High-performance enhancement-mode AlGaN/GaN MOS-HEMTs with fluorinated stack gate dielectrics and thin barrier layer

We present high-performance enhancement-mode AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistors (MOS-HEMTs) by a fluorinated gate dielectric technique. A nanolaminate of an Al₂O₃/La_xAl_1-xO₃/Al₂O₃ stack (x≈0.33) grown by atomic layer deposition is employed to avoid fluorine ions implantation into the scaled barrier layer. Fabricated enhancement-mode MOS-HEMTs exhibit an excellent performance as compared to those with the conventional dielectric-last technique, delivering a large maximum drain current of 916 mA/mm and simultaneously a high peak transconductance of 342 mS/mm. The balanced DC characteristics indicate that advanced gate stack dielectrics combined with buffered fluorine ions implantation have a great potential for high speed GaN E/D-mode integrated circuit applications.     

Effective numerical methods for elasto-plastic contact problems with friction

Several effective numerical methods for solving the elasto-plastic contact problems with friction are presented. First, a direct substitution method is employed to impose the contact constraint conditions on condensed finite element equations, thus resulting in a reduction by half in the dimension of final governing equations. Second, an algorithm composed of contact condition probes and elasto-plastic iterations is utilized to solve the governing equation, which distinguishes two kinds of nonlinearities, and makes the solution unique. In addition, Positive-Negative Sequence Modification Method is used to condense the finite element equations of each substructure and an analytical integration is introduced to determine the elasto-plastic status after each time step or each iteration, hence the computational efficiency is enhanced to a great extent. Finally, several test and practical examples are presented showing the validity and versatility of these methods and algorithms. The Project Supported by National Natural Science Foundation of China.     

结构安定分析的Galerkin边界元方法

基于Melan静力安定定理,利用Galerkin边界元方法建立了多组交变载荷作用下结构安定分析的下限计算格式.在给定载荷域的载荷角点所对应载荷作用下,采用Galerkin边界元法计算相应的虚拟弹性应力场,并且利用结构在Galerkin边界元弹塑性增量计算中同一增量步中不同迭代步之间的应力差作为自平衡应力场的基矢量,通过这些基矢量的线性组合构造了自平衡应力场,大大降低了所形成的数学规划问题的未知变量数.并通过复合形法对非线性规划问题直接进行求解,得到了结构在交变载荷作用下的下限安定乘子.计算结果表明,所采用的方法具有较高的精度和计算效率.     

确定裂纹体等效弹性模量的边界元方法

采用边界元方法计算含有序分布裂纹的裂纹体在压缩载荷作用下的等效弹性模量，利用一种能适当考虑裂纹有间相作用的自洽理论，建立了相应的迭代格式，通过算例研究了裂纹方向，裂纹面间摩擦系数对裂纹体等效弹性模量的影响。     

The variation in essential oils composition,phenolic acids and flavonoids is correlated with changes in antioxidant activity during Cinnamomum loureirii bark growth

Cinnamomum loureirii is one of the most important medicinal and aromatic plants. It is used by the food, perfumery, cosmetic, and pharmaceutical industries. The objective of this study was to examine the relationships between the chemical composition and antioxidant activity of essential oil (EOs) and ethanol extracts from 10 samples of the bark from C. loureirii trees (6–15 years old). Obtained results showed that C. loureirii bark EO content at 12–15 years old had high oil yields (4.52–5.48%). The major components in the EOs were trans-cinnamaldehyde (50.2–92.9%) and α-copaene (0.5–21.3%). The highest content of trans-cinnamaldehyde in bark EOs was obtained from 10 to 12-year-old trees, while the highest content of α-copaene was obtained at 13–15 years. The highest total phenolic (429.85 and 474.45 mg TAE /g DW) and total flavonoid contents (85.54 and 102.80 mg RE /g e DW) were obtained from the 13- to 14-year-old trees. Our results indicated that the EO and ethanol extract of 13- to 14-year-old bark showed the strongest antioxidant properties. Moreover, GC–MS, PCA and correlation analysis indicated that the changes in α-copaene, beta-caryophyllene, τ-muurolene, γ-muurolene, δ-cadinene and τ-muurolol were positively correlated with the changes in antioxidant activity in oils. Meanwhile, procyanidin B2 and hyperoside were the main contributors to the antioxidant activity of the ethanol extract from C. loureirii bark. This study is the first one that report the antioxidant potential and phenolic profile of C. loureirii plant. These results provide reference information for the rational utilization of C. loureirii resources and the harvest of C. loureirii bark as medicinal materials during the optimal period.     

Combinatorial identities from contour integrals of rational functions

We employ the theory of contour integrals to systematically investigate three kinds of general combinatorial identities in a unified way. As applications some well-known combinatorial identities are presented as special cases, and several new identities are derived.     

Polymer Vesicles with Upper Critical Solution Temperature for Near-infrared Light-triggered Transdermal Delivery of Metformin in Diabetic Rats

Near-infrared light(NIR)triggered transdermal drug delivery systems are of great interest due to their on-demand drug release,which enable to enhance drug treatment efficiency as well as reduce side effect.Herein,a NIR-triggered microneedle(MN)patch array has been fabricated through depositing the photothermal conversion agent and anti-diabetic drug-loaded polymer vesicles with upper critical solution temperature(UCST)into dissolvable polymer matrix.The UCST-type polymer has a clearing point temperature of 41℃ and the drug-loaded polymer vesicles present excellent NIR-triggered and temperature responsive drug release behavior in vitro due to the disassociation of polymer vesicles upon NIR irradiation.After applying MNs to diabetic rats,significant hypoglycemic effect is achieved upon interval NIR irradiation and the blood glucose concentration can decrease to normal state for several hours,which enables to achieve the goal of on-demand drug release.This work suggests that the NIR-triggered MN drug release device has a potential application in the treatment of diabetes,especially for those requiring an active drug release manner.     

Effect of microfluidizing cycles after citric acid hydrolysis on the production yield and aspect ratio of cellulose nanocrystals

Cellulose - In recent years, a new strategy of using citric acid (CA) to produce carboxylic cellulose nanocrystals (CNCs) has received attractive interest. However, mainly due to the weak acidity...     

钴基费托合成催化剂的表界面性质调控

合成气经费托合成(Fischer-Tropsch synthesis,FTs)转化为燃料和高附加值化学品是解决煤炭等资源清洁利用问题的重要途径,是现代煤化工的重要组成部分,对于降低石油进口依赖度,保证国家能源战略安全具有重要意义。钴基催化剂因活性高、链增长活性强、CO₂选择性低、寿命长等而成为目前研究最为广泛的FTs催化剂之一。如何通过调控表界面性质来打破还原度和分散度的依赖关系,提高催化剂的反应活性以及一定碳链范围内的产物选择性依然是高效钴基FTs催化剂开发面临的重要挑战。本文分别从结构敏感性(尺寸和晶面效应)、金属-载体间相互作用和限域效应三个方面阐述钴基FTs催化剂表界面性质调控策略的最新研究进展,以期为钴基FTs催化剂微观结构设计及反应性能调控提供理论依据。     

在均匀剪切流动中的Stokes波

本文从Euler方程出发讨论在均匀剪切流动中的Stokes波·把未知函数和波速展开成渐近级数,利用Fredholm择一定理来确定待定常数。得到了在均匀剪切流中二阶波形并研究了均匀剪切流对增水的影响。当流速为零时,本文的结果就退化为已有的在静水中的stokes波。