Area Moment Research Articles

Design and Analysis of Broadband Ultrathin Reflective Linear-to-Circular Polarization Converter Using Polygon-Based Anisotropic-Impedance Surface

A broadband reflective linear-to-circular polarization converter (LCPC) is designed using a polygon-based single-layer anisotropic-impedance surface on an ultrathin (thickness is 0.053λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>0</b></sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>0</b></sub> is the wavelength corresponding to the mid operating frequency) ground-backed substrate. Using the admittance analysis of the equivalent circuit model (ECM) and extraction of the admittance through the area moment of inertia equations, simple and generalized design guidelines are presented. The proposed polarization converter produces left-handed circularly polarized (LHCP) and right-handed circularly polarized (RHCP) reflected waves, respectively, for the linearly polarized (LP) TE and TM incident waves. It offers 46% (7.62-12.16 GHz) 3 dB axial ratio bandwidth (ARBW) for normal incidences of both the TE- and TM-polarized waves. Moreover, for oblique incidences (up to 30°) of both the LP waves, the ARBW response remains quite stable. The far-field radiation characteristics, which are often not studied, are provided to show its usability as a dual-LP to dual-CP converting reflector for X-band communications. The measurement results show good agreement with the numerically simulated results.

On The Vibrations of Pyramidal Beams With Rectangular Cross-Section and Application to Unswept Wings

Summary The bending frequencies of an unswept wing are calculated based on the model of a beam clamped at the root and free at the tip. For a tapered wing with straight leading- and trailing-edges, the chord is a linear function of the span; the same linear function of the span applies to thickness, in the case of constant thickness-to-chord ratio. The latter is usually small, so that the beam differs from the more frequent cases of a conical beam with a circular cross-section or a prismatic beam with a square cross-section. Thus, the bending modes of a non-uniform beam are considered, with mass and area moment of inertia which are respectively quadratic and quartic functions of the span. There is no exact solution expressible in finite terms using elementary functions, and thus power series expansions are used. The bending frequencies are calculated for a delta wing and compared with a rectangular wing, with the same span, mean chord and thickness, mass density and Young’s modulus. It is shown that the fundamental frequency is higher by a factor 4.96 for the delta wing; it is also shown that the general case of the tapered wing is intermediate between the delta and the rectangular wing. Lastly, the analytical results obtained for the bending modes are compared with numerical modal analyses of general tapered wing beams using high-fidelity finite-element model software.

Heuristic Operator for Reliability Assessment of Frame Structures

In structural design of steel frames, in order to achieve proper safety, the effect of uncertainties in the design and loading parameters of the structure must be considered. This approach is obtained by defining a reliability index. In this study, the Modified Dolphin Monitoring (MDM) operator was used to evaluate the reliability index of three well-known steel frame structures based on the Hasofer-Lind method. The reliability index was evaluated using the EVPS and VPS algorithms and with considering the MDM operator on them. The constraint of the last story drift is considered as limit state function. The random variables consist of external loads, modulus of elasticity, moment of inertia and cross-sectional areas. According to the number of evaluations of the limit state function, the results show the efficiency of this method in comparison to the Monte Carlo simulation method. Also, the values of the most probable point (MPP) are examined.

Shape optimisation of singly-symmetric cold-formed steel purlins

This paper presents the results of a study aiming at shape optimising singly-symmetric cold-formed steel purlins. The “self-shape” optimisation algorithm previously developed, proven to be robust and to converge to known solutions is used for this purpose. Eight optimisation cases are considered, consisting of 1.5 mm and 1.9 mm thick purlins, spanning either 3000 mm or 8000 mm and drawn with either 4, 6 or 8 elements per half cross-section. The aim of the algorithm is to minimise the cross-sectional area subjected to the following constraints: (i) the sections must at least match the second moment of area, and the inward and outward bending capacities of commercial purlins used as reference profiles, (ii) be readily manufacturable using existing roll-forming process, (iii) can be connected similarly to existing purlins by offering vertical and horizontal flat elements long enough and strategically positioned to bolt the purlins to gusset plates and screw the roof to them, respectively, and (iv) have an opening wide enough to run services. The restraints provided by the roof sheeting is considered in the algorithm when calculating the bending capacities. Results show that the algorithm converges to consistent solutions and satisfactory satisfies all constraints, resulting in manufacturable and useable purlins. When compared to the reference purlins, the optimised solutions result in saving up to 6.6% of steel. This cost saving in material is quite significant for a mass-produced product such as purlins. The efficiency of the optimised purlins relative to the reference sections were further validated with FE analysis. The FE analyses confirm that the optimised 1.5 mm thick purlins are superior to the reference section. The optimised purlins may therefore benefit the cold-formed steel industry as they represent more economical solutions without compromising on the usability and performance of the products. However, the FE model shows that the 1.9 mm thick purlins may not have the expected performance and experimental testing is fully validate the optimised sections.

Planform Geometry and Excitation Effects of PVDF-Based Vibration Energy Harvesters

In the present paper, we report a systematic investigation of planform geometry and excitation level effects on the dynamics and power generation characteristics of polyvinylidene difluoride (PVDF)-based cantilevered vibration energy harvesters. Piezoelectric vibration energy harvesters provide a promising energy harvesting solution for widespread use of wireless sensors in remote locations. Highly flexible PVDF polymers offer resonant frequencies at suitable range for harvesting mechanical energy within low-frequency applications, though information on the efficient sizing of these devices is currently limited. We test the response of a set of eight harvesters to typical vibration sources excitation levels in the range 0.2–0.6 g. This set comprises four widths and two lengths, incrementing each time by a factor of two. The selected range of dimensions is sufficient to identify optimal power output versus width for both lengths tested. This optimal width value depends on excitation amplitude in such a way that narrower harvesters are more suited for small excitations, whereas wider harvesters perform better upon experiencing large excitations. Non-linear effects present in longer harvesters are demonstrated to significantly reduce performance, which motivates the selection of planform dimensions inside the linear range. Finally, we explore the correlation of performance with various geometric quantities in order to inform future design studies and highlight the value of using the second moment of planform area to measure harvester efficiency in terms of power density. This points towards the use of harvesters with non-rectangular planform area for optimal performance.

COMPUTER TECHNOLOGIES IN THE CALCULATION OF GEOMETRIC CHARACTERISTICS OF COMPLEX SECTIONS

None of the calculations for machine parts, structure elements and constructions for strength, rigidity and stability can be performed without using the geometric cross-section characteristics. These include: cross-sectional area, axial, centrifugal and polar moments of inertia, radius of gyration, axial and polar resistance moments of cross-section, etc. The article discusses the problem of technical specialties students` training quality improvement with information technologies aids. There is a review and proposed methodology of usage the software for calculating the geometric cross-sections properties. There are two groups of software: 1) software developed by teachers of higher educational institutions to use in the educational process; 2) industrial software for design engineers, which can also be used during the educational process. Using as an example the calculation of the geometric cross-sections properties of a complex section formed from several rolled profiles, it is demonstrated that the usage of programs "Geom 2006", "Compass 3D", "Consul" and "Constructor of sections" has the following advantages: decrease the costs of effort and time for routine mathematical calculations, makes it easier to find and correct errors made by manual calculations during individual study, which has a positive effect on the learning process; the implementation of calculation and graphic tasks using computer software significantly increases the interest of students for the discipline that is being studied and contributes to the better consolidation of theoretical knowledge and practical skills; students acquire skills in creating design schemes, preparing initial data, analyzing the obtained results, which are necessary for their further work with software systems for structures calculations during the course and for diploma design; it is especially useful to use the proposed programs for distance learning as an effective tool to organize individ-ual study.

Fast Shot Boundary Detection Based on Separable Moments and Support Vector Machine

The large number of visual applications in multimedia sharing websites and social networks contribute to the increasing amounts of multimedia data in cyberspace. Video data is a rich source of information and considered the most demanding in terms of storage space. With the huge development of digital video production, video management becomes a challenging task. Video content analysis (VCA) aims to provide big data solutions by automating the video management. To this end, shot boundary detection (SBD) is considered an essential step in VCA. It aims to partition the video sequence into shots by detecting shot transitions. High computational cost in transition detection is considered a bottleneck for real-time applications. Thus, in this paper, a balance between detection accuracy and speed for SBD is addressed by presenting a new method for fast video processing. The proposed SBD framework is based on the concept of candidate segment selection with frame active area and separable moments. First, for each frame, the active area is selected such that only the informative content is considered. This leads to a reduction in the computational cost and disturbance factors. Second, for each active area, the moments are computed using orthogonal polynomials. Then, an adaptive threshold and inequality criteria are used to eliminate most of the non-transition frames and preserve candidate segments. For further elimination, two rounds of bisection comparisons are applied. As a result, the computational cost is reduced in the subsequent stages. Finally, machine learning statistics based on the support vector machine is implemented to detect the cut transitions. The enhancement of the proposed fast video processing method over existing methods in terms of computational complexity and accuracy is verified. The average improvements in terms of frame percentage and transition accuracy percentage are 1.63% and 2.05%, respectively. Moreover, for the proposed SBD algorithm, a comparative study is performed with state-of-the-art algorithms. The comparison results confirm the superiority of the proposed algorithm in computation time with improvement of over 38%.

Modeling and parameter analysis of deflection of a beam

In this paper, we present the model equation of a beam when it applies compression forces on ends of the beam and carries a load. For the structural point of view, there should be a suitable model to understand the behavior under different conditions of loading of a beam. Mathematical modeling is the simulation of a physical structure or physical phenomenon by constructing suitable analytic and numerical solution. We analyze the deflections of the beam by taking different structures of beam. The structures of beam depend on the compression forces on beams with different beams with different weights. We observe the deflection by applying various compression forces at the ends of the beam. The influence of the effect of some parameters appeared in mathematical formulations such as area moment of inertia (I), Young’s modulus (E), load (W) and compressive force (P) on deflection variation are investigated in this paper. We analyze the results that how compression forces affect the system. We use finite difference method to solve the model equation numerically. We analyze and compare the numerical result with analytic solution.&#x0D; BIBECHANA 18 (2021) 75-82

Automated and qualitative structural evaluation of floor plans for remodeling of apartment housing

Abstract Many floor plans are proposed during the early stage of an apartment housing remodeling project as it involves a multitude of entities with different stakes. Consequently, the process to converge the opinions per the individual's preference on an agreed remodeling floor plan becomes repetitive and time consuming. For these reasons, structural evaluation of each proposed conceptual plan is often bypassed and postponed until a finalized floor plan is determined. An automated structural evaluation application for architectural floor plans of apartment housing with the load-bearing wall system is developed on this necessity. The application reads the conceptual drawings and returns various supportive information regarding structural performance, almost instantly. The outputs from the application include the amount of removed, remaining, and new bearing walls, 3D views of each wall component overlaid on the floor plans and their dimensions, area moment of inertia (AMOI) of the walls, torsional resistance of the floor plans, and other supportive indices. For easy and intuitive communication with the users, an abstract and simple quantitative value, structural index (SI), is suggested and included as one of the outputs in the application. In order to validate the developed automated application, a case study is conducted with an ongoing remodeling project, and the results, accuracy, and processing time are compared with the conventional hand calculation method. The application is accurate with errors of less than 1.3%, while the processing speed is nearly seven times faster. With the developed application, the designers could evaluate their conceptual drawings in almost real time. In addition, the stakeholders would communicate in a more straightforward language with the outputs of the application, such as the AMOI evaluation and SI results. Consequently, it is anticipated that the decision-making process during the early stage of a remodeling project would be expedited with the help of the developed automated application.

Structure-Controlled Variable Stiffness Robotic Joint Based on Multiple Rotary Flexure Hinges

Variable stiffness actuator (VSA) plays an important role for achieving safety and robustness for robots to physically interact with environments. This article proposes a structure-controlled approach in developing a new variable stiffness robotic joint with the merits of compactness, high stiffness, and high displacement-to-stiffness ratio. Unlike the common methods of using antagonist springs and lever concept, the structure-controlled approach achieves stiffness variation through the adjustment of mechanical structure configuration inside the actuator. Specifically, the stiffness variation is realized by changing the effective second moment of area through rotating a combination of leaf flexure hinges arranged in a radial configuration. A range of configurations are studied and the configuration we identified has the advantages of minimum unbalanced twists in the mechanism while providing high transmission torque, large stiffness, range and minimum lateral buckling effects. The performance characteristics are accomplished through a novel variable stiffness mechanism and a position-based control strategy for both position and torque control modes. A prototype system was implemented to verify the characteristic and performance of the design concept. It demonstrated that the new VSA system is effective for realising independent joint-stiffness and joint-position control of robot joints.

Evaluation of experimental, analytical, and computational methods to determine long-bone bending stiffness

Methods used to evaluate bone mechanical properties vary widely depending on the motivation and environment of individual researchers, clinicians, and industries. Further, the innate complexity of bone makes validation of each method difficult. Thus, the purpose of the present research was to quantify methodological error of the most common methods used to predict long-bone bending stiffness, more specifically, flexural rigidity (EI). Functional testing of a bi-material porcine bone surrogate, developed in a previous study, was conducted under four-point bending test conditions. The bone surrogate was imaged using computed tomography (CT) with an isotropic voxel resolution of 0.625 mm. Digital image correlation (DIC) of the bone surrogate was used to quantify the methodological error between experimental, analytical, and computational methods used to calculate EI. These methods include the application of Euler Bernoulli beam theory to mechanical testing and DIC data; the product of the bone surrogate composite bending modulus and second area moment of inertia; and finite element analysis (FEA) using computer-aided design (CAD) and CT-based geometric models. The methodological errors of each method were then compared. The results of this study determined that CAD-based FEA was the most accurate determinant of bone EI, with less than five percent difference in EI to that of the DIC and consistent reproducibility of the measured displacements for each load increment. CT-based FEA was most accurate for axial strains. Analytical calculations overestimated EI and mechanical testing was the least accurate, grossly underestimating flexural rigidity of long-bones.

Interspecific anatomical differences result in similar highly flexible stems in Bignoniaceae lianas.

Lianas are intriguing forest components in the tropics worldwide. They are characterized by thin and flexible stems, which have been related to a unique stem anatomy. Here, we hypothesized that the anatomical diversity of lianas, varying in shapes, proportions, and dimensions of tissues and cell types, would result in different stem bending stiffnesses across species. To test this hypothesis, we chose four abundant liana species of central Amazonia belonging to the monophyletic tribe Bignonieae (Bignoniaceae) and compared their basal stems for their anatomical architectures and bending properties. Measurements of anatomical architecture and bending stiffness (structural Young's modulus) included light microscopy observations and three-point bending tests, which were performed on basal stems of eight individuals from four Bignonieae species. All analyses, including comparisons among species and relationships between stem stiffness and anatomical architecture, were performed using linear models. Although the anatomical architecture of each species consists of different qualitative and quantitative combinations of both tissues and cell types in basal stems, all species analyzed showed similarly lower bending stiffnesses. This similarity was shown to be directly related to high bark contribution to the second moment of area, vessel area and ray width. Similar values of stem bending stiffness were encountered in four liana species analyzed despite their variable anatomical architectures. This pattern provides new evidence of how different quantitative combinations of tissue and cell types in the basal stems of lianas can generate similarly low levels of stiffness in a group of closely related species.

Reducing the Risk of Ring Breakage in Taylor Spatial Frames: The Effect of Frame Configuration on Strain at the Half-ring Junction.

AimWe have encountered four cases with Taylor spatial frames (TSF) (Smith & Nephew, Memphis, TN, USA) with breakage at the half-ring junction of the distal ring. This study examines the strain produced on different locations of the distal ring during loading and the effects on the strain of altering the frame construct.Materials and methodsWe mounted two ring TSF constructs on tibia saw bone models. The proximal ring was the same in all constructs and consisted of a 2/3 180 mm ring attached with three wires. Construct 1 is reproducing the configuration of cases where failure was seen. The distal 155 mm ring is attached with three half pins. The half-ring junction is located in the midline. Construct 2 has a different half pin placement and an additional wire on the distal ring. Constructs 3 and 4 have the same half pin configuration to construct 1 but the distal ring is rotated 60° internally and externally, respectively. Strain gauges were attached to different locations and measurements recorded during loading. Statistical analysis was performed.ResultsHighest strain values were recorded at the half-ring junction of constructs 1 and 2 (>600 microstrains (με) in tension). Rotating the ring 60° internally significantly reduces the strain at the half-ring junction (<300 με) whilst external rotation by 60° further reduces the strain (<180 με). Ring strain is higher in areas close to half pin attachments.ConclusionThe highest strain is in the half-ring junction as the half rings are subjected to different loading modes. The thickness of the half-ring is halved and the second moment of area reduced further increasing breakage risk. Placing this junction close to the half pin–frame interface, as dictated by the anatomical safe zone further increases the strain. Rotating the distal ring 60° significantly reduces the strain at the half-ring junction.Clinical significanceRing breakage is a rare but significant complication. This is the first study to address this potential mode of TSF failure. Insights and technical tips from this study can help reduce this.How to cite this articleIliadis AD, Bebja R, Wang K, et al. Reducing the Risk of Ring Breakage in Taylor Spatial Frames: The Effect of Frame Configuration on Strain at the Half-ring Junction. Strategies Trauma Limb Reconstr 2020;15(3):146–150.

Effects of acidosis on the structure, composition, and function of adult murine femurs

Physiologic pH is maintained in a narrow range through multiple systemic buffering systems. Metabolic Acidosis (MA) is an acid-base disorder clinically characterized by a decrease in systemic pH and bicarbonate (HCO3−) levels. Acidosis affects millions annually, resulting in decreased bone mineral density and bone volume and an increased rate of fracture. We developed an adult murine model of diet-induced metabolic acidosis via graded NH4Cl administration that successfully decreased systemic pH over a 14 day period to elucidate the effects of acidosis on the skeletal system. Blood gas analyses measured an increase in blood calcium and sodium levels indicating a skeletal response to 14 days of acidosis. MA also significantly decreased femur ultimate strength, likely due to modifications in bone morphology as determined from decreased microcomputed tomography values of centroid distance and area moment of inertia. These structural changes may be caused by aberrant remodeling based on histological data evidencing altered OCL activity in acidosis. Additionally, we found that acidosis significantly decreased bone CO3 content in a site-specific manner similar to the bone phenotype observed in human MA. We determined that MA decreased bone strength thus increasing fracture risk, which is likely caused by alterations in bone shape and compounded by changes in bone composition. Additionally, we suggest the temporal regulation of cell-mediated remodeling in MA is more complex than current literature suggests. We conclude that our model reliably induces MA and has deleterious effects on skeletal form and function, presenting similarly to the MA bone phenotype in humans.

Peak values of twist-to-bend ratio in triangular flower stalks of Carex pendula: a study on biomechanics and functional morphology.

Because of their own weight and additional wind forces, plants are exposed to various bending and torsional loads that sometimes require contradictory structural characteristics and mechanical properties. The resulting trade-off between flexural and torsional rigidity can be quantified and compared using the dimensionless twist-to-bend ratio. The flexural rigidity of the stems of Carex pendula was determined by 2-point bending tests. Additionally, 4-point bending tests and torsional tests were carried out on segments of two internodes directly below the inflorescences to measure flexural and torsional rigidity. Anatomical investigations were performed to quantify the cross-sectional distribution of their tissues. The flexural rigidity of the stems, segments of the apical internode 1, and the more basal internode 2 differed significantly from each other, whereas the bending elastic moduli were not significantly different. The torsional rigidity of segments of internode 2 was a factor of 3.3 higher than that of internode 1, whereas the torsional moduli did not differ significantly. The twist-to-bend ratios of segments of internode 1 and 2 reached values between 85 and 403. Light microscopic investigations revealed a triangular stem possessing individual sclerenchyma strands, with internode 2 having significantly more strands than internode 1. In the case of Carex pendula, flexural and torsional rigidity are adapted to the given mechanical constraints by significant changes in morphometric variables (axial and polar second moment of area, number of sclerenchyma strands), whereas the material properties (bending and torsional modulus) do not change markedly along the stem.

Theoretical chemistry study on the toxicity of some polychlorobiphenyl (PCB) compounds using molecular descriptors

This study was carried out to establish, validate and apply a model that relates the toxicity of some PCBs (2,4-dichlorobiphenyl, 2,4’5-trichlorobiphenyl, 2,2’3,4,4’,5’,6-heptachlorobiphenyl, 2,2’,5,5’-tetrachlorobiphenyl and 2,3,3’4,4’-pentachlorobiphenyl) to molecular descriptors (quantum chemical, physicochemical and topological descriptors) through quantitative structure toxicity relationship. The established model reveal that the total molecular energy, electronic energy, core repulsion energy, energy of the highest occupied molecular orbital, energy of the lowest unoccupied molecular orbital, cosmo area, cosmo volume and dipole moment displayed excellent correlation with LD50 values of the PCBs. Some topological parameters (namely molecular topological index, Weiner index, total connectivity and Balaban index) also exhibited excellent correlation with experimentally determined LD50 data. Two equations suitable for estimating theoretical LD50 values of the studied PCBs were derived using quantum chemical and topological descriptors. These equations gave perfect fitness when experiment and theoretical LD50 values were plotted (i.e. R2 value approximated unity) against each other. Perfect correlation was also obtained between theoretical and experimentally derived LD50 values for 2,2’,3,4’,5’,6-hexaxhlorobiphenyl, 2,2’,4,5,5’-pentachlorobiphenyl, 2,3’,4,4’-tetrachlorobiphenyl and 2,2’,4,4’,5,5’-hexachlorobiphenyl, where were PCBs used for model validation. The model was also used to predict the toxicity of other PCBs that lacks accurate experimental data. The study revealed that the reactivity of PCBs can be influence by the number of substituted chlorine atom and by the position of the reactive aromatic carbon. From the results and findings of the study, it was concluded that the applications of quantitative structure-toxicity relation principles to quantum and topological parameters provide excellent avenue for estimating the degree of toxicity of PCBs.

Genetic variation of keel and long bone skeletal properties for 5 lines of laying hens

Fractures to the keel bone is one of the greatest problems facing the laying hen industry. With most severe effects observed in non-cage housing, frequencies are expected to dramatically increase as the industry continues transitioning away from battery cages. Incidences within commercial systems are well documented, where the main cause is believed to be high egg production and the associated need for calcium drawing on endogenous reserves (i.e., bone) leaving bone weakened and prone to fracture. The current work sought to characterize various bone mineral and biomechanical properties of 5 distinct purebred or crossbred laying hen lines (3 commercial: Bovans Brown, Dekalb White, and Institut de Sélection Animale Dual Brown; 2 non-commercial: Experimental Brown and Experimental White), following previous work that demonstrated differences in susceptibility to keel fracture using an ex vivo impact testing apparatus. The keel was then removed to undergo analysis by computer tomography; the humerus and tibia were also removed for biomechanical testing. The keel bone mineral density and moment of area correlated moderately with hen weight and susceptibility to fracture. The biomechanical properties of the tibia, but not the humerus, showed a strong relationship with hen weight. One commercial genetic line (Dekalb White) with a high susceptibility to fracture exhibited a mean tibia strength below the value expected from its mean weight. Our results suggest that for the purebred or crossbred lines other than Dekalb White, rather than properties of bone, lower mean weight may imply higher levels of activity, higher risk of collisions, and lower soft tissue protection that reflect greater susceptibility to keel fracture.

Structural and functional changes of the protein β-lactoglobulin under thermal and electrical processing conditions

In the present study we have tried to explore the effect of static external electric field of strength 3.0 V/nm on the conformational changes adopted by the protein β-lactoglobulin. We have chosen different temperatures viz. 300 K, 400 K and 450 K to evaluate the temperature dependent effect of electric field. We have observed that combined effect of high temperature and static external electric field show significant changes on the structural conformation of the protein which in turn may affect the functional properties of the protein. Calculations of root mean square deviations reveal that both helical and β-sheet regions of the protein are noticeably affected at high temperature. We have used solvent accessible surface area (SASA) and dipole moment values to explain that there is changes in hydrophobicity of the protein surface due to presence of external electric field. The study reveals that electric field in combination with high temperature can be used to alter the conformation of the protein and the effect of external electric field is more pronounced at high temperature than that of low temperature. The study provides a better understanding of the conformational changes adopted by the protein under the stress of external electric field and high temperature and provide guidance to choose optimum conditions for processing without loss of nutritional properties.

Temperature-induced modification of the dewatering behaviour of Ferri-Oxyhydroxide precipitates formed from low tenor solutions

Mining activities generate Acid Mine Drainage (AMD) and wastewater streams rich in dissolved inorganic species that negatively affect water quality. Conventional lime treatment of AMD leads to the precipitation of a voluminous sludge, comprising mainly of Ferri-Oxyhydroxide (Fe-O-OH) and gypsum, whose matrix renders it difficult to dewater. Such precipitates also show poor post-precipitation stability, and they are disposed of to landfills where metal remobilization can occur over time. This paper proposes that temperature assisted structural maturation of primary precipitates results in aged precipitates with improved dewatering behaviour (in terms of settleability, specific resistance to filtration (SRF) and filterability). A precipitate produced from the neutralization of aqueous acidic Fe2(SO4)3 (ferric concentration of 100, 300 and 800 mg/L) by sub-stoichiometric Ca(OH)2 solutions at room temperature was continuously matured in a holding mixed tank reactor kept at 30, 40 and 50 °C. The aged precipitates were analysed for particle size distribution, number of particles formed, mass moment and surface area moment mean particle size, crystal habit, morphology and zeta (ζ)-potential. The results demonstrate that(i)at [Fe(III)] = 100 mg/L, discernible spherical agglomerated Fe-O-OH particles are formed, whose surface area moment mean size and filtration rate attain a maximum at 40 °C, beyond which the particles experienced re-dissolution leading to size reduction. These particles exhibited poor settleability at all ageing temperatures, implying that continuous ageing had no noticeable effect on settling;(ii)at [Fe(III)] = 300 mg/L, a transition zone exists where there is maximum settleability of 2.7 ± 0.2 mm/min at 40 °C, a near neutral surface charge (ζ-potential = +1.1 mV) that favours agglomeration, the largest mean particle sizes (D4,3 = 26.27 μm, D3,2 = 17.0 μm) but a crystal habit that hindered filterability. This [Fe(III)] and ageing temperature (40 °C) showed potential for enhanced dewatering behaviour, should the ageing time be increased;(iii)at [Fe(III)] = 800 mg/L, formation of small densely packed spherulites whose degree of interlocking and interconnected layers decreased whilst the particle size increased with temperature leading to improved filterability.Based on these results, the operational implications for lime neutralization plants are that there is a temperature and [Fe(III)] trade-off at which higher throughput of sludge with improved settling characteristic is realized. However, additional ageing time is required in order for the structural maturation to effect changes in particle size, packing and morphology that yield increases in the filtration rates – as was shown by the [Fe(III)] of 300 mg/L at 40 °C.

Buckling behavior of a wire-like electrode with a concentration-dependent elastic modulus based on a deformed configuration

Buckling behavior may occur during the lithiation process of wire-like electrodes, and it can cause the mechanical degradation of lithium-ion batteries (LIBs). In this study, we focused on the stress evolution and buckling behavior of wire-like electrodes with a concentration-dependent elastic modulus, and we considered the two-phase reaction. The elastic finite deformation theory was adopted to establish the mechanics equations under the assumption of the elastic modulus being a linear function of the lithium concentration. The modified second moment of area and the Euler-forward finite scheme based on a deformed configuration were adopted to determine the onset of buckling behavior. The mass transport equations were established based on the Cahn-Hilliard phase-field theory to mimic the two-phase reaction during lithiation. The coupled equations were solved with the partial differential equation (PDE) module of COMSOL Multiphysics. The results showed that the concentration-dependent elastic modulus of the silicon electrodes led to the later onset of buckling due to the lithiation-induced softening of the electrodes, and this trend became slight for the electrodes with a large ratio of length to radius, since the phase separation had not yet occurred. The critical buckling state of charge (SOC) of the electrode with a concentration-dependent elastic modulus was larger than that of the electrode with a constant elastic modulus. The critical buckling time decreased with the ratio of the length to the radius of the electrode and the charging rate whether the electrode had a concentration-dependent modulus or a concentration-independent elastic modulus.