Maximum a posteriori estimation of activation energies that control silicon self-diffusion

Self-diffusion in crystalline silicon is controlled by a network of elementary steps whose activation energies are important to know in a variety of applications in microelectronic fabrication. The present work employs maximum a posteriori (MAP) estimation to improve existing values for these activation energies, based on self-diffusion data collected at different values of the loss rates for interstitial atoms to the surface. Parameter sensitivity analysis shows that for high surface loss fluxes, the energy for exchange between an interstitial and the lattice plays the leading role in determining the shape of diffusion profiles. At low surface loss fluxes, the dissociation energy of large-atom clusters plays a more important role. Subsequent MAP analysis provides significantly improved values for these parameters.     

Third-order cumulants based methods for continuous-time errors-in-variables model identification

In this paper, the problem of identifying stochastic linear continuous-time systems from noisy input/output data is addressed. The input of the system is assumed to have a skewed probability density function, whereas the noises contaminating the data are assumed to be symmetrically distributed. The third-order cumulants of the input/output data are then (asymptotically) insensitive to the noises, that can be coloured and/or mutually correlated. Using this noise-cancellation property two computationally simple estimators are proposed. The usefulness of the proposed algorithms is assessed through a numerical simulation.     

聚乙烯醇基质球状疏水吸附树脂的制备及表征

以聚乙烯醇(PVA)为原料,甲醛作交联剂,采用悬浮聚合法制备了球状交联PVA颗粒。并对水溶液中PVA含量、表面活性剂种类、反应温度等影响因素进行了考察,最佳工艺条件为:PVA质量分数15%,表面活性剂V(Span-80):m(油酸钠)为2 mL/g,在88～92℃进行悬浮聚合。以球状交联PVA颗粒为基质,用醇钠溶液预处理后,通过Williamson醚化反应制备了球状疏水吸附树脂,最佳醚化反应条件为:醇钠溶液浓度2.0 mol/L,NaOH浓度4mol/L,醚化温度50～60℃。     

Optimal sensor locations for nonparametric identification of viscoelastic materials

The problem of optimal sensor locations in nonparametric identification of viscoelastic materials is considered. Sensor locations have previously been assigned in an ad hoc manner, resulting in a sub-optimal experiment design with a comparatively high variance of the estimates. Different scalar criteria of the covariance matrix, connected to A- and D-optimal experiment design, are considered and evaluated. The results indicate that the accuracy of the estimates can be greatly improved by the use of optimally placed sensors. The theoretical study has been verified by experiments. The presented results can be used to design experiments with improved accuracy of the estimates.     

Emulsion polymerization: State of the art in kinetics and mechanisms

Over decades of carefully designed kinetic experiments and the development of complementary theory, a more or less complete picture of the mechanisms that govern emulsion polymerization systems has been established. This required means of determining the rate coefficients for the individual processes as functions of controllable variables such as initiator concentration and particle size, means of interpreting the data with a minimum of model-based assumptions, and the need to perform experiments that had the potential to actually refute a given mechanistic hypothesis. Significant advances have been made within the area of understanding interfacial processes such as radical entry and exit into and out of an emulsion polymerization particle, for electrostatic, steric and electrosteric stabilizers (the latter two being poorly understood until recently). The mechanism for radical exit is chain transfer to monomer within the particle interior to form a monomeric radical which can either diffuse into the water phase or propagate to form a more hydrophobic species which cannot exit. Entry is through aqueous-phase propagation of a radical derived directly from initiator, until a critical degree of polymerization z is reached; the value of z is such that the z-meric species is sufficiently surface active so that its only fate is to enter, whereas smaller aqueous-phase radical species can either be terminated in the aqueous phase or undergo further propagation. For both entry and exit, in the presence of (electro)steric stabilizers, two additional events are significant: transfer involving a labile hydrogen atom within the stabilizing layer to form a mid-chain radical which is slow to propagate and quick to terminate, and which may also undergo β-scission to form a water-soluble species. Proper consideration of the fates of the various aqueous-phase radicals is essential for understanding the overall kinetic behaviour. Intra-particle termination is explained in terms of diffusion-controlled chain-length-dependent events. A knowledge of the events controlling entry and exit, including the recent discoveries of the additional mechanisms operating with (electro)steric stabilizers, provides an extension to the micellar and homogeneous nucleation models which enables particle number to be predicted with acceptable reliability, and also quantifies the amount of secondary nucleation occurring during seeded growth. This knowledge provides tools to understand the kinetics of emulsion polymerization, in both conventional and controlled/living polymerization systems, and to optimize reaction conditions to synthesize better polymer products.     

注入锁定铜蒸气激光器的时空、能量以及偏振特性

采用P分量的偏振光注入到平行平面腔的铜蒸气激光器中,结果表明,与未加注入光时的振荡器比较,注入锁定铜蒸气激光器的输出功率提高了43％,P分量的偏振度从0.30提高到0.78,脉宽由36ns加宽到48ns,输出光的发散角显著改善,由7.8mrad降到1.1mrad,与注入光束基本相同。