Gear Combinations Research Articles

A comprehensive analysis on coast side contact behaviour of thermoplastic gears against steel gear: a FEA approach

PurposeThe research paper comprehensively investigates the gear tooth deflection of standard thermoplastic gears with steel gear as the driver and driven companions. An accurate mapping of characteristic contact regions between the meshing gears was done, and the behaviour of the gear tooth in the premature and prolonged contact zones was studied.Design/methodology/approachThe study employs the finite element method to conduct a quasi-static 2D analysis of meshing gear teeth. The finite element model was created in AutoCAD and analysed using the ANSYS 19.1 simulation package.FindingsIn the polymer-polymer gear combinations, premature and prolonged contact primarily occurs along the addendum radii of meshing gears, whereas a novel contact phenomenon was observed in the coast side for polymer-metal and metal-polymer combinations, exhibiting a path perpendicular to the standard drive side contact. As well, the deflection of the tooth alters the load distribution across the interlocking gears, leading to a decrement in the root stresses.Originality/valueThe Lewis bending equation demonstrates that bending stresses depend solely on the applied load and the geometry of the tooth. It does not consider the effects of deflection. However, the computational results showed that the gear tooth deflection caused by different gear pair combinations also affects the bending stresses. The contact stresses observed in the polymer-polymer gear combination were observed to be within the material’s proportional limit. However, when a steel gear is paired with a polymer gear, the contact stresses exceed the proportional limit due to coast side contact.

Open-source spring-driven syringe pump with 3D-printed components for microfluidic applications

The operation of microfluidic devices requires precise and constant fluid flow. Microfluidic systems in low-resource settings require a portable, inexpensive, and electricity-free pumping approach due to the rising demand for microfluidics in point-of-care testing (POCT). Open-source alternatives, employing 3D printing and motors, offer affordability. However, using motors require electrical power, which often relies on external sources, hindering the on-site use of open-source pumps. This study introduces a spring-driven, 3D-printed syringe pump, eliminating the need for an external power source. The syringe pump is operated by the flat spiral spring’s torque. By manually winding up the mainspring, the syringe pump can be operated without electricity. Various flow rates can be achieved by utilizing different syringe sizes and choosing the right gear combinations. All the parts of the syringe pump can be fabricated by 3D printing, requiring no additional components that require electricity. It operates by winding a mainspring and is user-friendly, allowing flow rate adjustments by assembling gears that modulate syringe plunger pushing velocity. The fabrication cost is $25–30 and can be assembled easily by following the instructions. We expect that the proposed syringe pump will enable the utilization of microfluidic technologies in resource-limited settings, promoting the adoption of microfluidics. Detailed information and results are available in the original research paper (https://doi.org/10.1016/j.snb.2024.135289).

Enhanced tunable cavity development for axion dark matter searches using a piezoelectric motor in combination with gears

Most search experiments sensitive to quantum chromodynamics (QCD) axion dark matter benefit from microwave cavities, as electromagnetic resonators, that enhance the detectable axion signal power and thus the experimental sensitivity drastically. As the possible axion mass spans multiple orders of magnitude, microwave cavities must be tunable and it is desirable for the cavity to have a tunable frequency range that is as wide as possible. Since the tunable frequency range generally increases as the dimension of the conductor tuning rod increases for a given cylindrical conductor cavity system, we developed a cavity system with a large dimensional tuning rod in order to increase this. We, for the first time, employed not only a piezoelectric motor, but also gears to drive a large and accordingly heavy tuning rod, where such a combination to increase driving power can be adopted for extreme environments as is the case for axion dark matter experiments: cryogenic, high-magnetic-field, and high vacuum. Thanks to such higher power derived from the piezoelectric motor and gear combination, we realized a wideband tunable cavity whose frequency range is about 42% of the central resonant frequency of the cavity, without sacrificing the experimental sensitivity too much.

Some warning signs detected in coastal pelagic fisheries of the west coast of Sri Lanka: Declining trend of <em>Amblygaster sirm</em> suggesting the need for immediate management initiatives

Coastal fisheries, mainly characterized by small pelagic species, are significant on the west coast of Sri Lanka in terms of livelihood and food security. However, currently, the fishery has faced numerous challenges, particularly with the stock depletion allied with poor management practices. The present study was carried out using the time series data of 2001–2020 on the west coast of Sri Lanka representing four fisheries districts - Kalutara, Colombo, Negombo, and Chilaw - to explore the present status and the tendency of the fishery towards management considerations. The analysis was based on the outboard engine fiber-reinforced plastic boats (OFRP) with small meshed gillnets, which are the main boat gear combination that exists in the fishery. The recent five-year landings within the study period indicated that the highest average catch rates resulted in the onset of the southwest monsoon and extended until the end of the northeast monsoon. The catch rates of fishery exhibited greater inter-annual fluctuations during a two-decade period, with an average of 66.7 ± 17.3 kg per trip from 2011 to 2020. Over the past two decades, the Mean Trophic Level (MTL) of the coastal fish landings ranged from 3.13 to 3.62 and showed a declining trend with the forecast of 3.38 for 2022-2026. Moreover, the catch rates and the relative contribution of Amblygaster sirm, one of the main target species in the country, showed a declining trend over the past two decades while indicating the need for immediate management initiatives.

Fully 3D-printed, nonelectric, spring-powered syringe pump for operating microfluidic devices

Microfluidic devices require a precise and steady flow for fluid control. The high demand for microfluidics in point-of-care testing (POCT) necessitates a portable, low-cost, and electricity-free pumping method for operating microfluidic platforms in low-resource settings. This study presents a fully 3D-printed and portable syringe pump operated by torque from a flat spiral spring. The syringe pump can be operated by manually winding up the spring, and various flow rates can be obtained using different syringe sizes and selecting appropriate gear combinations. It generated a steady flow rate ranging from 1.4 µL/min to 12.0 µL/min with high repeatability. The pump is suitable for the on-site use of microfluidic platforms because it does not require electricity and does not occupy a large space. The 3D printed pump proposed in this study is named precise, rapid-prototyped, nonelectric, torque-driven (PRNTD) pump. The versatility and utility of the pump are demonstrated by generating a linear concentration gradient using a microfluidic gradient generator and microdroplets using a T-channel microfluidic chip. The PRNTD pump can facilitate the on-site application of microfluidic platforms in resource-limited settings and contribute to the widespread use of microfluidic technologies.

Sliding mode control of an outer-rotor magnetic-gear-integrated motor with a Halbach array

In this paper, the magnetic-gear-integrated motor with a Halbach array is analyzed. The combination of coaxial magnetic gear and permanent magnet synchronous motor (PMSM) replaces the role of mechanical gear in transmission structure and realizes the transmission characteristics of low-speed and high torque. Halbach permanent magnet array has the effect of good unilateral magnetic shielding, which can make the waveform closer to the sine wave. Aiming at the problem that the position sensor limits the control accuracy during the operation of the motor, founded on the analysis of the mathematical model of the magnetic-gear-integrated motor, an improved sliding mode observer is proposed. Also, the sliding mode controller (SMC) replaces the PI regulation in the speed loop to increase the robustness of the system. Lyapunov is utilized to prove the stability of the system, and the simulation is built in MATLAB/ Simulink. A 3.6 kW prototype is manufactured and tested. The feasibility of the sensorless-driven system is proven by simulation and experiments.

Kinematic synthesis and simulation of a vegetable pot seedling transplanting mechanism with four exact task poses

To obtain a picking and planting integrated transplanting mechanism (PITM) with ideal trajectory shape, reasonable operating attitude, and compact structure for vegetable pot seedling transplanting, a symmetrical structural PITM composed of two planetary carriers and driven by a cam–noncircular gear combination mechanism was proposed in this paper. In accordance with the requirements of transplanting agronomy, the shape of the motion trajectory and the attitude of the end tip of the clamping claw at several specific positions (the starting and end points of picking seedling, the starting point of pushing seedling, and a special point on the return segment) were planned. To make the clamping claws of PITM pass through a set of prescribed positions, the mechanism was simplified to an open-chain 3R mechanism. An accurate four-position-based method for solving the open-chain mechanism model was adopted to obtain the curves of its fixed hinge point (central point) and dynamic hinge point (circle point). The ratio of adjacent bars’ lengths was analyzed to determine the feasible interval of the central and circle point curves and the reasonable link length. A desired closed transplanting trajectory that goes through the given points and the corresponding transmission ratio model of the open-chain mechanism was established. After the transmission ratio of each stage of gear and cam pairs was calculated and distributed, the prototype of PITM was designed and manufactured. Lastly, the effectiveness and feasibility of the design were verified through a preliminary experiment of the prototype. Keywords: kinematic synthesis, transmission ratio, non-circular gear, planetary carrier DOI: 10.25165/j.ijabe.20231602.6739 Citation: Sun L, Xu H C, Zhou Y Z, Shen J H, Yu G H, Hu H F, et al. Kinematic synthesis and simulation of a vegetable pot seedling transplanting mechanism with four exact task poses. Int J Agric & Biol Eng, 2023; 16(2): 85-95.

Performance comparison of series–parallel hybrid transmissions with multiple gears and modes based on efficiency model

Although multi-gear and multi-mode series–parallel hybrid transmissions (MGMM-SPHTs) can significantly improve the economy and power performance of hybrid electric vehicles (HEVs), few studies have elucidated their inherent mechanism. The present study quantitatively explores how different numbers of gears, the speed ratio range, and the working mode improve the economy and power performance of SPHTs. Moreover, the cost factor is considered in the comprehensive evaluation index. First, the speed ratio range of SPHT with different gears is defined, and the possible working modes of SPHT with different gear combinations are examined. Second, the efficiency model of the SPHT components is constructed on the basis of the energy flow, which provides a foundation for the subsequent construction of the power loss model. Moreover, by taking the minimum power loss in the power transmission process as the objective function, the dynamic programming method is used to evaluate the energy utilization performance of SPHT with different numbers of gears. Finally, on the basis of the aforementioned research, the comprehensive performance of MGMM-SPHTs is quantitatively compared, and the various influencing factors are analyzed in detail. The comparative analysis shows that increasing the number of engine direct drive gears has a significant effect on improving the economy. In particular, when the number of gears is increased from one to two, the fuel consumption is reduced by 4.007% on average; by contrast, when the number of gears is increased from two to three, the fuel consumption is reduced by only 1.173%. In addition, increasing the number of engine and motor direct drive gears has a significant effect on improving the power performance. Furthermore, this study elucidates the energy-saving mechanism of MGMM-SPHT, which can effectively guide the product design and development of SPHT.

Combining sampling gear to optimally inventory species highlights the efficiency of eDNA metabarcoding

AbstractBiodiversity surveys may require the use of multiple types of sampling gear to maximize the efficiency of species detections, yet few studies have investigated how to optimally distribute effort among gear. In this study, we conducted eDNA metabarcoding and capture‐based sampling surveys (electrofishing, fyke netting, gillnetting, and seining) to sample fish species richness in a large northern temperate lake. We evaluated the success of the sampling methods individually and in combination to determine the allocation of effort and cost across sampling gear that provides the optimal approach for lake‐wide species inventories. We found that eDNA metabarcoding detected more species than any other sampling method, including 11 species that were not detected with any capture‐based approach. Optimal gear combination analyses revealed that detected species richness is maximized when most of the effort or budget is allocated to eDNA metabarcoding, with smaller allocations to seining and fyke netting. eDNA metabarcoding and capture sampling gear showed similar patterns of spatial heterogeneity in the fish community across habitat types, with pelagic samples forming a group that was distinct from nearshore samples. Our results indicate that eDNA metabarcoding is a rapid and cost‐efficient tool for biodiversity monitoring and that assessing the complementarity of multiple sampling types can inform the development of optimal approaches for measuring fish species richness.

Evaluating the efficacy of nursery gear types for cultivating Atlantic surfclams (Spisula solidissima)

The Atlantic surfclam (Spisula solidissima) is a promising candidate for species diversification in the United States Northeast because it is native, grows rapidly, and is relatively recognizable to the public. However, gaps in the surfclam husbandry literature have left aquaculture practitioners without a complete understanding of how to best cultivate this species on commercial scales. In particular, relatively few studies have examined which culture conditions are necessary for rearing juvenile surfclams during the nursery phase. To fill this gap, controlled experiments were conducted to evaluate the efficacy of various gear types that are commonly used to rear other juvenile bivalve species. Specifically, growth and survival of early juvenile surfclams (0.4–2.7 mm) were compared when reared in different gear combinations, including downwellers, upwellers, and bell siphon systems. Similarly, growth and survival of late juvenile surfclams (1.1–18.0 mm) were compared when reared in upwellers and shallow raceways, with and without sand. Sediment accumulation, a proxy for culture cleanliness and system maintenance, was also monitored during the late nursery experiment. Results indicate that multiple rearing methods can effectively produce commercial-scale quantities of surfclams, but flow rate, food availability, and temperature are important factors that can limit gear efficiency. All early nursery gear systems performed similarly, while the late nursery upweller system performed significantly better than both types of shallow raceway systems. This study reinforces the feasibility of surfclams as a culture species that aligns well with the Northeast’s established shellfish farming framework.

Optimizing size selectivity and catch patterns for hake (Merluccius merluccius) and blue whiting (Micromesistius poutassou) by combining square mesh panel and codend designs

Gear modifications in fisheries are usually implemented to obtain catch patterns that meet management objectives. In the Basque bottom trawl fishery, gear regulations include the use of a square mesh panel (SMP) placed at the top panel of the extension piece of the trawl to supplement diamond mesh codend selectivity. However, the catch patterns obtained with this combination have raised concern among scientists and authorities. This study combines new data on different SMP and codend designs with existing data from the literature to produce new results that are applied to predict the size selectivity and catch patterns of different gear combinations for a variety of fishing scenarios. A systematic approach based on the concept of treatment trees was outlined and applied to depict the effect of individual and combined gear design changes on size selectivity and catch patterns for hake (Merluccius merluccius) and blue whiting (Micromesistius poutassou). This approach led to identification of the gear combination with the most appropriate exploitation pattern for these two species and improved the readability and interpretation of selectivity results. The results demonstrated that changes both in SMP and, especially, codend designs have a significant effect on hake and blue whiting size selectivity and catch patterns. Therefore, we believe that further research should prioritize codend size selectivity, and additional selection devices may be added once codend designs with good selective properties are achieved.

A model formulation for the prediction of churning power loss in worm gear transmission

Churning power loss is a complex process that causes significant loss of energy under splash lubrication of gear units. A set of empirical equations are available that allows for precise churning power losses calculation for only the parallel axis gears. The main objective of this study is to formulate a new mathematical model for worm gear based on the experiment result. The mathematical model is formulated using the dimensional analysis method and has been experimentally validated over a wide range of speeds in terms of revolutions, types of lubricants, lubricant temperature, and immersion depths. The simple direct torque measurement method was used to measure the churning loss. The influence of inertia force, viscous force, and gravitational forces were also investigated therefore correlations with Froude and Reynolds numbers are presented. Hardened steel and bronze were used as a material combination of worm and worm gear, respectively. A new formula for worm gear under splash lubrication has been derived and validated by comparison with experimental evidence. A very little discrepancy was found between the experiment result and the mathematical equation.

Indo-Sri Lanka Fishing Conflict in the Palk Bay and Its Implications for Fisheries

The Palk Bay constitutes exceptionally rich fishing grounds for the fishers of India and Sri Lanka. In the recent past, dispute between Indian and Sri Lankan fishers has emerged in exploiting fisheries resources, posing serious threats to the livelihoods of thousands of fishery dependents in the two countries. Present study comprehensively explores all aspects of Indo-Sri Lanka fishing conflict, reviewing articles published during 1995-2018. Twenty-five articles that addressed the Palk Bay fishing conflict were obtained, using a systematic search strategy. The present study unfolds that fishers were engaged in fishing activities in Palk Bay, using different craft and gear combinations over many decades. Conspicuously, several factors are influential for the emergence and escalation of Indo-Sri Lanka fishing conflict, including; (1) establishment of International Maritime Boundary Line (IMBL); (2) introduction of mechanized trawls by Indian fishers in 1960s with the expansion of the export market demand for shrimp; (3) imposition of fishing ban by Sri Lankan government during civil war during 1983-2009; (4) recommencement of distant water fisheries in the Palk Bay by Sri Lankan fishers with the conclusion of civil war in 2009, and (5) damage to fishing crafts and gears of artisanal fishers. Moreover, the study elucidates that Indo-Sri Lanka fishing conflict has a detrimental impact on the fisheries industry, livelihoods of the fishers, economy and political stability of India and Sri Lanka. Furthermore, the fishing conflict has caused many negative impacts including depletion of fishery resources, increase in enforcement cost, reduction of foreign exchange earnings, arresting fishers, presence of illegal trading and smuggling of arms and ammunition. Several measures have been taken by Indian and Sri Lankan Governments to resolve the fishing conflict. Albeit, they have yet to come to a common agreement to find an amicable long-lasting solution, vital for moving forward the industry in a sustainable manner.

Comparison of Two Fish Sampling Techniques for Low‐Conductivity, Lowland Headwater Streams

AbstractDespite being common, low‐conductivity (<70 µS/cm), headwater streams are often understudied compared with larger waters that support recreational and commercial fisheries. However, recent conservation efforts that have focused on native, nongame species have created the need to develop and test sampling methods in these habitats. We compared a novel combination of gears (electrofishing coupled with kick‐seining) to three‐pass electrofishing for sampling fish assemblages in low‐conductivity streams. At each site, each method was used to sample separate reaches equal to 35‐fold the mean stream width. We compared CPUE and species richness between the two methods and used logistic regression to estimate the probability of capturing a new species on the second and third passes when electrofishing. We calculated the capture probabilities for the most common species encountered using the Carle–Strub depletion method, with the three‐pass electrofishing data. When compared with the combination method, three‐pass electrofishing resulted in significantly greater CPUE and species richness (0.21 vs. 0.13 fish/m2 and 7.24 vs. 5.00 species, respectively). There was a 67% probability of capturing a new species on the second pass and 30% probability of capturing a new species on the third pass when using three‐pass electrofishing. The capture probabilities ranged from 0.50 to 0.87 for the 13 species examined. The use of kick‐seining after a single electrofishing pass provided no benefit compared with additional electrofishing passes. We recommend making at least three passes while electrofishing when estimating relative abundance and species richness in low‐conductivity wadeable streams.

Gear sound model for an approach of a Mechanical Acoustic Vehicle Alerting System (MAVAS) to increase EV’s detectability

Hybrid-electric and electric vehicles significantly reduce noise road emissions. This noise mitigation also causes a reduction in the sound detectability and therefore it increases the potential of causing accidents. A suitable solution arises with the Acoustic Vehicle Alerting Systems (AVAS) emitting a warning sound to alert pedestrians about the presence of a silent vehicle. This paper details an acoustic prediction model capable of simulating the sound produced by a pair of spur dry gears used as a Mechanical Acoustic Vehicle Alerting System (MAVAS). This proposal that tries to reproduce a sound closer to the mechanical sound of a conventional vehicle would be used as an alternative to existing systems. The prediction model developed is validated and consists in two consecutive parts: first, a dynamic model studies the rattle of the gears, then, an analytical model reproduces the sound of each impact of the gear teeth. This sound model makes it possible to characterize a proposed gear combination of the MAVAS, verifying its compliance with the European legislation.

Development of a Bionic Dolphin Flexible Tail Experimental Device Driven by a Steering Gear

In order to study the mechanism of the tail swing of the bionic dolphin, a flexible tail experimental device based on a steering engine was developed. This study was focused on the common three joint steering gear and its use in a bionic dolphin tail swing mechanism, and it was found that the bionic dolphin driven by the steering gear had the problem of excessive stiffness. In order to solve this problem, we designed a bionic dolphin tail swing mechanism. The tail swing mechanism was designed rationally through the combination of a steering gear drive and two flexible spines. Analysis of kinematic and dynamic modeling was further completed. Through simulation using, the research on the bionic dolphin tail swing mechanism was verified. Experiments showed that the swing curve formed by the steering gear-driven bionic dolphin tail swing mechanism with two flexible spines fit the real fish body wave curve better than the original bionic dolphin tail swing mechanism.

СОВЕРШЕНСТВОВАНИЕ МЕТОДИЧЕСКОГО ОБЕСПЕЧЕНИЯ ОПЕРАТИВНОЙ НАЛАДКИ УНИВЕРСАЛЬНЫХ МЕТАЛЛОРЕЖУЩИХ СТАНКОВ АВТОРЕМОНТНЫХ ПРЕДПРИЯТИЙ

The investigation purpose: simplification and ensuring tooling high performance of two-pair gear trains in machines with change gears. Methods used: numerical experiments for the characteristics definition of change gear sets in gear trains, a comparative analysis of different sets characteristics, a result visualization in a table form. Relevance of the method offered is substantiated with considerable labor intensity in the definition of the gear combination in gear trains by existing methods based on tables use mainly through possible way selection. Novelty: there are offered special algorithms of setup calculations decreasing operation time for the choice of gear combinations of gear trains. Basic results: there are developed computer programs for the definition of gear train combinations required and an electronic directory for machine-tool two-pair gear train setups recommended for use by workers of technological departments and in design service in production activities of engineering and motor car repair companies, in research centers and colleges (in thesis investigations, in training processes of engineering experts).

Design of clamping-pot-type planetary gear train transplanting mechanism for rice wide–narrow-row planting

To design a clamping-pot-type wide–narrow-row pot seedling transplanting (WPST) mechanism with desired spatial beak-shaped trajectory and working posture, a new design method of planetary gear train transplanting mechanism (PGTM) with non-circular gears based on several key spatial poses (position and posture) was proposed. The PGTM was simplified to a spatial open-loop chain with two-revolute (2R) joints. The geometric constraint equations containing only the structural parameters of the chain were then established on the basis of the three key spatial poses, and the homotopy algorithm was used to obtain all the required parameters of the mechanism. In accordance with the parameters obtained, the relative angular displacement relation between the planet carrier and the transplanting arm was optimized, the trajectory of the mechanism was replayed, and the total transmission ratio was determined. The degree of freedom of the spatial 2R mechanism was reduced by attaching to the unequal gear pair, and the transmission ratio was distributed in accordance with the gear type to realize the design of a non-circular gear pitch curve. Lastly, a clamping-pot-type PGTM for rice WPST driven by the combination of planar non-circular and non-conical gears was designed, and virtual simulation and prototype test were conducted. Results showed that the simulation and prototype test trajectories were consistent with the desired trajectory. Under the operating speeds of 50 r/min and 90 r/min, the success rates of seedling picking were 95.32% and 90.15%, respectively, which verified the feasibility of the theoretical method. This method could provide a reference for the design of a spatial PGTM with nonuniform transmission. Keywords: rice pot seedling, wide–narrow-row transplanting, spatial trajectory, planetary gear train, non-circular gear DOI: 10.25165/j.ijabe.20211402.5975 Citation: Wang L, Sun L, Huang H M, Yu Y X, Yu G H. Design of clamping-pot-type planetary gear train transplanting mechanism for rice wide–narrow-row planting. Int J Agric & Biol Eng, 2021; 14(2): 62–71.

Actuation Selection for Assistive Exoskeletons: Matching Capabilities to Task Requirements.

Selecting actuators for assistive exoskeletons involves decisions in which designers usually face contrasting requirements. While certain choices may depend on the application context or design philosophy, it is generally desirable to avoid oversizing actuators in order to obtain more lightweight and transparent systems, ultimately promoting the adoption of a given device. In many cases, the torque and power requirements can be relaxed by exploiting the contribution of an elastic element acting in mechanical parallel. This contribution considers one such case and introduces a methodology for the evaluation of different actuator choices resulting from the combination of different motors, reduction gears, and parallel stiffness profiles, helping to match actuator capabilities to the task requirements. Such methodology is based on a graphical tool showing how different design choices affect the actuator as a whole. To illustrate the approach, a back-support exoskeleton for lifting tasks is considered as a case study.

Development of an Anthropomorphic Prosthetic Hand with Underactuated Mechanism

An anthropomorphic prosthetic hand for wrist or forearm amputees is developed herein. The prosthetic hand was designed with an underactuated mechanism, which makes self-adaptive grasping possible, as well as natural motions such as flexion and extension. The finger and thumb modules were designed with four degrees of freedom by motions of the distal interphalangeal, proximal interphalangeal, and metacarpophalangeal joints. In this research, we pursued several novel trials in prosthetic hand design. By using two four-bar linkages composed of a combination of linkages and gears for coupling joints at each finger, it was possible to make a compact design, and the linkage has advantages such as accurate positioning, uniform power transmission, and high payload. Also, by using constant-velocity joints, torque is transferred to finger modules regardless of adduction/abduction motions. In addition, adduction/abduction and self-adaptive grasping motions are passively realized using torsional springs. The developed prosthetic hand was fabricated with a weight of 475 g and a human hand size of 175 mm. Experiments with diverse objects showed its good functionality.