Higher Anisotropy Values Research Articles

Structural and magnetic properties of high magnetization FexCo100-x nanoparticles investigated at the nanoscale: Unveiling the origin of the observed anisotropy

In this work the authors have performed the synthesis of FexCo100-x (0<x<100) alloy nanoparticles (NPs) with different compositions, as well as pure Fe and Co NPs for comparison, by a chemical reduction technique. The subsequent characterization demonstrated excellent quality NPs with the expected bcc cubic (for Fe and FeCo alloys) and hcp hexagonal (for Co NPs) structures showing a room temperature magnetization as high as 235 emu/g for the Fe66Co34 composition alloy. Nevertheless, this soft magnetic character is accompanied by determined values of effective anisotropy as high as 2 MJ/m3. Aiming to deep into the properties of these FeCo alloys as well as to unveil the origin of that observed high anisotropy value, we now present an extensive study at the nanoscale of the synthesized Fe, Co and FexCo100-x alloy nanoparticles by using nuclear techniques as neutron powder diffraction, EXAFS and XANES spectroscopies. Mössbauer spectroscopy revealed that the FeCo alloys are in an A2 disordered solid solution. The obtained results, combined with AFM/MFM images, have demonstrated that despite the cubic bcc structure observed for all FeCo alloys (in excellent concordance with the pure Fe one) the NPs show a "flaky" shape of 50–60 nm size (diameter) but only 3–4 nm thickness, giving rise to a strong shape anisotropy contribution to the observed total effective anisotropy.

Effect of particle size and composition on local magnetic hyperthermia of chitosan-Mg1-xCoxFe2O4 nanohybrid.

In this study, Mg1-xCoxFe2O4 (0≤x ≤ 1 with ∆x = 0.1) or MCFO nanoparticles were synthesized using a chemical co-precipitation method and annealed at 200, 400, 600, and 800°C respectively to investigate the structural properties of the materials by X-ray diffractometer (XRD), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR). Controlled annealing increased particle size for each value of x. The aim was to investigate how specific loss power (SLP) and maximum temperature (Tmax) during local magnetic hyperthermia were affected by structural alterations associated with particle size and composition. The lattice parameter, X-ray density, ionic radius, hopping length, bond length, cation-cation distance, and cation-anion distance increase with an increase in Co2+ content. Raman and FTIR spectroscopy reveal changes in cation distribution with Co2+ content and particle size. Magnetic properties measured by the physical property measurement system (PPMS) showed saturation magnetization (Ms), coercivity (Hc), remanent magnetization (Mr/Ms), and anisotropy constant (K1) of the Mg1-xCoxFe2O4 nanoparticles increase with Co2+ content and particle size. When exposed to an rf magnetic field, the nanohybrids experienced an increase in both the SLP (specific loss power) and Tmax (maximum temperature) as the particle size initially increased. However, these values reached their peak at critical particle size and subsequently decreased. This occurs since a modest increase in anisotropy, resulting from the presence of Co2+ and larger particle size, facilitates Néel and Brownian relaxation. However, for high anisotropy values and particle size, the Néel and Brownian relaxations are hindered, leading to the emergence of a critical size. The critical size increases as the Co2+ content decreases, but it decreases as the Co2+ content increases, a consequence of higher anisotropy with the increase in Co2+. Additionally, it is noteworthy that the maximum temperature (Tmax) rises as the concentration of nanohybrids grows, but the specific loss power (SLP) decreases. An increased concentration of chitosan-MCFO nanohybrids inhibits both the Néel and Brownian relaxation processes, reducing specific loss power.

Mesoscopic Assessment of Microstructure in Glioblastomas and Metastases by Merging Advanced Diffusion Imaging with Immunohistopathology.

Glioblastomas and metastases are the most common malignant intra-axial brain tumors in adults and can be difficult to distinguish on conventional MR imaging due to similar imaging features. We used advanced diffusion techniques and structural histopathology to distinguish these tumor entities on the basis of microstructural axonal and fibrillar signatures in the contrast-enhancing tumor component. Contrast-enhancing tumor components were analyzed in 22 glioblastomas and 21 brain metastases on 3T MR imaging using DTI-fractional anisotropy, neurite orientation dispersion and density imaging-orientation dispersion, and diffusion microstructural imaging-micro-fractional anisotropy. Available histopathologic specimens (10 glioblastomas and 9 metastases) were assessed for the presence of axonal structures and scored using 4-level scales for Bielschowsky staining (0: no axonal structures, 1: minimal axonal fragments preserved, 2: decreased axonal density, 3: no axonal loss) and glial fibrillary acid protein expression (0: no glial fibrillary acid protein positivity, 1: limited expression, 2: equivalent to surrounding parenchyma, 3: increased expression). When we compared glioblastomas and metastases, fractional anisotropy was significantly increased and orientation dispersion was decreased in glioblastomas (each P < .001), with a significant shift toward increased glial fibrillary acid protein and Bielschowsky scores. Positive associations of fractional anisotropy and negative associations of orientation dispersion with glial fibrillary acid protein and Bielschowsky scores were revealed, whereas no association between micro-fractional anisotropy with glial fibrillary acid protein and Bielschowsky scores was detected. Receiver operating characteristic curves revealed high predictive values of both fractional anisotropy (area under the curve = 0.8463) and orientation dispersion (area under the curve = 0.8398) regarding the presence of a glioblastoma. Diffusion imaging fractional anisotropy and orientation dispersion metrics correlated with histopathologic markers of directionality and may serve as imaging biomarkers in contrast-enhancing tumor components.

In-plane anisotropic mechanical properties of two-dimensional NbOI2

Two-dimensional niobium oxide diiodide (NbOI2) has recently attracted extensive attention due to its highly anisotropic band structures and rich physical characteristics in electronics and optoelectronics. Nevertheless, mechanical properties of NbOI2 have not been systematically investigated, which are critical parameters for applications. Here, we determine the directional dependence of Young's modulus of thin NbOI2 flakes by using an atomic force microscopy-based nanoindentation technique. We find that Young's moduli along two perpendicular in-plane crystalline axis, the c-axis and the a-axis, were 97.27 ± 2.12 and 51.51 ± 8.21 GPa, respectively. The anisotropic ratio is up to 1.89, which is a high anisotropy value in two-dimensional materials reported so far.

Atomic Ordering in Fe2NiZ (Z = Al, Ga, In, Sn) Alloys: Effects on the Anisotropy and Properties of the Ground State

The effect of atomic configurations on the magnetic and structural properties of Fe2NiZ (Z = Al, Ga, In, Sn) Heusler alloys has been studied within the density functional theory. The competition between five structural motifs of the cubic phase due to permutations of Fe and Ni atoms is discussed. A new structure of the cubic phase with layer-by-layer atomic ordering of Fe and Ni atoms in the ground state is predicted. In this structural modification, the considered compounds have high magnetocrystalline anisotropy values that several times exceed the values for the FeNi alloy with tetragonal symmetry.

Laboratory measurements of ultrasonic wave velocities and anisotropy across a gold-hosting structure: A case study of the Thunderbox Gold Mine, Western Australia

Most lode gold deposits worldwide are associated with structures such as shear zones. Thanks to their capacity to couple resolution and depth of investigation, seismic methods can identify these indirect indicators of mineralization and help extend gold exploration targets to greater depths. Rocks from shear zones are usually seismically anisotropic. Seismic anisotropy is generally related to the intrinsic texture of the rock and the presence of cracks at depth, although the impact of the latter relative to the former fades out with increasing depth. Understanding the seismic impedance contrast between the rocks and determining seismic anisotropy in relation to the texture of the rock, and its evolution with depth (pressure) is therefore necessary to help interpret exploratory seismic surveys. To do so, we characterized in the laboratory 126 core samples representing different stages of alteration and different lithologies from the Thunderbox Gold Mine in Western Australia. Laboratory measurements consist of ultrasonic wave velocity at ambient and in situ pressure, density, mineralogy, texture analysis, and estimation of P-wave anisotropy by inverting the ultrasonic data. These experimental data were used as input in different rock physics models to calculate texture-derived velocities and to model the effects of seismic anisotropy on seismic reflectivity. Except for massive basalt samples that present a remarkable elastic impedance contrast with all lithologies and for the talc schist samples (shear zone samples) that present high seismic anisotropy values, the seismic reflectivity between the lithological units encountered at the Thunderbox Gold Mine is low. According to seismic reflectivity modelling, seismic anisotropy along the shear zone significantly affects the seismic reflectivity, with values of reflectivity reducing more with the increasing angle of seismic reflection than if the shear zone is considered as an isotropic interface. The good agreement between calculated texture-derived velocities with experimental measurements shows that the crystallographic preferred orientation of minerals of the shear zone samples is the main source of seismic anisotropy. This study seeks to improve the understanding of the seismic response across mineral deposits that are structurally controlled by shear zones.

Statistical Analysis of the Distribution and Evolution of Mirror Structures in the Martian Magnetosheath

The mirror-mode structures in the Martian magnetosheath that were observed by Mars Atmosphere and Volatile Evolution during 2015–2018 are analyzed statistically. It is found that most mirror-mode events occurred close to the bow shock. Morphological categorization based on skewness of the magnetic field shows that ∼46.57% of the observed mirror-mode events are peak-like, ∼40.25% are wave-like, and ∼13.18% are dip-like. The mirror-mode structures mostly saturate in a very short time after their formation near the bow shock, which is a result of the high temperature anisotropy and high plasma beta at this location. Carried downstream by the magnetosheath flow, the mirror-mode structures remain in nonlinear saturation states. Meanwhile, the dayside magnetosheath plasma largely deviates from marginal stability, which is a state commonly that is expected in the terrestrial magnetosheath. By flowline tracing in an MHD model, it is found the mirror structures can be divided into two groups: ∼80% of the events that are observed near the bow shock evolve less than 10 s in plasma with high temperature anisotropy and high plasma beta value, keeping in saturated states; the other 20% of the events evolve following a similar process to that at the Earth, undergoing morphology transition in response to the local plasma conditions. However, the dayside magnetosheath is largely in an unstable condition, which prevents the mirror-mode structures from fully evolving into the decaying phase. Our results suggest that energy dispassion through wave-particle interaction might not be sufficient to remove the free energy that is introduced by the solar wind–Mars interaction.

The talar morphology of a hypochondroplasic dwarf: A case study from the Italian Late Antique period

AbstractThis project aims to test whether geometric morphometric (GM) and trabecular analyses may be useful tools in identifying talar characteristics related to hypochondroplasia. We quantified the external and internal talar morphology of a hypochondroplasic dwarf (T17) from Modena (northern Italy) dated to the sixth century AD. External talar morphology of T17 was compared with a broad sample of modern human tali (n = 159) using GM methods. Additionally, a subsample of these tali (n = 41) was used to investigate whole talar trabecular changes in T17. Our results show that GM and trabecular analyses identify a combination of traits linked to the dwarfing disorder of hypochondroplasia. These traits include decreased scaled talar dimensions compared with normal‐sized individuals, presence of an accessory antero‐lateral talar facet, high bone volume fraction, and high anisotropy values throughout the entire talus. In our case study, hypochondroplasia does not appear to substantially modify external talar morphology probably due to the fast growth of the talus. We suggest that small talar dimensions are associated with hypochondroplasia. An antero‐lateral talar facet may result from the talus and calcaneus coalition (i.e., talocalcaneal abnormal bridging) possibly related to an everted foot posture that was limited by overgrowth of the fibula. We suggest that high talar trabecular density and strut orientation provide insights into pathological development of the trabecular plates in T17. Finally, our study suggests that high talar trabecular density and strut orientation, and small talar dimensions, may be added as possible concomitant talar hallmarks for hypochondroplasia.

Velocity anisotropy and trend in Niger Delta, Nigeria

In geophysical data interpretation, matching the vertical velocity direction from seismic data with borehole-derived velocities is a challenging task because seismic-derived velocities are faster than borehole recorded velocities. This geophysical phenomenon is caused by velocity anisotropy. In this study, we used an empirical approach to estimate the degree of velocity anisotropy in the study area. The results showed that the delta anisotropy in sandstone beds varies from − 2.5% to 7.2% while most of them concentrate between 3.2% and 6.1%. The epsilon ranges between -6.4% and 9.3% while many of them concentrate between 3.2% and 7.2%. The gamma varies from − 6.3% to 7.3% while most of them concentrate between 1.2% and 5%. At shale beds, delta anisotropy varies from − 11.2% to 11.1% but most of them concentrate between 4.3% and 10.5%. The epsilon varies from − 7.2% to 14.5% while most of them concentrate between 4.5% and 10.5%. The gamma varies from 6.4% to 8.2% while majority of them concentrate between 2% and 5.3%. The results indicate that the study area is weakly to moderately anisotropic with shale beds having higher anisotropy values than sandstone beds. This probably results from preferential alignment of clay mineral orientations which also affect in situ velocity propagation. Three distinct velocity gradients (low, moderate and very high) were identified in the study area. These velocities vary erratically but showed northeast–southwest increase in velocities. Thus, the need to derive correction factors for individual wells for improved exploration success.

Investigation of nonlinearity of longitudinal displacement function from mechanical and geometric characteristics of the plate

Layered composite materials are characterized by a high transverse anisotropy and low values of relations between the transverse shear modulus and the modulus of longitudinal elasticity. As a result, the behavior of longitudinal displacements and longitudinal normal stresses differs from the linear law, and the behavior of transverse tangential stresses differs from the parabolic law. The paper presents the analysis of the degree of the plate displacement nonlinearity functions depending on its elastic properties and geometric shape. The article considers a 2D square plate deformation problem. In non-dimensional terms, the authors could received a complete and demonstrative solution. A similar 3D problem is more bulky but it has no principle differences. The study of the degree of the longitudinal displacement nonlinearity functions due to elastic properties and the geometric shape of the deformable plate is based on the finite element method. The potential energy of the deformable plate is expressed through a square form of the variables with coefficients that are polynomials of dimensionless parameters such as plate size, ratio of the elasticity and shear moduli, Poisson's modulus. It is shown that the variational principle reduces the problem to the solution of the system of linear equations. As a result, the subareas of linearity and nonlinearity of the plate longitudinal displacements are constructed with an accuracy acceptable for engineering calculations of 5 %. It is necessary to consider the plate nonlinear longitudinal deformations for a length of the composite plate on order more than its thicknesses. As for steel, nonlinearity is characteristic for quite thick plates. The constructed areas of linearity and nonlinearity of the longitudinal displacements make it possible to construct the strain-stress state models with a smaller number of variables.

Lattice Distortion in Mixed-Anion Lead Halide Perovskite Nanorods Leads to their High Fluorescence Anisotropy

Semiconductor nanorods (NRs) with strong fluorescence anisotropy are considered promising polarized light sources for liquid crystal displays. Here, we achieved a high fluorescence anisotropy value of 0.4 in the mixed-anion lead halide perovskite NRs, which constitutes a four-fold enhancement as compared to pristine CsPbBr3 NRs. This was realized by substituting some smaller bromine anions with larger iodine anions in the orthorhombic CsPbBr3 NRs via anion exchange. The resulting CsPbBr1.2I1.8 NRs kept a highly uniform length of ∼36 nm and width of ∼8.6 nm, and possessed a high emission quantum yield of 83%. On the basis of the DFT calculations, we attribute the improved polarized emission of the mixed-anion perovskite NRs to a moderate structural distortion of PbX6 octahedra units in the orthorhombic perovskite lattice, which results in a preferred direction of the optical transition dipole moment along the Pb–X–Pb axis. Our study provides a guidance for design and fabrication of perovskite NRs with high fluorescence anisotropy.

Strong anisotropy in the mixed antiferromagnetic system Mn1−xFexPSe3

We report the magnetic phase diagram of ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{PSe}}_{3}$, which represents a random magnet system of two antiferromagnetic systems with mixed spin, mixed spin anisotropies, mixed nearest-neighbor magnetic interactions, and mixed periodicities in their respective antiferromagnetic structure. Bulk samples of ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{PSe}}_{3}$ have been prepared and characterized phase pure by powder x-ray and neutron diffraction and x-ray fluorescence. Nature and extent of magnetically ordered state has been established using powder neutron diffraction, dc magnetic susceptibility, and heat capacity. Long-range magnetic ordering exists between $x=0.0$ and 0.25 (${\mathrm{MnPSe}}_{3}$ type) and between $x=0.875$ and 1 (${\mathrm{FePSe}}_{3}$ type). A short-range magnetic order with the existence of both ${\mathrm{MnPSe}}_{3}$- and ${\mathrm{FePSe}}_{3}$-type nanoclusters has been established between $x=0.25$ and 0.875. Irreversibility in dc magnetization measurements, also characterized by isothermal and thermoremanent magnetization measurements, suggest similarities to magnetic nanoparticles where uncompensated surface spins result in diverging thermoremanent and isothermal remanent magnetization responses, further reinforcing existence of magnetic nanoclusters or domains. A spin-glass state, observed in analogous ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{PS}}_{3}$, has been ruled out, and formation of nanoclusters exhibiting both ordering types results from unusually high anisotropy values. The effect of ligand contributions to the spin-orbit interactions has been suggested as a possible explanation for high $D$ values in these compounds.

Formability Analyses of a Novel Alloy Cold-rolled Batch Annealed Dual Phase Steel

Modelling of batch annealing process parameters of dual phase steels is crucial to obtain targeted steel microstructure, hence desired mechanical properties and enhanced formability. By developing unique annealing profile parameters -including but not limited to critical annealing temperature, isoholding duration and cooling rate- in consideration with chemical composition; high strength steel products possessing better cold formability, strain hardenability and higher anisotropy values are attained. In this study, the correlations of material properties with micro-scale features and processing parameters are investigated. Nakazima tests along with microstructural investigations are performed. Cold-rolled and batch annealed materials of this study are compared with conventionally produced dual phase steels and superior formability is validated through mechanical and microstructural characterization.

High Thermal Conductivity and Anisotropy Values of Aligned Graphite Flakes/Copper Foil Composites.

Much attention has been paid to graphite flakes/copper (GFs/Cu) composites for thermal management due to their remarkable thermal properties. Most studies focus on the interface interaction between GFs and Cu in composites. However, controlling the orientation of GFs still remains a challenge. Herein, we report a reliable method to ensure consistent orientation of GFs in the composites. Firstly, the disorder GFs were well arranged on the surface of copper foil by tape casting process in the casting machine. Then highly aligned GFs/Cu composites were fabricated by hot pressing process in a vacuum hot-pressing furnace, with the volume fraction of graphite from 30% to 70%. The SEM images show that the obtained GFs/Cu composites presented a layer-by-layer structure or network structure with a different content of GFs. The thermal conductivity of GFs/Cu composites exhibited an extreme anisotropy due to the highly aligned GFs. The ultrahigh thermal conductivity of GFs/Cu composites with 70 vol% GFs reached 741 W/(m·K), while through-plane thermal conductivity was just 42 W/(m·K). The alignment of GFs and interfacial thermal resistance were deeply analyzed and a thermal conductivity model for GFs/Cu composites was established. Our work provides a new idea to significantly enhance the thermal transportation performance of GFs/Cu composites by well controlled alignment of GFs in Cu matrix.

High energy product of MnBi by field annealing and Sn alloying

Permanent-magnet materials are one cornerstone of today’s technology, abundant in disk drives, motors, medical equipment, wind generators, and cars. A continuing challenge has been to reconcile high permanent-magnet performance with low raw-material costs. This work reports a Mn-Bi-Sn alloy exclusively made from inexpensive elements, exhibiting high values of Curie-temperature, magnetization, anisotropy, coercivity, and energy product. The samples are produced by field annealing of rapidly quenched Sn-containing MnBi alloys, where the improvement of the magnetic properties is caused by the substitutional occupancy of the 2c sites in the hexagonal NiAs structure by Sn. The substitution modifies the electronic structure of the compound and enhances the magnetocrystalline anisotropy, thereby improving the coercivity of the compound. The energy product reaches 114 kJ/m3 (14.3 MGOe) at room temperature and 86 kJ/m3 (10.8 MGOe) at 200 °C; this value is similar to that of the Dy-free Nd2Fe14B and exceeds that of other rare-earth-free permanent-magnet bulk alloys, as encountered in automotive applications.

Enhancing domain wall velocity through interface intermixing in W-CoFeB-MgO films with perpendicular anisotropy

We study the influence of He+ irradiation induced interface intermixing on magnetic domain wall (DW) dynamics in W-CoFeB (0.6 nm)-MgO ultrathin films, which exhibit high perpendicular magnetic anisotropy and large Dzyaloshinskii-Moriya interaction (DMI) values. Whereas the pristine films exhibit strong DW pinning, we observe a large increase in the DW velocity in the creep regime upon He+ irradiation, which is attributed to the reduction of pinning centers induced by interface intermixing. Asymmetric in-plane field-driven domain expansion experiments show that the DMI value is slightly reduced upon irradiation, and a direct relationship between DMI and interface anisotropy is demonstrated. Our findings provide insights into the material design and interface control for DW dynamics, as well as for DMI, enabling the development of high-performance spintronic devices based on ultrathin magnetic layers.

On the Application of Coefficient of Anisotropy as an Index of Groundwater Potential in a Typical Basement Complex of Ado Ekiti, Southwest, Nigeria

This paper examines the application of the Dar Zarrouk parameter, the Coefficient of Anisotropy to Groundwater Potential Evaluation in a typical Basement Complex Terrain of Ado-Ekiti Southwest, Nigeria. A regional Geoelectric Depth sounding was carried out across the metropolis using the Schlumberger electrode array. Resistivity-depth image in terms of layer thickness and resistivity was used to compute the Coefficients of Anisotropy for the VES locations occupied. Thematic maps of the geoelectric parameters were generated using the Concept of Geographical Information System (GIS). Comparative Map Analysis revealed that a range of 1.3 to 1.6 Anisotropy values was observed across the zones characterized by thick overburden, Weathered Basement Thickness in excess of 25m, low weathered basement resistivity, fractured bedrock and basement depressions in the study area. Anisotropy values ranging from 1.8 to 2.8 were observed across the basement ridges and zones characterized by thin overburden, Weathered Basement Thickness of generally less than 15m and Weathered Basement resistivity greater than 1500 Ω-m with least groundwater potential. The regions of Anisotropy values ranging from 1.3 to 1.6 are demarcated as high groundwater potential zones. Areas characterized by higher Anisotropy values can be associated with low porosity and permeability with less hydro geological appeal.

Shear localisation in anisotropic, non-linear viscous materials that develop a CPO: A numerical study

Localisation of ductile deformation in rocks is commonly found at all scales from crustal shear zones down to grain scale shear bands. Of the various mechanisms for localisation, mechanical anisotropy has received relatively little attention, especially in numerical modelling. Mechanical anisotropy can be due to dislocation creep of minerals (e.g. ice or mica) and/or layering in rocks (e.g. bedding, cleavage). We simulated simple-shear deformation of a locally anisotropic, single-phase power-law rheology material up to shear strain of five. Localisation of shear rate in narrow shear bands occurs, depending on the magnitude of anisotropy and the stress exponent. At high anisotropy values, strain-rate frequency distributions become approximately log-normal with heavy, exponential tails. Localisation due to anisotropy is scale-independent and thus provides a single mechanism for a self-organised hierarchy of shear bands and zones from mm-to km-scales. The numerical simulations are compared with the natural example of the Northern Shear Belt at Cap de Creus, NE Spain.

Delineation of Groundwater Potential and Recharge Zone Using Electrical Resistivity Method Around Veeranam Tank, Tamil Nadu, India

Veeranam tank is one of the largest tank in Tamil Nadu, India which plays a vital role in groundwater recharge to the surrounding aquifer. Electrical resistivity survey were carried out in ten locations around the Veeranam tank. The resistivity, thickness of subsurface formations, longitudinal conductance (S), transverse resistance (R), average longitudinal resistivity (ST), average transverse resistivity (RT) and anisotropy (λ) were used to characterize the lithological formations and also groundwater potential and recharge zones were delineated. The four major zones clay, clayey sand, saline sand and sandstone were identified as a result of primary geo-electrical parameters which includes resistivity and thickness of the formations. The sandstone formation is identified as good water bearing formation and this formation possess low longitudinal conductance, high transverse resistance, and low anisotropy values. The clay and saline formation possess high longitudinal conductance, low transverse resistance and high anisotropy values and these formations are identified as moderate groundwater water bearing formations. High longitudinal conductance is observed in eastern region of the study area due to intrusion of saline water. Sandstone formation of low longitudinal conductance is associated with high percolation rate and groundwater potential is also good in this formation. High transverse resistance zones are associated with high infiltration rate and high transmissivity whereas groundwater potential is good in these zones. VES 2 and VES 3 stations comprises of sandstone formation as second layer and Veeranam tank water infiltrated into these zones due to high infiltration rate of these formations. The resistivity value is decreased in VES 10 station due to intrusion of sea water. The true resistivity near the Veeranam tank is high and decreases towards east which clearly indicates that groundwater recharge is the major process that occurs nearby the downstream shore of tank and intrusion of saline water in the eastern part of the study area. Thus good interaction between exists between Veeranam tank and its downstream zones and interaction decreases as the distance increases from the tank.

Investigation of the change in soil fabric during cone penetration in silt using 2D measurements

Interpretation of CPTU testing in silt is non-trivial because of the partially drained conditions that are likely to occur during penetration. A better understanding of the pore pressure generation/dissipation is needed in order to obtain reliable design parameters. Following a previous study using X-ray computed tomography (micro-CT) with volumetric digital image correlation (3D-DIC) that clearly showed the formation of distinct dilation and compression areas around the cone; the present work takes a closer look at those areas in order to link volumetric behavior to changes in soil fabric. High-resolution 2D backscattered electron images of polished thin sections prepared from frozen samples at the end of penetration are used. The images have a spatial resolution of 0.4 µm/pixel that allow a clear identification of grains and pore spaces. Image processing techniques are developed to quantify local porosity and obtain the statistical distribution of the particle orientation for the zones around the cone tip and shaft. It is shown that the formation of compaction regions is related to the ability of the grains to rearrange and align along a well-defined preferred orientation forming a more closed-fabric characterized by high anisotropy values, while zones of dilation are associated with a more open packing with grains randomly oriented and with large voids within. These observations suggested that for a saturated soil, water will move from a compressive zone to a neighboring dilative zone, creating a short drainage path. By shedding light on the link between soil fabric and drainage patterns, this study contributes toward a better understanding of the measured macro-response during CPTU tests on silt.