Mechanics of carbon nanotube scission under sonication

As-produced carbon nanotubes come in bundles that must be exfoliated for practical applications in nanocomposites. Sonication not only causes the exfoliation of nanotube bundles but also unwanted scission. An understanding of how precisely sonication induces the scission and exfoliation of nanotubes will help maximising the degree of exfoliation while minimising scission. We present a theoretical study of the mechanics of carbon nanotube scission under sonicaton, based on the accepted view that it is caused by strong gradients in the fluid velocity near a transiently collapsing bubble. We calculate the length-dependent scission rate by taking the actual movement of the nanotube during the collapse of a bubble into account, allowing for the prediction of the temporal evolution of the length distribution of the nanotubes. We show that the dependence of the scission rate on the sonication settings and the nanotube properties results in non-universal, experiment-dependent scission kinetics potentially explaining the variety in experimentally observed scission kinetics. The non-universality arises from the dependence of the maximum strain rate of the fluid experienced by a nanotube on its length. The maximum strain rate that a nanotube experiences increases with decreasing distance to the bubble. As short nanotubes are dragged along more easily by the fluid flow they experience a higher maximum strain rate than longer nanotubes. This dependence of the maximum strain rate on nanotube length affects the scaling of tensile strength with terminal length. We find that the terminal length scales with tensile strength to the power of 1/1.16 instead of with an exponent of 1/2 as found when nanotube motion is neglected. Finally, we show that the mechanism we propose responsible for scission can also explain the exfoliation of carbon nanotube bundles

Effect of polydextrose and soluble maize fibre on energy metabolism, metabolic profile and appetite control in overweight men and women.

High-fibre diets offer several beneficial health effects. The objective of the present study was to investigate whether replacement of 30% of the available carbohydrates with polydextrose (PDX) or soluble maize fibre (SCF) at breakfast and lunch would result in an increased fat oxidation rate and satiety, which may be of relevance for body weight control and diabetes prevention. In a single-blind, randomised cross-over study, eighteen overweight men and women underwent four different dietary interventions, which consisted of a PDX diet, a SCF diet and two control diets (full energetic and isoenergetic, comparable with PDX with respect to g or energy percentage of macronutrients, respectively). Glycaemic profile, energy expenditure and substrate oxidation were measured for 24h in a respiration chamber. Circulating insulin, NEFA and TAG concentrations were determined over a 14h period during daytime. Appetite ratings were assessed using visual analogue scales. The replacement of available carbohydrates with PDX or SCF reduced the peak glucose response, which was accompanied by reduced postprandial insulin responses. Moreover, higher concentrations of circulating NEFA were observed after consumption of both fibre diets, which were accompanied by an increased fat oxidation over 24h. This effect was mainly attributed to the lower energetic value of the fibre diets and not to the fibres per se. Besides increasing fat oxidation, PDX exerted a pronounced suppressive effect on appetite ratings. The replacement of available carbohydrates with PDX may be of special interest because of its beneficial effects on metabolic profile and it may affect body weight control in the long term

Перспективы развития рынка огнеупоров для сталеплавильного комплекса Украины

Основной эффект в снижении удельного расхода огнеупоров достигается за счет создания новых видов огнеупорных материалов, технологических усовершенствований при их производстве, развития новых конструкционных схем футеровки технологических агрегатов, совершенствования условий эксплуатации и ремонта футеровки и т. п. На металлургических предприятиях Украины в этом плане в последние годы наблюдается достаточно устойчивая тенденция повышения стойкости футеровки конвертеров, дуговых сталеплавильных печей, сталеразливочных и промежуточных ковшей.Основний ефект у зниженні питомої витрати вогнетривів досягається за рахунок створення нових видів вогнетривких матеріалів, технологічних удосконалень при їх виробництві, розвитку нових конструкційних схем футерівки технологічних агрегатів, удосконалення умов експлуатації та ремонту футерівки тощо. На металургійних підприємствах України в цьому плані в останні роки спостерігається досить стійка тенденція підвищення стійкості футерівки конвертерів, дуго- вих сталеплавильних печей, сталерозливних і проміжних ковшів.The main effect in reducing the specific consumption of refractories is reached by the creation of new types of refractory materials, technological improvements in their production, development of new structural patterns lining process units, improved operating conditions and lining repair, etc. In this regard, at Ukrainian metallurgical enterprises in recent years there has been quite stable tendency to increase the resistance of lining converters, electric arc steel furnaces, steel-teeming and tundish ladles

Evolving ecological networks and the emergence of biodiversity patterns across temperature gradients

In ectothermic organisms, it is hypothesized that metabolic rates mediate influences of temperature on the ecological and evolutionary processes governing biodiversity. However, it is unclear how and to what extent the influence of temperature on metabolism scales up to shape large-scale diversity patterns. In order to clarify the roles of temperature and metabolism, new theory is needed. Here, we establish such theory and model eco-evolutionary dynamics of trophic networks along a broad temperature gradient. In the model temperature can influence, via metabolism, resource supply, consumers' vital rates and mutation rate. Mutation causes heritable variation in consumer body size, which diversifies and governs consumer function in the ecological network. The model predicts diversity to increase with temperature if resource supply is temperature-dependent, whereas temperature-dependent consumer vital rates cause diversity to decrease with increasing temperature. When combining both thermal dependencies, a unimodal temperature–diversity pattern evolves, which is reinforced by temperature-dependent mutation rate. Studying coexistence criteria for two consumers showed that these outcomes are owing to temperature effects on mutual invasibility and facilitation. Our theory shows how and why metabolism can influence diversity, generates predictions useful for understanding biodiversity gradients and represents an extendable framework that could include factors such as colonization history and niche conservatism