Mean Magnetic Susceptibility Research Articles

Quantitative evaluation of iron content in idiopathic rapid eye movement sleep behavior disorder.

Idiopathic rapid eye movement sleep behavior disorder is an early sign of neurodegenerative disease. This study aimed to quantitatively evaluate iron content in idiopathic rapid eye movement sleep behavior disorder patients using quantitative susceptibility mapping and to examine the potential of this technique to identify the prodromal stage of α-synucleinopathies. Twenty-five idiopathic rapid eye movement sleep behavior disorder patients, 32 Parkinson's disease patients, and 50 healthy controls underwent quantitative susceptibility mapping. The mean magnetic susceptibility values within the bilateral substantia nigra, globus pallidus, red nucleus, head of the caudate nucleus, and putamen were calculated and compared among groups. The relationships between the values and the clinical features of idiopathic rapid eye movement sleep behavior disorder and Parkinson's disease were measured using correlation analysis. Idiopathic rapid eye movement sleep behavior disorder patients had elevated iron in the bilateral substantia nigra compared with healthy controls. Parkinson's disease patients had increased iron in the bilateral substantia nigra, globus pallidus, and left red nucleus compared with healthy controls and had elevated iron levels in the bilateral substantia nigra compared with idiopathic rapid eye movement sleep behavior disorder patients. Mean magnetic susceptibility values were positively correlated with disease duration in the left substantia nigra in idiopathic rapid eye movement sleep behavior disorder patients. Quantitative susceptibility mapping can detect increased iron in the substantia nigra in idiopathic rapid eye movement sleep behavior disorder, which becomes more significant as the disorder progresses. This technique has the potential to be an early objective neuroimaging marker for detecting α-synucleinopathies. © 2019 International Parkinson and Movement Disorder Society.

Imaging diamagnetic susceptibility of collagen in hepatic fibrosis using susceptibility tensor imaging.

To characterize the magnetic susceptibility changes of liver fibrosis using susceptibility tensor imaging. Liver biopsy tissue samples of patients with liver fibrosis were obtained. Three-dimensional gradient-echo and diffusion-weighted images were acquired at 9.4 T. Susceptibility tensors of the samples were calculated using the gradient-echo phase signal acquired at 12 different orientations relative to the B0 field. Susceptibility anisotropy of the liver collagen fibers was quantified and compared with diffusion anisotropy, measured by DTI. For validation, a comparison was made to histology including hematoxylin and eosin staining, iron staining, and Masson's trichrome staining. Areas with strong diamagnetic susceptibility were observed in the tissue samples forming fibrous patterns. This diamagnetic susceptibility was highly anisotropic. Both the mean magnetic susceptibility and susceptibility anisotropy of collagen fibers exhibited a strong contrast against the surrounding nonfibrotic tissues. The same regions also showed an elevated diffusion anisotropy but with much lower tissue contrast. Masson's trichrome staining identified concentrated collagens in the fibrous regions with high susceptibility anisotropy, and a linear correlation was found between the susceptibility anisotropy and the histology-based staging. Diamagnetic susceptibility indicates the presence of collagen in the fibrotic liver tissues. Mapping magnetic susceptibility anisotropy may serve as a potential marker to quantify collagen fiber changes in patients with liver fibrosis.

Rapid quantitative susceptibility mapping of intracerebral hemorrhage.

Quantitative susceptibility mapping (QSM) offers a means to track iron evolution in hemorrhage. However, standard QSM sequences have long acquisition times and are prone to motion artifact in hemorrhagic patients. To minimize motion artifact and acquisition time by performing rapid QSM in intracerebral hemorrhage (ICH) using single-shot echo planar imaging (EPI). Prospective method evaluation. Forty-five hemorrhages were analyzed from 35 MRI exams obtained between February 2016 and March 2019 from 27 patients (14 male / 13 female, age: 71 ± 12 years) with confirmed primary ICH. 3T; susceptibility-weighted imaging (SWI) with 4.54-minute acquisition and 2D single-shot gradient EPI with 0.45-minute acquisition. Susceptibility maps were constructed from both methods. Measurement of ICH area and mean magnetic susceptibility were made manually by three independent observers. Motion artifacts were quantified using the magnitude signal ratio of artifact-to-brain tissue to classify into three categories: mild or no artifact, moderate artifact, or severe artifact. The cutoff for each category was determined by four observers. Pearson's correlation coefficient and paired t-test using α = 0.05 were used to compare results. Inter- and intraclass correlation was used to assess observer variability. Using 45 hemorrhages, the ICH regions measured on susceptibility maps obtained from EPI and SWI sequences had high correlation coefficients for area (R2 ≥ 0.97) and mean magnetic susceptibility (R2 ≥ 0.93) for all observers. The artifact-to-tissue ratio was significantly higher (P < 0.01) for SWI vs. EPI, and the standard deviation for the SWI method (SD = 0.05) was much larger than EPI (SD = 0.01). All observers' measurements showed high agreement. Single-shot EPI-QSM enabled rapid measurement of ICH area and mean magnetic susceptibility, with reduced motion as compared with more standard SWI. EPI-QSM requires minimal additional acquisition time and could be incorporated into iron tracking studies in ICH. 2 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2020;51:712-718.

Magnetic Anisotropy vs. Shape Preferred Orientation in Quartzites with Negative Susceptibility – Implications for Analysing Strain Intensity Variations

ABSTRACT Through this study the robustness of using anisotropy of magnetic susceptibility (AMS) data is tested as a gauge of intensity of shape preferred orientation (SPO) in pure quartzites that have a low mean magnetic susceptibility (Km). AMS of eight quartzite samples from the Rengali province (eastern India) is measured, and the degree of magnetic anisotropy Pj, which is a measure of the intensity of magnetic fabric is calculated. Quartz grain size, shape as well as orientation data are obtained based on SEM-EBSD analysis of each sample. Using these microstructural data, intensity of SPO of quartz grains in each sample is quantified by measuring (i) the concentration parameter (κq) and (ii) the azimuthal anisotropy of fractal dimension (AAD). Magnitude of 2D strain (E) is also estimated for each sample. Based on these data the statistical relationship between the various parameters is evaluated viz. Pj vs. κq, Pj vs. AAD, Pj vs. E, κq vs. AAD, κq vs. E, AAD vs. E. A strong linear relationship is established in each case. It is argued that quartz aspect ratio, dominant slip systems/recrystallization mechanisms cannot explain the strong linear correlations between magnetic anisotropy, SPO and strain. To further support findings of the above determined relationships, positive Km quartzites were also investigated. It is found that the latter do not show a strong relationship between the intensity of AMS, SPO and strain. It is therefore, established that whilst the variation in intensity of magnetic fabric can be used to gauge variation in intensities of strain as well as SPO in the investigated negative Km quartzites, the same is not true for positive Km quartzites, where the AMS is controlled the para/ferromagnetic phases present in the rock.

Variability of outcrop magnetic susceptibility and its relationship to the porphyry Cu centers in the Highland Valley Copper district

The Highland Valley Copper porphyry Cu-(Mo) centers compose Canada’s largest porphyry Cu mining district, and are hosted in plutonic rocks of the Late Triassic Guichon Creek batholith in the Quesnel terrane, British Columbia. Here we evaluate the relationship between variations in magnetic susceptibility and alteration in order to define a footprint around the porphyry Cu centers using a district-scale dataset of 1610 minimally weathered outcrops and 11,432 magnetic susceptibility measurements. Statistical analysis of the outcrop-based measurements revealed changes in outcrop geometric mean magnetic susceptibility and the coefficient of variation (extent of variability in relation to the mean) are proportional to vein frequency and altered rock volume estimates. At a confidence interval of 95% and 9 degrees of freedom, the average standard error (uncertainty) of the geometric mean and coefficient of variation from 10 magnetic susceptibility outcrop measurements is 7.3% and 13.2%, respectively. Modeling of outcrop magnetic susceptibility data shows that domains of coefficient of variation of >0.3 extend 1–4 km away from the porphyry centers, whereas pronounced susceptibility lows of <10 × 10−3 SI have a smaller footprint centered on the Cu-mineralization. The magnitude of change of magnetic susceptibility coefficient of variation between protolith and altered rocks in the porphyry Cu footprint is greater than the corresponding change in susceptibility geometric means. Thus, with some caveats, variability in magnetic susceptibility provides a good signal that corresponds to vein and alteration intensity, and can potentially be used to map ore-forming processes and to vector to porphyry Cu centers.

Simulation and experimental measurements of internal magnetic field gradients and NMR transverse relaxation times (T2) in sandstone rocks

NMR T2 measurements are widely used to determine various petrophysical properties of rock cores. Internal magnetic field gradients, which occur in rock cores during NMR measurements due to magnetic susceptibility differences between the rock matrix and the pore fluid, can however distort these T2 measurements. Here we implement a FEM simulation of these internal magnetic field gradients on 3D digital μCT images for five different sandstone rocks, coupled with a random walk simulation of the T2 NMR signal relaxation process. The FEM simulations required the magnetic susceptibility of each sandstone, this was directly measured using a SQUID magnetometer over a range of magnetic field strengths. The resultant probability distributions of internal magnetic field gradients were then compared against equivalent experimental measurements; they were generally in reasonable agreement, however the simulations failed to capture the larger magnetic field gradients that were observed experimentally. By consideration of various potential reasons for this, we identify the assumption of a single mean magnetic susceptibility as being the primary source of the variation between simulated and measured results. Simulations of 2 MHz T2 relaxation process are shown however to be in good agreement with experimental measurements across the five sandstones studied.

Surface Current Approximation in Certain Problems of the Classical Theory of Superconductivity

The problems of the behavior of superconducting infinite plane-parallel plate and cylinder in an external magnetic field are solved in the approximation of the model of surface currents. The latter, in contrast to the conventional notation, enter as the currents of superconducting electrons into the boundary conditions for the magnetic induction. Surface currents are understood as the volumetric current flowing in the thickness of the near-surface layer, which is associated with the thickness of the London penetration depth of the field and currents into the thickness of the superconductor. It is shown that in this case, a jump in the magnetic quantities occurs at this thickness. The calculated average magnetization of the magnet is reduced to the strength of the external field. The proportionality coefficient, which is reasonable to call the mean magnetic susceptibility, turns out to be not exactly equal to –1, but has a slightly less value, because the field does not weaken immediately. The possibilities of experimental verification of the obtained effect are discussed.

Kinematic evolution of the Mbakop Pan–African granitoids (western Cameroon domain): An integrated AMS and EBSD approach

This study integrates anisotropy of magnetic susceptibility, microstructural and crystallographic preferred orientation (CPO) data from the Mbakop granitic pluton (MGP; Pan-African age) in order to decipher its kinematic evolution. The MGP lies close to NE-SW branch of Central Cameroon Shear Zone (CCSZ) and is emplaced in gneissic basement. High mean magnetic susceptibility and presence of multi–domain magnetite are recorded. Quartz CPO measured using Electron Backscatter diffraction reveals dominance of rhomb <a>, prism <a> and prism <c> slip in different samples, which is consistent with microstructures developed under upper greenschist/amphibolite facies conditions. Quartz CPO along with other kinematic indicators (feldspar porphyroclasts/mineral fish) indicate non-coaxial deformation was important during tectonic evolution of the MGP. Contrasting sense of shear is recorded implying multi-stage mylonitization in the Western Cameroon Domain. Top-towards-south sense of shear is related to regional D2 deformation (613–585 Ma), while top-towards-north is related to D3 (585–540 Ma). The magnetic fabric in MGP records D3. The obliquity between mean orientation of magnetic foliation (N12°E) and the NE-SW CCSZ branch (N48°E) gives kinematic vorticity number of 0.95. This indicates dominantly simple shear with a minor pure shear component. It is concluded that regional transpression was important during MGP emplacement.

Quantitative susceptibility mapping (QSM) as a means to monitor cerebral hematoma treatment.

Quantitative susceptibility mapping (QSM) offers a consistent hemorrhage volume measurement independent of imaging parameters. To investigate the magnetic susceptibility of intracerebral hemorrhage (ICH) as a quantitative measurement for monitoring treatment in hematoma patients. Prospective. Twenty-six patients with acute ICH were recruited and enrolled in treatment including surgery or medication (mannitol) for 1 week. A 3D gradient echo sequence at 3.0T. The hematoma volumes on computed tomography (CT) and QSM were calculated and used for correlation analysis. Magnetic susceptibility changes from pre- to posttreatment were calculated and compared to the National Institutes of Health stroke scale (NIHSS) measure of neurological deficit for each patient. Mean susceptibility values were calculated over each region of interest (ROI). A one-sample t-test was used to assess the changes of total volumes and mean magnetic susceptibility of ICH identified between pre- and posttreatment images (P < 0.05 was considered significant) and the Bland-Altman analysis with 95% limits of agreement (average difference, ±1.96 SD of the difference). Regression of volume measurements on QSM vs. CT and fitted linear regression of mean susceptibility vs. CT signal intensity for hematoma regions were conducted in all patients. Good correlation was found between hemorrhage volumes calculated from CT and QSM (CT volume = 0.94*QSM volume, r = 0.98). Comparison of QSM pre- and posttreatment showed that the mean ICH volume was reduced by a statistically insignificant amount from 5.74 cm3 to 5.45 cm3 (P = 0.21), while mean magnetic susceptibility was reduced significantly from 0.48 ppm to 0.38 ppm (P = 0.004). A significant positive association was found between changes in magnetic susceptibility values and NIHSS following hematoma treatment (P < 0.01). QSM in hematoma assessment, as compared with CT, offers a comparably accurate volume measurement; however, susceptibility measurements may enable improved monitoring of ICH treatment compared to volume measurements alone. 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:907-915.

Magnetic and Electronic Transition in Samarium Chalcogenides

In the present paper, we have been studied the magnetic and electronic transition in samarium chalcogenides [(SmX, X=S, Se and Te)] under the effect of pressure. We have reviewed relaxation time mean free path, magnetic susceptibility, electronic polarizability and dielectric constant by simple calculation. Our calculated values are close agreement with the experimental results.

Magnetic Response of Heavy Metal Pollution in Playground Dust of an Industrial Area

The use of mineral magnetic measurements as a potential pollution proxy is explored as an alternative means of monitoring heavy metal pollution in playground dust in industrial areas. Dust samples were collected from playgrounds in an industrial area in Nanjing. The magnetic properties of the samples were analyzed, and the total and acid-extractable concentrations of heavy metals were measured.Mineral magnetic concentration parameters[mean magnetic susceptibility (χlf) 939.31×10-8 m3·kg-1 and saturation isothermal remanent magnetization (SIRM) 16618.74×10-5 A·m2·kg-1] indicate that the dust samples contain high concentrations of magnetic minerals when compared to the non-industrial zone of the city. High and stable S-ratio values (mean 0.97, standard deviation 0.01) indicate the prominence of ferromagnetic minerals. Low values of anhysteretic remanent magnetization (χARM)/χlf(2.35) and χARM/SIRM (0.12×10-3 m·A-1) indicate predominantly coarse pseudo single domain (PSD) and multi-domain (MD) magnetic grain size assemblages. The playground dust is considered moderately to highly polluted, and the enrichment factor values for Cd, Zn, Cu, and Pb indicate extremely high contamination levels in the playground dust. Mineral magnetic parameters[χlf, SIRM, hard isothermal remanent magnetization (HIRM), χARM, and χARM/SIRM] reveal significant correlations with total and acid-extractable concentrations of the trace metals, and the correlations with total concentrations are stronger. The most significant correlations were found with mineral magnetic concentrations (χARM and SIRM) and total concentrations of the elements Mn, Ni, and Cr and the Tomlinson pollution load index (PLI) (0.69 ≤ r ≤ 0.86, P<0.01). Consistent spatial characteristics between them were also found, showing that the total concentrations of heavy metals and magnetic parameter values are higher in the playgrounds near and downwind of the power plant. Results of a principal component analysis indicate that anthropogenic activities (mainly from coal consumption by power plants) are the main sources for both heavy metals and magnetic minerals. In summary, significant correlations and consistent spatial characteristics between heavy metal contents and magnetic parameters and the same anthropogenic source for heavy metals and magnetic minerals confirm that magnetic parameters could be considered as efficient indicators for heavy metal contamination in the playground dust in industrial areas.

Seismic and magnetic susceptibility anisotropy of middle-lower continental crust: Insights for their potential relationship from a study of intrusive rocks from the Serre Massif (Calabria, southern Italy)

We investigated the relationships between fabric, seismic and magnetic anisotropy on lithotypes representative of a continental crust exposed in the Serre Massif (Southern Italy). In particular, from five granitoids and one metagabbro, cubes were cut according to the fabric elements and seismic properties up to 400MPa confining pressure were measured with a triaxial multi-anvil apparatus; we also calculated the elastic properties based on the mineral content and composition. In granitoids, measured average compressional wave velocity (Vp) of the fracture-free aggregate at 400MPa is 6.2km/s, whereas average shear wave velocity (Vs) is 3.6km/s, with Poisson's ratio ranging from 0.240 to 0.257, related to the modal proportions of quartz. In metagabbro, average Vp and Vs at 400MPa are 6.9km/s and 3.7km/s, respectively. Results showed that intrinsic velocity distribution, after microcracks closure, depends on progressive alignment of anisotropic minerals such as biotite, amphibole and pyroxene, with maxima velocities localized within the foliation plane. Mean magnetic susceptibility, Km, of the granitic rocks is <300×10−6SIunits, indicating that paramagnetic minerals such as biotite and amphibole control the intensity of magnetic anisotropy. Comparison of seismic and magnetic anisotropies highlighted the different role of constituting minerals over the petrophysical properties. Moreover, a positive correlation between seismic and magnetic anisotropy has been recognized, indicating that biotite and amphibole contribute to the petrophysical and textural anisotropy in the middle crust. Conversely, in metagabbro, the anisotropy of magnetic susceptibility (AMS) is controlled by magnetite and pyrrhotite although these form <10% of the rock, which dominantly comprises paramagnetic minerals such as biotite and orthopyroxene. Unlike granitoids, in metagabbro the petrophysical properties are controlled by the paramagnetic minerals, while the magnetic anisotropy is controlled by the ferromagnetic minerals. Results yielded useful constraints for the comprehension of the petrophysical behavior of the continental crust.

DIAMAGNETISM IN THE CYLINDRICAL QUANTUM DOT WITH PARABOLIC CONFINEMENT POTENTIAL

Diamagnetic properties of the electron gas in a cylindrical quantum dot with parabolic confinement potential have been investigated. The analytical expressions have been obtained for mean energy, mean magnetization and mean magnetic susceptibility of the electron gas. The diamagnetic character of such system has been shown.

A preliminary investigation of relationship between modern &amp;lt;italic&amp;gt;Pediastrum&amp;lt;/italic&amp;gt; and the level of Xingyun Lake, central Yunnan, and its implications for the interpretation of the fossil record

Fossil Pediastrum is frequently found in Quaternary lacustrine deposits and has attracted much attention because it can be well preserved and easily identified. However its palaeoenvironmental significance is unclear. Several studies suggest that the occurrence of a large amount of Pediastrum indicates a gradually decreasing lake-level, while others point out that Pediastrum mainly occurs in the deep areas of lakes. Thus clarifying the relationship between Pediastrum and lake levels is of great importance for improving the reliability of palaeoenviromental reconstruction. In this study, we investigated the occurrence of Pediastrum in Xingyun Lake, a semi-enclosed shallow fault and eutrophic lake located in central Yunnan Province, southwest China. We obtained 4 lake surface water samples at water depths of 4, 4.5, 5.2 and 6.5 m; 16 water samples collected at various depths within the water column at the deepest part of the lake; and 10 lake surface sediment samples taken at different water depths from the lake shore to the deepest part using a Grab sampler. We present the results of Pediastrum analysis of samples of both the lake water and surface sediments of Xingyun Lake and discuss the relationship between the Pediastrum distribution and the lake-level/water depth. The variation of the fossil records during the past 3000 years is also reported. The results show that two types of Pediastrum were identified in the water and lake sediment samples, including Pediastrum boryanum and Pediastrum simplex . The concentration of Pediastrum in the water samples is extremely low, varying from 2 to 6 grains mL - 1. Spatially, the concentrations of Pediastrum in the surface lake water samples exhibit little change with increasing water depth. In terms of the depth variation within the water column in the deepest part of the lake, the Pediastrum concentration of the bottom sample is the highest, which may be related to the effects of resuspension and redeposition of lake sediments caused by wind-induced turbulence in shallow water. With respect to the lake surface sediment samples, the Pediastrum content is relatively high. The concentration of Pediastrum varies from 60700 to 104000 grains g - 1, with an average of 81000 grains g - 1; and the relative percentage abundance ranges from 66%–80%, averaging around 76%. Interestingly, both the concentration and percentage content of Pediastrum in these samples exhibit no significant relationship with water depth. Based on comparison of the results from Xingyun Lake with those of other workers, we conclude that the relationship between the Pediastrum distribution and water depth inferred from the lake sediments of several relatively larger lakes mentioned in previous studies may be caused by depositional processes: turbulence resulting from wave activity in these larger lakes could result in the resuspension of Pediastrum in shallow water and its focusing into deeper areas. However, whether or not there is a large quantity of Pediastrum living in the lake water may be related to the physicochemical status of the lake water, determined by factors such as the river input, nutrient level, temperature, pH and salinity. In addition, these factors may vary between different lakes in different regions. Therefore, the variation of Pediastrum content cannot be used as an indicator of water depth or lake-level without careful consideration of these factors. In addition, it needs to be used in the context of multi-proxy studies. Both the percentage and the concentration of fossil Pediastrum in the sediments of Xingyun Lake exhibit distinct features over the last 3000 years: very low values before 2000 cal a BP followed by a rising trend, and then an abrupt increase after 1500 cal a BP. This is consistent with variations in the intensity of human activity revealed by frequent high-amplitude fluctuations in mean grain-size and by an abrupt increase in magnetic susceptibility. In addition, the abrupt changes in fossil Pediastrum in Xingyun Lake precede those of mean grain-size and magnetic susceptibility, suggesting that the Pediastrum from the Xingyun Lake sediments may be a sensitive indicator of the process of lake water eutrophication caused by human activities.

Susceptibility tensor imaging (STI) of the brain.

Susceptibility tensor imaging (STI) is a recently developed MRI technique that allows quantitative determination of orientation-independent magnetic susceptibility parameters from the dependence of gradient echo signal phase on the orientation of biological tissues with respect to the main magnetic field. By modeling the magnetic susceptibility of each voxel as a symmetric rank-2 tensor, individual magnetic susceptibility tensor elements as well as the mean magnetic susceptibility and magnetic susceptibility anisotropy can be determined for brain tissues that would still show orientation dependence after conventional scalar-based quantitative susceptibility mapping to remove such dependence. Similar to diffusion tensor imaging, STI allows mapping of brain white matter fiber orientations and reconstruction of 3D white matter pathways using the principal eigenvectors of the susceptibility tensor. In contrast to diffusion anisotropy, the main determinant factor of the susceptibility anisotropy in brain white matter is myelin. Another unique feature of the susceptibility anisotropy of white matter is its sensitivity to gadolinium-based contrast agents. Mechanistically, MRI-observed susceptibility anisotropy is mainly attributed to the highly ordered lipid molecules in the myelin sheath. STI provides a consistent interpretation of the dependence of phase and susceptibility on orientation at multiple scales. This article reviews the key experimental findings and physical theories that led to the development of STI, its practical implementations, and its applications for brain research. Copyright © 2016 John Wiley & Sons, Ltd.

Magnetic fabric (AMS, AAR) of the Santa Marta batholith (northern Colombia) and the shear deformation along the Caribbean Plate margin

Anisotropy of low-field magnetic susceptibility (AMS) and anhysteretic remanence (AAR) were measured in the Santa Marta Batholith formed by subduction of the Caribbean Plate beneath the northern South America. The batholith, elongated in the N-S direction, records multiple pulses of quartzdiorite to tonalite and granodiorite magmas between 58 and 49 Ma. The high mean magnetic susceptibility (4 × 10−3 SI) combined with thermomagnetic and partial magnetic remanence measurements indicate that the magnetic susceptibility depends on Ti-poor magnetite. AMS is defined by ellipsoids that are dominantly oblate. The foliation was used to distinguish a narrow band of E-trending magnetic structures that separate the batholith in two lobes. The southern lobe is characterized by foliations that are broadly parallel to the contact with the wall rocks, while the northern lobe by foliations oblique to the batholith elongation. Late tonalitic magmas dated at c. 50 Ma record, in turn, a fabric apparently controlled by E-trending tectonic events. Partial AAR indicates that the subfabrics of magnetite with different grain sizes are nearly parallel to AMS, therefore discarding the possibility of superposed fabrics with different orientations. The magnetic fabric pattern is consistent with a magma emplaced in an arc setting deformed by a dextral shear. Synthetic extensional shear bands localize the magmatic deformation along East-trending corridors that probably were exploited to emplace the late magmatic pulses. Accretion of the Eocene batholith and the Late Cretaceous metasedimentary host-rocks to the South American continent defines a major strike-slip shear suture that resulted from the oblique convergence of the Caribbean Plate.

Diamagnetic susceptibility of the electron gas in the cylindrical nanolayer

Diamagnetic properties of the electron gas in cylindrical nanolayer have been investigated. The dependence of mean energy, mean magnetization and mean magnetic susceptibility on the values of magnetic field is obtained. Comparison of these dependencies with the case, when the electron gas is localized in the cylindrical quantum dot, is carried out. In a nanolayer, the character of an effect of size quantization on the magnetic properties of the electron gas has been revealed.

Imaging Cerebral Microhemorrhages in Military Service Members with Chronic Traumatic Brain Injury.

To detect cerebral microhemorrhages in military service members with chronic traumatic brain injury by using susceptibility-weighted magnetic resonance (MR) imaging. The longitudinal evolution of microhemorrhages was monitored in a subset of patients by using quantitative susceptibility mapping. The study was approved by the Walter Reed National Military Medical Center institutional review board and is compliant with HIPAA guidelines. All participants underwent two-dimensional conventional gradient-recalled-echo MR imaging and three-dimensional flow-compensated multiecho gradient-recalled-echo MR imaging (processed to generate susceptibility-weighted images and quantitative susceptibility maps), and a subset of patients underwent follow-up imaging. Microhemorrhages were identified by two radiologists independently. Comparisons of microhemorrhage number, size, and magnetic susceptibility derived from quantitative susceptibility maps between baseline and follow-up imaging examinations were performed by using the paired t test. Among the 603 patients, cerebral microhemorrhages were identified in 43 patients, with six excluded for further analysis owing to artifacts. Seventy-seven percent (451 of 585) of the microhemorrhages on susceptibility-weighted images had a more conspicuous appearance than on gradient-recalled-echo images. Thirteen of the 37 patients underwent follow-up imaging examinations. In these patients, a smaller number of microhemorrhages were identified at follow-up imaging compared with baseline on quantitative susceptibility maps (mean ± standard deviation, 9.8 microhemorrhages ± 12.8 vs 13.7 microhemorrhages ± 16.6; P = .019). Quantitative susceptibility mapping-derived quantitative measures of microhemorrhages also decreased over time: -0.85 mm(3) per day ± 1.59 for total volume (P = .039) and -0.10 parts per billion per day ± 0.14 for mean magnetic susceptibility (P = .016). The number of microhemorrhages and quantitative susceptibility mapping-derived quantitative measures of microhemorrhages all decreased over time, suggesting that hemosiderin products undergo continued, subtle evolution in the chronic stage.

Distinctive diamagnetic fabrics in dolostones evolved at fault cores, the Dead Sea Transform

We resolve the anisotropy of magnetic susceptibility (AMS) axes along fault planes, cores and damage zones in rocks that crop out next to the Dead Sea Transform (DST) plate boundary. We measured 261 samples of mainly diamagnetic dolostones that were collected from 15 stations. To test the possible effect of the iron content on the AMS we analyzed the Fe concentrations of the samples in different rock phases. Dolostones with mean magnetic susceptibility value lower than −4 × 10−6 SI and iron content less than ∼1000 ppm are suitable for diamagnetic AMS-based strain analysis. The dolostones along fault planes display AMS fabrics that significantly deviate from the primary “sedimentary fabric”. The characteristics of these fabrics include well-grouped, sub-horizontal, minimum principal AMS axes (k3) and sub-vertical magnetic foliations commonly defined by maximum and intermediate principal AMS axes (k1 and k2 axes, respectively). These fabrics are distinctive along fault planes located tens of kilometers apart, with strikes ranging between NNW-SSE and NNE-SSW and different senses of motion. The obtained magnetic foliations (k1–k2) are sub-parallel (within ∼20°) to the fault planes. Based on rock magnetic and geochemical analyses, we interpret the AMS fabrics as the product of both shape and crystallographic anisotropy of the dolostones. Preferred shape alignment evolves due to mechanical rotation of subordinate particles and rock fragments at the fault core. Preferred crystallographic orientation results from elevated frictional heating (>300 °C) during faulting, which enhances c-axes alignment in the cement-supported dolomite breccia due to crystal-plastic processes. The penetrative deformation within fault zones resulted from the local, fault-related strain field and does not reflect the regional strain field. The analyzed AMS fabrics together with fault-plane kinematics provide valuable information on faulting characteristics in the uppermost crust.

Petrophysical Modelling For the Bahariya Formation, Egypt

Lithologic laminations have great consequences on the Bahariya sandstone, which are distinguished by the calculated reservoir statistical parameters. The non-laminated Bahariya studied samples have the lowest mean bulk density and specific internal surface values, while they have the highest mean porosity, permeability and Spor values. On the other hand, the laminated samples exhibit high values. The non-laminated Bahariya samples have the lowest mean permeability anisotropy, due to its relative pore-framework homogeneity. Contrary, the laminated Bahariya samples have the highest mean permeability anisotropy. By the same behaviour, the non-laminated Bahariya samples have the highest mean electrical resistivity value, due to the lack of conductive minerals, while the laminated Bahariya samples have the highest mean electrical resistivity.The non-laminated Bahariya samples show the lowest mean magnetic susceptibility value, while the laminated samples reveal high values. Sonic wave velocities (Vp and Vs) are statistically treated, while the velocity anisotropy is calculated for all samples. Laminated samples display higher velocity in comparable to the non-laminated ones. Thin sections and SEM-micrographs were made for some selected samples in order to recognize the Bahariya sandstone forming minerals. Glauconite, micas, zircon, rutile and pyrite minerals are composing the laminas in the laminated samples, while some glauconitic sandstone are predominant in the non-laminated ones.A number of linear regression models were performed among some measured petrophysical parameters, in order to differentiate between the laminated and the non-laminated sandstones, and to obtain reliable relationships permitting reservoir characterization.