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Reducing food portion size could reduce energy intake. However it is unclear at what point consumers respond to reductions by increasing intake of other foods. We predicted that a change to a served portion size would only result in significant additional eating within the same meal if the resulting portion size was no longer visually perceived as ‘normal’. Participants in two crossover experiments (Study 1: N = 45; Study 2: N = 37; adults, 51% female) were served different sized lunchtime portions on three occasions that were perceived by a previous sample of participants as ‘large-normal’, ‘small-normal’, and ‘smaller than normal’ respectively. Participants were able to serve themselves additional helpings of the same food (Study 1), or dessert items (Study 2). In Study 1 there was a small but significant increase in additional intake when participants were served the ‘smaller than normal’ compared to the ‘small-normal’ portion, m difference = 39 kcal, p = .002, d = 0.35, but there was no significant difference between the ‘small-normal’ and ‘large-normal’ conditions, m difference = 20 kcal, p = .08, d = 0.24. A similar pattern was observed in Study 2: m difference = 36 kcal, p = .06, d = 0.18; m difference = 20 kcal, p = .26, d = 0.10. However, smaller portion sizes were each associated with a significant reduction in total meal intake. The findings provide preliminary evidence that reductions that result in portions appearing ‘normal’ in size may limit additional eating, but confirmatory research is needed. (250/250 words)
Samples taken from the Dome C ice core, Antarctica, and the GRIP ice core, Greenland, are examined using the scanning electron microscope to determine their microstructure. In both cores, samples are taken from two differing climatic periods: the Holocene and the last glacial period. Many of the usual features observed in similar samples under the light microscope are observed, including: bubbles, grain boundaries and clathrate hydrates. Features not resolvable using the light microscope are also found. Dust particles are found in situ. Eighty-five per cent of those observed contained silicon, which was generally associated with aluminium and magnesium. An estimation is made of the relative proportions of dust particles located at grain boundaries and in the bulk of the ice grain. At Dome C a higher proportion than expected from a random distribution of particles was found located at grain boundaries, although in Greenland this was not found to be the case for most samples. Direct evidence is also presented indicating the role of dust particles and microscopical inclusions in impeding or ``pinning’’ grain-boundary migration. Soluble impurities are also detected at some triple junctions and grain boundaries.
Sea turtles host a diverse array of epibionts, yet it is not well understood what factors influence epibiont community composition. To test whether epibiont communities of sea turtles are influenced by the hosts’ nesting or foraging habitats, we characterized the epibiota of leatherback, olive ridley and green turtles nesting at a single location on the Pacific coast of Costa Rica. We also compared the epibiota of these turtles to conspecific populations nesting elsewhere in the East Pacific. If epibiont communities are influenced by nesting habitats, we predicted that sympatrically nesting turtles would have comparable epibiont taxa. Alternatively, if epibiont communities are influenced by foraging habitats, we predicted the diversity of epibiont taxa should reflect the type and diversity of the hosts’ foraging habitats. We identified 18 epibiont taxa from 18 leatherback, 19 olive ridley and six green turtles. Epibiont diversity was low on leatherbacks (four taxa), but higher for olive ridley and green turtles (12 and nine epibiont taxa respectively). The epibiont communities of olive ridley and green turtles were not statistically different, but both were different from leatherbacks. In addition, conspecific sea turtles from other nesting locations hosted more similar epibiont communities than sympatrically nesting, non-conspecifics. We conclude that epibiont diversity of nesting sea turtles is partially linked to the diversity of their foraging habitats. We also conclude that the surface properties of the skin and carapace of these turtles may contribute to the uniqueness of leatherback turtle epibiont communities and the similarities between olive ridley and green turtle epibiont communities.
In this paper we consider the relationship between the Assouad and box-counting dimension and how both behave under the operation of taking products. We introduce the notion of ‘equi-homogeneity’ of a set, which requires a uniformity in the cardinality of local covers at all length-scales and at all points, and we show that a large class of homogeneous Moran sets have this property. We prove that the Assouad and box-counting dimensions coincide for sets that have equal upper and lower box-counting dimensions provided that the set ‘attains’ these dimensions (analogous to ‘s-sets’ when considering the Hausdorff dimension), and the set is equi-homogeneous. Using this fact we show that for any α ∈ (0, 1) and any β, γ ∈ (0, 1) such that β + γ ⩾ 1 we can construct two generalised Cantor sets C and D such that dimBC = αβ, dimBD = α γ, and dimAC = dimAD = dimA (C × D) = dimB (C × D) = α.
Transition-metal dichalcogenides (TMDCs) are compounds consisting of a transition-metal M (Ti, Hf, Zr, V, Nb, Ta, Mo, W, Tc, Re, Pd, Pt) and chalcogen atoms X (S, Se, Te). There are approximately 60 compounds in the metal chalcogenide family, and two-thirds of them are in the form of layered structures where the in-plane bonds are strong (covalent), and the out-of-plane bonds are weak (van der Waals). This provides a means to mechanically or chemically thin (exfoliate) these materials down to a single atomic two-dimensional (2D) layer. While graphene, the 2D form of graphite, is metallic, the layered metal chalcogenides cover a wide range of electrical properties, from true metals (NbS2) and superconductors (TaS2) to semiconductors (MoS2) with a wide range of bandgaps and offsets. Multiple techniques are currently being developed to synthesize large-area monolayers, including alloys, and lateral and vertical heterostructures. The wide range of properties and the ability to tune them on an atomic scale has led to numerous applications in electronics, optoelectronics, sensors, and energy. This article provides an introduction to TMDCs, serving as a background for the articles in this issue of MRS Bulletin.
The use of smaller dishware as a way of reducing food consumption has intuitive appeal and is recommended to the general public. Recent experimental studies have failed to find an effect of plate size on food intake, although the methods used across studies have varied. The aim of the present study was to examine the effect that bowl size had on snack food consumption in a ‘typical’ snacking context (snacking while watching television).
Sixty-one adult participants served themselves and ate popcorn while watching television. Participants were randomly assigned to serve themselves with and eat from either a small or a large bowl.
The use of a smaller bowl size did not reduce food consumption. Unexpectedly, participants in the small bowl condition tended to consume more popcorn (34·0 g) than participants in the large bowl condition (24·9 g; 37 % increase, d=0·5), although the statistical significance of this difference depended on whether analyses were adjusted to account for participant characteristics (e.g. gender) associated with food intake (P=0·02) or not (P=0·07).
Counter to widely held belief, the use of a smaller bowl did not reduce snack food intake. Public health recommendations advising the use of smaller dishware to reduce food consumption are premature, as this strategy may not be effective.
Attentional and memory processes underpin appetite control, but whether encouraging overweight individuals to eat more ‘attentively’ can promote reductions in energy consumption is unclear. In the present study with a between-subjects design, a total of forty-eight overweight and obese females consumed a fixed lunchtime meal. Their ad libitum energy intake of high-energy snack food was observed during a second laboratory session that occurred later that day. In the focused-attention condition, participants ate their lunch while listening to audio instructions that encouraged them to pay attention to the food being eaten. In a control condition, participants ate while listening to an audio book with a neutral (non-food-related) content. To test whether focused attention influenced food intake via enhancing the memory of the earlier consumed meal, we measured the participants' memory of their lunchtime meal. Ad libitum snack intake was approximately 30 % lower for participants in the focused-attention condition than for those in the control condition, and this difference was statistically significant. There was limited evidence that attention decreased later food intake by enhancing memory representation of the earlier consumed meal. Eating attentively can lead to a substantial decrease in later energy intake in overweight and obese individuals. Behavioural strategies that encourage a more ‘attentive’ way of eating could promote sustained reductions in energy intake and weight loss.
We review recent research on the effect of social context on food intake and food choice and assess the implications for nutritional interventions. We focus on studies of modelling of eating behaviour and the impact of perceived eating norms on the amounts and types of food that individuals eat. We suggest that social context influences eating via multiple mechanisms, including identity signalling and self-presentation concerns. However, building on existing theoretical models, we propose that social factors may be particularly influential on nutrition because following the behaviour of others is adaptive and social norms inform individuals about behaviours that are likely to be optimal (‘if everyone else is doing it, I probably should be’). Guided by understanding of the potential underlying mechanisms, we discuss how social norms might be used to promote healthier nutrition.
The advent of graphene created a new era in materials science. Graphene is a two-dimensional planar honeycomb array of carbon atoms in sp2-hybridized states. A natural question is whether other elements of the IV-group of the periodic table (such as silicon and germanium), could also form graphene-like structures. Structurally, the silicon equivalent to graphene is called silicene. Silicene was theoretically predicted in 1994 and recently experimentally realized by different groups. Similarly to graphene, silicene exhibits electronic and mechanical properties that can be exploited to nanoelectronics applications.
In this work we have investigated, through fully atomistic molecular dynamics (MD) simulations, the mechanical properties of single-layer silicene under mechanical strain. These simulations were carried out using a reactive force field (ReaxFF), as implemented in the LAMMPS code. We have calculated the elastic properties and the fracture patterns.
Our results show that the dynamics of the whole fracturing processes of silicene present some similarities with that of graphene as well as some unique features.
Hexagonal boron nitride (h-BN), also known as white graphite, is the inorganic analogue of graphite. Single layers of both structures have been already experimentally realized.
In this work we have investigated, through fully atomistic reactive molecular dynamics simulations, the dynamics of hydrogenation of h-BN single-layers membranes.
Our results show that the rate of hydrogenation atoms bonded to the membrane is highly dependent on the temperature and that only at low temperatures there is a preferential bond to boron atoms. Unlike graphanes (hydrogenated graphene), hydrogenated h-BN membranes do not exhibit the formation of correlated domains. Also, the out-of-plane deformations are more pronounced in comparison with the graphene case. After a critical number of incorporated hydrogen atoms the membrane become increasingly defective, lost its two-dimensional character and collapses. The hydrogen radial pair distribution and second-nearest neighbor correlations were also analyzed.
Eating with others has been shown to influence the amount of food eaten in a meal or snack. We examined whether choosing food in the presence of another person who is choosing either predominantly low-energy-dense or high-energy-dense foods affects food choices. A between-subjects laboratory-based study was used. A group of 100 young females selected a lunch-time meal from a buffet consisting of a range of high-energy-dense and low-energy-dense foods, in the presence of an ‘unhealthy’ eating partner (who chose predominantly high-energy-dense foods) or a ‘healthy’ eating partner (who chose predominantly low-energy-dense foods) or when alone. Participants in the ‘unhealthy’ eating partner condition were significantly less likely to choose and consume a low-energy-dense food item (carrots), than when choosing alone or in the presence of a ‘healthy’ eater. Choice of high-energy-dense food did not differ across the conditions, nor did the total energy consumed. These data suggest that social influences on food choice are limited in this context but the presence of an ‘unhealthy’ eating partner may undermine intentions to consume low-energy-dense foods.
Novel ways to increase liking and intake of food are needed to encourage acceptance of healthier food. How enjoyable we remember food to have been is likely to be a significant predictor of food choice. Two studies examined whether remembered enjoyment of eating a food can be increased and whether this makes individuals more likely to eat that food in the future. In Study One, a simple manipulation of instructing participants to rehearse what they found enjoyable about a food immediately after eating it was used to increase remembered enjoyment (relative to controls). In a separate study; Study Two, the effect of increasing remembered enjoyment on food choice was tested by examining whether the manipulation to increase remembered enjoyment resulted in participants choosing to eat more of a food as part of a later buffet lunch. The experimental manipulation increased remembered enjoyment for the food (Study One). A change in remembered enjoyment was shown to have a significant effect on the amount of a food participants chose to eat the following day for lunch (Study Two). The present studies suggest that remembered enjoyment can be increased via a simple act of rehearsal, resulting in a later increase in the amount of food chosen and eaten. Interventions based on altering remembered enjoyment of healthy food choices warrant further investigation.