Moment Fluctuations Research Articles

Computational Tool for Determining Local Dielectric Constants in Heterogeneous Nanoscale Systems from Molecular Dynamics Trajectories.

In this work, we describe a computational tool designed to determine the local dielectric constants (ε) of charge-neutral heterogeneous systems by analyzing dipole moment fluctuations from molecular dynamics (MD) trajectories. Unlike conventional methods, our tool can calculate dielectric constants for dynamically evolving selections of molecules within a defined region of space, rather than for fixed sets of molecules. We validated our approach by computing the dielectric constants of TIP3P water nanospheres, achieving results consistent with literature values for bulk water. We then applied our tool to more complex systems, the water slabs around solvated phospholipid bilayers, where we observed a lower dielectric constant of water near the bilayer headgroups (ε = 20-50) compared to nanospheres of bulk water (ε = 58-62) with the same number of molecules. Our tool also enabled us to compute the dielectric constants of water in more heterogeneous systems, where water surrounding asymmetrically distributed phospholipids on single-walled carbon nanotubes also exhibited lower dielectric constants than in bulk water nanospheres. Addition of positively charged peptides that bind to phospholipid-nanotube conjugates further lowered the dielectric constants of water in the immediate vicinity of these conjugates. Moreover, we estimated dielectric constants for lipids in symmetric bilayers, where values are well-documented, and for asymmetric phospholipid-wrapped nanotube systems, which were previously unexplored, and found that dielectric constants of phospholipids depend on their arrangement in the assembled aggregate. The results align with the literature for bilayers and provide new insights for phospholipid-nanotube systems. The ability of our tool to provide local dielectric constants for both well-studied and novel systems advances our understanding of molecular environments and interactions.

Dielectric properties of nanoconfined water.

The dielectric function of a dipolar liquid exhibits a strong wavenumber dependence in the bulk homogeneous state. Such a behavior seems to suggest the possibility of a strong system size dependence of the dielectric constant (DC) of a nanoconfined liquid, although details have been revealed only recently. The dielectric properties of nanoconfined water, indeed, show a marked sensitivity not only to the size and shape (dielectric boundaries) of confinement but also to the nature of surface-water interactions. For geometries widely studied, namely, water confined in a narrow slit, nanocylinder, and nanospherical cavity, the asymptotic approach to the bulk value of the DC with the increase in confinement size is found to be surprisingly slow. This seems to imply the appearance of a dipolar cross correlation length, much larger than the molecular length-scale of water. In narrow slits and narrow cylinders, the dielectric function becomes both inhomogeneous and anisotropic, and the longitudinal and transverse components display markedly different system size dependencies. This sensitivity can be traced back to the dependence of the DC on the ratio of the mean square dipole moment fluctuation to the volume of the system. The observed sensitivity of collective dipole moment fluctuations to the length scale of confinement points to the possibility of using DC to estimate the orientational correlation length scale, which has been an elusive quantity. Furthermore, the determination of volume also requires special consideration when the system size is in nanoscale. We discuss these and several other interesting issues along with several applications that have emerged in recent years.

A Computational Tool for Determining the Local Dielectric Constants within Heterogenous Nanoscale Systems from Molecular Dynamics Trajectories

The dielectric properties play a significant role in shaping the characteristics and functional behavior of heterogeneous nanoscale systems. We have implemented a simple method and developed a flexible computational tool to determine the dielectric constant of various subcomponents of neutral inhomogeneous systems, based on dipole moment fluctuations measured in molecular dynamics (MD) trajectories. We first validate our computational approach by evaluating the dielectric constant (epsilon) of TIP3P waters, determined to be ~ 82. The dielectric of water molecules in a system surrounding a lipid bilayer decreases to ~ 62. Our method successfully calculates the dielectric constant of lipids as 9, with the headgroups exhibiting an epsilon value of approximately 8, and the hydrophobic tails possessing an epsilon value close to 1. These results are in good agreement with the known values reported in the literature. Finally, we have applied our method to optical nanosensor systems for which it has been hypothesized that the local dielectric constant changes are the key determinant of their optical sensing response. Namely, we examined the local dielectric constants in systems of single-walled carbon nanotubes functionalized with lipid molecules, in the presence and absence of target analytes (in this case, antimicrobial disruptor peptides). Our tool is currently designed for neutral species and systems but has a potential for being extended for use on the charged systems. It is a flexible computational tool that can be used to determine the local dielectric constants of subcomponents within neutral heterogeneous nanoscale systems studied in MD simulations, a functionality that, to the best of our knowledge, was not available among other codes and packages used by the computational chemistry community.

Determination of unsteady wing loading using tuft visualization

Unsteady separated flow affects the aerodynamic performance of many large-scale objects, posing challenges for accurate assessment through low-fidelity simulations. Full-scale wind tunnel testing is often impractical due to the object’s physical scale. Small-scale wind tunnel tests can approximate the aerodynamic loading, with tufts providing qualitative validation of surface flow patterns. This investigation demonstrates that tufts can quantitatively estimate unsteady integral aerodynamic lift and pitching moment loading on a wing. We present computational and experimental data for a NACA0012 wing, capturing unsteady surface flow and force coefficients beyond stall. Computational data for varying angles of attack and Reynolds numbers contain the lift coefficient and surface flow. Experimental data, including lift and moment coefficients for a tuft-equipped NACA0012 wing, were obtained at multiple angles of attack and constant Reynolds number. Our results show that a data-driven surrogate model can predict lift and pitching moment fluctuations from visual tuft observations.

B - 96 Relationships between Self-Reported Cognitive Dysfunction, Functional Activities, and Intraindividual Cognitive Variability in Persons with Multiple Sclerosis (Pwms)

Abstract Objective To examine the relationships between intraindividual cognitive variability (IIV) and self-reported cognitive and functional difficulties in persons with multiple sclerosis (pwMS). We hypothesized higher perceived cognitive and functional difficulties would be associated with higher IIV. Method Participants (n = 35) were pwMS from a prospective memory intervention study. During the baseline evaluation, participants completed an objective neuropsychological test battery and a self-report measure of cognitive functioning (Perceived Deficits Questionnaire; PDQ Total). Participants were asked if they had problems in eight different functional areas due to their memory, with the number of endorsed problems summed. Two measures of IIV, an intraindividual standard deviation (ISD) score and maximum discrepancy score (MDS), were created from 11 indices. The relationship between the IIV and PDQ were assessed with individual linear regressions, controlling for demographics and disease-related characteristics, while Spearman correlations examined the associations with the number of reported functional memory problems. Results The PDQ was not significantly associated with either the ISD (b = −0.03, 95% CI: −0.15, 0.10, p = 0.672) or MDS (b = −0.01, 95% CI: −0.51, 0.32, p = 0.645). The overall number of functional memory problems was correlated with both the PDQ (ρ = 0.40, p = 0.018) and ISD (ρ = −0.35, p = 0.039), but not MSD (ρ = −0.22, p = 0.201). Conclusion(s) Perceived cognitive dysfunction was not associated with IIV. However, self-reported functional problems with memory were associated with perceived cognition, as well as one metric of IIV. ISD may better reflect moment to moment fluctuations that lead to difficulties with daily functioning, as opposed to MDS which may reflect underlying variation (e.g., base rates of impairment) in cognitive performance.

A strategy for accurate prediction of dielectric permittivity and dielectric strength in polyimide

AbstractA strategy was proposed to predict accurately the dielectric permittivity and dielectric strength based on the Onsager local field theory. The molecular dynamic simulation was utilised to analyse the dipole moment fluctuation in polyimide (PI) to reflect the polarisation response of applied electric field. The simulation results revealed that the optical dielectric permittivity and static dielectric permittivity were 2.62 and 3.34, showing that the electronic displacement polarisation of the PI acted as a major contributor. The deviation between simulated and measured values of the frequency‐dependent relative dielectric permittivity was no more than 5%, which exhibited high accuracy. As the polarisation response of the polar groups in the PI was at infrared frequencies, the conductive loss may be the dominant role in 102–106 Hz at room temperature. Moreover, the effect of Joule heat on the structure, dielectric permittivity and Young modulus was considered to accurately predict the dielectric strength of the PI (359 kV/mm), which was in agreement with experimental values in the literature. These results establish a clear correlation between structural characteristics and dielectric properties of the PI, which would be the theoretical insights into the design and synthesis of the PI with tailored dielectric properties.

Measuring the Magnetic Dipole Moment and Magnetospheric Fluctuations of Accretion-powered Pulsars in the Small Magellanic Cloud with an Unscented Kalman Filter

Many accretion-powered pulsars rotate in magnetocentrifugal disequilibrium, spinning up or down secularly over multiyear intervals. The magnetic dipole moment μ of such systems cannot be inferred uniquely from the time-averaged aperiodic X-ray flux 〈L(t)〉 and pulse period 〈P(t)〉, because the radiative efficiency of the accretion is unknown and degenerate with the mass accretion rate. Here, we circumvent the degeneracy by tracking the fluctuations in the unaveraged time series L(t) and P(t) using an unscented Kalman filter, whereupon μ can be estimated uniquely, up to the uncertainties in the mass, radius, and distance of the star. The analysis is performed on Rossi X-ray Timing Explorer observations for 24 X-ray transients in the Small Magellanic Cloud, which have been monitored regularly for ∼16 yr. As well as independent estimates of μ, the analysis yields time-resolved histories of the mass accretion rate and the Maxwell stress at the disk–magnetosphere boundary for each star, and hence auto- and cross-correlations involving the latter two state variables. The inferred fluctuation statistics convey important information about the complex accretion physics at the disk–magnetosphere boundary.

Research on material jetting fabrication and dielectric constant calculation of LTCC based on silica-borosilicate glass

Several material systems are available for low-temperature co-fired ceramics, and to achieve more efficient designs and applications using additive manufacturing (AM) techniques such as material jetting, the predictability of the dielectric constant of the sintered structure will significantly reduce the consumption of material development. In this work, the LTCC part was fabricated by 3D material jetting using silica-borosilicate glass LTCC ink and densified at 850°C. The borosilicate glass composition was derived from nanopowders prepared by radio frequency plasma spheronisation and configured as surface-grafted glass sols. Scanning electron microscopy results showed that silica particles were embedded in the glass matrix by a liquid phase sintering mechanism accompanied by several confined pores that were difficult to remove. A dielectric constant of around 3.78 was tested from room temperature to 100°C. Molecular dynamics sintering simulation was used to create sintered structures that matched the experimental values. The dipole moment fluctuation of the silica/glass bulk was counted to obtain an accurate value of the dielectric constant, and then the Bruggeman model based on the effective medium theory predicted the dielectric constant of the sintered body, with a prediction of 3.65, which is within 4 % difference from the measured value (3.78). The dielectric constant was predicted for different ceramic/glass compositions and sintering temperatures and found that 35 wt% and 60 wt% should be the upper and lower bounds for borosilicate glass additions to satisfy a stable structure with a relatively low dielectric constant range (3.38–4.42). In conclusion, an effective molecular dynamics approach to predict the dielectric constant of sintered bodies was developed to assist material design in LTCC AM fabrication.

Scalable Analysis of Dipole Moment Fluctuations for Characterizing Intermolecular Interactions and Structural Stability.

Accurately predicting protein-ligand interactions is essential in computational molecular biochemistry and in silico drug development. Monitoring changes in molecular dipole moments through molecular dynamics simulations provides valuable insights into dipole-dipole interactions, which are critical for understanding protein structure stability and predicting protein-ligand binding affinity. In this study, we propose a novel method to monitor changes in the interangle between dipole vectors of residue molecules within proteins and ligand molecules, aiming to evaluate the strength and consistency of interactions within the complex. Additionally, we extend the concept of positional root-mean-square fluctuation (RMSF), commonly used for protein structure stability analysis, to dipole moments, thus defining dipole moment RMSF. This enables us to analyze the stability of dipole moments for each residue within the protein and compare them across residues and between binding and non-binding complexes. Using the CRBP1-retinoic acid complex as our model system, we observed a significant difference in the interangle change of dipole moments for the key residue at the residue-level between the non-binding and binding complexes. Furthermore, we found that the dipole moment RMSF value of the non-binding complex was substantially larger than that of the binding complex, indicating greater dipole moment instability in the non-binding complex. Leveraging the concept of scalability inherent in the calculation of dipole moment vectors, we systematically expanded the residues within the protein's primary secondary structure. Our dipole moment analysis approach can provide valuable predictive insights into complex candidates, especially in situations where experimental comparisons are challenging.

New insight into tuning magnetic phases of RMn6Sn6 kagome metals

Predicting magnetic ordering in kagome compounds offers the possibility of harnessing topological or flat-band physical properties through tuning of the magnetism. Here, we examine the magnetic interactions and phases of ErMn6Sn6 which belongs to a family of RMn6Sn6, R = Sc, Y, Gd–Lu, compounds with magnetic kagome Mn layers, triangular R layers, and signatures of topological properties. Using results from single-crystal neutron diffraction and mean-field analysis, we find that ErMn6Sn6 sits close to the critical boundary separating the spiral-magnetic and ferrimagnetic ordered states typical for non-magnetic versus magnetic R layers, respectively. Finding interlayer magnetic interactions and easy-plane Mn magnetic anisotropy consistent with other members of the family, we predict the existence of a number of temperature and field dependent collinear, noncollinear, and noncoplanar magnetic phases. We show that thermal fluctuations of the Er magnetic moment, which act to weaken the Mn-Er interlayer magnetic interaction and quench the Er magnetic anisotropy, dictate magnetic phase stability. Our results provide a starting point and outline a multitude of possibilities for studying the behavior of Dirac fermions in RMn6Sn6 compounds with control of the Mn spin orientation and real-space spin chirality.

Superparamagnetic effects in the linear magnetic response of polydisperse ensembles of nanoparticles suspended in a fluid.

Within a kinetic theory, the linear magnetic response of uniaxial single-domain particles suspended in a fluid is analyzed. The main qualitatively different types of frequency dependence of the longitudinal dynamic magnetic susceptibility of such particles are described. It is shown that superparamagnetic (related to orientation thermal fluctuations of the magnetic moment inside a particle) peculiarities of the response of a particle to a probing magnetic field are not fully determined by the ratio of anisotropy energy to thermal energy when a stationary bias field is applied. For a case where the indicated ratio is much greater than one, a simple approximate expression for the dynamic magnetic susceptibility of a particle is proposed. The developed approach is extended to polydisperse suspensions of noninteracting uniaxial nanoparticles. It is shown that polydispersity does not vanish away specific superparamagnetic features in the dynamic magnetic response of such systems. Quantitative estimates of the corresponding effects are performed in different frequency ranges of the applied field. It is demonstrated that under certain restrictions on the disperse composition of a suspension, the internal diffusion of the magnetic moment can lead to a splitting of the absorption spectrum of the system. The significant role of the bias field is revealed. In particular, it can cause an additional absorption maximum provided the particle-size distribution meets the outlined condition. Also, it enables one to assess how important it is to take into account superparamagnetism of particles: the effect of the biasing is stronger for particles with smaller anisotropy and thereby more pronounced superparamagnetic properties. A qualitative agreement of some of the inferences with the experimental data is briefly discussed.

Measuring the Magnetic Dipole Moment and Magnetospheric Fluctuations of SXP 18.3 with a Kalman Filter

The magnetic dipole moment μ of an accretion-powered pulsar in magnetocentrifugal equilibrium cannot be inferred uniquely from time-averaged pulse period and aperiodic X-ray flux data, because the radiative efficiency η 0 of the accretion is unknown, as are the mass, radius, and distance of the star. The degeneracy associated with the radiative efficiency is circumvented if fluctuations of the pulse period and aperiodic X-ray flux are tracked with a Kalman filter, whereupon μ can be measured uniquely up to the uncertainties in the mass, radius, and distance. Here, the Kalman filter analysis is demonstrated successfully in practice for the first time on Rossi X-ray Timing Explorer observations of the X-ray transient SXP 18.3 in the Small Magellanic Cloud (SMC), which is monitored regularly. The analysis yields μ=8.0−1.2+1.3×1030Gcm3 and η0=0.04−0.01+0.02 , compared to μ=5.0−1.0+1.0×1030Gcm3 as inferred traditionally from time-averaged data assuming η 0 = 1. The analysis also yields time-resolved estimates of two hidden state variables, the mass accretion rate and the Maxwell stress at the disk–magnetosphere boundary. The success of the demonstration confirms that the Kalman filter analysis can be applied in the future to study the magnetic moments and disk–magnetosphere physics of accretion-powered pulsar populations in the SMC and elsewhere.

Diagnosis of abrasive wear of steels by machine learning in Python

Comparative tribotechnical tests of wear-resistant equal-hard steels of the martensitic class Hardox 450, Quard 450 in comparison with ferrite-pearlite steel 09G2S were carried out. The wear resistance “ε” increased in the direction of 1.0 → 7.9 → 18.1 in steels 09G2S → Hardox 450 → Quard 450, respectively. As it turned out, after testing for abrasive wear of samples made of Quard 450 steel with maximum wear resistance, traces of martensitic transformation were found on the friction sites. Using machine learning in Python, graphs of fluctuations of friction moments in time of the studied steels were constructed, their smoothing (averaging) by the Hannah method was carried out. The Fourier transform was performed, the amplitude-frequency characteristics of the friction moments were calculated and frequency spectrograms were constructed. It is shown that a decrease in the amplitude of the sinusoids of the first (main) harmonic occurred in the direction of 3.40 → 2.15 → 1.40 in steels 09G2S → Hardox 450 → Quard 450, respectively. Unlike the 09G2S and Hardox 450 steels, in the Quard 450 steel with maximum wear resistance, the second harmonic was split into two with amplitudes of 0.85 and 0.70. The spectra of two exciting forces (abrasive wear and structural-phase (martensitic) transformation) were found in it, strengthening the surface in the contact zone and increasing its wear resistance.

Analysis of lateral dynamic response characteristics of drilling riser during installation of deep-water Christmas tree

In this research, in order to investigate the safety risk of drilling riser during deep-water Christmas tree lowering process and determine the basic parameters for the safety calculation of the upper part of the Christmas tree, wave-current force calculation method is explained based on modified Morison equation. According to differential element method, the dynamic equations of vertical and horizontal bending of riser under wave and current conditions are derived and equation solution method and calculation stability conditions are analyzed. By combining the upper and lower boundaries of riser during Christmas tree connection and environmental load factors, dynamic responses of riser under different wave, top tension, platform drift, operating water depth and other parameters are investigated. The obtained results show that maximum lateral displacement, corresponding water depth and bending moment of riser as well as the amplitude and period of displacement fluctuation at riser bottom are increased with the increase of wave velocity and water depth. It is also found that increase of top tension reduced the maximum lateral displacement of riser and increased corresponding water depth, but excessive tension increased the fluctuations of displacement and bending moment at riser bottom. Increase of platform drift increased maximum lateral displacement fluctuation range, bottom string displacement and bending moment of the riser and decreased corresponding maximum displacement water depth. Drift is found to increase the fluctuations of dynamic parameters at riser bottom. Increase of operating water depth increased riser maximum lateral displacement and decreased the period and amplitude of bottom bending moment fluctuations; also, maximum water depth position approached to "1/3" position on sea surface.

Real-space observation of ergodicity transitions in artificial spin ice

Ever since its introduction by Ludwig Boltzmann, the ergodic hypothesis became a cornerstone analytical concept of equilibrium thermodynamics and complex dynamic processes. Examples of its relevance range from modeling decision-making processes in brain science to economic predictions. In condensed matter physics, ergodicity remains a concept largely investigated via theoretical and computational models. Here, we demonstrate the direct real-space observation of ergodicity transitions in a vertex-frustrated artificial spin ice. Using synchrotron-based photoemission electron microscopy we record thermally-driven moment fluctuations as a function of temperature, allowing us to directly observe transitions between ergodicity-breaking dynamics to system freezing, standing in contrast to simple trends observed for the temperature-dependent vertex populations, all while the entropy features arise as a function of temperature. These results highlight how a geometrically frustrated system, with thermodynamics strictly adhering to local ice-rule constraints, runs back-and-forth through periods of ergodicity-breaking dynamics. Ergodicity breaking and the emergence of memory is important for emergent computation, particularly in physical reservoir computing. Our work serves as further evidence of how fundamental laws of thermodynamics can be experimentally explored via real-space imaging.

Structure of the normal state and origin of the Schottky anomaly in the correlated heavy-fermion superconductor UTe2

The recently discovered $\mathrm{U}{\mathrm{Te}}_{2}$ superconductor is regarded as a heavy-fermion mixed-valence system with very peculiar properties within the normal and superconducting (SC) states. It shows no signs of magnetic order, but has a strong anisotropy of magnetic susceptibility and SC critical field. In addition to a heavy-fermion-like behavior in the normal state, it exhibits a distinctive Schottky-type anomaly at $\ensuremath{\sim}12$ K and a characteristic excitations gap $\ensuremath{\sim}35\ensuremath{-}40$ K. Here, we show, by virtue of dynamical mean-field theory calculations with a quasiatomic treatment of electron correlations, that ab initio-derived crystal-field splitting of the $5{f}^{2}$ ionic configuration yields agreement with these experimental observations. A close analogy of the normal paramagnetic state of $\mathrm{U}{\mathrm{Te}}_{2}$ to that of $\mathrm{U}{\mathrm{Ru}}_{2}{\mathrm{Si}}_{2}$ in the Kondo arrest scenario is revealed. We consider the impact of anisotropic superexchange interactions within the U-U structural dimer on magnetization and development of strong orbital and magnetic moment fluctuations in $\mathrm{U}{\mathrm{Te}}_{2}$.

Distance-dependent dielectric constant at the calcite/electrolyte interface: Implication for surface complexation modeling

HypothesisThe electrical double layer formed at the mineral/electrolyte interface is often modeled using mean-field approaches based on a continuum description of the solvent whose dielectric constant is assumed to decrease monotonically with decreasing distance to the surface. In contrast, molecular simulations show that the solvent polarizability oscillates near the surface similar to the water density profile – as shown previously, for example, by Bonthuis et al. (D.J. Bonthuis, S. Gekle, R.R. Netz, Dielectric Profile of Interfacial Water and its Effect on Double-Layer Capacitance, Phys Rev Lett 107(16) (2011) 166102). We showed that molecular and mesoscale pictures agree by spatially averaging the dielectric constant obtained from molecular dynamics simulations over the distances relevant to the mean-field representation. In addition, the values of capacitances used to describe the electrical double layer in Surface Complexation Models (SCMs) of the mineral/electrolyte interface can be estimated using molecularly informed spatially averaged dielectric constants and positions of hydration layers. ExperimentsFirst, we used molecular dynamics simulations to model the calcite 101¯4/electrolyte interface. Next, by using atomistic trajectories, we calculated the distance-dependent static dielectric constant and water density in the direction normal to the. Finally, we applied spatial compartmentalization consistent with the model of parallel-plate capacitors connected in series to estimate SCM capacitances. FindingsComputationally expensive simulations are required to determine the dielectric constant profile of interfacial water near the mineral surface. On the other hand, water density profiles are readily assessable from much shorter simulation trajectories. Our simulations confirmed that dielectric and water density oscillations at the interface are correlated. Here, we parametrized linear regression models to estimate the dielectric constant directly from the local water density. This is a significant computational shortcut compared to slowly converging calculations relying on total dipole moment fluctuations. The amplitude of the interfacial dielectric constant oscillation can exceed the dielectric constant of the bulk water, suggesting an ice-like frozen state, but only if there are no electrolyte ions. The interfacial accumulation of electrolyte ions causes a decrease in the dielectric constant due to the reduction of water density and re-orientation of water dipoles in ion hydration shells. Finally, we show how to use the computed dielectric properties to estimate SCM's capacitances.

Quantum Optical Description of Radiation by a Two-Level System in Strong Laser Fields

We develop a quantum optical description of radiation from a two-level system (TLS) in strong laser fields, which provides a clear insight into the final states of the TLS and the harmonics field. It is shown that there are two emission channels: the Rayleigh-like channel and the Raman-like channel, which correspond to the TLS ending up in the ground state and excited state after the emission, respectively. The numerical result shows that the harmonics are mainly produced by the Rayleigh-like channel. In addition, according to the coherence of emission among the emitters, the radiation is divided into coherent parts that result from the semi-classical dipole oscillation and incoherent parts that result from the quantum fluctuations of the dipole moment. In the weak field limits, the Rayleigh-like channel corresponds to the coherent parts, and the Raman-like channel corresponds to the incoherent parts. However, in strong laser fields, both channels contribute to coherent and incoherent radiation, and how much they contribute depends on the final excitation. By manipulating the laser field, we can make the Rayleigh-like channel produce either coherent or incoherent radiation.

Multiple electron & phonon scattering effect achieves highly efficient thermoelectricity due to nanostructuring

To enhance the thermoelectric efficiency of a material, the decoupling of transport parameters in the dimensionless figure of merit, zT is important. The SnTe with MnTe magnetic nanoprecipitates was synthesized resulting in a high figure of merit. The gigantic localized spin moment of MnTe nanoprecipitates effectively scatters the conduction electron in SnTe, decoupling Seebeck coefficient, S, and electrical conductivity, σ. As a result, the powerfactor, S2σ was enhanced dramatically over the entire temperature range. The localized spin moment of MnTe nanoprecipitates was significantly larger than that of conventional magnetic atomic substitution in the alloy. Therefore, the spin moment fluctuation of superparamagnetic nanoprecipitates could effectively scatter electrons even at a high temperature. The first quantitative theoretical analysis for electron scattering was conducted in this work, to verify the spin dependent scattering. The weak localization measurement also supported the enhanced electron scattering by localized spin moment. The coherent MnTe nanoprecipitates in the SnTe matrix also reduced lattice thermal conductivity significantly. The slight difference in the lattice parameter between matrix SnTe and precipitates MnTe induced lattice strain and enhanced phonon scattering. The thermoelectric figure of merit zT was recorded 1.8 at 923 K in the eco-friendly material.

The study on the dielectric properties of structural changes of surfactant aqueous solution by molecular dynamics simulation

Dielectric constant is an important physical and chemical property of liquid in regulating solute–solvent interaction and solvation microstructure. Herein this work deals with the procedure for calculating dielectric property based on the raw data of molecular dynamics (MD) simulation. The fluctuations of the dipole moment and current which are obtained from MD can be directly related to the frequency-dependent permittivity. In this article, we have taken the sodium dodecyl sulfate (SDS) aqueous micelle system containing free charges as an example, and the dielectric behavior of micellar systems with different structures were studied. In the high frequency range, the response of positive and negative ions is shielded due to the intrinsic dipole moment polarization of the molecule. At low frequencies, the static dielectric constant can reveal the microstructral transformation of the micelles properly. Our results show that the dielectric constant is closely related to the atomic structure of the micelles, and the static dielectric constant could serve as an important method to determine the microscopic phase change process.