Decrease In Anisotropy Research Articles

Elastic Anisotropy of 1,3,5‐Triamino‐2,4,6‐Trinitrobenzene as a Function of Temperature and Pressure: A Molecular Dynamics Study

AbstractThe equation of state of the triclinic compound 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) as well as its second‐order isothermal elastic tensor were computed through classical molecular dynamics simulations under various temperature and pressure conditions. Hydrostatic pressures similar to previous diamond anvil cell experiments were imposed up to 60 GPa and temperatures chosen between 100 and 900 K in conjunction with the most recent version of an all‐atom fully flexible molecule force field. The isothermal elastic constants were computed using the generalized Hooke's law by fitting Cauchy stress vs. linear strain curves for pressures below 50 GPa. Along isobaric loadings, TATB single crystal stiffnesses are found to undergo softening, less pronounced at high pressure, while maintaining its elastic anisotropy. On the other hand, along an isothermal loading, a non‐linear increase is observed in the elastic constants with respect to pressure with a significant decrease in anisotropy. Towards a precise mesoscopic modelling of TATB single crystal mechanical behavior, we provide “ready to plug‐in” analytical formulations of the P, V, T equation of state and pressure‐temperature dependent non‐linear elasticity.

Alterations in white matter microstructural properties after lingual strength exercise in patients with dysphagia.

Central nervous system effects of lingual strengthening exercise to treat dysphagia remain largely unknown. This pilot study measured changes in microstructural white matter to capture alterations in neural signal processing following lingual strengthening exercise. Diffusion-weighted images were acquired from seven participants with dysphagia of varying etiologies, before and after lingual strengthening exercise (20 reps, 3×/day, 3 days/week, 8 weeks), using a 10-min diffusion sequence (9 b0, 56 directions with b1000) on GE750 3T scanner. Tract-Based Spatial Statistics evaluated voxel-based group differences for fractional anisotropy, mean diffusivity, axial diffusivity, radial diffusivity and local diffusion homogeneity (LDH). Paired t-tests evaluated treatment differences on each metric (P < 0.05). After lingual strengthening exercise, lingual pressure generation increased (avg increase = 46.1 hPa; nonsignificant P = 0.52) with these changes in imaging metrics: (1) decrease in fractional anisotropy, forceps minor; (2) increase in mean diffusivity, right inferior fronto-occipital fasciculus (IFOF); (3) decrease in mean diffusivity, left uncinate fasciculus; (4) decrease in axial diffusivity, both left IFOF and left uncinate fasciculus; (5) increase in LDH, right anterior thalamic radiation and (6) decrease in LDH, temporal portion of right superior longitudinal fasciculus. There was a positive correlation between diffusion tensor imaging metrics and change in lingual pressure generation in left IFOF and the temporal portion of right superior longitudinal fasciculus. These findings suggest that lingual strengthening exercise can induce changes in white matter structural and functional properties in a small group of patients with dysphagia of heterogeneous etiologies. These procedures should be repeated with a larger group of patients to improve interpretation of overall lingual strengthening exercise effects on cortical structure and function.

Machine learning-based prediction of motor status in glioma patients using diffusion MRI metrics along the corticospinal tract

Along tract statistics enables white matter characterization using various diffusion MRI metrics. These diffusion models reveal detailed insights into white matter microstructural changes with development, pathology and function. Here, we aim at assessing the clinical utility of diffusion MRI metrics along the corticospinal tract, investigating whether motor glioma patients can be classified with respect to their motor status. We retrospectively included 116 brain tumour patients suffering from either left or right supratentorial, unilateral World Health Organization Grades II, III and IV gliomas with a mean age of 53.51 ± 16.32 years. Around 37% of patients presented with preoperative motor function deficits according to the Medical Research Council scale. At group level comparison, the highest non-overlapping diffusion MRI differences were detected in the superior portion of the tracts’ profiles. Fractional anisotropy and fibre density decrease, apparent diffusion coefficient axial diffusivity and radial diffusivity increase. To predict motor deficits, we developed a method based on a support vector machine using histogram-based features of diffusion MRI tract profiles (e.g. mean, standard deviation, kurtosis and skewness), following a recursive feature elimination method. Our model achieved high performance (74% sensitivity, 75% specificity, 74% overall accuracy and 77% area under the curve). We found that apparent diffusion coefficient, fractional anisotropy and radial diffusivity contributed more than other features to the model. Incorporating the patient demographics and clinical features such as age, tumour World Health Organization grade, tumour location, gender and resting motor threshold did not affect the model’s performance, revealing that these features were not as effective as microstructural measures. These results shed light on the potential patterns of tumour-related microstructural white matter changes in the prediction of functional deficits.

Microstructure and mechanical property of high power laser powder bed fusion AlSi10Mg alloy before and after T6 heat treatment

ABSTRACT This paper focuses on the microstructure and mechanical property of the high power laser powder bed fusion AlSi10Mg alloy before and after T6 heat treatment. The results demonstrate that the as-printed sample presents a columnar grain structure along the build direction and a strong <100> texture. Inside the columnar α-Al grains, there are cellular dendrites decorated with network eutectic Si. Both the α-Al matrix and eutectic Si have high-density dislocations. Besides, nano-twins and stacking faults are observed in eutectic Si. After T6 treatment, although the α-Al matrix still exhibits a columnar solidification feature, the cellular dendrites disappear and the proportion of equiaxed grains increase. And the eutectic Si presents as separate plates or nanoscale particles, in which nano-twins and stacking faults are not found. The tensile property anisotropy decreases and the strength-ductility balance improves after T6 treatment. The evolution mechanisms of the microstructure and tensile property are revealed.

Plasma Neurofilament Light and Glial Fibrillary Acidic Protein Levels over Thirty Days in a Porcine Model of Traumatic Brain Injury.

To establish the clinical relevance of porcine model of traumatic brain injury (TBI) using the plasma biomarkers of injury with diffusion tensor imaging (DTI) over 30 days, we performed a randomized, blinded, pre-clinical trial using Yorkshire pigs weighing 7-10 kg. Twelve pigs were subjected to Sham injury (n = 5) by skin incision or TBI (n = 7) by controlled cortical impact. Blood samples were collected before the injury, then at approximately 5-day intervals until 30 days. Both groups also had DTI at 24 h and at 30 days after injury. Plasma samples were isolated and single molecule array (Simoa) was performed for glial fibrillary acidic protein (GFAP) and neurofilament light (NFL) levels. Afterwards, brain tissue samples were stained for β-APP. DTI showed fractional anisotropy (FA) decrease in the right corona radiata (ipsilateral to injury), contralateral corona radiata, and anterior corpus callosum at 1 day. At 30 days, ipsilateral corona radiata showed decreased FA. Pigs with TBI also had increase in GFAP and NFL at 1-5 days after injury. Significant difference between Sham and TBI animals continued up to 20 days. Linear regression showed significant negative correlation between ipsilateral corona radiata FA and both NFL and GFAP levels at 1 day. To further validate the degree of axonal injury found in DTI, β-APP immunohistochemistry was performed on a perilesional tissue as well as corona radiata bilaterally. Variable degree of staining was found in ipsilateral corona radiata. Porcine model of TBI replicates the acute increase in plasma biomarkers seen in clinical TBI. Further, long term white matter injury is confirmed in the areas such as the splenium and corona radiata. However, future study stratifying severe and mild TBI, as well as comparison with other subtypes of TBI such as diffuse axonal injury, may be warranted.

Discrete element modeling of particles sphericity effect on sand direct shear performance

Particle surface morphology is an important factor influencing sand structure and mechanical properties. In this study, the effect of sand particle sphericity on sand direct shear performance is investigated by using the discrete element method (DEM). Two ways are adapted to simulate different approaching methods from round particles to irregular sand. The macroresponse shows that irregular sand has a higher shear strength at lower normal stress than round particles. The shape of the particle has less influence on shear strength at higher normal stress. The irregular shape of sand leads to an increase in the shear band proportion. However, the shear band proportion is not related to the sphericity. Under all conditions, particles within the shear band have a larger average rotation angle than those outside the shear band. When the particle shape approaches round (regardless of the round particle proportion and particle shape), the average rotation angle of particles within and without shear bands increase, while the coordinate number and contact anisotropy decrease.

Interactive effects of interfacial energy anisotropy and solute transport on solidification patterns of Al-Cu alloys

Combined effects of the cooling rate, alloy composition, and crystal-melt (CM) interfacial anisotropy on solidification of Al-Cu alloys are studied by integrating molecular dynamics and phase-field simulations. Capillary fluctuation method is used to determine the CM interfacial energy properties by molecular dynamics simulations for alloys ranging from 3 to 11 at% Cu. While the average CM interfacial energy decreases with increasing Cu content, its anisotropy does not present a clear trend with composition change. Primary and secondary dendrite arm spacings as well as θ-phase fraction are calculated by phase-field simulations, and validated against experimental measurements and analytical solutions at cooling rates ranging from 1 to 1250 K/s. Results show that the θ-phase fraction decreases with increasing the cooling rate, and this reduction is more drastic in alloys with a higher Cu content. Also, the microstructure features are influenced by the growth dynamics, where seaweed structure formation results in a more homogenous distribution of θ-phase and a finer microstructure. The effects of temperature gradient, Cu concentration gradient, and interfacial energy properties on the dendritic growth morphology of Al-Cu alloys are summarized by a map of supercooling versus the CM interfacial anisotropy to predict pattern formation. The results show that, irrespective of Cu content and cooling rate, the seaweed structure formation is halted at CM interfacial anisotropies larger than 0.005. As the anisotropy decreases, different seaweed structures can form regarding the constitutional supercooling. At low anisotropies (Al-3 and Al-8.4 at% Cu) and low supercooling (Al-3 at% Cu) fractal or degenerate seaweed is dominant while at high supercooling (Al-8.4 at% Cu) compact seaweed forms. This difference in supercooling stems from different solute atom transport rates.

Effect of high pressure on temperature dependences of the resistivity in the ab-plane of Y0.77Pr0.23Ba2Cu3O7-δ single crystals

In the present work, we investigated the influence of high hydrostatic pressure up to 11 kbar on the conductivity in the basal ab-plane of medium-doped with praseodymium (x≈0.23) single-crystal Y1-xPrxBa2Cu3O7-δ samples. It was determined that, in contrast to the pure YBa2Cu3O7-δsamples with the optimal oxygen content, the application of high pressure leads to the formation of phase separation in the basal plane of Y0.77Pr0.23Ba2Cu3O7-δ single crystals. Possible mechanisms of the effect of Pr doping and high pressure on the two-step resistive transition to the superconducting state are discussed. It was determined that in the normal state, the conductivity is metallic and is limited by phonons scattering (Bloch-Grüneisen regime) and defects. The fluctuation conductivity is considered within the Lorentz-Doniach model. Hydrostatic pressure, accompanied by a decrease in anisotropy, leads to a decrease in the residual and phonon resistances. Debye temperature and coherence length are independent of pressure. The applicability of the McMillan formula in the presence of significant anisotropy is discussed.

Magnetic annealing of extruded thermoplastic magnetic elastomers for 3D-Printing via FDM

Magnetorheological elastomers (MREs) are magnetoactive smart materials that exhibit mechanical deformation in the presence of magnetic fields. The greatest performance in these materials has been seen from magnetic annealing, which creates high internal anisotropy. This work studies how different magnetic annealing setups (no field, uniform field, and non-uniform field) can be applied to thermoplastic MRE extrusion geometries and how each setup affects the resulting magnetic and magnetoactive properties. The uniform field resulted in an increase of both magnetic anisotropy and magnetoactive performance when compared to no field (but was difficult to make samples with). The non-uniform magnetic annealing setup resulted in similar magnetic properties but decreased magnetoactive performance when compared to the no field samples likely due to interference with the naturally occurring anisotropy that results from extrusion flow. This work demonstrates that certain magnetic annealing setups can be applied to extrusion geometries for increased anisotropy effects resulting in greater magnetoactive response compared to no magnetic annealing, while others can lead to a decrease in anisotropy and less magnetoactive response.

Role of NODDI in the MRI Characterization of Hippocampal Abnormalities in Temporal Lobe Epilepsy: Clinico-histopathologic Correlations.

The identification of possible hippocampal alterations is a crucial point for the diagnosis and therapy of patients with unilateral temporal lobe epilepsy (TLE). This study aims to investigate the role of neurite orientation dispersion and density imaging (NODDI) compared to diffusion tensor imaging (DTI) in the comprehension of hippocampal microstructure in TLE. DTI and NODDI metrics were calculated in the hippocampi of adult patients with TLE, with and without histology-confirmed hippocampal sclerosis (HS), and in age/sex-matched healthy controls (HC). Diffusion metrics and hippocampal volumes of the pathologic side were compared within participants and between participants among the HS, non-HS, and HC groups. Diffusion metrics were also correlated with hippocampal volume and patients' clinical features. After surgery, hippocampal specimens were processed for neuropathology examinations. Fifteen patients with TLE (9 with and 6 without HS) and 11 HC were included. Hippocampal analyses resulted in a significant increase in fractional anisotropy (FA) and mean diffusivity (MD; mm2/s × 10-3) and decrease in orientation dispersion index (ODI) comparing the pathologic side of patients with HS and their relative nonpathologic side (0.203 vs 0.183, 0.825 vs 0.724, 0.366 vs 0.443, respectively), the pathologic side of patients without HS (0.203 vs 0.169, 0.825 vs 0.745, 0.366 vs 0.453, respectively), and HC (0.203 vs 0.172, 0.825 vs 0.729, 0.366 vs 0.447, respectively). Moreover, neurite density (ND) was significantly decreased comparing both hippocampi of patients with HS (0.416 vs 0.460). A significant increase in free-water isotropic volume fraction (fiso) was found in the comparison of pathologic hippocampi of patients with HS and nonpathologic hippocampi of patients with HS (0.323 vs 0.258) and HC (0.323 vs 0.226). Hippocampal volume of all patients with TLE negatively correlated with MD (r = -0.746, p = 0.0145) and positively correlated with ODI (r = 0.719, p = 0.0145). Fiso and ND of sclerotic hippocampi positively correlated with disease duration (r = 0.684, p = 0.0424 and r = 0.670, p = 0.0486, respectively). Immunohistochemistry in sclerotic hippocampal specimens revealed neuronal loss in the pyramidal layer and fiber reorganization at the level of stratum lacunosum-moleculare, confirming ODI and ND metrics. This study shows the capability of diffusion MRI metrics to detect hippocampal microstructural alterations. Among them, ODI seems to better highlight the fiber reorganization observed by neuropathology in sclerotic hippocampi.

Heritability of abnormalities in limbic networks of autism spectrum disorder children: Evidence from an autism spectrum disorder twin study.

Although the limbic system is closely related to emotion and social behaviors, little is known about the integrity of limbic pathways and how genetics influence the anatomical abnormalities of limbic networks in children with autism spectrum disorder (ASD). Therefore, we used an ASD twin study design to evaluate the microstructural integrity and autism-related differences in limbic pathways of young children with ASD and to estimate the heritability of limbic tracts microstructure variance. We obtained diffusion tensor imaging scans from 33 pairs of twins with ASD aged 2-9 years and 20 age-matched typically developing children. The ACE model was used to estimate the relative effects of additive genetic factors (A), shared environmental factors (C) and specific environmental factors (E) on the variability of diffusivity measurements. We found a significant decrease in fractional anisotropy (FA) in the bilateral fornix and uncinate fasciculus (UF), as well as increased mean diffusivity (MD) and radial diffusivity (RD) in the bilateral fornix and right UF of ASD children. Correlation analysis showed that FA, MD, and lateralization indices of UF were correlated with autism diagnostic observation schedule scores. The ACE model revealed that genetic effects may drive some of the variability of microstructure in the bilateral fornix, cingulum, and left UF. In conclusion, in children with ASD, there are abnormalities in the white matter microstructure of the limbic system, which is related to the core symptoms; these abnormalities may be related to the relative contribution of genetic and environmental effects on specific tracts. LAY SUMMARY: Autism spectrum disorder (ASD) children have abnormal white matter structure in limbic system related to ASD symptoms, and genetic factors play an important role in the development of limbic tracts.

Case Report: True Motor Recovery of Upper Limb Beyond 5 Years Post-stroke

Most of motor recovery usually occurs within the first 3 months after stroke. Herein is reported a remarkable late recovery of the right upper-limb motor function after a left middle cerebral artery stroke. This recovery happened progressively, from two to 12 years post-stroke onset, and along a proximo-distal gradient, including dissociated finger movements after 5 years. Standardized clinical assessment and quantified analysis of the reach-to-grasp movement were repeated over time to characterize the recovery. Twelve years after stroke onset, diffusion tensor imaging (DTI), functional magnetic resonance imaging (fMRI), and transcranial magnetic stimulation (TMS) analyses of the corticospinal tracts were carried out to investigate the plasticity mechanisms and efferent pathways underlying motor control of the paretic hand. Clinical evaluations and quantified movement analysis argue for a true neurological recovery rather than a compensation mechanism. DTI showed a significant decrease of fractional anisotropy, associated with a severe atrophy, only in the upper part of the left corticospinal tract (CST), suggesting an alteration of the CST at the level of the infarction that is not propagated downstream. The finger opposition movement of the right paretic hand was associated with fMRI activations of a broad network including predominantly the contralateral sensorimotor areas. Motor evoked potentials were normal and the selective stimulation of the right hemisphere did not elicit any response of the ipsilateral upper limb. These findings support the idea that the motor control of the paretic hand is mediated mainly by the contralateral sensorimotor cortex and the corresponding CST, but also by a plasticity of motor-related areas in both hemispheres. To our knowledge, this is the first report of a high quality upper-limb recovery occurring more than 2 years after stroke with a genuine insight of brain plasticity mechanisms.

Characterization of AAV-mediated dorsal root ganglionopathy

Recent studies in non-human primates administered recombinant adeno-associated viruses (rAAVs) have shown lesions in the dorsal root ganglia (DRG) of unknown pathogenesis. In this study, rAAV9s manufactured using different purification methods alongside a non-expressing Null AAV9 vector was administered to groups of cynomolgus monkeys followed by neuropathological evaluation after 4 weeks. Lesions, including neuronal degeneration, increased cellularity, and nerve fiber degeneration, were observed in the DRG, regardless of purification methods. Animals did not develop any neurological signs throughout the study, and there was no loss of function observed in neuro-electrophysiological endpoints or clear effects on intraepidermal nerve fiber density. However, magnetic resonance imaging (MRI) of animals with axonopathy showed an increase in short tau inversion recovery (STIR) intensity and decrease in fractional anisotropy. In animals administered the Null AAV9 vector, DRG lesions were not observed despite vector DNA being detected in the DRG at levels equivalent to or greater than rAAV9-treated animals. This study further supports that DRG toxicity is associated with transgene overexpression in DRGs, with particular sensitivity at the lumbar and lumbosacral level. The data from this study also showed that the nerve fiber degeneration did not correlate with any functional effect on nerve conduction but was detectable by MRI.

Anisotropy and size effects in Bi1-xSbx semiconductor wires in a magnetic field

The electron transport and longitudinal and transverse magnetoresistance (MR) of glass-insulated Bi0.92Sb0.08 single-crystal wires with diameters of 180 nm to 2.2 μm and the (1011) orientation along the wire axis have been studied. The wires have been prepared by liquid-phase casting. It has been first found that the energy gap ΔE increases by a factor of 4 with a decrease in wire diameter d due to the manifestation of the quantum size effect, which can occur under conditions of a linear energy–momentum dispersion law characteristic of both the gapless state and the surface states in topological insulators (TIs). It has been revealed that, in strong magnetic fields at low temperatures, a semiconductor–semimetal transition occurs, which is evident as an anomalous decrease in the transverse MR anisotropy and the appearance of a metallic temperature dependence of resistance at T &lt; 100 K. It has been found that the effect of negative MR, the appearance of an anomalous maximum in the longitudinal MR, and the dependence of Hmax ~ d-1 at 4.2 K is a manifestation of the classical MacDonald–Chambers size effect. The calculated value of the component of the Fermi momentum perpendicular to the magnetic induction vector H is 2 times higher than the value for pure bismuth wires. The features of the manifestation of the quantum size effect in Bi0.92Sb0.08 wires, semiconductor–semimetal electronic transitions induced by a magnetic field, and a decrease in the transverse MR anisotropy indicate the occurrence of new effects in low-dimensional structures based on semiconductor wire TIs, which require new scientific approaches and applications.

Surfactant induced bilayer-micelle transition for emergence of functions in anisotropic hydrogel.

Tuning the self-assembled structures in amorphous hydrogels will enrich the functionality of hydrogels. In this study, we tuned the structure of a photonic hydrogel, which consists of polymeric lamellar bilayers entrapped inside a polyacrylamide network, simply by molecular triggering using an ionic surfactant. Owing to the binding of ionic surfactants (sodium dodecyl sulfate), the lamellar bilayers comprising non-ionic polymeric surfactants [poly(dodecyl glyceryl itaconate)] changed to micelles, whereas the unidirectional lamellar structure was preserved in the hydrogel. The bilayer-micelle structure transition caused a dramatic decrease in the swelling anisotropy and mechanical softening of the photonic gel. With the micelle structure, the softened gel shows fast (0.3 s) and reversible color change over the entire visible light range in response to a small mechanical pressure (5 kPa). This low stress-induced color-changing hydrogel could be applied as a visual tactile sensor in various fields, especially in biomedical engineering.

Cerebral perfusion and tractography in obese children

To study the relationship of the structure of the white matter of the brain, neurovascularization and cognitive functions in obese children and adolescents. The study included 64 obese patients, aged 12-17 years, and 54 children without excess body weight. A general clinical examination, neuropsychological testing (the Raven's test with the calculation of IQ, MoCA, the Rey 15-Item Memory Test (RMT), 1 and 2), magnetic resonance imaging (MR) tractography and contrast-free perfusion of the brain were conducted. Obese children and adolescents had both a decrease in scores on MoCA and the Raven's test, and in terms of IQ, while according to RMT-1, there were significant differences in the two groups, and in RMT-2 the results were comparable. Perfusion analysis showed a decrease in vascularization in the white matter area of the occipital lobe on the left and its increase in the temporal lobe area also on the left. When assessing the white matter according to MR tractography, a decrease in fractional anisotropy was noted in the area of the hook-shaped beam on the right and left, anterior and posterior commissural tracts. These changes were correlated with neuropsychological results. In obese children and adolescents, there was a destruction of the integrity of the white matter and neurovascularization of the brain associated with a deficit of cognitive functions.

Temperature dependence of intrinsic critical current in perpendicular easy axis CoFeB/MgO magnetic tunnel junctions

Current induced magnetization switching in CoFeB/MgO-based magnetic tunnel junctions (MTJs) with a perpendicular easy axis is studied above room temperature. The intrinsic critical current IC0 of the MTJs decreases with increasing temperature. From a vector-network-analyzer ferromagnetic resonance measurement with a heating system, temperature dependence of magnetic anisotropy and damping constant is evaluated. We find that the reduction of IC0 at elevated temperature is mainly due to a decrease in magnetic anisotropy. A slight increase in the damping constant with temperature rise is also observed, consistent with the mechanism considering electron scattering through the inter-band transition.

Moiré Tuning of Spin Excitations: Individual Fe Atoms on MoS_{2}/Au(111).

Magnetic adatoms on properly designed surfaces constitute exquisite systems for addressing, controlling, and manipulating single quantum spins. Here, we show that monolayers of MoS_{2} on a Au(111) surface provide a versatile platform for controllably tuning the coupling between adatom spins and substrate electrons. Even for equivalent adsorption sites with respect to the atomic MoS_{2} lattice, we observe that Fe adatoms exhibit behaviors ranging from pure spin excitations, characteristic of negligible exchange and dominant single-ion anisotropy, to a fully developed Kondo resonance, indicating strong exchange and negligible single-ion anisotropy. This tunability emerges from a moiré structure of MoS_{2} on Au(111) in conjunction with pronounced many-body renormalizations. We also find striking spectral variations in the immediate vicinity of the Fe atoms, which we explain by quantum interference reflecting the formation of Fe-S hybrid states despite the nominally inert nature of the substrate. Our work establishes monolayer MoS_{2} as a tuning layer for adjusting the quantum spin properties over an extraordinarily broad parameter range. The considerable variability can be exploited for quantum spin manipulations.

Rare-earth moment reduction and local magnetic anisotropy in Pr2Fe14B and Tm2Fe14B

Magnetization curves for Pr2Fe14B single crystals were measured between 300 K and 900 K. The saturation magnetization Ms along the [100] direction was found to be 3% to 6% smaller than that for the [001] direction, not only at 300 K but also up to the Curie temperature. Published magnetization curves for Tm2Fe14B single crystals were reexamined, in which Ms along the [001] direction exceeds that for the [100] direction. We attributed these differences in Ms to the reduction of the rare-earth (R) moment when forced to be aligned along the hard direction by external fields. Significant anisotropy was observed in the paramagnetic susceptibility χ up to 900 K in the Pr2Fe14B (R = Pr) system. Based on the crystalline electric field parameters for R = Pr and Tm systems obtained by first-principles calculations, we numerically evaluated the magnetization and paramagnetic susceptibility at high temperatures. The differences in Ms and χ obtained from the calculation were in good agreement with the experiments. We found that the reduction rate for the Pr moment at the 4f site is much smaller than that at the 4 g site. This result suggests a crucial decrease in the local magnetic anisotropy at the Pr(4f) site.

Older age, male sex, and cerebral microbleeds predict white matter loss after traumatic brain injury.

Little is known on how mild traumatic brain injury affects white matter based on age at injury, sex, cerebral microbleeds, and time since injury. Here, we study the fractional anisotropy of white matter to study these effects in 109 participants aged 18-77 (46 females, age μ ± σ = 40 ± 17years) imaged within [Formula: see text] 1week and [Formula: see text] 6months post-injury. Age is found to be linearly associated with white matter degradation, likely due not only to injury but also to cumulative effects of other pathologies and to their interactions with injury. Age is associated with mean anisotropy decreases in the corpus callosum, middle longitudinal fasciculi, inferior longitudinal and occipitofrontal fasciculi, and superficial frontal and temporal fasciculi. Over [Formula: see text] 6months, the mean anisotropies of the corpus callosum, left superficial frontal fasciculi, and left corticospinal tract decrease significantly. Independently of other predictors, age and cerebral microbleeds contribute to anisotropy decrease in the callosal genu. Chronically, the white matter of commissural tracts, left superficial frontal fasciculi, and left corticospinal tract degrade appreciably, independently of other predictors. Our findings suggest that large commissural and intra-hemispheric structures are at high risk for post-traumatic degradation. This study identifies detailed neuroanatomic substrates consistent with brain injury patients' age-dependent deficits in information processing speed, interhemispheric communication, motor coordination, visual acuity, sensory integration, reading speed/comprehension, executive function, personality, and memory. We also identify neuroanatomic features underlying white matter degradation whose severity is associated with the male sex. Future studies should compare our findings to functional measures and other neurodegenerative processes.