The nature of the transformation by which a supercooled liquid 'freezes' to a glass-the glass transition-is a central issue in condensed matter physics but also affects many other fields, including ...biology. Substantial progress has been made in understanding this phenomenon over the past two decades, yet many key questions remain. In particular, the factors that control the temperature-dependent relaxation and viscous properties of the liquid phase as the glass transition is approached (that is, whether the glass-forming liquid is 'fragile' or 'strong') remain unclear. Here we show that the fragility of a glass-forming liquid is intimately linked to a very basic property of the corresponding glass phase: the relative strength of shear and bulk moduli, or Poisson's ratio.
Charge transport and structural dynamics in low molecular weight and polymerized 1-vinyl-3-pentylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids (ILs) are investigated by a combination of ...broadband dielectric spectroscopy, dynamic mechanical spectroscopy and differential scanning calorimetry. While the dc conductivity and fluidity exhibit practically identical temperature dependence for the non-polymerized IL, a significant decoupling of ionic conduction from structural dynamics is observed for the polymerized IL. In addition, the dc conductivity of the polymerized IL exceeds that of its molecular counterpart by four orders of magnitude at their respective calorimetric glass transition temperatures. This is attributed to the unusually high mobility of the anions especially at lower temperatures when the structural dynamics is significantly slowed down. A simple physical explanation of the possible origin of the remarkable decoupling of ionic conductivity from structural dynamics is proposed.
Polymerized ionic liquids (PolyILs) are promising candidates for a wide range of technological applications due to their single ion conductivity and good mechanical properties. Tuning the glass ...transition temperature (T g) in these materials constitutes a major strategy to improve room temperature conductivity while controlling their mechanical properties. In this work, we show experimental and simulation results demonstrating that in these materials T g does not follow a universal scaling behavior with the volume of the structural units V m (including monomer and counterion). Instead, T g is significantly influenced by the chain flexibility and polymer dielectric constant. We propose a simplified empirical model that includes the electrostatic interactions and chain flexibility to describe T g in PolyILs. Our model enables design of new functional PolyILs with the desired T g.
Combining dielectric spectroscopy and neutron scattering data for hydrated lysozyme powders, we were able to identify several relaxation processes and follow protein dynamics at different hydration ...levels over a broad frequency and temperature range. We ascribe the main dielectric process to protein’s structural relaxation coupled to hydration water and the slowest dielectric process to a larger scale protein’s motions. Both relaxations exhibit a smooth, slightly super-Arrhenius temperature dependence between 300 and 180 K. The temperature dependence of the slowest process follows the main dielectric relaxation, emphasizing that the same friction mechanism might control both processes. No signs of a proposed sharp fragile-to-strong crossover at T ∼ 220 K are observed in temperature dependences of these processes. Both processes show strong dependence on hydration: the main dielectric process slows down by six orders with a decrease in hydration from h ∼ 0.37 (grams of water per grams of protein) to h ∼ 0.05. The slowest process shows even stronger dependence on hydration. The third (fastest) dielectric relaxation process has been detected only in samples with high hydration (h ∼ 0.3 and higher). We ascribe it to a secondary relaxation of hydration water. The mechanism of the protein dynamic transition and a general picture of the protein dynamics are discussed.
An approach to the application of modern information technologies and mathematical methods to solve the problem of energy woodproduction and logistics technologies selection is described in the ...article. The general statement of the problem, the methodology, methodsand models used are given.A decision support system for energy wood production can evaluate and compare various technological schemes for the harvesting and processing of woody biomass to energy woodand identify the most effective choice At the operational level, the approach allows to optimize the current plans for the harvesting, initial processing and transportation of the energy wood for available production capacities, taking into account the commercial roundwood production providing at the same time. Proposed approach isa practical tool for ensuring profitability and sustainable growth of the energy wood production, which, will stimulate the development of bioenergy in Russia.
Strontium ruthenate (Sr2RuO4) continues to present an important test of our understanding of unconventional superconductivity, because while its normal-state electronic structure is known with ...precision, its superconductivity remains unexplained. There is evidence that its order parameter is chiral, but reconciling this with recent observations of the spin part of the pairing requires an order parameter that is either finely tuned or implies a new form of pairing. Therefore, a definitive resolution of whether the superconductivity of Sr2RuO4 is chiral is important for the study of superconductivity. Here we report the measurement of zero-field muon spin relaxation—a probe sensitive to weak magnetism—on samples under uniaxial stresses. We observe stress-induced splitting between the onset temperatures of superconductivity and time-reversal symmetry breaking—consistent with the qualitative expectations for a chiral order parameter—and argue that this observation cannot be explained by conventional magnetism. In addition, we report the appearance of bulk magnetic order under higher uniaxial stress, above the critical pressure at which a Lifshitz transition occurs in Sr2RuO4.When strain is applied to strontium ruthenate, superconductivity emerges at a different temperature to the breaking of time-reversal symmetry. This indicates that the superconductivity could have a chiral d-wave order parameter.
Indirect effects of climate change are often mediated by trophic interactions and consequences for individual species depend on how they are tied into the local food web. Here we show how the ...response of demographic rates of an arctic bird of prey to fluctuations in small rodent abundance changed when small rodent community composition and dynamics changed, possibly under the effect of climate warming. We observed the breeding biology of rough‐legged buzzards (Buteo lagopus) at the Erkuta Tundra Monitoring Site in southern Yamal, low arctic Russia, for 19 years (1999–2017). At the same time, data on small rodent abundance were collected and information on buzzard diet was obtained from pellet dissection. The small rodent community experienced a shift from high‐amplitude cycles to dampened fluctuations paralleled with a change in species composition toward less lemmings and more voles. Buzzards clearly preferred lemmings as prey. Breeding density of buzzards was positively related to small rodent abundance, but the shift in small rodent community lead to lower numbers relative to small rodent abundance. At the same time, after the change in small rodent community, the average number of fledglings was higher relative to small rodent abundance than earlier. These results suggest that the buzzard population adapted to a certain degree to the changes in the major resource, although at the same time density declined. The documented flexibility in the short‐term response of demographic rates to changes in structure and dynamics of key food web components make it difficult to predict how complex food webs will be transformed in a warmer Arctic. The degree of plasticity of functional responses is indeed likely to vary between species and between regions, depending also on the local food web context.
Indirect effects of climate change are often mediated by trophic interactions and consequences for individual species depend on how they are tied into the local food web. Here we show that the breeding density of an arctic bird of prey decreased when small rodents, its main prey, experienced a shift from high‐amplitude cycles to moderate fluctuations paralleled with a change in species composition toward less lemmings and more voles. At the same time, however, the birds still breeding had on average larger broods, suggesting that the population adapted to a certain degree to the changes in the major resource.
The perception of actions underwrites a wide range of socio-cognitive functions. Previous neuroimaging and lesion studies identified several components of the brain network for visual biological ...motion (BM) processing, but interactions among these components and their relationship to behavior remain little understood. Here, using a recently developed integrative analysis of structural and effective connectivity derived from high angular resolution diffusion imaging (HARDI) and functional magnetic resonance imaging (fMRI), we assess the cerebro-cerebellar network for processing of camouflaged point-light BM. Dynamic causal modeling (DCM) informed by probabilistic tractography indicates that the right superior temporal sulcus (STS) serves as an integrator within the temporal module. However, the STS does not appear to be a “gatekeeper” in the functional integration of the occipito-temporal and frontal regions: The fusiform gyrus (FFG) and middle temporal cortex (MTC) are also connected to the right inferior frontal gyrus (IFG) and insula, indicating multiple parallel pathways. BM-specific loops of effective connectivity are seen between the left lateral cerebellar lobule Crus I and right STS, as well as between the left Crus I and right insula. The prevalence of a structural pathway between the FFG and STS is associated with better BM detection. Moreover, a canonical variate analysis shows that the visual sensitivity to BM is best predicted by BM-specific effective connectivity from the FFG to STS and from the IFG, insula, and STS to the early visual cortex. Overall, the study characterizes the architecture of the cerebro-cerebellar network for BM processing and offers prospects for assessing the social brain.
Cognitive decline because of aging and neurodegeneration has become increasingly prevalent. This calls for the implementation of efficacious, motivating, standardized and widely available cognitive ...interventions for the elderly. In this context, serious video games and virtual reality may represent promising approaches. Here, we review recent research on their potential for cognitive prevention and neurorehabilitation of age-related cognitive decline and mild cognitive impairment (MCI).
The majority of currently available data in this evolving domain lacks the methodological quality to draw reliable conclusions on the potential of novel technology for cognitive training in older people. However, single well designed randomized controlled trials have reported promising effects of cognitive interventions involving serious video games and virtual reality. The cognitive benefits of exergames promoting physical exercise with and without combined cognitive training remain unclear.
The immersion into stimulating and motivating environments along with training content based on neuroscientific and neuropsychological models may represent a significant advance as compared with conventional computerized cognitive training. Additional research with sound methodology including sufficient sample sizes, active control groups and meaningful outcome measures of everyday function is needed to elucidate the potential of serious video games and virtual reality in multifactorial neurorehabilitation of cognitive decline in aging and neurodegeneration.
Despite the fruitful achievements in the development of hydrogen production catalysts with record-breaking performances, there is still a lack of durable catalysts that could work under large current ...densities (>1000 mA cm
). Here, we investigated the catalytic behaviors of Sr
RuO
bulk single crystals. This crystal has demonstrated remarkable activities under the current density of 1000 mA cm
, which require overpotentials of 182 and 278 mV in 0.5 M H
SO
and 1 M KOH electrolytes, respectively. These materials are stable for 56 days of continuous testing at a high current density of above 1000 mA cm
and then under operating temperatures of 70 °C. The in-situ formation of ferromagnetic Ru clusters at the crystal surface is observed, endowing the single-crystal catalyst with low charge transfer resistance and high wettability for rapid gas bubble removal. These experiments exemplify the potential of designing HER catalysts that work under industrial-scale current density.
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