Fast staggered schemes for the phase-field model of brittle fracture based on the fixed-stress concept

Phase field models are promising to tackle various fracture problems where a diffusive crack is introduced and modelled using the phase variable. Owing to the non-convexity of the energy functional, the derived partial differential equations are usually solved in a staggered manner. However, this method suffers from a low convergence rate, and a large number of staggered iterations are needed, especially at the fracture nucleation and propagation. In this study, we propose novel staggered schemes, which are inspired by the fixed-stress split scheme in poromechanics. By fixing the stress when solving the damage evolution, the displacement increment is expressed in terms of the increment of the phase variable. The relation between these two increments enables a prediction of the displacement and the active energy based on the increment of the phase variable. Thus, the maximum number of staggered iterations is reduced, and the computational efficiency is improved. We present three staggered schemes by fixing the first invariant, second invariant, or both invariants of the stress, denoted by S1, S2, and S3 schemes. The performance of the schemes is then verified by comparing with the standard staggered scheme through three benchmark examples, i.e., tensile, shear, and L-shape panel tests. The results exhibit that the force-displacement relations and the crack patterns computed using the fast schemes are consistent with the ones based on the standard staggered scheme. Moreover, the proposed S1 and S2 schemes can largely reduce the maximum number of staggered iterations and total CPU time in all benchmark tests. The S2 scheme performs comparably except in the shear test, where the underlying assumption is violated in the region close to the crack.Comment: 26 pages, 16 figures, 5 table

The effects of road surface concrete grinding residue (CGR) on selected soil properties and plant growth

Diamond grinding is a widely used operation for smoothing cement concrete road surface, which can improve road riding quality and longevity. Concrete grinding residue (CGR) is a byproduct from diamond grinding. CGR deposited along roadsides can affect soil chemical properties, while studies of CGR influences on soil physical properties and plant growth are limited. This study focuses on CGR impacts on soil physical properties, including soil bulk density, saturated hydraulic conductivity, surface water infiltrability, and plant growth, including plant species, plant biomass, and seedling emergence. A preliminary roadside measurement, a greenhouse study and a controlled field experiment were performed. For the preliminary roadside measurements, soil physical properties and plant biomass measurements were made within CGR affected areas and non-CGR areas at two Minnesota highway roadside locations. For the greenhouse study, the seedling emergence rate and plant biomass of Indian grass, Canada wild-rye, Partridge pea and Wild bergamot were measured in a 60-day period, in pots with 0, 2.24, 4.48, 8.96 kg m-2 CGR rates and two application methods, i.e., uniformly mixed with soil or directly applied on the soil surface. For the controlled field experiments, CGR with rates 0, 2.24, 4.48, 8.96 kg m-2 was applied to replicated 4 m2 plots in an Iowa field, and soil physical properties and plant biomass were measured before, one month, seven months and twelve months after the CGR application; while plant identifications were performed before, ten months and twenty months after the CGR applications. CGR showed non-significant effects on soil physical properties in all of the experiments, except for one roadside location, where the soil bulk density values in the CGR affected areas were significantly larger than those in the non-CGR areas, and the saturated hydraulic conductivity values in the CGR affected areas were significantly smaller than those in the non-CGR areas. CGR did not have significant effects on plant biomass, seedling emergence and plant species indices, such as richness, diversity and evenness. However, from the controlled field and greenhouse experiments, relatively small CGR rates tended to promote plant growth, while relatively large CGR rates tended to inhibit plant growth. In conclusion, CGR did not cause significant effects on soil physical properties and plant growth, and no local environmental risks were observed for CGR applications up to 8.96 kg m-2

Portable canopy chamber measurements of evapotranspiration in corn, soybean and reconstructed prairie

Evapotranspiration (ET) is the combination of soil water evaporation and plant transpiration. ET is a vital component of a field water balance; however, accurate determination of ET is difficult. Indirect methods and direct methods are used to measure ET at the field scale. Typical indirect methods estimate ET with energy balance or field water balance measurement. One possible direct method for determining ET involves the use of canopy chambers. The objectives of this study are to construct a portable canopy chamber; to quantify the diurnal and seasonal trends of ET in three cropping systems; and to compare reference evaporation (Priestley-Taylor method), ET estimated from field water balance components (i.e., rainfall, soil water storage and drainage), and portable canopy chamber measured ET. Three cropping systems, including corn and soybean in a corn-soybean rotation and reconstructed prairie, were studied at the Comparison of Bio-fuel Systems (COBS) research site in central Iowa. Portable canopy chambers were used to measure ET in the different cropping systems during the part of growing season in 2013, and the whole growing season in 2014. Three different chamber sizes were used to match different crop growth stages. Data were collected on 18 days (i.e., maximum ET flux measurements, average ET flux measurements, and diurnal measurements) during the part of 2013 crop growing season and 15 days (diurnal measurements) during the 2014 crop growing season. In 2013 (DOY 164 - 206 for corn and DOY 164 - 255 for prairie and soybean) the cumulative chamber measured ET values were less than half of the reference evaporation values, due to relatively dry soil conditions. In 2014 (DOY 156 - 261 for corn and DOY 156 - 277 for prairie and soybean), because of wet weather condition, cumulative chamber measured ET fluxes were 80% (corn), 70% (prairie), and 67% (soybean) of the reference evaporation, respectively. The cumulative chamber measured ET values were similar to the cumulative water balance estimated ET values for both growing seasons. The differences between chamber measured ET and reference evaporation were expected. However, the agreements between chamber measured ET and water balance estimated ET in both years provided strong evidence that the portable canopy chamber accurately measured field ET at the plot (m^2) scale

Concrete Grinding Residue: Its Effect on Roadside Vegetation and Soil Properties

Concrete grinding residue (CGR) is a slurry waste consisting of water and concrete fines generated from diamond grinding operations that is used to smooth a concrete pavement surface. During this process, CGRs are mostly disposed along the roadside, which can influence soils and plant communities along the roadways. To understand the effects of CGR on soil physical and chemical properties and plant growth, a controlled field site at the Kelly Farm in Iowa was used with CGR application rates of 0, 10, 20, and 40 dry ton/acre to test properties of soils and plants before the application and one month, six months and one year after the CGR application. Two roadsides along Interstate 90 in Minnesota where CGR material was applied in the past were investigated as well. Laboratory and field experiments were conducted to measure plant biomass, bulk density, hydraulic conductivity, infiltration, pH, electrical conductivity (EC), alkalinity, metals, cation exchange capacity (CEC), exchangeable sodium percentage (ESP), and percentage base saturation (PBS) of soil samples collected from the test sites. Statistical analyses were conducted to correlate the CGR additions to the properties of soils and plants. The results of statistical analyses from the Kelly Farm indicated that CGR material did not significantly affect soil physical properties and plant biomass but impacted the chemical properties of soil. Changes in some soil properties such as pH and percent base saturation (PBS) due to CGR did not persist after one year. The results from two Minnesota roadsides indicated that the areas receiving CGR applications in the past did not negatively affect soil quality and plant growth

How interior design responds to neurodiversity: implementing wearable technologies in neurodesign processes

This perspective article, looking through the lens of neurodiversity, discusses the benefits and challenges of implementing virtual environments and wearable technologies in interior design and related fields. While the relationship between human perception and built environments has long been studied in the environmental design disciplines, the direct impact on occupant performance related to neurodiversity has been underexplored in research, with a shortage of knowledge supporting how it can be applied in design practice concerning the end users. Individuals’ perceptual, cognitive, and affective responses to their surroundings vary, as neurodiversity plays a key role in the invisible, human-environment interaction. Thus, measuring, analyzing, and understanding affective, perceptual, and cognitive experiences is a challenging process in which various factors come into play, and no single method or measurement can adequately work for all. Due to such challenges, research has also utilized various biometric measurements and tools for immersive experiments in physical and virtual environments, e.g., eye tracking used in studies on gaze behaviors and immersive virtual reality (IVR) used in studies on the spatial perception of dementia patients. Along with empirical methods, studies have stressed the contribution of phenomenology to looking into the hidden dimension, the ‘why factors’ of perception, cognition, and affectivity. Concerning the methodological approach, this perspective article shares insights into a novel process model, Participatory Neurodesign (PND) framework, used in wayfinding research and design processes utilizing eye tracking and IVR. Opportunities for neurodesign research and design practice are also discussed, focusing on the health, safety, and wellbeing of end-users

The Influence of Concrete Grinding Residue on Soil Physical Properties and Plant Growth

Diamond grinding is a concrete pavement maintenance technique, and concrete grinding residue (CGR) is the byproduct. Concrete grinding residue deposited along roadsides affects soil chemical properties, but impacts of CGR on soil physical properties and plant growth are rarely studied. In this study, a controlled field experiment was performed to determine the influence of CGR on selected soil physical properties (i.e., bulk density [ρb], saturated hydraulic conductivity [Ks], and water infiltrability [It]) and on plant biomass and plant coverage under four application rates (0, 2.24, 4.48, and 8.96 kg m−2). Field measurements were performed before the CGR applications, and 1, 7, and 12 mo after the CGR applications. No significant CGR effects on soil physical properties were detected. The ρb was relatively stable for all of the treatments, whereas some nonsignificant variations (e.g., 10–30% of mean Ks values and mean It values among four CGR rates) were found. Plant biomass with a CGR rate of 2.24 kg m−2 tended to be 10 to 40% larger than biomass in the control treatment, whereas plant biomass with a CGR rate of 8.96 kg m−2 tended to be ∼10% smaller than the control treatment. Concrete grinding residue had no significant effects on plant coverage, richness, Simpson’s diversity, and evenness. Thus, CGR applications up to 8.96 kg m−2 did not significantly affect soil physical properties and plant growth in this controlled field study. This study can serve as a reference for results obtained from roadsides in Minnesota and Iowa that receive CGR applications

Polymer-templated nucleation and crystal growth of perovskite films for solar cells with efficiency greater than 21%

The past several years have witnessed the rapid emergence of a class of solar cells based on mixed organic-inorganic halide perovskites. Today's state-of-the-art perovskite solar cells (PSCs) employ various methods to enhance nucleation and improve the smoothness of the perovskite films formed via solution processing. However, the lack of precise control over the crystallization process creates a risk of forming unwanted defects, for example, pinholes and grain boundaries. Here, we introduce an approach to prepare perovskite films of high electronic quality by using poly(methyl methacrylate) (PMMA) as a template to control nucleation and crystal growth. We obtain shiny smooth perovskite films of excellent electronic quality, as manifested by a remarkably long photoluminescence lifetime. We realize stable PSCs with excellent reproducibility showing a power conversion efficiency (PCE) of up to 21.6% and a certified PCE of 21.02% under standard AM 1.5G reporting conditions