Local Voids Research Articles

Structural concrete measurements: New distributed approach for standard specimens

Concrete structures are widely used in construction because of their many advantages, including high corrosion resistance, durability, low operating costs, and the ability to design any geometry. However, they also have some disadvantages, such as their high dead weight and susceptibility to cracking. Although this material is widely used globally, new types of concrete, such as high-strength or lightweight aggregate-based, are still being developed. This requires constant control and testing in both laboratory and field conditions. Concrete is a heterogeneous material due to the influence of aggregate grains and local discontinuities, voids or pores. Given these characteristics, it is clear that most conventional diagnostic solutions, such as spot foil strain gauges or extensometers, are unable to accurately analyse these localised effects as they average local strains over the measurement base. In contrast, distributed fibre optic sensing (DFOS) enables strain readings to be taken with millimetre geometric resolution, significantly extending the structural assessment capability. The article describes research on standard concrete cylinders equipped with surface-mounted optical fibres for simultaneous measurements of distributed strains in both the longitudinal direction (compression zone) and circumference direction (tension zone). The novelty of the proposed approach, apart from the way of arranging the sensing fibres on the specimens, lies mainly in the new diagnostic approach that allow (1) the evaluation of the homogeneity of the concrete using statistical parameters, (2) the identification of microcracking and (3) the identification of near-to-failure state based on Poisson’s ratio analysis. Twenty cylindrical specimens were laboratory tested using reference techniques to validate the performance of the DFOS-based system and to provide data for statistical evaluation. The results indicate the possibility of detecting the approaching damage even without knowledge of the material properties of the specimen or the initial stress level at the moment of starting the measurements. The discussion also covered future research directions and potential improvements.

Interfacial competing interaction eliminates voids in the buried interface for efficient and stable perovskite solar modules on bare NiOX

Perovskite solar cells (PSCs) with impressive efficiency is promising for commercialization. However, when scaling up PSCs to large-area perovskite solar modules (PSMs), the rapid degradation of performance and stability still remains a grand challenge. One of the main causes of the degradation is the presence of local voids in the buried interface for large-area films, which we find could be attributed to the unbalanced interfacial interaction between precursor solvent and substrate. Here we improve a scalable and low-temperature sequential two-step chemical bath deposition process aiming for high quality NiOX. Further with the modulation of A-site cations to enhance the interaction between DMSO and perovskite precursor, the potential for DMSO absorbing on the NiOX could be eliminated. This strategy can inhibit the delay movement of DMSO on NiOX and improve the buried interfacial quality, with compact morphology and absent of voids. The inverted structured PSCs and PSMs based on the bare NiOX and modified perovskite precursor reach a champion efficiency of 22.40% and 19.09%, respectively, which are both among the highest reported values. The highly efficient PSMs also exhibit a long-term operational stability, which retain 84% of the initial performance after 1056 h operating under one-sun illumination.

Scratching the surface of urban change: Art collectives as public entrepreneurs

This article examines art collectives in Venice that use their artistic and cultural projects to act as public entrepreneurs seeking to improve urban welfare and elicit social change for reasons of societal betterment. These ventures are developed against a backdrop of ongoing socio-economic challenges arising from exploitative tourism in the city. Interviews with some art collective members revealed that: (1) their local rootedness is shaped by issues of gentrification and a search for a city that benefits all; (2) their core values are translated into artistic propositions addressing local demands and institutional voids and (3) their private goals have a public-service background. Our study unveils a unique type of entrepreneur that mediates local demands but has no significant impact at the policy level, thus only scratching the surface of institutional change. This insight contributes to our understanding of artists as public entrepreneurs who, despite their use of activist language channelling public demands, are constrained by the very institutional voids they seek to close.

Experimental Study on the Diffusion Law of Coal-Based Solid Waste Slurry with Grouting Filling in the Gangue Voids of the Caving Zone.

Due to the concealment of the caving zone, it is difficult to detect and grasp the diffusion law of the slurry in the voids of the gangue pile. On the preparation of reasonable grouting filling materials, a large-scale three-dimensional gangue grouting filling test system has been established to detect the slurry pressure and resistivity inside the gangue pile and analyze the flow pattern of the slurry in the voids of the gangue pile. The research results show that the slump and bleeding rate of the filling slurry are significantly reduced with the increase of the fly ash content. The optimal ratio of fly ash, coal gangue, and gasification slag is 7:2:1, with a mass fraction of 72%. In the process of grouting, the internal pressure of the gangue pile can be divided into the initial stable stage, the step growth stage, and the pressure stability stage, and the change curve of the pressure sensor at the lower level is similar. The resistance value of the original broken gangue in the experiment is approximately 1600 Ω. Grouting filling forms a slurry-rock mixture, and its resistance continuously decreases with the stable injection of the slurry (minimum value 150 Ω). It is determined that the slurry near the grouting hole mainly diffuses longitudinally with a good void filling effect. The void channels of slurry diffusion are randomly distributed and have different shapes, which hinder slurry flow and diffusion. Slurry particles accumulate and settle at local small voids. Meanwhile, the surface of the gangue blocks is dry, and the slurry absorbs part of the water during diffusion, resulting in the increase of the slurry concentration and the weakening of the lateral diffusion ability. Secondary or multiple grouting can effectively fill the void of the broken gangue and further improve the filling effect.

Simulating the LOcal Web (SLOW)

Context. Several observations of the Local Universe point toward the existence of very prominent structures: massive galaxy clusters and local superclusters on the one hand, but also large local voids and underdensities on the other. However, it is highly nontrivial to connect such different observational selected tracers to the underlying dark matter (DM) distribution. Aims. Therefore, constructing mock catalogs of such observable tracers using cosmological hydrodynamics simulations is needed. These simulations have to follow galaxy formation physics and also have to be constrained to reproduce the Local Universe. Such constraints should be based on observables that directly probe the full underlying gravitational field, such as the observed peculiar velocity field, to provide an independent test on the robustness of these distinctive structures. Methods. We used a 500 h−1 Mpc constrained simulation of the Local Universe to investigate the anomalies in the local density field, as found in observations. Constructing the initial conditions based on peculiar velocities derived from the CosmicFlows-2 catalog makes the predictions of the simulations completely independent from the distribution of the observed tracer population, and following galaxy formation physics directly in the hydrodynamics simulations also allows the comparison to be based directly on the stellar masses of galaxies or X-ray luminosity of clusters. We also used the 2668 h−1 Mpc large cosmological box from the Magneticum simulations to evaluate the frequency of finding such anomalies in random patches within simulations. Results. We demonstrate that halos and galaxies in our constrained simulation trace the local dark matter density field very differently. Thus, this simulation reproduces the observed 50% underdensity of galaxy clusters and groups within the sphere of ≈100 Mpc when applying the same mass or X-ray luminosity limit used in the observed cluster sample (CLASSIX), which is consistent with a ≈1.5σ feature. At the same time, the simulation reproduces the observed overdensity of massive galaxy clusters within the same sphere, which on its own also corresponds to a ≈1.5σ feature. Interestingly, we find that only 44 out of 15 635 random realizations (i.e., 0.28%) match both anomalies, thus making the Local Universe a ≈3σ environment. We finally compared a mock galaxy catalog with the observed distribution of galaxies in the Local Universe, finding a match to the observed factor of 2 overdensity at ∼16 Mpc as well as the observed 15% underdensity at ∼40 Mpc. Conclusions. Constrained simulations of the Local Universe which reproduce the main features of the local density field open a new window for local field cosmology, where the imprint of the specific density field and the impact on the bias through the observational specific tracers can be investigated in detail.

Superpixel-based change detection for GPR time-lapse slices using fuzzy c-means and the Markov random field method

Ageing and complex underground utility infrastructure present a significant challenge for modern society, requiring long-term monitoring and maintenance to prevent economic and social costs associated with infrastructure degradation and failure. In this study, we proposed an unsupervised superpixel-based change-detection method using ground-penetrating radar time-lapse slices combining fuzzy c-means and the Markov random field model to investigate an invisible subsurface change due to buried void using time-series measurements. First, simple linear iterative clustering was applied to the difference image, which was generated using paired time-lapse images after intensity registration to create different scales superpixel maps. Then, fuzzy c-means clustering was used to generate superpixel-based change maps. Finally, the Markov random field model was used to integrate the information of adjacent neighbourhoods in three dimensions to iteratively refine the change map. We designed two underground cavities (one representing shallow local voids and the other representing voids near pipeline networks) to verify the capability and adaptability of the proposed method. The experimental results demonstrate the feasibility of the method, with F1-scores of 0.82, 0.69, 0.69, and 0.65 and kappa coefficients of 0.81, 0.69, 0.68, and 0.64. Our method represents a significant contribution to the field of GPR-based change detection and has the potential to improve the long-term monitoring and maintenance of complex underground utility infrastructure.

Effects of salt and ash deposits on corrosion behaviour of Ni-25Cr in Ar-60CO2-20H2O gas at 650 oC

ABSTRACT A Ni-25Cr (wt.%) alloy coated with the salts and mixtures of these salts with an industrial coal ash was exposed to Ar-60CO2-20 H2O at 650 °C for 300 h. The alloy without any deposit developed a uniform internal oxidation zone (IOZ) and an external metallic nickel layer surmounted by a thin NiO scale. Salt deposits changed the scale constituents and morphology. Predominantly, a duplex scale of NiO over a Cr2O3 layer grew with an underlying IOZ containing large Cr-rich oxide precipitates. Under a deposit of ash plus salts, the basic reaction morphology was the same as in the gas-only case, but the oxide layer was non-uniform. Local voids were formed within the alloy beneath chloride plus ash deposits. Under ash with sulphates, the alloy formed both partially protected areas and non-protective multi-layered scales. Spherical ash particles were enveloped by NiO in both salt-ash deposits.

Sociology and hierarchy of voids: A study of seven nearby CAVITY galaxy voids and their dynamical CosmicFlows-3 environment

Context. The present study addresses a key question related to our understanding of the relation between void galaxies and their environment: the relationship between luminous and dark matter in and around voids. Aims. To explore the extent to which local Universe voids are empty of matter, we study the full (dark+luminous) matter content of seven nearby cosmic voids that are fully contained within the CosmicFlows-3 volume. Methods. We obtained the matter-density profiles of seven cosmic voids using two independent methods. These were built from the galaxy redshift space two-point correlation function in conjunction with peculiar velocity gradients from the CosmicFlows-3 dataset. Results. The results are striking, because when the redshift survey is used, all voids show a radial positive gradient of galaxies, while based on the dynamical analysis, only three of these voids display a clear underdensity of matter in their center. Conclusions. This work constitutes the most detailed observational analysis of voids conducted so far, and shows that void emptiness should be derived from dynamical information. From this limited study, the Hercules void appears to be the best candidate for a local Universe pure “pristine volume”, expanding in three directions with no dark matter located in that void.

Features of structural assessment of long life mine shafts

The issues of restoration and reconstruction of mine shafts become of increasingly higher concern these days. Timely accomplishment and complex safety are the first-order conditions of the successful project implementation. The existing regulatory documents in this sphere are inexhaustive. In this respect, and integrated approach is proposed, including geophysical investigation of shaft siding areas, experimental estimation of load-bearing capacity of support systems, experimental computations using 3D finite element method, as well as the analysis and prediction of structural reliability. The authors exemplify implementation of the complex approach. The GRP measurements and seismic research in some shafts revealed long intervals of fractured rocks and damaged rock/lining interface zones, as well as local voids in the space behind the lining. These data were used to adjust mathematical models with the identification of local zones in the fractured shaft side rock mass with low deformation characteristics, and some series of calculations were performed. In the test area of a mine shaft, the calculations and the in-situ measurements of stresses and deformations agreed sufficiently. The authors highlight that the research-based data array enables better reasoned decision-making on design, construction and technology at integrated safety and enhanced efficiency of operations. Moreover, understanding of the actual condition of the shaft lining and adjacent rock mass can help avoid causeless repair which decreases load-bearing capacity of shaft support down to extreme values in the short run, and continually ends with incidents and large accidents in actual practice.

Effect of tension on the formation of local voids and integral damages in DC04 steel sheets

Effect of tension on the formation of local voids and integral damages in DC04 steel sheets

The Influence of Structural and Materials on Bridge Stability and Stabilization Measures

Bridges are now not only an auxiliary tool for travel, but it is also an important way to measure a country's comprehensive strength. Because the stability of a bridge structure is affected by a variety of professional knowledge and various aids which made by advanced technology. So whether the bridge is stable and how to be more stable are the focus of discussion. This paper mainly analyzes and summarizes the stability of the bridge from the perspective of influencing factors and structural principles, and puts forward some measures which could improve stability accordingly. It includes the most common natural factors: earthquake and flood, which need to be considered from different perspectives due to their different failure principles and structures. As for the bridge structure itself, its upper and lower structures have cracks or lack bearing capacity, resulting in uneven settlement of the foundation. The sliding and tilting of the foundation and the local voids in the foundation are all factors that endanger the stability of the bridge. As for the effects of cracks, freeze-thaw denudation, scouring and grinding, cavitation erosion, water erosion, weathering and denudation of materials, they should be considered as important factors. Moreover, the improvement of the existing technology, such as strengthening the anti-corrosion layer, waterproof layer and protective layer, are also important.

Interplay of Dynamic Constriction and Interface Morphology between Reversible Metal Anode and Solid Electrolyte in Solid State Batteries.

In an all-solid-state battery, the electrical contact between its individual components is of key relevance in addition to the electrochemical stability of its interfaces. Impedance spectroscopy is particularly suited for the non-destructive investigation of interfaces and of their stability under load. Establishing a valid correlation between microscopic processes and the macroscopic impedance signal, however, is challenging and prone to errors. Here, we use a 3D electric network model to systematically investigate the effect of various electrode/sample interface morphologies on the impedance spectrum. It is demonstrated that the interface impedance generally results from a charge transfer step and a geometric constriction contribution. The weights of both signals depend strongly on the material parameters as well as on the interface morphology. Dynamic constriction results from a non-ideal local contact, e.g., from pores or voids, which reduce the electrochemical active surface area only in a certain frequency range. Constriction effects dominate the interface behavior for systems with small charge transfer resistance like garnet-type solid electrolytes in contact with a lithium metal electrode. An in-depth analysis of the origin and the characteristics of the constriction phenomenon and their dependence on the interface morphology is conducted. The discussion of the constriction effect provides further insight into the processes at the microscopic level, which are, e.g., relevant in the case of reversible metal anodes.

Void states perspective for critical hydraulic gradient of internally unstable non-cohesive soils

The critical hydraulic gradient ([Formula: see text]) for internally unstable soils is observed to be significantly less than the [Formula: see text] given by Terzaghi's classical equation. The difference is due to the uneven stress contributions by fine and coarse fractions of internally unstable soils, and thus an empirical stress reduction factor ([Formula: see text]) was considered for [Formula: see text] predictions. Internally unstable soils are coarse fraction dominant with a void ratio of the fine fraction higher than the void ratio of overall internally unstable soil. The differential stress states lead to washout of the fines from the local voids of the coarse fraction at a hydraulic gradient of less than the [Formula: see text] given by the classical equation. This study presents a theoretical approach for predicting [Formula: see text] based on the notion of the effective stress of the fine fraction within the voids of a coarse fraction being equal to zero for internally unstable soils. A comparison of predicted [Formula: see text] based on the proposed approach and experimental observations obtained from the literature and the current study has demonstrated the validity of the proposed approach. The applicability of the proposed approach is also illustrated for the estimation of a critical hydromechanical envelope.

Toward homogenous AlN via reaction of Al nanoparticles with N2 and NH3: Reactive molecular dynamics simulation

AbstractIn this study, reactive molecular dynamics simulations were implemented to study the initial events in synthesizing AlN via aluminum nanoparticles (ANPs) with N2/NH3. The dissolution and diffusion behavior of N and H atoms in ANPs is elaborated. Without sufficient N2 supply and lower temperatures (below 2000 K), AlN nucleates and grows in an island shape, and the phase separation occurs through N atoms diffusion. The increase in N2 density accelerates the dissolution of N atoms through the nitride film to the core. In the NH3 atmosphere, H atoms generated by the cleavage of NH3 on ANPs surface dominate inward penetration, while N atoms are at a disadvantage in competition. ANPs have a large number of internal stress and form interwoven dislocations in the combustion. The number and distribution of dislocations are affected by temperatures and reaction time. ANPs not only expand in volume but also have local voids generated by hot spots at high temperatures. In the analysis of ANPs/NH3 species, the instability of the N‐H bond causes aluminum‐containing substances to spill out. Furthermore, N2 atmosphere together with a small amount of NH3 can loosen the nitride film and promote the diffusion of N atoms into the ANPs core. A homogeneous AlN could be tuned and fabricated under an optimal ratio of N2/NH3 (∼6:1).

The impact of aging time on fracture mode of a metastable β alloy with network-like microstructure

Metastable β alloys (Ti-5Al-2Sn-2Zr-4Cr-4Mo) with network-like microstructure were obtained by aging at 630 °C for 1–25 h, and subjected to the tensile fracture at room temperature. The obtained alloy (equiaxed α and precipitated α phases) has the high strength and good plasticity, which are comparable to those of near-β forged alloys. The tensile fracture mode of the short-time aging alloy is the ductile fracture with local long voids. The micro-cracks initiation at the grain boundary α layer and adjacent equiaxed α phases gives rise to the long voids. As the aging time increases up to 25 h, Al atoms penetrate within equiaxed α phase and Mo atoms pile up along the α/β interface. During the tensile process, the release of local stress is due to the α/β interface softening. The ductile fracture of the long-time aging alloy is determined by the void growth and coarsening.

Structural similarity of an ionic liquid and the mixture of the neutral molecules

Using coarse-grained molecular dynamics simulations we present a comparison between the structure of an ionic liquid (IL) and its neutral counterpart (a mixture of the same molecules at the same density, but without charges). We show that there is a surprising structural similarity between the two studied systems with respect to the packing of the molecules, regardless of the fact that the arrangement of anions and cations in the ionic liquid differs significantly from the arrangement of their analogues in the neutral mixture. Rather similar behavior was obtained for the computed total (all-grain) radial distribution functions of the entire systems, as well as for the sizes and shapes of the local voids defined by Delaunay simplices. This structural similarity was also observed for an IL with a modified charge distribution on the cations, and for an uncharged Lennard-Jones liquid, both at the same density. We would like to emphasize that the overall structure of a dense disordered molecular system is determined, above all, by the impenetrability of atoms, i.e. by the geometric laws of atomic packings.

CAVD, towards better characterization of void space for ionic transport analysis

Geometric crystal structure analysis using three-dimensional Voronoi tessellation provides intuitive insights into the ionic transport behavior of metal-ion electrode materials or solid electrolytes by mapping the void space in a framework onto a network. The existing tools typically consider only the local voids by mapping them with Voronoi polyhedra vertices and then define the mobile ions pathways using the Voronoi edges connecting these vertices. We show that in some structures mobile ions are located on Voronoi polyhedra faces and thus cannot be located by a standard approach. To address this deficiency, we extend the method to include Voronoi faces in the constructed network. This method has been implemented in the CAVD python package. Its effectiveness is demonstrated by 99% recovery rate for the lattice sites of mobile ions in 6,955 Li-, Na-, Mg- and Al-containing ionic compounds extracted from the Inorganic Crystal Structure Database. In addition, various quantitative descriptors of the network can be used to identify and rank the materials and further used in materials databases for machine learning.

Au-WO3 Nanocomposite Coatings for Localized Surface Plasmon Resonance Sensing.

Localized surface plasmon resonance (LSPR) gas sensors are gaining increasing importance due to their unique tuneable functional properties. Au-WO3−x nanocomposite coatings, in particular, can be outstandingly sensitive to many different gases. However, a proper understanding of their optical properties and the way in which those properties are correlated to their structure/microstructure, is still needed. In this work, Au-WO3 nanocomposite coatings, with Au contents between 0–11 atomic percent, were grown using reactive magnetron co-sputtering technique and were characterized concerning their optical response. The precipitation of Au nanoparticles in the oxide matrix was promoted through thermal annealing treatments until 500 °C. Along with the Au nanoparticles’ morphological changes, the annealing treatments stimulated the crystallization of WO3, together with the appearance of oxygen-deficient WO3−x phases. Through theoretical simulations, we have related the LSPR effect with the different structural and morphological variations (namely, size and distribution of the nanoparticles and their local environment), which were a function of the Au content and annealing temperature. Our results suggest that local voids were present in the vicinity of the Au nanoparticles, for all temperature range, and that they should be present in a wide variety of Au-WO3 nanocomposites. A theoretical study concerning the refractive index sensitivity was carried out in order to predict the optimal coating design parameters for gas sensing experiments.

On complex structure of local free volume in bond fluctuation model of polymer matrix

Complex dynamics in model polymer-based host-guest systems is ascribed to jamming effects resulting from inhomogeneous dynamics of local free volume in polymer matrix. As a first step towards quantification of this assumption we study the local free volume in static configurations in Monte Carlo Bond Fluctuation Model (BFM), using specially devised local free volume parameter V. Statistical analysis, including various correlation functions and probabilistic distributions, yields a quantitative characterization of a typical equilibrium local volume configuration V(r→) on large, intermediate and local scales. Two types of spatial organizations of local free volume are found and characterized: a liquid-like, constrained by steric interactions, and local voids nearly free of monomers. Those voids form large scale-free clusters with power-law distribution of sizes and complex fractal structure with fractal dimension dependent on cluster's size. The emerging physical picture offers a promising starting point for the characterization of inhomogeneous dynamics of local free volume in BFM and of guest molecules embedded in local volume mosaic states of BFM.

The Local Perspective on the Hubble Tension: Local Structure Does Not Impact Measurement of the Hubble Constant

Abstract We use the largest sample to date of spectroscopic supernova (SN) Ia distances and redshifts to look for evidence in the Hubble diagram of large-scale outflows caused by local voids suggested to exist at z < 0.15. Our sample combines data from the Pantheon sample with the Foundation survey, and the most recent release of light curves from the Carnegie Supernova Project, to create a sample of 1295 SNe over a redshift range of 0.01 < z < 2.26. We make use of an inhomogeneous and isotropic Lemaitre–Tolman–Bondi metric to model a void in the SN Ia distance–redshift relation. We conclude that the SN luminosity distance–redshift relation is inconsistent at the 4–5σ confidence level with large local underdensities ( , where the density contrast δ = Δρ/ρ) proposed in some galaxy count studies, and find no evidence of a change in the Hubble constant corresponding to a void with a sharp edge in the redshift range 0.023 < z < 0.15. With an empirical precision of , we conclude that the distance ladder measurement is not affected by local density contrasts, in agreement with a cosmic variance of , predicted from simulations of large-scale structure. Given that uncertainty in the distance ladder value is , this does not affect the Hubble tension. We derive a 5σ constraint on local density contrasts on scales larger than of . The presence of local structure does not appear to impede the possibility of measuring the Hubble constant to 1% precision.