Marginal Variation Research Articles

Experimental-Numerical Assessment of Mechanical Behavior of Laboratory-Made Steel and NiTi Shape Memory Alloy Wire Ropes

The mechanical behaviors of laboratory-fabricated steel and superelastic shape memory alloy (SMA) wire ropes are assessed in this study through a comprehensive approach encompassing both experimental investigations and finite element (FE) numerical simulations. The assessment of steel wire ropes involves experimental scrutiny under sinusoidal cyclic loading and natural earthquake loading conditions. In parallel, SMA wire ropes’ behaviors are analyzed utilizing FE simulations employing the widely acknowledged ABAQUS software version 2020. The validation of all numerical simulations is undertaken against the experimentally observed behaviors. Moreover, full-scale steel wire ropes are subjected to shaking table tests to validate the simulations, facilitating a comparative analysis between the mechanical responses of SMA and steel wire ropes. The findings demonstrate that SMA wire ropes exhibit superelastic behavior akin to SMA wires, with marginal variations in overall response observed across distinct configurations, akin to steel wire ropes. Furthermore, augmenting the helix angle of SMA wire ropes results in reduced stress and increased strain when exposed to the El Centro earthquake scenario. Nevertheless, the mechanical response of SMA wire ropes closely mirrors that of a single wire.

Development of Curved Shape Diffuser Duct for Aero Engines With a Backend Centrifugal Compressor

In the present study, a design of the curved shape diffuser-duct is proposed to apply to the compressor stage for aero-engines with a backend centrifugal compressor. For these configurations, the flow exiting radially from the centrifugal impeller needs to be changed from radial-to-axial direction to meet downstream combustion chamber requirements. Hence, the specially designed exit duct with a curved shape to manage the flow from the radial-to-axial direction was later diffused using the diffuser-shaped exit duct. This study aims to design and develop an efficient diffuser-duct for the adequate deceleration of flow in the exhaust diffuser and, as a result, a uniform and low-velocity flow at the exit. This configuration comprises a radial-to-axial turning annular passage at the centrifugal impeller exit. Then, the passage is directed to either a purely axial direction or is inclined to the axial direction by a slight angle. The results indicate a uniform total pressure at the stage exit with marginal variation along the span. It shows equivalent end wall effects near both the shroud and hub surfaces. This endwall effect may be occurring mainly due to the growth of the boundary layer across the diffuser passage.

Immediate Placement and Loading of Maxillary Single-Tooth with Scalloped Shape Implants and Digitalized Customized Restoration: A 5-Year Prospective Study of Marginal Bone Level.

To evaluate, within a period of 5 years, the bone level in mesial, distal, palatal, and buccal areas around scalloped shape implants immediately placed and loaded with temporary crowns fixed on final prefabricated abutments, and also to evaluate the thickness of buccal bone. 18 implants were inserted and loaded immediately using computer-assisted design/computer-assisted manufacturing technology on 18 patients to replace single tooth in the esthetic part of the maxilla. The marginal bone level across the scalloped implant neck was measured mesially and distally using intraoral standardized radiographs after crown fixations and 1, 3, and 5 years later. Cone beam computed tomography para-axial cuts images were used to measure bone level buccally and palatally from the implant neck to the implant-to bone contact after 5 years of loading and to evaluate the thickness of the buccal bone at the implant neck and 4 mm apically, immediately after implant placement and 5 years later. All implants were assessed clinically and radiologically after 5 years. No implant failure was recorded, and the average marginal bone variation on mesial and distal sites was 0.114 ± 0.135 mm at crown cementation, 0.239 ± 0.158 mm 1 year later, 0.233 ± 0.182 mm 3 years later, and 0.180 ± 0.182 mm 5 years later. Our findings indicate that at T0, the average thickness of the buccal bone was 2.27 mm at implant neck M0 (ranging from 1.9 to 2.4) and 2.33 mm at 4 mm apically to the implant neck M1 (ranging from 1.9 mm to 2.9 mm). By T4, the mean had decreased to 1.94 mm at M0 (with a range of 1.7 mm to 2.3 mm) and 2.14 mm at M1 (with a range of 1.8 mm to 2.4 mm). After 5 years the mean changes at buccal and palatal bone for all implants were +0.187 ± 0.52 mm and +0.06 ± 0.38 mm respectively. Minor prosthetic problems were observed over the five years: incisal ceramic chipping occurred in two crowns, and two crowns were replaced for esthetic reasons after one year. No loosening of crowns or abutments was reported. Scalloped neck implants demonstrated a comparable behavior to regular neck implants with similar designs in an immediate implantation and temporization protocol over a five-year period.

Lifespan increase of electrical terminal crimping punches for the automotive industry

In the Automotive Industry (AI), and in all other industries linked to it, the increase in competitiveness and the compliance with environmental requirements are mandatory. Thus, the efforts to increase the lifespan of fabrication equipment and tooling are greater than ever. This work was developed around this real need, seeking to increase the lifespan of electrical terminal crimping punches for the AI. The process to achieve the objective of the practical work began with the collection of samples from the main competitors in the market, to be able to analyze and characterize them. Subsequently, brainstorming sessions were carried out, enabling to choose which alternative samples would be produced, analyzed, and characterized. New crimping punches were then characterized at different stages of production, to study the importance and impact of the finishing stages of the production process. Finally, new samples were produced, put to the test at a real customer and advanced characterization tests were done, which allowed a better understanding of the evolution of tool wear during its lifetime. This work contributed to a better clarification of the lifespan of crimping punches, making it possible to identify potential wear mechanisms and, consequently, propose a solution that maximizes the lifespan of crimping punches. Moreover, significant lifespan improvements were attained with marginal production cost variation.

Economic and geopolitical uncertainty vs energy variables: exploring connectedness in the LNG freight market

ABSTRACT This paper contributes to the literature by applying quantile connectedness methodology to explore the impact of geopolitical and economic uncertainty on the volatility of LNG freight rates. Our findings justify modelling this market using econometric methodologies that depart from the classical Gaussian assumptions. First, we find asymmetric spillover effects between LNG freight rates, uncertainty, and energy variables, with the impact of uncertainty on the LNG rates becoming more intense at the tails of the distribution. Second, we find that the marginal variation in LNG freight rates after a shock is attributable to geopolitical and economic uncertainty, as the energy variables appear to absorb the marginal effects. Our results point to profound spillovers in the LNG freight market resulting from the pandemic, the war in Ukraine and government interventions to mitigate the adverse impact of these developments. These findings contribute to the LNG freight rate risk management. This article is a revised and expanded version of a paper entitled «Assessing the Impact of uncertainty and energy variables on LNG freight rates: A dynamic quantile connectedness analysis» presented at European Financial Management Association (EFMA) 2023 annual conference, Cardiff Business School, Cardiff University, on Thursday, June 29, 2023.

Hematological Trends in Severe Burn Patients: A Comprehensive Study for Prognosis and Clinical Insights.

Severe burn injuries pose diagnostic challenges, contributing to increased fatality rates with delayed diagnoses. This study aims to identify early risk factors and understand their impact on clinical outcomes by examining hematological dynamics in severe burn cases. The focus includes age-related patterns, total body surface area (TBSA) affected by burns, hospital stay duration, and changes in hematological markers during burn injuries. An analytical cross-sectional study at the burn care center involved 135 participants hospitalized between January 2018 and December 2021. Demographic data and hematological markers were recorded, and statistical analysis was performed using IBM SPSS 25.0. Nonsurvivors exhibited a greater mean TBSA, shorter hospital stay, and an enhanced early immune response indicated by white blood cell count on the first day. Hematological markers, including hemoglobin, red cell count (RCC), and platelet count, showed dynamic patterns over the study period. Marginal variations in platelet counts and intriguing patterns in RCC suggested potential consequences like disseminated intravascular coagulation. The study provides crucial insights into hematological responses to severe burn injuries. Early identification of risk factors, particularly age-related patterns and immune responses, informs clinicians about predicting outcomes and guiding therapeutic interventions. Despite limitations, this work underscores the need for further multicenter research to comprehensively understand the complex relationships between burn injuries, hematological responses, and clinical outcomes.

Mineral Geochemistry of Apatite in the Jiama Porphyry‐Skarn Deposit, Tibet and its Geological Significance

AbstractThe Jiama deposit, a significant porphyry‐skarn‐type copper polymetallic deposit located within the Gangdese metallogenic belt in Tibet, China, exemplifies a typical porphyry metallogenic system. However, the mineral chemistry of its accessory minerals remains under‐examined, posing challenges for resource assessment and ore prospecting. Utilizing electron microprobe analysis and LA‐ICP‐MS analysis, this study investigated the geochemical characteristics of apatite in ore‐bearing granite and monzogranite porphyries, as well as granodiorite, quartz diorite, and dark diorite porphyries in the deposit. It also delved into the diagenetic and metallogenic information from these geochemical signatures. Key findings include: (1) The SiO2 content, rare earth element (REE) contents, and REE partition coefficients of apatite indicate that the dark diorite porphyry possibly does not share a cogenetic magma source with the other four types of porphyries; (2) the volatile F and Cl contents in apatite, along with their ratio, indicate the Jiama deposit, formed in a collisional setting, demonstrates lower Cl/F ratios in apatite than the same type of deposits formed in a subduction environment; (3) compared to non‐ore‐bearing rock bodies in other deposits formed in a collisional setting, apatite in the Jiama deposit exhibits lower Ce and Ga contents. This might indicate that rock bodies in the Jiama deposit have higher oxygen fugacity. Nevertheless, the marginal variation in oxygen fugacity between ore‐bearing and non‐ore‐bearing rock bodies within the deposit suggests oxygen fugacity may not serve as the decisive factor in the ore‐hosting potential of rock bodies in the Jiama deposit.

Formulation of Energy Bars by using Sunflower Seeds

The study discusses the popularity and nutritional benefits of snack foods, with a focus on granola bars as a versatile and nutrient-dense option. The importance of energy bars for athletes and individuals with busy lifestyles is highlighted. The study aims to develop a high-protein, high-energy nutritional bar using plant sources. Oats are emphasized for their rich nutrient profile, including carbohydrates, fiber, proteins and various bioactive compounds. Dates and almonds contribute additional nutrients and health benefits. Sunflower seeds are recognized for their therapeutic benefits, while honey is for its antibacterial and nutritional properties. The energy bars, including a basic version and two variations, were analyzed for various nutritional parameters. The moisture content exhibited slight increments, measuring from 6.83±0.01, to 7.03±0.01, while the ash content showed minimal differences at 0.05±0.01. Energy content increased from 380±0.032 to 410±0.026, and protein content ranged from 9.17±0.01 to 9.19±0.01. Fat composition showed marginal variations while the fiber content was measured at 6.67±0.01, 6.77±0.01 and 6.78±0.01 grams. Ascorbic acid concentrations increased from 0.7±0.015 to 0.81±0.0026, while thiamine and riboflavin concentrations showed slight fluctuations. Sensory evaluation revealed that T2 (30% honey) scored highest in various categories, including color (8.5±0.527), taste (8.6±0.516), texture (8.2±0.788), flavor (8.5±0.707), appearance (8.5±0.527) and overall acceptability (8.6±0.516). T2 emerged as the most preferred, followed by T1 (25% honey) and T3 (35% honey).

Response, awareness and requester identity in FOI law: Evidence from a field experiment

Freedom of Information (FOI) is considered a crown jewel of reforms fostering public administration transparency and accountability. However, FOI's symbolic power alone cannot overcome the organizational barriers and obstacles to its effective implementation. This paper presents the results of a field experiment performed in Italy, a late FOI adopter, where an FOI request was sent to the 307 municipalities with more than 30k inhabitants. The experimental design exploits marginal wording variation in the requests to test whether municipalities discriminate between ordinary citizens and high-profile requesters. The experimental evidence suggests that most Italian municipalities reply to FOI requests. The results show two opposite types of discretionary bias: Northern municipalities tend to favor high-profile requesters, whereas Southern municipalities tend to respond to them with a higher degree of attrition. The study investigates the determinants of this difference.

The Sino-US trade friction would exacerbate global inequalities in achieving SDGs

Trade has given rise to global inequalities in sustainable development, while the occurrence of trade frictions between China and the US has led to changes in the global trade market landscape. Whether these changes will exacerbate disparities in sustainable development between regions remains uncertain. Quantifying the impact of changes in the trade market landscape is of significant importance in accelerating global progress towards sustainable development. Therefore, this article, based on the GTAP 10.0 database and using the GTAP model, calculates the extent to which changes in tax policies affect the global achievement of sustainable development goals (SDGs) by assessing the impact of alterations in trade patterns. The research findings are as follows: (1) The decoupling of China and the US has intensified these inequalities. Economically advanced regions have made significant progress in sustainable development compared to relatively underdeveloped regions, such as the US and Sub-Saharan Africa. (2) Regions closer to China and the US are more affected by changes in trade taxes, with economically advanced regions in close proximity to China and the US benefiting more than those farther away. (3) Environmental aspects of SDGs have shown the lowest growth rates, with marginal variations across different regions. (4) Global inequalities in achieving SDGs primarily stem from inter-regional disparities. Over time, inter-regional inequalities decrease while intra-regional inequalities increase, with underdeveloped regions experiencing higher levels of intra-regional inequality compared to developed regions. The growth in tax rates between China and the US contributes to a comprehensive increase in both inter-regional and intra-regional inequalities. Based on these conclusions, this study aims to provide a scientific basis for promoting global sustainable development and reducing regional disparities in the process.

Atmospheric Pressure Plasma Jet Exposure of Polylactic Acid Surfaces for Better Adhesion: Plasma Parameters towards Polymer Properties.

Polymers play a crucial role in multiple industries; however, surface modification is necessary for certain applications. Exposure to non-thermal plasma provides a viable and environmentally beneficial option. Fused deposition molding utilizes biodegradable polylactic acid, although it encounters constraints in biomedical applications as a result of inadequate mechanical characteristics. This study investigates the effects of atmospheric pressure plasma generated by a dielectric barrier discharge system using helium and/or argon on the modification of polylactic acid surfaces, changes in their wettability properties, and alterations in their chemical composition. The plasma source was ignited in either He or Ar and was tailored to fit the best operational conditions for polymer exposure. The results demonstrated the enhanced wettability of the polymer surface following plasma treatment (up to 40% in He and 20% in Ar), with a marginal variation observed among treatments utilizing different gases. The plasma treatments also caused changes in the surface topography, morphology, roughness, and hydrophilicity. Plasma exposure also resulted in observable modifications in the dielectric characteristics, phase transition, and structure. The experimental findings endorse the utilization of plasma technologies at normal air pressure for environmentally friendly processing of polymer materials, specifically for applications that necessitate enhanced adhesion and have carefully selected prerequisites.

Investigating the microstructure and mechanical behavior of optimized eutectic Al[sbnd]Si alloy developed by direct energy deposition

Wire arc additive manufacturing (WAAM) is a direct energy deposition process majorly used to fabricate large and medium-sized components. However, the process encounters defects, such as anisotropic microstructure and mechanical properties, residual stresses, excessive oxidation, and geometrical irregularities. Hence, efforts have been made to address the issues by optimizing the process parameters and incorporating in situ and post-process treatment to improve mechanical properties. In line with this, the present work deals with statistical-based process parameter optimization based on a multicriteria approach. The responses were quantified, statistically analyzed, and correlated with the process parameters. Travel speed exhibited a minor effect on all responses, while the current and wire feed speed significantly affected the responses. The percentage porosity was more sensitive to welding current than the other parameters. The maximum ultimate tensile strength (UTS) of 193.73 ± 3.93 MPa and yield strength (YS) of 108.09 ± 12.28 were displayed by Wall 2. YS and UTS showed marginal variation in vertical and horizontal directions, while % elongation showed significant variation. The desirability Wall (DW) exhibits better-forming quality due to the minimization of the contact angle, and fibrous silicon was observed between the layers. In contrast, it appears to be fragmented silicon at the interfacial region due to remelting and breakdown of Si. However, there were a few limitations to the DW wall's mechanical properties due to coarser dendrites and bulk eutectic at the interface. The average grain size of the bottom and top region for the optimized parameter is 111.156 μm and 173.66 μm, respectively. The observed texture components in the top region include C{001} 〈110〉, A2* (111) [112¯], A (11¯1) [110], and B (11¯2) [110], exhibiting a maximum texture intensity of 10.414. In the bottom region, the identified texture components are B¯ (1¯12¯) [1¯1¯0], B (11¯2) [110], A (11¯1) [110], C{001} <110> with a maximum texture intensity of 10.110.

Early Detection of Potential Infestation by Capnodis tenebrionis (L.) (Coleoptera: Buprestidae), in Stone and Pome Fruit Orchards, Using Multispectral Data from a UAV

Wood-boring insect pests pose a significant threat to orchards, potentially leading to tree mortality. In the initial stages of infestation, no visible symptoms are apparent, but as infestations progress, rapid and widespread symptoms emerge, resulting in accelerated tree decline. Therefore, the timely detection of early wood-boring insect symptoms is critical for effective pest control, necessitating advanced methods such as remote sensing. In this study, remote sensing is utilized to identify the early symptoms of peach flatheaded root borer (PFRB) infestation in trees. A multispectral sensor attached to a UAV captures aerial imagery data from stone fruit and pome fruit orchards. These data undergo processing in photogrammetric and GIS programs, where NDVI, NDRE, and the tree crown area are computed. On-site observations confirm PFRB infestations. Various machine-learning models, including logistic regression (LR), artificial neural network (NN), random forest (RF), and extreme gradient boosting (XGBoost), are compared using mean NDVI values, mean NDRE values, crown area, mean temperature, and mean relative humidity. Mean NDVI values emerge as the most crucial factor for predicting PFRB infestation across all machine-learning models. The XGBoost model proves the most effective, achieving an accuracy of 0.85, with marginal variations from the other tested models.

Deposition of Ti[sbnd]Zr alloy films using Ti and Zr dual-cathode high-power impulse magnetron co-sputtering

In this study, titanium–zirconium binary alloy films were deposited using heterogeneous dual-cathode high-power impulse magnetron sputtering with a closed magnetron field. For both Ti and Zr cathodes, the discharge voltage pulses were synchronized with an equal pulse width. In addition, we investigated the effects of the average discharge power ratios of the two cathode materials, deposition pressure, and substrate bias voltage on the mechanical strength and microstructure of the deposited films. The results revealed that the film composition could be controlled by the average power ratio of the two cathodes at a constant deposition pressure; however, the deposition rate of each element varied with the deposition pressure. At a constant average power ratio at the two cathodes, the Zr content in the films decreased with decreasing the deposition pressure. Decreasing the deposition pressure can smoothen the film surface, but the dependence of the film composition on two cathode powers also changes. An adequate enhancement of the negative substrate bias can further increase the film hardness and reduce the film elastic modulus, yielding only a moderate loss in the film deposition rate and marginal variations in the film composition. However, the magnitudes of the increase in hardness and the decrease in elastic modulus brought by enhancing negative substrate bias varies with the film composition, and will be minimized when the atomic fractions of Ti and Zr are near equal. Notably, with adjusting the negative substrate bias, adding Zr can change the film hardness from 4.8 to 10.6 GPa, and the film elastic modulus from 100 to 162 GPa. Overall, the advantageous mechanical and structural properties of the TiZr alloy films deposited using HiPIMS might be useful in tools, biomedical devices, wearable equipment applications.

Tribological Behaviour of Furcraea Foetida Fiber-Reinforced Epoxy Composites under Varying Applied Loads

This study investigates the tribological behaviour of Furcraea Foetida fibre-reinforced epoxy composites under varying applied loads. The aim is to understand the influence of applied load on the frictional behaviour and wear characteristics of the composites. The study employs a pin-on-disk test to examine the frictional force, coefficient of friction (COF), and specific wear rate (SWR) of identical samples subjected to four different loads (80 N, 100 N, 120 N, 140 N). Scanning electron microscopy (SEM) is used to analyse the surface morphology under different loads. The frictional force versus sliding distance graph demonstrates an increasing trend from 80 N to 120 N, followed by minimal change at 140 N. Similarly, the COF versus applied load graph shows a progressive increase from 80 N to 120 N, with the least increase observed at 140 N. The SWR versus applied load graph indicates an increasing trend from 80 N to 120 N, with marginal variation at 140 N. SEM analysis reveals that only the sample subjected to 140 N shows evidence of plastic deformation. In conclusion, the results indicate that the applied load significantly influences the frictional behaviour and wear characteristics of the Furcraea Foetida fibre-reinforced epoxy composites. At higher loads, the increase in frictional force, COF, and SWR becomes less pronounced, suggesting potential saturation in the composites' response. The presence of plastic deformation at 140 N further highlights the unique behaviour observed at this load. These findings contribute to a better understanding of the tribological performance of the composites and have implications for their practical applications.

Study on the Dynamic Stability and Spectral Characteristics of a Toppling Dangerous Rock Mass under Seismic Excitation

To evaluate the dynamic stability of dangerous rock masses under seismic excitation more reasonably, a mass viscoelasticity model was adopted to simulate the two main controlling surfaces of a toppling dangerous rock mass. Based on the principles of structural dynamics, a dynamic response analysis model and motion equations were established for toppling dangerous rock masses. The Newmark-β method was utilized to establish a calculation method for the dynamic stability coefficient of a toppling dangerous rock mass. This method was applied to the WY2 dangerous rock mass developed in a steep cliff zone in Luoyi Village, and the dynamic stability coefficient time history was calculated. Subsequently, the acceleration response signals of the dangerous rock mass in different directions were analyzed using wavelet packet transform. The results show that the sum of the energy proportions of the first to third frequency bands in the n1 and s2 directions exceeded 95%. This suggests that the n1 and s2 directions of the WY2 dangerous rock mass suffered the initial damage under bidirectional seismic actions. Finally, the marginal spectra variations of the acceleration response signals in different directions were analyzed based on the HHT. The results show that the seismic energy in the n1 and s2 directions of the dangerous rock mass was found to be the most significant under seismic loading, indicating that the rock mass experienced the most severe damage along these two directions. This reveals that the failure mode of the dangerous rock mass is inclined toppling, consistent with the results of wavelet packet analysis.

The Effect of Prolonged Consumption of Aqueous Extract of Raphia Hookeri Pulp Fruit on Selected Immune Parameters on Male Wistar Rats

This research aims to ascertain the effect of oral administration of a aqueous fruit extract of Raphia Hookeri on selected immune parameters in male wistar rats. The fruits were obtained from Emoh community in Abua/Odual L.GA, Rivers State, A total of 28 apparently healthy male rats weighing between 137-190g were divided into four groups, 7 rats in each group. Group 1 served as the control were given feed and water, group 2 given 500mg/kg, group 3 given 1000mg/kg, group 4 given 2000mg/kg of the extract for 28 days and blood samples collected. Laboratory test done and statistical analysisexpressed as mean± SEM using Statistical Packages for Social Sciences (SPSS version 24).The result for IgA when compared the treated groups and control, there was slight variation in values but the result is not significant at P&lt;0.05, there were marginal variation in IgE, when compared the treated groups with the control, the result showed no significant difference, there was a significant decrease in group 2 for IgM, also a slight variation in group 3 and 4 when compared with the control not statistically significant at P&lt;0.05.Very plausible to state that there is no proportional effect of the aqueous extract on Immunoglobulin A (IgA), Immunoglobulin E (IgE). There was a significant decrease in Immunoglobulin in (IgM) level noticed in group2 and no significant difference in groups 3 and 4.The findings of the study has proven that prolonged consumption of Raphia Hookeri fruit extract boost immunity via immunoglobulins in male wistar rats.

Memory effect of spider major ampullate gland silk in loading-unloading cycles and the structural connotations

Spider silk is repeatedly stretched while performing biological functions. There is a close relationship between the shape change of the fibre materials and their mechanical properties. However, the effect of the deformation and interval time on the structure and tensile behaviour properties of spider silk after repeatedly stretching by given strain value has been rarely reported. Here we found that spider major ampullate gland silk (MAS) can revert its tensile behaviour independent of its previous loading history via intervals of approximately 8 s to 5 min with constant and increased elongation, respectively, after being subjected to yield and hardening regions. The true stress-true strain curve beyond a given value of true strain is independent from the previous loading history of the sample. Even after longer intervals (≥1 h), MAS can reproduce the last tensile behaviour via one stretched. Despite recognizing the development of irreversible deformations in the material when tested in air, the reversible change in tensile behaviour outside the spider silk's elastic region has rarely been observed before. MAS has at least one proper ground state that allows it to present good shape and mechanical behaviour memory in terms of longitudinal stretching, functioning as a new strategy to achieve certain tensile properties. The analysis of the true stress–true strain curves was performed from a series of loading‒unloading tests to evaluate the evolution of those mechanical parameters with the cycle number. The elastic modulus measured in the loading steps increases monotonously with increasing values of true strain reached in the cycles. In contrast, a marginal variation is found in the values of the yield stress measured in the different cycles. The memory and variation in the mechanical behaviour and performance of MAS can be accounted for through the irreversible and reversible deformation micromechanisms and its combination in which the viscoelasticity of the material plays a leading role. These findings may be helpful to guide the biomimetic design of novel fibre materials such as spider silk gut via artificially stretching spider silk glands.

High dielectric Al2O3-(20–30 wt%) HDPE composites processed via cold sintering

In the present work, the dielectric properties of cold sintered alumina (Al2O3) reinforced with 20–30 wt% HDPE composite was investigated. The Al2O3-HDPE composites were successfully processed via cold sintering at extremely low temperature in the range of 80–120 °C for 120 min with the application of uniaxial pressure of 500 MPa under vacuum. In fact, cold sintering is a promising method to consolidate ceramic-polymer composites with very large difference in melting points and other thermo-physical/chemical properties. In the present work, high dielectric constant (ε’) of 11.73 and low dielectric loss (tanδ) of 0.0076 measured for Cold Sintering Processed (CSPed) Al2O3-20HDPE and a little low ε’ of 9.13 and low tanδ of 0.0066 was evident for CSPed-Al2O3-30HDPE at 1 MHz. Such differences in the dielectric properties of the Al2O3-20,30 HDPE composites depend on the crystallite size, dangling bond density and microstrain of the materials. Increase in ε’ with temperature is noticed for CSPed-A20H. Moreover, for CSPed-A20H at 1 MHz the temperature variation of dielectric constant (TCC) of 186.94 ppm/°C (or 0.018694 %/°C) was estimated and it reflects a marginal variation of ε’ with temperature. The coefficient of thermal expansion (CTE) of 87.25 × 10−6 °C−1 and 109.3 × 10−6 °C−1 was estimated for CSPed-A20H and CSPed-A30H, respectively. Overall, the cold sintered Al2O3-20HDPE composites exhibited comparable or better dielectric properties than Al2O3 based materials (as reported in the literature) processed by conventional sintering or cold sintering processes.

Effect of marginal variation of aspect ratio and frequency with kinematic asymmetry on flow field around flapping rigid wing in hover

Phase-locked two dimensional particle image velocimetry (PIV) measurements are used to capture flow field around rigid flat plate wings undergoing main flapping motion (hover) with water as fluid medium in quiescent condition. Experiments are conducted using asymmetric upper-lower stroke single degree of freedom main flapping motion. Two different aspect ratio (AR) 1.5 and 1.0 rectangular wings at 1.5 Hz and 2.0 Hz flapping frequency and chord based Reynolds number of the order of 104 are studied. To achieve the desired aspect ratio, wing span is varied while wing chord remains fixed. Flow features for downstroke and upstroke are comparable for all four cases investigated. This includes vortex shedding from wingtip during wing stroke, vorticity intensification caused due to vortex stretching which occurs more dominantly for AR = 1.0, occurrence of KH instability in shear layer formed due to wing sweep and added mass effect due to the flow dragged by flapping wing. Vortex filamentation and fragmentation phenomena are observed during downstroke and upstroke respectively due to faster downstroke and slower upstroke. Rossby number, which is the ratio of inertial to Coriolis force is significant for rotational flapping wing. With increase in Rossby number there is a reduction in the spanwise flow over wing which influences strength of wingtip vortex at beginning of a stroke. It is found that spanwise flow for AR = 1.5 is stronger than AR = 1.0 and consequently the strength of wingtip vortex is higher for higher aspect ratio. However, peak vorticity is higher for AR = 1.0 due to vortex stretching effect which is expected to be more dominant at lower AR due to three dimensional effects. Effect of marginal variation in wing aspect ratio, flapping frequency with kinematic asymmetry are studied using velocity field, vorticity (ωz) contours, λ2 criterion, peak vorticity variation and its spatial distribution as well as kinetic energy variation of the flow field. Kinetic energy distribution and its connection with wake capture is explored.