Thermal energy transport in harmonic systems

One and two-dimensional oscillator systems are constructed so that individual oscillators are bound to their home positions and coupled to nearest neighbors by linear forces; both systems are treated for the case of weak coupling. The two-dimensional system has a tensor binding force that does not permit it to be decoupled into two noninteracting systems.Segments and strips are treated as thermodynamic systems in contact with a heat bath and Gaussian initial probability densities are used to compute correlations. Expressions for entropy and “temperature” are computed by relating initial system and bath variances to equilibrium temperature.Asymptotic relations for “temperature” are found that show the degree of coupling between dimensions affects the rate of approach to equilibrium, but only through the coefficient of time and not its power. Both systems approach equilibrium as t^?1 rather than $\text{t}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ as predicted by continuum theory.     

一种适用于飞行器航电综合的故障检测和重构方法

鉴于特殊的飞行任务需求,某型号航电综合单一的故障逻辑难以满足多元故障状态下自主重构需求,降低了系统容错性。为解决航电综合多元故障模式难以量化表征影响故障重构的工程难题,创新的提出了一种适用于航电综合的故障检测和重构方法,基于决策表数据挖掘技术的航电综合故障预测流程和多源信息故障检测技术确保常规故障检测率大于98%,航电系统重构状态的量化表征分类方式确保了系统快速重构设计,本文提出的故障检测和重构方法极大地提高航电综合系统的故障检测率与容错能力。     

Kinetic resolution and chemoenzymatic dynamic kinetic resolution of functionalized gamma-hydroxy amides

[reaction: see text] An efficient kinetic resolution of racemic gamma-hydroxy amides 1 was performed via Pseudomas cepacia lipase (PS-C)-catalyzed transesterification. The enzyme PS-C tolerates both variation in the chain length and different functionalities giving good to high enantioselectivity (E values of up to >250). The combination of enzymatic kinetic resolution with a ruthenium-catalyzed racemization led to a dynamic kinetic resolution. The use of 2,4-dimethyl-3-pentanol as a hydrogen source to suppress ketone formation in the dynamic kinetic resolution yields the corresponding acetates in good yield and good to high enantioselectivity (ee's up to 98%). The synthetic utility of this procedure was illustrated by the practical synthesis of the versatile intermediate gamma-lactone (R)-5-methyltetrahydrofuran-2-one.     

Magnetic field dependence of electron spin polarization generated through radical-triplet interactions

The magnetic field dependence of electron spin polarization (ESP), generated in free radicals when they encounter photoexcited triplets, was measured experimentally and analyzed theoretically. The time-resolved electron paramagnetic resonance measurements were performed with a microwave setup consisting of low-loss dielectric ring resonators with tunable microwave frequencies and the corresponding magnetic fields. The ESP of the radical was found in the magnetic field range of 170-370 mT, and the results of the calculation based on the numerical solution of the stochastic Liouville equation were found to be in line with the experimental data showing that ESP decreases when the magnetic field increases.     

Sol–gel synthesis and characterization of polycrystalline GdFeO<Subscript>3</Subscript> and Gd<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> thin films

Thin films of the perovskite and garnet structured gadolinium ferrites GdFeO₃ and Gd₃Fe₅O₁₂ have been synthesized by a sol–gel method, based on stoichiometric mixtures of acetyl acetone chelated Gd³⁺ and Fe³⁺ dissolved in 2-methoxy ethanol. After spin coating onto Si wafers, and heating in air at 700 °C for 20 h, neatly grown essentially single phase films were obtained. From X-ray photoelectron spectroscopy an iron deficiency is observed in the uppermost layer of both films, implying that the crystallites preferably end in planes rich in Gd and O but not in Fe. The films were also characterized by X-ray powder diffraction, scanning electron microscopy, infrared spectroscopy, and magnetic measurements.     

Doubly uniform semiclassical quantization formula for resonances

The radial Schrödinger equation with an effective potential containing a single well and a single barrier is treated with an improved uniform semiclassical method. The improved quantization formula for complex energies (or resonances) contains a correction term that originates from a uniform treatment of the classically forbidden region near the origin in addition to the more familiar uniform treatment of the barrier region. In the present case the origin has a second-order pole, due to the centrifugal barrier potential term, and/or a Coulomb-type singularity, and these terms dominate the region inside the innermost classical turning point.Numerical results for first-order and third-order approximate complex resonance energies are compared with those of a standard (first- and third-order) barrier-uniform semiclassical method and also with those of ‘exact’ numerical computations.The improved quantization formula provides results in significantly better agreement with the exact results as the angular momentum quantum number l approaches zero.     

Materials,technologies, and circuit concepts for nanocrossbar-based bipolar RRAM

The paper reports on the characterization of bipolar resistive switching materials and their integration into nanocrossbar structures, as well as on different memory operation schemes in terms of memory density and the challenging problem of sneak paths. TiO₂, WO₃, GeSe, SiO₂ and MSQ thin films were integrated into nanojunctions of 100×100 nm². The variation between inert Pt and Cu or Ag top electrodes leads to valence change (VCM) switching or electrochemical metallization (ECM) switching and has significant impact on the resistive properties. All materials showed promising characteristics with switching speeds down to 10 ns, multilevel switching, good endurance and retention. Nanoimprint lithography was found to be a suitable tool for processing crossbar arrays down to a feature size of 50 nm and 3D stacking was demonstrated. The inherent occurrence of current sneak paths in passive crossbar arrays can be circumvented by the implementation of complementary resistive switching (CRS) cells. The comparison with other operation schemes shows that the CRS concept dramatically increases the addressable memory size to about 10¹⁰ bit.     

Effect of pectin extraction method on properties of cellulose nanofibers isolated from sugar beet pulp

In this study, the effect of pectin extraction method on the properties of cellulose nanofibers (CNFs) isolated from sugar beet pulp (SBP) was studied. Pectin was extracted by the industrially practiced method by sulfuric acid hydrolysis or by enzymatic hydrolysis using a cellulase/xylanase enzymes mixture. The CNFs were then isolated by high-pressure homogenization and investigated in terms of their chemical composition, crystallinity, size, degree of polymerization, and re-dispersion in water after freeze-drying. The mechanical properties and surface characteristics of CNF films were also studied. The results showed that fibrillation of the de-pectinated SBP was more efficient for the acid hydrolyzed SBP. CNFs from the acid-hydrolyzed SBP had a slightly wider diameter, higher crystallinity, viscosity, and α-cellulose content but a lower degree of polymerization than CNFs from the enzyme-hydrolyzed SBP. Owing to the presence of more residual hemicelluloses in the CNFs from the enzyme-hydrolyzed SBP, the CNFs had higher re-dispersion ability in water. CNF films from enzyme-hydrolyzed SBP displayed slightly better mechanical properties and higher water contact angle than acid-hydrolyzed CNF films.

Graphic abstract

     

The nanostructures of amorphous silicas.

Topologically modeled amorphized silica structures have been refined using a molecular dynamics simulation technique. Several metastable structures with substantially different medium-range connectivities, as characterized by primitive ring statistics, were obtained. Whereas the total correlation function is insensitive to these differences, the first step diffraction peak derived from energy-filtered electron diffraction shows a promising correlation to medium-range structure.     

Switchable ionic liquids enable efficient nanofibrillation of wood pulp

Use of switchable ionic liquid (SIL) pulp offers an efficient and greener technology to produce nanofibers via ultrafine grinding. In this study, we demonstrate that SIL pulp opens up a mechanically efficient route to the nanofibrillation of wood pulp, thus providing both a low cost and chemically benign route to the production of cellulose nanofibers. The degree of fibrillation during the process was evaluated by viscosity and optical microscopy of SIL treated, bleached SIL treated and a reference pulp. Furthermore, films were prepared from the fibrillated material for characterization and tensile testing. It was observed that substantially improved mechanical properties were attained as a result of the grinding process, thus signifying nanofibrillation. Both SIL treated and bleached SIL treated pulps were fibrillated into nanofibers with fiber diameters below 15 nm thus forming networks of hydrophilic nature with an intact crystalline structure. Notably, it was found that the SIL pulp could be fibrillated more efficiently than traditional pulp since nanofibers could be produced with more than 30% less energy when compared to the reference pulp. Additionally, bleaching reduced the energy demand by further 16%. The study demonstrated that this switchable ionic liquid treatment has considerable potential in the commercial production of nanofibers due to the increased efficiency in fibrillation.