Search Results (34)

Dielectric elastomer actuators (DEAs) are increasingly recognized for their potential in robotic applications due to their ability to undergo significant deformation when subjected to an electric field. However, they are often limited by their low output power, which can make their integration into dynamic systems like hopping robots particularly challenging. This research optimizes the performance by introducing a cone DEA with a novel type of semi-diamond preload mechanism. This type of preload mechanism can meet the requirements of a negative-stiffness preload and a light weight. According to the experiments, the DEA can provide 3.62 mW power and its mass is only about 17.5 g. In order to drive hopping robots based on a cone DEA, this research introduces an energy accumulation mechanism coupled with a constant-torque cam for a hopping robot. The hopping robot weighs approximately 30.3 g and stands 10 cm tall in its upright position. Its energy accumulation mechanism involves a gear and cam transmission system, which is the key to store and release energy efficiently. The primary components of this mechanism include a torsion spring that stores mechanical energy when twisted, a constant-torque actuation cam that ensures the consistent application of torque during the energy storage phase, and a conical DEA that acts as an actuator. When the conical DEA is activated, it pushes a one-way clutch to the rocker, rotating the gear and cam mechanism and subsequently twisting the torsion spring to store energy. Upon release, the stored energy in the torsion spring is rapidly converted into kinetic energy, propelling the robot into the air. The experiments reveal that the designed DEA can drive the hopping robot by using the energy storage mechanism. Its hopping height is related to the pre-compression angle of the torsion spring. The DEA can drive the rigid hopping mechanism, and the maximum hopping height of the robot is up to 2.5 times its height. DEA hopping robots have obvious advantages, such as easy control, quietness and safety. Full article

Abandoned mine drainage treatment ponds could have contrasting effects on the reproductive success of birds living in the vicinity. The ponds and associated vegetation may, like any other body of freshwater, provide beneficial habitats for the insects that the birds use to feed their young; or instead, the ponds may act as an ecological trap, attracting the birds to a habitat that is poor in quality and negatively impacting their productivity. We monitored nests of an aerial insectivore, the Tree Swallow (Tachycineta bicolor), to determine whether the distance between the ponds and the nests affected various reproductive parameters including clutch size, hatch rate, number of nestlings, nestling size and mass, number of fledglings, fledging rate, and fledge date. Data were collected over two breeding seasons (2022 and 2023) from a swallow population in southwestern Pennsylvania, USA. We found that the nests closest to the treatment ponds had significantly more nestlings and fledglings, earlier fledge dates, and a better fledging rate when compared to nests that were more distant from the ponds. However, all these parameters were well below previously published values, which suggests that the mine drainage ponds provide good nesting habitats relative to what is available in the region but that they do not represent high-quality habitats for this species overall. Full article

When launching a heavy-duty vehicle, torque and position control during automatic clutch engagement is critical, and the driver’s intention to launch and changes in the vehicle’s launching resistance make clutch control more complex. This paper analyses the automatic engagement process of automated mechanical transmission (AMT) clutches and proposes an optimal control of the clutch torque for launching heavy-duty vehicles. Firstly, a fuzzy neural network (FNN)-based vehicle launching states recognition (LSR) system is designed for distinguishing the driver’s launching intention and the vehicle’s launching equivalent moment of resistance. Secondly, jerk, friction work, and launching reserve power are taken as the performance indexes for clutch torque optimization, the weight coefficients of each performance index are adjusted according to the LSR results, and the optimal clutch torque is solved by using the minimum value principle based on the shooting method. Finally, simulations and tests are conducted to validate the strategy of optimizing clutch torque, and the impact of torque optimization on the position change during the engagement process is analyzed. The results indicate that under different driver’s intentions, vehicle masses, and road gradient conditions, the jerk, friction work, and slipping time of heavy vehicles during the launching process are improved by applying the optimization strategy. Full article

We designed a common garden design to collect data on female reproductive traits from three populations of the southern grass lizard Takydromus sexlineatus, testing the hypothesis that a species-specific pattern of seasonal shifts in reproductive allocation should be shared by geographically separated populations. Of the seven examined traits, six differed among populations, with four of the six also differing among successive clutches. Females grew longer during the breeding season and produced more eggs in the first clutch than in the subsequent clutches; egg size was unchanged throughout the breeding season. After removing the influence of female size or postpartum body mass we found the following. First, postpartum body mass, clutch mass, and relative clutch mass were greater in the Wuzhishan population than in the Shaoguan and Zhaoqing populations. Second, egg size was greatest in the Wuzhishan population and smallest in the Zhaoqing population. Third, clutch size was greatest in the Wuzhishan population and smallest in the Shaoguan population. Females did not trade-off egg size against number within each population × clutch combination. Our study validates the hypothesis tested, supports the conventional view that reproductive output is highly linked to maternal body size in lizards, and follows the classic prediction that females with different amounts of resources to invest in reproduction should give priority to adjusting the total number rather than size of their offspring. Full article

Fine particles from vehicles occur in a range of particulate matter (PM) sizes and influence the roadside atmosphere. The contribution of fine dust from automobiles to road pollution has reportedly been extremely high. Researchers have estimated that non-exhaust fine dust originating from brakes, tires, clutches, and road surface wear rate is increasing. Several studies have shown that brake pads account for a significant proportion of non-exhaust emissions. In this study, a friction test using vehicle brake pads was carried out with a friction tester to reveal the harmfulness of brake pad particles by the driver’s driving habits. Conditions were made considering the pressure, vehicle speed, and temperature and assuming the amount of deceleration of the vehicle. Particle collection devices were used to analyze the concentration of number and the mass distribution of particles produced in the experiment, with a range from 6 nm to 7.3 μm to gauge the toxicity of particles. The results showed that the number concentration of fine particles tended to increase linearly with changes in vehicle deceleration (braking energy) in the particle diameter region around 0.75–7.3 μm. The number concentration of fine particles tended to increase exponentially in the particle diameter region around 71–120 nm. The rapid occurrence of ultrafine particles in nanometers varied depending on the test conditions. Full article

The paper presents a redesign of the custom disc-on-disc-type tribometer intended for the experimental characterization of the friction and wear of automotive dry clutch friction lining. The redesign is aimed at expanding the operating range at which the machine is not sensitive to shudder vibrations. This is achieved through a set of hardware and software upgrade measures. First, the natural frequency of the normal load-generation linear axis of the machine is increased by enlarging its bending stiffness and reducing the suspended mass. The former is realized by replacing the single, two-axial force/torque piezoelectric sensor with a set of three three-axial piezoelectric force sensors, adding a set of stiff linear guides, and reducing the lengths of the cantilevers of lateral forces acting on the linear axis guide system. The latter is accomplished by reducing the overall dimensions of the cooling disc and redesigning the thermal insulation components. The shudder sensitivity resistance is further reduced through individual normal force-readings-based adjustment of parallelism between friction contact surfaces and the increase in the stiffness of eccentrically positioned water-cooling pipes. Finally, the stability of the coefficient of friction and, consequently, the wear process are boosted by adjusting the control routines to minimize the circumferential and/or radial temperature gradients. These adjustments include the introduction of a clutch lock-up interval at the end of the clutch closing cycle, a minimum cooling delay inserted between two closing cycles, and maximum normal force demand of the clutch torque controller. The performance gain of the upgraded tribometer is demonstrated through a study of the dry clutch friction plate static wear experimental characterization for a wide range of operating conditions. Full article

The variation in egg and clutch mass in sympatric species at high altitudes is poorly understood, and the potential causes of variation are rarely investigated. This study aimed to describe the interspecific variation in avian egg and clutch mass among 22 sympatric bird species at an altitude of 3430 m. Our objective was to reduce potential confounding effects of biotic/abiotic factors and investigated hypotheses concerning allometry, clutch size, parental care, nest predation, and lifespan as possible correlates and explanations for the observed variation. Our findings indicated that both egg and clutch mass evolve with body mass across species. We found that egg mass variation was not explained by clutch size when controlling for allometric effects, which contrasts the “egg mass vs. clutch size trade-off” hypothesis. Additionally, we found that clutch mass was positively associated with parental care (reflected by development period) but negatively associated with predation rate. By substituting egg mass and clutch size into the models, we found that clutch size was significantly correlated with parental care, predation rate, and lifespan, while egg mass was only significantly associated with development period. Overall, these findings support life-history theories suggesting that reduced clutch size or mass is associated with a higher risk of predation, reduced parental care, but longer adult lifespan. Interestingly, our results indicate that clutch size has a greater influence on these factors compared to egg mass. This could be attributed to the fact that smaller clutch sizes result in a more notable decrease in energetic allocation, as they require a reduced effort in terms of offspring production, incubation, and feeding, as opposed to solely reducing egg size. These findings contribute to the growing evidence that life-history and ecological traits correlate with egg and clutch mass variation in sympatric species. However, further research is needed to explore the potential evolutionary causes underlying these patterns. Full article

Hopping locomotion has the potential to enable small-scale robots to maneuver lands quickly while overcoming obstacles bigger than themselves. To make this possible, in this paper, we propose a novel design of a high-power linear actuator for a small-scale hopper. The key design principle of the linear actuator is to use a power spring and an active clutch. The power spring provides a near constant torque along the wide range of output displacement. The active clutch controls the moving direction and operation timing of the linear actuator, which enables the hopper to take off at the right timing. As a result, the hopper has a size of 143 mm, a mass of 45.9 g, and hops up to 0.58 m. Full article

Due to the influence of bio-geographical and environmental factors, as well as anthropogenic landscape features, organisms show different reproductive strategies among different populations. There is a lack of detailed information on the reproductive biology of Kentish plover Charadrius alexandrinus in arid lands in Central Asia. In this study, we summarized the characteristics of the reproductive biology of three geographically distinct plover populations in Aibi Lake in northwestern Xinjiang, Taitema Lake in southern Xinjiang and artificial reservoirs around Urumqi City in northern Xinjiang, based on 440 eggs from 158 nests observed and analyzed from April to July of 2019 and 2020. We found that there was no significant difference in clutch size among the three populations. However, the egg size of the Taitema Lake population was significantly larger than those of the other two populations, whilst the egg volume and clutch volume of the artificial reservoirs’ populations were significantly larger than that of Aibi Lake. With the postponement of laying dates, the northern and northwestern populations showed the characteristics of a small clutch size and a relatively small egg size, respectively, and a decrease in reproductive output. The heavier female plovers in Taitema Lake laid eggs earlier, and there was a significantly positive correlation between female body mass and clutch size and egg size. The tarsometatarsus length of the female plovers was significantly positively correlated with the reproductive output in all three populations. The model selection results show that female body size and ambient temperature restrict the egg size and reproductive output of Kentish plovers, which is consistent with the upper limit hypothesis of the maternal condition and maternal constraint. Our data support the hypothesis that Kentish plovers show distinct flexibility in their breeding strategies to cope with the harsh natural environment in the arid lands of Xinjiang, China. The results of a relatively high average clutch size and average egg size imply that the saline wetlands of Western China are important breeding habitats for Kentish plovers. Full article

Offspring size-number trade-off is a critical component of life-history theory and is important for further understanding the reproductive strategies of animals. The relationship between this trade-off and maternal size has been explored in several turtle species, except for the Asian yellow pond turtle, Mauremys mutica. To investigate how the maternal condition affects offspring size and number, we explored the relationships among the maternal body size and the number and size of cultured M. mutica hatchlings using a 4-year dataset. Our results showed that different females not only produced different sizes of offspring but also produced different numbers of offspring. No trade-off in egg size number was detected. According to regression analysis, we did not find that the maternal body size significantly influenced the offspring mass; however, we detected that the offspring size was significantly correlated with the clutch size and maternal age. The mean body mass of offspring increased with maternal age, and the clutch size varied significantly over four years, which was correlated with offspring size, maternal body size and age. However, the number of offspring per female increased with the maternal plastron length rather than age. Our results were inconsistent with the optimal offspring size theory in that females did not increase their offspring size but rather increased the offspring number to increase their fitness, which will also provide a basis for the efficient cultivation management of turtles. Full article

Maternal effects can reduce offspring susceptibility to predators by altering resource allocation to young and reproducing larger offspring. While the perception of predation risk can vary according to a prey’s life stage, it is unclear whether maternally experienced intraguild predation (IGP) risk during different life stages influences the maternal effects of predatory insects. We investigated the influence of exposure to intraguild predators (Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)) during the larval and/or adult stages on reproductive decisions and offspring growth in Menochilus sexmaculatus (Fabricius). Independent of the life stage, when M. sexmaculatus females experienced IGP risk, their body weight and fecundity decreased, but the proportion of trophic eggs produced increased. However, egg mass, egg clutch number, and egg clutch size were not influenced by the treatment. Next, when offspring encountered H. axyridis, mothers experiencing IGP risk during the larval and/or adult stages could increase their offspring’s weight. Moreover, offspring in IGP environments reached a similar size as those with no-IGP environments when mothers experienced IGP risk during the larval and/or adult stages. Overall, M. sexmaculatus larval and/or adult exposure to IGP risk had no influence on egg size, but increased offspring body size when faced with H. axyridis. Additionally, mothers experiencing IGP risk during different life stages showed increased production of trophic eggs. Because IGP is frequently observed on M. sexmaculatus and favours relatively larger individuals, different stages of M. sexmaculatus express threat-sensitively to IGP risk; inducing maternal effects can be an adaptive survival strategy to defend against H. axyridis. Full article

This article aims to review a redesign approach of a student racing car’s clutch lever component, which was topologically optimized and manufactured by Additive Manufacturing (AM). Finite Element Method (FEM) analysis was conducted before and after a Topology Optimization (TO) process in order to achieve equivalent stiffness and the desired safety factor for the optimized part. The redesigned clutch lever was manufactured by using AM–Selective Laser Melting (SLM) and printed from powdered aluminum alloy AlSi10Mg. The final evaluation of the study deals with the experimental test and comparison of the redesigned clutch lever with the existing part which was used in the previous racing car. Using TO as a main redesign tool and AM brought significant changes to the optimized part, especially the following: reduced mass of the component (10%), increased stiffness, kept safety factor above the 3.0 value and ensured the more aesthetic design and a good surface quality. Moreover, using TO and AM gave the opportunity to consolidate multi-part assembly into a single component manufactured by one manufacturing process that reduced the production time. The experimental results justified the simulation results and proved that even though the applied load was almost 1.5× higher than the assumed one, the maximum von Mises stress on the component was still below the yield limit of 220 MPa. Full article

Maternal hormones such as estrogens deposited into the yolk of turtle eggs follow circulating levels in adult females, and they may alter the sexual fate of developing embryos in species with temperature-dependent sex determination (TSD). In temperate regions, this deposition occurs during the spring when estrogens increase in adult females as ambient temperatures rise, drop after the first clutch, and peak again (albeit less) in the fall. Global warming alters turtle nesting phenology (inducing earlier nesting), but whether it affects circulating hormones remains unknown, hindering our understanding of all potential challenges posed by climate change and the adaptive potential (or lack thereof) of turtle populations. Here, we addressed this question in painted turtles (Chrysemys picta) by quantifying estradiol, estrone, and testosterone via mass spectrometry in the blood of wild adult females exposed to 26 °C and 21 °C in captivity between mid-August and mid-October (15 females per treatment). Results from ANOVA and pairwise comparisons revealed no differences between treatments in circulating hormones measured at days 0, 2, 7, 14, 28, and 56 of the experiment. Further research is warranted (during the spring, using additional temperatures) before concluding that females are truly buffered against the indirect risk of climate change via maternal hormone allocation. Full article

In Corozalito beach, Costa Rica, Olive Ridley turtles (Lepidochelys olivacea) nest both solitarily and in arribadas. The predation of solitary nests was monitored from 2008 to 2021, recording date, time, sector of the beach, zone, status of nest (predated or partially predated) and predator when possible. We recorded 4450 predated nests in total (N = 30,148 nesting events); predation rates showed a fluctuating trend, with recent percentages reaching up to 30%, with four distinctive dips in 2010, 2014, 2016 and 2017. The spatial distribution of predated nests along the beach showed significant differences among the sectors regardless of the seasons (Friedman test, chi-squared = 14.778, df = 2, p-value = 0.000), with most predated nests (47.62%) occurring in the northern sectors of the beach. Predators were identified by their tracks and/or direct observations (N = 896, 24.08%). The most conspicuous predators identified were raccoons (55.69%) and black vultures (22.77%). As seen in Corozalito, predation rates have increased in recent years despite established conservation efforts. A comprehensive assessment of all threats towards the overall hatching success for clutches is needed, considering predation during mass nesting events, poaching and beach erosion, among other factors, to fully understand the nesting dynamics occurring in this beach. Full article

Dynamic muscular workload assessments of tractor operators are rarely studied or documented, which is critical to improving their performance efficiency and safety. A study was conducted to assess and model dynamic load on muscles, physiological variations, and discomfort of the tractor operators arriving from the repeated clutch and brake operations using wearable non-invasive ergonomic transducers and data-run techniques. Nineteen licensed tractor operators operated three different tractor types of varying power ranges at three operating speeds (4–5 km/h), and on two common operating surfaces (tarmacadam and farm roads). During these operations, ergonomic transducers were utilized to capture the load on foot muscles (gastrocnemius right [GR] and soleus right [SR] for brake operation and gastrocnemius left [GL], and soleus left [SL] for clutch operation) using electromyography (EMG). Forces exerted by the feet during brake and clutch operations were measured using a custom-developed foot transducer. During the process, heart rate (HR) and oxygen consumption rates (OCR) were also measured using HR monitor and K4b2 systems, and energy expenditure rate (EER) was determined using empirical equation. Post-tractor operation cycle, an overall discomfort rating (ODR) for that operation was manually recorded on a 10-point psychophysical scale. EMG-based maximum volumetric contraction (%MVC) measurements revealed higher strain on GR (%MVC = 43%), GL (%MVC = 38%), and SR (%MVC = 41%) muscles which in normal conditions should be below 30%. The clutch and brake actuation forces were recorded in the ranges of 90–312 N and 105–332 N, respectively and were significantly affected by the operating speed, tractor type, and operating surface (p < 0.05). EERs of the operators were measured in the moderate-heavy to heavy ranges (9–24 kJ/min) during the course of trials, suggesting the need to refine existing clutch and brake system designs. Average operator ODR responses indicated 7.8% operations in light, 48.5% in light-moderate, 25.2% in moderate, 10.7% in moderate-high, and 4.9% operations in high discomfort categories. When evaluated for the possibility of minimizing the number of transducers for physical workload assessment, EER showed moderate-high correlations with the EMG signals (r_GR = 0.78, r_GL = 0.75, r_SR = 0.68, r_SL = 0.66). Similarly, actuation forces had higher correlations with EMG signals for all the selected muscles (r = 0.70–0.87), suggesting the use of simpler transducers for effective operator workload assessment. As a means to minimize subjectivity in ODR responses, machine learning algorithms, including K-nearest neighbor (KNN), random forest classifier (RFC), and support vector machine (SVM), predicted the ODR using body mass index (BMI), HR, EER, and EMG at high accuracies of 87–97%, with RFC being the most accurate. Such high-throughput and data-run ergonomic evaluations can be instrumental in reconsidering workplace designs and better fits for end-users in terms of agricultural tractors and machinery systems. Full article