Changes In Local Density Research Articles

Elastic Strain Effects on Wave Scattering: Implications for Coda Wave Interferometry (CWI)

AbstractCoda Wave Interferometry (CWI) is a highly sensitive monitoring technique built on the sensitivity of elastic coda waves to small changes in a diffusive medium. However, a clear connection between the physical processes involved in the evolution of the medium and the time changes observed by CWI has not been clearly described yet. Here, we quantify the impact of elastic deformation on CWI measurements at laboratory scales. We compare experimental results from wave scattering measurements during a uniaxial compression test to those of a numerical approach based on the combination of two codes (SPECFEM2D and Code_Aster), which allows us to model wave propagation in complex diffusive media during its elastic deformation. In both approaches, the reversible time delays measured between waveforms increase with the elastic deformation of the sample. From the numerical modeling, we gain insight to the relative contributions of different physical effects on the CWI measurement: local density changes from volumetric strain, the deformation of scatterers, and acoustoelastic effects. Our results suggest that acoustoelastics effects related to nonlinear elasticity are dominant.

Formation of solitary structures and envelope solitons in electron acoustic wave in inner magnetosphere plasma with suprathermal ions

AbstractThe propagation of electron acoustic solitary waves is investigated in magnetized two‐temperature electron plasma with supra‐thermal ion. By using the reductive perturbation technique, the Korteweg de‐Vries (KdV) equation is derived. Later solving this equation, a solitary wave solution has been derived. These are mainly in astrophysical plasmas where changes of local charge density, temperature, and energy of particles produce considerable effects on the plasma system. The effects of supra‐thermality, density, and Mach number on solitary structures are studied in detail. The results show that the supra‐thermal index (κ) and ion to electron temperature ratio (σ) alters the regime where solitary waves may exist. While studying the solitary profile for different parametric variation some interesting conclusion can be drawn; it is shown that the solitary profile becomes flatter. This can be due to the thermal energy associated with the hot electrons. However, with the increase in ion density with respect to the cold electrons' density, the solitary waves become steeper and sharper. This is due to the comparatively heavier mass of ions. The density of cold electron also increases the solitary structures in a similar manner. The higher the density of cold electrons, sharper will be the profile. The above findings will be helpful in understanding many astrophysical phenomena and data obtained by space missions. For a further study, we keep the investigation of the formation of other kinds of stationary structures like shocks, double layers, etc.

Interface tracking characteristics of color-gradient lattice Boltzmann model for immiscible fluids.

We study the interface tracking characteristics of a color-gradient-based lattice Boltzmann model for immiscible flows. Investigation of the local density change in one of the fluid phases, via a Taylor series expansion of the recursive lattice Boltzmann equation, leads to the evolution equation of the order parameter that differentiates the fluids. It turns out that this interface evolution follows a conservative Allen-Cahn equation with a mobility which is independent of the fluid viscosities and surface tension. The mobility of the interface, which solely depends upon lattice speed of sound, can have a crucial effect on the physical dynamics of the interface. Further, we find that, when the equivalent lattice weights inside the segregation operator are modified, the resulting differential operators have a discretization error that is anisotropic to the leading order. As a consequence, the discretization errors in the segregation operator, which ensures a finite interface width, can act as a source of the spurious currents. These findings are supported with the help of numerical simulations.

In-situ characterization of initial marine corrosion induced by rare-earth elements modified inclusions in Zr-Ti deoxidized low-alloy steels

In the present research, the effects of rare-earth (RE) elements modified inclusions on initial marine corrosion of Zr-Ti deoxidized low-alloy steels were studied by first principle modeling and a variety of analytical methods including in-situ scanning vibrating electrode technique (SVET), scanning electron microscopy with x-ray microanalysis (SEM/EDS), and confocal Raman microscopy (CRM). The obtained results revealed that two types of complex inclusions with intertwined components of RExZryOz-RE2O2S and RExZryOz-RE2O2S-TiN were formed. RE2O2S preferentially dissolved in 0.5wt% NaCl solution, whereas the dissolution of RExZryOz propagated from the periphery to the middle of the inclusions and subsequently, formed stable pits on the steel surface. TiN was stable in the marine environment and finally, became detached from the substrate. Moreover, in-situ SVET results demonstrated the local current density change during corrosion process was influenced by single and multiple inclusions, indicating that the dissolution of inclusions induced the electrochemical activities of pitting corrosion and further inhibited the propagation of local corrosion. Furthermore, the corrosion tendency of inclusions and the Fe matrix was examined by first principle modeling. Finally, two schematic models were proposed to demonstrate the effects of inclusions on initial marine corrosion of low-alloy steels.

Structural changes and kinetics of shear banding in metallic glass composites

In this work we studied the mechanical behavior, structural changes and kinetics of shear banding during compression tests of Cu–Zr-based metallic glass composites using molecular dynamics simulations. Starting from a Cu45Zr45Al10 metallic glass model, two composite models were generated by adding 2% in volume of CuZr (B2 structure) nanocrystals of 4 and 17 nm in diameter, respectively. The three models were then deformed in compression using embedded-atom method (EAM) interatomic potentials. Local shear strain analyses showed that the kinetics of shear banding could be modeled as a two-stage process: 1) shear band formation due to the coalescence of shear transformation zones, and 2) shear band coarsening/thickening. The growth rate of the first stage (coalescence of shear transformation zones) varied upon the addition of CuZr nanocrystals, while the growth rate of the second stage remained unchanged. The addition of CuZr nanocrystals did not induce significant changes in the radial distribution function and distribution of Voronoi polyhedra of the glassy matrix, independently of the nanocrystal size. However, the addition of CuZr nanocrystals induced changes in the rate at which the local density of Cu-centered ⟨0,0,12,0,0⟩ icosahedra decreased with strain (“kinetics of icosahedra destruction”). These changes in local density were also modeled as a two-stage process with corresponding growth rates very similar to those obtained for the kinetics of shear banding, thus indicating a close relationship between the kinetics of icosahedra destruction and the kinetics of shear banding.

Fully experiment-based evaluation of few digital volume correlation techniques.

Digital Volume Correlation (DVC) is a powerful set of techniques used to compute the local shifts of 3D images obtained, for instance, in tomographic experiments. It is utilized to analyze the geometric changes of the investigated object as well as to correct the corresponding image misalignments for further analysis. It can therefore be used to evaluate the local density changes of the same regions of the inspected specimens, which might be shifted between measurements. In recent years, various approaches and corresponding pieces of software were introduced. Accuracies for the computed shift vectors of up to about 1‰ of a single voxel size have been reported. These results, however, were based either on synthetic datasets or on an unrealistic setup. In this work, we propose two simple methods to evaluate the accuracy of DVC-techniques using more realistic input data and apply them to several DVC programs. We test these methods on three materials (tuff, sandstone, and concrete) that show different contrast and structural features.

Sperm morphology and count vary with fine-scale changes in local density in a wild lizard population

Given that sperm production can be costly, theory predicts that males should optimally adjust the quantity and/or quality of their sperm in response to their social environment to maximize their paternity success. Although experiments demonstrate that males can alter their ejaculates in response to manipulations of the social environment and studies show that ejaculate traits covary with social environment across populations, it is unknown whether individual variation in sperm traits corresponds to natural variation found within wild populations. Using an island population of brown anole lizards (Anolis sagrei), we tested the prediction that sperm traits (sperm count, sperm morphology, sperm velocity) respond to natural variation in the risk of sperm competition, as inferred from the local density and operational sex ratio (OSR) of conspecifics. We found that males living in high-density areas of the island produced relatively larger sperm midpieces, smaller sperm heads, and lower sperm counts. Sperm traits were unrelated to OSR after accounting for the covariance between OSR and density. Our findings broaden the implications of sperm competition theory to intrapopulation social environment variation by showing that sperm count and sperm morphology vary with fine-scale differences in density within a single wild population.

Spectral Reshaping of Single Dye Molecules Coupled to Single Plasmonic Nanoparticles.

Fluorescent molecules are highly susceptible to their local environment. Thus, a fluorescent molecule near a plasmonic nanoparticle can experience changes in local electric field and local density of states that reshape its intrinsic emission spectrum. By avoiding ensemble averaging while simultaneously measuring the super-resolved position of the fluorophore and its emission spectrum, single-molecule hyperspectral imaging is uniquely suited to differentiate changes in the spectrum from heterogeneous ensemble effects. Thus, we uncover for the first time single-molecule fluorescence emission spectrum reshaping upon near-field coupling to individual gold nanoparticles using hyperspectral super-resolution fluorescence imaging, and we resolve this spectral reshaping as a function of the nanoparticle/dye spectral overlap and separation distance. We find that dyes bluer than the plasmon resonance maximum are red-shifted and redder dyes are blue-shifted. The primary vibronic peak transition probabilities shift to favor secondary vibronic peaks, leading to effective emission maxima shifts in excess of 50 nm, and we understand these light-matter interactions by combining super-resolution hyperspectral imaging and full-field electromagnetic simulations.

The attraction of urban cores: Densification in Dutch city centres

Urban growth is typically considered a process of expansion. As population grows and transport costs decrease urban density gradients are expected to gradually flatten. This is a basic feature of cities, explained by urban economic models and empirically supported by a plethora of studies about urban density development from all over the world. However, additional forces, such as changes in demographic composition and locational preferences of the urban population acting at local levels, may counteract the flattening tendency of urban gradients. In this paper, we suggest a methodology to test the impact of local density changes on urban gradients, looking at spatio-temporal developments in terms of housing and population. Using highly detailed data on individual housing units and inhabitants in major Dutch cities, we first assess and compare urban density gradients during the period 2000–2017. In all the analysed Dutch cities, both dwelling and population density gradients are becoming steeper over time, contradicting standard predictions from urban economic literature and empirical reports worldwide. The observed trend of steepening urban gradients is partly explained by the presence of historical monuments and urban amenities.

Hydrogen Arrangements on Defective Quasi-Molecular BN Fragments.

Considering the ever-increasing interest in metal-free materials, some potential chemical applications of quasi-molecular boron nitride (BN) derivatives were tested. Specifically, the behavior of BN fragments was analyzed when given defects, producing local electron density changes, were introduced by using topological engineering approaches. The inserted structural faults were Schottky-like divacancy (BN-d) defects, assembled in the fragment frame by the subtraction of one pair of B and N atoms or Stone–Wales (SW) defects. This study is aimed at highlighting the role of these important classes of defects in BN materials hypothesizing their future use in H2-based processes, related to either (i) H2 activation or (ii) H2 production, from preadsorbed hydrogenated molecular species on BN sites. Here, it has been observed that BN species, embodying SW defects, are characterized by endothermic H2 adsorption and fragmentation phenomena in order to guess their potential use in processes based on the transformation or production of hydrogen. On the contrary, in the presence of BN-d defects, and for reasons strictly related to local structural changes occurring along with the hydrogen rearrangements on the defective BN fragments, a possible use can be inferred. Precautions must be however taken to decrease the material rigidity that could actually decrease the ability of the BN fragment to flatten. This conversely seems to be a necessary requirement to have strong exothermic effects, following the rearrangements of the H2 molecules.

Nuclear failure, DNA damage, and cell cycle disruption after migration through small pores: a brief review.

In many contexts of development, regeneration, or disease such as cancer, a cell squeezes through a dense tissue or a basement membrane, constricting its nucleus. Here, we describe how the severity of nuclear deformation depends on a nucleus' mechanical properties that are mostly determined by the density of chromatin and by the nuclear lamina. We explain how constriction-induced nuclear deformation affects nuclear contents by causing (i) local density changes in chromatin and (ii) rupture of the nuclear lamina and envelope. Both processes mislocalize diffusible nuclear factors including key DNA repair and regulatory proteins. Importantly, these effects of constricted migration are accompanied by excess DNA damage, marked by phosphorylated histone γH2AX in fixed cells. Rupture has a number of downstream consequences that include a delayed cell cycle-consistent with a damage checkpoint-and modulation of differentiation, both of which are expected to affect migration-dependent processes ranging from wound healing to tumorigenic invasion.

Malocclusion Generates Anxiety-Like Behavior Through a Putative Lateral Habenula-Mesencephalic Trigeminal Nucleus Pathway.

Malocclusion is an important risk factor for temporomandibular disorder (TMD), a series of disorders characterized by dysfunction in the orofacial region involving the temporomandibular joint (TMJ) and jaw muscles. We recently showed that experimental unilateral anterior crossbite (UAC) produced masseter hyperactivity through a circuit involving the periodontal proprioception, trigeminal mesencephalic nucleus (Vme), and trigeminal motor nucleus (Vmo). Anxiety is a common complication in patients with TMD. The lateral habenula (LHb) is involved in emotional modulation and has direct projections to the Vme. Therefore, the present research examined whether UAC facilitates excitatory input from the LHb to the Vme and, subsequently, anxiety-like behaviors in rats. The LHb activation was evaluated by the electrophysiological recording, assessment of vesicular glutamate transporter-2 (VGLUT2) mRNA expression, and measurement of anxiety-like behaviors. The effects of LHb activity on Vme were evaluated by electrophysiological recording from Vme neurons and local changes in VGLUT2 protein density. UAC produced anxiety in modeled rats and increased neuronal activity in the LHb. VGLUT2 mRNA expression was also increased in the LHb. Further, VGLUT2-positive boutons were observed in close apposite upon parvalbumin (PV)-labeled Vme neurons. VGLUT2 protein expression was also increased in the Vme. Significantly, injection of VGLUT2-targeted shRNA into the LHb reduced the expression of VGLUT2 protein in the Vme, attenuated UAC-associated anxiety-like behaviors, and attenuated electrophysiological changes in the Vme neurons. In conclusion, we show that UAC activates the LHb neurons as well as the periodontal proprioceptive pathway to provide excitatory input to the Vme and produce anxiety in rats. These findings provide a rationale for suppressing activity of the LHb to attenuate both the physical and psychological effects of TMD.

Manipulation of the RKKY exchange by voltages

In the last years, electric fields have been used to control the magnetic exchange interactions and anisotropies in nanometric devices. In this paper, we study the spin-spin exchange interaction between two magnetic impurities embedded in a three-dimensional nonrelativistic electron gas, namely the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. The gas is confined in an insulating structure, and an applied voltage produces local changes in the electron density, which modulates the Fermi level of the system. Using a simple model, we demonstrate that this voltage modifies the strength and wavelength of the coupling between the impurities. Depending on the voltage, the effective RKKY exchange can change from a ferro- to an antiferromagnetic coupling, and vice versa. The spin-spin coupling can also be switched on and off by the voltage.

Individual variation in phenotypic plasticity of the stress axis

Phenotypic plasticity-one individual's capacity for phenotypic variation under different environments-is critical for organisms facing fluctuating conditions within their lifetime. North American red squirrels (Tamiasciurus hudsonicus) experience drastic among-year fluctuations in conspecific density. This shapes juvenile competition over vacant territories and overwinter survival. To help young cope with competition at high densities, mothers can increase offspring growth rates via a glucocorticoid-mediated maternal effect. However, this effect is only adaptive under high densities, and faster growth often comes at a cost to longevity. While red squirrels can adjust hormones in response to fluctuating density, the degree to which mothers differ in glucocorticoid plasticity across changing densities remains unknown. Findings from our reaction norm approach revealed significant individual variation not only in a female red squirrel's mean endocrine phenotype but also in endocrine plasticity in response to changes in local density. Future work on proximate and ultimate drivers of variation in endocrine plasticity and maternal effects is needed, particularly in free-living animals experiencing fluctuating environments.

High-resolution tip-enhanced Raman scattering probes sub-molecular density changes

Tip-enhanced Raman spectroscopy (TERS) exhibits new selection rule and sub-nanometer spatial resolution, which is attributed to the plasmonic near-field confinement. Despite recent advances in simulations of TERS spectra under highly confined fields, a simply physical mechanism has remained elusive. In this work we show that single-molecule TERS images can be explained by local sub-molecular density changes induced by the confined near-field during the Raman process. The local sub-molecular density changes determine the spatial resolution in TERS and the gradient-based selection rule. Using this approach we find that the four-fold symmetry of meso-tetrakis(3,5-di-tert-butylphenyl)porphyrin (H2TBPP) TERS images observed in experiments arises from the combination of degenerate normal modes localized in the functional side groups rather than the porphyrin ring as previously considered. As an illustration of the potential of the method, we demonstrate how this new theory can be applied to microscopic structure characterization.

The Comparison of Crowd Counting Algorithms based on Computer Vision

This paper aims to compare the three mainstream solutions for today’s crowd counting and analyze the highlights of each model. In MCNN, they proposed a multi-column parallel convolutional neural network structure that generates population density maps by adapting crowd changes caused by camera view-points and resolution using filters with different size receptive fields. In Switch-CNN, they added a density classifier to the MCNN to enable the use of local density changes in the crowd. In CSRNet, they abandoned the structure of a multi-column convolutional neural network, using the first ten layers of VGG-16 as the front part and the convolutional neural network as the latter part. From the analysis results, CSRNet shows advanced performance. In addition, we analyzed the comparison results of three convolutional neural networks, and derived the trend of convolutional neural network structure.

Synthesis and Spectroscopic Characterization of 2-(het)Aryl Perimidine Derivatives with Enhanced Fluorescence Quantum Yields

Perimidines are a particularly versatile family of heterocyclic compounds, whose properties are exploited in several applications ranging from industrial to medicinal chemistry. The molecular structure of perimidine incorporates a well-known efficient fluorophore, i.e.: 1,8-diaminonaphthalene. The high fluorescence quantum yield shared by most naphthalene derivatives, has enabled their use as stains for bio-imaging and biophysical characterizations. However, fluorescence is dramatically depressed in perimidine as well as in the few of its derivatives analysed so far to this respect. The use of perimidine-like molecules in life sciences might be notably fostered by enhancement of their fluorescence emission. Even more excitingly, the concomitance of both biologically active moieties and a fluorophore in the same molecular structure virtually discloses application of perimidines as drug compounds in state-of-art theranostics protocols. However, somewhat surprisingly, relatively few attempts were made until now in the direction of increasing the performances of perimidines as fluorescent dyes. In this work we present the synthesis and spectroscopic characterization of four perimidine derivatives designed to this aim, two of which result to be endowed with fluorescence quantum yields comparable to 1,8-diaminonaphthalene. A rationalization for such improved behaviour has been attempted employing TD-DFT calculations, which have unravelled the interrelations among bond structure, lone pair conjugation, local electron density changes and fluorescence quantum yield.

Heterogeneous Solvation in Distinctive Protein-Protein Interfaces Revealed by Molecular Dynamics Simulations

Water, despite being a driving force in biochemical processes, has an elusively complex microscopic behavior. While water can increase its local density near amphiphilic protein surfaces, water is also thought to evaporate from hydrophobic surfaces and cavities, an effect known as “dewetting”. The existence and extent of dewetting effects remains elusive due to the difficulty in observing clear “drying” transitions in experiments or simulations. Here, we use explicit solvent molecular dynamics (MD) simulations to study the molecular solvation at the binding interfaces of two distinctive molecular complexes: the highly hydrophilic barnase-barstar and the highly hydrophobic MDM2-p53. Our simulations, in conjunction with simple volumetric analyses, reveal a strikingly different water behavior at the binding interfaces of these two molecular complexes. In both complexes, we observe significant changes in the water local density as the two proteins approach, supporting the existence of a clear dewetting transition in the case of MDM2-p53, with an onset distance of 5.6-7.6Å. Furthermore, the solvation analysis reported herein is a valuable tool to capture and quantify persistent or transient dewetting events in future explicit solvent MD simulations.

Влияние пузырьков газа на вибрационные параметры измерительных трубок кориолисового расходомера

In developing a methodology for measuring the mass flow rates of liquid-gas flows by Coriolis mass flowmeters (CMF), an attempt is made to estimate the effect of the presence of gas bubbles on the observed parameters of the vibrations of the CMF measuring tube. The finite-element model CMF with a straight tube, created in MATLAB package, is presented. The fluid flow is described in the 1D-approximation, the presence of a gas bubble is modeled by a local change in the flux density at the bubble location at a given time (the size of the bubble depends on the size of the finite element). Bending vibrations of the tube are carried out by means of an external harmonic force applied at the center of the tube. The drive frequency is set equal to the modal frequency of the filled tube. A series of numerical experiments has been performed, in which the gas volume fraction (GVF) and the fluid velocity varied. The dependence of the phase shift between the flowmeter arms oscillations caused by the Coriolis effect on these factors has been revealed. The error in determining the mass flow due to the bubbles presence is estimated. A series of experiments has been conducted with an industrial DU15 flowmeter to observe bubble effects. The results of the experiments are compared with the predictions of numerical calculations and their qualitative agreement is found

Influence of electrophysical treatment on oilseed crops structure with Х-ray micro tomography application

Morphological capillary-porous structure analysis of the oilseed materials, using x-ray microtomography in the longitudinal and transverse section and FESEM analysis of the surface microstructure after electrical and microwave treatment presented in current paper. Experimental data were obtained on the basis of the Institute of Materials Research and Engineering (Singapore). Two types of treatment considered: non-thermal pulsed electric field treatment, creating an electroporation effect of the oilseeds structure and microwave treatment. The main characteristic of capillary-porous structure of oil-bearing materials is given. Local changes in the electron density of the oilseed object under study, during the passage of radiation, made it possible to determine clearly the air cavities in the structure of the sunflower nucleus. The influence of a pulsed electric field treatment on the integrity of the structure of oil-cell membranes has been obtained with the creation of a material that has a greater permeability for diffusion processes. Experimentally was determined that over 2500 electric pores were formed on an area of 1 sq.cm as a result of a pulsed electric field treatment. In the case of a pulsed electric field treatment, the oil body material model can be represented as a capillary model with capillary and electroporation radii, thus expanding the model of a bidispersed structure with the addition micro capillaries, formed by an electric field. The data obtained are of interest not only for the technology of processing oilseeds, but also for the analysis methods of new electrophysical treatments.