Crystals of Aliphatic Derivatives of [Cu(acac)2] have Distinct Atomic-Scale Mechanisms of Bending

Molecular crystals displaying elastic flexibility have important applications in the fields of optoelectronics and nanophotonic technologies. Understanding the mechanisms by which these materials bend is critical to the design of future materials incorporating these properties. Based on the known elastic properties of bis(acetylacetonato)copper(II), a series of 14 aliphatic derivatives are synthesized and crystallized. All those which grew in a needle morphology display noticeable elasticity, with 1D chains of π-stacked molecules parallel to the long metric length of the crystal a consistent crystallographic feature. Crystallographic mapping is used to measure the mechanism of elasticity at an atomic-scale. Symmetric derivatives with ethyl and propyl side chains are found to have different mechanisms of elasticity, which are further distinguished from the previously reported mechanism of bis(acetylacetonato)copper(II). While crystals of bis(acetylacetonato)copper(II) are known to bend elastically via a molecular rotation mechanism, the elasticity of the compounds presented is facilitated by expansion of their π-stacking interactions.     

从微孔洞起始的热冲击裂纹的数值研究——Ⅱ:能量释放率分析

利用商业的有限元软件ABAQUS,分析了具有微孔洞结构氧化铝陶瓷材料在受到热冲击作用下,从处于材料表面上的开口微孔洞以及临近材料表面的闭口微孔洞的底部起始的裂纹扩展。结果表明:对于从开口微孔洞和闭口微孔洞底部起始的裂纹,其能量释放率随冷却时间的变化规律类似,即随冷却时间t由零开始增加,能量释放率也由零开始快速增大,在冷却时间大约为t=0.1 s时,达到其最大值,随后开始降低。另外对于从开口微孔洞底部起始的裂纹,结果发现裂纹的能量释放率随裂纹长度的增加、微孔洞半径的增加而增加,而对于从闭口微孔洞底部起始的裂纹,其能量释放率随裂纹长度的增加、微孔洞半径的增加、以及微孔洞与材料受热冲击面距离的增加而增加。以开口微孔洞底部起始的裂纹为例,研究了裂纹与临近微孔洞之间的作用,发现临近微孔洞的存在可以明显减小裂纹的能量释放率。这些结果对于从材料的微结构角度设计材料的抗热冲击性能有参考价值。     

Three-dimensional electron backscattered diffraction analysis of deformation in MgO micropillars

Small-scale testing is extensively used to study the effects of size on plasticity or characterise plastic deformation of brittle materials, where cracking is suppressed on the microscale. Geometrical and experimental constraints have been shown to affect small-scale deformation and efforts are underway to understand these better. However, current analytical techniques tend to possess high resolution in only one or two dimensions, impeding a detailed analysis of the entire deformed volume. Here electron backscattered diffraction in three dimensions is presented as a way of characterising three-dimensional (3-D) deformation at high spatial resolution. It is shown that, by reconstruction of compressed and then successively sliced and indexed MgO micropillars, this 3-D technique yields information complementary to μ-Laue diffraction or electron microscopy, allowing a correlation of experimental artefacts and the distribution of plasticity. In addition, deformation features which are difficult to visualise by standard scanning electron microscopy are easily detected, for example where only small surface traces are produced or minimal plastic strain can be introduced before failure in brittle materials.     

Scalable peer-to-peer streaming for live entertainment content

We present a system for streaming live entertainment content over the Internet originating from a single source to a scalable number of consumers without resorting to centralized or provider-provisioned resources. The system creates a peer-to-peer overlay network, which attempts to optimize use of existing capacity to ensure quality of service, delivering low startup delay and lag in playout of the live content. There are three main aspects of our solution: first, a swarming mechanism that constructs an overlay topology for minimizing propagation delays from the source to end consumers; second, a distributed overlay anycast system that uses a location-based search algorithm for peers to quickly find the closest peers in a given stream; and finally, a novel incentive mechanism that encourages peers to donate capacity even when the user is not actively consuming content.     

The cracking of zirconia refractory tubes under hot shock

The evolution of stresses and strains in a zirconia-containing refractory tube subjected to a hot shock on the outer surface and convective cooling at the inner surface is analysed with the method of finite elements. To account for the temperature-induced phase transformation in the zirconia as well as the overall thermal expansion, a coefficient of total dilatation is introduced. The parameters that control the time-dependent stress and strain responses are identified by performing finite element calculations that span the range of variables relevant to steel making. The effects of tube thickness, hot shock duration, initial temperature, temperature dependence of elastic modulus, and transformation amplitude on stress and strain distributions are discussed, and heating and process strategies to eliminate surface cracking are suggested.     

Pink discoloration in canned pears I.—Role of tin in pigment formation

The major pigment in discoloured canned pears is identified as a purple-pink insoluble tin-anthocyanin complex from the effect of reagents for anthocyanins on the spectra of solid and syrup fractions of the product. This characterisation is supported by significant correlations between the intensity of reflected colour and the insoluble tin content of the solid fraction. It is suggested that formation of a tin complex is essential for the occurrence of pink discolorations in canned pears, and experiments are described designed to vary the intensity of discoloration by modifying the conditions controlling complex formation.     

Perturbations in hyperthermia temperature distributions associated with counter-current flow: numerical simulations and empirical verification

Two numerical techniques are used to calculate the effect of large vessel counter-current flow on hyperthermic temperature distributions. One is based on the Navier-Stokes equation for steady-state flow, and the second employs a convective-type boundary condition at the interface of the vessel walls. Steady-state temperature fields were calculated for two energy absorption rate distributions (ARD) in a cylindrical tissue model having two pairs of counter-current vessels (one pair with equal diameter vessels and another pair with unequal diameters). The first assumed a uniform ARD throughout cylinder; the second ARD was calculated for a tissue cylinder inside an existing four antenna Radiofrequency (RF) array. A tissue equivalent phantom was constructed to verify the numerical calculations. Temperatures induced with the RF array were measured using a noninvasive magnetic resonance imaging technique based on the chemical shift of water. Temperatures calculated using the two numerical techniques are in good agreement with the measured data. The results show: 1) the convective-type boundary condition technique reduces computation time by a factor of ten when compared to the fully conjugated method with little quantitative difference (approximately 0.3 degree C) in the numerical accuracy and 2) the use of noninvasive magnetic resonance imaging (thermal imaging) to quantitatively access the temperature perturbations near large vessels is feasible using the chemical shift technique.     

Microprocessor Architecture

This marks the second issue of Computer devoted to the Asilomar Workshop on Microprocessors. As with the first such issue (January 1976), no attempt has been made to cover the workshop in toto (a summary report appeared in the July 1976 Computer). Rather, the goal has been to spotlight a few of the more interesting developments and philosophies that were explored during the April 1976 workshop.     

Gas absorption accompanied by a large heat effect and volume change in the liquid phase: the system hydrogen chloride/ethylene glycol

Using a predicted value of the liquid phase diffusivity, the Chiang and Toor model is shown to give a good estimate of the measured rate of absorption of hydrogen chloride by ethylene glycol. A liquid surface temperature rise of 20°C is calculated. Unlike the previously tested ammonia-water system, temperature and volume effects do not compensate, and the absorption rate in this system is considerably higher than the isothermal prediction.