膨胀土原位剪切模量–剪应变衰减曲线与特征分析

为了评价原位应力状态膨胀土在小应变作用下的刚度衰减特性,综合原位地震扁铲侧胀和室内共振柱试验,分析应力历史、应力状态和试样扰动对膨胀土剪切模量衰减规律的影响。结果表明,应力状态和应力历史对膨胀土剪切模量影响较大,相同应力历史下,剪切模量随围压增加而增大,随着应变的发展,衰减较快;相同应力状态下,经历加载–卸载过程的剪切模量–剪应变(G-γ)衰减曲线位于仅经历加载过程的曲线上方,但经历加载–卸载和加载–卸载–再加载过程后土的G-γ衰减曲线基本重合;另外,相同应力历史条件下,土的原位剪切模量较室内共振柱试验所得剪切模量值大,且衰减更快,说明取样卸荷、运输及制样等扰动因素对土体结构造成了不可逆的损伤,通过室内加卸载过程无法还原其原位力学性状;参考剪应变不同时,推求得到的原位G-γ衰减曲线的中间部分差异较大,参考剪应变越小,剪切模量衰减越快,说明合理选取参考曲线和小应变剪切模量是推求原位G-γ衰减曲线的关键。该研究可为类似场地地震分析和沉降分析提供理论基础和技术支持。     

植物精油对草莓果实腐烂和品质的影响

以“丰香”草莓为试材,研究不同添加量(0.5、1、5、10μL/L)的香芹酚、肉桂醛、紫苏醛、沉香萜醇和异硫氰酸稀丙酯(AITC)处理对草莓果实常温和低温保鲜的效果。结果表明,五种植物精油都能显著抑制草莓果实在20℃和5℃贮藏期间腐烂的发生,其中以AITC处理的效果最好。但处理水平过高,即AITC和紫苏醛处理水平达到5μL/L、其他3种精油处理水平为10μL/L时,会对果实产生药害。采用适宜处理水平的各种植物精油处理还可显著抑制果实在5℃贮藏时质量损失率的上升和硬度的下降、保持较高的可滴定酸、可溶性固形物、VC、总糖和还原糖含量,从而保持果实品质。因此,植物精油处理在草莓果实防腐保鲜中具较好的应用前景。     

BABA处理对葡萄果实采后灰霉病的影响及机理

以‘巨峰’葡萄果实为实验材料,研究β-氨基丁酸（β-aminobutyric acid,BABA）处理对葡萄果实灰霉病、抗病相关酶活性和总酚含量的影响。葡萄果实先用75 mmol/L的BABA溶液处理后刺伤接种灰霉葡萄孢菌,然后转入25 ℃贮藏60 h。结果发现,BABA处理有效抑制了‘巨峰’葡萄果实的腐烂和病斑的扩展;同时BABA处理还诱导了果实中几丁质酶、β-1,3葡聚糖酶、苯丙氨酸解氨酶、4-香豆酸辅酶A连接酶和肉桂酸羟化酶等抗病相关酶活性以及总酚含量的提高。结果表明,BABA可诱导葡萄果实产生抗病性,从而减少灰霉病的发生。     

灯用稀土荧光粉的若干技术发展和探索（上）

本文简要介绍了灯用稀土三基色荧光粉的组成、结构及发光机理等基本概况,以及灯用稀土三基色荧光粉的技术现状,市场状况及技术发展方向,并介绍了近年来彩虹集团在灯用稀土三基色荧光粉上所做的基础性及应用特性方面的研究工作。     

冲击机械能量传递研究

冲击机械是一种广泛运用于工程领域的产品,具有结构紧凑,能量密度大的特点,冲击机械在工作过程中能量传递的效率至关重要。文章运用冲击动力学理论,介绍了冲击系统能量传递效率的定义,主要的冲击元件模型特性,以及在矩形波和指数衰减形波作用下能量传递效率的计算方法及计算公式,并给出了一个算例。结果表明：冲击系统的能量传递效率叩只与匹配参数β有关,而β是由岩石的性质、冲击速度和冲击钻具波阻决定的;矩形波的能量传递效率比指数衰减形更高：     

Realization of wavelength conversion with hyperbolic secant femtosecond pulse in normal dispersion regime

Realization of wavelength conversion based on second-order femtosecond dark solitons with hyperbolic secant pulse is presented. This is achieved by introducing localized dispersion perturbation along the optical fiber. We demonstrate that an initial 30 fs second-order pulse decays to similar sub-pulses by applying perturbation using a step increment of β₂ from 6.3 to 15.75 ps² km^?1. This shows that the realization of a 1 × 2 channel wavelength converter for femtosecond pulses is possible. Recent research shows the possibility of realizing wavelength conversion generated from picosecond solitons neglecting nonlinear effects. However, employing the same method for femtosecond pulses fails due to the manifestation of nonlinear effects. In this paper, pulse deformation under different levels of perturbation was tested, and appropriate perturbation leading to similar sub-pulses is achieved.     

Spontaneous emission by an ensemble of dipoles coupled to a plasmonic nanoresonator

ABSTRACT

Spontaneous emission from ensembles of quantum emitters (QEs) such as atoms, molecules or semiconductor quantum dots can be greatly enhanced by cooperative effects arising from electromagnetic correlations. We describe a cooperative mechanism for emission of light by an ensemble of QEs based upon cooperative energy transfer from QEs to localized surface plasmons in metal-dielectric structures followed by plasmon radiation at a rate that scales with the ensemble size. For large QE ensembles saturating the plasmon mode volume, we derive universal, i.e. independent of local field distribution, expression for cooperative Purcell factor that can by far exceed the field enhancement limits for individual QE in a hot spot. We also derive radiated power spectrum that retains the plasmon resonance lineshape and, in contrast to common cooperative mechanisms, is insensitive to natural variations of QEs' emission frequencies.     

Experimental investigation on axial velocity distribution for ship’s twin-propeller jets

Abstract

The investigation of twin-propeller jets as ships undergo acceleration is essential. This form of jet has been triggering problematic consequences such as seabed scouring. In order to prevent such scouring, near-bed velocities must first be analyzed in order to design the necessary protection when the under keel clearance of a ship is low when it is near port structures. This paper presents experimental work performed by Laser Doppler Anemometry. It is noticed that research into twin-propeller jet profiles still remains limited in the literature. Therefore, we intend to analyze twin-propeller axial velocity profiles and look into several flow characteristics such as efflux velocity and its decay pattern. Also, the measured velocity profile is compared to that of a single-propeller jet. Current results show that scouring is more severe in the case of the twin-propeller jets.     

Electrochemical impedance spectroscopy evaluation of behaviour of Pb–Ag anodes for zinc electrowinning

Abstract

Pb–0·5–0·7Ag anodes are widely used in the industry of zinc electrowinning. Two commercial lead anodes containing 0·56 and 0·69%Ag were studied by electrochemical impedance spectroscopy to evaluate their electrochemical activity. An industrial acid zinc sulphate electrolyte containing glue and chloride ion, but without manganese addition, was considered. In this study, 5 h of electrolysis at a density of 50 mA cm^?2 (currently used in practice) and also 6 h of potential decay were made to represent electrowinning periods of maintenance both at 38°C. During the 5 h polarisation, the average double layer capacity of Pb–0·56Ag alloy was higher (～9%) than that of Pb–0·69Ag alloy. During the first hour of potential decay, the Warburg impedance controls the electrochemical reaction. For the period from the second to sixth hour, the double layer capacity decreased with immersion time, and the charge transfer resistance increased with time. During the potential decay, the average charge transfer resistance of Pb–0·69Ag anode was higher (～52%) than that of Pb–0·56Ag anode.