Liquid-Phase Transport During Removal of Organic Binders in Injection-Molded Ceramics

A method has been developed for calculating hydraulic pressures induced by thermal expansion of liquid binders early in the removal cycle, when evaporative losses are negligible and fully saturated conditions prevail. Specific results were obtained for flat compacts containing a common wax binder, mixed with varying amounts of low-density polyethylne. In general, these results show how the risk of hydraulic fracture increases with heating rate and compact thickness. Although pressures are minimal when the binder consists entirely of wax, the continual addition of polyethylene eventually gives rise to unacceptable risk levels, even for relatively thin compacts. Binder removal at elevated temperatures is considered subsequently. In this case, vapor pressures eventually approach a critical level, thereby allowing mass removal by evaporation to overcome the effect of thermal expansion in maintaining full saturation. With the onset of void formation, the developing capillary pressure supersedes hydraulic pressure as the driving force in liquid transport. Besides representing capillary flow, the present formulation also accounts for thermal degradation of the binder during removal. The resulting system of equations was solved numerically for a variety of representative debinding conditions. Predictions for flat compact containing a balanced wax/polyethylene binder indicate that thermal degradation of the polyethylene can give rise to a marked improvement in debinding rates. It turns out, however, that this enhancement is far more effective in thinner compacts.     

Separation of kinetics and mass-transfer in a batch alkoxylation reaction

The quantitative aspects of the role of interfacial mass-transfer and reaction kinetics in ethoxylation of lauryl alcohol were examined in a batch recirculation reactor. The liquid droplets falling through a gas column were obtained by utilizing a recirculation loop and a set of spray nozzles. The CO₂/NaOH reaction was employed to characterize the interfacial area. The alkoxylation reaction was studied at temperatures between 124°C and 171°C, at catalyst levels between 0.09 and 0.50 weight percent and at ethylene oxide partial pressures between 68 kPa and 204 kPa. A model was developed which permits the prediction of reactor performance at various operating conditions. The mass-transfer during free fall dominates the interfacial mass-transfer and the contributions during the drop formation and coalescence stages are small. The rate of ethylene oxide (EO) addition to lauryl alcohol was constant during the batch run, indicating similar activity for the unreacted lauryl alcohol and the lauryl alcohol ethoxylated to varying extents. The rate of ethoxylation is first-order in both catalyst and ethylene oxide concentrations. The liquid-phase reaction kinetics and interfacial mass-transfer occur in series, with kinetics dominating the overall ethoxylation rate. As expected, an increasing role of mass transfer is observed at higher temperatures, and/or higher catalyst concentrations where the kinetic rate becomes significantly high. The intrinsic activation energy for the ethoxylation of lauryl alcohol is 55.2 kJ/mole.     

基于RTP的流媒体传输系统的设计与实现

旨在解决流媒体实时传输的效率和系统的可拓展性问题。介绍了流媒体传输的基本协议RTP,并针对实时传输过程中的特殊要求,设计出了一种流媒体传输的结构模型,在流量控制、组包算法和缓存管理等方面进行研究,给出了详细的实现过程。     

光传送网络成帧器设计

针对超高速率的光传送网络(Optical Transport Network,OTN)数据信号,在研究光传送网络帧结构的基础上,提出了一种适合高速率、大位宽的成帧器处理电路,将48比特的FAS信号分为两部分进行比较,第一部分为64个24比特比较器,第二部分为一个24比特比较器。将电路的规模降低了一半,提高了电路的处理速率。通过软件仿真后,使用综合工具综合的结果显示,电路处理速率可达到235.74MHz。     

物理升华法生长ZnO晶体的研究

Zinc oxide（ZnO） has a wide band gap, high stability and a high thermal operating range that makes it a suitable material as a semiconductor for fabricating light emitting diodes（LEDs） and laser diodes, photodiodes, power diodes and other semiconductor devices. Recently, a new crystal growth for producing ZnO crystal boules was developed, which was physical vapor transport（PVT）, at temperatures exceeding 1500 ？C under a certain system pressure. ZnO crystal wafers in sizes up to 50 mm in diameter were produced. The conditions of ZnO crystal growth, growth rate and the quality of ZnO crystal were analyzed. Results from crystal growth and material characterization are presented and discussed. Our research results suggest that the novel crystal growth technique is a viable production technique for producing ZnO crystals and substrates for semiconductor device applications.     

Large-area,high-quality self-assembly electron transport layer for organic optoelectronic devices

We propose a self-assembly method for forming large-area high-quality solution-processed titanium oxide (TiO₂) films as efficient electron transport layer for organic solar cells. The self-assembled solution-processed TiO₂ layers are highly ordered and significantly improved in surface morphology over commonly-used spin-coating process resulting in better charge collection and significant material saving. When incorporated into polymer solar cells, the TiO₂ device shows enhanced performance. Furthermore, we demonstrate the TiO₂ can form large-area films, and achieve very uniform and improved device performances. Consequently, the self-assembled TiO₂ films can be efficient and low-cost electron transport layer potentially for large-area organic optoelectronics.     

Dihydroazulene Photoswitch Operating in Sequential Tunneling Regime: Synthesis and Single‐Molecule Junction Studies

Molecular switches play a central role for the development of molecular electronics. In this work it is demonstrated that the reproducibility and robustness of a single‐molecule dihydroazulene (DHA)/vinylheptafulvene (VHF) switch can be remarkably enhanced if the switching kernel is weakly coupled to electrodes so that the electron transport goes by sequential tunneling. To assure weak coupling, the DHA switching kernel is modified by incorporating p‐MeSC₆H₄ end‐groups. Molecules are prepared by Suzuki cross‐couplings on suitable halogenated derivatives of DHA. The synthesis presents an expansion of our previously reported bromination–elimination–cross‐coupling protocol for functionalization of the DHA core. For all new derivatives the kinetics of DHA/VHF transition has been thoroughly studied in solution. The kinetics reveals the effect of sulfur end‐groups on the thermal ring‐closure of VHF. One derivative, incorporating a p‐MeSC₆H₄ anchoring group in one end, has been placed in a silver nanogap. Conductance measurements justify that transport through both DHA (high resistivity) and VHF (low resistivity) forms goes by sequential tunneling. The switching is fairly reversible and reenterable; after more than 20 “ON‐OFF” switchings, both DHA and VHF forms are still recognizable, albeit noticeably different from the original states.     

“一带一路”背景下厦门港海铁联运的发展研究

文章对“一带一路”政策下厦门港海铁联运市场的发展机遇进行了分析, 结合厦门港的海铁联运发展现状, 探讨其发展过程中的瓶颈, 并提出了以“一带一路”为契机推动厦门港海铁联运发展的建议。     

Stacked graphene–TiO2 photoanode via electrospray deposition for highly efficient dye-sensitized solar cells

A series of TiO₂–graphene stacked photoanodes for dye-sensitized solar cells (DSSCs) were fabricated by electrospray (E-spray) deposition. Among devices incorporating single graphene layer with different deposition times, device with 1 min graphene deposition gave the best performance. For multi-graphene-layer involved devices, best result was obtained with 3 layers of graphene. The working principles were analyzed by scanning electron microscopy, transmittance spectra, electrochemical impedance spectroscopy and incident-photo-conversion efficiency data. We found that although graphene layers incorporated in TiO₂ photoanode slightly decreased dye adsorption, they were able to significantly improve the electron transport, and the charge recombination at the interfaces of TiO₂/dye and TiO₂/electrolyte were greatly suppressed, leading to dramatic improvement in power conversion efficiency. When inserting three layers of pure graphene into the TiO₂ photoanode, high efficiency of 8.9% was obtained, constituting an over 23.6% improvement. Further increasing graphene layers to five, although electron lifetimes is the longest, both the largest charge transfer resistance and the least amount of the dye loading lead to the lowest device efficiency. Our work demonstrated, that pure graphene layer can be successfully incorporated into TiO₂ photoanode by E-spray method with easiness of thickness control and the photoanode with graphene/TiO₂ alternatively layered structure is an excellent candidate for DSSCs.     

Linking Glass-Transition Behavior to Photophysical and Charge Transport Properties of High-Mobility Conjugated Polymers

The measurement of the mechanical properties of conjugated polymers can reveal highly relevant information linking optoelectronic properties to underlying microstructures and the knowledge of the glass transition temperature (T_g) is paramount for informing the choice of processing conditions and for interpreting the thermal stability of devices. In this work, we use dynamical mechanical analysis to determine the T_g of a range of state-of-the-art conjugated polymers with different degrees of crystallinity that are widely studied for applications in organic field-effect transistors. We compare our measured values for T_g to the theoretical value predicted by a recent work based on the concept of effective mobility ζ. The comparison shows that for conjugated polymers with a modest length of the monomer units, the T_g values agree well with theoretically predictions. However, for the near-amorphous, indacenodithiophene–benzothiadiazole family of polymers with more extended backbone units, values for T_g appear to be significantly higher, predicted by theory. However, values for T_g are correlated with the sub-bandgap optical absorption suggesting the possible role of the interchain short contacts within materials’ amorphous domains.