On an analytic generalization of the Busemann-Petty problem

In this paper, we establish an extension of the connections between an analytic generalization of the Busemann-Petty problem and the positive definite distributions. Our results show that the structure of the positive definite distributions in Rn is closely related to the analytic generalization of the Busemann-Petty problem which was posed by Koldobsky.     

Bandwidth and stability enhancement of optical parametric amplification using chirped ferroelectric superlattice

We report a theoretical analysis and numerical simulation of bandwidth and stability enhancement in optical parametric amplification (OPA) when using chirped periodically poled KTiOPO₄. Calculation results show that the bandwidth and stability are enhanced significantly by the use of a chirped grating. Temperature-gradient and fanned gratings are introduced and chirp factors of them are deduced and calculated. The use of a fanned grating flattens the Quasi-phase-matching response and improves the efficiency. Finally, we propose a method to reduce the instability induced by an unstable pump.     

I-V curve oscillation observed by atomic force microscopy

Oscillation on the current-voltage curve measured by atomic force microscopy is observed when the distance between the tip and sample is large enough and beyond a critical value. The appearance of the oscillation is attributed to the excitation of electron standing waves between the tip and sample. From the first peak position and the voltage difference between the first two peaks on the current-voltage curve, the value of the work function at the detected point on silver film surface and the distance between the tip and the detected point can be calculated.     

Calculation of Specific Heat for Aluminium Thin Films

We employ Prasher＇s non-dimensional form to analyse the size effects on specific heat of Al thin films. Compared the calculation results of pure aluminium film with the experimental data, it is found that the reduction of phonon states is not the main reason of the size effect on the specific heat Al thin films with thickness from lOnm to 37Onm. However, the Al thin film in air usually has an oxidation layer and the specific heat of the layer is smaller than Al. By including the contribution of the oxidation layer to the thin-film specific heat, the calculation results are much closer to the experimental data. This may be a possible reason of the size effects on specific heat of Al thin films.     

Design,synthesis and biological evaluation of biphenylurea derivatives as VEGFR-2 kinase inhibitors(Ⅱ)

Inhibition of VEGFR-2 signaling pathway is one of the most promising approaches for the treatment of cancer. In this paper, we reported the design, synthesis, and biological evaluation of a series of biphenylurea derivatives as VEGFR-2 inhibitors. Among these compounds, 39 exhibited potent inhibitory activity against VEGFR-2 both in vitro and in vivo. The antiangiogenesis activity of 39 was further confirmed by both tube formation assay and chick chorioallantoic membrane assay.     

Synthesis and Characterization of a Fluorinated Phenolic Resin/phenolic Resin Blend

Fluorine atoms were introduced into the molecular chain of a phenolic resin (PR) by a two-step acid synthesis process to improve its thermal and hydrophobic properties. The successful synthesis of a fluorinated phenolic resin/phenolic resin blend (F-PR/PR) was proven by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance 19F (¹⁹F-NMR). The thermal properties of F-PR/PR were analyzed by differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA) and the results indicate that the F-PR/PR had good thermal stability. The hydrophobic properties of PR were effectively modified as demonstrated by the water drop contact angles. The flexural and tribological properties of F-PR/PR were also investigated. The fluorine atom, by virtue of its electronegativity, size and bond strength with carbon, can be used to create composites from F-PR/PR with remarkable properties. For comparison, two other resin blends were also synthesized.     

Thermal Degradation Behavior and Kinetics of Polybenzoxazine Based on Bisphenol-S and Allylamine

The thermal degradation behavior of polybenzoxazine based on bisphenol-S/allylamine was studied by Fourier transform–infrared spectroscopy and thermogravimetry–mass spectrometry. The reaction proceeded through detaching of Schiff bases and cleavage of aromatic C–S bonds and the Mannich bridge structures; the scission temperature of the aromatic C–S bond was lower than those of C–N and C–C bonds. The activation energy of the thermal degradation was evaluated with the Flynn–Wall–Ozawa method.     

Application of the Ru(bipy)2(dpp)2+ / C2O4 2− electrochemiluminescence reaction to the determination of phenol

The electrochemiluminescence (ECL) of the ruthenium di(2,2′-bipyridine)- (4,7-diphenyl-1,10-phenanthroline) complex (Ru-bipy-dpp) produced on a glassy carbon electrode was studied by cyclic voltammetry. The anodic oxidation of Ru-bipy-dpp produces ECL in the presence of oxalate in oxygen-free aqueous solutions. Threefold ECL efficiencies were obtained for Ru-bipy-dpp relative to Ru(bipy)₃ as a standard. The ECL of Ru-bipy-dpp is quenched by both oxygen and phenol. The luminescence intensity was proportional to the concentration of phenol in the range of 5–100 μM. At a phenol concentration of 100 μM, the ECL of Ru-bipy-dpp peaking at 597 nm was completely quenched. Correspondence: Dan Xiao, College of Chemistry and Chemical Engineering, Sichuan University, Chengdu 610065, P.R. China     

Photochemical reaction of cyclohexyl phenyl ketone within lyotropic liquid crystals

Lyotropic liquid crystals (LCs) formed by sodium dodecyl sulfate (SDS), n-pentanol, and H₂O at room temperature in their tertiary phase diagram have been explored as a confined medium for the typical photochemical reaction of cyclohexyl phenyl ketone (1), which can lead to either intramolecular hydrogen abstraction product 2 or intermolecular reduction product 3 in isotropic solutions upon irradiation. Studies on the product distributions of ketone 1 in the absence and presence of electron donors in this work demonstrate that LC not only restricts the movement of the substrates and intermediates but also encapsulates the substrates and electron donors together during photoirradiation, thereby giving rise to the formation of intermolecular hydrogen abstraction product 3 with high efficiency. A comparison of the same reaction in SDS micelle reveals that LC provides much better constraint than the micelles. The solution-like LC can be used as a microreactor to direct the reaction pathway of ketone 1 by controlling the viscosity and close contact between substrates and electron donors.     

Morphology transition and aggregation-induced emission of an intramolecular charge-transfer compound

An intramolecular charge-transfer (ICT) compound, (TCBD)2OPV3, has been synthesized and fabricated into one-dimensional nanotubes by a reprecipitation method. The observation of SEM and TEM showed the nanotubes were formed from their zero-dimensional precursors of hollow nanospheres. Reconstruction was found to happen during the morphology transition progress. The morphology transition and reconstruction are proposed to be a "curvature strain releasing" process driven by donor-acceptor dipole-dipole interactions. An aggregation-induced emission (AIE) effect was observed for (TCBD)2OPV3. Both aggregates of vesicles and nanotubes were observed to be good red emitters with near-infrared end emission of 750-850 nm, which endows the material with potential applications in the fields of optical devices, biosensors, and biolabels.