Evidence for a new type of vanadyl pairs in (VO)2P2O7: an ESR and magnetisation study

ESR and magnetisation experiments have identified a new type of antiferromagnetic pairing of vanadyl groups in the butane oxidation catalyst vanadylpyrophosphate. This pairing is an order of magnitude weaker than the coupling predominantly found in crystalline (VO)₂P₂O₇.     

Viscometric Behaviour of Viscosity‐Index Improvers in Lubricant Base Oil over a Wide Temperature Range: II. Polyalphaolefin Synthetic Base Oil

A polyalphaolefin (PAO) synthetic base oil was used to solvate four polymers known to be viscosity‐index improvers in lubricants, these being an olefin copolymer (OCP), a dispersant olefin copolymer (DOCP), a polymethacrylate (PMA), and a hydrogenated diene polymer (HDP). The kinematic viscosity and density data for each polymer were measured at five concentrations (0.1, 0.2, 0.3, 0.5, and 0.7% by mass) by capillary viscometry over the temperature range −20 to 150°C. The data were analysed using the Huggins equation. When compared to an earlier study using a hydroprocessed (Group II) base oil, the thickening efficiencies of the polymers were generally lower in PAO, which was mainly attributed to the weaker intermolecular hydrodynamic interactions.     

Modelling collective navigation via non-local communication

Collective migration occurs throughout the animal kingdom, and demands both the interpretation of navigational cues and the perception of other individuals within the group. Navigational cues orient individuals towards a destination, while it has been demonstrated that communication between individuals enhances navigation through a reduction in orientation error. We develop a mathematical model of collective navigation that synthesizes navigational cues and perception of other individuals. Crucially, this approach incorporates uncertainty inherent to cue interpretation and perception in the decision making process, which can arise due to noisy environments. We demonstrate that collective navigation is more efficient than individual navigation, provided a threshold number of other individuals are perceptible. This benefit is even more pronounced in low navigation information environments. In navigation ‘blindspots’, where no information is available, navigation is enhanced through a relay that connects individuals in information-poor regions to individuals in information-rich regions. As an expository case study, we apply our framework to minke whale migration in the northeast Atlantic Ocean, and quantify the decrease in navigation ability due to anthropogenic noise pollution.     

Zr41.25Ti13.75Ni10Cu12.5Be22.5块体非晶合金的拉伸断裂行为

Zr41．25Ti13.75Ni10Cu12．5Be22．5块体非晶合金在过冷液相区内的拉伸断裂行为与拉伸温度及应变速率有关．在室温条件下拉伸表现为剪切带扩展形成脆性断裂,在断口表面层出现了大量放射状脉状纹络,断口表面层的绝热升温现象导致断裂层温度超过了液相线温度,从而在断面上出现熔融状液滴．在玻璃化转变温度点,断裂模式依然为脆性断裂,韧窝状形貌及脉状纹络代替了放射状的脉状纹络分布于断口表面,同时伴随有熔融状液滴．计算表明,断口表面层绝热升温温度依然高于液相线温度．在更高温度或较低应变速率条件下,断裂方式转变为颈缩断裂模式,在颈缩点顶端依然存在脉状纹络,而未能观察到熔融状液滴．分析表明,在较高温度或较低应变速率条件下,绝热升温对断裂层的影响非常微弱,断口表层的温度没有明显升高．     

Effect of temperature on the ageing behaviour of unsaturated ester‐based lubricants

The ageing behaviour of trimethylolpropane trioleate was investigated at different temperatures in a modified rotary bomb test apparatus. Some physicochemical properties of ageing oil samples, such as acid value, kinematic viscosity, and iodine value, were measured. The oil samples were analysed using gas chromatography, gas chromatography‐mass spectrometry, and gel permeation chromatography to assess the influence of temperature on the ageing behaviour of ester‐based oils. The results revealed that an increase in temperature could greatly speed up the ageing reaction and increase the formation of decomposition products. However, the degree of oil ageing remained similar when the same quantity of oxygen was consumed.     

稀土磁性塑料充模流动过程模拟

介绍了用高压毛细管流变仪,测试研究钕铁硼磁性塑料的流变特性,并利用非线性回归分析技术得到的流变参数,建立流动本构方程和钕铁硼流变体在注射模浇注系统内的流动模型,运用该模型对磁性材料注射模流道和浇口设计、流道料的冷却凝固时间等进行优化。实验及其分析表明,钕铁硼熔料体系符合假塑性连续流体的流动特性,遵从幂律流体的流动模型,具有超高的熔体粘度,在流道内流动压降远远高于普通塑料流动压降,有其特殊的成型加工规律。     

氰酸酯树脂的结构与性能

氰酸酯树脂是一种含三嗪环网状结构的高性能树脂;该结构赋予它优异的介电性能、较高的玻璃化温度、较低的收缩率和优异的力学性能。氰酸酯树脂有不同的化学结构,不同的结构它们表现出不同的物理性能。以上海慧峰科贸有限公司生产的不同型号、结构的氰酸酯树脂为例,叙述它们的各种性能。     

Influence of perfluorinated surfactants on the electrochemical behaviour of a lead electrode in sulfuric acid solution

The influence of various types of perfluorinated surfactants and their analogous hydrocarbon chain surfactants on the electrochemical behaviour of a lead electrode in sulfuric acid is studied by linear sweep voltammetry and cyclic voltammetry. The hydrogen evolution reaction is affected mainly by the type of the hydrophobic chain of the added surfactant (perfluorinated or hydrogenated). Nevertheless, these surfactants exert little expander acticn on the negative electrode, or even show an adverse effect on the discharge capacity of the lead electrode. A possible explanation is given in terms of the adsorption properties of different surfactants on the electrode surface during charge and discharge.     

BCC-BP算法在RGB值到LAB值色彩空间转换中的应用

目的 为了有效克服BP神经网络算法权阈值随机选取造成的模型预测精度不高、结果输出不稳定的问题.方法 提出细菌群趋药性(BCC)算法和BP神经网络算法相结合的BCC-BP神经网络算法,采用BCC算法来选取BP神经网络初始权阈值,克服初始权阈值随机选取带来的问题,并将该算法应用到RGB到LAB色彩空间转换模型中.结果 按照国家普通印刷品的允许误差范围规定在6个标准色差单位以下的要求,在色差小于6的预测区间,基于BCC-BP算法的预测准确率达到81.07％,好于BP,GA-BP和PSO-BP算法,同时对于平均色差ΔE小于6个标准色差单位的要求,BCC-BP算法10次预测结果全部低于6.结论 采用BCC算法辅助BP神经网络进行初始权阈值的选取,可以有效提高BP神经网络模型在色彩空间转换应用中值的输出精度和稳定性.     

Thirty years of ‘quiet eye’ with etafilcon A contact lenses

Frequent replacement contact lenses made from the etafilcon A hydrogel lens material were introduced onto the market over 30 years ago, and etafilcon A remains the most widely used hydrogel lens material today. Although the prescribing of silicone hydrogel lenses is increasing, millions of lens wearers globally have been wearing hydrogel lenses for many years and exhibit a physiologically-stable ‘quiet eye’, with a low profile of adverse events. Hydrogel lenses are demonstrated to maintain a low inflammatory response and infection risk profile during daily wear, which in the case of etafilcon A, may be related to its low modulus, and the naturally-protective, anti-microbial, non-denatured lysozyme absorbed into the lens from the tear fluid. Although improved corneal physiology from decreased hypoxia with silicone hydrogel lenses is well accepted, equivalent levels of corneal oxygenation are maintained during daily wear of low to medium powered hydrogel lenses, which do not impede the daily corneal de-swelling process, and do not induce clinically significant changes in ocular health. Therefore, hydrogel lenses remain an important alternative for daily wear in modern contact lens practice.