The influence of hard‐segments on two‐phase structure and shape memory properties of PCL‐based segmented polyurethanes

Poly(ε‐caprolactone)‐based segmented polyurethanes (PCLUs) were prepared from poly(ε‐caprolactone) diol, diisocyanates (DI), and 1,4‐butanediol. The DIs used were 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluenediisocyanate (TDI), isophorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI). Differential scanning calorimetry, small‐angle X‐ray scattering, and dynamic mechanical analysis were employed to characterize the two‐phase structures of all PCLUs. It was found that HDI‐ and MDI‐based PCLUs had higher degree of microphase separation than did IPDI‐ and TDI‐based PCLUs, which was primarily due to the crystallization of HDI‐ and MDI‐based hard‐segments. As a result, the HDI‐based PCLU exhibited the highest recovery force up to 6 MPa and slowest stress relaxation with increasing temperature. Besides, it was found that the partial damage in hard‐segment domains during the sample deformation was responsible for the incomplete shape‐recovery of PCLUs after the first deformation, but the damage did not develop during the subsequent deformation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 557–570, 2007     

Preparation of nanosized ZnO using α brass

Nanosized ZnOs were synthesized on the surface of α brass coated a film of nickel catalyst at 500-700 °C under atmosphere of O₂ and CH₄ gases. The nanosized ZnOs have shapes including pillar, leaf, sheet and rod, which were determined by the synthesis temperature and the flow rates of O₂ and CH₄ gases. The nanosized ZnOs were characterized by electron microscopy including transmission electron microscope for crystal structure, morphology and high resolution images, both field emission scanning electron microscope and scanning electron microscope for morphology, and energy dispersive X-ray spectroscope equipped in electron microscope for chemical composition. A mechanism was proposed for the growth of nanosized ZnO obtained in this work.     

Photoinitiated cationic polymerization of cycloaliphatic epoxide with siloxane or alkoxysilane functionalized polyol coatings

Polyols were reacted with tetraethyl orthosilicate (TEOS) or 3-isocyanatopropyltriethoxysilane (IPTES) to form siloxane functionalized polyols. The UV-reactivity of these siloxane functionalized polyols were investigated using real-time FT-IR spectroscopy. The reactivity of TEOS modified polyols was dependent on the relative humidity. However, for the IPTES functionalized polyols the effect of relative humidity was dependent on the degree of IPTES functionalization. When the polyols were only partially functionalized with IPTES, the effect of relative humidity was minimal. However, when polyols were fully functionalized with IPTES, the curing was dependent on relative humidity. The siloxane functionalized polyols were formulated with a cycloaliphatic epoxide and cationic photoinitiator. The photo-induced curing kinetics of these cycloaliphatic epoxide/siloxane functionalized polyol coatings were also investigated. Unlike the TEOS functionalized polyols, the addition of IPTES functionalized polyols into the formulation inhibited the curing speed. This inhibition was attributed to the basicity nitrogen of the urethane linkage. The effect of relative humidity on the UV-curing reaction of cycloaliphatic epoxide coatings was lowered by the incorporation of the TEOS functionalized polyols.     

Bis[μ‐1‐(1,10‐phenanthrolin‐2‐yl)‐2‐pyridone]bis{aqua[1‐(1,10‐phenanthrolin‐2‐yl)‐2‐pyridone]cadmium(II)} tetrakis(perchlorate)

In the title centrosymmetric binuclear complex, [Cd₂(C₁₇H₁₁N₃O)₄(H₂O)₂](ClO₄)₄, the Cd^II ion assumes a distorted octahedral geometry. There are π–π stacking interactions between the pyridine and 1,10‐phenanthroline ring systems of adjacent ligands at the same Cd^II centre. Intermolecular hydrogen bonds between the coordinated aqua ligand and the O atom of a keto group connect adjacent complex cations into extended chains. Hydrogen bonds also exist between the complex cations and the perchlorate anions. Compared with the fluorescence spectrum of the organic ligand, the complex displays strong fluorescent emission and an ipsochromic shift of the emission peaks, which may be attributed to the structural character.     

A semi-analytic meshfree method for Almansi–Michell problems of piezoelectric cylinders

Saint-Venant’s Problem, Almansi–Michell Problems, Meshfree Methods, Piezoelectricity. We present a semi-analytical method for analyzing prismatic nonhomogeneous piezoelectric cylinders with arbitrary cross-sectional geometry. The prescribed loads considered in this study include axial forces, torques, moments, and voltage resultants prescribed at the cylinder’s ends, as well as body forces, lateral surface shears, voltages, and pressures as long as they can be represented by a power series in the axial coordinate. This problem can be considered as an extension of Saint-Venant and Almansi–Michell problems for elastic bodies to piezoelectric bodies. In this computationally efficient method, the cross-sectional plane is discretized with a meshfree approach, and the solution is obtained analytically with respect to the axial coordinate. A number of examples are provided to demonstrate the veracity and utility of the proposed method.     

红黑排序混合算法收敛速度分析

The algorithm of applying the block Gauss elimination to the Red-Black or-dering matrix to reduce the order of the system then solve the reduced system byiterative methods is called Hybrid Red-Black Ordering algorithm.In this paper,we discuss the convergence rate of the hybrid methods combined with JACOBI,CG,GMRES(m).Theoretical analysis shows that without preconditioner thesethree hybrid methods converge about 2 times as fast as the corresponding natural ordering methods.For the case that all the eigenvalues is near the real axis, the GMRES(m) algorithm converges about 3 times faster than the natural ordering GMRES(m).Various numerical experiments are presented.For large scale prob-lem with preconditioners, numerical experiments show that the GMRES(m) hybrid methods converge from about 3 times to even 5 times as fast as the natural order-ing methods and the computing time is reduced to about 1/3 even 1/6 of that of the natural ordering methods.     

The supersymmetric WKB approximation of ring-shaped oscillator potential in r and θ dimensions with spherical polar coordinates

According to calculation of the energy spectrum of ring-shape oscillator potential by using the supersymmetric WKB approximation, it is shown that the energy spectrum of some noncentral separable potentials can be exactly obtained in r and θ dimensions by above method.     

卤代对苝醌类光敏剂光敏活性影响的量子化学研究

以一种新型的醌类光敏剂—菌生素 (HMB)为模型化合物 ,利用量子化学从头算HF/ 6 31G和含时密度泛函TD B3LYP/ 6 31G方法计算研究了卤代作用对醌类光敏剂分子性质和光敏活性的影响 .结果发现 ,卤代作用降低了HMB母体的HOMO和LUMO能级 (EHOMO和ELUMO)及其差值△E ,随卤族元素从上到下 ,EHOMO和ELUMO呈增大趋势 ,而△E呈减小趋势 ,使得分子激发光谱有不同程度的红移 ,在增加PQP三重态量子产率的同时降低了分子最低三重激发态的能量 ,两种作用相互抵消 ,使得卤代物的 1O2 量子产率与母体相似 ;增加了分子的绝热电子亲合势 ,使分子产生O2 -的能力下降 ;卤原子的引入 ,降低了HMB母体分子内氢键的强度 ,同时使顺式构型的分子内质子传递势垒增大 ,而使反式构型势垒减小 .     

Diethoxyphosphinyl acetic acid hydrazide: a uniquely versatile reagent for the preparation of fused [5,5]-, [5,6]-, and [5,7]-3-[(E)-2-(arylvinyl)]-1,2,4-triazoles

Diethoxyphosphinyl acetic acid hydrazide is a unique reagent that provides a convenient and efficient process to prepare fused [5,5]-, [5,6]-, and [5,7]-3-[(E)-2-(arylvinyl)]-1,2,4-triazoles from aldehydes and alkoxyimines. The process involves three steps without isolation of any intermediates to afford 1,2,4-triazoles in modest to excellent overall yield.     

Fractional Order Disturbance Observer for Robust Vibration Suppression

For the first time, the fractional order disturbance observer (FO-DOB) is proposed for vibration suppression applications such as hard disk drive servo control. It has been discovered in a recently published US patent application (US20010036026) that there is a tradeoff between phase margin loss and strength of the low frequency vibration suppression. Given the required cutoff frequency of the low pass filter, also known as the Q-filter, it turns out that the relative degree of the Q-filter is the major tuning knob for this tradeoff. The solution in US20010036026 was based on an integer order Q-filter with a variable relative degree. This actually motivated the use of a fractional order Q-filter. The fractional order disturbance observer is based on the fractional order Q-filter. The implementation issue is also discussed. The nice point of this paper is that the traditional DOB is extended to the fractional order DOB with the advantage that the FO-DOB design is now no longer conservative nor aggressive, i.e., given the cutoff frequency and the desired phase margin, we can uniquely determine the fractional order of the low pass filter.