Drop sizes of emulsions related to turbulent energy dissipation rates

Emulsion droplet sizes are compared with rates of turbulent energy dissipation in various types of practical equipment. These rates can be very high locally—up to 400 MW · kg⁻¹ in valve homogenizers. The role of adosrbed surface films is discussed, and it is deduced that drop break-up involves an interface from which the adsorbed surface film is removed.The viscosity of the dispersed phase can be important in determining droplet size, and this is treated theoretically. Results are compared with systems of practical interest, including milk and bitumen emulsions.The calculations support the contention that turbulence is the basic mechanism of drop break-up.     

金属诱导晶化基础与应用研究进展

将非晶半导体与金属相接触,可以诱导非晶半导体在极低的温度下结晶,这一现象被称为金属诱导晶化。薄膜状态的晶体半导体是用于众多先进技术中的关键材料,被广泛应用于微电子、光电子、显示技术和光伏技术等领域。金属诱导晶化为低温晶体半导体器件的制造、纳米多孔金属材料的合成以及金属材料界面工程提供了一种崭新的途径,引起了学术界和工业界的广泛关注。本文综述了金属诱导晶化的研究进展,对不同金属/非晶半导体体系中存在的金属诱导晶化现象进行了归纳分类总结,对其热力学原理和动力学机制进行了详细的计算与分析,突出了界面热力学在薄膜体系的固→固相变中的作用,最终阐明了金属诱导晶化过程的内在机理,并对金属诱导晶化过程未来的研究趋势进行了展望。     

Atomic-scale investigations of enhanced hydrogen separation performance from doping boron and nitrogen in graphdiyne membrane

Separation of hydrogen from gases mixtures is of great interest as hydrogen energy is among the most promising renewable energies. Graphdiyne shows huge potential as membrane for gas separation due to its uniform pore and atomic-scale thickness. In this work, hydrogen separation performance of graphdiyne, B-doped graphdiyne and BN-doped graphdiyne membranes are evaluated through first principles and molecular dynamics calculations. It is revealed that the selectivity of BN-doped graphdiyne to H₂ is much greater than those of graphdiyne and B-doped graphdiyne in this study and that of N-doped graphdiyne reported in previous work. The permeance of H₂ for the BN-doped graphdiyne membrane exceeds the industrial production limit at various temperatures. A high separation efficiency of H₂ can be achieved by reducing temperature below 275, 225 and 390 K for graphdiyne, B-doped graphdiyne and BN-doped graphdiyne membranes, respectively. Therefore, BN-doped graphdiyne is a prospective membrane for highly selective hydrogen separation at room temperature, and it is also demonstrated by molecular dynamics simulations of permeation process. This study provides an effective approach to evaluate selectivity and permeance of graphdiyne-based membranes for gases separation.     

The locally twisted thiophene bridged phenanthroimidazole derivatives as dual-functional emitters for efficient non-doped electroluminescent devices

A series of locally twisted dual-functional materials namely PIPT, PITT and PIFT have been designed and synthesized by introducing different polyaromatic hydrocarbon groups to a phenanthroimidazole backbone through a thiophene bridge. In these molecules, the thiophene bridge and phenanthroimidazole platform are nearly coplanar and this endows these materials with relatively shallow HOMO levels (−5.35 to −5.21 eV). On the other hand, the bulky polyaromatic hydrocarbon units introduce non-planar twisty structures which reduce molecular aggregations. These three materials show color-tunable emission (emission peak from 468 to 532 nm in film) and high thermal stability (T_g > 160 °C). Simple trilayer devices using these three phenanthroimidazole derivatives as non-doped emitting layers exhibit low turn-on voltages (2.3–2.7 V) and high maximum efficiencies of 3.74, 6.15 and 6.89 cd/A for PIPT, PITT and PIFT, respectively. Above all, owing to their shallow HOMO levels for enabling efficient hole-injection, even simpler bilayer devices employing these materials as hole-transporting emitters show low turn-on voltages (2.6–2.8 V) and high efficiencies of 5.77 cd/A for PIPT, 6.03 cd/A for PITT and 6.04 cd/A for PIFT, respectively. These comparable performances with those of the trilayer configurations show the efficient hole-injection/transport ability of these three newly developed emitters.     

Inkjet printed flexible electrodes for surface electromyography

Recording of surface ElctroMyoGraphic (sEMG) signal represents a challenge, due to the nature both stochastic and deterministic of the biopotential. The sEMG signal results from the superimposed activity of a high number of motor units, artifacts, and background noise. Among the different non-invasive techniques to measure the muscle electrical activity, recent studies showed how High-Density surface EMG (HD-sEMG) constitutes a very effective tool. HD-sEMG uses multiple closely spaced electrodes overlying a restricted area of the skin and provides high definition temporal and spatial information on muscle activity. To optimize the features of the current devices for HD-sEMG signal detection, this paper reports on the realization of the first inkjet printed HD electrode matrix. The matrix was built by inkjet printing of a commercial silver-based ink on a flexible Kapton® substrate. While bringing about all advantages of drop-on-demand inkjet technology, such as rapid prototyping and simple CAD re-desing of customizable devices, the printed matrix produces interesting electrical results in terms of resolution, resistance and electrode–skin contact impedance. Electrode–skin impedance obtained with our measurement setup was indeed always in line, while not better than the one obtained with commercial electrodes.     

Spin-charge disparity of polarons in organic ferromagnets

Polaron formation in quasi-one-dimensional organic ferromagnets is studied based on an extended Su–Schrieffer–Heeger model combined with a Kondo term. The charge distribution of the polaron is found to be highly asymmetric under spatial reflection, due to the spin radicals. On the contrary, the spin density is nearly symmetric; the spin asymmetry introduced by the extra electron inducing the polaron formation is nearly compensated by the spin polarization of the lower-energy states. We discuss these results on the basis of real-space mean-field calculations and symmetry arguments.     

Interfacial charging originated from the conductivity decrease of C60 layer in IZO/pentacene/C60/Al organic double-layer solar cells

The origin of interfacial charging process in double-layer organic solar cells (OSCs) was studied by using the normal structure of Indium–Zinc–Oxide/pentacene/C₆₀/Al and its inverted double-layer system. Optical electric-field-induced second-harmonic generation (EFISHG) measurement was employed and results suggested that interfacial charging in these two kinds of OSCs led to charge accumulation with opposite charge polarity, owing to the conductivity decrease of C₆₀ layer. Applying the EFISHG measurements to the inverted OSCs also showed that the significant charge accumulation on donor–acceptor interface is responsible for the low I–V performance of the inverted OSCs. Thus, Maxwell–Wagner type interfacial charging, which is governed by the conductivity of C₆₀, can cause the degradation of the I–V performance of OSCs. The protection of C₆₀ layer from the conductivity decrease is a way to improve OSCs performance.     

An energy-efficient virtual machine placement and route scheduling scheme in data center networks

The increasing requirements of big data analytics and complex scientific computing impose significant burdens on cloud data centers. As a result, not only the computation but also the communication expenses in data centers are greatly increased. Previous work on green computing in data centers mainly focused on the energy consumption of the servers rather than the communication. However, for those emerging applications with big data-flows transmission, more energy consumption could be consumed by communication links, switching and aggregation elements. To this end, based on data-flows’ transmission characteristics, we proposes a novel Job-Aware Virtual Machine Placement and Route Scheduling (JAVPRS) scheme to reduce the energy consumption of data center networks (DCN) while still meeting as many network QoS (Quality of Service) requirements as possible. Our proposed scheme focuses on not just migrating large data flows, but also integrating small data flows to improve the utilization rate of the communication links. With more idle switches turned off, DCN’s energy consumption will thus be reduced. Besides the data flows’ migration and integration, the Traffic Engineering (TE) technique is also applied to decrease the transmission delay and increase the network throughput. To evaluate the performance of our proposed scheme, a number of simulation studies are performed. Compared to the selected benchmarks, the simulation results showed that JAVPRS can achieve 22.28%–35.72% energy saving while reducing communication delay by 5.8%–6.8% and improving network throughput by 13.3%.