Low Magnetic Intensity Research Articles

PEMODELAN BAWAH PERMUKAAN MANIFESTASI MINERAL DENGAN METODE GEOMAGNETIK DAERAH PACITAN JAWA TIMUR

Tulakan Subdistrict, Pacitan Regency, East Java Province. This area is part of the Southern Mountain Zone of East Java, which is the Sunda-Banda magmatic arc of Oligo-Miocene age, where there are alterations and indications of valuable ore minerals. Field magnetic data is taken in an area of 1 x 1 km, with the looping method on the grid trajectory within 200 x 100 m. Then, magnetic data correction and data processing were carried out with Oasis Montaj. From the magnetic anomaly map, the value of high magnetic intensity in the southern part is fresh (intrusive) andesit-dasitic rock as host rock which causes alteration, in the middle has a low magnetic intensity value which is in the direction of the relatively NE-SW river direction, whereas in the north with high intensity is fresh andesite lava. From the image data, it can be seen that the straightness pattern of the geological structure which is dominated by the extensional structure with the direction of NE-SW and E-W is the main trap of epithermal veins carrying ore mineralization mainly Cu, Pb in the study area.

Depth to Magnetic Sources Using Spectral Analysis of High Resolution Aeromagnetic Data Over Machina and Environs, Northeastern Nigeria

Analysis of high resolution aeromagnetic data over Machina and its environment shows areas of low total magnetic intensity contour values are hosts to thicker overburden sediments and near surface intrusive rock bodies reside over high total magnetic intensity contour regions. Positive and negative residual anomaly values depict the presence of basic and acid rock units; however, the acid rocks dominate over the basic components. Major linear features of the residual anomaly are oriented along the NE – SW direction. Some linear features however, cross cut the major lineaments along the NW – SE, N –S, and E – W directions. A NW – SE cross section of the residual anomaly shows irregularity of the bedrock floor. The negative residual anomalies are underlain by granite rocks, while the positive values are within the domain of basic intrusive. Determination of the magnetic source depth revealed depths to the top of the deeper and the shallower sources ranging from 0.6 – 2.0 km and from 0.4 - 0.9 km respectively. Thicker sedimentary covers are underlain by basement rocks while; shallower magnetic horizons are composed of intrusive igneous bodies. Maximum sedimentary thickness of 2.0 km in the study area might not be adequate enough for hydrocarbon maturation and accumulation. Segment directional histogram data shown on rose diagram exhibits strike directions along the E – W, NE – SW, NW – SE, NNE – SSW and NNE – SSW. Most of the fracture lines dip at angles lower than 10 degrees. The north dipping direction group of lineaments is prevalent. Orientations of the structural elements are in conformity with the dominant regional structural grain of the country. Cross- cutting of the lineaments may be related to the geothermal energy in the area as higher interconnected lineaments are associated with higher geothermal energy. Rugged terrain reliefs might have resulted from the effects of tectonic and structural evolution in the area. Variability of the dip angles is associated with non-uniform framework of the forces of deformation on the rocks and/or differential responses of the rocks to the stress imposed on them.

Adsorption of arsenic (V) on magnetite-enriched particles separated from the mill scale

The magnetite-enriched particles (MEP) were separated from the mill scale on low magnetic intensity ranging from 300 to 500 gauss. The characterization of the MEP was done with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The adsorption efficiency of MEP was investigated with batch tests and column operation. The maximum adsorption capacity was observed about 12.69 mg of arsenate on 1 g of adsorbent. Langmuir and Freundlich isotherm models were used to explain the experimental data and it was found that adsorption followed the Langmuir model more closely. Four columns were operated based on empty bed contact time (0.5 h and 1 h) and particle size (75–150 µm and 150–300 µm). The operated columns successfully removed arsenate from influent (0.5 mg/L concentration) during continuous operation for 6 weeks. This study introduces a cost effective and ecofriendly process for arsenate removal with MEP separated at low intensity of magnetic field.

Reservoir Magnetic Anomaly at Geothermal Area of Mount Pandan, East Java, Indonesia

The magnetic method has been applied to identify the geothermal reservoir in the Mt. Pandan East Java, Indonesia. The magnetic survey was performed using PPM G-856 and measured on 80 magnetic stations that cover an area of 9 x 10 km². The magnetic stations cover two hot springs, Jari and Banyukuning in the Mt. Pandan. The magnetic data were processed by 2D and 3D data modeling. The results showed that total magnetic intensity ranged from -446.7 nT to 526.3 nT. The residual anomaly of contour map revealed that geothermal reservoir was suspected in an area with the low magnetic intensity value around the hot spring and identified as the volcanic breccia and tuffaceous sandstone. The tentative model from magnetic residual anomaly can shows location, depth, and the thickness of the geothermal reservoir. The flow pattern the reservoir to manifestation, show the alleged presence of a secondary structure. This indicates that Jari and Banyukuning manifestation have different reservoirs.

High-resolution environmental magnetic study of a Holocene sedimentary record from Zaca Lake, California

Mineral magnetic studies of Holocene lake sediments recovered from Zaca Lake, in coastal southern California have yielded a 3000-year high-resolution record of terrestrial hydrologic variability and paleolimnology. Samples for magnetic analysis were obtained from an 8.73 m core recovered from the central region of Zaca Lake. Ages, constrained using a combined paleomagnetic and radiocarbon chronostratigraphy, yield sedimentation rates of 2–10 mm/yr with an average rate of 3 mm/yr over the 3000-year interval. Parameters reflecting decadal-scale variability in magnetic concentration (susceptibility, ARM, SIRM) and grain size (ARM/Chi) were measured every 2 cm. Additional rock magnetic tests on whole rock samples and magnetic separates indicate that magnetite and an iron sulfide are the chief magnetic carriers. Detailed analysis of the rock magnetic record reveals four major temporal intervals: 0–135 cm (~AD 2009–1757) the period of European settlement; 135–270 cm (~AD 1757–1275) the period of Native American, Chumash occupation of the watershed encompassing the bulk of the wet interval known as the little ice age (LIA); 270–600 cm (AD 1275–100) encompassing the drier Medieval Climate Anomaly (MCA); and 600–875 cm (2000–3000 ybp) an era dominated by a long interval of low magnetic mineral intensity and concentration that has been interpreted as a time of epic drought. Beginning with the cessation of drought conditions at Zaca Lake around ~2000 ybp, the magnetic proxy record of rock magnetic cyclicity and hydrologic variability shows a pronounced decadal to centennial-scale periodicity. We interpret these periodicities as oscillations between summer-dominated sedimentary sequences, characterized by whiting events with their resulting carbonate deposits, and winter dominated sedimentary sequences, typified by sulfide-rich clastics, reflecting lacustrine overturn and enhanced advection of detrital flux during winter storm events. The long-term variation of summer versus winter-dominated weather patterns reflects the climate variability of central California coast-ranges.

A Great Basin lake-level response to 38–34 ka Dansgaard–Oeschger oscillations

Paleontological, geochemical, and geophysical data from pluvial Lake Chewaucan, Oregon, northwestern Great Basin provide a high-resolution paleoclimate record spanning the interval (38–34 ka) that includes the Mono Lake paleomagnetic excursion, Dansgaard–Oeschger Interstadials #8–#6, and the end of Heinrich Event 4. New climate proxies presented here from the BB3-I core, whose chronology was established in a recent publication focusing on its paleomagnetic record, consist of sediment grain-size, Corg/N, ostracode faunal counts, lipid molecular stratigraphy, and palynology. They build on previously publised proxies from this basin based on environmental magnetism and supporting lithological features found in outcrop and core. Results from granulometry, geochemical analysis and the presence of the ostracode Cytherissa lacustris consistently demonstrate the correspondence of low lake conditions and colder water temperatures during Dansgaard–Oeschger stadials during a time interval including the low magnetic intensity feature of the Mono Lake Excursion, a paleomagnetic event found both in the lake core of this study and the composite Greenland ice core record between Interstadials #7 and #6. Pollen data also support this finding, suggesting colder and drier continental montane woodland conditions during stadials versus warmer and wetter semi-arid woodland conditions during interstadials. This is further supported with lipid molecular stratigraphy, indicating a consistent tendency toward terrestrial-sourced vegetation, reflecting increased stream discharge into deeper lakes during interstadials versus dominance of aquatic vegetation during low-discharge, low lake stadials. These results suggesting wet interstadials confirm those of earlier studies at Summer Lake and for other lake records in the Great Basin for millennial-scale climate change during MIS 3 age.

Revised potential field model of the Gilmore Fault Zone

The Gilmore Fault Zone (GFZ) marks a distinct geophysical contrast between metasediments of the Wagga Metamorphic Belt (high gravity and low magnetic intensity) and the Macquarie Arc and Silurian rift basins (low gravity and high magnetic intensity) in the Eastern Lachlan Orogen, Australia. This study uses a geologically constrained inversion of magnetic and gravity data to provide a revised model of the GFZ.This model results in a significant improvement in fit to all previous models of the same profiles and involves repeated two-way exchange between geologists and geophysicists.Two profiles corresponding to the seismic reflection lines 99AGSL1-L2 and 99AGSL3, and extending for more than 80 km, were simultaneously inverted by forward modelling of total magnetic intensity and gravity data. This was done through iterative modification of body geometry correlating to mapped geology. Profiles were further constrained by reflection seismics and physical property contrasts.This model is used to clearly define the dip direction of the GFZ (west-dipping) and suggests a separate classification of the Barmedman Fault (east-dipping). The Barmedman Fault is a shallow fault flake, previously considered part of the GFZ, which has contributed to the confusion around the regional extent of the GFZ. This new work also has the potential to inform future tectonic interpretations of this area.

Extended interaction oversized coaxial relativistic klystron amplifier with gigawatt-level output at Ka band

In this paper, an extended interaction oversized coaxial relativistic klystron amplifier (EIOC-RKA) with Gigawatt-level output at Ka band is proposed. We introduce the oversized coaxial and multi-gap resonant cavities to increase the power capacity and investigate a non-uniform extended interaction output cavity to improve the electronic efficiency of the EIOC-RKA. We develop a high order mode gap in the input and output cavities to easily design and fabricate the input and output couplers. Meanwhile, we design the EIOC-RKA by using the particle-in-cell simulation. In the simulations, we use an electron beam with a current of 6 kA and a voltage of 525 kV, which is focused by a low focusing magnetic flux intensity of 0.5 T. The simulation results demonstrate that the saturated output power is 1.17 GW, the electronic efficiency is 37.1%, and the saturated gain is 57 dB at 30 GHz. The self-oscillation is suppressed by adopting the absorbing materials. The proposed EIOC-RKA has plenty of advantages such as large power capacity, high electronic efficiency, low focusing magnetic, high gain, and simple structure.

A 10,000 yr record of high-resolution Paleosecular Variation from a flowstone of Rio Martino Cave, Northwestern Alps, Italy

Speleothems are potentially excellent archives of the Earth's magnetic field, capable of recording its past variations. Their characteristics, such as the continuity of the record, the possibility to be easily dated, the almost instantaneous remanence acquisition and the high time-resolution make them potentially unique high-quality Paleosecular Variation (PSV) recorders. Nevertheless, speleothems are commonly characterized by low magnetic intensities, which often limits their resolution. Here we present a paleomagnetic study performed on two cores from a flowstone from the Rio Martino Cave (Western Alps, Italy). U/Th dating indicates that the flowstone's deposition covers almost the entire Holocene, spanning the period ca. 0.5–9.0 ka, while an estimation of its mean growth rate is around 1 mm per 15 years. The flowstone is composed of columnar calcite, characterized by a highly magnetic detrital content from meta-ophiolites in the cave's catchment. This favorable geological context results in an intense magnetic signal that permits the preparation and measurement of thin (∼3 mm depth equivalent) samples, each representing around 45 yr. The Characteristic Remanent Magnetization (ChRM), isolated after systematic stepwise Alternating Field demagnetization, is well defined, with Maximum Angular Deviation (MAD) generally lower than 10°. Paleomagnetic directional data allow the reconstruction of the PSV path during the Holocene for the area. Comparison of the new data with archeomagnetic data from Italian archeological and volcanic records and using the predictions of the SHA.DIF.14k and pfm9k.1a global geomagnetic field models shows that the Rio Martino flowstone represents an excellent recorder of the Earth's magnetic field during the last 9,000 years. Our high resolution paleomagnetic record, anchored by a high-quality chronology, provides promising data both for the detection of short term geomagnetic field variations and for complementing existing regional PSV curves for the prehistoric period, for which well-dated data are still scarce.

Interpretation of Ground Magnetic Data, Over Suspected Gold Deposit In Gwam, Paikoro LGA Niger State.

An interpretation of the ground magnetic data over suspected gold deposit using proton procession magnetometer and to determine the depth of gold deposits was carried out in Gwam area of Paiko LGA, Niger State. The Geotron Model G5 Proton Memory Magnetometer was used in interpreting the data of two hundred and nine (209) magnetic stations in twenty-six (26) profiles, while the Garmin(Oregon 550) GPS was used in measuring direction and orientation of profile lines. The survey area was 500m and twenty six (26) profiles were created with a spacing of 20m. On every profile line, a magnetic base station was established, total magnetic field reading and time were measured after every 1minute 30seconds on every station. Raw Magnetic data collected on the field sheet were transferred on the excel sheet for diurnal and IGRF corrections and the residual anomaly and the latitude and longitude was transferred into the originpro8 software for the production of a colored contour map. The colored map aided the visibility of a wide range of anomalies in the magnetic map and the ranges of their intensities were also shown. The result shows that low magnetic intensities dominated the entire study area and it also correlates with properties of a diamagnetic material.Since gold is a diamagnetic material, it means that the probability of finding gold in the study area Gwam is high. The obtained depth to the magnetic source of the study area Gwam along the profiles ranges from 6.57m to 543.33m and the averaged depth obtained is 93.12m for the entire region.

Aeromagnetic mapping of basement structures and mineralisation characterisation of Ilesa Schist Belt, Southwestern Nigeria

This paper analysed aeromagnetic data over the southern Ilesa schist belt of Nigeria with a view to assessing the sub surface structural settings that might favour mineralisation in the study area. Enhancement of the total magnetic intensity map was carried out to improve the anomaly characteristic of source bodies through upward continuation and reduction to the equator (RTE) of the magnetic field intensity. Estimation of depth to the deep, intermediate and near surface structures was based on the Spectral analysis and Euler deconvolution of the aeromagnetic data. Extracted magnetic anomalies from the RTE map range in amplitude from −115 to 134 nT, with the high magnetic intensities occurring over amphibolite, schist, porphyritic granite, gneiss and undifferentiated Migmatite, while low magnetic intensities were observed over quartzite and the undifferentiated schist. The Euler deconvolution solutions revealed that the area is mainly affected by sill/dyke and horizontal cylinder/pipe geologic model with estimated depth to the magnetic source ranging from 73 m–345 m. The depth estimated from the spectral analysis was in the range of 100 m–300 m for the intermediate and shallow sources; this compares reasonably well with the results from the Euler deconvolution. The orientations of lineaments extracted from the total horizontal derivative, source edge detection and Euler deconvolution suggest predominantly NE-SW trending structures, characteristic of primary geologic events in the area, while few E-W trending lineaments are imprints of secondary structural alteration in magnetic fabrics in this direction. Thus, the delineated structures are believed to be the hosts to the mineralised targets as observed from small scale mining activities in the area.

Turbulent geodynamo simulations: a leap towards Earth’s core

We present an attempt to reach realistic turbulent regime in direct numerical simulations of the geodynamo. We rely on a sequence of three convection-driven simulations in a rapidly rotating spherical shell. The most extreme case reaches towards the Earth's core regime by lowering viscosity (magnetic Prandtl number Pm=0.1) while maintaining vigorous convection (magnetic Reynolds number Rm>500) and rapid rotation (Ekman number E=1e-7), at the limit of what is feasible on today's supercomputers. A detailed and comprehensive analysis highlights several key features matching geomagnetic observations or dynamo theory predictions -- all present together in the same simulation -- but it also unveils interesting insights relevant for Earth's core dynamics.In this strong-field, dipole-dominated dynamo simulation, the magnetic energy is one order of magnitude larger than the kinetic energy. The spatial distribution of magnetic intensity is highly heterogeneous, and a stark dynamical contrast exists between the interior and the exterior of the tangent cylinder (the cylinder parallel to the axis of rotation that circumscribes the inner core).In the interior, the magnetic field is strongest, and is associated with a vigorous twisted polar vortex, whose dynamics may occasionally lead to the formation of a reverse polar flux patch at the surface of the shell. Furthermore, the strong magnetic field also allows accumulation of light material within the tangent cylinder, leading to stable stratification there. Torsional Alfv{\'e}n waves are frequently triggered in the vicinity of the tangent cylinder and propagate towards the equator.Outside the tangent cylinder, the magnetic field inhibits the growth of zonal winds and the kinetic energy is mostly non-zonal. Spatio-temporal analysis indicates that the low-frequency, non-zonal flow is quite geostrophic (columnar) and predominantly large-scale: an m=1 eddy spontaneously emerges in our most extreme simulations, without any heterogeneous boundary forcing.Our spatio-temporal analysis further reveals that (i) the low-frequency, large-scale flow is governed by a balance between Coriolis and buoyancy forces -- magnetic field and flow tend to align, minimizing the Lorentz force; (ii) the high-frequency flow obeys a balance between magnetic and Coriolis forces; (iii) the convective plumes mostly live at an intermediate scale, whose dynamics is driven by a 3-term 1 MAC balance -- involving Coriolis, Lorentz and buoyancy forces. However, small-scale (E^{1/3}) quasi-geostrophic convection is still observed in the regions of low magnetic intensity.

Effects of magnetic assistance on improving tool wear resistance and cutting mechanisms during steel turning

This paper provides a novel magnetic assisted turning mechanism for machining steel alloy specimens by HSS tools. The presented setup reduces air gap on a closed magnetic circuit and applies the magnetic field on both tool and workpiece, simultaneously. The usage of closed magnetic field contributes to using the magnetic field advantages at lower magnetic intensity. Using the design of experiments method, full factorial technique, 33×2 tests were conducted to study the influence of effective parameters i.e., magnetic field, depth of cut, feed rate and spindle speed. The flank wear and the cutting force were measured to quantitatively investigate the effect of magnetic treatment on machining process. The results were investigated by the analysis of variance (ANOVA) method and the magnetic field was revealed as the most pivotal factor. The analysis of variance results, micrographs of tool wear and dynamometer's force diagrams proved the advantages of the proposed method. Through this technique, a maximum 94% reduction in flank wear and 66% improvement of cutting force were achieved.

Understanding the 3D structure of the Gilmore Fault Zone through geophysical modelling: implications for Lachlan tectonic reconstructions

This study aims to clarify the tectonic evolution of the Lachlan Orogen by modelling the subsurface morphology of the Gilmore Fault Zone (GFZ). The GFZ marks a distinct geophysical contrast between (high gravity, low magnetic intensity) high-grade metamorphic rocks found in the Wagga metamorphic belt (WMB), to the west, and the (low gravity, uniformly high magnetic intensity) low-grade volcanic rocks found in the Macquarie Arc and Silurian rift basins to the east. Understanding the structure of this fault at depth should provide constraints on existing models for the tectonic evolution of the Lachlan Orogen. Subsurface structure around the GFZ in the vicinity of Barmedman has been inverted by iterative 2.5D potential-field modelling of gravity and magnetics, constrained by pre-existing reflection seismic profiles, potential-field interpretations by previous workers, and physical properties data collected on representative lithologies. Preliminary findings show that the surface structure mapped as the Gilmore Fault is an east-dipping, shallow thrust fault, and doesn’t correspond to the major crustal ‘suture’ envisaged in regional tectonic studies. It is a secondary antithetic structure off the main west-dipping, crustal penetrating fault that separates the Macquarie arc and the WMB. Another, steeper west-dipping fault cuts these structures and separates the WMB from the Silurian Tumut Trough. This larger structure defines the regionally extensive tectonic feature of the GFZ. The trace of the mappable Gilmore Fault (as opposed to the GFZ) is curved, and terminates abruptly to the north, indicating the Gilmore Fault is the base of a series of thrust flakes imposed on the pre-existing main fault in the GFZ. West-dipping crustal-penetrating thrust faults east of the GFZ are indicative of successive collision, accretion and extension events. Thus far the modelled structure of the GFZ is not consistent with the terrane accretion model but is consistent with the accretionary orogen and orocline model.

Low loss and narrow-band THz filter based on magnetic photonic crystals

As a key point to applying and studying magnetic photonic crystal technology, communication devices such as the magnetic photonic crystal filters with high performance and easy integration are developed. We investigate the feasibility of ferrite magnetism materials that can be used to make photonic crystal filters. The optical properties of the magnetic materials may be tuned by adjusting the magnetic field or temperature. The band gap of the magnetic photonic crystal can thus be transferred by changing the external magnetic field. This kind of magnetic photonic crystal has a great application prospect. A low insertion loss and narrow-band filter is designed based on a magnetic field-controlled ferrite defect in a photonic crystal for a terahertz (THz) wave. Ferrite is a ferromagnetic metal oxide with high dielectric constant, low saturation magnetization intensity, and high magnetic permeability at high frequencies. According to the crystal structure it can be divided into three categories: spinel, garnet and magnetic rock types. The garnet ferrite crystal can be used to realize THz band transmission, and its absorption coefficient is low (0.05-0.3) in uniform polarization. In this paper, a novel magnetic THz photonic crystal filter is proposed, in which point defects are produced by the introduction of garnet ferrite magnetic materials. Based on the coupling characteristics between the linear defect wave guide and the point defects, THz wave with a certain wave length can be well coupled by changing the radius and arrangement of the resonant cavity, so as to achieve high efficiency filter function. The permeability properties of ferrite magnetic materials are changed with the variation of the intensity of the external magnetic field, and the tuning of the frequency of the resonance mode. The optical properties of the filter are analyzed in detail by using plane waves method(PWM) in finite difference time domain(FDTD). Simulation results show that by changing the point defect structure and the radius of a certain dielectric cylinder, the insertion loss and 3 dB bandwidth of the filter are 0.0997 dB and 8.22 GHz, respectively.

Integrating geophysical data in GIS for geothermal power prospecting

Geographic information system (GIS)–based resource assessment is an important and relatively inexpensive tool for identifying areas that are of interest for geothermal power production. Of particular interest is the under-exploited industry of co-produced fluids and low-temperature formation waters in oil- and gas-producing basins. Obtaining bottom-hole temperature (BHT) data is now free and easily accessible due to the efforts of the National Geothermal Data System (NGDS). Oil- and gas-producing sedimentary basins in Colorado, Illinois, Michigan, and North Dakota contain formation waters of a temperature that is adequate for geothermal power production (90–150 °C) using existing binary power plant technology. While resource assessment gives a broad picture of the energy available in a basin, the problem remains of knowing where a power plant must go, and if it is economically feasible to do so in any given area. The Denver, Illinois, Michigan, and Williston sedimentary basins were evaluated using a play fairway analysis methodology to identify optimum locations for geothermal power production. These regions have been previously assessed for thermal energy in place, and geothermal gradients from that study, along with gravity anomaly information, magnetic intensity, and digital elevation models (DEMs) for slope analysis were incorporated into a geodatabase for map generation. Raster layers were created and then reclassified into nine classes each, with high geothermal gradient, low magnetic intensity, low Bouger anomaly, and low slope receiving the highest values. The layers were then weighted using a matrix weight assignment similar to that used in the Environmental Protection Agency’s DRASTIC water pollution model, and combined with the “Raster Algebra” tool in ArcGIS. Areas of greatest potential were identified and overlaid on a DEM layer. This shows locations where temperature will be highest at the shallowest depths in regions of soft sediments, refining the map creation process.

Preservation and detectability of shock‐induced magnetization

AbstractAn understanding of the effects of hypervelocity impacts on the magnetization of natural samples is required for interpreting paleomagnetic records of meteorites, lunar rocks, and cratered planetary surfaces. Rocks containing ferromagnetic minerals have been shown to acquire shock remanent magnetization (SRM) due to the passage of a shock wave in the presence of an ambient magnetic field. In this study, we conducted pressure remanent magnetization (PRM) acquisition experiments on a variety of natural samples as an analog for SRM acquisition at pressures ranging up to 1.8 GPa. Comparison of the alternating field (AF) and thermal demagnetization behavior of PRM confirms that AF demagnetization is a more efficient method for removing SRM overprints than thermal demagnetization because SRM may persist to unblocking temperatures approaching the Curie temperatures of magnetic minerals. The blocking of SRM to high temperatures suggests that SRM could persist without being eradicated by viscous relaxation over geologic timescales. However, SRM has been rarely observed in natural samples likely because of two factors: (1) other forms of impact‐related remanence (e.g., thermal remanent magnetization from impact‐related heating or chemical remanent magnetization from postimpact hydrothermal activity) are often acquired by target rocks that overprint SRM, and (2) low SRM acquisition efficiencies may prevent SRM from being distinguished from the underlying primary remanence or other overprints due to its low magnetization intensity.

Asteroid impact vs. Deccan eruptions: The origin of low magnetic susceptibility beds below the Cretaceous–Paleogene boundary revisited

The respective roles of an asteroid impact and Deccan Traps eruptions in biotic changes at the Cretaceous–Paleogene (K–Pg) boundary are still debated. In many shallow marine sediments from around the world, the K–Pg boundary is marked by a distinct clay layer that is often underlain by a several decimeter-thick low susceptibility zone. A previous study of the Gubbio section, Italy (Lowrie et al., 1990), attributed low magnetization intensity in this interval to post-depositional dissolution of ferrimagnetic minerals. Dissolution was thought to be a consequence of downward infiltration of reducing waters that resulted from rapid accumulation of organic matter produced by mass extinctions after the K–Pg event. We compare the magnetic properties of sediments from the Gubbio section with those of the Bidart section in southern France. The two sections are similar in their carbonate lithology and the presence of a boundary clay and low susceptibility zone. When compared to background Cretaceous sediments, the low susceptibility zone in both sections is marked by an absence of biogenic magnetite, a decrease in total ferrimagnetic mineral content, and a preferential loss of magnetite with respect to hematite – features that are consistent with reductive dissolution. However, unlike the Gubbio section, where the low susceptibility zone starts immediately below the boundary clay, the low susceptibility zone and the clay layer at Bidart are separated by a ∼4-cm carbonate interval that contains abundant biogenic magnetite. Such separation casts doubt on a causal link between the impact and sediment bleaching. More likely, the low susceptibility layer marks a different environmental event that preceded the impact. An episode of increased atmospheric and oceanic acidity associated with Deccan Traps volcanism that occurred well before the K–Pg impact is argued here to account for the distinct magnetic properties of the low susceptibility intervals.

Graphene functionalized with 3-mercatopropionic acid capped zinc peroxide nanoparticles: A potential ferromagnetic material at room-temperature

The literature reveals that ferromagnetism in zinc peroxide (ZnO2) is due to the exchange interaction between localized electron spin moments resulting from oxygen vacancies at the surface of nanoparticles, while in graphene may be due to existence of various defects. However ZnO2 show paramagnetic behaviour, whereas graphene exhibits very low magnetic intensity (0.0004 emu g−1). To enhance magnetization, graphene was treated with 3-mercatopropionic acid followed by coating with polyvinylpyrrolidone (PVP) capped ZnO2 nanoparticles. Interestingly coating of graphene over ZnO2 does not enhance magnetization, whereas coating of 15–20% ZnO2 nanoparticles over graphene enhances magnetization more than 30 times, which gradually decreases on increasing concentration of ZnO2 nanoparticles. Such coated graphene shows highest saturation of magnetization at room temperature ever reported in graphene (130 memu g−1). The Magnetic measurements studies of ZnO2 nanoparticles coated graphene indicates excellent room temperature ferromagnetic behaviour, which has been further confirmed by Electron Paramagnetic Resonance and Magnetic Force Microscopy studies. A comparative study was also done with ZnO nanoparticles with graphene and only 60 memu g−1 magnetization has been observed. It has been concluded that higher magnetization in graphene coated with ZnO2 than ZnO is due to more oxygen vacancies in ZnO2 nanoparticles.

Noise reduction of nuclear magnetic resonance (NMR) transversal data using improved wavelet transform and exponentially weighted moving average (EWMA)

NMR logging and core NMR signals acts as an effective way of pore structure evaluation and fluid discrimination, but it is greatly contaminated by noise for samples with low magnetic resonance intensity. Transversal relaxation time (T2) spectrum obtained by inversion of decay signals intrigued by Carr–Purcell–Meiboom–Gill (CPMG) sequence may deviate from the truth if the signal-to-noise ratio (SNR) is imperfect. A method of combing the improved wavelet thresholding with the EWMA is proposed for noise reduction of decay data. The wavelet basis function and decomposition level are optimized in consideration of information entropy and white noise estimation firstly. Then a hybrid threshold function is developed to avoid drawbacks of hard and soft threshold functions. To achieve the best thresholding values of different levels, a nonlinear objective function based on SNR and mean square error (MSE) is constructed, transforming the problem to a task of finding optimal solutions. Particle swarm optimization (PSO) is used to ensure the stability and global convergence. EWMA is carried out to eliminate unwanted peaks and sawtooths of the wavelet denoised signal. With validations of numerical simulations and experiments, it is demonstrated that the proposed approach can reduce the noise of T2 decay data perfectly.