Effective Relaxation Time Research Articles

Non-Debye Behavior of the Néel and Brown Relaxation in Interacting Magnetic Nanoparticle Ensembles.

We used ac-susceptibility measurements to study the superspin relaxation in Fe3O4/Isopar M nanomagnetic fluids of different concentrations. Temperature-resolved data collected at different frequencies, χ″ vs. T|f, reveal magnetic events both below and above the freezing point of the carrier fluid (TF = 197 K): χ″ shows peaks at temperatures Tp1 and Tp2 around 75 K and 225 K, respectively. Below TF, the Néel mechanism is entirely responsible for the superspin relaxation (as the carrier fluid is frozen), and we found that the temperature dependence of the relaxation time, τN(Tp1), is well described by the Dorman-Bessais-Fiorani (DBF) model: τNT=τrexp⁡EB+EadkB T. Above TF, both the internal (Néel) and the Brownian superspin relaxation mechanisms are active. Yet, we found evidence that the effective relaxation times, τeff, corresponding to the Tp2 peaks observed in the denser samples do not follow the typical Debye behavior described by the Rosensweig formula 1τeff=1τN+1τB. First, τeff is 5 × 10-5 s at 225 K, almost three orders of magnitude more that its Néel counterpart, τN~8 × 10-8 s, estimated by extrapolating the above-mentioned DBF analysis. Thus, 1τN≫1τeff, which is clearly not consistent with the Rosensweig formula. Second, the observed temperature dependence of the effective relaxation time, τeff(Tp2), is excellently described by τB-1T=Tγ0exp⁡-E'kBT-T0', a model solely based on the hydrodynamic Brown relaxation, τB(T)=3ηTVHkBT, combined with an activation law for the temperature variation of the viscosity, ηT=η0exp⁡E'/kB(T-T0'. The best fit yields γ0=3ηVHkB = 1.6 × 10-5 s·K, E'/kB = 312 K, and T0' = 178 K. Finally, the higher temperature Tp2 peaks vanish in the more diluted samples (δ ≤ 0.02). This indicates that the formation of larger hydrodynamic particles via aggregation, which is responsible for the observed Brownian relaxation in dense samples, is inhibited by dilution. Our findings, corroborating previous results from Monte Carlo calculations, are important because they might lead to new strategies to synthesize functional magnetic ferrofluids for biomedical applications.

An analytical model to ascertain A.C. electrical conductivity of metal matrix composites

ABSTRACT With regard to an inherent understanding of electrical conductivity exhibited by monolithic metals and alloys system and metal matrix composite system under alternating current field, a long-standing unresolved issue, an analytical model is developed following classical free electron theory along with a typical conceptualisation of ‘effective relaxation time’ that combines conventional relaxation time (in view of collision of free electrons with lattice defects) and the time between successive cyclic reversals of electric field (the inverse of frequency). Two prime phenomena (electron scattering and polarisation at particle–matrix interface) are further conceived for metal matrix composite system containing particles. The developed model is found to closely follow (% deviation << 10) the available experimental result in the literature on A.C. electrical conductivity of 6063Al alloy and 6063Al–TiO2 composite systems. The model further ascertains certain system-specific parameters; such as, relaxation time under A.C. field, effective scattering factor and effective relaxation time aid from interface polarisation to specify the system behaviour under alternating current field. Accordingly, the model adequately explains the declining trend of A.C. electrical conductivity with increasing frequency in monolithic alloy system and an enhancement of A.C. electrical conductivity in metal matrix composite system in the presence of particles together with a non-declining trend even on increasing frequency.

Analytical description of the ionic relaxation in the presence of surface adsorption

The temporal evolution of the surface electric field in a cell in the presence of ionic adsorption is investigated. The analysis is performed in the framework of the Poisson–Nernst–Planck model, based on the conservation of particles and the equation of Poisson for the actual electric potential across the cell, assuming that only the ions of a given sign are mobile. The adsorption is described using a kinetic equation of Langmuir’s type. The simple case of small adsorption is considered, in which the saturation effect can be neglected, and the fundamental equations of the model can be linearized. In this framework, the effective relaxation time describing the dynamics of the system is evaluated, as well as the profiles of the ions and the electric field. The case in which the sample is a half-space is first considered. A more realistic situation where the sample is a slab of thickness d, limited by two identical or different electrodes, is analyzed too. The difference in electric potential due to the adsorption phenomenon between the electrodes is determined. Our analysis shows that its time dependence, when the electrodes have different adsorption properties, is not monotonic.

A simple model for short-range ordering kinetics in multi-principal element alloys

Short-range ordering (SRO) in multi-principal element alloys influences material properties such as strength and corrosion. While some degree of SRO is expected at equilibrium, predicting the kinetics of its formation is challenging. We present a simplified isothermal concentration-wave (CW) model to estimate an effective relaxation time of SRO formation. Estimates from the CW model agree to within a factor of five with relaxation times obtained from kinetic Monte Carlo (kMC) simulations when above the highest ordering instability temperature. The advantage of the CW model is that it only requires mobility and thermodynamic parameters, which are readily obtained from alloy mobility databases and Metropolis Monte Carlo simulations, respectively. The simple parameterization of the CW model and its analytical nature makes it an attractive tool for the design of processing conditions to promote or suppress SRO in multicomponent alloys.

Spontaneous resolution and magnetic properties of lanthanide metal organic frameworks based on oxydiacetate

Chiral lanthanide metal organic frameworks (Ln-MOFs) have become a kind of promising platform for developing various chiral functional materials. However, their members are still scarce up to now, especially those obtained from spontaneous resolution. In this work, two pairs of enantiomers of chiral Ln-MOFs, namely, [Ln2(oda)3(H2O)4]·2H2O [Ln = Dy (Λ-1 and Δ-1), Gd (Λ-2 and Δ-2); oda = oxydiacetate], have been prepared from an achiral H2oda ligand by spontaneous resolution. They display homochiral Λ- or Δ-configurational 2D grid-like frameworks in the absence of any chiral source, where four carboxylate groups of oda2− ligands within each [LnIII(oda)3]3− module link to adjacent four Ln ions either in a left- or right-handed fashions. Their homochirality was further confirmed by solid-state circular dichroism (CD) spectrum. Magnetic measurements revealed that Λ-1 exhibits field-induced dual-relaxation behavior of single-molecule magnet (SMM). The effective energy barrier (Ueff) and relaxation time (τ0) of slow relaxation (SR) process are 92.63 K and 1.49 × 10−12 s, respectively. Furthermore, Λ-2 was found to show magnetocaloric effect (MCE), with the maximum magnetic entropy change (−ΔSm) of 10.02 J kg−1 K−1 at 7.0 T and 2.0 K.

Structural regulation strategy for Dy-MOFs based on [Qn+][Dy(β-diketonate)4-]n (Qn+ = Et3NH+, Et4N+, R-H2MPPA2+)

In this study, [Qn+][Dy(β-diketonate)4-]n (β-diketonate = Hfac, Hbtfa, Hdbm; n = 1, Q+ = Et3NH+, Et4N+; n = 2, Q2+= R-H2MPPA2+) was used to regulate the hydrolysis process of DyIII ions to generate different secondary building units (SBUs). The SBUs were further connected with fumaric acid ligands, exhibiting diverse coordination modes. Five dysprosium-based metal–organic frameworks (Dy-MOFs; 1–5) with various structural connections and topologies were synthesized. When cations in [Qn+][Dy(β-diketonate)4-]n were Et3NH+ and the anions changed from [Dy(fac)4]- to [Dy(dbm)4]- and [Dy(btfa)4]-, three SBUs (C2v Dy1O8, D2d Dy2O8 in 1; C2v Dy1O8 in 2; C4v Dy1O9 in 3) were formed. When anions in [Qn+][Dy(β-diketonate)4-]n were [Dy(btfa)4]- and the cations changed from Et3NH+ to Et4N+ and R-H2MPPA2+, four SBUs (C4v Dy1O9 in 3; Cs Dy1O9, D3h Dy2O9 in 4; D4d Dy1O8 in 5) were formed. Further magnetic characterization indicated that 2, 3, and 4 exhibited antiferromagnetic behavior, while 1 and 5 exhibited ferromagnetic properties. The alternating-current magnetic susceptibilities of 1 and 5 exhibited significant frequency and temperature dependence. The Cole–Cole plot of 1 and 5 displayed a semicircular shape, and the effective energy barrier and relaxation time were 77.54 K and 3.20 × 10–8 s and 6.8 K and 7.50 × 10–5 s for 1 and 5, respectively.

Heat Dissipation Mechanisms in Hybrid Superconductor-Semiconductor Devices Revealed by Joule Spectroscopy.

Understanding heating and cooling mechanisms in mesoscopic superconductor-semiconductor devices is crucial for their application in quantum technologies. Owing to their poor thermal conductivity, heating effects can drive superconducting-to-normal transitions even at low bias, observed as sharp conductance dips through the loss of Andreev excess currents. Tracking such dips across magnetic field, cryostat temperature, and applied microwave power allows us to uncover cooling bottlenecks in different parts of a device. By applying this "Joule spectroscopy" technique, we analyze heat dissipation in devices based on InAs-Al nanowires and reveal that cooling of superconducting islands is limited by the rather inefficient electron-phonon coupling, as opposed to grounded superconductors that primarily cool by quasiparticle diffusion. We show that powers as low as 50-150 pW are able to suppress superconductivity on the islands. Applied microwaves lead to similar heating effects but are affected by the interplay of the microwave frequency and the effective electron-phonon relaxation time.

A fast protocol for multicenter and multiparametric quantitative MRI studies in brain tumor patients using vendor sequences.

Multiparametric quantitative MRI (mp-qMRI) provides noninvasive, quantitative measurements sensitive to a variety of tissue properties. In brain tumors (BTs), longitudinal relaxation time (T1), effective transverse relaxation time (T2*), transverse relaxation time (T2), water content (H2O), and quantitative susceptibility (χ) give valuable insights into the microenvironment. To generate large multicenter datasets, protocols need to be short and implementable on any scanner. The goal of this work was to develop and validate an 8-min, 3T mp-qMRI protocol for BT patients solely using generalized pulse sequences (mGRE and EPI). A protocol was developed and tested on a multicompartment phantom, 5 healthy subjects (mean age: 31.64 years), and 4 BT patients (mean age:39.5 years). Phantom and healthy subject longitudinal relaxation time (T1) maps were compared to those obtained using 2 reference methods. The 5 healthy subjects were scanned on 3T MRI scanners at 2 different sites and the reproducibility between scanners was assessed by computing Coefficients of Variance (COV) maps, performing Bland-Altman analysis and t-tests. Clinical feasibility was tested on 4 BT patients. T1 values obtained using the proposed mp-qMRI protocol agree with those obtained using the reference methods in volunteers (mean error = 8.94ms). The qMRI maps (T1, T2*, H2O, and χ) of the volunteers showed good reproducibility between scanners with no significant differences for mean WM and GM qMRI values. WM and GM mean qMRI values agreed well with literature values. H2O gave the lowest COV and χ maps the highest. The proposed vendor sequence-based 3T mp-qMRI protocol gives interpolated,high resolution (1mm isotropic) T1, T2*, H2O, and maps in 8min of acquisition.

The fluid dynamics of a viscoelastic fluid dripping onto a substrate.

Extensional flows of complex fluids play an important role in many industrial applications, such as spraying and atomisation, as well as microfluidic-based drop deposition. The dripping-on-substrate (DoS) technique is a conceptually-simple, but dynamically-complex, probe of the extensional rheology of low-viscosity, non-Newtonian fluids. It incorporates the capillary-driven thinning of a liquid bridge, produced by a single drop as it is slowly dispensed from a syringe pump onto a solid partially-wetting substrate. By following the filament thinning and pinch-off process the extensional viscosity and relaxation time of the sample can be determined. Importantly, DoS allows experimentalists to measure the extensional properties of lower viscosity solutions than is possible with commercially available capillary break-up extensional rheometers. Understanding the fluid mechanics behind the operation of DoS will enable users to optimise and extend the performance of this protocol. To achieve this understanding, we employ a computational rheology approach, using adaptively-refined time-dependent axisymmetric numerical simulations with the open-source Eulerian code, Basilisk. The volume-of-fluid technique is used to capture the moving interface, and the log-conformation transformation enables a stable and accurate solution of the viscoelastic constitutive equation. Here, we focus on understanding the roles of surface tension, elasticity and finite chain extensibility in controlling the elasto-capillary (EC) regime, as well as the perturbative effects that gravity and substrate wettability play in setting the evolution of the self-similar thinning and pinch-off dynamics. To illustrate the interplay of these different forces, we construct a simple one-dimensional model that captures the initial rate of thinning when the dynamics are dominated by a balance between inertia and capillarity. This model also captures the structure of the transition region to the nonlinear EC regime in which the rapidly growing elastic stresses in the thread balance the capillary pressure as the filament thins towards breakup. Finally, we propose a fitting methodology based on the analytical solution for FENE-P fluids to improve the accuracy in determining the effective relaxation time of an unknown fluid.

Frequency‐Scanning Considerations in Axionlike Dark Matter Spin‐Precession Experiments

AbstractGalactic dark matter may consist of axionlike particles (ALPs) that can be described as an “ultralight bosonic field” oscillating at the ALP Compton frequency. The ALP field can be searched for using nuclear magnetic resonance (NMR), where resonant precession of spins of a polarized sample can be sensitively detected. The ALP mass to which the experiment is sensitive is scanned by sweeping the bias magnetic field. The scanning either results in detection of ALP dark matter or rules out ALP dark matter with sufficiently strong couplings to nuclear spins over the range of ALP masses corresponding to the covered span of Larmor frequencies. In this work, scanning strategies are analyzed with the goal of optimizing the parameter‐space coverage via a proper choice of experimental parameters (e.g., the effective transverse relaxation time).

Entropic stress of grafted polymer chains in shear flow.

We analyze the shear response of grafted polymer chains in shear flow via coarse-grained molecular dynamics simulations with an explicit solvent. We find that the solvent flow penetrates into almost the whole brush for "mushroom"-type brushes but only a few bond distances for dense brushes. In all cases, the external stress on the wall equals the entropic stress associated with the distorted polymer conformations. We find that the external stress increases linearly with shear rate at low rates and sublinearly at high rates. The transition from linear to sublinear scaling occurs where chains react to flow by reorienting. Sublinear scaling with shear rate disappears if the shear rate is nondimensionalized with the effective relaxation time of chain subsegments located in the outer part of the brush that experiences flow.

Investigation on elastic, optical and thermoelectric properties of 2D MgX (X= O, S, Se, Te) materials under DFT framework

The first principles study of two-dimensional magnesium (Mg) chalcogenides (X = O, S, Se, Te) in square lattice (s-MgX) and hexagonal phases (h-MgX) is investigated for the first time. Except for h-MgSe and h-MgTe, all the square lattice and hexagonal structures in MgX compounds are dynamically stable, agreeing to phonon dispersion calculations. The electronic band structure and projected density of states of s- and h-MgX materials provided insight into the essence of electronic properties of these compounds. All s- and h-MgX compounds are found to be indirect wide band gap semiconductors, according to calculations using PBE and HSE06 functionals. The effective mass, mobility and relaxation time of electrons and holes carriers from the band structure of s- and h-MgX are examined to acquire a better intuition into these materials. Along the zigzag direction, h-MgTe has a largest mobility as well as relaxation time of 78104.92 cm2 V−1s−1 and 64385.56 fs, respectively in the entire MgX series. Additionally, we examined their mechanical stability through elastic characteristics, and the derived elastic parameters and polar graphs of Young's modulus and Poisson's ratio verifying their mechanical stability. In application of parallel and perpendicular field polarizations, the optical properties of s- and h-MgX are examined. The thermoelectric properties of the complete s- and h-MgX series are examined for the temperature range from 50 K to 800 K. The results of the present study reveal that s-MgO and h-MgS are the better thermoelectric materials in the considered series. Finally, since these compounds are mostly UV-active, they may find useful applications in UV-protectant and UV-photodetectors materials.

Elastic, Optical, and Thermoelectric Properties of 2D Square Lattice and Hexagonal Zinc Chalcogenides under First‐Principles Calculations

Herein, elastic, optical, and thermoelectric properties of zinc chalcogenides with 2D square lattice and hexagonal phases [s‐ and h‐ZnX (X = GrVI)] are reported. The s‐ZnX and h‐ZnX structures are achieved to be dynamically stable, according to the phonon dispersion studies. All s‐ and h‐ZnX compounds are found to be semiconductor, with direct and indirect bandgaps ranging from 0.81 to 2.77 eV under PBE and 1.70 to 4.15 eV by HSE06 calculations. The effective mass, mobility, and relaxation time of electron and hole carriers in the band structures of s‐ and h‐ZnX are investigated to gain a better insight of these materials. In addition to the phonon dispersion analysis, their mechanical stability in terms of elastic properties is evaluated, and the resulting elastic parameters validate their mechanical stability. The optical properties of s‐ and h‐ZnX are inspected in the occurrence of field polarizations across parallel and perpendicular directions. At room temperature, s‐ZnTe compound has an optimum figure of merit (ZT) value, indicating it as the superlative thermoelectric material in the entire series. These compounds may also be explored in ultraviolet lasers, solar cells, electronic image displays, high‐density optical memory, photodetectors, and solid‐state laser devices.

A multiscale approach to coupled nuclear and electronic dynamics. II. Exact and approximated evaluation of nonradiative transition rates.

This work follows a companion article, which will be referred to as Paper I [Campeggio et al., J. Chem. Phys. 158, 244104 (2023)] in which a quantum-stochastic Liouville equation for the description of the quantum-classical dynamics of a molecule in a dissipative bath has been formulated in curvilinear internal coordinates. In such an approach, the coordinates of the system are separated into three subsets: the quantum coordinates, the classical relevant nuclear degrees of freedom, and the classical irrelevant (bath) coordinates. The equation has been derived in natural internal coordinates, which are bond lengths, bond angles, and dihedral angles. The resulting equation needs to be parameterized. In particular, one needs to compute the potential energy surfaces, the friction tensor, and the rate constants for the nonradiative jumps among the quantum states. While standard methods exist for the calculation of energy and dissipative properties, an efficient evaluation of the transition rates needs to be developed. In this paper, an approximated treatment is introduced, which leads to a simple explicit formula with a single adjustable parameter. Such an approximated expression is compared with the exact calculation of transition rates obtained via molecular dynamics simulations. To make such a comparison possible, a simple sandbox system has been used, with two quantum states and a single internal coordinate (together with its conjugate momentum). Results show that the adjustable parameter, which is an effective decoherence time, can be parameterized from the effective relaxation times of the autocorrelation functions of the conjugated momenta of the relevant nuclear coordinates.

Functional magnetic resonance imaging reveals dysfunction of the paraspinal muscles in patients with chronic low back pain: a cross-sectional study.

Patients with chronic low back pain (CLBP) undergo structural changes of the paraspinal muscles; however, it is unclear if functional changes also occur. This study aimed to examine the metabolic and perfusion function changes in the paraspinal muscles of patients with CLBP as indirectly reflected by blood oxygen level-dependent (BOLD) imaging and T2 mapping. All participants were consecutively enrolled at our local hospital from December 2019 to November 2020. Patients were diagnosed with CLBP in the outpatient clinic, and asymptomatic participants were considered to be those with no CLBP or other diseases. This study was not registered on a clinical trial platform. Participants underwent BOLD imaging and T2 mapping scans at the L4-S1 disc level. The effective transverse relaxation rate (R2* values) and transverse relaxation time (T2 values) of the paraspinal muscles were measured on the central plane of the L4/5 and L5/S1 intervertebral discs. Finally, the independent samples t-test was used to assess the differences in R2* and T2 values between the 2 groups, while Pearson correlation analysis was used to determine their correlation with age. A total of 60 patients with CLBP and 20 asymptomatic participants were enrolled. The paraspinal muscles of the CLBP group had higher total R2* values [46.7±2.9 vs. 44.0±2.9 s-1; 95% confidence interval (CI): 1.2-4.2; P=0.001] and lower total T2 values (45.4±4.2 vs. 47.1±3.7 ms; 95% CI: -3.8 to 0.4; P=0.109) than did the asymptomatic participants. For the different muscles, R2* values for the erector spinae (ES) (L4/5: 45.5±2.6 vs. 43.0±3.0 s-1, 95% CI: 1.1-4.0, P=0.001; L5/S1: 48.5±4.9 vs. 45.9±4.2 s-1; 95% CI: 0.2-5.1; P=0.035) and the R2* values of the multifidus (MF) muscles (L4/5: 46.4±2.9 vs. 43.7±3.5 s-1, 95% CI: 1.1-4.3, P=0.001; L5/S1: 46.3±3.5 vs. 42.5±2.8 s-1, 95% CI: 2.1-5.5, P<0.001) of the CLBP group at both spinal levels were higher than those of the asymptomatic participants. In the patients with CLBP, the R2* values at the L4/5 (45.9±2.1 s-1) were lower than those at the L5/S1 (47.4±3.6 s-1; 95% CI: -2.6 to -0.4; P=0.007). The R2* values were positively correlated with age in both groups (CLBP group: r=0.501, 95% CI: 0.271-0.694, P<0.001; asymptomatic group: r=0.499, 95% CI: -0.047 to 0.771; P=0.025). The R2* values were higher in the paraspinal muscles of patients with CLPB and may suggest metabolic and perfusion dysfunction of the paraspinal muscles in these patients.

Dielectric spectrum of a ferrofluid layer exposed to a gradient magnetic field.

A low-frequency dielectric response of a ferrofluid based on transformer oil and MnZn ferrite nanoparticles is investigated in a gradient magnetic field. Four ferrofluid samples of various nanoparticle concentrations were introduced into planar micro-capacitors located over a magnetized tip. The dielectric spectra were measured in the frequency range from 0.1Hz to 200kHz and in the local magnetic field up to 100 mT. The spectra exhibit a dielectric relaxation ascribed to nanoparticle interfacial polarization. The low-frequency spectrum of each ferrofluid decreases upon application of the magnetic field up to 20 mT. The decrease in dielectric permittivity is caused by a magnetic force acting on larger nanoparticles in the gradient magnetic field. It is assumed that the interfaces of the concentrated nanoparticles in the gradient field do not contribute to the effective dielectric response. This reduces the effective relaxation time and shifts the relaxation toward higher frequencies. The dielectric spectra are well described by a relaxation fit function consisting of one Havriliak-Negami and a conductivity term. The fitting confirms that the only effect of the gradient magnetic field on the dielectric spectra is the shift of the dielectric relaxation and the decrease of the amplitude in the imaginary permittivity. This behavior is evident from a master plot, where all dielectric relaxations are superimposed on a single line. The knowledge of the presented behavior of the ferrofluid may be valuable when applying a ferrofluid to sharply magnetized parts of various electrical equipment (wires, tips, screws, nails, edges) as a liquid dielectric medium.

Teragertsevaya spektroskopiya s vremennym razresheniem (THZ–TDS) svetodiodnykh geterostruktur s tremya i pyat'yu kvantovymiyamami InxGa1−xN/GaN

Using terahertz time-domain spectroscopy (THz-TDS), we have detected resonance frequencies of plasmon oscillations excited in heterostructures with multiple InxGa1 – xN/GaN quantum wells by laser pulses with a duration of 130 fs in the temperature range from 90 to 170 K. The fast Fourier transform of temporal forms of terahertz pulses has made it possible to obtain frequency spectra of the power and of the phase shift of terahertz radiation, the interpretation of which has allowed us to estimate the quasi-momentum relaxation time (τ = 10–12 s), mobility (μ = 4 × 103 cm2/(V s)), and effective mass (m* = 0.45m) of majority charge carriers in these heterostructures. Based on the frequency spectra of power and phase shift of terahertz radiation, we have obtained the temperature dependences of the effective mass and relaxation time of the quasi-momentum of a 2D electron gas (2DEG). The 2DEG mobility value obtained by the THz-TDS method is in good agreement with the Hall measurement data.

Multiparametric Quantitative MRI of Peripheral Nerves to Differentiate Axonal from Demyelinating Neuropathies (P11-8.002)

<h3>Objective:</h3> To develop a multiparametric quantitative MRI (qMRI) method to track pathological changes of peripheral nerves in patients with peripheral neuropathies. <h3>Background:</h3> Irrespective of the causes or types of polyneuropathies, peripheral nerves are mainly afflicted by two kinds of pathologies – axonal loss and demyelination. It is critical to differentiate the two as treatments are different for the two conditions. While nerve conduction studies (NCS) have been used to differentiate the two pathologies in the distal nerves, there are no tools to probe the pathologies in the proximal peripheral nerves. This is particularly needed when distal nerves become non-responsive in NCS. <h3>Design/Methods:</h3> We have developed a multiparametric qMRI method that quantifies the sciatic and tibial nerves with 10 parameters that are sensitive to different aspects of myelin and axonal pathologies: magnetization transfer ratio (MTR), magnetization transfer saturation index (MTsat), longitudinal relaxation time (T1), proton density (PD), effective transverse relaxation time (T2*), fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD), and nerve fascicular volume (fVol). In this pilot study, we studied 4 patients with Charcot-Marie-Tooth type-1A (CMT1A), 2 patients with CMT type-2S (CMT2S), and 17 healthy controls. <h3>Results:</h3> Compared with healthy controls, patients with CMT2S (reportedly as axonal type) had comparable MTR, MTsat, T1, PD and fVol, but reduced T2*. While patients with CMT1A (dysmyelinating type) had reduced MTR and MTsat, increased fVol, T1 and PD, and comparable T2*. All the 6 patients shared changes of reduced FA which was driven by a reduced AD and an increased RD. <h3>Conclusions:</h3> The data show different qMRI patterns between axonal and demyelinating neuropathies. The differential changes will be further verified in a larger cohort of patients with peripheral neuropathies. <b>Disclosure:</b> Dr. Chen has nothing to disclose. Mr. Baraz has nothing to disclose. Ms. Xuan has nothing to disclose. Sadaf Saba has nothing to disclose. Dr. Yang has nothing to disclose. Dr. Castoro has nothing to disclose. Yang Xuan has nothing to disclose. Dr. Roth has nothing to disclose. The institution of Dr. Dortch has received research support from NIH. The institution of Dr. Dortch has received research support from DOD. Dr. Li has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Guidepoint. The institution of Dr. Li has received research support from NIH. Dr. Li has a non-compensated relationship as a Board of Directors with ANA that is relevant to AAN interests or activities.

A first-principles study of hydrostatic strain engineering on the electronic properties of β-Ga2O3

β-Ga2O3 has some prominent advantages over other wide band gap semiconductors for application in electronics and optoelectronics. Through density functional theory, the effects of hydrostatic strain on the electronic properties of β-Ga2O3 are investigated. It is found that the band gap of β-Ga2O3 increases and subsequently decreases almost linearly with the hydrostatic strain from −8% to 7%, thus, resulting in the band gap within 3.45–6.28eV. As the strain exceeds −8% or 7%, the phase transition emerges, and its electronic properties exhibit abnormal variation trends as compared to primitive β-Ga2O3. In addition, properties, such as electron effective mass, elastic constants, relaxation time and mobility, show remarkable anisotropy. For the β-Ga2O3 phase with strains, electron mobility along a, b and c directions can be modulated about 2–3 times. The significant range of electronic parameters indicates that strain engineering may be an important approach to meet the different requirements of future electronics.

Magnetization relaxation dynamics in polydisperse ferrofluids.

When a ferrofluid is magnetized in a strong magnetic field, and then the field is switched off, the magnetization decays from its saturation value to zero. The dynamics of this process are controlled by the rotations of the constituent magnetic nanoparticles, and for the Brownian mechanism, the respective rotation times are strongly influenced by the particle size and the magnetic dipole-dipole interactions between the particles. In this work, the effects of polydispersity and interactions on the magnetic relaxation are studied using a combination of analytical theory and Brownian dynamics simulations. The theory is based on the Fokker-Planck-Brown equationfor Brownian rotation and includes a self-consistent, mean-field treatment of the dipole-dipole interactions. The most interesting predictions from the theory are that, at short times, the relaxation of each particle type is equal to its intrinsic Brownian rotation time, while at long times, each particle type has the same effective relaxation time, which is longer than any of the individual Brownian rotation times. Noninteracting particles, though, always relax at a rate controlled only by the Brownian rotation times. This illustrates the importance of including the effects of polydispersity and interactions when analyzing the results from magnetic relaxometry experiments on real ferrofluids, which are rarely monodisperse.