Optical joint density of states in InGaN/GaN-based multiple-quantum-well light-emitting diodes

The optical joint densities of states of three InGaN/GaN-based light-emitting diodes with different emission wavelengths (violet, blue and green) operated at various currents were investigated. The results indicate that the blueshift of the emission with increasing current is related to the variation in optical joint density of states. Thus, the blueshift is ascribed to the screening of the piezoelectric field by carriers. A tail at the low-energy end of the density of states, corresponding to localized states, was found, and the presence of these tails broadens the spectra of the devices.     

二甲基亚砜和四氢呋喃对胃蛋白酶催化动力学和分子光谱的影响

为了研究二甲基亚砜(DMSO)和四氢呋喃(THF)对胃蛋白酶(Pepsin, PP)催化活性的影响及其作用本质, 测定了在这两种有机溶剂的作用下胃蛋白酶的催化活性、 动力学参数、 紫外吸收光谱、 紫外差示光谱和荧光发射光谱的变化. 结果表明, 体积分数为9%的DMSO使PP活性提高83.4%; 而体积分数为1%的THF只能使PP活性提高3.59%. 在盐酸溶液中, PP的动力学参数K_m=2.22 mg/mL, v_max=1.1×10⁶ U/mg Pro; 在9%DMSO中, 其K_m=1.50 mg/mL, v_max=0.5×10⁶ U/mg Pro; 在1%THF中的K_m=1.91 mg/mL, v_max=0.51×10⁶ U/mg Pro. 9%DMSO强烈抑制PP分子肽键的紫外吸收, 而对芳香族氨基酸无影响; 1%THF则对PP的紫外吸收光谱影响不大. 9%DMSO和1%THF都使PP的紫外差示光谱出现明显的负吸收峰和正吸收峰. 9%DMSO使酶分子的荧光发射峰向短波方向移动1 nm; 而1%THF则对其无影响. 实验结果表明, 在9%DMSO和1%THF中, PP分子的立体构象发生了变化, 使酶分子的K_m下降, 酶分子对底物的亲和力有所升高, 从而导致酶分子的催化活性有不同程度的提高.     

Painleve Property and New Analytic Solutions for a Variable-Coefficient Kadomtsev--Petviashvili Equation with Symbolic Computation

A variable-coemcient Kadomtsev-Petviashvili equation is investigated. The Painlev6 analysis leads to its explicit Painlevd-integrable conditions. An auto-Backlund transformation and the bilinear form are presented via the truncated Painlev6 expansion and symbolic computation. Several families of new analytic solutions arepresented, including the soliton-like and periodic solutions.     

Stabilization of a high-spin three-coordinate Fe(iii) imidyl complex by radical delocalization

High-spin, late transition metal imido complexes have attracted significant interest due to their group transfer reactivity and catalytic C–H activation of organic substrates. Reaction of a new two-coordinate iron complex, Fe{N(^tBu)Dipp}₂ (1, Dipp = 2,6-diisopropylphenyl), with mesitylazide (MesN₃) afforded a three-coordinate Fe–imidyl complex, Fe{N(^tBu)Dipp}₂( NMes) (2). X-ray crystallographic characterization of single crystals of 2 showed a long Fe–N distance of 1.761(1) Å. Combined magnetic and spectroscopic (Mössbauer and X-ray absorption near edge structure spectroscopy, XANES) characterization of 2 suggests that it has an S = 2 ground state comprising an S = 5/2 Fe(iii) center antiferromagnetically coupled to an S = 1/2 imidyl ligand. Reaction of 1 and 1-azidoadamantane (AdN₃) generated a putative, transient Fe{N(^tBu)Dipp}₂( NAd) (3′) complex that yielded an intramolecular C–H amination product, Fe{N(^tBu)Dipp}{κ²-N,N′-_N(CMe₂CH_2̲NHAd)Dipp} (3). Quantum mechanical calculations further confirmed the spectroscopic assignment of 2 and 3′, as well as the differences in their stability and reactivity. Importantly, imidyl radical delocalization onto the mesityl ring significantly increased the stability of 2 and reduced its reactivity toward potential hydrogen atom transfer (HAT) reagents. In contrast, quantum mechanical calculations of 3′ revealed that the radical was solely localized on the imidyl N, leading to a high reactivity toward the proximal C–H bond of the N(^tBu)Dipp⁻ ligand.

A stable three-coordinate Fe imido radical (i.e. imidyl) complex can be stabilized via N radical delocalization onto the aryl imido substituent.     

Quantitative Detection of PremicroRNA-21 Based on Chimeric Molecular Beacon

As an important tumor marker, the expression level of premicroRNA-21 (pre-miR-21) can provide important information for early diagnosis, drug treatment and prognosis of tumor. Thus, developing pre-miR-21 detection is of great importance for diagnosis of disease. Herein, a direct, simple and rapid method for quantitative detection of pre-miR-21 was developed. This detecting system contained the tool of molecular beacon which could hybridize specifically with pre-miR-21 and form duplex to induce fluorescence signal change. When loop bases hybridized with the pre-miR-21 in the solution to form a double-stranded duplex, the fluorophore and the quencher was separated and caused fluorescence recovery. We developed the new method for pre-miR-21 assay with detection limit of 0.5 nM. Under the optimal conditions, the method was used to detect the level of pre-miR-21 in different tumor cells and tissues. The results showed that pre-miR-21 level was tightly related with tumor cells origins and malignancy degree. In 16 cases of gastric cancer tissues and adjacent tissues, the level of pre-miR-21 in 12 cases of cancer tissues was higher than that of adjacent tissues; 3 cases had lower expression level than that of adjacent tissues, and 1 case had no significant difference. Furthermore, Quantitative real-time PCR (qRT-PCR) method was used in to confirm the reliability of the detection results. The consistent results of the two different methods clearly showed that the molecular beacon assay with advantages of simplicity and rapidity for pre-miR-21 detection was hopeful for the wide usability in the function research and clinical diagnosis of pre-microRNA.     

FCC催化剂氢气还原活化脱镍研究

我国的FCC催化剂在使用中镍污染较为严重, 镍不仅会破坏催化剂的结构, 而且还会影响反应产物的分布, 增加企业的生产成本. 本研究提出了氢气还原活化＋稀硝酸洗涤的脱镍新方法, 具有良好的效果. 镍在FCC催化剂上以NiAl₂O₄和Ni₂SiO₄的形式存在, 这些物种在700 ℃以下就可以被氢气还原, 并且随着温度的升高, 不仅催化剂表面的镍能够被还原, 而且催化剂体相中的镍也可以迁移到表面从而被还原, 但这种迁移受到平衡的限制. 还原后生成的金属镍可以溶于稀硝酸, 因而可以洗涤除去. 在适宜的条件下, 经过一次还原＋酸洗处理, 脱镍率可达到50%以上; 经过两次处理, 脱镍率可达75%以上. 脱镍后催化剂的微反活性可以得到大幅度提高.     

Bridging the gap between mathematical conjecture and proof through computer-supported cognitive conflicts

In many mathematical problems, students can feel that the universalityof a conjecture or a formula is validated by their experimentand experience. In contrast, students generally do not feelthat deductive explanations strengthen their conviction thata conjecture or a formula is true. In order to cope up withstudents’ conviction based only on empirical experienceand to create a need for deductive explanations, we developeda problem-solving activity with technology support intendedto cause cognitive conflict. In this article, we describe theprocess conducted for this activity that led students to contradictionsbetween conjectures and findings. The teacher could create familiarproblem-solving situations and use students’ naïveinductive approaches to make students think mathematically andestablish the necessity for proof via computer support.     

Effects of tethering alkyl chains for amphiphilic ruthenium complex dyes on their adsorption to titanium oxide and photovoltaic properties

Ruthenium (II) complex dye, Ru(4,4'-dicarboxyl-2,2'-bipyridine)(4-nonyl-2,2'-bipyridine) (NCS)(2), (denoted as RuC9) tethering single alkyl chain was synthesized and well characterized. Its adsorption behavior onto the mesoporous TiO(2) and photovoltaic properties were compared with Z907 which has similar chemical structure but tethers two alkyl chains. RuC9 dyes tend to aggregate into vesicles in the acetonitrile/t-butanol co-solvent as a result of the amphiphilic structure, whereas Z907 dyes aggregate into lamellae. The dye-sensitized solar cell (DSSC) with RuC9 dye showed higher short-circuit photocurrent than that with Z907, attributing to its higher molar optical extinction coefficient and more adsorption amount onto the mesoporous TiO(2). However, the DSSC with Z907 dye has higher open-circuit photovoltage and power conversion efficiency, presumably due to the fact that Z907 with more alkyl chains formed a molecular layer with higher hydrophobicity. It reduced the charge recombination in the interface between the dye-sensitized mesoporous TiO(2) and electrolyte as verified by the electrochemical impedance spectroscopy and intensity modulated photocurrent and photovoltage spectroscopies.     

Proteomic analysis of chondrocytes exposed to pressure

Chondrocytes are the only cell type present in mature articular cartilage (2-5% of total tissue). The biological activities of the chondrocyte population are regulated by genetic, biologic and biochemical factors, as well as environmental factors (stress, flow and electric field). Although compressive forces within joint articular cartilage are required for maintenance of the normal composition of articular cartilage, there is a lack of knowledge about the number of pressure-related proteins expressed in articular cartilage. Two-dimensional gel electrophoresis (2-DE) and high-performance liquid chromatography-electrospray/tandem mass spectrometry (HPLC/ESI-MS/MS) were used to identify the levels of pressure-related proteins expressed by chondrocytes grown in the presence or absence of hydrostatic pressure. A total of 266 spots were excised from the gels and analyzed by HPLC/ESI-MS/MS. Functional classification of up-regulated proteins indicated that energy and protein fate were the main biological processes occurring in pressurized chondrocytes. Furthermore, membrane-bound transferrin-like protein p97, a marker of chondrocyte differentiation, was only expressed in chondrocytes under hydrostatic pressure. These data suggest that hydrostatic pressure can induce cell differentiation by increasing the expression level of energy metabolism- and protein fate-related proteins, indicating that hydrostatic pressure may be needed for normal biosynthesis and differentiation of articular chondrocytes.     

基于双分子信标对猪圆环病毒Ⅱ型的简单快速检测

根据猪圆环病毒(PCV2)基因组为单链DNA的特点,设计了两条可与PCV2基因组序列特异性杂交的分子信标,建立了基于双分子信标法检测PCV2的方法。实验结果表明,双分子信标法比单分子信标法的灵敏度更高。在10 mmol/L MgCl2、20 mmol/L Tris-HCl(pH=8.0)的杂交缓冲溶液,40℃孵育30 min的优化检测体系下,此方法可实现对检测样本在2~200 nmol/L线性范围内的检测,检出限可达1 nmol/L。将双分子信标检测体系用于18例可疑猪瘟样品病毒检测,其中8例呈PCV2阳性,检测结果与PCR法一致,证明此双分子信标法可用于实际猪感染PCV2的诊断。