Range Of Structural Configurations Research Articles

Disorder-induced Fickian, yet non-Gaussian diffusion in heterogeneous media

Fickian yet non-Gaussian diffusion is observed in several biological and soft matter systems, yet the underlying mechanisms behind the emergence of non-Gaussianity while retaining a linear mean square displacement remain speculative. Here, we characterize quantitatively the effect of spatial heterogeneities on the appearance of non-Gaussianity in Fickian diffusion. We study the diffusion of fluorescent colloidal particles in a matrix of micropillars having a range of structural configurations: from completely ordered to completely random. We show that non-Gaussianity emerges as a direct consequence of two coupled factors; individual particle diffusivities become spatially dependent in a heterogeneous randomly structured environment, and the spatial distribution of the particles varies significantly in such environments, further influencing the diffusivity of a single particle. The coupled mechanisms lead to a considerable non-Gaussian nature even due to weak disorder in the arrangement of the micropillars. A simple mathematical model validates our hypothesis that non-Gaussian yet Fickian diffusion in our system arises from the superstatistical behavior of the ensemble in a structurally heterogeneous environment. The two mechanisms identified here are relevant for many systems of crowded heterogeneous environments where non-Gaussian diffusion is frequently observed, for example in biological systems, polymers, gels and porous materials.

Electrochemical properties of vertically aligned graphenes: tailoring heterogeneous electron transfer through manipulation of the carbon microstructure.

The electrochemical response of different morphologies (microstructures) of vertically aligned graphene (VG) configurations is reported. Electrochemical properties are analysed using the outer-sphere redox probes Ru(NH3)62+/3+ (RuHex) and N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), with performances de-convoluted via accompanying physicochemical characterisation (Raman, TEM, SEM, AFM and XPS). The VG electrodes are fabricated using an electron cyclotron resonance chemical vapour deposition (ECR-CVD) methodology, creating vertical graphene with a range of differing heights, spacing and edge plane like-sites/defects (supported upon underlying SiO2/Si). We correlate the electrochemical reactivity/response of these novel VG configurations with the level of edge plane sites (%-edge) comprising their structure and calculate corresponding heterogeneous electron transfer (HET) rates, k0. Taller VG structures with more condensed layer stacking (hence a larger global coverage of exposed edge plane sites) are shown to exhibit improved HET kinetics, supporting the claims that edge plane sites are the predominant source of electron transfer in carbon materials. A measured k0eff of ca. 4.00 × 10−3 cm s−1 (corresponding to an exposed surface coverage of active edge plane like-sites/defects (% θedge) of 1.00%) was evident for the tallest and most closely stacked VG sample, with the inverse case true, where a VG electrode possessing large inter-aligned-graphene spacing and small flake heights exhibited only 0.08% of % θedge and a k0eff value one order of magnitude slower at ca. 3.05 × 10−4 cm s−1. Control experiments are provided with conventional CVD (horizontal) grown graphene and the edge plane of highly ordered pyrolytic graphite (EPPG of HOPG), demonstrating that the novel VG electrodes exhibit ca. 3× faster k0 than horizontal CVD graphene. EPPG exhibited the fastest HET kinetics, exhibiting ca. 2× larger k0 than the best VG. These results are of significance to those working in the field of 2D-carbon electrochemistry and materials scientists, providing evidence that the macroscale electrochemical response of carbon-based electrodes is dependent on the edge plane content and showing that a range of structural configurations can be employed for tailored properties and applications.

Development of a new proof of plate capacity under combined in-plane loads

ABSTRACTIn this paper, the development of a new proof of plate capacity under combined in-plane loads for ship design and classification is described. The new proof is based on an improved understanding of plating collapse obtained from an extensive series of non-linear buckling analyses using the finite element method and covering the full range of structural configurations and load combinations relevant for the shipbuilding industry. Compared to existing proofs, the new proof incorporates a more physically based approach towards tensile stress effects on plate capacity and better captures the influences of both plate slenderness and aspect ratio under compressive biaxial loads. Moreover, the new proof can be solved without the need for iterations and may be used directly with stresses obtained from finite element analyses, thereby eliminating the need for a correction of stresses due to Poisson effects.

Template-Induced Structure Transition in Sub-10 nm Self-Assembling Nanoparticles

We report on the directed self-assembly of sub-10 nm gold nanoparticles confined within a template comprising channels of gradually varying widths. When the colloidal lattice parameter is mismatched with the channel width, the nanoparticles rearrange and break their natural close-packed ordering, transiting through a range of structural configurations according to the constraints imposed by the channel. While much work has been done in assembling ordered configurations, studies of the transition regime between ordered states have been limited to microparticles under applied compression. Here, with coordinated experiments and Monte Carlo simulations we show that particles transit through a more diverse set of self-assembled configurations than observed for compressed systems. The new insight from this work could lead to the control and design of complex self-assembled patterns other than periodic arrays of ordered particles.

Effect of relative failure consequences in reliability based dual performance design

During its design life, a structure has to satisfy several performance requirements. It is now common to express all safety requirements, as well as some functionality requirements, in reliability based formats. Failure consequences (hence target reliabilities), structural behavior, capacity, loads and modeling uncertainties and thus the limit states themselves are different at these various performance levels, and the design must take these aspects into account. This paper develops optimal partial safety factors over a range of structural configurations for the design of partially prestressed sections in flexure corresponding to two performance levels — cracking and collapse — satisfying respective target reliabilities. Detailed numerical examples and derivations are presented. The role of relative failure consequences at the two performance levels in determining the governing limit state, the “balance point” where both limit states are active, and the possible implication on maintenance strategies, meas...

Gas Flow Rate through Damaged Low Aspect Ratio Shearwalls

Squat reinforced concrete (RC) shearwalls are often used to contain nuclear material or other dangerous gases in the U.S. Department of Energy's (DOE) complex. Damage to such walls can be expected even during minor earthquake shaking. The escape of dangerous gases post-event is therefore of concern. In this paper, the flow rate of air through damaged squat RC walls is analytically predicted for a broad range of structural configurations, loading conditions, and concrete compressive strengths at different differential pressures. Design charts relating shearwall lateral drift ratio and air leakage rate are presented. Among the parameters considered in this study, the shearwall boundary element size has the most significant effect on the flow rate. The paper concludes with a design example demonstrating the use of the design charts.

Structural design of high-strength austenitic stainless steel

Efficient use of material is an important factor in achieving economical and sustainable structures. Typically, annealed austenitic stainless steel has a material strength of around 220 N/mm 2, somewhat lower than that of common structural carbon steel grades. This lower strength, coupled with the higher material cost, puts stainless steel at a significant disadvantage when considering material selection, despite its other desirable properties. However, the strength of stainless steel may, at relatively low expense, be considerably enhanced through modification of the chemical composition and through the process of cold working due to the strain hardening nature of the material. This strength enhancement has not generally been utilised in practice due to a lack of knowledge on the structural behaviour of this high-strength material. Given the high material cost of stainless steel, the need to optimise the efficiency of design methods and to develop the performance, availability and diversity of the current product range is clear. To this end, this paper describes tests, numerical modelling and the development of design guidance for high-strength stainless-steel members in a range of structural configurations. Material tensile tests, member tests in compression and member tests in bending have been described. The results of the tests have been successfully replicated numerically, and subsequent sensitivity studies and parametric studies have been performed. Test and numerical results have been compared against two design methods developed for standard-strength material (Eurocode 3 Part 1.4 and the deformation capacity based design method). The comparisons have revealed that both design methods provide a similar level of reliability to that offered for standard-strength material, and thus, extension of both design methods to the high-strength grades has been recommended.