An angular trapezoidal phase mask used for a wideband coronagraph is proposed. The azimuthal phase of the mask is double-periodic and has both trapezoidal and constant parts in each period. This kind of continuous phase distribution can be employed to avoid the abrupt phase variation of the 6-level phase distribution we proposed previously. Numerical calculations show that this more practical phase mask can still keep its superior performance in terms of starlight elimination, small inner working angle, and good achromatism. It is of great importance that there is no singularity in this kind of mask except for a singularity at the center. This mask design is close to real manufacturing conditions, and the process technology is superior. 相似文献
Poly(?-caprolactone) grafted poly(2-hydroxyethyl methacrylate) functionalized hydroxyapatite (HAP@PHEMA-g-PCL) nanocomposites were synthesized by the combination of reversible addition fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP). The RAFT agent was anchored on the surface of hydroxyapatite nanocrystals (HAPs) through the silane condensation process of 3-chloropropyltrimethoxysilane followed by reaction with potassium xanthogenate. Poly(2-hydroxyethyl methacrylate) (PHEMA) was covalently functionalized on the surface of HAPs by RAFT polymerization. Then, poly(?-caprolactone) (PCL) was grafted on HAPs by ROP based on the hydroxyl groups of PHEMA to afford HAP@PHEMA-g-PCL. The structure and composition of HAP@PHEMA-g-PCL nanocomposites were characterized by FT-IR, XRD, and TGA analyses. The morphology and formation of the polymer encapsulating HAPs were demonstrated from SEM and TEM images, while the 1H MNR analysis of the cleaved PHEMA-g-PCL confirmed the grafting. 相似文献
Binary polymer blends of hydrophobic poly(vinylidene fluoride) (PVDF) and hydrophilic poly(vinylpyrrolidone) (PVP) were prepared by melt blending. The crystallization behavior, mechanical properties and hydrophilicity of the binary blends were investigated using Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffractometry (WAXD), differential scanning calorimeter (DSC) scanning, non-isothermal crystallization kinetics, successive self-nucleation and annealing (SSA) fractionation, tensile tests and contact angle tests. The analysis of FTIR, WAXD, DSC scanning, non-isothermal crystallization kinetics and SSA fractionation showed that the addition of PVP greatly influenced the crystallization behavior of the sample. As the PVP content increased, the crystallization temperature, crystallization rate, degree of crystallinity, and the amount of thick lamellaes decreased gradually. Meanwhile, PVP favored the formation of β-phase of PVDF. The results of tensile test revealed that the addition of PVP increased the elongation at break of the sample, and lowered the yield stress. Besides, the result of contact angle test indicated that the hydrophilicity of PVDF was remarkably improved in the presence PVP. The relationship between crystallization behavior and the tensile behavior, hydrophilicity were discussed. 相似文献
The complexes [PdX2Py]2(di-NHC) (X = Br or Cl) in which di-NHC represents a di-N-heterocyclic carbene, featuring a rigid phenylene spacer between the carbene units, have been prepared from reactions of the corresponding diimidazolium halide salts with PdCl2 in pyridine. The molecular structures of three of the complexes were determined by X-ray diffraction studies. The influences of different substitutions and of the halide ligand (Br or Cl) on the structure and reactivity of the complexes have been studied. The catalytic activity of the binuclear palladium complexes was tested in the Mizoroki–Heck reaction of styrene with bromobenzene. 相似文献
A detailed theoretical study on the reaction mechanisms for the formations of H2O2 + 3O2 from the self-reaction of HO2 radicals under the effect of NH3, H3N···H2O, and H2SO4 catalysts was performed using the CCSD(T)/CBS//M06-2X/aug-cc-pVTZ method. The rate constant was computed using canonical variational transition state theory (CVT) with small curvature tunneling (SCT). Our results indicate that NH3-, H3N···H2O-, and H2SO4-catalyzed reactions could proceed through both one-step and stepwise routes. Calculated rate constants show that the catalyzed routes in the presence of the three catalysts all prefer stepwise pathways. Compared to the catalytic efficiency of H2O, the efficiencies of NH3, H3N···H2O, and H2SO4 are much lower due to their smaller relative concentrations. The present results have provided a definitive example of how basic and acidic catalysts influence the atmospheric reaction of HO2 + HO2 → H2O2 + 3O2. These results further encourage one to consider the effects of basic and acidic catalysts on the related atmospheric reactions. Thus, the present investigation should have broad implications in the gas-phase reactions of the atmosphere. 相似文献
Here we described the design and synthesis of a discrete 3D amphiphilic metallacage 4,in which the tetragonal prismatic frameworks act as the hydrophobic cores and the poly(ethylene glycol)(PEG)chains as the hydrophilic tails.The structure of 4 was characterized by 1H NMR,31P NMR and electrospray ionization time-of-flight mass spectrometry(ESI-TOF-MS).Notably,4 with its Iong PEG tails was subsequently ordered into micelles at a low concentration(1.20×10^-6 mol/L)in water.As the concentration and cultivation time increased,the micelles can further self-assembly into nanofibers and nanoribbons.Considering the dynamic property of the coordination bond,these structures show reversible transformation under external stimuli. 相似文献
In this study, a novel quad-stable energy harvester (QEH) is developed, in which its coordinates of equilibrium points can be user-defined like programming. This programmable feature distinguishes the proposed QEH from all reported magnet-type or buckling-type vibration energy harvesters. It has the advantage that it is easy to develop a high-performance QEH by appropriately programming these coordinate points and customizing a personalized QEH for different vibration environments. The dynamic model is established by the Ritz method and the Lagrange equation. The analytical steady periodic response is obtained by the average method. When the excitation acceleration is 2 m/s2, the peak power is 575 μW at 8.5 Hz. Also, the influence of the coordinate arrangement of the equilibrium points on the energy harvesting performance is studied. A formula that can quickly determine the equilibrium point coordinates is given, and the QEH designed according to this formula has superior performance. At last, the performance of the designed QEH is compared with other reported vibration energy harvesters. It shows that the QEH has a high average output power (287 μW), high normalized power density (59.8 μW/cm3/g2), and wide operating frequency range (8.4 Hz) among these harvesters.
The first bisgermylene with an acyclic structure was synthesized for the first time by one-pot, two-step ligand substitution reactions from the 1,4-dioxane complex of germanium dichloride. The reactions of the bisgermylene with organic halides gave corresponding oxidative addition products, and with organic dihalides gave oligomeric polyadditon products. 相似文献
Aqueous rechargeable zinc-ion batteries (ZIBs) provide high theoretical capacity, operational safety, low-cost and environmental friendliness for large-scale energy storage and wearable electronic devices, but their future development is plagued by low capacity and poor cycle life due to the lack of suitable cathode materials. In this work, a covalent organic framework (Tp-PTO-COF) with multiple carbonyl active sites is synthesized and successfully introduced in aqueous rechargeable ZIBs for the first time. Tp-PTO-COF delivers high specific capacities of 301.4 and 192.8 mA h g−1 at current densities of 0.2 and 5 A g−1, respectively, along with long-term durability and flat charge–discharge plateaus. The remarkable electrochemical performance is attributed to the abundance of nucleophilic carbonyl active sites, well defined porous structure and inherent chemical stability of Tp-PTO-COF. Moreover, the structural evolution and Zn2+ ion intercalation mechanism are discussed and revealed by the experimental analysis and density functional theory calculations. These results highlight a new avenue to develop organic cathode materials for high performance and sustainable aqueous rechargeable ZIBs.A covalent organic framework (Tp-PTO-COF) with carbonyl active sites was proposed as a novel cathode material and successfully applied in aqueous rechargeable zinc-ion batteries (ZIBs).相似文献
This review of the current status of conducting polymers will focus on recent progress which demonstrates that the initial promise of the late 1970's has become reality. Conducting polymers are now available as materials with truly unique properties: They combine the important electronic and optical properties of semiconductors and metals with the attractive mechanical properties and processing advantages of polymers. Conducting polymer blends based upon polyaniline (PANI) are a new class of materials in which the threshold for the onset of electrical conductivity (σ) can be reduced to volume fractions below 1%, well below that required for classical percolation (16% by volume for globular conducting objects dispersed in an insulating matrix in three dimensions). The origin of this remarkably low threshold for the onset of electrical conductivity is the self-assembled network morphology of the PANI polyblends which forms during the course of liquid-liquid separation. Since the average density of the conducting network near threshold is small, the conductivity increases smoothly and continuously over many orders of magnitude as the concentration of conducting polymer increases above threshold. The low percolation threshold and the continuous increase of σ(f) above threshold are particularly important; as a result of this combination, conducting polyblends can be reproducibly fabricated with controlled levels of electrical conductivity while retaining the desired mechanical properties of the matrix polymer.1-3)相似文献