CIS在瞬时多光谱爆温测量中的应用研究

对利用CMOS图像传感器进行爆温测量的方法进行了理论和实验研究。提出了一种更符合实际测量要求的瞬时多光谱爆温测量系统,并用激光器的特征谱线对系统进行了标定。利用该装置结合多光谱色温回归计算方法,测量了温度快速变化的卤钨灯的温度,得到了其随时间的变化曲线。     

Can preoperative diffusion-weighted MRI predict postoperative hepatic insufficiency after curative resection of HBV-related hepatocellular carcinoma? A pilot study

Liver fibrosis determines the functional liver reserve. Several studies have reported that the apparent diffusion coefficient (ADC) values of diffusion-weighted magnetic resonance imaging (DW-MRI) can assess liver fibrosis. We investigated whether DW-MRI predicts postoperative hepatic insufficiency and liver fibrosis in patients with hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC). Twenty-six patients with HBV-related HCC who received preoperative DW-MRI on a 3-T MRI system were enrolled between July and December 2008. ADC values were measured twice by two observers. Three “b values” were used: 50, 400 and 800 s/mm². Postoperative hepatic insufficiency was defined as persistent hyperbilirubinemia (total bilirubin level >5 mg/dl for more than 5 days after surgery) or postoperative death without other causes. The mean age (21 men and 5 women) was 51.4 years. Three patients experienced postoperative hepatic insufficiency. liver stiffness measurement predicted postoperative hepatic insufficiency, advanced fibrosis (F3–4), and cirrhosis significantly [area under the receiving operator characteristic curve (AUROC)=0.942, 0.771 and 0.818, respectively, with P=.047, 0.048 and 0.006, respectively]; ADC values of DW-MRI, however, did not (AUROC=0.797, 0.648 and 0.491, respectively, with P=.100, 0.313 and 0.938, respectively). Reliability of ADC values between right and left hepatic lobes (ρ=0.868 and ρ=0.910 in the first and second measures of Observer A; ρ=0.865 and ρ=0.831 in the first and second measures of Observer B) was high and the intra- and interobserver reliability (ρ=0.958 in observer A and ρ=0.977 in observer B; ρ=0.929 in the first measure and ρ=0.978 in the second measure between the two observers) were high. All reliability was significant (P<.001). Our results suggest that DW-MRI on a 3-T MRI system is not suitable for predicting postoperative hepatic insufficiency, advanced liver fibrosis, and cirrhosis in patients with HBV-related HCC, despite significantly high reliability.     

二硫化钼纳米点中的缺陷辅助载流子俘获超快动力学

二硫化钼纳米点正在成为有潜质的半导体材料用于光电设备的应用.然而,关于对其中激子动力学的研究却很少.本文利用飞秒瞬态吸收光谱学来研究二硫化钼纳米点的载流子动力学.结果显示,缺陷辅助的载流子再复合过程与观测到的动力学相符,通过俄歇散射对光激载流子进行俘获至少存在两种不同俘获速率的缺陷.四个过程参与了载流子驰豫,在受到光激发后,立即在~0.5 ps内载流子冷却,然后大部分载流子被缺陷快速俘获,随着泵浦能量的增加,该过程对应的时间从~4.9 ps增加到~9.2 ps,这可以用缺陷态的饱和来解释.接下来,拥有相对慢的载流子俘获速率的其它类型缺陷对小部分载流子进行俘获,该过程约65 ps.最后,剩余的少量载流子通过直接带间跃迁发生电子-空穴再复合,时间约为1 ns.研究结果可以深入了解二硫化钼纳米点中的载流子动力学基本原理,引导其更多的应用.     

Time-dependent Viscoelastic Behavior of an LDPE Melt

Two differential constitutive equations, i.e. Giesekus model and Johnson–Segalman model were employed here to predict the time-dependent viscoelastic behavior of an LDPE melt in thixotropy-loop experiments and step shear rate experiment. Multiple relaxation modes were adopted, and the parameters used to describe the nonlinear viscoelasticity in the two models were obtained by fitting the shear-thinning viscosity. The predictions on those transient shear characteristics by the two models are found in qualitative agreement with our previous experiments. Johnson– Segalman model predicts oscillation behavior in the thixotropy-loop and step shear rate experiments, whereas Giesekus model does not. Both models predict higher shear stresses than the experimental data in the case of long time shearing, implying that both models are not able to completely characterize the time-dependent shear stress of the melt at high shear rate.The project was supported by the National Natural Science Foundation of China (10402024, 50335010).The English text was polished by Yunming Chen.     

Chemically Fueled Autonomous Sol→Gel→Sol→Gel→Sol Transitions

Complex non-equilibrium phase behaviors are a hallmark of natural self-assembling systems. Here we show how intricate phase transitions can be achieved through a chemically fueled reaction cycle to yield autonomous sol→gel→sol→gel→sol transitions. A relay of chemical transformations based on thiazinane metathesis leads to two consecutive transient gelations in a closed system. Within seconds of fuel addition to deactivated thiazinane monomers, an imine-based hydrogel forms that consists of fibrillar microspheres. This gel quickly loses its mechanical strength and forms a solution, from which a second aldehyde-based gel nucleates and remains stable for over one day. Overall, our reaction cycle gives rise to two consecutive re-entrant phase transitions without any experimental intervention.     

Site-Selective C−H Functionalization of Carbazoles

Carbazole alkaloids hold great potential in pharmaceutical and material sciences. However, the current approaches for C1 functionalization of carbazoles rely on the use of a pre-installed directing group, severely limiting their applicability and hindering their overall efficiency. Herein, we report for the first time the development of direct Pd-catalyzed C−H alkylation and acylation of carbazoles assisted by norbornene (NBE) as a transient directing mediator. Notably, the involvement of a six-membered palladacycle intermediate was suggested in this case, representing the first example of such intermediacy within the extensively studied Pd/norbornene reactions realm.     

Enantioselective Hydroalkenylation and Hydroalkynylation of Alkenes Enabled by a Transient Directing Group: Catalyst Generality through Rigidification**

The catalytic enantioselective synthesis of α-chiral alkenes and alkynes represents a powerful strategy for rapid generation of molecular complexity. Herein, we report a transient directing group (TDG) strategy to facilitate site-selective palladium-catalyzed reductive Heck-type hydroalkenylation and hydroalkynylation of alkenylaldehyes using alkenyl and alkynyl bromides, respectively, allowing for construction of a stereocenter at the δ-position with respect to the aldehyde. Computational studies reveal the dual beneficial roles of rigid TDGs, such as L-tert-leucine, in promoting TDG binding and inducing high levels of enantioselectivity in alkene insertion with a variety of migrating groups.     

Photoinitiated Energy Transfer in Porous-Cage-Stabilised Silver Nanoparticles

We report a new composite material consisting of silver nanoparticles decorated with three-dimensional molecular organic cages based on light-absorbing porphyrins. The porphyrin cages serve to both stabilize the particles and allow diffusion and trapping of small molecules close to the metallic surface. Combining these two photoactive components results in a Fano-resonant interaction between the porphyrin Soret band and the nanoparticle-localised surface-plasmon resonance. Time-resolved spectroscopy revealed the silver nanoparticles transfer up to 37 % of their excited-state energy to the stabilising layer of porphyrin cages. These unusual photophysics cause a 2-fold current increase in photoelectrochemical water-splitting measurements. The composite structure provides a compelling proof of concept for advanced photosensitiser systems with intrinsic porosity for photocatalytic and sensing applications.     

Tuning of graphitic carbon nitride (g-C3N4) for photocatalysis: A critical review

Graphitic carbon nitride (g-C₃N₄) is a remarkable semiconductor catalyst that has attracted widespread attention as a visible light photo-responsive, metal-free, low-cost photocatalytic material. Pristine g-C₃N₄ suffers fast recombination of photogenerated electron-hole pairs, low surface area, and insufficient visible light absorption, resulting in low photocatalytic efficiency. This review presents the recent progress, perspectives, and persistent challenges in the development of g-C₃N₄-based photocatalytic materials. Several approaches employed to improve the visible light absorption of the materials including metal and non-metal doping, co-doping, and heterojunction engineering have been extensively discussed. These approaches, in general, were found to decrease the material’s bandgap, increase the surface area, reduce charge carrier recombination, and promote visible light absorption, thereby enhancing the overall photocatalytic performance. The material has been widely used for different applications such as photocatalytic hydrogen production, water splitting, CO₂ conversion, and water purification. The work has also identified various limitations and weaknesses associated with the material that hinders its maximum utilization under visible illumination and presented state-of-the-art solutions that have been reported recently. The summary presented in this review would add an invaluable contribution to photocatalysis research and facilitate the development of efficient visible light-responsive semiconducting materials.