Carbon-assisted morphological manipulation of CdS nanostructures and their cathodoluminescence properties

CdS nanostructures with different morphologies and sizes were successfully fabricated through a facile and effective carbon-assisted thermal evaporation method. Through simply changing the positions of silicon substrates, the temperatures and the effects of carbon in different zones were modified, and thus the morphologies of CdS nanostructures were varied from multipods to nanobrushes to nanocups. These nanostructures were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDS), X-ray powder diffraction (XRD) and Raman spectroscopy. Cathodoluminescence (CL) measurement shows that the as-grown CdS nanostructures display different luminescent properties. CdS multipods and nanocups show mainly green emission centered at 496 nm. However, nanobrushes exhibit predominant red emission band peaking at 711 nm. These interesting results show that carbon not only affected the growth process but also influenced the properties of CdS nanostructures.     

Theoretical studies on QSAR and mechanism of 2‐indolinone derivatives as tubulin inhibitors

The theoretical studies on three‐dimensional quantitative structure activity relationship (3D‐QSAR) and action mechanism of a series of 2‐indolinone derivatives as tubulin inhibitors against human breast cancer cell line MDA‐MB‐231 have been carried out. The established 3D‐QSAR model from the comparative molecular field analysis (CoMFA) shows not only significant statistical quality but also predictive ability, with high correlation coefficient (R² = 0.986) and cross‐validation coefficient (q² = 0.683). In particular, the appropriate binding orientations and conformations of these 2‐indolinone derivatives interacting with tubulin are located by docking study, and it is very interesting to find that the plot of the energy scores of these compounds in DOCK versus the corresponding experimental pIC₅₀ values exhibits a considerable linear correlation. Therefore, the inhibition mechanism that 2‐indolinone derivatives were regarded as tubulin inhibitors can be theoretically confirmed. Based on such an inhibition mechanism along with 3D‐QSAR results, some important factors improving the activities of these compounds were discussed in detail. These factors can be summarized as follows: the H atom adopted as substituent R₁, the substituent R₂ with higher electropositivity and smaller bulk, the substituents R₄–R₆ (on the phenyl ring) with higher electropositivity and larger bulk, and so on. These results can offer useful theoretical references for understanding the action mechanism, designing more potent inhibitors, and predicting their activities prior to synthesis. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

化学分析中的质量控制

从人、机、料、法、环、测6方面讨论了化学分析中质量控制手段,结合分析化学实验室多年的实践经验提出了具体的质量控制措施,对如何保证分析结果的准确性和可靠性进行了详细论述.     

Facile synthesis of PtRu/C electrocatalyst with high activity and high loading for passive direct methanol fuel cell by synergetic effect of ultrasonic radiation and mechanical stirring

The PtRu/C electrocatalyst with high loading (PtRu of 60 wt%) was prepared by synergetic effect of ultrasonic radiation and mechanical stirring. Physicochemical characterizations show that the size of PtRu particles of as-prepared PtRu/C catalyst is only several nanometers (2–4 nm), and the PtRu nanoparticles were homogeneously dispersed on carbon surface. Electrochemistry and single passive direct methanol fuel cell (DMFC) tests indicate that the as-prepared PtRu/C electrocatalyst possessed larger electrochemical active surface (EAS) area and enhanced electrocatalytic activity for methanol oxidation reaction (MOR). The enhancement could be attributed to the synergetic effect of ultrasound radiation and mechanical stirring, which can avoid excess concentration of partial solution and provide a uniform environment for the nucleation and growth of metal particles simultaneously hindering the agglomeration of PtRu particles on carbon surface.     

Superior high-rate cycling performance of LiFePO4/C-PPy composite at 55 °C

A facile chemical polymerization method was applied to prepare LiFePO₄/C-PPy composite using Fe(III)tosylate as oxidant. The as-prepared LiFePO₄/C-PPy sample with PPy content of approximately 4 wt% showed great rate capability with a discharge capacity of 115 mAh/g at 20C. High temperate cycling performance of the LiFePO₄/C-PPy sample was compared with bare LiFePO₄/C at 5C charge–discharge rate at 55 °C. The LiFePO₄/C-PPy cathode showed superior cycling stability with an initial capacity of 155 mAh/g. Ninety percentage of this initial capacity was retained after 300 cycles, compared to 40% of that of bare LiFePO₄/C. The LiFePO₄/C-PPy electrode showed stable discharge plateau voltage of 3.35–3.25 V vs. Li⁺/Li during long term cycling. The superior performance of the LiFePO₄/C-PPy electrode was due to the enhanced electrical conductivity, negligible iron dissolution and alleviated electrode cracking contributed by PPy coating.     

PtCeOx/C as a novel methanol-tolerant electrocatalyst of oxygen reduction for direct methanol fuel cells

A prominent methanol-tolerant characteristic of the PtCeO_x/C electrocatalyst was found during oxygen reduction reaction process. The carbon-supported platinum modified with cerium oxide (PtCeO_x/C) as cathode electrocatalyst for direct methanol fuel cells was prepared via a simple and effective route. The synthesized electrocatalysts were characterized by X-ray diffraction and transmission electron microscopy. It was found that the cerium oxide within PtCeO_x/C present in an amorphous form on the carbon support surface and the PtCeO_x/C possesses almost similar disordered morphological structure and slightly smaller particle size compared with the unmodified Pt/C catalyst.     

Chiral separation of raltitrexed by cyclodextrin-modified micellar electrokinetic chromatography

A rapid and effective method was developed for the chiral separation of raltitrexed (RD) enantiomers by carboxymethyl-beta-cyclodextrin (CM-β-CD)-modified micellar electrokinetic chromatography (MEKC). Optimization of conditions including the type and concentration of the chiral selector, concentration of sodium dodecyl sulfate (SDS), pH and concentration of the background electrolyte (BGE), capillary temperature, and applied voltage was investigated. The enantiomers of raltitrexed could be separated with satisfactory resolution and linear response by using 75 mM Tris-phosphate at pH 8.0 containing 30 mM SDS and 8 mM CM-β-CD as buffer system. Furthermore, the usefulness of this method was demonstrated in a purity test of a real synthetic drug sample. Figure Chiral separation of raltitrexed by CM-β-CD MEKC was optimized and applied to test the purity of a synthetic drug sample     

Direct numerical method for an inverse problem of a parabolic partial differential equation

A coefficient inverse problem of the one-dimensional parabolic equation is solved by a high-order compact finite difference method in this paper. The problem of recovering a time-dependent coefficient in a parabolic partial differential equation has attracted considerable attention recently. While many theoretical results regarding the existence and uniqueness of the solution are obtained, the development of efficient and accurate numerical methods is still far from satisfactory. In this paper a fourth-order efficient numerical method is proposed to calculate the function u(x,t) and the unknown coefficient a(t) in a parabolic partial differential equation. Several numerical examples are presented to demonstrate the efficiency and accuracy of the numerical method.     

The optimal ordering policy of the EOQ model under trade credit depending on the ordering quantity from the DCF approach

This paper discusses the optimum order quantity of the EOQ model that is not only dependent on the inventory policy but also on firm’ credit policy. Here, the conditions of using a discounted cash-flows (DCF) approach and trade credit depending on the quantity ordered are discussed. We consider that if the order quantity is less than at which the delay in payments is permitted, the payment for the item must be made immediately. Otherwise, the fixed trade credit period is permitted.     

On the interaction of deep water waves and exponential shear currents

A train of periodic deep-water waves propagating on a steady shear current with a vertical distribution of vorticity is investigated by an analytic method, namely the homotopy analysis method (HAM). The magnitude of the vorticity varies exponentially with the magnitude of the stream function, while remaining constant on a particular streamline. The so-called Dubreil–Jacotin transformation is used to transfer the original exponentially nonlinear boundary-value problem in an unknown domain into an algebraically nonlinear boundary-value problem in a known domain. Convergent series solutions are obtained not only for small amplitude water waves on a weak current but also for large amplitude waves on a strong current. The nonlinear wave-current interaction is studied in detail. It is found that an aiding shear current tends to enlarge the wave phase speed, sharpen the wave crest, but shorten the maximum wave height, while an opposing shear current has the opposite effect. Besides, the amplitude of waves and fluid velocity decay over the depth more quickly on an aiding shear current but more slowly on an opposing shear current than that of waves on still water. Furthermore, it is found that Stokes criteria of wave breaking is still valid for waves on a shear current: a train of propagating waves on a shear current breaks as the fiuid velocity at crest equals the wave phase speed. Especially, it is found that the highest waves on an opposing shear current are even higher and steeper than that of waves on still water. Mathematically, this analytic method is rather general in principle and can be employed to solve many types of nonlinear partial differential equations with variable coefficients in science, finance and engineering.