Hole Size Distribution Research Articles

Reinforcement of cementitious mortars with hemp fibers and shives

Abstract Polypropylene, steel, and carbon fibers are used to increase the ductility and toughness of concrete materials. In recent years, studies on the use of natural fibers have increasingly continued. Among natural fibers, hemp fiber has the highest tensile strength value. The aim of this study was to discuss and present the results of the experimental study on the use of cement-based hemp shives and fibers to increase the ductility of mortars. Another aim is to increase the use of hemp in the construction field by using more economical and natural fibers. Various binders and different amounts of fibers and shives were added and their effects on flexural strength were investigated. Water absorption and flexural tests and scanning electron microscope and X-ray diffraction analysis were performed on the produced samples. Particle and hole size distributions and stereo microscope images of the samples are given. The use of hemp fibers was observed to improve flexural strength, while shives were not significantly improved flexural strength.

Not Every Circle Is a Crater: Kettle Hole Size Distributions and Their Implications in Planetary Surface Age Dating

Circular landscape features, including kettle lakes, sinkholes, pingos, calderas, and craters, develop from a variety of different geomorphic processes on Earth. On many rocky extraterrestrial surfaces, including Mars, the most common circular landscape features are craters, and the density of these craters is commonly used to estimate the age of the surface. On planetary bodies where fluvial, volcanic, and glacial geomorphic processes are not present, alternative interpretations of circular features can safely be ignored. However, Mars once hosted an Earth-like climate and many elements of the Martian landscape that are visible today were formed by ancient fluvial, glacial, or volcanic processes. In this work, we focus on the potential presence of postglacial kettle hole depressions on Mars. We explore the size and density distribution of kettle lakes in three analog postglacial landscapes on Earth and discuss the implications for planetary surface age dating if kettles and craters are present together in the landscape on Mars.

Molecular dynamics study of the environmental stress cracking agent assisted cavitation in linear and branched polyethylene

We used molecular dynamics (MD) simulation to investigate whether an environmental stress cracking (ESC) agent would help the cavitation process in linear polyethylene (LPE) and branched polyethylene (BPE) by examining the free volume hole size and spatial distributions at the [PE]-[ESC agent] interfaces. The BPE models used contained 10 and 82 butyl/hexyl branches/1000 backbone carbons and the ESC agent used was nonyl ethoxylate (NE) at concentrations 0.001–1.4 wt%. The results show that there exist no significant changes in the packings of LPE and BPE chains, as characterized by their radial distribution functions (RDFs), in the presence of NE regardless its concentration. However, molecular packings at the [PE]-[NE] interfaces vary with NE concentration. In particular, ethylene (E) segments of NE, compared to the ethylene oxide (EO) segments, exhibit stronger association with LPE and BPE chains. We used the Voronoi tessellation method to determine the size and spatial distributions of free volume holes at the [PE]-[NE] interfaces and found that more and larger free volume holes formed around the E-segments than the EO-segments. And such effect was found to be more pronounced in the case of LPE chains than the BPE chains. We further investigated the free volume holes coalescence dynamics using the Fourier mode analysis. The number of frequency modes and the corresponding intensities of the E-segments were significantly higher than those of EO-segments, suggesting that E-segments exhibited a higher tendency to form more and larger free volume holes. This suggests that [PE]-[E-segments] interfaces have a higher chance to form larger voids (i.e., cavitation, a feature of brittle failure that is experimentally observed in ESC). The tendency intensified with increasing NE concentration but was reduced by the presence of short chain branches. The high mobility of terminal carbons in the short chain branches is believed to suppress the formation of large free volume holes at the [PE]-[E-segments] interfaces by absorbing the newly formed free volume by that of the terminal carbons.

Fabrication of ferrous tungstate with enhanced sonocatalytic performance for meloxicam removal

The composites ferrous tungstate (FeWO4) were fabricated as the sonocatalyst for degradation of meloxicam (MEL) in water. The composites are prepared carefully via hydrothermal reaction of sodium tungstate dehydrate and ferrous ammonium sulfate hexahydrate. The morphology of FeWO4 were controlled successfully, by adjusting the acidity of the reaction solution (pH = 5, 6, 7, 8, 9). Multiple characterization results revealed that the obtained FeWO4 shared the similar nano-microspheres structure, but with different BET surface area and energy gap. The sonocatalytic experiments showed that FeWO4 nanomaterials with various synthetic pH values had different sonocatalytic performance on degradation of meloxicam (MEL), and FeWO4 synthesized at pH 6 reaches maximum of 73.5% on degradation of MEL. This phenomenon was not only due to the moderate BET surface area (31.18 m2/g), moderate pore size distribution (10–30 nm) and moderate energy gap (1.73 eV) of FeWO4 nano-microspheres, ·OH and holes also played a key role in the removal of MEL. The obtained catalyst was proved to be stable enough after four cycles. Our study demonstrates a novel finding, not reported previously, that FeWO4 could be utilized as a promising sonocatalyst to degrade MEL by ultrasound-driven.

Size distributions of the largest hole in the largest percolation cluster and backbone

At criticality in two dimensions, the size distribution of holes within a large percolation cluster or backbone was recently found to be governed by a power law with the exponent given by a hyperscaling relation. It was also found that, though the boundary of the largest hole is a fractal, the size of the largest hole itself is proportional to Ld, where L represents the linear system size and d=2 is the spatial dimension. In this work, we study the probability distribution of the size of the largest hole in the largest percolation cluster and that in the largest backbone, and compare them with the probability distribution of the size of the largest percolation cluster and that of the largest backbone themselves. We obtain these four size distributions in the critical region by Monte Carlo simulations for the two-dimensional bond percolation model on the square lattice with periodic boundary conditions. It is found that each of these distributions can be described by a different single-variable function P(C,L)dC=P̃(x)dx, with x≡C∕LdC, where C is the size of the structure whose (fractal) dimension is dC. The function P̃(x) is generally not unimodal, and interestingly, for the largest cluster hole, symmetric properties are found in its size distribution due to duality, e.g., P̃(x) is symmetric around the mean value x=1 at the percolation threshold pc. We characterize these size distributions by calculating the variance and different dimensionless cumulant ratios, which exhibit rich critical behaviors at the pseudocritical and critical points. For example, the extremum of the excess kurtosis and the zero point of the skewness locate at the same (pseudocritical) point, whose values are different for the four structures but approach pc in the limit L→∞. We also perform wrapping analyses for each size distribution, showing that different wrapping types contribute to the overall distribution in different forms.

Self-assembly of superstructures at all scales

Summary Controllable assembly of molecular and nanoscale building blocks into uniform superstructures up to bulk dimensions remains a key challenge in the next phase of nanotechnology development. Here, we report the self-assembly of superstructures at all scales by taking advantage of the partial miscibility of water and 1-butanol to generate transient aqueous emulsion droplets that can encapsulate the target materials and introduce them into template holes. Further diffusion of water into 1-butanol depletes the emulsion droplets, assembling the building blocks into one well-defined superstructure in each hole. Superstructuring of various types and shapes of nanoparticles, biomolecules, and inorganic compounds could be achieved without the need for surfactants and chemical modifications. The versatility, scalability, low-cost, and accurate positioning are crucial advantages for the future development of advanced precision manufacturing.

A new look at release event frequencies

Within the context of a quantitative risk analysis (QRA), the two main constituents used to describe petrochemical risks are, and have always been, consequence and probability. The consequences of hazardous material accidents are easy to apprehend – if a hazard is realized it can injure people or cause fatalities, damage equipment or other assets, or cause environmental damage. Frequencies for these consequences, on the other hand, are not as easy to understand. Process safety professionals develop event frequencies by evaluating historical data and calculating incident rates, which represent, in the QRA context, how often a release of a hazardous material has occurred. Incident rates are further modified by probabilities for various hole sizes, release orientations, weather conditions, ignition timing, and other factors, to arrive at unique event probabilities that are applied in the QRA. This paper describes the development of incident rates from historical database information for various equipment types, as well as defining a methodology for assigning hole size probabilities from the same data, such that a hole size distribution can be assigned within each QRA study. The combination of total incident rates and a hole size distribution relationship can then serve as a foundation within the frequency side of many QRA studies.

Evaluation of mixing performance for the industrial-scale radial multiple jets-in-crossflow mixing structure

The radial multiple jets-in-crossflow mixing structure (RMJCMS) is extensively used in industrial manufacture. In this research, flow behavior induced by an industrial-scale RMJCMS is investigated via computational fluid dynamics considering the example of the mixing of TiCl4 and O2 in the chloride process. The flow features of RMJCMS are accurately captured through simulation. The momentum ratio and size distribution of jet holes are notable elements for controlling the mixing performance. For an injection ring with single-diameter jet holes, the optimal momentum ratio was 3.2. To improve the mixing performance of RMJCMS, a design strategy that maximized the effect of convective mixing by modifying the distribution of the jet hole diameters was proposed based on the simulation results to guide the design of the injection ring. With the designed injection ring, the dimensionless mixing distance decreased by 50% compared with the equal-hole case, validating the effectiveness of the design strategy.

Effect of the Mass Fraction of Ceramic Particles on the Porosity of Wear-Resistant Composites Fabricated by Combustion Synthesis

Combustion synthesis was employed to fabricate a wear-resistant composite using reactions between Ti, Al, Fe3O4, B4C, and CrO3 powders on the steel plate. CaF2 was used to improve the fluidity and decrease the melting temperature of Al2O3. A large number of holes were found in the top of the composite with different contents of ceramic particles. To elucidate the relationship between the mass fraction of ceramic particles and porosity, the adiabatic temperatures of different combustion systems were calculated. The porosity and size distribution of the holes of samples with different ceramic particle contents were studied, and the distributions and compositions of the ceramic particles were analyzed. The compositions surrounding and inside the holes were studied, and the hardness of the composite was also tested. The results show that the formation of holes is associated with the vaporization of Al and Cr. The porosity increases with an increase in the ceramic particle contents which is the combined effect of the decreasing adiabatic temperature, the increasing nucleation rate, the increasing ceramic particle sizes, the increasing viscosity of the metal, and the wetting angle between the liquid and solid phase, while the composition of ceramic particles has little effect. The hardness values of all composites exceed 60 HRC.

Densely-stacked N-doped porous carbon monolith derived from sucrose for high-volumetric energy storages

Development of carbon electrodes with high volumetric electrochemical performance is challenging for high-performance energy storage devices. In this work, we demonstrate a novel sucrose-derived porous carbon monolith (NPC-m) constructed by holey carbon nanosheets for super-high volumetric energy storages.NPC-m, derived from sucrose via a facile yet scalable and economic “bottom-up” synthesis route, exhibits a high specific surface area of 1376m2g−1, a narrow hole size distribution, and a high N content (∼6.65 at. %). Most importantly, a self-stacking density as high as 1.26gcm−3 can be achieved via simple drying processes. The electrodes based on NPC-m in carbon electrodes deliver super-high volumetric capacities of 1385mAhcm−3 (0.1Ag−1) for Li-ion batteries and 380Fcm−3 (0.5Ag−1) for supercapcacitors, highlighting their great potentials for high-performance energy storages.

Load bearing and failure characteristics of perforated square CFRP tubes under axial crushing

Open holes or cutouts have been commonly used in composite structures for various engineering purposes. This paper aims to investigate the load bearing behavior and failure characteristics of the square weave carbon fiber reinforced plastic (CFRP) tubes with open holes subjected to axial compression. Effects of hole size, hole shape and hole distribution on failure modes and mechanical behaviors were evaluated experimentally and numerically. Different with the progressive crushing mode seen in the intact CFRP tubes, mid-height collapse and unstable local buckling were observed in the axial crushing tests. The peak load and specific energy absorption (SEA) of the perforated tubes decreased by around 3–22% and 26–57%, respectively, compared to those of the intact CFRP counterparts. It was found that the effect of hole size on failure strength in tubes was less sensitive than that in perforated composite laminates, but was relatively stronger than the perforation shape and distribution. The damage mechanisms were explored in-depth using strain gauge tests and finite element analysis, which showed a significant increase in shear stress around the holes prior to final failure.

Electrically conductive epoxy-polyester-graphite nanocomposites modified with aromatic amines

Abstract Epoxy resin nanocomposites containing graphite nanosheets (GNS) and unsaturated polyester resin (UPR) were prepared by incorporating GNS in semi interpenetrating network (semi-IPN) of epoxy resin and unsaturated polyester resin (E-UPR). GNS are prepared by thermal shock treatment of sulphuric acid-graphite intercalation compound (GIC) followed by ultra-sonication. The E-UPR-GNS semi-IPNs were further modified with aromatic amines such as benzidine (Bz) and diphenyl amine (DPA). All the samples were prepared by mixing Triethylenetetramine (TETA) as the curing agent at two different temperatures viz. room temperature (RT) and low temperature (LT; 5 °C). A transition is observed in the conducting properties of the samples: from an electrical insulator to an electrical semiconductor in case of nanocomposites especially on addition of GNS to E-UPR semi-IPNs. A sharp improvement is observed in conductivity after modification with diphenyl amine (DPA) cured at LT. The nanocomposites obtained at LT exhibit homogeneity with minimum anisotropy in conductivity. The morphology, mechanical, thermal and electrical properties were evaluated using various analytical techniques. Positron annihilation spectroscopy was carried out to correlate the measured properties with the free volume and free volume hole size distribution. The results are consistent with the reported studies.

Effect of supercritical carbon dioxide on nanoporous polyhexafluoropropylene

The effect of supercritical CO2 (sc-CO2) on the size distribution of free volume holes (nanopores) in a polyhexafluoropropylene (PHFP) polymer matrix has been studied. Residual (after CO2 release) swelling improves gas transport properties of the material. Relaxation of these properties over time has been compared with changes in permeability and nanoporosity. For PHFP samples with different histories, the data on nanoporosity have been obtained using positron annihilation lifetime spectroscopy (micropores) and the lowtemperature gas sorption technique (mesopores and part of micropores). Matching of the data is intended to reveal the role of pores of different sizes in permeability of membrane materials to different gases and determine the specifics of application of the positron annihilation technique to studying sc-CO2-modified objects.

Solvent and relative humidity effect on highly ordered polystyrene honeycomb patterns analyzed by Voronoi tesselation

ABSTRACTHighly ordered honeycomb‐patterned polystyrene surfaces are efficiently prepared by static breath figure method. The structured arrays can be obtained by casting a dilute solution polymer on glass substrates under various conditions. Tetrahydrofuran and chloroform are used as solvent to form cavities of several micrometers. The analysis of the surfaces indicates nonlinear relation between concentration and pore size in this system. Voronoi tessellations of the polystyrene surfaces at different relative humidity (RH) are achieved, and each conformational entropy determined. Optimum parameters of concentration and RH are obtained for both solvents. Analysis of hole size distribution and conformational entropy demonstrates the high order of the films obtained. This is a promising method for the fabrication of homogeneous and highly porous films from polystyrene. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44004.

Hole size distributions in cardo-based polymer membranes deduced from the lifetimes of ortho-positronium

To clarify the free volume size distributions of the cardo-based polymer membranes, where ortho-positronium (o-Ps) undergoes pick-off annihilation, the o-Ps lifetime distributions were analyzed by the LT9 programme. It was found that the cardo-based polysulfone membrane has much narrower o-Ps lifetime/hole size distributions than the cardo-based polyimide membranes with the 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) moiety. Further, the lifetime/hole size distributions of the cardo-based polymer membranes are appreciably broadened with increasing temperature. This suggests that in these membranes there are holes not only of different sizes but also of different thermal expansion coefficients. It is also shown that in a membrane with a wider hole size distribution the average o-Ps lifetime tends to be longer than would be expected from the correlation between the o-Ps lifetime and the total free volume for common polymers.

Specifics of positron studies of microheterogeneous systems as applied to new polymeric sorbents

The size distribution of free volume holes in mesoporous, microheterogeneous polymer sorbents based on linear rubber-modified divinylbenzene copolymers has been studied. Analysis of the results of the study and published data has shown that positron annihilation lifetime spectroscopy (PALS) applied to microheterogeneous systems, in contrast to homogeneous systems, is not necessarily sensitive to mesopores that occur at the boundaries of heterogeneities and determine the sorption or membrane properties of the modified materials. To obtain the complete information, additional procedures such as low-temperature (BET) gas adsorption and thermally stimulated luminescence (TSL) need to be used. This circumstance is due to a considerably long distance between mesopores in heterogeneous systems and limited mobility of positronium during its localization in a pore. In addition to the BET data, which largely give information on mesopores, PALS appears useful for studying micropores. The TLS technique makes it possible to judge on heterogeneity of test materials. The minimal concentration of mesopores detectable by the positron technique in the systems of interest has been determined.

Optical quality assurance of GEM foils

An analysis software was developed for the high aspect ratio optical scanning system in the Detector Laboratory of the University of Helsinki and the Helsinki Institute of Physics. The system is used e.g. in the quality assurance of the GEM-TPC detectors being developed for the beam diagnostics system of the SuperFRS at future FAIR facility. The software was tested by analyzing five CERN standard GEM foils scanned with the optical scanning system. The measurement uncertainty of the diameter of the GEM holes and the pitch of the hole pattern was found to be 0.5μm and 0.3μm, respectively. The software design and the performance are discussed. The correlation between the GEM hole size distribution and the corresponding gain variation was studied by comparing them against a detailed gain mapping of a foil and a set of six lower precision control measurements. It can be seen that a qualitative estimation of the behavior of the local variation in gain across the GEM foil can be made based on the measured sizes of the outer and inner holes.

Low-temperature positron annihilation study of B+-ion implanted PMMA

Temperature dependent positron annihilation lifetime spectroscopy (PALS) measurements in the range of 50–300 K are carried out to study positronium formation in 40 KeV B+-ion implanted polymethylmethacrylate (B:PMMA) with two ion doses of 3.13 × 1015 and 3.75 × 1016 ions/cm2. The investigated samples show the various temperature trends of ortho-positronium (o-Ps) lifetime τ3 and intensity I3 in PMMA before and after ion implantation. Two transitions in the vicinity of ∼150 and ∼250 K, ascribed to γ and β transitions, respectively, are observed in the PMMA and B:PMMA samples in consistent with reference data for pristine sample. The obtained results are compared with room temperature PALS study of PMMA with different molecular weight (Mw) which known from literature. It is found that B+-ion implantation leads to decreasing Mw in PMMA at lower ion dose. At higher ion dose the local destruction of polymeric structure follows to broadening of lifetime distribution (hole size distribution).

Positron annihilation in cardo-based polymer membranes.

Positron annihilation lifetime spectroscopy (PALS) is applied to a series of bis(aniline)fluorene and bis(xylidine)fluorene-based cardo polyimide and bis(phenol)fluorene-based polysulfone membranes. It was found that favorable amounts of positronium (Ps, the positron-electron bound state) form in cardo polyimides with the 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) moiety and bis(phenol)fluorene-based cardo polysulfone, but no Ps forms in most of the polyimides with pyromellitic dianhydride (PMDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BTDA) moieties. A bis(xylidine)fluorene-based polyimide membrane containing PMDA and BTDA moieties exhibits a little Ps formation but the ortho-positronium (o-Ps, the triplet state of Ps) lifetime of this membrane anomalously shortens with increasing temperature, which we attribute to chemical reaction of o-Ps. Correlation between the hole size (V(h)) deduced from the o-Ps lifetime and diffusion coefficients of O2 and N2 for polyimides with the 6FDA moiety and cardo polysulfone showing favorable Ps formation is discussed based on free volume theory of gas diffusion. It is suggested that o-Ps has a strong tendency to probe larger holes in rigid chain polymers with wide hole size distributions such as those containing cardo moieties, resulting in deviations from the previously reported correlations for common polymers such as polystyrene, polycarbonate, polysulfone, and so forth.

Self‐Assembly: Sacrificial‐Post Templating Method for Block Copolymer Self‐Assembly (Small 3/2014)

Block copolymer (BCP) thin films self-assemble to form nanoscale patterns, as K. K. Berggren and co-workers report on page 493. On a smooth substrate, the polystyrene-block-poly(dimethylsiloxane) copolymer forms randomly oriented inplane cylinders with a 35-nm period (images on the left). A set of sacrifical nanoposts made of poly(methyl methacrylate) directed the self-assembly to form (center top to bottom): square arrays of spheres or holes, and square and hexagonal meshes with bimodal hole-size distributions. The posts and the polystyrene are removed by etching and the final pattern consists of oxidized poly(dimethylsiloxane)