LIPID MICRORESISTOR AS MIMICKING OLFACTORY SENSOR - THE RULE OF THE RESPONSE OF LIPIDS TO C-1-C-4 ALCOHOLS

Phosphatidylcholine (PC) and six other PC-similar lipids are coated on interdigital electrodes, IEs, as sensitive membranes. Eight alcohols (C-1-C-4) are tested in a flow system at room temperature. It is found that all responses are log(response)-log(concentration) linear relations. These results agree with Steven's law in psychophysics. Moreover, the thresholds of the sensors are coincident with human olfactory thresholds. The authors have analysed the data of the lipid hypothesis suggested by Kurihara et al. We have found that this hypothesis is also in agreement with Steven's law. Lipid microresistors are real mimicking olfactory sensors. A definition of an olfactory sensor is suggested.

First principles based predictions of the toughness of a metal/oxide interface

We describe a first-principles-based strategy to predict the macroscopic toughness of a gamma-Ni(Al)/alpha-Al2O3 interface. Density functional theory calculations are used to ascertain energy changes upon displacing the two materials adjacent to the interface, with relaxation conducted over all atoms located within adjoining rows. Traction/displacernent curves are obtained from derivatives of the energy. Calculations are performed in mode I (opening), mode II (shear) and at a phase angle of 45 degrees. The shear calculations are conducted for displacements along < 110 > and < 112 > of the Ni lattice. A generalized interface potential function is used to characterize the results. Initial fitting to both the shear and normal stress results is required to calibrate the unknowns. Thereafter, consistency is established by using the potential to predict other traction quantities. The potential is incorporated as a traction/displacement function within a cohesive zone model and used to predict the steady-state toughness of the interface. For this purpose, the plasticity of the Ni alloy must be known, including the plasticity length scale. Measurements obtained for a gamma-Ni superalloy are used and the toughness predicted over the full range of mode mixity. Additional results for a range of alloys are used to demonstrate the influences of yield strength and length scale.

薄膜/基体界面的层裂行为研究

近年来，薄膜/基体结构在微/纳米工程中得到广泛的应用，研究薄膜/基体界面的力学性能得到广泛的关注。为了检验薄膜和基体间的黏结强度，早在20世纪50年代，人们就设计了一种简单的实验方法－－撕裂试验，该试验由于其简单易于操作至今仍在许多领域都有广泛的应用。早期对于撕裂试验的研究多局限于弹性撕裂，即将薄膜和基体都作为弹性材料来处理。后来，对于韧性薄膜，为了预测由于塑性耗散引起能量释放率(撕裂力)的增大，Kim及其合作者提出并采用了梁的弯曲模型对撕裂中的塑性耗散进行预测。Wei和Hutchinson在分析弹塑性薄膜的撕裂问题时，采用了一种不同于Kim的弯曲模型的方法，除已脱胶部分之外，薄膜的脱胶过程由平面应变弹塑性有限元方法模拟，在分析过程中采用黏聚力模型来刻画韧性薄膜沿基体界面被撕裂或脱胶过程，所得结果无论是在定性还是定量上均与Kim的梁弯曲模型结果有很大区别。\newline 鉴于几种关于韧性薄膜撕裂模型对结果预测的不一致，几位学者联名倡议提出开展关于薄膜撕裂实验刻画模型有效性检验的国际合作。在倡议中指出无论采用何种方法，都须采用黏聚力模型来刻画界面断裂过程。而此后有很多工作都采用黏聚力模型来刻画界面。\newline 如果考虑残余应力的影响，涂层或黏结于基体上的薄膜或多层材料中的单独片层等均不可避免地承受着残余应力的作用。薄膜中的残余应力的主要来源于沉积过程，外延，以及热膨胀失配等因素。承受应力状态的薄膜/基体体系往往在边缘处产生很强的应力集中，极易导致其在该处界面起始层裂发生。如何评价残余应力对薄膜/基体体系界面的影响也显得至关重要。\newline 本文将对撕裂试验以及热失配引起残余应力作用下的薄膜/基体体系的界面层裂行为展开研究。薄膜/基体体系界面采用混合性黏聚力模型来刻画。研究了对应不同薄膜材料参数和不同界面参数情况下的撕裂行为，给出了撕裂力和界面分离功以及界面分离强度等参数之间的关系，并对界面层裂模式进行了分析。同时对多角度撕裂的界面破坏形式进行了系统的研究，给出了稳态撕裂力及相角与撕裂角度之间的关系。\newline 对由于热失配引起残余应力作用下的薄膜/基体体系的界面层裂行为的研究。假设薄膜和基体材料分别为弹塑性材料和弹性材料。研究了对应不同薄膜材料参数和不同界面参数情况的界面层裂发生机制，给出了层裂发生时临界温度荷载与薄膜/基体几何参数、材料参数以及模型参数之间的关系。

仿生单纤维黏附的尺寸效应

<正>针对纳米柱状纤维黏附中的尺寸效应开展研究。生物材料具有明显的线弹性特性,利用数值方法研究了黏弹性柱状纤维界面黏附的尺寸效应。纤维遵循线性黏弹性本构关系,黏附界面利用Tvergaard-Hutchinson黏结区模型来描述,分别研究了黏弹性纤维拉伸及扭转状态下,一定的加载速率下,尺寸对黏附的影响,以及加载速率对缺陷不敏感尺寸的影响,给出了加载速率与缺陷不敏感尺寸

基于第一性原理的金属/氧化物界面结合强度与宏观韧性的系统性研究

<正>总结介绍作者们多年来发展的基于第一性原理的系统性研究金属/氧化物界面结合强度和宏观韧性的策略方法。以应用广泛的γ-Ni/α-Al_2O_3界面为例,从第一性原

First principles based predictions of the toughness of a metal/oxide interface

We describe a first-principles-based strategy to predict the macroscopic toughness of a gamma-Ni(Al)/alpha-Al2O3 interface. Density functional theory calculations are used to ascertain energy changes upon displacing the two materials adjacent to the interface, with relaxation conducted over all atoms located within adjoining rows. Traction/displacernent curves are obtained from derivatives of the energy. Calculations are performed in mode I (opening), mode II (shear) and at a phase angle of 45 degrees. The shear calculations are conducted for displacements along < 110 > and < 112 > of the Ni lattice. A generalized interface potential function is used to characterize the results. Initial fitting to both the shear and normal stress results is required to calibrate the unknowns. Thereafter, consistency is established by using the potential to predict other traction quantities. The potential is incorporated as a traction/displacement function within a cohesive zone model and used to predict the steady-state toughness of the interface. For this purpose, the plasticity of the Ni alloy must be known, including the plasticity length scale. Measurements obtained for a gamma-Ni superalloy are used and the toughness predicted over the full range of mode mixity. Additional results for a range of alloys are used to demonstrate the influences of yield strength and length scale.

Photodissociation dynamics of the methyl radical at 212.5 nm: Effect of parent internal excitation

Photodissociation dynamics of the CH3 radical at 212.5 nm has been investigated using the H atom Rydberg tagging time-of-flight method with a pure CH3 radical source generated by the photolysis of CH3I at 266 nm. Time-of-flight spectra of the H atom products from the photolysis of both cold and hot methyl radicals have been measured at different photolysis polarizations. Experimental results indicate that the photodissociation of the methyl radical in its ground vibrational state at 212.5 nm excitation occurs on a very fast time scale in comparison with its rotational period, indicating the CH3 dissociation at 212.5 nm occurs on the excited 3s Rydberg state surface. Experimental evidence also shows that the photodissociation of the methyl radical in the nu(2)=1 state of the umbrella mode at 212.5 nm excitation is characteristically different from that in the ground vibrational state. (C) 2004 American Institute of Physics.