Size-scale Effects Research Articles

Far-from-equilibrium bidirectional transport system with constrained entrances competing for pool of limited resources.

Motivated by the wide occurrence of limited resources in many real-life systems, we investigate two-lane totally asymmetric simple exclusion process with constrained entrances under finite supply of particles. We analyze the system within the framework of mean-field theory and examine various complex phenomena, including phase separation, phase transition, and symmetry breaking. Based on the theoretical analysis, we analytically derive the phase boundaries for various symmetric as well as asymmetric phases. It has been observed that the symmetry-breaking phenomenon initiates even for very small number of particles in the system. The phases with broken symmetry originates as shock-low density phase under limited resources, which is in contrast to the scenario with infinite number of particles. As expected, the symmetry breaking continues to persist even for higher values of system particles. Seven stationary phases are observed, with three of them exhibiting symmetry-breaking phenomena. The critical values of a total number of system particles, beyond which various symmetrical and asymmetrical phases appear and disappear are identified. Theoretical outcomes are supported by extensive Monte Carlo simulations. Finally, the size-scaling effect and symmetry-breaking phenomenon on the simulation results have also been examined based on particle density histograms.

Investigation of the model scale and particle size effects on the point load index and tensile strength of concrete using particle flow code

In this paper the effects of particle size and model scale of concrete have been investigated on point load index, tensile strength, and the failure processes using a PFC2D numerical modeling study. Circular and semi-circular specimens of concrete were numerically modeled using the same particle size, 0.27 mm, but with different model diameters of 75 mm, 54 mm, 25 mm, and 12.5 mm. In addition, circular and semi-circular models with the diameter of 27 mm and particle sizes of 0.27 mm, 0.47 mm, 0.67 mm, 0.87 mm, 1.07 mm, and 1.27 mm were simulated to determine whether they can match the experimental observations from point load and Brazilian tests. The numerical modeling results show that the failure patterns are influenced by the model scale and particle size, as expected. Both Is(50) and Brazilian tensile strength values increased as the model diameter and particle sizes increased. The ratio of Brazilian tensile strength to Is(50) showed a reduction as the particle size increased but did not change with the increase in the model scale.

Size Scaling of Photonic Crystal Surface Emitting Lasers on Silicon Substrates

We report here the lateral cavity size scaling and confinement effects on the lasing performance in defect-free photonic crystal surface-emitting lasers (PCSEL) on silicon substrates. Hybrid PCSELs with different lateral cavity sizes and different lateral confinement geometries have been fabricated using transfer printing technology and controlled selective etching. The measured lasing properties show a strong dependence on the lateral cavity size below 100 μ m. In particular, the finite lateral dimension significantly affects the laser threshold and side mode suppression ratio (SMSR) of the PCSEL devices. On the other hand, by controlling the lateral confinement using vertical etching, a reduction of the laser threshold is observed. The experimental results agree well with theoretical predictions. The work presented here can lead to ultra-compact PCSELs for on-chip integration with excellent energy efficiency.

Effect of nozzle size scaling in co-flow water cavitation jet peening

Water Cavitation Peening (WCP) employs cavitation to introduce compressive residual stresses in metals while limiting the surface roughening typical of similar surface enhancement processes such as shot peening and laser shock peening. As shown by a number of authors, cavitation intensity is greatly affected by the jet velocity as well as by the nozzle dimensions and shape. This paper reports on an investigation how nozzle dimensions affect cavitation intensity and peening performance in co-flow WCP of Al 7075-T651. Scalability of the process is investigated by comparing co-flow nozzles of increasing size but the same diameter ratios. The results show a substantial increase in cavitation intensity with nozzle size and a considerable decrease in the processing time required for saturation of the strip curvature and residual stress. The observed trends are explained by means of high-speed video imaging analysis and pitting tests, which show that the increase in cavitation intensity is due to an increase in the amount of cavitation when nozzle dimensions increase, while the pit depths and pit shape factor, which are measures of the strength of the cavitation events occurring at the workpiece surface, are largely unaffected. The process yields compressive residual stresses as high as 400MPa and as deep as 350μm below the surface, which are both a significant improvement upon previous results reported for shot peening.

Effects of aggregate size and specimen scale on asphalt mixture cracking using a micromechanical simulation approach

A micromechanical model based on discrete element method (DEM) was employed to investigate the effects of aggregate size and specimen scale on the cracking behavior of asphalt mixture. An algorithm for generating three-dimensional aggregates that can reflect the realistic geometry such as shape, size and fracture surface of aggregate particles was developed using a user-defined procedure coded with FISH language in particle flow code in three-dimensions (PFC3D). The parallel-bond model (PBM), linear contact model (LCM), and slip model(SM), whose sets of micro parameters were obtained by comparing experimental tests with numerical simulation results, were used to characterize the internal contact behavior of asphalt mixture. Digital asphalt mixture specimens were used to simulate the effects of aggregate size and specimen scale on the cracking behavior by the indirect tensile (IDT) test. Some conclusions can be drawn as follows: Both cracks and IDT strength decrease with increasing aggregate size. However, the heterogeneity of contact-force distribution augments with increasing aggregate size, especially with 13.2-16 mm aggregate. The aggregate size of 4.75-9.5 mm dominates in forming skeleton structure for asphalt mixture. The IDT strength decreases and cracks augment with increasing sample scale. The crack growth can be well interpreted from the perspective of energy analysis. The conclusions show that the proposed micromechanical model is suitable for the simulation of crack propagation. This study provides an assistant tool to further study the cracking behavior of particle-reinforced composites material such as asphalt mixture and Portland cement concrete.

Size-scale effects of inboard Store-Y on X-plane model: A parametric study using CFD

This paper presents the computational fluid dynamics (CFD) study on the effects of the Store-Y integration to the inboard pylon of X-plane model to its aerodynamic performance. Parametric study in terms of the size-scale of the Store-Y model is simulated at various angles of attack and air velocities. The resultant lift, drag and moment force parameters are recorded in each simulation and then analysed. The findings show that the size-scale effect of Store-Y model is insignificant to the aerodynamic performance, hence offers a possibility of other types of store to be integrated at this station without affecting the overall aircraft performance.

Statistical analysis of fracture characteristics of industrial iron ore pellets

The fracture load of iron ore pellets in the 12.5 to 16-mm size range is routinely measured in pellet plants following the ISO 4700 standard. The analysis of such data, however, seldom goes beyond averages and standard deviations of the load required for fracturing each pellet. Iron ore pellets are produced in the range from approximately 8 to 19mm, so the entire distribution of fracture strengths over the range of sizes produced is relevant. This study analyzed in great detail the variability and the size-scale effect on the strength of five industrial iron ore pellets. The fracture strength data of pellets contained in five size ranges were analyzed on the basis of 12 probability distributions, as well as different parameter estimation methods. Further, other measures collected from compression tests, that is, pellet stiffness and specific pellet fracture energy, were also analyzed as a function of pellet size. Results show that the Weibull distribution provided comparably good fitting to pellet strength data. Fracture energy data could be described well using the normal distribution with square root transformation, although the Gumbel distribution was identified as the best fit-for-purpose distribution describing the data. The maximum likelihood parameter estimation method was demonstrated to be marginally more capable of fitting the data than the least-squares technique. It was also shown that the fracture strength of pellets increases with a reduction in pellet size. This size effect on strength was found to be more pronounced than that predicted using Weibull theory on the basis of variability in pellet strengths.

Dislocation and Structural Studies at Metal–Metallic Glass Interface at Low Temperature

In this paper, molecular dynamics (MD) simulation deformation studies on the Al (metal)–Cu50Zr50 (metallic glass) model interface is carried out based on cohesive zone model. The interface is subjected to mode-I loading at a strain rate of 109 s−1 and temperature of 100 K. The dislocations reactions and evolution of dislocation densities during the deformation have been investigated. Atomic interactions between Al, Cu and Zr atoms are modeled using EAM (embedded atom method) potential, and a timestep of 0.002 ps is used for performing the MD simulations. A circular crack and rectangular notch are introduced at the interface to investigate the effect on the deformation behavior and fracture. Further, scale size effect is also investigated. The structural changes and evolution of dislocation density are also examined. It is found that the dominant deformation mechanism is by Shockley partial dislocation nucleation. Amorphization is observed in the Al regions close to the interface and occurs at a lower strain in the presence of a crack. The total dislocation density is found to be maximum after the first yield in both the perfect and defect interface models and is highest in the case of perfect interface with a density of 6.31 × 1017 m−2. In the perfect and circular crack defect interface models, it is observed that the fraction of Shockley partial dislocation density decreases, whereas that of strain rod dislocations increases with increase in strain.

Longitudinal waves in carbon nanotubes in the presence of transverse magnetic field and elastic medium

In the present paper, the coupling effect of transverse magnetic field and elastic medium on the longitudinal wave propagation along a carbon nanotube (CNT) is studied. Based on the nonlocal elasticity theory and Hamilton's principle, a unified nonlocal rod theory which takes into account the effects of small size scale, lateral inertia and radial deformation is proposed. The existing rod theories including the classic rod theory, the Rayleigh-Love theory and Rayleigh-Bishop theory for macro solids can be treated as the special cases of the present model. A two-parameter foundation model (Pasternak-type model) is used to represent the elastic medium. The influence of transverse magnetic field, Pasternak-type elastic medium and small size scale on the longitudinal wave propagation behavior of the CNT is investigated in detail. It is shown that the influences of lateral inertia and radial deformation cannot be neglected in analyzing the longitudinal wave propagation characteristics of the CNT. The results also show that the elastic medium and the transverse magnetic field will also affect the longitudinal wave dispersion behavior of the CNT significantly. The results obtained in this paper are helpful for understanding the mechanical behaviors of nanostructures embedded in an elastic medium.

In Vivo Single-Cell Fluorescence and Size Scaling of Phytoplankton Chlorophyll Content.

In unicellular phytoplankton, the size scaling exponent of chlorophyll content per cell decreases with increasing light limitation. Empirical studies have explored this allometry by combining data from several species, using average values of pigment content and cell size for each species. The resulting allometry thus includes phylogenetic and size scaling effects. The possibility of measuring single-cell fluorescence with imaging-in-flow cytometry devices allows the study of the size scaling of chlorophyll content at both the inter- and intraspecific levels. In this work, the changing allometry of chlorophyll content was estimated for the first time for single phytoplankton populations by using data from a series of incubations with monocultures exposed to different light levels. Interspecifically, our experiments confirm previous modeling and experimental results of increasing size scaling exponents with increasing irradiance. A similar pattern was observed intraspecifically but with a larger variability in size scaling exponents. Our results show that size-based processes and geometrical approaches explain variations in chlorophyll content. We also show that the single-cell fluorescence measurements provided by imaging-in-flow devices can be applied to field samples to understand the changes in the size dependence of chlorophyll content in response to environmental variables affecting primary production.IMPORTANCE The chlorophyll concentrations in phytoplankton register physiological adjustments in cellular pigmentation arising mainly from changes in light conditions. The extent of these adjustments is constrained by the size of the phytoplankton cells, even within single populations. Hence, variations in community chlorophyll derived from photoacclimation are also dependent on the phytoplankton size distribution.

Allometric scaling of physiological rates in the New Zealand geoduck clam, Panopea zelandica

The New Zealand geoduck clam Panopea zelandica (Quoy and Gaimard, 1835) is among the largest burrowing clams throughout the world. However, the effects of size scaling on physiology have not been studied for any geoduck species. In this study, we determined the allometric coefficients of respiration rate (RR) and clearance rate (CR) for P. zelandica. The allometric coefficients (β) of RR and CR in P. zelandica were 0.73±0.03 and 0.62±0.07, respectively. Since the clearance rate and oxygen consumption of bivalves are known to scale with dry weight, these coefficients may be used as mass exponent correction in physiological studies for P. zelandica.

Momentum enhancement due to hypervelocity impacts into pumice

Momentum enhancement refers to the effect of more momentum being transferred to a target than resides in the impactor. This increased momentum transfer is due to crater ejecta leaving the impacted body in the direction opposite to the impactor travel direction. An application for this effect is using hypervelocity impactors to deflect potentially hazardous asteroids and comet nuclei. A concern with historical work with consolidated material is the effect of porosity in the impacted body on momentum enhancement. Hypervelocity impact tests were performed of aluminum spheres striking pumice boulders. The pumice boulders ranged in mass from 70 to 486 kg and had an estimated porosity of 70 – 75%. Two different projectiles diameters were used (2.54 cm and 4.45 cm) to study the effect of size scale. Impacts occurred at roughly 2.1 km/s. Depth of penetration was measured, an estimated crater radius was measured (though the crater geometries were irregular), and momentum enhancement was measured. Significant scatter was observed in the results even though the tests were carefully controlled, with measured momentum enhancements ranging from 1 to 1.69 and the average being β = 1.3.

Учет масштабного эффекта при обосновании прочности магистральных трубопроводов

Учет масштабного эффекта при обосновании прочности магистральных трубопроводов

Size-dependent mechanical behavior and boundary layer effects in entangled metallic wire material systems

This paper describes the influence on the compressive and dissipative behavior of entangled metallic wire material (EMWM) samples provided by their size and mutual connectivity. The mechanical properties of EMWM specimens with different thicknesses are obtained from quasi-static compressive and cyclic loading. The behavior of the stress–strain curves, tangent modulus, and loss factor are strongly dependent on the thickness of the samples. The analysis from samples connected in different layouts shows that apart from the global thickness, size scale effects and contact interface also play important roles in controlling the behavior of EMWM systems. The importance of the sample size and its connectivity with adjacent different layers are defined by the unique microstructure and contact properties of the wires near the specimen boundary layer. The boundary layer produces different mechanical behaviors and a distinct structural configuration compared to the EMWM bulk solid. These peculiar characteristics are confirmed by microstructural and qualitative observations obtained from computed tomography scanning. The results and analysis presented in this work are relevant to designing EMWM material systems with adaptive performance under different loading and geometric constraints.

Scale effects in physical piano key weirs models

ABSTRACTWith inertia and gravity representing the dominant forces for most open channel flow applications (e.g. weir flow), Froude similitude is commonly used for scaling hydraulic performance data from the model to prototype structures. With weir flow, as the upstream head decreases, however, the relevance of surface tension and viscosity forces can increase to the point when the model and prototype similitude is not fully achieved through Froude scaling. Such discrepancies are referred as size-scale effects, and among other things, can result in variations in the head–discharge relationship, nappe trajectory, and air entrainment. Published criteria for avoiding significant size-scale effects for free flow over linear weirs have suggested that minimal heads of ∼0.02 to 0.07 m be respected, independently of the model size. In this study, the size-scale effect, minimum upstream head, and Weber number limits are investigated for four piano key weirs with geometric model scales of 1:1, 1:7, 1:15, and 1:25.

Thermal charging study of compressed expanded natural graphite/phase change material composites

The thermal charging performance of paraffin wax combined with compressed expanded natural graphite foam was studied for different graphite bulk densities. Constant heat fluxes between 0.39 W/cm2 and 1.55 W/cm2 were applied, as well as a constant boundary temperature of 60 °C. Thermal charging experiments indicate that, in the design of thermal batteries, thermal conductivity of the composite alone is an insufficient metric to determine the influence of the graphite foam on the thermal energy storage. By dividing the latent heat of the composite by the time to end of melt for each applied boundary condition, the energy storage performance was calculated to show the effects of composite thermal conductivity, graphite bulk density, and latent heat capacity. For the experimental volume, the addition of graphite beyond a graphite bulk density of 100 kg/m3 showed limited benefit on the energy storage performance due to the decrease in latent heat storage capacity. These experimental results are used to validate a numerical model to predict the time to melt and for future use in the design of heat exchangers with graphite-foam based phase change material composites. Size scale effects are explored parametrically with the validated model.

A methodology for in-situ micro-compression testing of fiber composites

Abstract A methodology for in-situ micro-compression testing of fiber composites has been developed. The tests were performed on carbon fiber reinforced bismaleimide matrix unidirectional composite, IM7/BMI 5250-4. Micro-size specimens were prepared from the bulk composite plaque through a two-step micro-fabrication process and then tested by using a micro-mechanical testing device placed inside the scanning electron microscope chamber. Results show that the fundamental properties (modulus and strength) of the fiber composites obtained from micro-size specimens are consistent with the theoretical estimations and significantly higher than those from macro-size specimens, which may have revealed the presence of size-scale effects in composite materials. The in-situ testing shows that the overall failure mode of the present composite is caused by “micro-buckling” of fibers in shear-mode. High shear strains are seen to occur at the fiber–matrix interfaces, which lead to the micro-cracking and ultimate failure of the composite.

Cover Image, Volume 99, Issue 8

Scanning electron micrographs of barium titanate in different microstructure scaling embodiments showing (red) a single crystal with ferroelastic domain structure, (green) a micrometer‐scale grain size bulk ceramic, and (blue) a polycrystalline nano‐scale grain size thin film. The respective polarization versus electric field hysteresis responses are superimposed showing the effects of size scaling on ferroelectric performance. Please see Feature Article, “Scaling Effects in Perovskite Ferroelectrics: Fundamental Limits and Process‐Structure‐Property Relations” by Jon F. Ihlefeld, David T. Harris, Ryan Keech, Jacob L. Jones, Jon‐Paul Maria, and Susan Trolier‐McKinstry. image

Evolutionary fracture analysis of masonry arches: Effects of shallowness ratio and size scale

Masonry arch structures can be determined by means of a detailed analysis that takes into account the intermediate cracking stage, which takes place when the tensile strength of the material has been exceeded, even though the collapse mechanism has not formed yet. Such a hypothesis is based on a constitutive law that returns a closer approximation to the actual material's behaviour. This paper presents the evolutionary analysis for the fracturing assessment of masonry arches. This method allows capturing the damaging process that occurs when the linear elastic behaviour's conditions in tension no longer apply, and before achieving the limit conditions. Furthermore, the way the thrust line is influenced by the formation of cracks and the consequent internal stresses redistribution, representing the “fracturing benefit”, can be assessed numerically. Size scale effects are also taken into account, as well as the influence of the arch's shallowness ratio.

Size-dependent pyroelectric properties of gallium nitride nanowires

The size scale effect on the pyroelectric properties is studied for gallium nitride (GaN) nanowires (NWs) based on molecular dynamics simulations and the theoretical analysis. Due to the significant influence of the surface thermoelasticity and piezoelectricity at the nanoscale, the pyroelectric coefficient of GaN NWs is found to depend on the cross-sectional size. This size-dependent pyroelectric coefficient of GaN NWs together with the size-dependent dielectric constant reported in our previous study is employed to study the pyroelectric potential of GaN NWs subjected to heating. The results show that the size scale effect is significant for thin NWs (cross-sectional size in nanometers) and may raise the pyroelectric potential of GaN NWs by over 10 times. Such a size scale effect on the pyroelectric properties of NWs originates from the influence of thermoelasticity, piezoelectricity, and dielectricity at the nanoscale and decreases with increasing cross-section of GaN NWs. It is expected that the present study may have strong implication in the field of energy harvesting at the nanoscale, as pyroelectricity offers a new avenue to the design of novel nanogenerators.