Climbing parrots achieve pitch stability using forces and free moments produced by axial-appendicular couples

During vertical climbing, the gravitational moment tends to pitch the animal's head away from the climbing surface and this may be countered by 1) applying a correcting torque at a discrete contact point, or 2) applying opposing horizontal forces at separate contact points to produce a free moment. We tested these potential strategies in small parrots with an experimental climbing apparatus imitating the fine branches and vines of their natural habitat. The birds climbed on a vertical ladder with four instrumented rungs that measured three-dimensional force and torque, representing the first measurements of multiple contacts from a climbing bird. The parrots ascend primarily by pulling themselves upward using the beak and feet. They resist the gravitational pitching moment with a free moment produced by horizontal force couples between the beak and feet during the first third of the stride and the tail and feet during the last third of the stride. The reaction torque from individual rungs did not counter, but exacerbated the gravitational pitching moment, which was countered entirely by the free moment. Possible climbing limitations were explored using two different rung radii, each with low and high friction surfaces. Rung torque was limited in the large-radius, low-friction condition, however, rung condition did not significantly influence free moments produced. These findings have implications for our understanding of avian locomotor modules (i.e., coordinated actions of the head-neck, hindlimbs, and tail), the use of force couples in vertical locomotion, and the evolution of associated structures.

Free moment induced by oblique transverse tarsal joint: investigation by constructive approach

The human foot provides numerous functions that let humans deal with various environments. Recently, study of the structure of the human foot and adjustment of an appropriate reaction force and vertical free moment during bipedal locomotion has gained attention. However, little is known about the mechanical (morphological) contribution of the foot structure to the reaction force and free moment. It is difficult to conduct a comparative experiment to investigate the contribution systematically by using conventional methods with human and cadaver foot experiments. This study focuses on the oblique transverse tarsal joint (TTJ) of the human foot, whose mechanical structure can generate appropriate free moments. We conduct comparative experiments with a rigid foot, a non-oblique joint foot (i.e. mimicking only the flexion/extension of the midfoot), and an oblique joint foot. Axial loading and walking experiments were conducted with these feet. The axial loading experiment demonstrated that the oblique foot generated free moment in the direction of internal rotation, as observed in the human foot. The walking experiment showed that the magnitude of the free moment generated with the oblique foot is significantly lower than that with the rigid foot during the stance phase. Using this constructive approach, the present study demonstrated that the oblique axis of the TTJ can mechanically generate free moments. This capacity might affect the transverse motion of bipedal walking.

Relationship between the nutritional status and food consumption inside the school in adolescents of Mexico City

There is a concern that the bad habits and lifestyles of adolescents such as the consumption of foods rich in sugars and fats in free moments, like school recess acts as a factor that intervenes in the increase of weight. The aim of this study was to determine the relationship between the nutritional status and the food consumption inside the school in adolescents of Mexico City. A sample of 1457 first-grade adolescents from high schools was obtained. A food consumption frequency questionnaire was applied inside the school. Likewise, anthropometric measures were taken and through the use of Who Anthro Plus program, the nutritional status diagnosis was obtained. The obtained data was analyzed with the statistical package IBM SPSS Statistics® version 20.0 for Windows. It was found that adolescents who frequently consume sweets, snacks, flavored waters, bottled juices, confectionery products and ice cream have a higher prevalence of obesity (15.2%, 17.4%, 21.4%, 17.7%, 16.2% and 19.9%, respectively), compared to adolescents who never consume these products (11.6%, 12.6%, 11.9%, 10.5%, 14.6%, and 12.1%, respectively). Likewise, it was found that adolescents who frequently consume fruit, water, yogurt, vegetables and milk have a lower prevalence of obesity (10.2%, 12.2%, 10.3%, 10.1% and 9.35, respectively) in comparison with adolescents who never consume these foods during school hours (19.1%, 18.6%, 17.8%, 15.9% and 16.3%, respectively), finding a highly significant difference (p < 0.01) in the consumption of flavored water, fruit, natural water and yogurt. It was found that the food consumed during school hours has an impact on the nutritional status of adolescents, similar to the results found in the literature, so it is suggested to promote healthy habits and lifestyles at school and at home so that adolescents opt for healthy snack choices.

Family bliss or blitz? Parents’ and children’s mixed emotions towards family holidays

Purpose This paper aims to explore mixed emotions experienced by parents and children on holiday, how they are dealt with and how they influence the way “family” is “staged” and “done”. Design/methodology/approach This paper draws on 24 qualitative interviews with Danish parents and a questionnaire study reporting answers from 66 Danish children (11-15-year-old). Findings Problems external and internal to the family are identified and the latter are associated with more unease particularly among parents. This paper shows that parents invest significant narrative efforts in transcending gaps between ideals and practices. Also children are aware of the gaps between ideals and practices; they seem more matter-of-fact, however, regarding critical aspects of holidays. Research limitations/implications The informants of the study solely represent two-parent hetero-sexual families of Danish origin, and so inclusion of a wider range of families would have added interesting perspectives. Furthermore, children’s perspectives on critical holiday incidents need further research. Practical implications Creators of family holiday products and marketing should present a more nuanced imagery taking a more diverse approach to what “family” on holiday looks like. They could take up the challenge of depicting a broader range of family situations, also showing less harmonious moments, using humour, and showing opportunities for some “alone time” for both parents and children should relational overload happen. Also occasional “wifi-free” moments seem to be much appreciated by all family members, and development of offline family experiences would seem to strike a chord. Social implications The contemporary paradigm of intensive parenting along with strong ideals for family holidays make it essential for parents to narratively deal with and legitimize and transform less happy moments. To take pressure off contemporary families, it is important to bring to the fore the less glossy aspects of family holidays. Originality/value The originality of this paper is to illustrate the strong efforts applied by families to keep up a certain front to be the family that “ought to be” by nurturing and narrating positive emotions in relation to family holidays. The inclusion of children’s voices gives insights into children’s annoyance with parents’ rowing, relational overload and parents’ occasional lack of attention to children, for example through parental use of mobile phones during holiday togetherness.

Quantification of vertical free moment induced by the human foot–ankle complex during axial loading

Axial loading of the human cadaver lower leg is known to generate eversion of the calcaneus and internal rotation of the tibia if the plantar surface of the foot does not slide on the floor. Such kinematic coupling between calcaneal eversion and internal tibial rotation has been described previously, but no studies have actually quantified the innate ability of the human foot to generate ground reaction moment around the vertical axis of the floor (vertical free moment) due to axial loading of the human cadaver lower leg. This study investigated the vertical free moment generated by eight cadaveric lower leg specimens loaded vertically with traction of the Achilles’ tendon using a six-component force plate. The vertical free moments in all specimens were oriented toward the direction of internal rotation, and the mean magnitude of the vertical free moments was −1.66 N m when an axial load of 450 N was applied. A relatively large ground reaction moment can be applied to the body during walking due to the innate structural mobility of the foot. The structurally embedded capacity of the human foot to generate the vertical free moment may facilitate compensation of the moment generated around the vertical axis of the body during walking due to trunk rotation and leg swing.

Normalization of Ground Reaction Forces, Joint Moments, and Free Moments in Human Locomotion

Authors who report ground reaction force (GRF), free moment (FM), and resultant joint moments usually normalize these variables by division normalization. Normalization parameters include body weight (BW), body weight x height (BWH), and body weight x leg length (BWL). The purpose of this study was to explore the appropriateness of division normalization, power curve normalization, and offset normalization on peak GRF, FM, and resultant joint moments. Kinematic and kinetic data were collected on 98 subjects who walked at 1.2 and 1.8 m/s and ran at 3.4 and 4.0 m/s. Linear curves were best fit to the data, and regression analyses performed to test the significance of the correlations. It was found that the relationship between peak force and BW, as well as joint moments and BW, BWH, and BWL, were not always linear. After division normalization, significant correlations were still found. Power curve and offset normalization, however, were effective at normalizing all variables; therefore, when attempting to normalize GRF and joint moments, perhaps nonlinear or offset methods should be implemented.

Firing Order Selection in Relation to Vibration Aspects

Selecting the optimum firing order for a combustion engine is an important decision to make when developing an engine. Typically, the optimum choice is made on the basis of a weighted balance between a number of interrelated engine vibration characteristics, such as: balancing, free forces and free moments, guide force distribution, inner bending moments, bearing load, and torsional and axial vibration behaviour. Also gas dynamic properties making each cylinder do the same amount of work is considered. In addition to the traditional firing sequence selection, implying the same firing interval between cylinder units, also so-called irregular firing orders, characterized by different intervals between the individual firings, are considered. Various methods and strategies can be applied, considering that different engine applications exhibit completely different vibratory behaviour, e.g. marine propulsion plants compared with stationary installations. This paper will give examples relating to various applications for both two-stroke and four-stroke engines. Four-stroke: Realizing that the engine is often an integrated part of a complex system, it is demonstrated in this paper that analysing the whole system in terms of linear vibrations, the optimum firing order is different from the firing order determined with traditional methods. The system analysed here is a genset for marine or stationary application consisting of a 9-cylinder diesel engine, alternator and base frame. All three parts are bolted together as one unit, resiliently mounted on a ship or a land-based foundation. Two-stroke: The traditional 7-cylinder marine propulsion engine firing sequence is modified in order to be able to run safely directly at a two-node torsional resonance without installing a T/V damper. The 12-cylinder stationary engine has been modified so as to reduce installation costs and improve the coupled torsional-axial vibratory behaviour. The 10-cylinder marine engine firing sequence has been modified in order to achieve more favourable structural vibration characteristics.