Microgravity experiments of single droplet combustion in oscillatory flow at elevated pressure

An experimental study for 1-butanol single droplet flames in constant and oscillatory flow fields was conducted under microgravity conditions at elevated pressure. In the constant flow experiments, flow velocities from 0 to 40 cm/s were tested. Using obtained data of d², the burning rate constants were evaluated. The burning rate constant in the quiescent condition was also calculated successfully at high pressure by the extrapolation method based on the Frössling relation. In the oscillatory flow experiments, the flow velocities were varied from 0 to 40 cm/s at the frequencies of 2–40 Hz. Results showed that the burning rate constant during the droplet lifetime varied following the quasi-steady relation at 0.1 MPa; however, in the conditions with higher frequencies at 0.4 MPa, the average burning velocity became larger than that for the constant flow case with the velocity equivalent to the maximum velocity in the oscillatory flow. Under the condition where the burning rate constant increased, it was observed that the flame did not sufficiently move back upstream, leading to enhancement of the heat transfer from the flame to the droplet surface. Therefore, the instantaneous burning rate constant increased. To investigate the mechanism of such flame behavior, the ratio of two characteristic times, τ_f/τ_D (τ_f: flow oscillation characteristic time, τ_D: diffusion characteristic time), were compared. As the flow oscillatory frequency increased, τ_f/τ_D becomes smaller. τ_f/τ_D also became smaller at high pressure. If τ_f/τ_D is small due to the small mass diffusion rate, the droplet flame could not move back to the appropriate position for the minimum velocity in steady flow, leading to an increase of the burning rate constant, especially in the case of higher frequency at high pressure.     

Sex Differences in Physical Activity in People After Stroke: A Cross-sectional Study

OBJECTIVE: Adequate physical activity after stroke is critical for cardiovascular health. Although sex is a potential factor associated with post-stroke physical activity, its mechanism remains unclear. This study aimed to examine sex differences in human physical activity following stroke. METHOD: A cross-sectional study with 62 participants (men: 42, women: 20) was conducted. Physical activity was measured for three consecutive days using a step activity monitor. The walking durations per day in light physical activity, moderate-to-vigorous physical activity, and total physical activity were calculated. Sex differences in walking duration were compared using Welch''s t-tests or Mann-Whitney U tests. RESULTS: Women had a significantly greater walking duration in light physical activity and in total than did the men. In contrast, no significant differences were found in moderate-to-vigorous physical activity. CONCLUSION: This study reported sex differences in the walking duration after stroke. Moreover, it found that women spent more time in low intensity physical activity than men. Our results will be useful for planning interventions to increase physical activity and decrease sedentary behavior after stroke.     

Block-Iterative Reconstruction from Dynamically Selected Sparse Projection Views Using Extended Power-Divergence Measure

Iterative reconstruction of density pixel images from measured projections in computed tomography has attracted considerable attention. The ordered-subsets algorithm is an acceleration scheme that uses subsets of projections in a previously decided order. Several methods have been proposed to improve the convergence rate by permuting the order of the projections. However, they do not incorporate object information, such as shape, into the selection process. We propose a block-iterative reconstruction from sparse projection views with the dynamic selection of subsets based on an estimating function constructed by an extended power-divergence measure for decreasing the objective function as much as possible. We give a unified proposition for the inequality related to the difference between objective functions caused by one iteration as the theoretical basis of the proposed optimization strategy. Through the theory and numerical experiments, we show that nonuniform and sparse use of projection views leads to a reconstruction of higher-quality images and that an ordered subset is not the most effective for block-iterative reconstruction. The two-parameter class of extended power-divergence measures is the key to estimating an effective decrease in the objective function and plays a significant role in constructing a robust algorithm against noise.     

The intralayer order-disorder transition in monoclinic Cr3±xSe4

The Cr_3±xSe₄ shows an order-disorder transition from the monoclinic Cr₃Se₄ type to the CdI₂-type structure. This transition originates in the intralayer disordering of metal vacancies in the alternate partially filled metal layers along thec axis. The transition is reversible and of first order. The transition temperature vs composition curve has a maximum (～900°C) at a stoichiometric composition of Cr₃Se₄. A statistical treatment of this phenomenon was attempted via the Bragg-Williams approximation.     

Stepwise controlled immobilization of colloidal crystals formed by polymer-grafted silica particles

Colloidal crystals formed by polymer-grafted silica particles were immobilized by a stepwise procedure consisting of gelation by radical copolymerization followed by solidification by ring-opening radical polymerization. In the first step, the poly(methyl methacrylate) (PMMA)-grafted silica colloidal crystal suspension was incorporated into the gel without altering the crystal structure by copolymerization of cross-linker, 1,2-dimethylacryloyloxyethane (DME) and methyl methacrylate (MMA). In the second step, ring-opening radical polymerization was performed after substituting the solvent with vinylidene-1,3-dioxolane. By this two-step procedure, the silica particle array of colloidal crystals was immobilized and made into durable material.     

Structural Features and Properties of Bacterial Cellulose Produced in Agitated Culture

The structure and some properties of bacterial cellulose produced in agitated culture were studied. Scanning electron microscopy revealed that there was almost no difference between reticulated structures of bacterial cellulose fibrils produced in agitated culture and in static culture. Nevertheless, bacterial cellulose produced in agitated culture exhibited microstuctural changes, namely, a low degree of polymerization and a low crystallinity index. A CP/MAS ¹³C NMR analysis revealed that the cellulose I content of the cellulose produced in agitated culture was lower than that of the cellulose produced in static culture. The bacterial cellulose produced in agitated culture had a lower Young's modulus of sheet, a higher water holding capacity and a higher suspension viscosity in the disintegrated form than that produced in static culture.     

Extraction and transport of lithium ion by a crown ether-alkylphosphoric acid system [1]

Mixed carrier systems composed of crown ethers and alkylphosphoric acids have been studied as lithium ionophores using a solvent extraction technique and in transport across liquid membranes. The combination of dibenzo-14-crown-4 and bis(2-ethylhexyl) phosphoric acid showed a synergistic enhancement on both lithium ion selectivity and transport rate. The synergistic effects depended strongly upon crown ether structure and the enhancement was observed only when the metal cation corresponded to the crown ether's cavity diameter. Complex formation in the organic phase was assessed by use of FAB-mass spectrometry.     

Flow-injection system for the fluorimetric determination of fructose with an immobilized mannitol dehydrogenase reactor

Immobilized mannitol dehydrogenase is used for the determination of D-fructose in a flow-injection system. The enzyme is immobilized on poly(vinyl alcohol) beads. The oxidation of NADH occurs simultaneously and the disappearance of NADH is measured fluorimetrically. The response is linearly related to fructose concentration in the range 6–600 μM; 30 samples per hour can be analysed. The immobilized enzyme retains over 80% of its initial activity after repetitive use for 2 months.     

A new strategy of tandem transetherification-intramolecular hetero Diels-Alder reaction with (E,Z)-mixture of ethyl 2-nitro-3-ethoxyacrylate and δ,ε-unsaturated alcohols leading to functionalized trans-fused bicyclic nitronates

Tandem reaction of (E,Z)-ethyl 2-nitro-3-ethoxyacrylate (E:Z=25:75) with δ,ε-unsaturated alcohols leading to functionalized trans-fused bicyclic nitronates as single stereoisomers in high yields has been developed under thermal condition and in the presence of a catalytic amount of a Lewis acid catalyst such as Yb(OTf)₃. This process involves the configurational control of transetherified intermediates under a rapid, reversible transetherification reaction pathway for affording stereoselective trans-fused cyclic nitronates as single stereoisomers in intramolecular hetero Diels-Alder reaction.