Pebble Shape Research Articles

Characteristics of pebble shape and the amount of pebble abrasion measured with a replica reproduced on a curling rink

The shape of pebbles on a curling rink was measured using a replica of the ice surface of the rink to understand the characteristics of pebbles after being in contact with stones. We focused on pebbles with flat tops for which the average shape was 3.81 mm in diameter at the lower base, 1.16 mm in diameter at the upper surface, 0.12 mm in maximum height, and 5.4° in contact angle. A scratch of about 1 µm in depth and 40 µm in width (traces of pebbles cut by a running band at the bottom of the stone) was observed on the upper surface. The pebbles were also found to have a moderate lower base diameter that preferentially contacted the nipper or stone due to its large maximum height value immediately after formation. Experiments to determine the amount of pebble abrasion associated with the passing of stones revealed that the average height of their upper surface decreased by 1 µm and the area of the upper surface increased by 0.21 mm2 for each stone passing as the stone cut the pebbles.

Effect of nitrogen flow ratio on the structure and optical properties of AlN film

Aluminum nitride (AlN) films with different optical properties were prepared by radio frequency (RF) reactive magnetron sputtering technique under different nitrogen (N2) flow ratios. The films' microstructure and optical properties were investigated by XRD, XPS, SEM, UV-VIS and PL. The results showed that all the prepared films had hexagonal wurtzite structure and the sample prepared at 35 % N2 flow ratio obtained higher crystal quality and larger grain size (39 nm). The selective orientation of the films changed from (100) to (002) with the N2 flow ratio, accompanied with a surface morphology changed from worm-like to mixed structure, and eventually to a very regular pebble shape with a compact arrangement. The average transmission of the films exceeded 83 % in the wavelength range of 300–800 nm. The major internal defect affecting the band gap of AlN films was nitrogen-vacancy (VN), and the growth orientation and internal defects of AlN films were controlled by the N2 flow ratio to achieve the regulation of the energy band gap in a small range (5.47–5.68 eV). This can meet the requirement of solar-blind ultraviolet (<280 nm) photoelectric detection.

Hydrazine-Fueled Solution Combustion Method: Fuel/Oxidizer Ratio Effects on Photocatalytic Performance of Bismuth Oxide

Bismuth oxide nanoparticles were synthesized through the solution combustion method with a variation of fuel: oxidizer (hydrazine: bismuth nitrate) ratios (ϕ) of ϕ&lt;1, ϕ=1 (stoichiometrically balanced) and ϕ&gt; 1. Bismuth oxide nanoparticles were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and UV-Visible Diffuse Reflectance Spectroscopy (UV-DRS). The FTIR spectra obtained implies that the bismuth oxide nanoparticles of the three ratios contain Bi-O-Bi and Bi-O groups indicating its successful formation. XRD diffractogram suggests that the synthesized bismuth oxide nanoparticles form the α-Bi2O3 crystalline phase for ϕ&lt;1 and ϕ&gt;1; meanwhile a mixture of α-/β- Bi2O3 phases for ϕ=1. The SEM image illustrates that bismuth oxide nanoparticles form pebble shapes with the ratios in the order of increasing particle sizes of ϕ&gt;1, ϕ=1, and ϕ&lt;1. The UV-DRS results show that the bismuth oxide with ϕ&lt;1, ϕ=1, and ϕ&gt;1 have respective band gap energies of 2.76 eV, 2.72 eV, and 2.78 eV. The evaluation of the photocatalytic activity of the three bismuth oxide samples shows bismuth oxide with ϕ=1 has the highest photocatalytic activity in remazol black B and methyl orange dyes with rate constants 6.744 x 10-5 s-1 and 7.369 x 10-5 s-1, respectively. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

DEPOSITIONAL ENVIRONMENT OF THE TERTIARY KERRI – KERRI FORMATION IN THE GONGOLA SUB-BASIN, NORTHERN BENUE TROUGH: PEBBLES MORPHOMETRIC AND GRAIN SIZE ANALYSIS APPROACH

Pebbles have been reported in the Sandstones units of the Kerri - Kerri Formation, but their application as a tool for interpreting the depositional environment is limited. In this context, 510 quartz pebbles and 16 sandstone samples were collected for pebble morphometric and grain size analyses in order to assess the depositional environment of the formation. For the pebble morphometric study, the long (L), intermediate (I), and short (C) axes of each pebble were measured. For each pebble, four geometrical parameters related to depositional environmental studies were computed, these are: Maximum Projection Sphericity, Oblate Prolate Index, Coefficient of Flatness, and Disk - Road - Index. The standard sieving method was used to sieve the sandstone samples. Mean grain size (Mz), sorting (I), skewness (SKI), and kurtosis (KG) were determined as statistical parameters of the grain size. The mean value of the computed pebble shape parameters for the pebbles of the Kerri – Kerri Formation indicates that the pebbles were deposited in a fluvial environment. Based on the grain size analysis, the sediments were deposited by fluvial action with moderate to low energy of deposition setting closer to the source of the sediments. The bivariate plots show that all the pebbles and sandstone samples lie clearlywithin the river field, which suggests fluvial origin

Characterization of Clasts in the Glen Torridon Region of Gale Crater Observed by the Mars Science Laboratory Curiosity Rover.

The morphology and composition of clasts have the potential to reveal the nature and extent of erosional processes acting in a region. Dense accumulations of granule- to pebble-sized clasts covering the ground throughout the Glen Torridon region of Gale crater on Mars were studied using data acquired by the Mars Science Laboratory Curiosity rover between sols 2300 and 2593. In this study, measurements of shape, size, texture, and elemental abundance of unconsolidated granules and pebbles within northern Glen Torridon were compiled. Nine primary clast types were identified through stepwise hierarchical clustering, all of which are sedimentary and can be compositionally linked to local bedrock, suggesting relatively short transport distances. Several clast types display features associated with fragmentation along bedding planes and existing cracks in bedrock. These results indicate that Glen Torridon clasts are primarily the product of in-situ physical weathering of local bedrock.

Acceleration-Based Method of Ice Quality Assessment in the Sport of Curling.

Despite the significant influence of ice conditions on results in the sport of curling, players and ice technicians lack a measurement device that would objectively measure ice quality during a curling competition. This paper presents such a new measurement method by using a device consisting an inertial measurement unit (IMU) attached to the handle of the curling stone and data processing software. IMU is used to measure the vibration of curling stone during its movement on the surface of the ice. The acceleration signal is recorded, and then the software calculates the value of so-called R parameter in frequency domain. The value of R allows one to determine if an ice sheet had been pebbled and if the shape of pebbles is suitable for the game of curling. The presented system was tested in various ice conditions—on both freshly prepared and used ice. Ice technicians and players may use the proposed system to decide whether the ice surface is suitable for play or if it should be remade.

Experimental measurements of gas pressure drop of packed pebble beds

The nearly spherical shaped ceramic pebble beds in the breeder blanket of the future fusion reactor are purged by low-pressure gas to channelize the produced tritium fuel into the tritium extraction system. The required pumping power for the flowing gas in pebble beds can be estimated using the pressure drop across the pebble beds. The aim of this work is to measure the gas pressure drop experimentally across packed pebble beds as a function of pebble sizes, pebble shapes, pebble materials, and gas velocity. The pebble beds are packed in a cylindrical-shaped stainless steel container with an inner diameter of 24 mm and a length of 130 mm. The various experiments have been performed on stainless steel spheres (Diameter: 1 mm, 2 mm, 3 mm, and 4 mm), alumina pebbles (Mean diameter: 1 mm and 1.5 mm), and lithium meta-titanate pebbles (Mean diameter: 1 mm and 1.3 mm). The gas flow has been controlled and measured using a digital mass flow controller. The static differential pressure across the pebble beds has been monitored by a differential pressure transducer. The pressure drop significantly increases with a decrease in the diameter of pebbles/spheres and an increase in the packing fraction of the bed. The material type does not affect the results which are too obvious for the fixed pebble bed which is considered in these experiments. The obtained experimental results of gas pressure drop have been compared and agreed well with the prediction of the Ergun’s correlation.

Morphometric Characteristics, Shapes and Provenance of Holocene Pebbles from the Sava River Gravels (Zagreb, Croatia)

Morphometric analysis of Holocene pebbles from Sava River gravel in NW Croatia revealed shape distributions as observed along a 30 km long watercourse. Limestones, dolomites, and sandstones were identified as the major (&gt;4%) and effusive magmatics in this alluvial aquifer system in Zagreb, with cherts and tuffs as minor pebble lithologies (up to 4%). Their distributions mainly indicate distant Alpine provenance for carbonate pebbles (limestone and dolomite) and local input for sandstones and minor lithotypes, laterally from the Samoborska Gora and Medvednica mountain. Carbonates are predominantly disc- and sphere-shaped, implying distant sources. Scattered distributions of pebble shapes (sphere, disc, blade, and rod) for sandstones and minor lithotypes possibly indicate multiple sources, some of them probably local. The tentatively interpreted “original sedimentary environments” for the main pebble lithotypes (calculated from their flatness ratios) possibly indicate that they are predominantly lake beach pebbles, followed by moraine and riverbed pebbles. However, these results should be strongly questioned.

Discrete Element Analysis of the Reconstruction Method for Randomly Shaped Pebbles

The pebble shape is a critical factor that affects the bearing characteristics of truck escape ramps. In this paper, a reconstruction method was proposed for randomly shaped pebbles used in truck escape ramps, and statistical analysis was conducted on the results of pebble compression tests. First, 100 pebble samples were randomly selected, and the pebble outlines were fitted in three views. The overlapping method was implemented to fill the three views with ball elements, and the ball elements were then extended into three-dimensions. The results demonstrated that the proposed method satisfactorily monitored the real pebble shapes. Second, statistical analyses were conducted on the parameters of the outlines, and corresponding data sets were built. The key parameters of the pebble DEM model, such as the friction coefficient, were calibrated based on the compression test results, and repeated simulation results verified the feasibility of the proposed pebble DEM model. Next, statistical analysis was conducted on the probability distribution of the contact forces. Third, simulations were conducted with different pressing plate velocities and pebble shapes. The results indicated that the pressing plate velocities had minor effects on the contact forces. As the pressing plate velocity increased, the slope of the contact forces correspondingly increased. The particle shape was a critical factor affecting the simulation results. With the same contact parameters, the simulation results of different pebble shapes varied greatly, which further indicated the importance of the proposed pebble shape reconstruction method. The proposed pebble DEM model could be further used in the design of truck escape ramps.

Preparation of High Sphericity Li&lt;sub&gt;2&lt;/sub&gt;TiO&lt;sub&gt;3&lt;/sub&gt; Tritium Breeder by Polymer Assisted Sedimentation Method

The tritium breeder materials used in solid tritium breeding blanket of fusion reactor are lithium-based ceramics, like lithium titanate (Li2TiO3), lithium orthosilicate (Li4SiO4), lithium aluminate（LiA1O2) and lithium zirconate (Li8ZrO6). Among them, Li2TiO3 has the advantages of stable chemical property, high mechanical strength and high lithium content, so it has become one of the preferred materials. Based on the design of solid blanket and tritium extraction process, breeder materials need to be made into a certain shape of pebbles. B Spherical breeder is widely used in the design of fusion reactor for the larger specific surface area, more channels between the pebbles to diffuse and release tritium, and easier loading or unloading. However, due to the high requirements of the breeder pebbles, the production control are not complete. In this paper, a new preparation method of ceramic pellets with high sphericity, polymer assisted sedimentation method, was used to prepare ceramic pebbles. The slurry consists of micro-scaled ceramic powder and organic monomers. Spherical droplets of ceramic slurry were obtained by sedimentation method in viscous liquids. The organic monomer contained in the droplets was heated to polymerize into small pellet preforms during the sedimentation process. By optimizing the sintering process, the fabricated pebbles could perform high compressive load (&gt;18 N), spherical shape (0.95~1.02), uniform particle size (0.8~1.2mm) and porosity (15~20 %). The main advantages of this method is the mild preparation conditions (50~110 °C), the simplified transfer and purification process and convenient industrialization.. The obtained product has high spherical shape, uniform particle size, high compactness and mechanical strength.

Studies on Deformation Characteristics of Conglomerate along Jonk River, Sonakhan, Balodabazaar District, Chhattisgarh

Abstract Jonk river conglomerate occurs along the river Jonk of the late Archean-Paleoproterozoic Sonakhan greenstone belt in the northern-eastern part of the central India craton (CIC)/Bastar block of Central India. To quantify finite strain, the Rf/ϕ and Fry techniques were used. For the 3D strain analysis, conventional Flinn diagram was computed, on which variation of finite strain as computed from harmonic mean for the different localities, that most of the pebble shapes designates at the oblate field and have nearly plain strain ellipsoid.

High-strain deformation of conglomerates: Numerical modelling, strain analysis, and an example from the Wutai Mountains, North China Craton

Conglomerates have been widely used to investigate deformation history and rheology, strain, vorticity and viscosity. Previous studies reveal that several factors, such as pebble shapes and concentrations, as well as material properties, affect conglomerate deformation. However, how pebble concentration and interaction between pebbles affect deformation is not understood very well. We use the 2D numerical modelling platform ELLE coupled to the full field crystal visco-plasticity code (VPFFT) to simulate the deformation of conglomerates with various viscosity contrasts between pebbles and matrix and different pebble concentrations, with both linear (stress exponent n = 1) and power-law (n = 3) viscous rheologies, under simple shear conditions up to a shear strain of ten. Pebbles can behave as effectively passive, deformable or effectively rigid. An increase in pebble concentrations/viscosity contrasts enhances pebble deformation, but reduces their rotation. A mean aspect ratio (Rf) - orientation (ϕ) plot is proposed to gain an estimate of pebble deformation behaviour and the amount of bulk strain. Closely spaced rigid or deformable pebbles can form clusters that mechanically act as single inclusions. Rigid clusters rotate and survive for only short strain increments, whereas the more stable deformable ones keep on elongating with minor rotation. We provide a natural example of deformed conglomerates from the Wutai Mountains, North China Craton. These consist of banded-iron-formation (BIF) pebbles embedded in a schistose matrix. Using the mean Rf-ϕ plot, a finite strain of ∼6 under simple shear could be determined. The viscosity of the pebbles is estimated at about 5–8 times that of the matrix for a linear rheology (n = 1), or 2 to 5 times if a power-law rheology with n = 3 is assumed.

Evaluating a 2D image-based computerized approach for measuring riverine pebble roundness

The geometrical characteristics of pebbles are important features to study transport pathways, sedimentary history, depositional environments, abrasion processes or to target sediment sources. Both the shape and roundness of pebbles can be described by a still growing number of metrics in 2D and 3D or by visual charts. Despite new developments, existing tools remain proprietary and no pebble roundness toolbox has been available widely within the scientific community. The toolbox developed by Roussillon et al. (2009) automatically computes the size, shape and roundness indexes of pebbles from their 2D maximal projection plans. Using a digital camera, this toolbox operates using 2D pictures taken of pebbles placed on a one square meter red board, allowing data collection to be quickly and efficiently acquired at a large scale. Now that the toolbox is freely available for download,11https://github.com/EVS-GIS/2D-Roundness-Toolbox. an evaluation is needed to help end users sample, process and interpret the data. We first assess the influence of pebble position and of the resolution and enhancement of pictures and errors associated with the sampling size. Second, we run experimental flume tests of roundness trends that confirm the great potential of the toolbox for river geomorphic diagnoses as well as for targeting sediment sources. We also validate the correlation between roundness metric trends and particle abrasion.

A Shape Evolution Model Under Affine Transformations

In this note we describe a discrete dynamical system acting on the similarity classes of a plane convex body within the affine class of the body. We find invariant elements in all affine classes, and describe the orbits of bodies in some special classes. We point out applications with abrasion processes of pebble shapes.

Controls on Pebbles’ Size and Shape in Streams of the Swiss Alps

Although the size and shape of pebbles reflect the ensemble of sediment supply and transport processes along a stream, neither positive nor negative correlations have been found between the grain size of gravel bars, sediment flux, water discharge, and river flow strengths in Swiss streams. The relative frequency of 20°–30° hillslope angles per catchment is the only variable that positively correlates with the size of the largest clasts (D96 percentile). We relate these observations to the detachment-limited states of the Swiss streams where ongoing fluvial dissection steepens the bordering hillslopes, thereby promoting the supply of material through lithology-controlled failure.

Effects of transport and insertion of radio frequency identification (RFID) transponders on resistance and shape of natural and synthetic pebbles: applications for riverine and coastal bedload tracking

AbstractRFID transponders, especially low‐frequency Passive Integrated Transponders (PIT tags), are now commonly used for assessing bedload mobility in gravel‐bed rivers. Early studies reported high PIT tag recovery rates in small streams, but recovery rates in larger systems remain low. Explanatory factors for low recovery rates have been identified, but only antenna detection ranges and clustering effects have been precisely characterized. Burial below detection limit and dispersion beyond the study site have been indirectly estimated, and PIT tag destruction is assumed to be negligible. In this study, we quantified the resistance of natural limestone pebbles equipped with PIT tags as related to tag insertion methods and distance travelled in an annular flume. We then compared the performance of these natural pebbles with synthetic pebbles made of polyurethane resin and corundum. Creation of synthetic pebbles makes it possible to test bigger transponders with a greater detection range and no clustering effects, bypassing the existing constraints of RFID tracking. We found that breakage of limestone particles leading to PIT tag destruction is far too rare to explain low recovery rates in situ. Further, breakage is more affected by initial pebble characteristics than by PIT tag insertion method. Synthetic pebbles are more sensitive to attrition, but less likely to break. Natural and synthetic pebbles show slight differences in mobility patterns, transport distances, and abrasion resistances. One of the two synthetic pebbles travelled faster than the other three indicating that mobility is not only related to density but also potentially to shape. To address clustering and detection range issues, we equipped synthetic pebbles with AIT‐tags (Active Integrated Transponders). These were tested for integrity and transponder endurance and show great promise for future applications. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Textural features of the beach sediments of Wast Water Lake, Northwest England

Abstract This study is dedicated to Wast Water Lake (Northwest England, Great Britain) and the character of its beach sediments. The aim of the study is to identify the textural features of the lake’s beach sediments based on two methods. The first is a granulometric analysis and the second a pebble shape analysis according to Zingg (1935) and Sneed &amp; Folk (1958). Both analyses were carried out for all of the lake’s accessible beaches and the cliffs adjacent to them. The transport and deposition history of the examined sediments was identified through field research and laboratory analysis. The results show that the textural features of the sediments at Wast Water are more often typical of a fluvial environment, rather than having been changed by lacustrine water movements.

Short term displacements of marked pebbles in the swash zone: Focus on particle shape and size

Abstract In this paper, two short term experiments with tracers on a mixed beach are presented. The aim was to understand how the size and shape of pebbles can affect their transport under low energy conditions. Sediment transport was studied by means of RFID technology to univocally monitor every single marked pebble. A size subdivision of injected pebbles was conducted based on three classes (“Big” from − 5.5 to − 6.5 phi; “Medium”, from − 5 to − 5.5 phi; and “Small”, from − 4.5 to − 5 phi). Two recoveries were realised 6 and 24 h after the injection. During a single day, the wave motion was very low in the first experiment and low to moderate in the second (never exceeding 0.4 m). The results showed that discs are less dynamic than spheres but can cover greater distances. Regarding the sediment size, “Big” pebbles are less dynamic if compared to finer classes, and they move preferentially down the swash zone towards the step or do not move up-slope if already at the step. Very low and steady energy conditions facilitate cross-shore and offshore movement of pebbles, rather than a slight raise in wave height producing predominant longshore transport even with non-marginal displacements. Low to moderate energy conditions can also produce some trend displacement based on the pebble shape even though T-tests showed that shape was not statistically significant for pebble displacement. The displacements of “Medium” and “Small” sized pebbles show a statistical dissimilarity compared to the “Big” ones. To refine the velocity estimation necessary to initiate pebble movement, the threshold velocity formulas known up to now should involve the shape parameter, especially for the short term. Better knowledge of the relationship between the sediment's characteristics and dynamics is critical to forecast the durability of replenishment material and to establish the suitability of fill material relative to native beach material. Hence, a better understanding of the role of particle characteristics is necessary.

Tendency towards sphericity symmetry of pebbles: The rate change of volume with surface

The primary effect of rocks and stones tending to erode towards sphericity symmetry can be identified with the rate change of volume with surface. Marble pebbles of various shapes and sizes are recorded and modeled mathematically as ellipsoids. The rate change of volume with surface dV/dA is computed for flat-shaped pebbles where the thickness dimension is assumed to be unity. Invoked is the hypothesis that the change of shape and size of pebbles can be characterized by a master curve derived from dA/dL, the 2D version of dV/dA. The sphericity symmetry is assumed to be concerned with the preference of roundness to slenderness regardless of the surface roughness, smoothness and the mineralogical composition. The erosiveness and abrasiveness of the surface and time effects can interact with sphericity, which is an issue beyond the scope of this work.

How River Rocks Round: Resolving the Shape-Size Paradox

River-bed sediments display two universal downstream trends: fining, in which particle size decreases; and rounding, where pebble shapes evolve toward ellipsoids. Rounding is known to result from transport-induced abrasion; however many researchers argue that the contribution of abrasion to downstream fining is negligible. This presents a paradox: downstream shape change indicates substantial abrasion, while size change apparently rules it out. Here we use laboratory experiments and numerical modeling to show quantitatively that pebble abrasion is a curvature-driven flow problem. As a consequence, abrasion occurs in two well-separated phases: first, pebble edges rapidly round without any change in axis dimensions until the shape becomes entirely convex; and second, axis dimensions are then slowly reduced while the particle remains convex. Explicit study of pebble shape evolution helps resolve the shape-size paradox by reconciling discrepancies between laboratory and field studies, and enhances our ability to decipher the transport history of a river rock.