The effect of friends on adolescent body weight

Using the first wave of the National Longitudinal Study of Adolescent Health (Add Health) survey, this paper examines the influence of peers on adolescent weight. A peer group is defined as a close circle of friends that are identified by a respondent adolescent. After controlling for school fixed effects and for a number of individual, demographic and family characteristics, we find that a higher Body Mass Index (BMI) of close friends is correlated to a higher BMI of the respondent adolescent. However, after instrumental variable analysis is performed, the effect remains significant only among women. We also found that adolescents are more responsive to the body weight of their same gender friends.     

The effect of constraint on the mechanical behaviour of trabecular bone specimens

The effect of the boundary conditions between trabecular bone specimens and the test columns of the testing machine was studied together with the effect of side-constraint on the mechanical behaviour of trabecular bone during axial compression. Cylindrical specimens taken from the upper tibial epiphysis of autopsy knees were tested non-destructively by cyclic compression to 0.8% strain under different conditions. Fixation of the specimens to the test columns by a thin layer of bone cement increased the stiffness by 40% and reduced the energy dissipation to 67% of those measured under unconstrained conditions (p less than 0.001). The thin cement layer alone increased the stiffness 19% and reduced energy dissipation to 86% (n.s.). When the machine was equipped with polished steel columns coated by a film of low-viscous oil, both the stiffness and the energy dissipation were reduced to 93% of those measured under standard conditions (p less than 0.005). Trabecular bone specimens tested side-constrained by the surrounding trabecular bone (in situ) showed a 19% larger stiffness than that measured during later testing of the corresponding machined specimens (p less than 0.005) whereas the energy dissipation was not altered significantly. The same specimens showed a 22% increase of stiffness and a 68% increase of energy dissipation when they were side-constrained by a closely fitting steel cylinder (p less than 0.005).     

The effects of baclofen on the feeding behaviour and body weight of vagally stimulated rats.

It is hypothesised that the GABA(B) receptor agonist baclofen increases or has no effect on food intake, and electrical stimulation of vagal nerves decreases food intake. The aim of this study was to evaluate the effects of baclofen in vagally stimulated rats. MATERIAL AND METHODS: Thirty two Wistar rats were divided into five groups: group A scheduled for microchip implantation for vagal stimulation, group B for sham operation, group C for microchip implantation and baclofen medication, group D for baclofen medication only and group E for gastric motility evaluation under influence of baclofen. The following parameters were then evaluated: food intake and body mass, gastric motility, leptin, insulin, and glucose serum levels. RESULTS: In the comparison of groups B and A, daily food intake and body weight gain decreased by 17% (p<0.05) and by 22% (p<0.05), respectively. Baclofen alone (group D) did not significantly change either food intake nor diurnal body weight compared to the controls, but when used in conjunction with the microchip (group C) it did significantly reduce effect of vagal neuromodulation (p<0.05). Furthermore, a significant decrease in leptin and glucose levels was detected in group C: 677 to 165 pg/ml (p<0.05) and 5,93 to 4,88 mmol/l (p<0.05), respectively. The administration of baclofen stimulated significantly gastric motility and elicited irregular motor migrating complex (327+/-200 against control 255+/-52 cmH2O/s). CONCLUSIONS: These results suggest that microchip vagal neuromodulation through increased vagal afferent activity induces an alteration in the feeding behaviour and decreases nocturnal food intake and body weight. These effects were partially attenuated by baclofen. The data suggests that GABA(B) receptors play an important role in the pathomechanism of attenuation of food intake induced by vagal nerve stimulation.     

The effect of body armature on escape behaviour in cordylid lizards

The possession of armour may affect escape behaviour in two ways. On one hand, by decreasing vulnerability to predators, armour may permit individuals to use habitats and behaviours that are too risky for unarmoured individuals. Alternatively, the possession of armour may have negative trade-offs on other traits involved in antipredator behaviour, such as sprint speed, thus constraining antipredator options relative to those available to unarmoured individuals. To examine these contrasting predictions, we examined species in the lizard family Cordylidae, which contains remarkable morphological diversity, ranging from completely unarmoured to heavily defended species. Moreover, phylogenetic analysis indicates that armour has been an evolutionarily labile trait. We found support for the second prediction. Degree of body armature was inversely correlated with distance run from a predator: heavily armoured species always entered refuges after short distances, whereas many unarmoured lizards continued to flee and could not be induced to enter a refuge. Possession of armour was also negatively related to use of vertical surfaces during escape behavour. These results were unchanged when analysed in a phylogenetic context. Thus, we conclude that the morphological requirements for active flight and armoured defence are incompatible. Heavily armoured species are bulky, have short legs and run more slowly than less armoured species. Rather than constituting an alternative to behavioural antipredator tactics, we conclude that the possession of armour is part of an antipredator syndrome that includes habitat use and behaviour as well as morphology. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

The effect of specimen geometry on the mechanical behaviour of trabecular bone specimens.

The effect of specimen geometry on the mechanical behaviour of trabecular bone specimens was studied by non-destructive uniaxial compression to 0.4% strain using cylindrical specimens with different sizes and length-to-diameter ratios, and by comparing cubic and cylindrical specimens with the same cross-sectional area. Both the length and the cross-sectional area of the specimen had a highly significant influence on the mechanical behaviour (p less than 0.0001). Within the actual range of length (2.75-11.0 mm) the normalized stiffness (Young's modulus) was related nearly linearly to the specimen length. This dependency on specimen length is suggested to be caused mainly by structural disintegrity of the trabecular specimens near the surface. The normalized stiffness (Young's modulus) was also positively correlated to the cross-sectional area. This dependency on cross-sectional area is probably due to friction-induced stress inhomogeneity at the platen-specimen interface. A cube with side length 6.5 mm or a cylindrical specimen with 7.5 mm diameter and 6.5 mm length are suggested as standard specimens for comparative studies on trabecular bone mechanics.     

The effect of body weight on the calcitonin gene-related peptide-induced relaxation of guinea pig gallbladder strips

Calcitonin gene-related peptide (CGRP) has been reported to relax, in a concentration-dependent manner, cholecystokinin-induced tension in guinea pig gallbladder strips. It is now shown that this CGRP-induced relaxation is body weight dependent with the degree of relaxation inversely related to weight. Radioimmunoassay demonstrated that the amount of CGRP in the gallbladder increased with body weight. Receptor binding showed that the number of binding sites and the affinity of the receptor decreased with increasing body weight. CGRP may play a role in the normal pattern of gallbladder contraction and relaxation. Decreased motility, even between periods of complete emptying, has been demonstrated to have a role in gallbladder diseases. The decreased sensitivity of the gallbladder to CGRP may explain the increase in abnormalities with age.     

Prediction of the effect of ofloxacine on intestinal absorption: effect of the body weight and substrate concentration

1. The effect of body weight and initial concentration on the rat small intestinal absorption of DL-8280 (ofloxacine) is studied using a recirculating perfusion technique and an improved HPLC method. 2. A prediction equation is developed under statistical and physiological considerations which correlates both factors with the intestinal absorption rate parameter Kapp.     

Fracture toughness of horns and a reinterpretation of the horning behaviour of bovids

The keratinous horns of bovids are used in intraspecific combat to gain access to females in oestrus. Horn sheath keratin is a composite material consisting of stiff protein fibres and a pliant protein matrix. Unlike antlers, horns are permanent structures which are likely to accumulate damage during fighting. Therefore, horn sheath keratin should be resistant to fracture (tough) and insensitive to surface defects (scratches and cracks) which may weaken horns by acting as stress concentrators.
The effect of water on the toughness and notch-sensitivity of horn sheath keratin was investigated in three-point bending and tensile tests. Several measures of toughness were made on dry (0% water content), fresh (20%) and wet (40%) horn keratin, including total work of fracture, Gurney & Hunt work of fracture, critical strain energy release rate and critical stress intensity factor.
The mean total work of fracture of fresh horn is about 40 kJ/m² which is relatively much greater than most biological and synthetic materials. Most of the work of fracture is due to plastic yielding of the matrix (50–75%); the rest is due to crack-tip specific fracture mechanisms such as fibre pull-out and Cook Gordon crack-stopping. Dehydration reduces the total work of fracture of horn keratin by preventing the yielding of the matrix.
The strength of fresh and wet horn is insensitive to notches, but dry horn is very notch-sensitive. Therefore, bovids must avoid dehydration of their horns due to the desiccating effect of the environment. The 'horning' behaviour of bovids may be a maintenance activity which ensures that the horn sheath is adequately hydrated to remain tough and notch-insensitive.     

The role of mechanical shear and cavitation on the behaviour of molds

The morphology of filamentous microorganisms does essentially affect the production of metabolites. Agitating conditions may affect the morphology and for this reason the production of metabolites too. The following parameters it was found to have an influence:

• Reynolds mixing number
• impeller blade tips velocity
• mean shear stress close to the impeller
• impeller power consumption per unit volume
• cavitation pressure drop

It were presumed three mechanisms for the mechanical effect on the microorganisms:

• 1 the direct impact of the impeller blades on the microorganisms-collision
• 2 the shear stress in the liquid phase
• 3 a sharp pressure decrease behind the impeller blades-cavitation

Mathematical relationships are developed for the different mechanisms.Using Aspergillus niger it is shown what morphological and physiological states of this microorganism are caused by mechanical straining and the conditions for the maximal production of citric acid are studied. Requirements for scale-up are discussed.     

The mechanical behaviour of cancellous bone

Cancellous bone has a cellular structure: it is made up of a connected network of rods and plates. Because of this, its mechanical behaviour is similar to that of other cellular materials such as polymeric foams. A recent study on the mechanisms of deformation in such materials has led to an understanding of how their mechanical properties depend on their relative density, cell wall properties and cell geometry. In this paper, the results of this previous study are applied to cancellous bone in an attempt to further understand its mechanical behaviour. The results of the analysis agree reasonably well with experimental data available in the literature.     

Non-gonadal mediated effect of photoperiod on hibernation and body weight cycles of the European hamster

1. Sexually active male European hamsters raised under short photoperiod display high levels of plasma testosterone, high body weight and do not hibernate. 2. Castrated males in May, raised under the same conditions, do not hibernate and do not present the physiological body weight rhythm. 3. Normal and castrated animals under natural conditions enter hibernation and display a normal body weight rhythm. 4. Normal and castrated animals not submitted to the natural succession of long and short days do not enter hibernation. 5. Photoperiod directly controls body weight and hibernation gonadal interactions.     

The design of an olfactometer and a method for quantitative stud on the effect of odours on insect behaviour

Vertical air-flow olfactometer suitable for study of the influence of odours on walking insect behaviour was described. The results of preliminary experiments proved that the olfactometer enables long-lasting "quasiethological" observations. Employed method of observation gave quantitative information about the influence of odours on ratios of basic predeterminate activities, insect distribution pattern and their tendency to choose zones with an odour. The Colorado beetle (Leptinotarsa decemilineata Say) males preferred zones with the female odour spending there more time. During emission of the pheromone males were more active. In zones with the pheromone males displayed the tendency to cluster, spent more time taping intensely and more frequently attempted to mate.