Mating Components Research Articles

Realizing Method and Application of Theoretically Relative Symmetry Zero Error for Two Coupling Components Based on Error Compensation

Mechanical systems often require the symmetry of the two assembly components. This paper presents a method for theoretical zero-symmetry error of the mating components in batch production. The method is based on symmetry principle of error compensation and sequential positioning of the two mating components, realizing the coincidence of the symmetrical lines between the two components, regardless the manufacturing errors of the two components. The method is suitable for processing positioning and assembly positioning precision requirements and multiple components of symmetry occasions.

Wear Behavior of Fiber Laser Textured TiN Coatings in a Heavy Loaded Sliding Regime

In heavy loaded mating components, such as sliders and sliding bearings, guaranteeing the efficiency of lubricant films for long times during severe service conditions is very complicated. In this work, the benefits deriving from the use of fiber laser sources for surface texturing of very thin TiN coatings in severe wear working conditions were demonstrated. Evaluations of the laser textured dimples shape, geometry and density are given. Wear performance of the fiber laser textured surfaces was evaluated in discontinuous oil lubricated conditions with a flat contact. High normal load and low sliding speed were applied. Comparison tests were also performed on commercial TiN and WC/C coatings. In terms of average wear volume and maximum wear depth, Laser Surface Texturing of TiN provided respectively a 70% and a 45% reduction if compared to plain TiN. If compared to WC/C the wear resistance gains were lower but LST TiN maintained such benefits for longer wear runs. SEM analysis also revealed that the laser interaction provided a localized thermal cracking to the TiN coating. However, the sliding action caused very limited and localized coating fragmentation or delamination.

Genetic and Environmental Transmission of Body Mass Index Fluctuation

This study sought to determine the relationship between body mass index (BMI) fluctuation and cardiovascular disease phenotypes, diabetes, and depression and the role of genetic and environmental factors in individual differences in BMI fluctuation using the extended twin-family model (ETFM). This study included 14,763 twins and their relatives. Health and Lifestyle Questionnaires were obtained from 28,492 individuals from the Virginia 30,000 dataset including twins, parents, siblings, spouses, and children of twins. Self-report cardiovascular disease, diabetes, and depression data were available. From self-reported height and weight, BMI fluctuation was calculated as the difference between highest and lowest BMI after age 18, for individuals 18-80 years. Logistic regression analyses were used to determine the relationship between BMI fluctuation and disease status. The ETFM was used to estimate the significance and contribution of genetic and environmental factors, cultural transmission, and assortative mating components to BMI fluctuation, while controlling for age. We tested sex differences in additive and dominant genetic effects, parental, non-parental, twin, and unique environmental effects. BMI fluctuation was highly associated with disease status, independent of BMI. Genetic effects accounted for ~34 % of variance in BMI fluctuation in males and ~43 % of variance in females. The majority of the variance was accounted for by environmental factors, about a third of which were shared among twins. Assortative mating, and cultural transmission accounted for only a small proportion of variance in this phenotype. Since there are substantial health risks associated with BMI fluctuation and environmental components of BMI fluctuation account for over 60 % of variance in males and over 50 % of variance in females, environmental risk factors may be appropriate targets to reduce BMI fluctuation.

Can sexual selection and disassortative mating contribute to the maintenance of a shell color polymorphism in an intertidal marine snail?

Abstract Littorina fabalis is an intertidal snail commonly living on the brown algae Fucus vesiculosus and showing frequent shell-color polymorphisms in the wild. The evolutionary mechanism underlying this polymorphism is currently unknown. Shell color variation was studied in mated and non-mated specimens of this species from different microareas in one locality from NW Spain, in order to estimate sexual selection and assortative mating that may (still) be operating in this population. The analyses across microareas allowed us to investigate frequency-dependent selection and assortative mating components, mechanisms that could maintain the polymorphism. The presence of shell scars caused by crab attacks, an environmental variable not related with sexual selection or assortative mating, was used as experimental control. This study provides new evidence of significant disas-sortative mating and some degree of sexual selection against some shell colors, supporting the results found 21 years ago in a similar study, i.e. in the same species and locality. The similarity of these estimates during the studied period suggests that this experimental approach is consistent and valid to be extended to other populations and organisms. In addition, sexual selection and assortative mating estimates did not change across microareas differing in shell color frequencies, suggesting than the polymorphism can not be maintained by a frequency-dependent (sexual selection-based) mechanism. Our main hypothesis is that negative assortative mating could contribute to the maintenance of the polymorphism, perhaps by males showing distinct female color preferences when searching for mates.

Sexual responses of the male rat medial preoptic area and medial amygdala to estrogen I: Site specific suppression of estrogen receptor alpha

Male rat copulation is mediated by estrogen-sensitive neurons in the medial preoptic area (MPO) and medial amygdala (MEA); however, the mechanisms through which estradiol (E2) acts are not fully understood. We hypothesized that E2 acts through estrogen receptor α (ERα) in the MPO and MEA to promote male mating behavior. Antisense oligodeoxynucleotides (AS-ODN) complementary to ERα mRNA were bilaterally infused via minipumps into either brain area to block the synthesis of ERα, which we predicted would reduce mating. Western blot analysis and immunocytochemistry revealed a knockdown of ERα expression in each brain region; however, compared to saline controls, males receiving AS-ODN to the MPO showed significant reductions in all components of mating, whereas males receiving AS-ODN to the MEA continued to mate normally. These results suggest that E2 acts differently in these brain regions to promote the expression of male rat sexual behavior and that ERα in the MPO, but not in the MEA, promotes mating.

Size-assortative mating and effect of maternal body size on the reproductive output of the nassariid Buccinanops globulosus

Size- assortative mating is usually present in populations where there is a positive relationship between female size and reproductive output. In this study, we tested for the presence of sexual size dimorphism, size-assortative mating and the effects of female size on reproductive output in a wild population of Buccinanops globulosus, an endemic nassariid of the Southwestern Atlantic Ocean with direct development. The results showed that: 1) females were larger than males, indicating sexual size dimorphism; 2) mate sizes were significantly correlated, indicating a component of size-assortative mating; 3) males of medium and large size classes were paired with larger females than small-sized males; 4) larger females were paired with large males; 5) maternal body size was positively related to some proxies of reproductive success (number of nurse eggs per egg capsule, egg capsular area and total length at hatching). Our results suggest that larger females may be favored as mates over smaller ones owing to their higher investment per offspring and consequently a larger initial juvenile size as juvenile.

Particle swarm optimization algorithm to maximize assembly efficiency

The demands on assembly accuracy require accurate operations both in machining and assembly in order to achieve the high performance of products. Although advanced machining technologies can be used to satisfy most of the demands on precision assembly, the corresponding manufacturing cost will also be increased. Selective assembly provides an effective way for producing high-precision assembly from relatively low-precision components. The accuracy of selective assembly is mainly based on the number of groups and the range of the group (allocated equally on the design tolerance). However, there are often surplus parts in some groups due to the imbalance of mating parts, especially in the cases of undesired dimensional distributions, which makes the methods developed and reported in the literature often not suitable for practice. In this work, a particle swarm optimization (PSO) algorithm is proposed by applying batch selective assembly method to a complex assembly with three mating components (as in ball bearing: an inner race, ball and outer race), to minimize the surplus parts and thereby maximizing the assembly efficiency. Due to the continuous nature of particle swarm optimization algorithm, standard PSO equations cannot be used to generate discrete combination of mating parts. An effective encoding scheme is developed to make the combination of mating parts feasible. The evolution performance of the PSO algorithm with different control parameter values is also analysed.

Effects of imposed displacement and initial coating thickness on fretting behaviour of a thermally sprayed coating

This paper describes the effects of imposed displacement and initial coating thickness on fretting wear behaviour of a thermally sprayed coating. Initial coating thickness and imposed displacement between two mating components are important parameters affecting durability of a thermally sprayed coating under fretting conditions. Nevertheless, the effects of imposed displacement and coating thickness at flat-and-rounded frictional contacts of aerospace dovetail connections are not sufficiently investigated. In this paper, fretting wear experiments with a double-layer thermally sprayed coating are performed under different displacement and coating thickness conditions. The effects of the parameters are then identified by directly comparing the ratio of maximum tangential force to normal force. Experimental results show that the ratio evolutions are similar on the ratio versus accumulated reciprocal sliding distance chart within the displacement range of 0.4–0.6 mm. In addition, it is demonstrated that durability of the coating is increased with increasing the initial thickness of the coating. Finally, the effect of the initial coating thickness is described with exponential evolution law of fretting damage.

Genetic algorithm to optimize manufacturing system efficiency in batch selective assembly

The demands on assembly accuracy require accurate operations both in machining and assembly in order to achieve the high performance of products. Although advanced machining technologies can be used to satisfy most of the demands on precision assembly, the corresponding manufacturing cost will also be increased. Selective assembly provides an effective way for producing high-precision assembly from relatively low-precision components. The accuracy of selective assembly is mainly based on the number of groups and the range of the group (allocated equally on the design tolerance). However, there are often surplus parts in some groups due to the imbalance of mating parts, especially in the cases of undesired dimensional distributions, which makes the methods developed and reported in the literature, often not suitable for practice. In this work, a genetic algorithm is proposed by applying batch selective assembly method to a complex assembly with three mating components (as in ball bearing: an inner race, ball, and outer race), to minimize the surplus parts and thereby maximizing the manufacturing system efficiency.The proposed algorithm is tested with a set of experimental problem datasets and is found outperforming traditional selective assembly and sequential assembly methods, in producing solutions with maximum manufacturing system efficiency.

Optimal Partitioning of Probability Distributions under General Convex Loss Functions in Selective Assembly

Selective assembly is an effective approach for improving the quality of a product which is composed of two mating components. This article studies optimal partitioning of the dimensional distributions of the components in selective assembly. It extends previous results for squared error loss function to cover general convex loss functions, including asymmetric convex loss functions. Equations for the optimal partition are derived. Assuming that the density function of the dimensional distribution is log-concave, uniqueness of solutions is established and some properties of the optimal partition are shown. Some numerical results compare the optimal partition with some heuristic partitioning schemes.

Optimal process design in selective assembly when components with smaller variance are manufactured at three shifted means

Selective assembly is an effective approach for improving the quality of a product that is composed of two mating components, when the quality characteristic of the product is the clearance between the mating components. In this approach, the components are sorted into several groups according to their dimensions, and the product is assembled by randomly selecting mating components from corresponding groups. A number of previous studies focused on equal width partitioning schemes, in which the dimensional distributions of the two components are partitioned so that all groups have equal widths. When there is a large difference between the variances of the two component dimensions, equal width partitioning will result in a large number of surplus components due to differences between the numbers of components in corresponding groups. Some authors have proposed a method of manufacturing the component with smaller variance at three shifted means to cope with this difficulty. In the present paper, an optimal manufacturing mean design that minimises the number of surplus components is derived. It is shown that the use of the optimal design considerably reduces the number of surplus components compared with using another previously proposed manufacturing mean design and the no-shift design.

Optimization of assembly tolerance variation and manufacturing system efficiency by using genetic algorithm in batch selective assembly

Quality of an assembly of any manufactured product is mainly based on the quality of mating components. Due to random variations in sources such as materials, machines, operators, and measurements, mating components manufactured by even the same process may vary in their dimensions. When mating components are assembled linearly, the resulting assembly tolerance will be the sum of the mating components tolerances. All precision assemblies demand for a closer assembly tolerance. A significant amount of research has already been done to minimize assembly variation using selective assembly, when the dimensions of components follow normal distribution. However, in reality, the dimensions of components produced especially in smaller to medium size batches, invariably have some skewness (non-normality), which makes the methods developed and reported in the literature, often not suitable for practice. In this work, batch selective assembly methodology is proposed for components having non-normal distributions to minimize the assembly tolerance variations. The proposed method which employs a genetic algorithm for obtaining the best combination of mating components is able to achieve minimum variations in assembly tolerances and also maximum number of acceptable assemblies. The proposed algorithm is tested with a set of experimental problem datasets and is found outperforming the other existing methods found in the literature, in producing solutions with minimum assembly variation.

Frictional Characteristics of IF-WS2 Nanoparticles in Simulated Engine Conditions

The efficacy of inorganic fullerene-like (IF) tungsten disulfide (WS2) nanoparticles as engine oil friction modifier additive was investigated using a high-stroke reciprocating piston ring–cylinder bore bench test system. Frictional characteristics of various IF-WS2 nanoparticle concentrations in mineral oil were experimentally analyzed in simulated engine conditions controlling oil temperature, speed, and normal load. Though the effect of IF-WS2 nanoparticles on piston ring and cylinder bore friction was minor in low concentrations, after a running period in a mixed lubrication regime with 10% additive, a considerable reduction in friction coefficient was observed when the IF-WS2 formulated oil was used. This reduction remains to some extent with reference mineral oil after solvent cleaning of the mating components. The results show that a thin tribofilm gradually forms on the piston ring and the cylinder bore surfaces, reducing the friction coefficient in a mixed lubrication regime. However, in order to obtain the friction reduction there seems to be a threshold in the concentration of IF-WS2 in mineral oil and film development period. The effects of lubrication regime, contact load, speed, and surface roughness on tribofilm formation are also discussed. The presence of WS2 tribofilm formed on the piston ring and the cylinder bore surfaces was further verified using Raman spectroscopy.

Variation in male courtship costs in butterflies

A cost of mating is common to both sexes but has predominantly been examined in females. In species where males provide resources to females at copulation, male mating costs are expected to be high as nutrient provisioning enhancing female fecundity is assumed to carry costs. In addition, males frequently court females prior to mating, which is known to carry survival costs to both sexes. However, the magnitude and basis of variation in males’ mating costs remains largely unknown. Here, I examine the effect of nutrient provisioning and courtship on male longevity across full-sib families in the paternally investing green-veined white butterfly, Pieris napi. Copulating males suffered a survival cost as did courting males prevented from copulating, indicating the courtship component of mating is costly. Male P. napi release aphrodisiacs during courtship to promote mating, indicating that these compounds may also be costly to produce. Contrary to expectation, nutrient provisioning was not associated with reduced survival relative to males only allowed to court females, although it is possible that this could be masked by the potentially elevated courtship rates of courting males relative to mating males. Families differed in magnitude of reduced male survivorship, indicating a likely genetic basis to variation in costs of courtship and copulation. Male weight was unrelated to longevity and mating success, whereas longevity strongly influenced male mating success, indicating lifespan is an important male fitness trait in this species.

Optimal Binning Strategies Under Squared Error Loss in Selective Assembly with a Tolerance Constraint

Selective assembly is an effective approach for improving the quality of a product assembled from two types of components when the quality characteristic is the clearance between the mating components. In this article, optimal binning strategies under squared error loss in selective assembly when the clearance is constrained by a tolerance parameter are discussed. Conditions for a set of constrained optimal partition limits are given, and uniqueness of this set is shown for the case when the dimensional distributions of the two components are identical and strongly unimodal. Some numerical results are reported that compare constrained optimal partitioning, unconstrained optimal partitioning, and equal width partitioning.

Endovascular Repair of Thoracoabdominal Aortic Aneurysms

Objectives: To evaluate the early outcomes following thoracoabdominal aortic aneurysm (TAAA) repair utilising fenestrated and branched endografts. Design and materials and methods: A prospective analysis of all patients undergoing endovascular repair of TAAA in a single academic centre. All patients were deemed unfit for open surgical repair. Customised endografts were designed using CT data reconstructed on 3D workstations. Post-operatively all patients were evaluated radiologically at hospital discharge, at 6, 12, 18 and 24 months, and annually thereafter. Results: Thirty-three consecutive patients (30 males) were treated over 33 months (August 2006 to April 2009). Median age and aneurysm size were 70 years (range 50–83 years) and 64 mm (range 55–100 mm) respectively. 114/116 (98%) of the targeted visceral vessels were successfully catheterised and perfused. The in-hospital mortality rate was 9% (3/33). Transient spinal cord ischaemia was diagnosed in 4/33 (12%) patients, and permanent paraplegia in one (3%). The median follow-up period was 11 months (range 1–33 months). Endoleaks were identified in 5/33 (15%) patients: type II in four patients and a type III endoleak in one patient which required the only secondary intervention. During follow-up, two patients died: one from stroke and the other from myocardial infarction 9 and 29 months respectively after the procedure. Conclusion: This preliminary study, which includes our learning curve, confirms the feasibility and safety of the endovascular repair of TAAA in high-risk patients. Meticulous follow-up to assess sac behaviour and visceral perfusion is critical in order to ensure optimal results of these complex endovascular repairs requiring numerous mating components.

Endovascular Repair of Thoracoabdominal Aortic Aneurysms

Objectives To evaluate the early outcomes following thoracoabdominal aortic aneurysm (TAAA) repair utilising fenestrated and branched endografts. Design and materials and methods A prospective analysis of all patients undergoing endovascular repair of TAAA in a single academic centre. All patients were deemed unfit for open surgical repair. Customised endografts were designed using CT data reconstructed on 3D workstations. Post-operatively all patients were evaluated radiologically at hospital discharge, at 6, 12, 18 and 24 months, and annually thereafter. Results Thirty-three consecutive patients (30 males) were treated over 33 months (August 2006 to April 2009). Median age and aneurysm size were 70 years (range 50–83 years) and 64 mm (range 55–100 mm) respectively. 114/116 (98%) of the targeted visceral vessels were successfully catheterised and perfused. The in-hospital mortality rate was 9% (3/33). Transient spinal cord ischaemia was diagnosed in 4/33 (12%) patients, and permanent paraplegia in one (3%). The median follow-up period was 11 months (range 1–33 months). Endoleaks were identified in 5/33 (15%) patients: type II in four patients and a type III endoleak in one patient which required the only secondary intervention. During follow-up, two patients died: one from stroke and the other from myocardial infarction 9 and 29 months respectively after the procedure. Conclusion This preliminary study, which includes our learning curve, confirms the feasibility and safety of the endovascular repair of TAAA in high-risk patients. Meticulous follow-up to assess sac behaviour and visceral perfusion is critical in order to ensure optimal results of these complex endovascular repairs requiring numerous mating components.

An X chromosome effect responsible for asymmetric reproductive isolation between maleDrosophila virilisand heterospecific females

Reproductive isolation between closely related species is expressed through uncoordinated courtship, failed fertilization, and (or) postzygotic barriers. Behavioural components of mating often form an initial barrier to hybridization between species. In many animals, females are responsible for mating discrimination in both intra- and interspecific crosses; males of Drosophila virilis group represent an exception to this trend. Using overall productivity tests, we show that a lower proportion of D. virilis males sire progeny when paired with a heterospecific female (Drosophila novamexicana or Drosophila americana texana) for 2 weeks. This suggests male mate discrimination or some other kind of asymmetrical incompatibility in courtship and mating or early zygote mortality. We used males from D. virilis-D. novamexicana and from D. virilis-D. a. texana backcross populations to map chromosome effects responsible for male reproductive isolation. Results from the analysis of both backcross male populations indicate a major X chromosome effect. Further, we conduct a male behavioural analysis to show that D. virilis males significantly fail to continue courtship after the first step of courtship, when they tap heterospecific females. The combined results of a major X chromosome effect and the observation that D. virilis males walk away from females after tapping suggest that future studies should concentrate on the identification of X-linked genes affecting the ability of males to recognize conspecific females.

Correct assembly sequence for robotic assembly using motion instability and part contact-level graphs

Determination of correct and stable assembly sequence is a must for automated assembly systems. The present work is a novel approach for generation of robotic assembly precedence constraints using directional part contact-level. This contains the information on directional connections for each pair of mating components. The part motion instability is crucial to the determination of stable assembly sequence because this affects the dexterity of robots. An example is presented to illustrate the concepts and procedure of the proposed scheme. This method can be effectively used to generate stable robotic assembly sequences.

Modelling and analysis of selective assembly using Taguchi's loss function

An assembly is the integrative process of joining components to make a completed product. It brings together the upstream process of design, engineering and manufacturing processes. The functional performance of an assembled product and its manufacturing cost are directly affected by the individual component tolerances. But, the selective assembly method can achieve tight assembly tolerance through the components manufactured with wider tolerances. The components are segregated by the selective groups (bins) and mated according to a purposeful strategy rather than being at random, so that small clearances are obtained at the assembly level at lower manufacturing cost. In this paper, the effect of mean shift in the manufacturing of the mating components and the selection of number of groups for selective assembly are analysed. A new model is proposed based on their effect to obtain the minimum assembly clearance within the specification range. However, according to Taguchi's concept, manufacturing a product within the specification may not be sufficient. Rather, it must be manufactured to the target dimension. The concept of Taguchi's loss function is applied into the selective assembly method to evaluate the deviation from the mean. Subsequently, a genetic algorithm is used to obtain the best combination of selective groups with minimum clearance and least loss value within the clearance specification. The effect of the ratio between the mating part quality characteristic's dimensional distributions is also analysed in this paper.