (lower than 100 Hz) characterized the rock-fall impact on the ground. These encouraging results offer the possibility of using the micro-seismic system to monitor high risk sections of coastline and to advance understanding of cliff failure mechanisms.

The very low frequency-electromagnetic (VLF-EM) technique was used to delineate two sub-parallel lava tubes, faults and dikes in Umm El-Quttein area, NE Jordan. The investigation of the lava tubes was conducted through 22 VLF-EM profiles across lava strike; the length of profiles ranged from 700 to 1700 m. The lava tubes outcrop at two sites: Azzam cave and Al-Howa tunnel, characterized by slightly weathered basalt, columnar joints and fissure zones; qualitative interpretation of Fraser and Karous-Hjelt maps differentiate those zones as linear, elongated and circular anomalous zones. The 2-D tipper inversion of VLF-EM data and resistivity imaging had the potential to screen out three anomalous zones of likely resistivity contrast: the lava tube body with resistivity over 2500 Θ·m, the fractured zones with resistivity less than 500 Θ·m, and the host vesicular basalt with resistivity of 1500 Θ·m. The strike of lava tubes varied from SW to NE direction with depth less than 20 m and width from 10 to 30 m.

In this paper we study the energy of ULF electromagnetic waves that were recorded by the satellite DEMETER, during its passing over Haiti before and after a destructive earthquake. This earthquake occurred on 12 January 2010, at geographic Latitude 18.46° and Longitude 287.47°, with Magnitude 7.0 R. Specifically, we are focusing on the variations of energy of Ez-electric field component concerning a time period of 100 days before and 50 days after the strong earthquake. In order to study these variations, we have developed a novel method that can be divided in two stages: first we filter the signal, keeping only the ultra low frequencies and afterwards we eliminate its trend using techniques of Singular Spectrum Analysis (SSA), combined with a third-degree polynomial filter. As it is shown, a significant increase in energy is observed for the time interval of 30 days before the earthquake. This result clearly indicates that the change in the energy of ULF electromagnetic waves could be related to strong precursory earthquake phenomena. Moreover, changes in energy associated with strong aftershock activity were also observed 25 days after the earthquake. Finally, we present results concerning the comparison between changes in energy during night and day passes of the satellite over Haiti, which showed differences in the mean energy values, but similar results as far as the rate of the energy change is concerned.

We propose a mechanism to explain suggested links between seismic activity and ionospheric changes detected overhead. Specifically, we explain changes in the natural extremely low-frequency (ELF) radio noise recently observed in the topside ionosphere aboard the DEMETER satellite at night, before major earthquakes. Our mechanism utilises increased electrical conductivity of surface layer air before a major earthquake, which reduces the surface-ionosphere electrical resistance. This increases the vertical fair weather current, and (to maintain continuity of electron flow) lowers the ionosphere. Magnitudes of crucial parameters are estimated and found to be consistent with observations. Natural variability in ionospheric and atmospheric electrical properties is evaluated, and may be overcome using a hybrid detection approach. Suggested experiments to investigate the mechanism involve measuring the cut-off frequency of ELF "tweeks", the amplitude and phase of very low frequency radio waves in the Earth-ionosphere waveguide, or medium frequency radar, incoherent scatter or rocket studies of the lower ionospheric electron density.

Large cell lymphomas (LCLs) are heterogeneous in morphology, clinical presentation, and behavior. We studied 52 de novo LCLs of B-cell type for rearrangements of the bcl-2 and c-myc oncogenes by Southern blot analysis and related these data to the primary site of presentation, stage, and cytomorphology. Thirteen tumors had comigrating rearrangements of JH and bcl-2, indicative of a t(14;18). Far more primary nodal lymphomas than extranodal lymphomas carried a t(14;18) (40% v less than 5%). Additionally, almost all lymphomas with a t(14;18) versus 41% of the tumors without a bcl-2 rearrangement presented with lymphadenopathy. c-myc rearrangements were seen in 35% of the extranodal lymphomas and 5% of the nodal lymphomas. No differences were observed in bone marrow involvement and staging according to Ann Arbor. bcl-2 rearrangements were found in 50% of the LCLs with cleaved nuclei, whereas c-myc rearrangements were relatively frequent (25%) in the noncleaved subtype. Our data support...

This study utilized the very low frequency-electromagnetic (VLF-EM) technique, a passive electromagnetic prospecting method working in the very low frequency range (15–30 KHz) to investigate the geo-environmental problems of shallow, low conductivity sedimentary layers in Taiwan. Field examples successfully demonstrate the advantages of using this method in locating non-mineralized shallow fault zones. The zero-crossings of in-phase and quadrature measurements in 2-D contour maps clearly locate the position of subsurface anomalous source bodies. Further analysis of the measured VLF single profile peaks reveals that this method is useful in determining subsurface structures and conductivity. The advantages of nondestructive, noninvasive, and low consumption of power make this method extremely friendly to the environment. The authors anticipate this method will have more profound impacts on the interactions between prospecting technology and the earth.

Low grade wastes produced by mining activities particularly in the sulphide deposits may cause detrimental impacts on the environment. In this situation, the remaining sulphide minerals within the waste dump may cause various toxic elements due to oxidation processes. The transportation of such elements into the surface and groundwater flow systems has serious impacts on the human being, aquatic life and other creatures. As the transportation of metallic pollutants by different physical and geochemical mechanisms could considerably change the conductivity of the polluted zone, so the electric and electromagnetic geophysical methods could successfully be used to map these zones. In this research, it is attempted the pollution potential of a sulphide mine located at the north-east of Iran to be investigated using the very low frequency electromagnetic (VLF- EM), resistivity (RES) and induced polarization (IP) geophysical methods. In addition, it is also aimed to perform a suitable num...