Regions Of High Concentration Research Articles

In situ experimental study on the synergistic strengthening and toughening mechanisms of multiple pore structures in deer antler

Antler is a kind of natural biological material that is an important weapon for attack and defense and has good strength and excellent toughness. Synchrotron radiation computed tomography technology was adopted in this paper to continuously observe the deformation and failure process of the internal microstructure of antlers during the tensile process. The corresponding full-field strain and evolution of information of the internal structure were quantitatively analyzed combined with digital volume correlation technology. In the experiment, a large quantity of internal canals and lacunae with various shapes and sizes, forming a complex 3D spatial arrangement in antlers, were observed. While realizing the overall lightweight design of the structure, these pore structures can also implement a decrease in local strain concentration and block the long-distance propagation of the high strain concentration region through their cooperation and respective advantages. In addition, there are special high shear strain distribution regions in the antler, which guide the frequent deflection and stepped expansion of cracks, thus playing an important role in the excellent load-bearing capacity and energy dissipation of the antler. These results have positive guiding significance for the lightweight design and performance optimization of artificial porous materials.

High-Sensitivity Grooved CSRR-Based Sensor for Liquid Chemical Characterization

In this work, a new complimentary split ring resonator (CSRR)-based sensor is proposed to sense chemical concentrations. A groove is created in the dielectric ring region of the CSRR to place the hollow tube containing the material under test (MUT). By placing the MUT in the region of high field concentration, higher sensitivity is achieved. The proposed novel and simple design alleviates the requirement of complex fluidic channels and space needed to place the MUT. The fabrication process is also simple with efficient utilization of the sensor’s sensitive region. The CSRR is excited uniquely through a transmission line with periodically placed capacitive gaps in series. By placing the capacitive gaps, effective negative permeability and permittivity are simultaneously achieved, and the structure exhibits metamaterial [composite right/left-handed transmission line (CRLH-TL)] left-handed behavior. Greater coupling of electromagnetic energy from the transmission line to the resonator is achieved by increasing the capacitive gap widths, which renders higher sensitivity. The main sensing parameter is the shift in the frequency of the transmission coefficient notch arising due to the placement of chemicals of varying concentrations throughout the ring region in the hollow tube. The sensor dimension is 4 cm (0.012 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda {g}$ </tex-math></inline-formula> ) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 4 cm (0.012 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda {g}$ </tex-math></inline-formula> ), with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda {g}$ </tex-math></inline-formula> being the guide wavelength. The large sensing bandwidth obtained is 1320 MHz that corresponds to high sensitivity of 14.66 MHz/unit change in concentration and 21.44 MHz/unit change in permittivity. The sensor is cheap and small, and the sensing process is simple offering instantaneous results.

(Invited, Digital Presentation) Evaluation of Polycrystalline-Si1-XGex Thin-Film Transistors Grown Laterally on a Glass Substrate Using a Continuous-Wave Laser

This study aims to understand the performance of continuous-wave laser lateral crystallization (CLC) poly-Si1-xGex TFTs. The transfer characteristics of n-ch CLC poly-Si1-xGex TFTs revealed that the threshold voltages shifted in the positive direction compared with those of CLC poly-Si TFTs with increasing Ge concentration. The characteristics of CLC n-ch poly-Si1-xGex TFTs can be explained by the formation of acceptors. For p-ch TFTs, the transfer characteristics of CLC poly-Si1-xGex TFTs exhibited a larger Ioff than those of CLC poly-Si TFTs. The Ion/Ioff ratio is small for p-ch parallel CLC poly-Si1-xGex TFTs and is weakly dependent on the gate length. In contrast, p-ch perpendicular CLC poly-Si1-xGex TFTs exhibit large Ion/Ioff values for long gate lengths. The variation in the Ion/Ioff ratio of p-ch CLC poly-Si1-xGex TFTs according to the parallel or perpendicular and long or short gate length is explained by Ge segregation along the grain boundary, resulting in the formation of a high-concentration p-type conduction region along the grain boundary, which connects the SD regions.

Magnetic-Field-Assisted Diffusion Motion of Magnetic Skyrmions.

Studies of the diffusion dynamics of magnetic skyrmions have generated widespread interest in both fundamental physics and spintronics applications. Here we report the magnetic-field-assisted diffusion motion of skyrmions in a microstructured chiral FeGe magnet. We demonstrate the enhancement of diffusion motion of magnetic skyrmions that is manipulated and driven by an oscillatory magnetic field. Further, the directed diffusion of skyrmions is observed when an in-plane field was introduced to break the symmetry of the system. Finally, we demonstrate the application of a magnetic field can induce an arrangements transition of skyrmions assemble in microstructure, that is, from a stiff hexagonal lattice to a weak interactional isotropic state. By using a step-ascended magnetic field we finished the observation of a particle-like diffusive motion for magnetic skyrmions that transport from high-concentration regions to low-concentration regions and the diffusion flux is proportional to the concentration gradient followed Fick's law.

SPECT imaging of 226Ac as a theranostic isotope for 225Ac radiopharmaceutical development

Objective. The development of alpha-emitting radiopharmaceuticals using 225Ac (t ½ = 9.92 d) benefits from the quantitative determination of its biodistribution and is not always easy to directly measure. An element-equivalent matched-pair would allow for more accurate biodistribution and dosimetry estimates. 226Ac (t ½ = 29.4 h) is a candidate isotope for in vivo imaging of preclinical 225Ac radiopharmaceuticals, given its 158 keV and 230 keV gamma emissions making it suitable for quantitative SPECT imaging. This work aimed to conduct a performance assessment for 226Ac imaging and presents the first-ever 226Ac SPECT images. Approach. To establish imaging performance with regards to contrast and noise, image quality phantoms were scanned using a microSPECT/CT system. To assess the resolution, a hot rod phantom with cylindrical rods with diameters between 0.85 and 1.70 mm was additionally imaged. Two collimators were evaluated: a high-energy ultra-high resolution (HEUHR) collimator and an extra ultra-high sensitivity (UHS) collimator. Images were reconstructed from two distinct photopeaks at 158 keV and 230 keV. Main results. The HEUHR SPECT image measurements of high activity concentration regions were consistent with values determined independently via gamma spectroscopy, within 9% error. The lower energy 158 keV photopeak images demonstrated slightly better contrast recovery. In the resolution phantom, the UHS collimator only resolved rods ≥1.30 mm and ≥1.50 mm for the 158 keV and 230 keV photopeaks, respectively, while the HEUHR collimator clearly resolved all rods, with resolution <0.85 mm. Significance. Overall, the feasibility of preclinical imaging with 226Ac was demonstrated with quantitative SPECT imaging achieved for both its 158 keV and 230 keV photopeaks. The HEUHR collimator is recommended for imaging 226Ac activity distributions in small animals due to its resolution <0.85 mm. Future work will explore the feasibility of using 226Ac both as an element-equivalent isotope for 225Ac radiopharmaceuticals, or as a standalone therapeutic isotope.

Resistive Switching of Self‐Assembled Silver Nanowire Networks Governed by Environmental Conditions

AbstractPercolating networks formed by coated metallic nanowires have recently shown to exhibit memristive properties, opening a path for the development of neuromorphic systems. In this work, the resistive switching phenomena occurring in percolative networks of silver nanowires (AgNWs) coated with a thin layer of polyvinylpyrrolidone is studied. By performing voltage‐driven excursions, the highly‐conductive pristine state irreversibly changes to a higher resistance state. Such an electroforming procedure enables the switching among multiple resistance states. The stability and controllability of the resistance levels are found to be highly dependent on the initial state and the environmental conditions. In low relative humidity environments, the system displays the most controlled switching operation, while in high humidity environments the system shows a high conductance level. Samples with hysteretic response display sharp and spontaneous transitions to different resistance states, exhibiting multilevel memory device features. Both behaviors can be associated with regions of high local concentration of AgNWs that can couple or decouple from the conduction paths according to external stimuli. Conductivity is determined at a fundamental level by electrochemical processes at critical junctions in which water molecules play a key role. These results are relevant for the development of AgNWs‐based electronics and in‐hardware neuromorphic computing.

Gas-Solid Flow and High-Efficiency and Low-NO x Combustion of a Novel Arch-Fired Boiler with Swirl Burners: Impact of Over-Fire Air

ABSTRACT For a 300 MWe anthracite- and arch-fired boiler with biased-swirling-secondary-air (BSSA) technology, the distribution law of gas/solid two-phase velocity in the furnace is obtained with the help of a 1:10 cold modeling experiment bench, and the combustion and NO x formation characteristics in the furnace are revealed by numerical calculation. The results show that, with the increase of over-fire air rate, the reflux velocity in the reflux zone under the arch decreases continuously, and when the main air flow from the furnace arch reaches the staged air region from the vent air region, the position of particle flow in the primary air turn upward is advanced, and the utilization rate of the space in the lower furnace will decrease continuously. In the regions of vent air and staged air, when the over-fire air rate increases from 15% to 25%, the maximum vertical velocity decreases by approximately 2 times, and the downward depth of air flow from the furnace arch decreases significantly. When the over-fire air rate is increased from 10% to 25%, the thermal resistance between the primary air of the burner and the high-temperature flue gas in the furnace center increases, the ignition of the primary pulverized coal air flow is advanced, the flue gas temperature in the center of the lower furnace is decreased. As a result, with the increase of over-fire air rate, the combustible content of fly ash increases continuously. Especially, when the over-fire air rate increases from 20% to 25%, the combustible content of fly ash increases significantly. With the increase of the over-fire air rate, the high CO concentration region in the primary combustion zone expands, the reducing atmosphere is strengthened, the formation of NO x is effectively restrained, and the NO x emission concentration at the furnace outlet continues to decreases. In particular, when the over-fire air rate increases from 15% to 20%, the NO x emission concentration decreases greatly. After the swirling secondary air of the arch-fired boiler is biased, the setting of over-fire air rate is recommended to be 20%, and the NO x emission concentration and combustible content of fly ash are 694 mg/m3(O2 = 6%) and 7.32%, respectively. Compared with a traditional swirling arch-fired boiler, the combustible content of fly ash and NO x emission concentration are reduced by 46.8% and 34.1%, respectively.

Structure of propagating high-stress fronts in a shear-thickening suspension

We report direct measurements of spatially resolved stress at the boundary of a shear-thickening cornstarch suspension revealing persistent regions of high local stress propagating in the flow direction at the speed of the top boundary. The persistence of these propagating fronts enables precise measurements of their structure, including the profile of boundary stress measured by boundary stress microscopy (BSM) and the nonaffine velocity of particles at the bottom boundary of the suspension measured by particle image velocimetry (PIV). In addition, we directly measure the relative flow between the particle phase and the suspending fluid (fluid migration) and find the migration is highly localized to the fronts and changes direction across the front, indicating that the fronts are composed of a localized region of high dilatant pressure and low particle concentration. The magnitude of the flow indicates that the pore pressure difference driving the fluid migration is comparable to the critical shear stress for the onset of shear thickening. The propagating fronts fully account for the increase in viscosity with applied stress reported by the rheometer and are consistent with the existence of a stable jammed region in contact with one boundary of the system that generates a propagating network of percolated frictional contacts spanning the gap between the rheometer plates and producing strong localized dilatant pressure.

Shift of charge inversion point of a trivalent ion solution in a nanofluidic channel

Understanding the surface properties and related liquid properties in 102 nm spaces (extended nanospaces) is critical for future device engineering. To this end, we used trivalent ions to investigate the charge inversion phenomenon in extended nanospaces. The charge inversion points in bulk didn't substantially differ between a La(NO3)3 solution and a Lu(NO3)3 solution. However, the charge inversion point of a La(NO3)3 solution in extended nanochannels shifted toward the higher-concentration region. The conductivity measurement results suggested a negatively charged surface in the extended nanospaces in the La(NO3)3 solution, consistent with the zeta-potential results. In addition, a much increase in the 1/T1 of the La(NO3)3 solution was shown compared with that of the bulk. We report a new finding that different trivalent ions exhibit different adsorption properties but only in extended nanospaces, not in bulk. We expect our results to contribute to the basic science to understand the liquid properties in nanospaces.

Third revision of the global surface seawater dimethyl sulfide climatology (DMS-Rev3)

Abstract. This paper presents an updated estimation of the bottom-up global surface seawater dimethyl sulfide (DMS) climatology. This update, called DMS-Rev3, is the third of its kind and includes five significant changes from the last climatology, L11 (Lana et al., 2011), that was released about a decade ago. The first change is the inclusion of new observations that have become available over the last decade, creating a database of 873 539 observations leading to an ∼ 18-fold increase in raw data as compared to the last estimation. The second is significant improvements in data handling, processing, and filtering, to avoid biases due to different observation frequencies which result from different measurement techniques. Thirdly, we incorporate the dynamic seasonal changes observed in the geographic boundaries of the ocean biogeochemical provinces. The fourth change involves the refinement of the interpolation algorithm used to fill in the missing data. Lastly, an upgraded smoothing algorithm based on observed DMS variability length scales (VLS) helps to reproduce a more realistic distribution of the DMS concentration data. The results show that DMS-Rev3 estimates the global annual mean DMS concentration to be ∼ 2.26 nM (2.39 nM without a sea-ice mask), i.e., about 4 % lower than the previous bottom-up L11 climatology. However, significant regional differences of more than 100 % as compared to L11 are observed. The global sea-to-air flux of DMS is estimated at ∼ 27.1 TgS yr−1, which is about 4 % lower than L11, although, like the DMS distribution, large regional differences were observed. The largest changes are observed in high concentration regions such as the polar oceans, although oceanic regions that were under-sampled in the past also show large differences between revisions of the climatology. Finally, DMS-Rev3 reduces the previously observed patchiness in high productivity regions. The new climatology, along with the algorithm, can be found in the online repository: https://doi.org/10.17632/hyn62spny2.1 (Mahajan, 2021).

Modeling the diffusion of flammable hydrogen cloud under different liquid hydrogen leakage conditions in a hydrogen refueling station

Constructing hydrogen refueling stations will be popular for hydrogen energy use in the future, and investigating the diffusion characteristics of hydrogen in a leakage incident is quite significant. The instantaneous evolution of flammable hydrogen clouds arising from liquid hydrogen leakage in a hydrogen refueling station is predicted using Ansys Fluent, and parametric analyses are conducted to reveal the effects of storage pressure, source height, and leakage direction on the distributions of the flammable regions. In addition, the feasibilities of heating the ceiling or the ground of the station after the leakage of liquid hydrogen to accelerate the hydrogen dilution are examined. The results show that the flammable region is stabilized at 90 s, the corresponding flammable hydrogen cloud volume is about 333 m3, and the extensions of downwind and vertical directions reach 10 m and 9.3 m. Storage pressure has a finite effect on the downwind diffusion distance of the flammable cloud. A lower source height tends to format the high-concentration hydrogen cloud near the ground while a higher source height helps separate the flammable clouds from the ground. The upward leakage direction leads to the maximum downwind diffusion distance of about 10.2 m while the downward leakage direction makes the high hydrogen concentration region confined below the ceiling. Just maintaining the ceiling at the initial temperature of 300 K is effective for accelerating the hydrogen dilution in the upward leakage. The maximum hydrogen concentration and the flammable volume can be reduced at rates of 0.35 vol % and 8% for every 50 K increase in heating temperature. For the downward leakage, keeping the ground at the initial temperature just works for the first 40 s in reducing the maximum hydrogen concentration, while increasing the heating temperature receives a gradually declined effect on reducing the flammable volume.

Dispersion medium crystallization effect on the magnetic susceptibility of ferrofluids

Ferrofluids (magnetic colloids) with a dispersion medium crystallizing with a decrease in temperature are investigated. Temperature dependences of the dynamic magnetic susceptibility of such ferrofluids were measured. For comparison, similar susceptibility dependences of ferrofluids with a dispersion medium that does not form a crystalline structure when solidified by cooling are also presented. It is demonstrated that crystallization of the dispersion medium leads to an inhomogeneous spatial distribution of dispersed phase particles and the formation of regions of high particle concentration. This does not happen in the case of colloids with a dispersion medium that does not form a crystalline structure. It is concluded that the formation of regions of high concentrations of dispersed phase particles during crystallization is the cause for a jump in colloid magnetic susceptibility. This conclusion refutes the previously existing opinion that the reason for the jump in the susceptibility of a ferrofluid at the temperature of transition to a solid state is the blocking of Brownian degrees of freedom of particles.

Shear properties and water connectivity of wet granules at high solid content concentration

The inner liquid distribution in wet granules strongly influences their mechanical properties. In this study, we examined the shear properties (internal friction angle, cohesion, storage modulus and loss modulus) of wet granules composed of graphite particles and water, and determined their inner water connectivity using X-ray refraction contrast imaging computed tomography (CT) to elucidate their correlation. At high solid content concentration (CSC) region (CSC = 85 wt.%), internal friction angle of wet granules was slightly lower than that of wet granules with lower CSC, and their cohesion becomes almost zero. Furthermore, storage modulus of wet granules at CSC = 85 wt.% was the highest among all wet granules. The X-ray CT and scanning electron microscopy (SEM) observations revealed that the water connectivity in the wet granules was in the pendular state and graphite particles fractured under shear test at CSC = 85 wt.%. From these results, it can be concluded that lower shear cohesion at CSC = 85 wt.% is caused by an increase in the number of isolated liquid bridges, and particle fracture results in a decrease in the internal friction angle owing to decreasing roughness of shear plane. Furthermore, the particle fracture also resulted in the higher storage modulus at CSC = 85 wt.% in rheological measurements.

Numerical simulation of quantum dots as a buffer layer in CIGS solar cells: a comparative study

Quantum bandgap buffer layers can improve sunlight absorption in the short wavelength region, hence improving the performance of CIGS solar cells. In this study, we use numerical modelling to determine the impact of various buffer layers' electrical characteristics on the performance of CIGS thin film photovoltaic devices, particularly, carrier concentration and the quantum effect. As well Ag2S buffer layer has been experimentally examined to fulfilment its effect in term of bulk and quantum bandgap. Experimental results depicted that, Ag2S QDs has polycrystalline nature of films, with smooth surface roughness, and average diameter 4 nm. Meanwhile, a simulation revealed that the Fermi level of the (n-buffer layer) material shifts closer to the conduction band with an increase in carrier concentration. The findings indicate that, a buffer layer with a wider bandgap and carrier concentration is an essential demand for achieving a device with a higher conversion efficiency and a broader bandgap-CBO window. It was attributed to beneficial synergistic effects of high carrier concentration and narrower depletion region, which enable carriers to overcome high CBO barrier. Most importantly, modelling results indicate that the optic-electrical characteristics of the buffer layer are critical in determining the progress of a CIGS solar cell.

Incorporating vascular-stasis based blood perfusion to evaluate the thermal signatures of cell-death using modified Arrhenius equation with regeneration of living tissues during nanoparticle-assisted thermal therapy

Cellular and biological tissue heating may result in reversible (or repairable injury) and irreversible (or lethal) thermal cell-death in living biological tissues. Continuous regeneration of living human tissues due to the continuous supply of oxygen through arterial blood must be taken into account to counter balance the thermal degradation at quasi-static thermal conditions. This study incorporates vascular-stasis based non-linear blood perfusion for magnetic nanoparticle assisted thermal therapy to model the thermal by-stander effect - a hyperthermia-induced deep infiltration of nanoparticles in the targeted tissue domain. Pennes bioheat model based on Fourier heat conduction theory is four-way coupled with Arrhenius and non-Arrhenius kinetic models of cell-death with healthy cells regeneration. In determination of treatment endpoint, the kinetic model must be coupled with quantitative and qualitative pathological biomarkers of thermal damage. Nanoparticle distribution volume increases by 39.62% after possible rupturing of cell membrane during heating. The release of intracellular solution by dead cells during heating promotes nanoparticle migration from the region of higher concentration to the regions of lower concentration thereby 80% enhancement in interstitial space and five-fold increase in diffusion coefficient. For such redistribution phenomenon, the heating time is sufficient to reduce the oxygen in erythrocytes (red blood cells) and maximize the necrosis zone inside tumour. However, at the interface, the regeneration of healthy cells triggers an immune response of biological tissue towards continued heating to suppress, prevent and restrict further accumulation of thermal damage within damage bounds of Ω ≤ 1. While modelling the kinetics of thermal damage of tumour, one must include and should not ignore the partial self-regeneration of connecting normal human tissues at the tumour periphery due to continuous matching of oxygen demands in the healthy tissue by the arterial blood.

Modification of lithium electrodeposition behavior by variation of electrode distance

Developing a better understanding and control over the lithium electrodeposition behavior will assist with the commercial application of lithium metal anodes for rechargeable batteries. Despite intensive research over the past decade, our understanding of the deposition of lithium is limited. Here a new observation on the effect of distance between the working electrode and the counter electrode for electrochemical lithium deposition behavior is reported. From this fundamental investigation of distance, the high lithium ion concentration regions formed by release of lithium ions from the counter electrode modify the lithium deposition behavior on the working electrode, resulting in the generation of non-uniform lithium dendrites with a thick diversely composed surface film. Alternatively, increasing the distance between the electrodes results in the deposition of a spherical lithium morphology with a thin LiF rich surface film. This fundamental study provides a deeper understanding of correlation between lithium deposition behavior and electrode separation and provides insight to inhibit lithium dendrite formation.

Cathodoluminescence Study of m‐Plane α‐Ga2O3 Grown by Mist Chemical Vapor Deposition

The cathodoluminescence (CL) properties of m‐plane α‐Ga2O3 grown by mist chemical vapor deposition are investigated. The m‐plane α‐Ga2O3 is found to have two types of characteristic luminescence bands: blue luminescence (BL) band (centered at 2.8 eV) and UV luminescence (UVL) band (centered at 3.7 eV). To characterize these bands, the Sn concentration and temperature dependences of the CL spectra are investigated using samples with varying Sn concentrations from 1 × 1017 to 1 × 1019 cm−3. The Sn concentration‐dependent CL spectra show that the luminescence from the UVL band is dominant in the low Sn concentration region, while that from the BL band is dominant in the high Sn concentration region. The temperature‐dependent CL spectra indicate that the peak intensity of the UVL band depending on temperature is larger than that of the BL band. The activation energies in the UVL band of the undoped and lightly Sn‐doped samples are determined as 110 meV. In addition, the parameters of the Huang–Rhys factor in the UVL band are obtained as 28.6 and 18.8, respectively. These results strongly suggest that the UVL band is derived from self‐trapped excitons, which is the recombination of free electrons and self‐trapped holes.

Pilot groundwater radon mapping and the assessment of health risk from heavy metals in drinking water of southwest, Nigeria

Radon and heavy metals are sources of groundwater pollution and are identified as potential carcinogens. Southwest Nigeria's populace mostly relies on groundwater source for drinking. This study aims to map radon distribution in groundwater of southwest Nigeria and to determine the health risk of radon and heavy metal in drinking water. Radon concentrations of 145 groundwater samples were measured using RAD7 electronic radon detector and heavy metal concentrations of 52 groundwater samples were measured using atomic absorption spectrophotometer. Radon concentration distributions were delineated using geographical information system. Radon concentration of water samples ranges between 1.6 Bq l−1 and 271 Bq l−1 with an average value of 35.9 ± 38.4 Bq l−1. The average groundwater radon concentration is higher than US-EPA recommended level of 11.1 Bq l−1 but lower than the WHO recommended limit of 100 Bq l−1. The estimated average annual effective radiation doses to infants, children, and adults are 29 μSvy−1, 41 μSvy−1 and 92 μSvy−1 respectively. The radon distribution map of the study area reveals regions of high, medium, and low groundwater radon concentrations. The average concentration values of heavy metals in groundwater samples are of the order Mn > Zn > Pb > Cu > Cr > Ni > Cd. 84% of groundwater exhibits good to excellent quality in terms of heavy metal pollution. However, about 16% of the samples which lie in the sedimentary regions of Ogun and Lagos States exhibit poor to very poor quality. Overall, ingestion of groundwater in the study area may not pose a serious health hazards from radon ingestion and heavy metal toxicity.

Front speed and pattern selection of a propagating chemical front in an active fluid.

Spontaneous pattern formation in living systems is driven by reaction-diffusion chemistry and active mechanics. The feedback between chemical and mechanical forces is often essential to robust pattern formation, yet it remains poorly understood in general. In this analytical and numerical paper, we study an experimentally motivated minimal model of coupling between reaction-diffusion and active matter: a propagating front of an autocatalytic and stress-generating species. In the absence of activity, the front is described by the well-studied Kolmogorov, Petrovsky, and Piskunov equation. We find that front propagation is maintained even in active systems, with crucial differences: an extensile stress increases the front speed beyond a critical magnitude of the stress, while a contractile stress has no effect on the front speed but can generate a periodic instability in the high-concentration region behind the front. We expect our results to be useful in interpreting pattern formation in active systems with mechanochemical coupling in vivo and in vitro.

The Modeling of the Fracture of Three-Phase Ceramic Composite

In the present study, elastic and strength properties of three-phase Al2O3–ZrB2–SiC composite are investigated based on numerical modeling. Representative volume element (RVE) consisting of Al2O3 matrix, pores, and ZrB2 and SiC inclusions is built based on the experimental data. The uniaxial tension loading of the RVE model under plane strain conditions is considered. The relations of an isotropic elastic-plastic medium with the Drucker–Prager yield criterion are used as constitutive equations. The determination of the effective mechanical properties of the composite is based on the analysis of numerical averaged stress-strain curves. The simulation results demonstrate that the cracks nucleate in the regions of high stress concentration caused by the pore shape. The alumina matrix fractures due to the criterion based on the tensile pressure, while the fracture of inclusions occurs when the criterion based on the accumulated inelastic strain is fulfilled. The influence of the fraction of SiC inclusions on the effective elastic properties of the composite material was studied. It was shown that the elastic moduli weakly depend on the increase of SiC volume fraction in the considered range from 0 % to 34 %.