Microscopic Quantities Research Articles

Mass Measurement of 28Si-Enriched Spheres at NMIJ for the Determination of the Avogadro Constant

The Avogadro constant, $N_{\mathbf {A}}$ , is the physical constant that connects microscopic and macroscopic quantities, and is indispensable especially in the field of chemistry. In addition, the Avogadro constant is closely related to the fundamental physical constants, namely, the electron relative atomic mass, fine-structure constant, Rydberg constant, and Planck constant. For several decades, the Avogadro constant has been determined using the x-ray crystal density (XRCD) method, which is currently one of the practical methods to redefine the kilogram based on fundamental physical constants. In this paper, we present the results of mass measurements of 28Si-enriched spheres, performed at the National Metrology Institute of Japan (NMIJ) in 2014, for the determination of the Avogadro constant using the XRCD method. The results of repeatability of the cleaning effect on the mass of the spheres and the determination of the physical adsorption of water vapor on the spheres are shown. These results establish the reliability of the mass measurement at NMIJ. In addition, we report the results of the mass measurements of 28Si-enriched sphere AVO28-S5c conducted in 2016 to participate in the Pilot Study organized by the Consultative Committee for Mass and Related Quantities aiming at the redefinition of the kilogram based on the fixed numerical value of the Planck constant.

Structural Analysis by Enhanced Raman Scattering.

Gold nanostructures focus light to a molecular length scale at their surface, creating the possibility to visualize molecular structure. The high optical intensity leads to surface enhanced Raman scattering (SERS) from nearby molecules. SERS spectra contain information on molecular position and orientation relative to the surface but are difficult to interpret quantitatively. Here we describe a ratiometric analysis method that combines SERS and unenhanced Raman spectra with theoretical calculations of the optical field and molecular polarizability. When applied to the surfactant layer on gold nanorods, the alkane chain is found to be tilted 25° to the surface normal, which matches previous reports of the layer thickness. The analysis was also applied to fluid phase phospholipid bilayers that contain tryptophan on the surface of gold nanorods. The lipid double bond was found to be oriented normal to the bilayer and 13 Å from the nitrogen atom. Tryptophan was found to sit near the glycerol headgroup region with its indole ring 43° from the bilayer normal. This new method can determine specific interfacial structure under ambient conditions, with microscopic quantities of material, and without molecular labels.

Piezoelectricity in two-dimensional materials: Comparative study between lattice dynamics andab initiocalculations

Elastic constant C_{11} and piezoelectric stress constant e_{1,11} of two-dimensional (2D) dielectric materials comprising h-BN, 2H MoS2 and other transition metal dichalcogenides (TMDCs) and -dioxides (TMDOs) are calculated using lattice dynamical theory. The results are compared with corresponding quantities obtained by ab-initio calculations. We identify the difference between clamped-ion and relaxed-ion contributions with the dependence on inner strains which are due to the relative displacements of the ions in the unit cell. Lattice dynamics allows to express the inner strains contributions in terms of microscopic quantities such as effective ionic charges and optoacoustical couplings, which allows us to clarify differences in the piezoelectric behavior between h- BN versus MoS2. Trends in the different microscopic quantities as functions of atomic composition are discussed.

Cubic ideal ferromagnets at low temperature and weak magnetic field

The low-temperature series for the free energy density, pressure, magnetization and susceptibility of cubic ideal ferromagnets in weak external magnetic fields are discussed within the effective Lagrangian framework up to three loops. The structure of the simple, body-centered, and face-centered cubic lattice is taken into account explicitly. The expansion involves integer and half-integer powers of the temperature. The corresponding coefficients depend on the magnetic field and on low-energy effective constants that can be expressed in terms of microscopic quantities. Our formulas may also serve as efficiency or consistency check for other techniques like Green's function methods, where spurious terms in the low-temperature expansion have appeared. We explore the sign and magnitude of the spin-wave interaction in the pressure, magnetization and susceptibility, and emphasize that our effective field theory approach is fully systematic and rigorous.

Investigating the electron density of multi-MeV X-ray-induced air plasmas at low pressures based on electromagnetic resonant cavity analysis

We investigate air plasmas generated by multi-MeV pulsed X-rays at pressures ranging from 10−5 to 10−1 mbar. The experimental approach used for these studies is based on measurements of resonant frequencies damping and shift for different electromagnetic modes within a cylindrical cavity. Time-integrated electron densities in X-ray-induced air plasmas are inferred from the damping rate of the measured magnetic fields and their corresponding frequency shifts. In the present study, electron densities ranging from 108 to 109 cm−3 at pressures ranging from 10−3 to 10−1 mbar have been measured. Experimental results were confronted to 3D Maxwell-Vlasov Particle-In-Cell simulations incorporating a radiation-induced electric conductivity model. The method used in this work enables determining microscopic and macroscopic physical quantities within low pressure air plasmas generated by pulsed X-ray.

Controlling magnetic interfaces using ordered surface alloys

We have investigated the growth and magnetic properties of Fe thin films on the clean W(100) surface and W(100)-M c(2 \ifmmode\times\else\texttimes\fi{} 2) ($M=\mathrm{Cu}$, Ag, Au) surface alloy substrates. The influence of the interface on magnetism is assessed experimentally by studying sensitive threshold behavior in magnetic ordering using spin-polarized low-energy electron microscopy. The onset of ferromagnetic order that occurs with increasing film thickness at room temperature due to finite-sized scaling of the Curie temperature varies reproducibly among films on W(100) and the surface alloys. Magnetic moments and exchange coupling constants of the magnetic ground states are also determined theoretically for films with ideal interfaces by first-principles density functional theory calculations. These microscopic quantities are consistently enhanced in Fe films on the noble metal-induced surface alloys compared to their values in films on the clean W(100) surface. We attribute the systematic variation of magnetic onset observed experimentally to the competition between the intrinsically enhanced magnetic coupling and moments on the surface alloy substrates and several extrinsic factors that could suppress magnetic ordering, including intermixing, substrate and film roughness, and surface alloy disorder. Tendencies for intermixing are explored theoretically by determining the energy barrier for noble metal segregation. Despite these possible extrinsic effects, the results suggest that the use of the broad class of ordered surface alloys as alternative substrates may offer greater opportunities for manipulating thin film magnetism.

Fermions on the low-buckled honey-comb structured lattice plane and classical Casimir–Polder force

We start with the well-known expression for the vacuum polarization and suitably modify it for 2[Formula: see text]1-dimensional spin–orbit coupled (SOC) fermions on the low-buckled honey-comb structured lattice plane described by the low-energy Liu–Yao–Feng–Ezawa (LYFE) model Hamiltonian involving the Dirac matrices in the chiral representation obeying the Clifford algebra. The silicene and germanene fit this description suitably. They have the Dirac cones similar to those of graphene and SOC is much stronger. The system could be normal or ferromagnetic in nature. The silicene turns into the latter type if there is exchange field arising due to the proximity coupling to a ferromagnet (FM) such as depositing Fe atoms to the silicene surface. For the silicene, we find that the many-body effects considerably change the bare Coulomb potential by way of the dependence of the Coulomb propagator on the real-spin, iso-spin and the potential due to an electric field applied perpendicular to the silicene plane. The computation aspect of the Casimir–Polder force (CPF) needs to be investigated in this paper. An important quantity in this process is the dielectric response function (DRF) of the material. The plasmon branch was obtained by finding the zeros of DRF in the long-wavelength limit. This leads to the plasmon frequencies. We find that the collective charge excitations at zero doping, i.e., intrinsic plasmons, in this system, are absent in the Dirac limit. The valley-spin-split intrinsic plasmons, however, come into being in the case of the massive Dirac particles with characteristic frequency close to 10 THz. Our scheme to calculate the Casimir–Polder interaction (CPI) of a micro-particle with a sheet involves replacing the dielectric constant of the sample in the CPI expression obtained on the basis of the Lifshitz theory by the static DRF obtained using the expressions for the polarization function we started with. Though the approach replaces a macroscopic constant by a microscopic quantity, it has the distinct advantage of the many-body effect inclusion seamlessly. We find the result that for the nontrivial susceptibility and polarizability values of the sheet and micro-particle, respectively, there is crossover between attractive and repulsive behavior. The transition depends only on these response functions apart from the ratio of the film thickness and the micro-particle separation ([Formula: see text]/[Formula: see text]) and temperature. Furthermore, there is a longitudinal electric field induced topological insulator (TI) to spin-valley-polarized metal (SVPM) transition in silicene, which is also referred to as the topological phase transition (TPT). The low-energy SVP carriers at TPT possess gapless (massless) and gapped (massive) energy spectra close to the two nodal points in the Brillouin zone with maximum spin-polarization. We find that the magnitude of the CPF at a given ratio of the film thickness and the separation between the micro-particle and the film are greater at TPT than at the TI and trivial insulator phases.

Identification of crystal plasticity parameters using DIC measurements and weighted FEMU

An inverse method for the identification of a set of crystal plasticity parameters is introduced and applied to in situ tensile tests on steel polycrystals. Various mean grain sizes are obtained with different conditioning of AISI 316LN austenitic stainless steel. Identification is based on a weighted Finite Element Model Updating (FEMU) using both displacement fields at the microscale and macroscopic load levels. The values of the identified parameters depend on the factor weighing the contributions of the microscopic and macroscopic quantities. On the one hand, surface displacement fields are measured by Digital Image Correlation (DIC). On the other hand, they are simulated by resorting to Finite Element calculations with a local crystal plasticity law (i.e.,Méric-Cailletaud’s model) and a 2D simulation of the microstructure. The parameters associated with isotropic hardening are calibrated for the different mean grain sizes. The benefits of considering full-field measurements are manifest for instance in the excellent Hall-Petch trend captured at the microstructural scale. The identification procedure is also applied to the estimation of hardening parameters describing the interaction between slip systems.

Intrinsic ferroelectric switching from first principles.

The existence of domain walls, which separate regions of different polarization, can influence the dielectric, piezoelectric, pyroelectric and electronic properties of ferroelectric materials. In particular, domain-wall motion is crucial for polarization switching, which is characterized by the hysteresis loop that is a signature feature of ferroelectric materials. Experimentally, the observed dynamics of polarization switching and domain-wall motion are usually explained as the behaviour of an elastic interface pinned by a random potential that is generated by defects, which appear to be strongly sample-dependent and affected by various elastic, microstructural and other extrinsic effects. Theoretically, connecting the zero-kelvin, first-principles-based, microscopic quantities of a sample with finite-temperature, macroscopic properties such as the coercive field is critical for material design and device performance; and the lack of such a connection has prevented the use of techniques based on ab initio calculations for high-throughput computational materials discovery. Here we use molecular dynamics simulations of 90° domain walls (separating domains with orthogonal polarization directions) in the ferroelectric material PbTiO3 to provide microscopic insights that enable the construction of a simple, universal, nucleation-and-growth-based analytical model that quantifies the dynamics of many types of domain walls in various ferroelectrics. We then predict the temperature and frequency dependence of hysteresis loops and coercive fields at finite temperatures from first principles. We find that, even in the absence of defects, the intrinsic temperature and field dependence of the domain-wall velocity can be described with a nonlinear creep-like region and a depinning-like region. Our model enables quantitative estimation of coercive fields, which agree well with experimental results for ceramics and thin films. This agreement between model and experiment suggests that, despite the complexity of ferroelectric materials, typical ferroelectric switching is largely governed by a simple, universal mechanism of intrinsic domain-wall motion, providing an efficient framework for predicting and optimizing the properties of ferroelectric materials.

Photoimmunotherapy of residual disease after incomplete surgical resection in head and neck cancer models

Antibody‐based photodynamic therapy, or photoimmunotherapy (PIT), is a novel, targeted cancer therapy, which can serve as both a diagnostic and a therapeutic agent. The primary objective of this study was to evaluate the capacity of panitumumab‐IRDye700DX (Pan‐IR700) to eliminate microscopic tumor remnants in the postsurgical setting, which was accomplished using novel in vitro and in vivo models of residual disease after incomplete resection. Additionally, PIT was evaluated in fresh human‐derived cancer tissue. To determine a threshold for cellular regrowth after PIT, an in vitro assay was performed using a range of cells representing microscopic disease quantities. Long‐term growth inhibition was induced after treatment of 5 × 103 and 1 × 104 cells at 6 J. A novel in vivo mouse model of subtotal tumor resection was used to assess the effectiveness of Pan‐IR700 mediated PIT to eliminate residual disease and inhibit recurrence in the post‐surgical wound bed. Mice receiving surgical treatment plus adjuvant PIT showed a threefold and fourfold reduction in tumor regrowth at 30 days post PIT in the 50% and 90% subtotal resection groups, respectively (as measured by bioluminescence imaging), demonstrating a significant (P < 0.001) reduction in tumor regrowth. To determine the translatability of epidermal growth factor receptor (EGFR)‐targeted PIT, SCCHN human tissues (n = 12) were treated with Pan‐IR700. A significant reduction (P < 0.001) in ATP levels was observed after treatment with Pan‐IR700 and 100 J cm−2 (48% ± 5%) and 150 J cm−2 (49% ± 7%) when compared to baseline. Targeting EGFR with Pan‐IR700 has robust potential to provide a tumor‐specific mechanism for eliminating residual disease in the surgical setting, thereby increasing therapeutic efficacy, prolonging progression‐free survival, and decreasing morbidity.

Application of a Clinical Whole-Transcriptome Assay for Staging and Prognosis of Prostate Cancer Diagnosed in Needle Core Biopsy Specimens

Molecular and genomic analysis of microscopic quantities of tumor from formalin-fixed, paraffin-embedded biopsy specimens has many unique challenges. Herein, we evaluated the feasibility of obtaining transcriptome-wide RNA expression to measure prognostic classifiers in diagnostic prostate needle core biopsy specimens. One-hundred fifty-eight samples from diagnostic needle core biopsy specimens (BX) and radical prostatectomies (RPs) were collected from 33 patients at three hospitals; each patient provided up to six tumor and benign samples. Genome-wide transcriptomic profiles were generated using Affymetrix Human Exon arrays for comparison of gene expression alterations and prognostic signatures between the BX and RP samples. A sufficient amount of RNA (>100 ng) was obtained from all RP specimens (n = 77) and from 72 of 81 of BX specimens. Of transcriptomic features detected in RP, 95% were detectable in BX tissues and demonstrated a high correlation (r=0.96). Likewise, an expression signature pattern validated on RPs (Decipher prognostic test) showed correlation between BX and RP (r=0.70). Of matched BX and RP pairs, 25% showed discordant molecular subtypes. Genome-wide exon arrays yielded data of comparable quality from biopsy and RP tissues. The high concordance of tumor-associated gene expression changes between BX and RP samples provides evidence for the adequate performance of the assay platform with samples from prostate needle biopsy specimens with limited tumor volume.

From solutions to molecular emulsions

Abstract Concentration fluctuations play an important role in the statistical description of the stability of liquids, particularly in the neighborhood of phase transitions. Classical thermodynamics is blind to fluctuations, and statistical thermodynamics is required to fully understand quantities such as the isothermal compressibility or heat capacity, by linking them to fluctuations of appropriate statistical microscopic quantities and showing that they are response functions. This is illustrated by the seminal Kirkwood–Buff theory of solutions. However, the existence of micro-heterogeneous structures, particularly in aqueous mixtures, which leads to large Kirkwood–Buff integrals, suggest that micro-heterogeneity is a form of concentration fluctuation. This interpretation becomes difficult to accept when extrapolated to larger micro-heterogeneous structures such as micellar aggregates in micro-emulsions. By analyzing how different methods, experimental, computer experiments and theoretical approaches deal with the underlying duality behind these two physical manifestations, we put in evidence the need to reconsider the description of liquids by incorporating the description of emergent “objects”, such as the micro-heterogeneous structures from a molecular point of view. On this path, the concept of “molecular emulsion” allows to describe in a unified way all type of disordered liquids, from solutions to the organized liquids of soft matter.

Polynomial-based Approximate Inverse Stochastic Homogenization Analysis of a Particle Reinforced Composite Material Considering Correlated Multiple Microscopic Random Variations

This paper describes an inverse stochastic homogenization analysis of a particle composite material considering correlated multiple microscopic random variations. Since a microscopic random variation will cause a random response of an equivalent material property or mechanical response of a composite structure, the analysis of its influence is important for reliability evaluation of the structure. On the other hand, in general, the probabilistic property of a microscopic quantity is unknown after manufacturing. From this reason, this study aims at development of the analysis method for the inverse stochastic homogenization problem, which identifies the microscopic probabilistic property from that of the macroscopic quantities. In particular, applicability of the polynomial-based approximation to the inverse stochastic homogenization analysis is investigated in this paper.

Topological cutoff frequency in a slab waveguide: Penetration length in topological insulator walls

Electromagnetic waves propagating in a slab waveguide, whose walls consist of three-dimensional topological insulator, experience a topological cutoff frequency, ωθ. Once ωθ depends upon the penetration length of the metallic surface states into the bulk, l, our findings suggest TI-made waveguides as useful apparatus to estimate the microscopic quantity l by measuring the optical response carried out by the macroscopic signature of ωθ.

Bond kinetics in simulated telechelic associating polymer networks

Telechelic associating polymers are simulated using a novel hybrid molecular dynamics (MD)/Monte Carlo (MC) algorithm. Within the simulation functionalised end groups, at both ends of the polymer chain, form reversible bonds according to MC rules, while the spatial positions of the polymers are dictated by MD. We study the kinetics of the MC process. From the observed rates of breakage and formation, the aggregate size distribution can be obtained using a master equation. These distributions are in agreement with those obtained directly from the simulation data. We report on the system at rest, under uniform shear, and under oscillatory shear. The rates provide insight in the dynamics of the system at a microscopic level. We found that in all cases formation is dominated by small aggregates of size 1-5 joining bigger ones, whereas dissociation is dominated by aggregates of sizes 45-55 breaking in two approximately equal halves. This work complements experiment, which can only access certain microscopic quantities, like aggregate size distribution, but not reaction rates such as those reported in this manuscript.

Classical and semiclassical dynamics in statistical environments with a mixed dynamical and statistical representation.

We present a basic theory to study real-time dynamics embedded in a large environment that is treated using a statistical method. In light of great progress in the molecular-level studies on time-resolved spectroscopies, chemical reaction dynamics, and so on, not only in the gas phase but also in condensed phases like liquid solvents and even in crowded environments in living cells, we need to bridge over a gap between statistical mechanics and microscopic real-time dynamics. For instance, an analogy to gas-phase dynamics in which molecules are driven by the gradient of the potential energy hyper-surfaces (PESs) suggests that particles in condensed phases should run on the free energy surface instead. The question is whether this anticipation is correct. To answer it, we here propose a mixed dynamics and statistical representation to treat chemical dynamics embedded in a statistical ensemble. We first define the entropy functional, which is a function of the phase-space position of the dynamical subsystem, being dressed with statistical weights from the statistical counterpart. We then consider the functionals of temperature, free energy, and chemical potential as their extensions in statistical mechanics, through which one can clarify the relationship between real-time microscopic dynamics and statistical quantities. As an illustrative example we show that molecules in the dynamical subsystem should run on the free-energy functional surface, if and only if the spatial gradients of the temperature functional are all zero. Otherwise, additional forces emerge from the gradient of the temperature functional. Numerical demonstrations are presented at the very basic level of this theory of molecular dissociation in atomic cluster solvents.

Computational homogenization of sound propagation in a deformable porous material including microscopic viscous-thermal effects

Porous materials like acoustic foams can be used for acoustic shielding, which is important for high-tech systems and human comfort. In this paper, a homogenization model is proposed to investigate the relation between the microstructure and the resulting macroscopic acoustic properties. The macroscopic absorption ability is due to the microscopic viscous-thermal coupling between an elastic solid skeleton and a gaseous fluid in the associated Representative Volume Element (RVE). The macro-to-micro relation is realized through the boundary conditions of the microscopic RVE, which relies on the macroscopic solid deformation and fluid pressure gradient. By assuming that the variation of the macroscopic energy per unit volume equals the volume average of the variation of the microscopic energy, the macroscopic solid stress and fluid displacement can be calculated from the corresponding microscopic quantities. Making additional assumptions on this approach, Biot׳s poroelastic theory is recovered. A case study is performed through the simulations of sound absorption in three porous materials, one made from aluminum and two from different polyurethane foams. For simplicity, an idealized partially open cubic microstructure is adopted. The homogenization results are evaluated by comparison with Direct Numerical Simulations (DNS), revealing an adequate performance of the approach for the studied porous material. By comparing the results of different solid materials, it is found that the solid stiffness has a limited effect when resonance does not occur. Nevertheless, due to the absence of the microscopic fluctuation, Biot׳s model with the parameters obtained from the homogenization approach predicts a higher resonance frequency than the DNS, whereas a full homogenization modification improves the prediction.

Non-extensive thermodynamics and neutron star properties

In the present work we apply non extensive statistics to obtain equations of state suitable to describe stellar matter and verify its effects on microscopic and macroscopic quantities. Two snapshots of the star evolution are considered and the direct Urca process is investigated with two different parameter sets. $q$-values are chosen as 1.05 and 1.14. The equations of state are only slightly modified, but the effects are enough to produce stars with slightly higher maximum masses. The onsets of the constituents are more strongly affected and the internal stellar temperature decreases with the increase of the $q$-value, with consequences on the strangeness and cooling rates of the stars.

On the microscopic fluctuations driving the NMR relaxation of quadrupolar ions in water.

Nuclear Magnetic Resonance (NMR) relaxation is sensitive to the local structure and dynamics around the probed nuclei. The Electric Field Gradient (EFG) is the key microscopic quantity to understand the NMR relaxation of quadrupolar ions, such as (7)Li(+), (23)Na(+), (25)Mg(2+), (35)Cl(-), (39)K(+), or (133)Cs(+). Using molecular dynamics simulations, we investigate the statistical and dynamical properties of the EFG experienced by alkaline, alkaline Earth, and chloride ions at infinite dilution in water. Specifically, we analyze the effect of the ionic charge and size on the distribution of the EFG tensor and on the multi-step decay of its auto-correlation function. The main contribution to the NMR relaxation time arises from the slowest mode, with a characteristic time on the picosecond time scale. The first solvation shell of the ion plays a dominant role in the fluctuations of the EFG, all the more that the ion radius is small and its charge is large. We propose an analysis based on a simplified charge distribution around the ion, which demonstrates that the auto-correlation of the EFG, hence the NMR relaxation time, reflects primarily the collective translational motion of water molecules in the first solvation shell of the cations. Our findings provide a microscopic route to the quantitative interpretation of NMR relaxation measurements and open the way to the design of improved analytical theories for NMR relaxation for small ionic solutes, which should focus on water density fluctuations around the ion.

Regularised crack behaviour effects on continuum modelling of quasi-brittle materials under cyclic loading

A continuum model for quasi-brittle materials able to reproduce mechanical phenomena related to cyclic loading is proposed. Specific care is taken to reproduce progressive stiffness recovery and hysteresis effects caused respectively by crack closure and friction. A virtual testing approach is set up to analyse the evolution of microscopic quantities during uni-axial cyclic tests and to justify an original and efficient modelling of these phenomena. Thus, a regularised formulation of the homogenised multiple contact problem induced by the non-simultaneous closure of microscopic cracks is presented. The proposed continuum model is validated by means of member-scale simulations of reversely loaded reinforced concrete shear walls.