Two Regioisomeric π‐Conjugated Small Molecules: Synthesis,Photophysical, Packing,and Optoelectronic Properties

Two regioisomeric D₁‐A‐D‐A‐D₁ type π‐conjugated molecules (1,4‐bis{5‐[4‐(5‐fluoro‐7‐(5‐hexylthiophen‐2‐yl)benzo[c ][1,2,5]thiadiazole)]­thiophen‐2‐yl}‐2,5‐bis(hexyldecyloxy)benzene (Prox‐FBT) and 1,4‐bis{5‐[4‐(6‐fluoro‐7‐(5‐hexylthiophen‐2‐yl)benzo[c ][1,2,5]thiadiazole)]­thiophen‐2‐yl}‐2,5‐bis(hexyldecyloxy)benzene (Dis‐FBT)) are synthesized, by controlling the fluorine topology to be proximal or distal relative to the central core. The different F geometries are confirmed by the ¹H–¹H nuclear Overhauer effect spectroscopy (NOESY). Clearly different optical, electrochemical, and thermal transition behaviors are obtained, i.e., stronger absorption, deeper valance band (by ≈0.2 eV), and higher melting/recrystallization temperatures (by 7–20 °C) are observed for Dis‐FBT. The different intermolecular packing and unit cell structures are also calculated for the two regioisomers, based on the powder X‐ray diffraction and 2D grazing‐incidence wide‐angle X‐ray diffraction measurements. A tighter π–π packing with a preferential monoclinic face‐on orientation is extracted for Dis‐FBT, compared to Prox‐FBT with bimodal orientations. Different topological structures significantly affect the electrical and photovoltaic properties, where Prox‐FBT shows higher parallel hole mobility (2.3 × 10^?3 cm² V^?1 s^?1), but Dis‐FBT demonstrates higher power conversion efficiency (5.47%) with a larger open‐circuit voltage of 0.95 V (vs 0.79 V for Prox‐FBT). The findings suggest that small changes in the topological geometry can affect the electronic structure as well as self‐assembly behaviors, which can possibly be utilized for fine‐adjusting the electrical properties and further optimization of optoelectronic devices.     

Enhancing Oil Recovery by Low Concentration of Alkylaryl Sulfonate Surfactant without Ultralow Interfacial Tension

Surfactant flooding plays a critical role in chemically enhanced oil recovery over the last half century, with the widely accepted mechanism of ultralow interfacial tension (IFT) by forming middle-phase microemulsions with high concentration of a lead surfactant and a cosurfactant. However, it is found practically from field trials that high oil recovery efficiency can be obtained from low concentration surfactant flooding without forming microemulsions, and the principle behind has not been clearly unraveled yet. Here the solubilization of paraffin oil by the micelles formed with a commercial enhanced oil recovery surfactant, raw naphthenic arylsulfonates (NAS), was investigated using ultraviolet-visible (UV–Vis) spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). It is found that paraffin oil can be well solubilized inside the NAS micelles, and mainly localized in the hydrophobic core of the micelles. The solubilization capacity of NAS micelles increases with increasing its concentration, and the size of micelles increases, but morphology of the micelles remains spherical with increasing the amount of paraffin oil, along with an appearance transition from transparent to opaque until the maximum solubilization capacity is reached. Core flooding results with crude oil indicate that in the presence of 0.24 wt.% polymer, addition of 0.1, 0.2, 0.5, and 1.0 wt.% NAS can get oil recovery factor of 24.1%, 27.0%, 30.5%, and 38.3%, which increases linearly with increasing NAS concentration though with the interfacial tension values only in the magnitude of 10⁻² mN m⁻¹ level. These findings prove preliminarily micellar solubilization can help increasing oil recovery efficiency even without ultralow IFT.     

Piezoelectric properties and domain structure of the orthorhombic (K,Na,Li)(Nb,Ta,Sb)O3 single crystal

ABSTRACT

In this work, (K,Na,Li)(Nb,Ta,Sb)O₃ (KNLNTS) crystal is in the orthorhombic phase at room temperature. The orthorhombic-tetragonal phase transition temperature is 50.0°C, and the Curie temperature T_C of the tetragonal-cubic phase transition temperature is 253.8°C. The crystal is poled, the defects were “pinned” in specific position, and has positive effect in domain wall motions and better ferroelectric property (P_r is 6.49 µC/cm², E_c is 6.66 kV/cm). The domain configrations of the crystal were studied by means of a polarizing light microscopy (PLM), with poling along [100]_C direction.     

Nitrogen Codoped Unique Carbon with 0.4 nm Ultra‐Micropores for Ultrahigh Areal Capacitance Supercapacitors

A full understanding of ion transport in porous carbon electrodes is essential for achieving effective energy storage in their applications as electrochemical supercapacitors. It is generally accepted that pores in the size range below 0.5 nm are inaccessible to electrolyte ions and lower the capacitance of carbon materials. Here, nitrogen‐doped carbon with ultra‐micropores smaller than 0.4 nm with a narrow size distribution, which represents the first example of electrode materials made entirely from ultra‐microporous carbon, is prepared. An in situ electrochemical quartz crystal microbalance technique to study the effects of the ultra‐micropores on charge storage in supercapacitors is used. It is found that ultra‐micropores smaller than 0.4 nm are accessible to small electrolyte ions, and the area capacitance of obtained sample reaches the ultrahigh value of 330 µF cm^?2, significantly higher than that of previously reported carbon‐based materials. The findings provide a better understanding of the correlation between ultra‐micropore structure and capacitance and open new avenues for design and development of carbon materials for the next generation of high energy density supercapacitors.     

高校在社会可持续发展中的科技政策研究

高等院校在实施可持续发展战略中具有重要的地位和作用。实施可持续发展使得经济社会发展观念发生了根本性的变化。目前,高等院校与经济社会已建立了比较密切的合作方式,因此,高等院校要及时调整科技发展政策,以适应经济社会的发展,并为经济社会的可持续发展做出贡献。     

服务于风电系统的改进缓存替换算法研究

针对风电系统中缓存命中率较低等问题,在最近最少使用算法(Least Recently Used,LRU)、最不经常访问算法(Least Frequently Used,LFU)、SIZE以及Hybrid算法的基础上,提出了一种基于综合因素的替换算法FST(Frequency,Object Size,Access Time),从而解决了传统算法考虑因素单一、系统性能较低等问题。该算法结合了访问频率、对象大小、访问时间间隔及最久未访问等特性,并根据最近访问时间长短采取分段的处理方法。在风电系统的缓存服务器中,将FST算法与LRU,LFU和SIZE算法进行实验对比,实验结果显示FST算法在提高命中率、减少延迟时间方面具有更好的性能。     

机动车轴重测量设备的自动检定与管理系统

在机动车轴重测量设备的检定中,为了提高检测的准确性和效率,采用计算机和虚拟仪器开发了机动车轴重自动检定系统.设计了可以模拟轴重标准信号的自动加压装置,完成了称重传感器数据的自动采集和数据管理等功能.结果表明该系统能准确高效地测量机动车轴重数据,实现了测量设备的自动检定.     

Cache-Conscious Data Cube Computation on a Modern Processor

As the speed gap between main memory and modern processors continues to widen,the cache behavior becomes more important for main memory database systems(MMDBs).Indexing technique is a key component of MMDBs. Unfortunately,the predominant indexes—B~+-trees and T-trees—have been shown to utilize cache poorly,which triggers the development of many cache-conscious indexes,such as CSB~+-trees and pB~+-trees.Most of these cache-conscious indexes are variants of conventional B~+-trees,and have better cache perf...