Initial Size Distribution Research Articles

Influence of Well Pattern Type on Remaining Oil Saturation and Distribution after Development

The reservoir heterogeneity of Q oilfield is more severe after long-term water injection development, and water flooding is ineffective. In this study, the combined technologies of profile control, profile control and flooding, and oil displacement were proposed to improve the water flooding development effect. Then, the influence of the well pattern type on the remaining oil distribution, after development, was investigated. Cr3+ polymer gel, which has an optimal gel-forming effect, was used as the profile control agent. Moreover, the entire molecular structure had a “network” structure. A polymer microsphere was used as a profile control and flooding agent, which showed a good hydration expansion capacity. The initial particle size distribution had a range of 7.2–11.1 μm, and the expansion multiple was 4.35–5.64 after 7 days. The surfactant was an oil displacement agent, and the interfacial tension was approximately 5.08–5.11 × 10−1 mN/m. After the “profile control + profile control and flooding + oil displacement” technologies, the horizontal well pattern had a large seepage area. The effect of expanding the sweep volume was significant, and the remaining oil saturation in each stage was lower than those of the vertical and horizontal–vertical combined well patterns. Compared with the first water flooding stage, the remaining oil saturation values of the three permeable layers changed by 11.9%, 17.3%, and 19.8% during the subsequent water flooding stage.

Novel Water-in-Oil Emulsions for Co-Loading Sialic Acid and Chitosan: Formulation, Characterization, and Stability Evaluation.

This study was designed to co-load sialic acid (SA) and chitosan in a water-in-oil (W/O) emulsion and investigated its characterization and stability. Emulsions were prepared using two different oils (olive oil and maize oil) and polyglycerol polyricinoleate (PGPR) alone or in combination with lecithin (LE) as emulsifiers. The results revealed that the aqueous phase of 5% (w/v) SA and 2% (w/v) chitosan could form a stable complex and make the aqueous phase into a transparent colloidal state. Increasing the concentration of PGPR and LE presented different effects on emulsion formation between olive oil-base and maize oil-base. Two stable W/O emulsions that were olive oil-based with 1.5% (w/v) PGPR+ 0.5% (w/v) LE and maize oil-based with 2% (w/v) PGPR+ 0% (w/v) LE were obtained. Initial droplet size distribution curves of the two stable emulsions displayed unimodal distribution, and the rheological curves displayed the characteristics of shear thinning and low static shear viscosity. Moreover, the storage stability showed that there was no significant change in droplet size distribution and Sauter mean diameter of the emulsions at room temperature (25 °C) for 30 days. These results indicated that the W/O emulsions could effectively co-load and protect sialic acid and chitosan and thus could be a novel method for increasing the stability of these water-soluble bioactive compounds.

Influences of Waste Inclusion on Impact and Crushing Force Resistance of Track Ballast

Recently, the incorporation of various waste materials into the ballast is studied in terms of physical and mechanical behavior. However, the inclusion of concrete debris (CD) and bottom ash (BA) waste, which are enlisted as the inventory materials for railway ballast have not been thoroughly examined. Hence, this paper investigates the improvement in damage resistance of waste incorporated conventional ballast (CB) under impact and crushing force using impact hammer and crushing machine. The initial and final particle size distribution (PSD) were obtained to analyze the damages through the Hardin‘s breakage index and fouling index. The results show that the resistance against crushing and impact force is better when the composition is in the ratio of 1:1 of conventional ballast (CB) and concrete debris (CD). Under crushing load, mixture with 50% of CD recorded breakage index with 4% deviation compared to using 100% of CB. However, integrating with 40% of CD and 10% of BA proved that the values are 2.14% lower than the ACV limit and 9.09% higher than the AIV limit set by British Standard. Although the impact and crushing index of 100% CB aggregates are below the allowable limit, mixing the CD and BA also records results which is only slightly different than the threshold limit. This is due to the cushioning effect caused by the waste acting as the buffering material that reduces the time of impact, which saves the angular materials from wearing off. This will reduce the ballast maintenance intervals that indirectly reduce the service cost and promotes sustainable construction. Based on the results from this study, further experiments are recommended to be carried out to relate and understand which waste material plays a major role in damage reduction or causing higher maitenance cost.

Estimating cloud condensation nuclei concentrations from CALIPSO lidar measurements

Abstract. We present a novel methodology to estimate cloud condensation nuclei (CCN) concentrations from spaceborne CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations) lidar measurements. The algorithm utilizes (i) the CALIPSO-derived backscatter and extinction coefficient, depolarization ratio, and aerosol subtype information; (ii) the normalized volume size distributions and refractive indices from the CALIPSO aerosol model; and (iii) the MOPSMAP (modelled optical properties of ensembles of aerosol particles) optical modelling package. For each CALIPSO height bin, we first select the aerosol-type specific size distribution and then adjust it to reproduce the extinction coefficient derived from the CALIPSO retrieval. The scaled size distribution is integrated to estimate the aerosol number concentration, which is then used in the CCN parameterizations to calculate CCN concentrations at different supersaturations. To account for the hygroscopicity of continental and marine aerosols, we use the kappa parameterization and correct the size distributions before the scaling step. The sensitivity of the derived CCN concentrations to variations in the initial size distributions is also examined. It is found that the uncertainty associated with the algorithm can range between a factor of 2 and 3. Our results are comparable to results obtained using the POLIPHON (Polarization Lidar Photometer Networking) method for extinction coefficients larger than 0.05 km−1. An initial application to a case with coincident airborne in situ measurements for independent validation shows promising results and illustrates the potential of CALIPSO for constructing a global height-resolved CCN climatology.

Airborne and aerosol pathogen transmission modeling of respiratory events in buildings: An overview of computational fluid dynamics.

Pathogen droplets released from respiratory events are the primary means of dispersion and transmission of the recent pandemic of COVID-19. Computational fluid dynamics (CFD) has been widely employed as a fast, reliable, and inexpensive technique to support decision-making and to envisage mitigatory protocols. Nonetheless, the airborne pathogen droplet CFD modeling encounters limitations due to the oversimplification of involved physics and the intensive computational demand. Moreover, uncertainties in the collected clinical data required to simulate airborne and aerosol transport such as droplets’ initial velocities, tempo-spatial profiles, release angle, and size distributions are broadly reported in the literature. There is a noticeable inconsistency around these collected data amongst many reported studies. This study aims to review the capabilities and limitations associated with CFD modeling. Setting the CFD models needs experimental data of respiratory flows such as velocity, particle size, and number distribution. Therefore, this paper briefly reviews the experimental techniques used to measure the characteristics of airborne pathogen droplet transmissions together with their limitations and reported uncertainties. The relevant clinical data related to pathogen transmission needed for postprocessing of CFD data and translating them to safety measures are also reviewed. Eventually, the uncertainty and inconsistency of the existing clinical data available for airborne pathogen CFD analysis are scurtinized to pave a pathway toward future studies ensuing these identified gaps and limitations.

Nonuniform Collective Dissolution of Bubbles in Regular Pore Networks

Understanding the evolution of solute concentration gradients underpins the prediction of porous media processes limited by mass transfer. Here, we present the development of a mathematical model that describes the dissolution of spherical bubbles in two-dimensional regular pore networks. The model is solved numerically for lattices with up to 169 bubbles by evaluating the role of pore network connectivity, vacant lattice sites and the initial bubble size distribution. In dense lattices, diffusive shielding prolongs the average dissolution time of the lattice, and the strength of the phenomenon depends on the network connectivity. The extension of the final dissolution time relative to the unbounded (bulk) case follows the power-law function, {B^k/ell }, where the constant ell is the inter-bubble spacing, B is the number of bubbles, and the exponent k depends on the network connectivity. The solute concentration field is both the consequence and a factor affecting bubble dissolution or growth. The geometry of the pore network perturbs the inward propagation of the dissolution front and can generate vacant sites within the bubble lattice. This effect is enhanced by increasing the lattice size and decreasing the network connectivity, yielding strongly nonuniform solute concentration fields. Sparse bubble lattices experience decreased collective effects, but they feature a more complex evolution, because the solute concentration field is nonuniform from the outset.

Statistical inference of the Equivalent Initial Flaw Size Distribution for an anisotropic material with the Dual Boundary Element Method

A methodology to estimate the fatigue life of an anisotropic structure under uncertainty is established in this work for the first time, utilizing the statistical inference of the Equivalent Initial Flaw Size Distribution (EIFSD). The challenges of detecting small cracks and predicting their fatigue propagation are overcome by the concept of the EIFSD, combined with a highly efficient computational tool for fatigue modelling problems: The Dual Boundary Element Method (DBEM). Bayesian updating is employed to enable the estimate of EIFSD to be refined by new information in the form of inspection data simulated using the DBEM. Although the DBEM is highly efficient, a significant number of DBEM simulations are needed to create the inspection data. Therefore, the DBEM is used to create a surrogate model to further improve efficiency. To demonstrate the proposed methodology, an example of a specimen with anisotropic material properties is investigated. The fatigue life estimated from the inferred EIFSD demonstrated only 0.11% error compared to the actual fatigue life when a low-level of uncertainty was considered in the anisotropic material properties, and only 1.9% error even when a high-level of uncertainty was considered. These fatigue life estimates found using the EIFSD can be coupled with reliability analysis techniques to determine suitable intervals for routine inspections in aircraft.

A short review of vapour droplet dispersion models used in CFD to study the airborne spread of COVID19

The use of computational fluid dynamics (CFD) to simulate the spread of COVID19 and many other airborne diseases, especially in an indoor environment needs accurate understanding of dispersion models. Modelling the transport/dispersion of vapour droplets within the atmosphere is a complex problem, as it involves the motion of more than one phase, as well as the interphase interactions between the phases. This paper reviews the current canon of research on dispersion modelling of vapour droplets by looking at three specific aspects: (i) physical definition/specification of the initial droplet size distribution; (ii) physics of evaporation/condensation models and (iii) transport equations (with molecular/turbulent dispersion models) to describe the movement of the vapour droplets as they propagate through the air. This review found that the state of modelling implements a wide range of models which shows variances in results thus leading to a state where it is difficult to know which model is most accurate. The authors suggest that further studies in this direction should focus on developing a principle set of equations by benchmarking the previously developed models to establish model uncertainty of the previously developed models with reference to a fixed theoretical model and be compared under identical conditions. However, it must be noted that due to the complex nature of microdroplet evaporation and dispersion coupled with the unpredictable way droplet size distributions are produced, current experimental methodologies that are available to validate such simulations, such as particle image velocimetry, are still not robust enough to provide detailed data to verify minute aspects of the simulations.

On compression behavior and particle breakage of carbonate silty sands

Carbonate soils are high in compressibility and low in particle strength, and therefore need special treatment for many geotechnical applications. This paper presents comprehensive one-dimensional compression tests to investigate the compression behavior and particle breakage of carbonate soils with various initial particle size distributions (PSDs) and a wide range of initial void ratios at a high effective vertical stress of 32 MPa. A clear shape transition in terms of the void ratio against effective vertical stress was observed with varying silt fraction and void ratio. The deformation mechanism for the samples with less silt fraction and higher void ratio is mainly dominated by the particle-breakage-induced unlocking effect. Samples with more silt fraction and lower void ratio will experience less particle breakage and their deformation mechanism is mainly attributed to interparticle locking effect. A ‘transitional’ mode of behavior without a unique normal compression line was identified for the samples with silt fraction ranging from 1.6% to 33%. It was also found that carbonate soil samples with both ‘transitional’ and ‘non-transitional’ modes of compression behavior may both experience considerable amount of particle breakage and show different trends in the evolution of particle shape.

Assessment of the sediment and associated nutrient/contaminant continuum, from permafrost thaw slump scars to tundra lakes in the western Canadian Arctic

AbstractWithin the Canadian Arctic, vast areas of previously frozen sediments and carbon are being released into aquatic ecosystems via the occurrence of permafrost thaw and retrogressive thaw slumps (RTSs). While knowledge of mass wasting RTS processes are more advanced, the significance of exposed retrogressive thaw slump scars (RTSSs) at various phases of stabilization to yield additional large quantities of ecologically relevant sediment to lakes and rivers is not well constrained. Using laboratory simulation (linked rainfall and lake flow dynamics), RTS sediments were investigated to assess the sediment continuum from the terrestrial RTSSs to depositional zones within two Arctic tundra lakes. Using an estimate of 30% of the RTSS areas contributing sediment under hypothetical 20‐ and 100‐year rainfall events, up to 598 and 997 kg hr−1 of RTSS sediment washoff was projected respectively. Eroded particle size, regardless of lake or initial bulk RTSS size distribution, was dominated by individual clay particles (<5 μm) that were winnowed from the RTSS surface sediment. Given this is the most biogeochemical relevant fraction, it has the potential for significant ecological impact on the lakes. This deposited fine sediment was found to be very unstable with a critical shear stress for erosion close to that of the critical shear for deposition (0.05 Pa). As such, wave energy is expected to have an impact on remobilization of fine sediments and associated compounds with concomitant implications for lake‐ecosystem health.

Effect of Particle Sizes on the Efficiency of Fluorinated Nanodiamond Neutron Reflectors.

Over a decade ago, it was confirmed that detonation nanodiamond (DND) powders reflect very cold neutrons (VCNs) diffusively at any incidence angle and that they reflect cold neutrons quasi-specularly at small incidence angles. In the present publication, we report the results of a study on the effect of particle sizes on the overall efficiency of neutron reflectors made of DNDs. To perform this study, we separated, by centrifugation, the fraction of finer DND nanoparticles (which are referred to as S-DNDs here) from a broad initial size distribution and experimentally and theoretically compared the performance of such a neutron reflector with that from deagglomerated fluorinated DNDs (DF-DNDs). Typical commercially available DNDs with the size of ~4.3 nm are close to the optimum for VCNs with a typical velocity of ~50 m/s, while smaller and larger DNDs are more efficient for faster and slower VCN velocities, respectively. Simulations show that, for a realistic reflector geometry, the replacement of DF-DNDs (a reflector with the best achieved performance) by S-DNDs (with smaller size DNDs) increases the neutron albedo in the velocity range above ~60 m/s. This increase in the albedo results in an increase in the density of faster VCNs in such a reflector cavity of up to ~25% as well as an increase in the upper boundary of the velocities of efficient VCN reflection.

A systematic approach to calibrate spray and break-up models for the simulation of high-pressure fuel injections

A novel calibration methodology is presented to accurately predict the fundamental characteristics of high-pressure fuel sprays for Gasoline Direct Injection (GDI) applications. The model was developed within the Siemens Simcenter STAR-CD 3D CFD software environment and used the Lagrangian–Eulerian solution scheme. The simulations were carried out based on a quiescent, constant volume, computational vessel to reproduce the real spray testing environment. A combination of statistic and optimisation methods was used for spray model selection and calibration and the process was supported by a wide range of experimental data. A comparative study was conducted between the two most commonly used models for fuel atomisation: Kelvin–Helmholtz/Rayleigh–Taylor (KH–RT) and Reitz–Diwakar (RD) break-up models. The Rosin–Rammler (RR) mono-modal droplet size distribution was tuned to assign initial spray characteristics at the critical nozzle exit location. A half factorial design was used to reveal how the various model calibration factors influence the spray properties, leading to the selection of the dominant ones. Numerical simulations of the injection process were carried out based on space-filling Design of Experiment (DoE) schedules, which used the dominant factors as input variables. Statistical regression and nested optimisation procedures were then applied to define the optimal levels of the model calibration factors. The method aims to give an alternative to the widely used trial-and-error approach and unveils the correlation between calibration factors and spray characteristics. The results show the importance of the initial droplet size distribution and secondary break-up coefficients to accurately calibrate the entire spray process. RD outperformed KH–RT in terms of prediction when comparing numerical spray tip penetration and droplet size characteristics to the experimental counterparts. The calibrated spray model was able to correctly predict the spray properties over a wide range of injection pressure. The work presented in this paper is part of the APC6 DYNAMO project led by Ford Motor Company.

Influence of the component composition of extinguishing fluids on the droplet distribution in an aerosol cloud

The key challenge in the process is to reliably predict the droplet size distributions of extinguishing liquids after they cover the distances from the drop/spray point to the flame combustion area when using aircraft, sprinkler systems, or high-altitude ground spraying systems. It is sensible to perform a comparative analysis of changes in the size of droplets of typical fire extinguishing composition free-falling or sprayed in a gas medium from a variable altitude. We used the compositions typical of fire-extinguishing systems: bishofite and fire-extinguishing agent solutions, bentonite suspension, foamer emulsion, and water. The variation rate of the average, minimum and maximum sizes of droplets in the aerosol composition was recorded. Experiments were performed with varying spray height and initial droplet size distribution to show significant differences in the resulting droplet size distribution of suspensions, emulsions and solutions. Conditions were established, in which the droplet distribution for different extinguishing compositions remains comparable.

The capping agent is the key: Structural alterations of Ag NPs during CO2 electrolysis probed in a zero-gap gas-flow configuration

We apply silver nanoparticles (Ag NPs) as catalysts of CO2 reduction in a zero-gap gas-flow electrolyser. Ag NPs stabilized by different ligands —branched polyethylenimine (BPEI), polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and citrate— are used in the experiments. The as-prepared NPs have almost identical initial size distributions, yet their catalytic performance, in terms of achievable current and CO selectivity, is different. During electrolysis all Ag NPs exhibit unambiguous morphology changes; the degradation pathway they follow, however, markedly depends on the chemical nature of the capping agent stabilizing them. Scanning electron micrographs obtained before and after constant-charge electrolyses carried out at different potentials reveal that amongst the studied ligands, BPEI seems to be the most effective stabilizer of Ag NPs; in turn, however, BPEI also limits CO formation the most. In case of PVP, mostly corrosion (particle shrinkage) is observed at practically relevant electrolysing potentials, while the application of PEG leads more to particle coalescence. Ostwald ripening seems to appear only at high applied (H2 forming) potentials in case of the three afore-mentioned ligands while in case of citrate it becomes significant already at mild (CO forming) voltages. By studying the effects of capping agent removal and exchange we demonstrate that apart from ligands directly attached to the Ag NPs, also the excess of capping agents (adsorbed on the electrode surface) plays a decisive role in determining the extent and mode of catalyst degradation. The results of SEM-based particle sizing are also confirmed by synchrotron based wide-angle X-ray scattering measurements that provide further insight into the evolution of crystallite size and lattice strain in the applied Ag NPs during electrolysis.

Contribution of Selected Herbivores’ Dung on the Soil Organic Carbon and Nitrogen in Serengeti National Park, Tanzania

This study was done to determine the contribution of selected herbivores’ dung in the grazed ecosystem of Serengeti National Park, Tanzania. To achieve this Soil Organic Carbon and Nitrogen were determined in four distinct textural soils in three sites, namely Serena with clay and clay loam, Barafu with sandy loam, sandy clay loam, and Seronera with sand clay loam. Thereafter the decomposition of dung pats in terms of weight change and percentage of nutrients in dung pats of four herbivore species (buffalo, zebra, wildebeest and elephant) incorporated into the soil beneath the dung pats were determined. Fresh dung, soil cores beneath the dung pats and control soils 1 m adjacent to the pats were taken for laboratory analysis. Dung pats and soil samples were analysed for initial percentage OC, N, pH and soil particle size distribution. Weight changes of the dung pats after each three weeks period were monitored. Similarly, monthly rainfalls during the study period were recorded from the rain gauges near the sites. The results indicate that the surface soil (0-15 cm depth) pH ranged from 6.0 - 7.5, 7.4 -7.9 and 6.1 - 7.4 for Serena, Barafu and Seronera respectively. While the soil texture was highly significantly different in percentage OC added after 18 weeks, the treatments and texture were both not significant for percentage N increased in the soil after 18 weeks. There was a difference of 1% between the ruminants and non-ruminants in percentage N increase although they were fluctuating over time due to weather changes. The C/N ratios of the controls and the treatments were on average 11 and 15 respectively, being highly significantly different and indicating that, treatments had a potential contribution to the soil OC and N in the ecosystem.

Streaming instability with multiple dust species – II. Turbulence and dust–gas dynamics at non-linear saturation

ABSTRACT The streaming instability is a fundamental process that can drive dust–gas dynamics and ultimately planetesimal formation in protoplanetary discs. As a linear instability, it has been shown that its growth with a distribution of dust sizes can be classified into two distinct regimes, fast- and slow-growth, depending on the dust-size distribution and the total dust-to-gas density ratio ϵ. Using numerical simulations of an unstratified disc, we bring three cases in different regimes into non-linear saturation. We find that the saturation states of the two fast-growth cases are similar to its single-species counterparts. The one with maximum dimensionless stopping time τs,max = 0.1 and ϵ = 2 drives turbulent vertical dust–gas vortices, while the other with τs,max = 2 and ϵ = 0.2 leads to radial traffic jams and filamentary structures of dust particles. The dust density distribution for the former is flat in low densities, while the one for the latter has a low-end cut-off. By contrast, the one slow-growth case results in a virtually quiescent state. Moreover, we find that in the fast-growth regime, significant dust segregation by size occurs, with large particles moving towards dense regions while small particles remain in the diffuse regions, and the mean radial drift of each dust species is appreciably altered from the (initial) drag-force equilibrium. The former effect may skew the spectral index derived from multiwavelength observations and change the initial size distribution of a pebble cloud for planetesimal formation. The latter along with turbulent diffusion may influence the radial transport and mixing of solid materials in young protoplanetary discs.

Hydro-mechanical behaviour of soil experiencing seepage erosion under cyclic hydraulic gradient

Numerous incidents and failures of earth slopes, dykes, levees and embankment dams are caused by internal erosion. At a time of global climate change, rapid pore-water pressure changes in soil masses are frequently induced by extreme rainfall, storm surges, waves, flash floods and so on. Under such complex cyclic hydraulic conditions, the soil erodibility, hydraulic conductivity and subsequent stress–strain behaviour may differ from those under the monotonic seepage condition, and are still poorly understood. In this study, preliminary laboratory tests have been conducted to investigate the development of internal erosion and changes in hydraulic conductivity under one-way cyclic seepage, and the post-erosion stress–strain behaviour. Representative internally stable and unstable soils were tested. The effects of mean hydraulic gradient and cyclic gradient amplitude were investigated in detail. Results show that the erosion development is significantly influenced by both the initial grain size distribution and the pattern of imposed cyclic hydraulic gradient. The cyclic seepage promotes the loss of fine particles and leads to larger hydraulic conductivity. For the internally unstable soil, the eroded soil mass and hydraulic conductivity increased significantly with increasing cyclic gradient amplitude. Nevertheless, the internally stable soil experienced a small amount of particle loss, even under large cyclic gradients. For both types of soil, a larger cyclic gradient amplitude corresponds to a stronger post-erosion contractive shearing behaviour and a smaller critical friction angle.

Improving mechanical properties of lean Mg–Zn–Ca alloy for absorbable implants via Double Equal Channel Angular Pressing (D-ECAP)

Mg alloys are suitable materials for biodegradable osteosynthesis implants which stabilize bone fractures as long as the fracture is healing but are absorbed by the human body after they have fulfilled this purpose. However, high degradation rates and/or low strength values can be seen as drawbacks of such alloys. The present study deals with a lean Mg–Zn–Ca alloy which exhibits a desired, low degradation rate and explores the possibilities to improve its mechanical properties by Severe Plastic Deformation (SPD) via Double Equal Channel Angular Pressing (D-ECAP). The effects of different D-ECAP process parameters on the microstructure, mechanical properties and degradation behavior are investigated in detail. The results show that grain refinement during D-ECAP occurs via dynamic recrystallization. Lowering the processing temperature leads to a reduction of the size of the smaller grains of the initial bimodal grain size distribution while a higher degree of deformation (higher number of D-ECAP passes) reduces almost only the area fraction of the larger grains. While the increase in hardness is mainly due to the small size of the recrystallized grains, the tensile strength is additionally determined by the remaining larger grains. Thus, the mechanical properties of the lean Mg–Zn–Ca alloy can be tailored by D-ECAP according to the requirements of the final application. For example, the tensile strength can be increased to more than 370 MPa while maintaining the elongation at fracture at 7%. The degradation rate is not affected by D-ECAP as the process does not change the number or size of intermetallic particles. The optimized mechanical properties, in combination with the low degradation rate, make the D-ECAP-processed alloy very suitable for biomedical applications as absorbable material for osteosynthesis implants.

Sediment size on talus slopes correlates with fracture spacing on bedrock cliffs: implications for predicting initial sediment size distributions on hillslopes

Abstract. The detachment of rock fragments from fractured bedrock on hillslopes creates sediment with an initial size distribution that sets the upper limits on particle size for all subsequent stages in the evolution of sediment in landscapes. We hypothesize that the initial size distribution should depend on the size distribution of latent sediment (i.e., fracture-bound blocks in unweathered bedrock) and weathering of blocks both before and during detachment (e.g., disintegration along crystal grain boundaries). However, the initial size distribution is difficult to measure because the interface across which sediment is produced is often shielded from view by overlying soil. Here we overcome this limitation by comparing fracture spacings measured from exposed bedrock on cliff faces with particle size distributions in adjacent talus deposits at 15 talus–cliff pairs spanning a wide range of climates and lithologies in California. Median fracture spacing and particle size vary by more than 10-fold and correlate strongly with lithology. Fracture spacing and talus size distributions are also closely correlated in central tendency, spread, and shape, with b-axis diameters showing the closest correspondence with fracture spacing at most sites. This suggests that weathering has not modified latent sediment either before or during detachment from the cliff face. In addition, talus at our sites has not undergone much weathering after deposition and is slightly coarser than the latent sizes because it contains unexploited fractures inherited from bedrock. We introduce a new conceptual framework for understanding the relative importance of latent size and weathering in setting initial sediment size distributions in mountain landscapes. In this framework, hillslopes exist on a spectrum defined by the ratio of two characteristic timescales: the residence time in saprolite and weathered bedrock and the time required to detach a particle of a characteristic size. At one end of the spectrum, where weathering residence times are negligible, the latent size distribution can be used to predict the initial size distribution. At the other end of the spectrum, where weathering residence times are long, the latent size distribution can be erased by weathering in the critical zone.

Phase field simulation of abnormal grain growth mediated by initial particle size distribution

The uniform initial particle size distribution was considered to be an important condition for the preparation of dense ceramics. With the rapid development of templated grain growth method, it is necessary to add large template particles into small matrix to promote the epitaxial growth of grains. However, abnormal grain growth will inevitably occur in this process. In this work, a phase field method was employed to study the growth behavior of the large grains into the small matrix. The effect of initial particle size distribution on the grain growth kinetics was investigated. Our simulations revealed that the growth rate of large grains slowed down as the initial grain size distribution widened. Regulating the initial grain size distribution will be an effective way to control abnormal growth of grain. It was found that the growth rate of a large grain was proportional to the number of surrounding grains. These results have implications for the design of the functional ceramics with a target grain microstructure.