Mechanical buckling usually means catastrophic failure in structural mechanics systems. However, controlled buckling of thin films on compliant substrates has been used to advantage in diverse fields such as micro‐/nanofabrication, optics, bioengineering, and metrology as well as fundamental mechanics studies. In this Feature Article, a mechanical buckling model is presented, which sprang, in part, from the buckling study of high‐quality, single‐crystalline nanomaterials. To check the mechanical‐buckling phenomenon down to the nano‐/molecular scale, well‐aligned single‐walled carbon nanotube arrays and cross linked carbon‐based monolayers are transferred from growth substrate onto elastomeric substrate and then they are buckled into well‐defined shapes that are amenable to quantitative analysis. From this nano‐ or molecular‐scale buckling, it is shown that the mechanical moduli of nanoscale materials can easily be determined, even using a model based on continuum mechanics. In addition, buckling phenomena can be utilized for the determination of mechanical moduli of organic functional materials such as poly(3‐hexylthiophene) (P3HT) and P3HT/6,6‐phenyl‐C61‐butyric acid methyl ester (PCBM) composite, which are widely used for organic transistors and organic photovoltaics. The results provide useful information for the realization of flexible and/or stretchable organic electronics. Finally, the fabrication and applications of “wavy, stretchable” single‐crystal Si electronics on elastomeric substrates are demonstrated. 相似文献
Although validation studies show that theoretical models for predicting the pKas of ionizable groups in proteins are increasingly accurate, a number of important questions remain: (1) What factors limit the accuracy of current models? (2) How can conformational flexibility of proteins best be accounted for? (3) Will use of solution structures in the calculations, rather than crystal structures, improve the accuracy of the computed pKas? and (4) Why does accurate prediction of protein pKas seem to require that a high dielectric constant be assigned to the protein interior? This paper addresses these and related issues. Among the conclusions are the following: (1) computed pKas averaged over NMR structure sets are more accurate than those based upon single crystal structures; (2) use of atomic parameters optimized to reproduce hydration energies of small molecules improves agreement with experiment when a low protein dielectric constant is assumed; (3) despite use of NMR structures and optimized atomic parameters, pKas computed with a protein dielectric constant of 20 are more accurate than those computed with a low protein dielectric constant; (4) the pKa shifts in ribonuclease A that result from phosphate binding are reproduced reasonably well by calculations; (5) the substantial pKa shifts observed in turkey ovomucoid third domain result largely from interactions among ionized groups; and (6) both experimental data and calculations indicate that proteins tend to lower the pKas of Asp side chains but have little overall effect upon the pKas of other ionizable groups. 相似文献
SAPO-34 is a crystalline microporous material, the characteristics of which are greatly influenced by synthetic parameters, especially the silica precursors and templates. In this study, the combination of templates and silica sources was optimized to obtain SAPO-34 phases in the purest form. The physicochemical properties of the thus-synthesized catalysts were characterized, and the Si environment in the SAPO-34 framework was analyzed. The catalytic performance in biomass gasification was investigated in a fixed-bed flow reactor. SAPO-34 synthesized with triethylamine/morpholine/tetraethylammonium hydroxide templates exhibited the highest total acidity, the smallest particle size, and high surface area, and produced a large amount of light hydrocarbons in biomass gasification. 相似文献
Durian (Durio zibethinus) fruit rinds are a promising source of bioactive phytochemicals, but they are currently wasted. This study optimised extraction conditions for flavonoids from durian fruit rinds and evaluated the biological activities of the flavonoid-rich extracts. The highest flavonoid content of 82.17 mg QE g−1 extract was achieved when performing the extraction at 60 °C using 75% ethanol and maceration time of 24 h. The crude ethanolic extract was then fractionated using liquid–liquid extraction to obtain three fractions (CHF, EAF and AQF). Among them, CHF demonstrated the highest amount of flavonoids (271.11 mg QE g−1 extract) and quercetin (1006.19 μg g−1 extract). This fraction also exhibited the highest ferric reducing power (IC50 of 307.88 μg vitamin C g−1), DPPH radical scavenging activity (IC50 of 38.72 μg mL−1), α-amylase and α-glucosidase inhibitory activity (IC50 of 685.76 μg mL−1 and 441.10 μg mL−1, respectively) and cytotoxicity against HepG-2 and MCF-7 cells with IC50 values of 490.30 μg mL−1 and 343.38 μg mL−1 respectively. The current work suggested that durian fruit rinds are a potential source of flavonoids and the CHF could be further used for pharmaceutical applications. 相似文献
In this reported work, two dual notched bands from 3.39 GHz to 3.92 GHz and from 4.43 GHz to 5.48 GHz for the WiMAX band (3.3–3.8 GHz) and for (lower) WLAN band (5.15–5.35 GHz) MIMO antenna with adjacent/orthogonal orientations has been investigated. Also, the proposed antenna is capable of controlling these notched bands whenever the need for power saving arises by reconfiguring them using PIN diodes. The issue of isolation between the radiating elements has been overcome by placing the radiating structures in the adjacent and orthogonal arrangement. The proposed antenna is characterized proving an average gain of 4.15/4.37 dBi and maximum radiation efficiency of 91/87% for adjacent/orthogonal orientation. The proposed antenna also shows good agreement with simulated and measured impedance bandwidth, diversity performances in terms of ECC, DG, TARC, and CCL for which values are well below the permissible range. 相似文献
Accelerating wound healing with minimized bacterial infection has become a topic of interest in the development of the new generation of tissue bio-adhesives. In this study, we fabricated a hydrogel system (MGC-g-CD-ic-TCS) consisting of triclosan (TCS)-complexed beta-cyclodextrin (β-CD)-conjugated methacrylated glycol chitosan (MGC) as an antibacterial tissue adhesive. Proton nuclear magnetic resonance (1H NMR) and differential scanning calorimetry (DSC) results showed the inclusion complex formation between MGC-g-CD and TCS. The increase of storage modulus (G’) of MGC-g-CD-ic-TCS after visible light irradiation for 200 s indicated its hydrogelation. The swollen hydrogel in aqueous solution resulted in two release behaviors of an initial burst and sustained release. Importantly, in vitro and in vivo results indicated that MGC-g-CD-ic-TCS inhibited bacterial infection and improved wound healing, suggesting its high potential application as an antibacterial tissue bio-adhesive. 相似文献
In this paper, we report the iron(III) chloride and dibutyl diselenide‐mediated cyclization of 1,3‐diynes which leads to 3,4‐bis(butylselanyl)selenophenes. The optimization studies showed that the reaction was best performed with equimolar amounts of iron(III) chloride and dibutyl diselenide in dichloromethane at 40 °C for 4 h. The method allows the synthesis of symmetrical and unsymmetrical selenophenes in moderate to good yields. A similar protocol was also extended to the synthesis of thiophene derivatives using dimethyl disulfide instead of dibutyl diselenide. The resulting selenophenes and thiophenes were further functionalized by selenium–halogen exchange reactions, Sonogashira cross‐coupling reactions and electrophilic cyclizations.
A double intramolecular 5‐endo‐dig cyclization of butyl[2‐(phenylbuta‐1,3‐diynyl)phenyl]chalcogens has been employed in a selective preparation of benzo[b]chalcogenopheno[2,3‐d]furans. Several reaction parameters were studied to determine the best reaction conditions and we observed that the reaction of butyl[2‐(phenylbuta‐1,3‐diynyl)phenyl]chalcogens (0.25 mmol) with iron(III) chloride hexahydrate (2.0 equiv.) and diorganyl diselenides (1.75 equiv.) at reflux of dichloromethane was the most appropriate to give the products in 35–89% yields. These standard reaction conditions were compatible with many functional groups in the substrates, such as methyl, chlorine, fluorine, methoxy and heteroaryl. This protocol was also efficient for diorganyl diselenides but it was ineffective with diorganyl disulfides and ditellurides. In a competition among selenium, sulfur and oxygen nucleophiles we observed that the nucleophilicity and steric effects of the competing functional groups were determinant factors for the selectivity of the cyclization. The benzo[b]chalcogenopheno[2,3‐d]furans had absorptions in the UV region (300–350 nm range) with molar absorptivity coefficient values ascribed to spin and symmetry allowed π–π* electronic transitions. An emission located in the purple region (380–440 nm range), with a Stokes shift of between 65–100 nm, is probably associated to the charge transfer character of the excited state.
Stretchable, elastomeric composite conductor made of multi-walled carbon nanotubes (MWNTs) and polydimethylsiloxane (PDMS) has been fabricated by simple mixing. Electrical percolation threshold, amount of filler at which a sharp decrease of resistance occurs, has been determined to be ∼0.6 wt.% of MWNTs. The percolation threshold composition has also been confirmed from swelling experiments of the composite; the equilibrium swelling ratio slightly increases up to ∼0.6 wt.%, then decreases at higher amount of filler MWNTs. Upon cyclic stretching/release of the composite, a fully reversible electrical behavior has been observed for composites having filler content below the percolation threshold value. On the other hand, hysteretic behavior was observed for higher filler amount than the threshold value, due to rearrangement of percolative paths upon the first cycle of stretching/release. Finally, mechanical moduli of the composites have been measured and compared by buckling and microtensile test. The buckling-based measurement has led to systematically higher (∼20%) value of moduli than those from microtensile measurement, due to the internal microstructure of the composite. The elastic conductor may help the implementation of various stretchable electronic devices. 相似文献
