Meso Structure Research Articles

Anhydrides of Arylfuran and Arylpyran Pseudoacids: Formation and Structures; C–O Bond Lengths Trends in Pseudo o-Formylbenzoic Acid Derivatives

Three methods for producing anhydrides of arylfuran and arylpyran pseudoacids were explored. These included thermal dehydration, phosgene or thionly chloride activation and decomposition, and dicyclohexylcarbodiimide activation and coupling. Derivatives of the cyclic forms of o-formylbenzoic acid, o-acetylbenzoic acid, 2-carboxyphenylacetaldehyde and of 4,4-dimethyl-3,4-dihydro-3-hydroxy-[1H]-isobenzopyran-1-one were formed including dipseudoanhydides and normal-pseudo anhydrides. Crystal and molecular structures for meso and (R,R/S,S)-bis(1[3H]-isobenzofuranone-3-yl)ether, (R,R/S,S)-bis(3-methyl-1[3H]-isobenzofuranone-3yl)ether, meso (3,4-dihydro-[1H]-isobenzopyran-1-one-3-yl)ether, 3-benzoyloxy-1[3H]-isobenzofuranone, 3-benzoyloxy-3-methyl-1[3H]isobenzofuranone, 3-(4′-nitrobenzoyloxy)-4,4-dimethyl-3,4-dihydro-[1H]-isobenzopyran-1-one, and (1[3H]-isobenzofuranone-3-yl)(4,4,dimethyl-3,4-dihydro-[1H]-isobenzopyran-1-one-3-yl)ether are reported. Endocyclic pseudoacyl C–O bonds are always longer than the exocyclic pseudoacyl C–O bonds. It is possible to refine the previously established C–O bond length dependencies on the pKa (of the conjugate acids) of the leaving groups for 3-substituted 1-[3H]-isobenzofuranones. Of six dipseudoanhydrides studied, conformations are found with exocyclic C–O(ether) linkages synclinal to the endocyclic C–O and away from the ring (exo conformation) in two meso structures, two of three RR/SS forms and in a chiral unsymmetrical form. An endo conformation is observed in one of the RR/SS forms. In three normal-pseudo anhydrides, both endo and exo conformations are observed. Synthetic methods for formation of anhydrides of several arylfuran and arylpyran pseudoacids are described, and the pseudoacyl C–O bond length trends are determined for leaving groups spanning over 30 pKa units.

Double and Reversible Alkyl Transfer from ZrBn4/HfBn4 to a Diiminepyridine Ligand

Reaction of MBn4 (M = Zr, Hf) with diiminepyridine ligands MeDIP, EtDIP and iPrDIP [RDIP = 2,6‐(2,6‐R2C6H3N=CMe)2‐C5H3N] results in the transfer of two benzyl groups to the DIP imine carbon atoms, generating mixtures of rac and meso isomers of [RDIP + 2Bn]MBn2. The diastereomers could in several cases be separated by fractional crystallization, and the X‐ray structures of rac and meso [EtDIP + 2Bn]ZrBn2, meso‐[MeDIP + 2Bn]ZrBn2 and meso‐[EtDIP + 2Bn]HfBn2 are reported. On heating either diastereomer of [EtDIP + 2Bn]ZrBn2 in solution, the other isomer grows back in, demonstrating reversibility of the alkyl transfer. Transfer to other positions of the DIP skeleton was not observed. The reaction of [EtDIP + 2Bn]ZrBn2 with two equivalents of TEMPO produced structurally characterized [EtDIP + 2Bn]Zr(Bn)(TEMPO) which shows no tendency to isomerize.

Global topology of failure surfaces of metallic foams in principal-stress space and principal-strain space studied by numerical simulations

Failure surfaces of foam materials in the principal-stress/strain space are quite different from those of dense materials. They cannot be deduced directly by several simple tests such as uniaxial loading and pure shear loading. However, it is difficult to carry out arbitrary proportional triaxial loading tests on materials, resulting in the global topology of failure surfaces of metallic foams remaining unknown. To overcome the difficulty of triaxial loading tests, we carried out numerical simulations by applying triaxial loadings on 3D Voronoi models, which have been used successfully to study the global topology of yield surfaces of metallic foams. In the numerical simulations, 3D Voronoi structures were used to simulate the meso–structures of metallic foams, and only the parameters of the matrix material (aluminum) are needed. Considering the influence of multi-axial effects on the failure of metallic foam, a new failure criterion for metallic foams based on the mass of failed elements was proposed, and sufficient failure points in the principal-stress/strain space were obtained to characterize the failure surfaces well. Results indicated that the failure surface in the in the principal-stress space looks more complicated than the failure surface in the principal-strain space, so it is better to depict the failure surface in the principal-strain space, which approaches an ellipsoid. Furthermore, self-similarity exists in failure surfaces of metallic foams with different relative densities. Because a metallic foam may not fail when the compressive loadings are dominant, the failure surface appears to be a “missing area” in the permissible principal-stress/strain space. The boundaries of missing areas were determined analytically and validated numerically.

Meso Mechanical Study of Cracking Process in Concrete Subjected to Tensile Loading

Abstract This project focused on how the cracking process in concrete is influenced by both the micro and meso structures of concrete. The aim was to increase knowledge pertaining to the effect of critical parameters on the cracking process and how this is related to the material’s macroscopic properties. A methodology based on the combination of different experimental methods and measuring techniques at different scales was developed. Crack propagation during tensile loading of small-scale specimens in a tensile stage was monitored by means of Digital Image Correlation (DIC) and Acoustic Emission (AE). After testing, crack patterns were studied using fluorescence microscopy.

Structure Based Modulation of Electron Dynamics in meso-(4-Pyridyl)-BODIPYs: A Computational and Synthetic Approach.

The effects of structural modification on the electronic structure and electron dynamics of cationic meso-(4-pyridyl)-BODIPYs were investigated. A library of 2,6-difunctionalized meso-(4-pyridyl)-BODIPYs bearing various electron-withdrawing substituents was designed, and DFT calculations were used to model the redox properties, while TDDFT was used to determine the effects of functionalization on the excited states. Structural modification was able to restructure the low-lying molecular orbitals to effectively inhibit d-PeT. A new meso-(4-pyridyl)-BODIPY bearing 2,6-dichloro groups was synthesized and shown to exhibit enhanced charge recombination fluorescence. The fluorescence enhancement was determined to be the result of functionalization modulating the kinetics of the excited state dynamics.

Investigation and Control of Single Molecular Structures of Meso- Meso Linked Long Porphyrin Arrays.

We have investigated conformational structures of meso- meso linked porphyrin arrays (Z n) by single molecule fluorescence spectroscopy. Modulation depths ( M values) were measured by excitation polarization fluorescence spectroscopy. The M value decreases from 0.85 to 0.46 as the number of porphyrin units increases from 3 to 128, indicating that longer arrays exhibit coiled structures. Such conformational changes depending on the length have been confirmed by coarse-grained simulation. The histograms of M values and traces of centroid position of emitting sites by localization microscopy showed that the structures of longer arrays changed to more stretched after solvent vapor annealing with tetrahydrofuran.

Multi-scale characteristics of coal structure by x-ray computed tomography (x-ray CT), scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP)

It is of great benefit to study the material and structural heterogeneity of coal for better understanding the coalbed methane (CBM) storage and enrichment. In this paper, multi-scale X-ray computed tomography (CT), scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) at multi scales were conducted to thoroughly study the material distribution, heterogeneity, pore development, porosity and permeability of coal. It is suitable and reasonable to divide the testing samples into three structural categories by average density and heterogeneity degree, and the meso structure in the three categories accords with the morphology on SEM images. The pore size distribution and pore development of each subsample cannot be correspondingly related to their respective structure category or morphology due to different observation scales, while the macro pore size development, accumulated macro pore volume and macro pores porosity accord with the meso structure category and morphology information by CT and SEM at the same scale very well. Given the effect of macro pores on permeability and the contribution of micro pores to CBM storage capacity, reservoirs with developed micro pores and macro pores may be the most suitable coal reservoir for CBM exploitation.

Implementing 3D Printed Structures as the Newest Textile Form

Pioneering studies on the applications of 3D printing technology and additive manufacturing have been focusing on textile and clothing sector from the last two decades. Moreover, the creative momentum of fabric-like 3D printed structures has come to the point of transforming as for the newest form of textile applications after the advent of chain-mail like structures and flexible micro or meso structures created by SLS rapid manufacturing. Thus, the primary aim of this paper is to discuss the important properties of traditional fabrics that are to be expected of 3D printed structures namely physical properties like flexibility, bending and and drapability. The secondary aim of this study is to compare the mentioned physical properties of 6 3D printed samples regarding same geometry with different sizes, structures and rapid manufacturing methods.

Polylactic acid (PLA) based green composites reinforced pineapple leaf fibres: evaluation of processing and tensile performance

This paper reports on a study of the compression moulding and the vacuum forming of unidirectional pineapple leaf fibres/polylactic acid composites and the influence of process variables on the tensile properties of the material. The characterisation of the micro and meso structures of the pineapple leaf fibres is reported. The effect of consolidation temperature on the fibre thermal stability and the tensile properties of the composites is investigated. The results show that vacuum forming was found to be preferable process with high stiffness modulus and UTS of the composites, compared to compression moulding. The insignificant detrimental effect of 165°C high consolidation temperature was observed. Finally, the fibre thermal degradation seems to dominate the composite tensile performance over its interfacial quality between the fibre and the matrix.

A 3D Voronoi and subdivision model for calibration of rock properties

Rock cleavages consist of the cracks between blocks and the internal faults in blocks. The built-in modeling module in the Three-dimension Distinct Element Code cannot accurately describe the internal structure and the cleavage development characteristics of rock. This study combined 3D Voronoi block elements and scanning electron microscope images, to construct a numerical model equivalent to the rock meso structures. Three strategies are proposed to refine the initial model by block subdivision to achieve a function that allows cleavages in the model to cross through the blocks. A physical uniaxial compression test was performed in the laboratory to calibrate the mechanical parameters of the siltstone and the calibrated parameters then were validated by a Brazilian disc test. Sensitivity analysis was conducted to investigate the relationship between the meso-parameters and the model’s macro-response, and a calibration procedure was established for accurate replication of rock mechanical behavior. The statistics and analyses of failure characteristics for joints in the model showed that when the compressive and tensile strength values peaked, the percentages of tensile failures were approximately 37% and 10%, respectively. Comparing the cleavages after sample failure in lab tests with the cleavage development paths predicted by the models, the compressive and tensile characteristics were analyzed and the results confirmed the reliability of applying the 3D Voronoi block and subdivision modeling method in the numerical simulation study of the mechanical properties of the rock.

Numerical Analysis on Usability of SHPB to Characterize Dynamic Stress–Strain Relation of Metal Foam

Split Hopkinson pressure bar (SHPB) technique is the most important test method to characterize dynamic stress–strain relations of various materials at different strain rates, and this technique requires uniform deformation of specimen during the experiment. However, some studies in recent years have found obvious deformation localization within metal foam specimens in SHPB tests, which may significantly affect the reliability of the results. Usability of SHPB to characterize dynamic stress–strain relation of metal foam becomes doubtful. In this paper, based on experimental verification, we carried out numerical simulative SHPB tests to study the problem, in which the metal foam specimens were modeled to have 3D meso structures with properties of their matrix material. Numerical simulative SHPB tests of aluminum foam specimens with varying thickness at different strain rates were performed. Deformation distribution in each local region of the specimen was examined and a concept of “effective specimen” was presented. Appropriate specimen thickness and range of testing strain rate were suggested based on quantitative analysis. Finally, we recommended a method how to revise the nominal strain and strain rate measured by traditional SHPB method to acquire the reliable dynamic stress–strain relation.

Surface morphology and physicochemical properties of ordered mesoporous silica SBA-15 synthesized at low temperature

The effects of process parameters on the surface morphology and physicochemical characteristics of ordered mesoporous silica SBA-15 synthesized at low temperature have been investigated in this study. SBA-15 particles were synthesized through sol-gel method using non-ionic surfactant Pluronic P123 and TEOS as a silica source with aqueous hydrochloric acid (HCl) as a catalyst under the following conditions: HCl concentration (1.0-2.5 M), ageing temperature (40-70ºC) and ageing time (12-48 hours). A series of physicochemical characterizations and material analyses were performed on SBA-15 particles including Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Transmission Electron Microscopy (TEM), BET surface area analysis, Fourier transform infrared (FTIR) analysis and X-ray Diffraction (XRD) analysis. From the experimental observation, the conditions of HCl concentration, ageing temperature and ageing time were able to influence the surface morphology of SBA-15 particles. The presence of the ordered structures in SBA-15 particles was observed through the formation of 1-D cylindrical channels and 2-D hexagonal pores, inspected by using TEM. The detected XRD peak at (100) reflection signified the presence of ordered meso structures within the SBA-15 particles. Therefore, synthesis of SBA-15 particles through sol-gel method at low temperature is feasible and more sustainable if compared to the energy intensive hydrothermal method.

A meso-macro numerical approach for crack-induced diffusivity evolution in concrete

In this paper, the authors present a meso-macro numerical approach in order to determine macroscopic diffusivity tensors in heterogeneous quasi-brittle materials such as concrete. The meso-structure is based on a two-phase 3D representation of heterogeneous materials with stiff aggregates embedded in a mortar matrix. In order to take into account these heterogeneities without any mesh adaptation, a weak discontinuity is introduced into the strain field of those finite elements containing more than a single material. In addition, a strong discontinuity is also added to take into account the crack formation and evolution. The mesoscale coupling with the mass transport part is based on Fick’s Law with a modified diffusion coefficient accounting for crack opening and aggregates. Then, by means of an homogenization procedure some macro values for the macroscopic diffusivity tensor are computed. The main original contribution of this paper is that the macroscopic diffusivity tensor integrates more complex features. Such features coming as a by-product results of the meso-macro analysis such as the cracking process – including evolution from diffuse cracks in the bulk to localized macro-crack(s) –, tortuosity of the crack’s path, induced-anisotropy and presence of aggregates. The defined tensor is used afterwards in order to estimate the service-life of concrete structures, including the effect of the cracking and the internal meso structure.

Characterization and Stability of Heteropolyacid Catalysts Supported on MCM-41 Materials Synthesized by Ultrasonic Irradiation

A series of solid acid catalyst of the Keggin-type 12-phosphotungstic acid, H3PW12O40, supported on ordered mesoporous silica MCM-41 were prepared by a simple and effective impregnation method. MCM-41 supports were synthesized in a relatively short time via a recently reported ultrasonic irradiation method. The synthesis sonication time has been systematically varied in order to investigate its influence on the structural order of the resulting materials. The prepared catalysts were characterized by nitrogen adsorption, X-ray diffraction, Raman spectroscopy and thermogravimetric analysis. The resulting materials exhibited hexagonally ordered meso structure, with high surface area of the order of several hundreds of m2g-1,relatively large pore volumes, with the pore diameter in the range of 2.19 to 2.41 nm and a corresponding pore wall thickness of over 1.67nm. The results have demonstrated that high quality MCM-41 materials can be synthesized via the ultrasonic irradiation in few tens of minutes, much shorter than the conventional synthesis methods. Despite their relatively high loading, all synthesized materials retained the characteristic MCM-41mesoporous structure after impregnation of the heteropolyacid active phase onto the inner pore surface, without crystallization, but preserving the Keggin structure as confirmed by Raman spectroscopy.

Experimental meso scale study on the distribution and evolution of methane adsorption in coal

To reveal the nature of methane storage in coal under different adsorption pressures, a method combining scanning electron microscopy and energy dispersive spectrometry (SEM-EDS) with infrared thermal imaging is used to observe meso structures, methane distribution, and evolution characteristics in coal. The results indicate that the different meso structures of coal have different methane adsorption characteristics, leading to a non-uniformity of the methane distribution and evolution. In other words, compared with the cavity pores and meso fractures in telocollinite, which are compactly filled with clay minerals, the cell cavity pores and meso fractures in telinite, which are non-compactly filled with clay minerals, have more inter-gravel pores and broken coal structures at different scales, and can store great amounts of methane owing to a larger surface area and greater number of adsorption sites for methane molecules. Therefore, the methane content in coal increases sharply in these meso structures with increasing adsorption pressure, resulting in a centralization of the adsorption locations and increasing inhomogeneity of methane storage at different locations. In addition, owing to the shallower potential wells for methane adsorption, the coverage rate of the adsorption sites in these meso structures increases more slowly during an increase in pressure, leading to a decreased aggregation of methane storage in coal.

Three-Dimensional simulation of metallic two-bar warp-knitted mesh based on loop structure geometry

In order to predict the appearance and porosity of the metallic two-bar warp-knitted mesh, a three-dimensional (3-D) loop model was developed by some key points on loop, and then based on the model meso structure of mesh was simulated. Firstly, a two-dimensional (2-D) loop geometry in metallic warp-knitted mesh was established. The loop geometry was described on the basis of the yarn property effect to loop sharp. And the underlap geometry was taken as an arc. To describe the 2-D loop geometry, coordinates of key points called databases were established. Then databases in 2-D loop geometry were relocated through the loop offset by stress distribution. Secondly, the 3-D loop geometry was ensured according to the yarn diameter, the angle between loop plane and fabric plane as well as the type of loops (front bar loop or back bar loop), etc. Finally, the coordinates of databases were imported to TexGen software to simulate the 3-D meso structures of the metallic mesh. By comparing simulation images with actual fabrics, the 3-D loop geometry model was fitted well for metallic two-bar warp-knitted mesh. And the simulation results demonstrated that the predicted porosity of mesh was in good agreement with experimental values.

A probability based model for the erosive wear of concrete by sediment bearing water

The purposes of this work were: (i) to understand how erosive wear is affected by the random meso structure of concrete, and (ii) to develop a model for erosive wear of concrete structures due to the action of sediment bearing water loads. An aggregate generation algorithm with certain novel features is used to generate a database comprising 400,000 aggregates with varying levels of angularity and flakiness. Using these aggregates, a probabilistic model for mass loss due to aggregate erosion was formulated. A Monte Carlo simulation is used to obtain the time to failure for single aggregates; these were used to obtain an estimate of slurry erosive loss from the concrete structure, where successive layers of aggregates are assumed to satisfy the ergodicity assumption. The mass loss estimates were compared with experimental results for a sediment bearing water jet. A good qualitative match was observed, with both experimental results and probabilistic estimates exhibiting very similar dependence on meso geometry.

Protocol for a Systematic Review: Provision of Information and Communications Technology (ICT) for Improving Academic Achievement and School Engagement in Students Aged 4‐18

Protocol for a Systematic Review: Provision of Information and Communications Technology (ICT) for Improving Academic Achievement and School Engagement in Students Aged 4‐18

Meso–meso Directly-linked trimeric and pentameric electron-deficient porphyrin–hexaphyrin hybrid arrays

meso–meso Directly-linked trimeric and pentameric porphyrin–hexaphyrin hybrid arrays 5 and 6 comprising of electron-deficient porphyrin units were prepared by cross-condensation of monomeric and dimeric electron-deficient meso-formyl porphyrins with a tripyrrane. The solid-state structures of 5 and 6 have been determined by single crystal X-ray diffraction analysis. The latter is the largest crystal structure of meso–meso linked multiporphyrinic array analogues reported to date.

繊維強化複合材料のメソ構造が剛性と浸透性に及ぼす影響

繊維強化複合材料のメソ構造が剛性と浸透性に及ぼす影響