Theoretical Elements Research Articles

Band gap mechanism and vibration attenuation of a quasi-zero stiffness metastructure

PurposeThe main purpose of this paper is to investigate the vibration isolation performance of a quasi-zero stiffness (QZS) metastructure by employing the band gap (BG) mechanism.Design/methodology/approachThe metastructure QZS characteristic was investigated through static analysis by numerical simulation. Based on that, the BG mechanism is primarily used in this article to investigate the wave propagation characteristics of this structure. The model's dispersion relation is then examined using theoretical (perturbation method) and finite element techniques. The dynamic response of the finite-size systems and experimental analysis is used to confirm the vibration mitigation property under investigation. Finally, the model's ability to absorb energy was examined and contrasted with a traditional model.FindingsThe analytical analysis reveals the dispersion curve and the effect of the nonlinear parameter on the curve shifting. The dispersion curve in the finite element method (FEM) result depicts five complete BGs within the range of 0–1,000 Hz, and the BG width accounted for 67.4% of the frequency concerned (0–1,000 Hz). Eigenmodes of the dispersion curves were analyzed to investigate the BG formation mechanisms. The dependence of BG opening and closure on structure parameters was also studied. Finally, the energy absorption property of the QZS metastructure was evaluated by comparing it with a classical model. The QZS structure absorbs 4.08 J/Kg compared to the 3.69 J/Kg absorbed by the classical model, which reveals that the QZS demonstrates better energy absorption performance. Based on the BG mechanism, it is clear that this model is an excellent vibration isolator, and the study reveals the frequencies at which complete vibration mitigation is achieved. As a result, this model could be a promising candidate for vibration mitigation engineering structures and energy absorption.Originality/valueThe tough vibration issue, which is primarily experienced in mechanical equipment, will be resolved in this study. This study provides a precise understanding of the QZS metastructure's isolation of vibration, including the frequencies at which this isolation occurs.

Three-dimensional probabilistic assessment of tunneling induced structural damage using Monte-Carlo method and hybrid finite element model

Probabilistic assessment methods can be used to estimate engineering demand parameters under significant uncertainty, such as in the assessment of building damage due to tunneling. This paper develops a new empirical, theoretical and finite element hybrid three-dimensional model, in which the soil–structure interaction is considered and window and door openings are modeled explicitly, to achieve a reasonably fast and accurate damage prediction. The proposed model is embedded in a Monte-Carlo based probabilistic assessment approach, so that the building damage probabilities under different input uncertainty can be computed. Typical methods to quantify the input uncertainty in tunnel-soil–structure interaction practice are suggested. The probabilistic assessment method and a variance-based (Sobol’s) sensitivity analysis are implemented with a computer program that runs in higher-performance computing clusters, and demonstrated with two case studies. The significance of the soil–structure interaction effect and three-dimensional building effect are studied.

Theorising With Sociomateriality: Interdisciplinary Collaboration in Socio-Technical Learning Environments

In this paper, we explore the possibilities offered by sociomateriality for academics to engage with complex learning environments. The focus is on a longitudinal design-based research (DBR) study that includes an interdisciplinary, collaborative student project between Information Systems (IS) and Urban Planning (URP) from two different higher education institutions in Cape Town, South Africa. In the project, student groups collaborate to find potential digital innovations for sustainability challenges in their local communities. The aim is to position the student as an active community member with intimate knowledge of local sustainability challenges, and to develop social digital innovations for the benefit of local communities. We apply sociomateriality as a theoretical lens to rethink socio-technical learning environments and propose four pedagogical propositions of relationality, reflexivity, responsiveness, and recognition to guide the pedagogical decision-making when designing complex learning environments. We conclude the paper by mapping student reflections and experiences to the four pedagogical propositions to illustrate how the theoretical sociomaterial elements translate into the learning environment.

Knowledge, expertise, craft, and practice: becoming and being a cycle technician

ABSTRACT This paper provides an account of the everyday workplace learning of cycle technicians. Derived from an ethnography of working cultures and practices at a bike shop in the North of England, this paper rests on a critical reading of Communities of Practice theory in order to explore the complex and heterogeneous learning of cycle technicians. Drawing on a series of vignettes constructed from the ethnographic data, the paper demonstrates the variety of experiences of both formal and informal learning that characterise the trajectories of new cycle technicians as they enter the industry. In addition to providing an account of a qualified and specialist workforce that is under-represented in extant research literature, the paper also provides an exemplar for ethnographic research as a vehicle for exploring working practices through a Communities of Practice lens, using the paradigmatic theoretical elements of the theory. The paper concludes by arguing that for cycle technicians, and perhaps other occupations as well, Communities of Practice theory can generate rich and complex accounts that do justice to the richness and complexity of the craft and practice being observed.

Electrodeposition of Redox Active Insulators

Formation of the redox active insulators such as Lithium peroxide (Li2O2), Lithium sulfide (Li2S) are the salient features for next generation ‘beyond intercalation’ batteries like metal-air (O2) and metal-sulfur (Li-S) batteries (1-3). The interest in these batteries arises from high theoretical energies, abundant elements, low cost, and environmental friendliness. The mechanism to deposit redox active insulators (Li2O2 for Li-O2 and Li2S for Li-S) during discharging these batteries governs their rate capability, capacity, and reversibility. The prime obstacles for rate capability, capacity, and reversibility for Li-O2 batteries are the parasitic reactions. Our previous works discovered that formation of highly active singlet oxygen is the main cause of these parasitic reactions (1, 4-6). On charging Li-O2 battery, the practically achieving high reversible capacities face the challenge to decompose large amounts of insulating Li2O2 while suppressing parasitic reactions. These challenges require understanding the detailed Li2O2 formation mechanism and the interplay between chemistry and morphological evolution.The techniques that we use to decipher the mechanism of the formation of Li2O2 include microscopy and electrochemical generator-collector experiments (hydrodynamic voltammetry and interdigitated electrodes). Previously we illustrated in-situ small and wide-angle X-ray scattering as a novel method to study the morphological evolution in Li-O2 and Li-S batteries (3, 7). The experimental data show that the redox active insulator Li2O2 forms exclusively as particles via solution mediated LiO2 disproportionation during discharging. This contradicts established understanding, stating that the separation between surface adsorbed and solvated LiO2 governs whether Li2O2 grows via a surface mechanism or solution mechanism. We also introduced tools to access complex electrochemical and growth mechanism useful for other systems. This helps us to decipher the mechanism to form and to deposit redox active insulators during charging/discharging of the batteries, and thus to understand the governing factors for capacity, rate capability and reversibility.

Comparison of the theoretical elements and application characteristics of STAMP, FRAM, and 24Model: A major hazardous chemical explosion accident

Owing to the flammable, explosive, and toxic characteristics of hazardous chemicals, chemical accidents always result in significant losses. Analysis of the parameters of process safety is an effective way to prevent hazardous chemical accidents and reduce losses. To promote the application of systemic accident models in practice, in this study, we clarify the theoretical elements of such models based on the development of system thinking and system science. Then, we discuss the characteristics of a new systemic model called 24Model and its systems thinking. We explore the differences in the practical application of different systemic models (System-Theoretic Accident Model and Processes (STAMP), Functional Resonance Accident Model (FRAM), and 24Model by analyzing a major hazardous chemical explosion accident that occurred in Tianjiayi Chemical Co., Ltd. in China. The results show that the elements of the systemic accident model are the system structure, component relationship, and dynamic behaviors. 24Model is proven to be a new systemic accident model developed by utilizing sequential models. The comparative results of the three analysis methods show that FRAM is suitable for accident prediction rather than accident analysis. STAMP and 24Model perform better in terms of the usability and reliability of accident analysis. Although STAMP fails to elaborately indicate the internal organizational causes of the accident, it is suitable for a small number of accidents in socio-technical systems. 24Model is a structured method for accident analysis and safety management frame of organization. With the classified accident causes and fewer training resources, it is more suitable for a number of accidents statistics and analysis. Finally, a universal frame to prevent hazardous chemical accidents is provided for companies and regulators.

Interprofessional Interventions Involving Pharmacists and Targeting the Medicines Management Process Provided to Older People Residing in Nursing Homes: A Systematic Review and Meta-Analysis of Randomised Controlled Trials.

Nursing home residents are often prescribed multiple medications, which increases their susceptibility to drug-related problems. The medicines management process involves multiple stages, for example, assessing, prescribing, dispensing, delivering and storing, administering, reviewing and monitoring. The medicine management process aims to optimise medicine use and associated patient outcomes. Interprofessional interventions of healthcare professionalsfrom different disciplines in many clinical settings, including the nursing home setting, have shown success in improving patients' clinical outcomes. However, reporting of the pharmacist's role and the impact of these interventions has been unclear. We aimed to systematically identify and describe interprofessional interventions involving pharmacists that target the medicine management process in nursing homes by (a) describing interprofessional interventions and the role of pharmacists within, (b) describing the impact of these interventions, (c) exploring which of the medicine management process stages were targeted and (d) identifying any reported theoretical underpinning. EMBASE, MEDLINE, CINAHL, SCOPUS, PsycInfo, Cochrane library, Web of Science and clinical trial registers were searched from the inception date until August 2021. Randomised controlled trials reporting interprofessional interventions involving pharmacists, targeting at least one stage of the medicine management process and provided to nursing home residents with a mean age ≥65 years, were included. The search had no restriction on outcomes measured. Included randomised controlled trials were assessed for quality and risk of bias using the Jadad scale and Cochrane Collaboration tool, respectively. The overall certainty of outcomes was assessed using GRADEpro. If present, details about theoretical underpinning were extracted using the theory coding scheme. Fixed and random-effects models were used to calculate the pooled effect estimates to compare outcomes between intervention and control groups, where feasible, or a narrative description was reported. Eighteen manuscripts describing interprofessional interventions involving pharmacists were identified: medication review (n = 14), education (n = 3) and medication simplification (n = 1) based interventions. The pharmacists' most frequent role was the provision of medicine-related recommendations, and they worked mostly with general practitioners and nurses. Residents/family members contributed in 44% of included interventions. A meta-analysis identified that interventions were significantly associated with significant improvements in prescribing appropriateness (standard mean difference -0.20; 95% confidence interval -0.33 to -0.77; I2 = 27%) but not with hospitalisation and mortality. None of the included studies reported a theoretical underpinning to intervention development. This systematic review provides a detailed description of the impact of interprofessional practice, involving pharmacists, which targets at least one stage of the medicine management process in the nursing home setting. The findings suggest that future research should prioritise improving prescribing inappropriateness rather than the number of long-term medications prescribed. It remains unknown if interventions are designed using theory and, therefore, it is not clear whether theory-derived interventions are more effective than those without a theoretical element. The protocol was published in the International Prospective Register of Systematic Reviews (PROSPERO) [Ref: CRD42020181744].

Theorising With Sociomateriality: Interdisciplinary Collaboration in Socio-Technical Learning Environments

In this paper, we explore the possibilities offered by sociomateriality for academics to engage with complex learning environments. The focus is on a longitudinal design-based research (DBR) study that includes an interdisciplinary, collaborative student project between Information Systems (IS) and Urban Planning (URP) from two different higher education institutions in Cape Town, South Africa. In the project, student groups collaborate to find potential digital innovations for sustainability challenges in their local communities. The aim is to position the student as an active community member with intimate knowledge of local sustainability challenges, and to develop social digital innovations for the benefit of local communities. We apply sociomateriality as a theoretical lens to rethink socio-technical learning environments and propose four pedagogical propositions of relationality, reflexivity, responsiveness, and recognition to guide the pedagogical decision-making when designing complex learning environments. We conclude the paper by mapping student reflections and experiences to the four pedagogical propositions to illustrate how the theoretical sociomaterial elements translate into the learning environment.

Design and finite element analysis of a circular steel profile frame using Autodesk Inventor

The paper aims to apply the technical knowledge of recreational vehicles and the skills of using CAD applications for the design and construction of a steel profile frame. After the synthesis of the specific theoretical elements, from the specialized literature, the paper explores subassemblies of a kart, for which it proposes modeling studies. One element under analysis is the go-kart chassis. Designed in two constructive variants, the chassis is investigated in terms of rigidity, using finite element analysis specific to the Autodesk Inventor Professional application. The obtained results and the additional calculation elements, regarding the dynamics of the designed minivehicle, allow the physical realization of a chassis with increased rigidity.

Punching shear behavior of FRP reinforced concrete slabs under different opening configurations and loading conditions

This study investigates the punching shear behavior of reinforced concrete (RC) flat slabs using theoretical and non-linear finite element analysis techniques (NLFEA). The internal slab-column connection was studied under the combined effect of openings and loading eccentricity. No additional reinforcement was introduced after the opening was made to simulate the effect of opening in an existing structure. Thirty-six slabs were simulated (1800 mm × 1800 mm × 120) mm3 for the length, width, and depth, respectively. The investigated parameters were: (i) reinforcement type (basalt FRP, carbon FRP, and steel); (ii) the existence of opening and its location (with or opposite to the eccentricity side); and (iii) eccentricity value (0, 75, 150, and 225 mm). The slabs were supported at 1500 mm in both directions using eight high-strength bolts and were analyzed up to failure under square column loading of 150 mm side. All simulated slabs failed in punching shear. It was concluded that both the opening and loading eccentricity adversely affected the behavior of the slab, where using FRP bars as an internal reinforcement causes the slab's ductility index to be significantly reduced. Moreover, Increasing the loading eccentricity value adversely affects the slab's behavior. It reduces its ultimate capacity, ultimate deflection, cracking deflection, plastic stiffness, and energy absorption. The type of reinforcement affects the general behavior of the flat slabs. Slabs reinforced with steel reinforcement have the highest cracking and ultimate load, followed by slabs with CFRP, and BFRP reinforcements, respectively. Meanwhile, the relationship is inversed for the ultimate deflection. Simulation results were compared to those obtained from different international design codes (ACI 318–19, EC2, MC 2010, ACI 440, CSA/S806–12, and JSCE), and all overestimated the punching shear capacity of the tested slabs with the JSCE and the ACI 318 the JSCE have approximately the same predictions.

A Miniaturized Piezoelectric MEMS Accelerometer with Polygon Topological Cantilever Structure.

This work proposes a miniaturized piezoelectric MEMS accelerometer based on polygonal topology with an area of only 868 × 833 μm2. The device consists of six trapezoidal cantilever beams with shorter fixed sides. Meanwhile, a device with larger fixed sides is also designed for comparison. The theoretical and finite element models are established to analyze the effect of the beam′s effective stiffness on the output voltage and natural frequency. As the stiffness of the device decreases, the natural frequency of the device decreases while the output signal increases. The proposed polygonal topology with shorter fixed sides has higher voltage sensitivity than the larger fixed one based on finite element simulations. The piezoelectric accelerometers are fabricated using Cavity-SOI substrates with a core piezoelectric film of aluminum nitride (AlN) of about 928 nm. The fabricated piezoelectric MEMS accelerometers have good linearity (0.99996) at accelerations less than 2 g. The measured natural frequency of the accelerometer with shorter fixed sides is 98 kHz, and the sensitivity, resolution, and minimum detectable signal at 400 Hz are 1.553 mV/g, 1 mg, and 2 mg, respectively. Compared with the traditional trapezoidal cantilever with the same diaphragm area, its output voltage sensitivity is increased by 22.48%.

The Applicability of the Hertzian Formulas to Point Contacts of Spheres and Spherical Caps

Hertzian formulas are commonly used for the evaluation of deformation and pressure distribution of non-conformal and slightly conformal mechanical pairs to estimate component stiffness and durability. For the sake of simplicity, their use is extended even to those cases in which Hertz’s hypotheses do not hold. This paper summarizes Hertz’s theory and compares the results obtained with theoretical and finite element analysis of the point contact of non-conformal and conformal pairs made of spheres, caps, and spherical seats. This study was motivated by the non-Hertzian behavior of a tilting pad bearing ball-and-socket pivot conforming contact observed by the authors in previous experiments. In particular, the displacement and force relation were investigated by varying the geometrical parameters, the materials, the boundary conditions, and the friction coefficient. In the case of non-conformal contact, the parameter variations had negligible effect in agreement with Hertz’s theory while for conformal contact, the cap and seat height and width and the relative clearance were the most influential parameters on the non-Hertzian behavior. These novel results indicate that in conformal pairs, such as for tilting pad bearing ball-and-socket pivots, whenever Hertz’s hypotheses are not satisfied and the assessment of contact stiffness is crucial, Hertzian formulas should not be applied as done in common practice, instead more accurate numerical or experimental evaluation should be made.

Real-Time Temperature Rise Estimation during Irreversible Electroporation Treatment through State-Space Modeling

To evaluate the feasibility of real-time temperature monitoring during an electroporation-based therapy procedure, a data-driven state-space model was developed. Agar phantoms mimicking low conductivity (LC) and high conductivity (HC) tissues were tested under the influences of high (HV) and low (LV) applied voltages. Real-time changes in impedance, measured by Fourier Analysis SpecTroscopy (FAST) along with the known tissue conductivity and applied voltages, were used to train the model. A theoretical finite element model was used for external validation of the model, producing model fits of 95.8, 88.4, 90.7, and 93.7% at 4 mm and 93.2, 58.9, 90.0, and 90.1% at 10 mm for the HV-HC, LV-LC, HV-LC, and LV-HC groups, respectively. The proposed model suggests that real-time temperature monitoring may be achieved with good accuracy through the use of real-time impedance monitoring.

Right to Clean Water: Lake Xochimilco, Mexico City

Lake Xochimilco is in the region of the same name in Mexico City. The objective of this article is to tell about the serious contamination that this body of water presents. In the first part, is the theoretical elements. They are addressed about the right of any human being to clean water. Later, the geographical factors are mentioned about the location of Lake Xochimilco. Yet a comparison of economically important elements is made. Such as economic units, the value of production, the employed personnel, the remunerations of the other districts that make up Mexico City. Likewise, the elements of a social nature such as the total population in a situation of poverty at Xochimilco and the other demarcations. In the end the contamination of this lake is described, some proposals are presented to gradually solve the pollution of this place through good governance, which is not only the result of good governance, but of an interaction of government organization, the private sector and civil society.

Soft-covered wearable thermoelectric device for body heat harvesting and on-skin cooling

The recent emergence of self-powered wearable electronics gives rise to a growing demand for flexible, sustainable, and portable power supply. Wearable thermoelectric devices (WTEDs) are promising power sources for wearable electronics through directly converting body heat into electricity. However, the output power of WTEDs is still low due to the extremely small effective temperature difference across thermoelectric pillars, which hinders their practical applications. Commonly used strategies to enlarge the effective temperature difference for WTEDs, such as introducing metallic heat sinks or increasing the length of thermoelectric pillars, usually lead to clunky devices that are not suitable for wearable electronics. Here, we report on a soft-covered WTED for body heat harvesting and on-skin cooling, which demonstrates the desirable performance and wearer comfort. Distinct from the previously reported flat soft heat spreaders, this work presents the design and fabrication of a pin–fin soft cover that can serve as a flexible heat sink for WTEDs. The pin–fin soft cover was fabricated by curing the liquid metal/elastomer composite in a meltable wax mold. Systematic theoretical and finite element analysis was conducted to optimize the output power and wearability of the soft-covered WTED. The optimized WTED achieves a power density of 6.63 μW cm−2 on a stationary human body under natural convection condition with an ambient temperature of 20 °C, which is higher than the previously reported WTEDs with flat soft covers made of high-thermal-conductivity elastomers. Furthermore, our WTED can realize a 1.5 °C temperature drop for the human skin through Peltier cooling. This work demonstrates a new route to develop soft-covered WTEDs for self-powered wearable electronics and personal thermoregulation.

Design and Analysis of a Compact Hydraulic Bolt Tensioner

In equipment like high pressure vessels, there will caps on which loads of the order of several thousands of tons acts. Such caps require a huge number of big-diameter bolts, often M70 to M150mm in diameter. Each bolt will be subjected to a tremendous amount of force, on the order of 300 tons. The use of hand-operated wrenches to apply such a load is deemed out. When a high number of bolts are tightened on the flange, the applied load is lost owing to friction at the clamping surface and the applied load is not uniform. It is advised that a hydraulic bolt tensioning system be used to address these drawbacks. The device operates at a pressure of 1500 bar, which is extremely high. Therefore, the equipment must be designed to ensure the device’s compactness and safety. Bolt tensioners are used to tighten bolts and studs in a variety of important applications. These devices would be imported. It was proposed in this work that a small hydraulic bolt tensioner be designed and analysed using both theoretical and finite element analysis (Non-liner static analysis). The required boundary conditions and applied pressure were computed. The tensioner’s design was optimized to assure its safety and compactness.

Seismic Performance of a Sliding Isolation Bridge System with a New Spring Re-Centering Device

Residual displacements between the girder and piers were observed in previous strong earthquakes. These are caused by the limited re-centering capacity of sliding isolation bearings. With this concern, a spring re-centering device is proposed to improve the re-centering capacity of sliding isolation systems. The working mechanism is illustrated, and the force–deformation relationship of this device was investigated in theoretical, experimental, and finite element methods. An extra-dosed multi-pylon cable-stayed bridge was introduced to demonstrate the re-centering effect. The results show that this spring re-centering device could slightly mitigate the seismic forces and significantly mitigate the residual displacement between the girder and piers. After that, the parametric analysis was conducted to investigate the effect of critical parameters of re-centering bearings on seismic performances.

Everything Stays the Same while Everything Changes

Everything Stays the Same while Everything Changes

Entrainment, diffusion and effective compressibility in a self-similar turbulent jet

An experimental Lagrangian study based on particle tracking velocimetry has been completed in an incompressible turbulent round water jet freely spreading into water. The jet is seeded with tracers only through the nozzle: inhomogeneous seeding called nozzle seeding. The Lagrangian flow tagged by these tracers therefore does not contain any contribution from particles entrained into the jet from the quiescent surrounding fluid. The mean velocity field of the nozzle seeded flow, $\langle \boldsymbol {U}_{\boldsymbol {\varphi }} \rangle$ , is found to be essentially indistinguishable from the global mean velocity field of the jet, $\langle \boldsymbol {U} \rangle$ , for the axial velocity while significant deviations are found for the radial velocity. This results in an effective compressibility of the nozzle seeded flow for which $\boldsymbol {\nabla }\boldsymbol {\cdot } \langle \boldsymbol {U}_{\boldsymbol {\varphi }} \rangle \neq 0$ even though the global background flow is fully incompressible. By using mass conservation and self-similarity, we quantitatively explain the modified radial velocity profile and analytically express the missing contribution associated with entrained fluid particles. By considering a classical advection–diffusion description, we explicitly connect turbulent diffusion of mass (through the turbulent diffusivity $K_T$ ) and momentum (through the turbulent viscosity $\nu _T$ ) to entrainment. This results in new practical relations to experimentally determine the non-uniform spatial profiles of $K_T$ and $\nu _T$ (and hence of the turbulent Prandtl number $\sigma _T = \nu _T/K_T$ ) from simple measurements of the mean tracer concentration and axial velocity profiles. Overall, the proposed approach based on nozzle seeded flow gives new experimental and theoretical elements for a better comprehension of turbulent diffusion and entrainment in turbulent jets.

The Management of Social Anxiety: More Than 25 Years Later, Where are we?

Behavioral and cognitive therapies are today the most effective toolbox and the most evidenced-based therapy for social anxiety. The purpose of this article is to provide an overview of some of the most popular methods for treating social anxiety. A selective review of literature published between 1997 and 2022 on social anxiety management. We have found that the majority of behavioral and cognitive treatment protocols are based on the following pillars: exposure to avoided situations, cognitive restructuring, assertiveness, and social skills training, as well as decentration techniques such as getting out of self-observation and cognitive fusion. Several psychotherapists agree on some components of social anxiety management while others do not. Within these agreements and disagreements, the path to the sketch of a new model should open. We argue that some techniques may ultimately be useless, counterproductive, and time-consuming. Alter the existing models and improve them in a different way in light of the multiple information and clinical examples is much needed. We suggest reconfiguring the theoretical and clinical elements to derive a new therapeutic combination of old techniques. In this new theoretical model of social anxiety, we scrupulously suggest including the cognitive and emotional elements and opt for primacy to be given to behavioral inhibition and the role of the biological part such as amygdala.