Anisotropy Of Susceptibility Research Articles

DTI Tract-Based Quantitative Susceptibility Mapping: An Initial Feasibility Study to Investigate the Potential Role of Myelination in Brain Connectivity Change in Cerebral Palsy Patients During Autologous Cord Blood Cell Therapy Using a Rotationally-Invariant Quantitative Measure.

Previous studies using diffusion tensor imaging (DTI)-based connectome analysis revealed improved connectivity in cerebral palsy (CP) patients who underwent autologous umbilical cord blood (UCB) stem-cell therapy. However, the potential mechanism for the connectivity increase remains unclear and needs to be further elucidated. To develop a technique with improved accuracy for quantitative susceptibility mapping (QSM) with unique sensitivity to myelin, and demonstrate its use in elucidating the underlying mechanism of the observed motor function improvement and brain connectivity increase in CP patients who received autologous UCB stem-cell therapy. Prospective. A cohort of eight pediatric CP patients (2.6 ± 0.6 years of age) with intact corticospinal tracts (CST) from a randomized, placebo-controlled trial of autologous UCB stem-cell therapy in CP children was included in this study. DTI and 3D spoiled gradient recalled (SPGR) QSM at 3.0T. Pre- and posttreatment magnetic susceptibility (χ) and the rotationally-invariant magnetic susceptibility anisotropy (MSA) along the CST were derived. Behavioral changes were assessed using the 66-item Gross Motor Function Measurement. Changes in χ and MSA were compared between patients with and without substantial behavioral improvements. Two-sample t-tests were performed to assess the differences in the changes of measurements of interest (Δχ, ΔMSA, and ΔFA) between patients who significantly improved and those who did not. Patients who demonstrated posttreatment motor improvements exceeding expectations showed significantly more diamagnetic Δχ in the periventricular region along the CST (P = 0.003). Further analysis on the ΔMSA of this region was significantly increased (P = 0.006) for high responders, along with concurrent FA increase. These initial findings suggest that the DTI tract-based QSM method has the potential to characterize white matter changes associated with behavioral improvements in CP children who underwent cord blood stem-cell therapy. 2 TECHNICAL EFFICACY: Stage 2.

How the Ligand Field in Lanthanide Coordination Complexes Determines Magnetic Susceptibility Anisotropy, Paramagnetic NMR Shift, and Relaxation Behavior.

ConspectusComplexes of lanthanide(III) ions are being actively studied because of their unique ground and excited state properties and the associated optical and magnetic behavior. In particular, they are used as emissive probes in optical spectroscopy and microscopy and as contrast agents in magnetic resonance imaging (MRI). However, the design of new complexes with specific optical and magnetic properties requires a thorough understanding of the correlation between molecular structure and electric and magnetic susceptibilities, as well as their anisotropies. The traditional Judd–Ofelt–Mason theory has failed to offer useful guidelines for systematic design of emissive lanthanide optical probes. Similarly, Bleaney’s theory of magnetic anisotropy and its modifications fail to provide accurate detail that permits new paramagnetic shift reagents to be designed rather than discovered.A key determinant of optical and magnetic behavior in f-element compounds is the ligand field, often considered as an electrostatic field at the lanthanide created by the ligands. The resulting energy level splitting is a sensitive function of several factors: the nature and polarizability of the whole ligand and its donor atoms; the geometric details of the coordination polyhedron; the presence and extent of solvent interactions; specific hydrogen bonding effects on donor atoms and the degree of supramolecular order in the system. The relative importance of these factors can vary widely for different lanthanide ions and ligands. For nuclear magnetic properties, it is both the ligand field splitting and the magnetic susceptibility tensor, notably its anisotropy, that determine paramagnetic shifts and nuclear relaxation enhancement.We review the factors that control the ligand field in lanthanide complexes and link these to aspects of their utility in magnetic resonance and optical emission spectroscopy and imaging. We examine recent progress in this area particularly in the theory of paramagnetic chemical shift and relaxation enhancement, where some long-neglected effects of zero-field splitting, magnetic susceptibility anisotropy, and spatial distribution of lanthanide tags have been accommodated in an elegant way.

Angle Distribution Measurement of Scattered Light Intensity From Needle-Shaped Crystals in a Magnetic Field for Gout Diagnosis

Monosodium urate (MSU), which causes gout, forms needle-shaped crystals with large diamagnetic susceptibility anisotropy that orient in a magnetic field of up to 500 mT. The light transmittance and reflectance of MSU suspensions change under an applied magnetic field. To use this phenomenon to diagnose gout, it would be necessary to collect light scattering information from all angles, including transmission and reflection. This is because the scattered light intensity from MSU crystals is different in forward, sideward, and backward directions under near-infrared (NIR) light (785 nm), which has high biopermeability and is used in NIR spectroscopy. Therefore, we measured the angular distributions of light scattering by MSU crystals before and after applying a magnetic field and evaluated their characteristics. In the case of MSU crystals of the size found in gout patients, the scattered light intensity decreased at all angles under an applied magnetic field compared with that without a magnetic field. The change ratio of the scattered light intensity was large in the forward and backward directions and relatively small in the sideward directions. This was ascribed to the combined effects of the decrease in the scattering cross section caused by the magnetic orientation and the accompanying change in diffraction behavior. Our findings indicated that for gout diagnosis, the incident light should be horizontal and that if transmission measurement is possible, a detection angle of about 30° is suitable. If transmission measurement is not practical, it is better to avoid a detection angle of around 90°.

Geochemical Signature and Magnetic Fabric of Capinha Massif (Fundão, Central Portugal): Genesis, Emplacement and Relation with W–Sn Mineralizations

The Fundão–Serra da Estrela–Capinha (FSEC) region is characterized by peraluminous to metaluminous Variscan granites intrusive in a complex and thick metasedimentary sequence. This work seeks to characterize the Capinha granite (CG), understand its spatial and genetic relationship with the host Peroviseu–Seia (PS), Belmonte–Covilhã (BC) and Fáguas granites, and evaluate its metallogenic potential. To achieve these goals, a multidisciplinary approach was undertaken, including field work and identification of the petrography and microstructures, whole rock geochemistry and anisotropy of magnetic susceptibility. Four distinct and independent differentiation trends were identified in the granites, namely, PS, BC, Fráguas and CG. The PS and BC played a role as host rocks for the W and Sn mineralizations. The Fráguas granite is anomalous in Sn and spatially related to the Sn–Li mineralizations, while the CG is anomalous in W and spatially related to W–Sn mineralizations. The post-tectonic CG is a peraluminous ilmenite-type whose ascent and emplacement were tectonically controlled. The Capinha magma used the intersection between the 25° N and 155° N strike–slip crustal scale faults for passive ascent and emplacement during the late-Variscan extensional phases. The magnetic fabric was drawn using an asymmetric tongue-shaped laccolith for CG. CG experienced two brittle deformation stages that marked the maximum compressive rotation from NE–SW to NNW–SSE.

Late Triassic extensional tectonics in the northern North China Craton, insights from a multidisciplinary study of the Wangtufang pluton

To better understand Late Triassic tectonic setting in the northern North China Craton (NCC), the emplacement mechanism of the Wangtufang pluton, which recorded the synmagmatic regional tectonic signature, has been investigated. Zircon U-Pb ages, and Hf isotopic data, and whole-rock geochemical analyses suggest that the Late Triassic Wangtufang pluton composed of syenogranite and diorite is derived from partial melting of lower crust with some depleted mantle components. Both the syenogranite and diorite appear isotropic. Anisotropy of magnetic susceptibility and gravity studies have been carried out to characterize internal fabrics and shape of the pluton. The diorite forms just thin remnants above the syenogranite. The syenogranite with a series of NW-SE trending dykes intruded into the diorite and its country rocks. In the syenogranite, the gently dipping magnetic foliations strike nearly parallel to the pluton border. The shallow plunging magnetic lineations mainly strike NE–SW. Combining NE-SW trending elongated subsurface shape with central root, unflat bottom, and moderate- to high- inward dipping sidewalls, the syenogranite could be considered as a lopolith-like intrusion. The syenogranite was likely emplaced by inflation of magma pulses from its central conduit and built up by floor depression. Emplacement of the syenogranite was in an extensional setting, considering: (1) the NE–SW striking magnetic lineation, (2) the NE–SW trending elongated subsurface pluton shape, and (3) the orthogonal NW–SE striking syenogranitic dykes considered as tension gashes during the NE–SW trending extension. The Wangtufang pluton provides reliable arguments to the Late Triassic intracontinental extensional setting already suggested in the northern NCC.

Anisotropic magnetocaloric properties of the ludwigite single crystal Cu2MnBO5

We report upon the specific heat and magnetocaloric properties of Cu2MnBO5 over a temperature range of 60–350 K and in magnetic fields up to 18 kOe. It is found that at temperatures below the Curie temperature (TC ∼ 92 K), CP(T)/T possesses a linear temperature-dependent behavior, which is associated with the predominance of two-dimensional antiferromagnetic interactions of magnons. The temperature independence of CP/T = f(T) is observed in the temperature range of 95–160 K, which can be attributed to the excitation of the Wigner glass phase. The magnetocaloric effect [i.e., the adiabatic temperature change, ΔTad (T,H)] is assessed through a direct measurement or an indirect method using the CP(T,H) data. Owing to its strong magnetocrystalline anisotropy, an anisotropic magnetocaloric effect (MCE) or the rotating MCE [ΔTadrot (T)] is observed in Cu2MnBO5. A deep minimum in the ΔTadrot (T) near the TC is observed and ascribed to the anisotropy of the paramagnetic susceptibility.

Magnetic properties of pseudotachylytes from western Jämtland, central Swedish Caledonides

Abstract. Fault kinematics can provide information on the relationship and assembly of tectonic units in an orogen. Magnetic fabric studies of faults where pseudotachylytes form have recently been used to determine direction and sense of seismic slip in prehistoric earthquakes. Here we apply this methodology to study magnetic fabrics of pseudotachylytes in field structures of the Köli Nappe Complex (central Swedish Caledonides), with the aim to determine fault kinematics and decipher the role of seismic faulting in the assembly of the Caledonian nappe pile. Because the pseudotachylyte veins are thin, we focused on small (ca. 0.2 to 0.03 cm3) samples for measuring the anisotropy of magnetic susceptibility. The small sample size challenges conventional use of magnetic anisotropy and results acquired from such small specimens demand cautious interpretation. Importantly, we find that magnetic fabric results show inverse proportionality among specimen size, degree of magnetic anisotropy and mean magnetic susceptibility, which is most likely an analytical artifact related to instrument sensitivity and small sample dimensions. In general, however, it is shown that the principal axes of magnetic susceptibility correspond to the orientation of foliation and lineation, where the maximum susceptibility (k1) is parallel to the mineral lineation, and the minimum susceptibility (k3) is dominantly oriented normal to schistosity. Furthermore, the studied pseudotachylytes develop distinct magnetic properties. Pristine pseudotachylytes preserve a signal of ferrimagnetic magnetite that likely formed during faulting. In contrast, portions of the pseudotachylytes have altered, with a tendency of magnetite to break down to form chlorite. Despite magnetite breakdown, the altered pseudotachylyte mean magnetic susceptibility is nearly twice that of altered pseudotachylyte, likely originating from the Fe-rich chlorite, as implied by temperature-dependent susceptibility measurements and thin-section observations. Analysis of structural and magnetic fabric data indicates that seismic faulting occurred during exhumation into the upper crust, but these data yield no kinematic information on the direction and sense of seismic slip. Additionally, the combined structural field and magnetic fabric data suggest that seismic faulting was postdated by brittle E–W extensional deformation along steep normal faults. Although the objective of finding kinematic indicators for the faulting was not fully achieved, we believe that the results from this study may help guide future studies of magnetic anisotropy with small specimens (<1 cm3), as well as in the interpretation of magnetic properties of pseudotachylytes.

Microscopic susceptibility anisotropy imaging.

PurposeThe gradient‐echo MR signal in brain white matter depends on the orientation of the fibers with respect to the external magnetic field. To map microstructure‐specific magnetic susceptibility in orientationally heterogeneous material, it is thus imperative to regress out unwanted orientation effects.MethodsThis work introduces a novel framework, referred to as microscopic susceptibility anisotropy imaging, that disentangles the 2 principal effects conflated in gradient‐echo measurements, (a) the susceptibility properties of tissue microenvironments, especially the myelin microstructure, and (b) the axon orientation distribution relative to the magnetic field. Specifically, we utilize information about the orientational tissue structure inferred from diffusion MRI data to factor out the B0‐direction dependence of the frequency difference signal.ResultsA human pilot study at 3 T demonstrates proxy maps of microscopic susceptibility anisotropy unconfounded by fiber crossings and orientation dispersion as well as magnetic field direction. The developed technique requires only a dual‐echo gradient‐echo scan acquired at 1 or 2 head orientations with respect to the magnetic field and a 2‐shell diffusion protocol achievable on standard scanners within practical scan times.ConclusionsThe quantitative recovery of microscopic susceptibility features in the presence of orientational heterogeneity potentially improves the assessment of microstructural tissue integrity.

Magnetic anisotropy reveals Acadian transpressional fabrics in an Appalachian ophiolite (Thetford Mines, Canada)

SUMMARY Magnetic anisotropy has proved effective in characterizing primary, spreading-related magmatic fabrics in Mesozoic (Tethyan) ophiolites, for example in documenting lower oceanic crustal flow. The potential for preservation of primary magnetic fabrics has not been tested, however, in older Palaeozoic ophiolites, where anisotropy may record regional strain during polyphase deformation. Here, we present anisotropy of magnetic susceptibility results from the Ordovician Thetford Mines ophiolite (Canada) that experienced two major phases of post-accretion deformation, during the Taconian and Acadian orogenic events. Magnetic fabrics consistent with modal layering in gabbros are observed at one locality, suggesting that primary fabrics may survive deformation locally in low strain zones. However, at remaining sites rocks with different magmatic origins have consistent magnetic fabrics, reflecting structurally controlled shape preferred orientations of iron-rich phases. Subhorizontal NW-SE-oriented minimum principal susceptibility axes correlate with poles to cleavage observed in overlying post-obduction, pre-Acadian sedimentary formations, indicating that the magnetic foliation in the ophiolite formed during regional NW-SE Acadian shortening. Maximum principal susceptibility axes plunging steeply to the NE are orthogonal to the orientation of regional Acadian fold axes, and are consistent with subvertical tectonic stretching. This magnetic lineation is parallel to the shape preferred orientation of secondary amphibole crystals and is interpreted to reflect grain growth during Acadian dextral transpression. This structural style has been widely reported along the Appalachian orogen, but the magnetic fabric data presented here provide the first evidence for transpression recorded in an Appalachian ophiolite.

Anisotropy of Magnetic Susceptibility (AMS) Analysis of the Gonjo Basin as an Independent Constraint to Date Tibetan Shortening Pulses

AbstractThe Tibetan Plateau accommodated major upper crustal shortening during Indian Plate oceanic and continental lithosphere subduction. Deciphering whether shortening was continuous or episodic, and how it correlates to major geodynamic changes is challenging. Here we apply anisotropy of magnetic susceptibility (AMS), a sensitive synsedimentary strain indicator, to a ~3 km thick magnetostratigraphically dated sedimentary section (69–41.5 Ma) in eastern Tibet. AMS shows “earliest deformation” fabrics from 69–52 Ma, followed by a sudden change to “pencil structure” fabrics with increasing anisotropy degree at ~52 Ma, dating a sudden increased synsedimentary shortening strain. This change coincides with enhanced sedimentation rates and synsedimentary vertical‐axis rotations of the Gonjo Basin, suggesting a causal link to a marked India‐Asia convergence rate deceleration. We show that AMS analysis provides a strong tool to distinguish between climatic and tectonic causes of sedimentological change and is an asset in identifying discrete tectonic pulses in intensely deformed terrane.

Ferromagnetic Kitaev interaction and the origin of large magnetic anisotropy in α-RuCl3

$\alpha$-RuCl$_3$ is drawing much attention as a promising candidate Kitaev quantum spin liquid. However, despite intensive research efforts, controversy remains about the form of the basic interactions governing the physics of this material. Even the sign of the Kitaev interaction (the bond-dependent anisotropic interaction responsible for Kitaev physics) is still under debate, with conflicting results from theoretical and experimental studies. The significance of the symmetric off-diagonal exchange interaction (referred to as the $\Gamma$ term) is another contentious question. Here, we present resonant elastic x-ray scattering data that provides unambiguous experimental constraints to the two leading terms in the magnetic interaction Hamiltonian. We show that the Kitaev interaction ($K$) is ferromagnetic, and that the $\Gamma$ term is antiferromagnetic and comparable in size to the Kitaev interaction. Our findings also provide a natural explanation for the large anisotropy of the magnetic susceptibility in $\alpha$-RuCl$_3$ as arising from the large $\Gamma$ term. We therefore provide a crucial foundation for understanding the interactions underpinning the exotic magnetic behaviours observed in $\alpha$-RuCl$_3$.

Possible sources and transport pathways of loess deposited in Poland and Ukraine from detrital zircon U-Pb age spectra

Abstract A provenance study was carried out on loess deposits of SE Poland and Ukraine. For this purpose, loess samples were taken from 18 loess outcrops, and the U-Pb ages of detrital zircons were determined using a SHRIMP IIe ion microprobe. Additionally, studies of the anisotropy of magnetic susceptibility were conducted in the selected sections in order to reconstruct palaeowind directions. Zircons from the youngest loess in SE Poland and western Ukraine yield predominantly Cadomian and younger ages. On the other hand, the pre-Cadomian zircons are the most frequent in the loess from the Dnipro Basin in central and northern Ukraine. While the number of zircon grains analysed does not allow a detailed assessment, the location of the boundary between these two provinces of zircon provenance indicates that the catchment areas of major rivers provided most of the aeolian material. This boundary delimits areas of mountain provenance-river and continental glacier provenance-river transport modes of loess origin. The loess patches located close to the large river valleys were supplied with aeolian material that was blown mainly from the neighbouring riverbeds, as it was inferred from the palaeowind directions. Similar age spectra characteristics for the fine- and coarse-grained zircons demonstrate a significant role for the local transport of detrital material. The same age spectra observed in the loess of different age can indicate a substantial redeposition of sediment.

Paleohydro-climatic changes revealed by anisotropy of magnetic susceptibility at the Heitugou section, Nihewan Basin, and its influences on human’s occupation

Paleohydro-climatic changes in the habitats of early humans are closely related to their evolution and occupation of specific niches. In the Nihewan Basin of North China, a large number of archaeological sites dating back to the early Pleistocene have been discovered which record the occupation history of human ancestors in the region. However, thus far, studies of the history of paleohydro-climatic changes in the Nihewan Basin and their influences on human occupation remain insufficient. Here, we report the results of a systematic investigation of variations in the anisotropy of magnetic susceptibility (AMS) and magnetic susceptibility stratigraphy in the Heitugou (HTG) section to partially rectify this paucity of data and interpretations. The HTG section is located in the eastern Nihewan Basin where, in 2006, a Paleolithic site was discovered and excavated at the bottom of the sequence. By comparing detailed magnetic susceptibility sequences in the HTG section with those of the nearby Xiaochangliang and Dachangliang sections, we found that the sedimentation of the HTG section began about 1.9 Ma, indicating that the HTG archaeological site possibly records the earliest human occupation of middle-to-high latitude North China. Our studies of the AMS in the HTG section indicate that it is characterized by a primary sedimentary magnetic fabric without significant disturbance, demonstrating its potential for tracing regional paleo-hydrological changes. In most samples dating between 1.9 Ma and 0.4 Ma, the maximum susceptibility axes ( K max) cluster along the SE-NW vector, suggesting hydrodynamic changes tracable in the study area were mainly influenced by the Huliu River. In addition, a relatively weak K max direction biased towards the SW-NE axis was also observed, possibly generated by the predominant flow of the Sanggan River. These two rivers – the Huliu and Sanggan – determined the paleohydrological changes in the eastern Nihewan paleolake basin. Meanwhile, AMS studies also suggest multiple-phase hydrodynamic changes in the Nihewan Basin. Around 1.9 Ma, a thick layer of gravel was deposited in the study area due to the emergence of the Huliu River, or tectonic subsidence of the Nihewan Basin. Strengthened hydrodynamic changes and higher water-levels of the Nihewan paleolake may have driven early human ancestors to occupy higher topographic locations. Between 1.9–1.8 Ma, the paleolake expanded and the hydrodynamic regime weakened accordingly, which may correspond with the enhancement of the summer monsoon cycle in East Asia. Between 1.8–1.5 Ma, the sedimentary hydrodynamic regime strengthened noticeably early on, and subsequently weakened continuously. During the period from 1.5–1.3 Ma, as the East Asian summer monsoon regime intensified, warmer and wetter climatic conditions resulted in deepening of the Nihewan paleolake, which may have subsequently weakened influences from fluvial input and was associated with decreased sedimentary hydrodynamics. Between 1.3–0.9 Ma, high-frequency fluctuations in the AMS are noted, indicating a dramatic change in lacustrine hydrodynamics possibly attributable to the Mid-Pleistocene Transition (MPT) event. After 0.9 Ma, the Nihewan paleolake deepened again. Relatively high-amplitude fluctuations during this period reflect a cyclicity of 100 ka, possibly indicating that it was controlled by global ice volume. In concordance with other Paleolithic sites in the Nihewan Basin that have been chronometrically investigated, our studies at Heitugou reveal that paleohydro-climatic changes had a significant influence on early hominin activities in the Nihewan Basin, which shaped the spatio-temporal distribution of Paleolithic sites there. For example, during the early Pleistocene, early humans lived mostly on lower lake terraces in the eastern Nihewan Basin, when the lake level was still quite low. Subsequently, they moved to topographically higher sites due to gradually increasing lake levels. During the Middle and Late Pleistocene, when the Nihewan paleolake shrank, early humans moved toward the upper reaches of the Sanggan River, and were widely distributed along river courses across the Nihewan Basin during the Late Pleistocene in order to maintain home ranges near permanent water sources.

Magnetic fabrics preserved by post-glacial sediment in two New York Finger Lakes (USA) revealed evidence for deformation during coring and an erosional unconformity

The oceanographic community routinely uses anisotropy of magnetic susceptibility to identify deformation associated with sediment core collection and sampling, as well as to reconstruct primary and post-depositional conditions. These measurements are also applicable to lacustrine settings. Using anisotropy of magnetic susceptibility, in combination with geochemical and physical analyses of lake sediments, permits differentiation of primary depositional conditions from sediment disturbance associated with post-depositional processes and core collection. Detailed analysis of piston cores from Seneca Lake and Owasco Lake, New York (USA) revealed evidence for relatively weak anisotropies that resulted from normal lacustrine sedimentation since ~ 16.8–16.6 cal ka BP. A middle to late Holocene lowstand and associated erosional unconformity was inferred in both lakes using the magnitude of the anisotropy, changes in lithofacies, and increase in % sand. Anomalous magnetic fabrics were also preserved in post-glacial sediment that resulted from core collection and subaqueous slides. Stratigraphic disruptions (“flow-ins”) that formed during coring were recognized by vertically oriented laminae or soupy sediment near the base and top of cores, respectively, and confirmed the rationale for using magnetic fabric measurements. Mid-core “flow-ins” throughout the uppermost 1–2 m of three of the four cores in this study could only be identified by a gradual shift in the dominant shape of the magnetic fabric. Imperfect piston coring likely resulted in vertical strain that produced overthickened sections without destroying the stratigraphic integrity of these sediments. Subaqueous slides were recognized in Owasco Lake by abrupt changes in lithofacies and magnetic fabric. Anisotropy of magnetic susceptibility proved to be a powerful tool to assess lacustrine core integrity in massive and laminated sediment prior to paleoenvironmental reconstruction.

Emplacement of dike swarms from the island of Ilhabela (SE Brazil) and its relationship with the South Atlantic Ocean opening revealed by magnetic fabrics

Magnetic fabric and rock-magnetism studies were performed on 153 dikes from diabase, lamprophyre and alkaline dike swarms that outcrop on the island of Ilhabela, NE São Paulo State. The dikes crosscut Archean and Proterozoic polymetamorphic rocks. Their thicknesses range from a few centimeters to 4 or 5 m. They trend predominantly N30-60E with a very steep (~60°) to vertical dip. Magnetic fabrics were determined using anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM). Rock-magnetism measurements reveal that the magnetic mineral of the three swarms is magnetite mainly with grains in the range of 2–5 μm. For a few dikes, these grains are the carriers of bulk magnetic susceptibility but are not responsible for the AMS, which is due to Fe-bearing minerals, as shown by AARM. The main AMS fabric recognized in the swarms is due to magma flow, in which the Kmax–Kint plane is parallel to the dike's plane, and the magnetic foliation pole (Kmin) is perpendicular to it. The analysis of the Kmax inclination showed that the dikes were fed by horizontal to vertical flows. However, for the minority of the dikes, the AMS and AARM tensors are not coaxial. The AARMmax is oriented N30–60 W, approximately perpendicular to the Kmax. The AARMmax orientation is similar to the direction of a fault system located mainly in the Santos marginal basin which, was formed in the Cretaceous rifting during the South Atlantic opening. The AARM fabric is tectonic in origin, and is parallel with the extensional paleostress responsible for the Gondwana break-up. The comparison of AMS and AARM fabrics suggests that diabase and lamprophyre dikes were emplaced in three distinct events in the earliest stages of the South Atlantic opening. Later, the alkaline dikes were emplaced in the final stages of the Atlantic opening.

Resonant X-ray Scattering Study of Anisotropic Charge Distribution of Gd Ions in GdB4

Temperature dependence of anisotropic tensor susceptibility (ATS) scattering intensities of GdB4 were measured near L-edges of Gd to investigate how spin ordering affects ATS. ATS scattering intensities for L2- and L3-edges show different temperature dependence below TN. At L3-edge the intensities reflect spin order parameter while intensities at L2-edge do not show noticeable change. The difference is explained in terms of spin-orbit coupling and isotropic distribution of spin-polarized 5d states of Gd ions. Above TN ATS scattering intensities demonstrate that thermal motions enhance charge distribution anisotorpy of Gd 5d states in paramagnetic phase.

The 2016 QSM Challenge: Lessons learned and considerations for a future challenge design.

The 4th International Workshop on MRI Phase Contrast and QSM (2016, Graz, Austria) hosted the first QSM Challenge. A single-orientation gradient recalled echo acquisition was provided, along with COSMOS and the χ33 STI component as ground truths. The submitted solutions differed more than expected depending on the error metric used for optimization and were generally over-regularized. This raised (unanswered) questions about the ground truths and the metrics utilized. We investigated the influence of background field remnants by applying additional filters. We also estimated the anisotropic contributions from the STI tensor to the apparent susceptibility to amend the χ33 ground truth and to investigate the impact on the reconstructions. Lastly, we used forward simulations from the COSMOS reconstruction to investigate the impact noise had on the metric scores. Reconstructions compared against the amended STI ground truth returned lower errors. We show that the background field remnants had a minor impact in the errors. In the absence of inconsistencies, all metrics converged to the same regularization weights, whereas structural similarity index metric was more insensitive to such inconsistencies. There was a mismatch between the provided data and the ground truths due to the presence of unaccounted anisotropic susceptibility contributions and noise. Given the lack of reliable ground truths when using in vivo acquisitions, simulations are suggested for future QSM Challenges.

Spin-Orbital-Intertwined Nematic State in FeSe

The importance of the spin-orbit coupling (SOC) effect in Fe-based superconductors (FeSCs) has recently been under hot debate. Considering the Hund's coupling-induced electronic correlation, the understanding of the role of SOC in FeSCs is not trivial and is still elusive. Here, through a comprehensive study of 77Se and 57Fe nuclear magnetic resonance, a nontrivial SOC effect is revealed in the nematic state of FeSe. First, the orbital-dependent spin susceptibility, determined by the anisotropy of the 57Fe Knight shift, indicates a predominant role from the 3dxy orbital, which suggests the coexistence of local and itinerant spin degrees of freedom (d.o.f.) in the FeSe. Then, we reconfirm that the orbital reconstruction below the nematic transition temperature (Tnem ~ 90 K) happens not only on the 3dxz and 3dyz orbitals but also on the 3dxy orbital, which is beyond a trivial ferro-orbital order picture. Moreover, our results also indicate the development of a coherent coupling between the local and itinerant spin d.o.f. below Tnem, which is ascribed to a Hund's coupling-induced electronic crossover on the 3dxy orbital. Finally, due to a nontrivial SOC effect, sizable in-plane anisotropy of the spin susceptibility emerges in the nematic state, suggesting a spin-orbital-intertwined nematicity rather than simply spin- or orbital-driven nematicity}. The present work not only reveals a nontrivial SOC effect in the nematic state but also sheds light on the mechanism of nematic transition in FeSe.

Generation and manipulation of isotropic droplets in nematic medium using switchable dielectrophoresis.

Dielectrophoresis (DEP) in a medium with anisotropic dielectric susceptibility is very different from typical DEP in an isotropic medium: The direction of particle actuation can be switched depending on the direction of the susceptibility tensor of the medium. However, the understanding of switchable DEP (SDEP) in an anisotropic medium is still in its infant stage. Here, we investigate SDEP using heat-generated isotropic droplets in a nematic liquid crystal (LC) medium. We demonstrate that the location of the generation of isotropic droplets can be partially controlled by controlling the temperature gradient within the LC cell using dielectric loss. The SDEP actuation of isotropic droplets is also highly dependent on the location of the isotropic droplets. Using this method, we fabricated different array patterns of isotropic and nematic phase separations under different applied signals.

Reply to Discussion on ‘The Mesoproterozoic Stac Fada proximal ejecta blanket, NW Scotland: constraints on crater location from field observations, anisotropy of magnetic susceptibility, petrography and geochemistry’, Journal of the Geological Society , 176, 830–846

Simms (2019) states in his discussion: > They dismiss the Lairg Gravity Low as a possible impact crater based on palaeoenvironments, yet the cited paper specifically states ‘the Stoer Group has nothing in common with any of the Moine sequences discussed here' (Friend et al. 2003, p. 254). A direct comparison between the Stoer Group and the Moine Supergroup was never intended; instead the point we made (Amor et al. 2019, p. 844) was that earlier meta-sediments of admittedly uncertain age, as found at the Shin inlier, and over which the much later Moinian sediments were thrust, can be interpreted as marine in origin (Conclusion 1 of Friend et al. 2003), and thus quite different from the sedimentary matrix of the Stac Fada impact debris, which resembles the Stoer Group sediments. These earlier meta-sediments (now metapelites, psammites and marble) lie on a Lewisian-type crustal basement that is located to the east of the present-day outcrop of the Stoer Group, in the vicinity of Lairg, and are presumed to have been thrust an unknown distance from the east during the emplacement of the Moine thrust complex. All geological and plate reconstructions for this time place the deposition of the Stoer Group sediments in a rift valley on the eastern or southeastern margin of Laurentia (Kinnaird et al. 2007; Dalziel 2010). Furthermore, Nicholson (1993), Rainbird et al. (2001), Williams & Foden (2011), Kinnaird et al. (2007), Krabbendam & Rainbird (2012) and Lelpi et al. (2016) agree that this was a discrete and isolated rift, with significant high ground of Lewisian gneiss to the east as evidenced by deeply cut canyons and current direction towards the west (Stewart 2002), although Simms & Ernstson (2019) infer an extension of the Stoer Group deposits much further to the east. While …