The reaction kinetics of the oxidative dehydrogenation of propane was studied at 475-550℃ over a VMgO catalyst. Vanadium-magnesium-oxides are among the most selective and active catalysts for the dehydrogenation of propane to propylene. Selectivity to propylene up to about 60% was obtained at 10% conversion, but the selectivity decreased with increasing conversion. No oxygenates were detected, the only by-products were CO and CO2. The reaction rate of propane was found to be first order in propane and close to zero order in oxygen, which is in agreement with a Mars van Krevelen mechanism with the activation of the hydrocarbon as the rate determining step. The activation energy of the conversion of propane was found to be 122±6 kJ/mol. 相似文献
Quorum sensing (QS) is the communication between bacterial cells governed by their population density and regulated by the genes controlling virulence factors and biofilm formation. Multiple mechanisms of biofilms are resistive to antimicrobial chemotherapy; therefore novel strategies are required to overcome its limitations. Here, we report the effect of various copper oxide nanostructures (CuO-NSs) on quorum sensing inhibition. The two-dimensional CuO-NSs such as interlaced nanodiscs, nanodiscs and leaf-shaped nanosheets are prepared via a simple chemical method. The Quorum sensing inhibition (QSI) activity of all the CuO-NS are examined using reporter strain Chromobacterium violaceum CV026 and Escherichia coli pSB1142. We found that the CuO-interlaced nanodisc structures exhibit better QSI activity than nanodiscs and leaf-shaped sheets. The interlaced nanodisc structures are inhibited various long-chain N-acyl homoserine lactones (AHLs) mediated QS individually and confirmed by other QS-associated phenomena for Pseudomonas aeruginosa, including biofilm inhibition, inhibition of virulence factors such as pyocyanin, protease production and swarming motility. Thus QSI activity of CuO-NSs is solely dependent on specific shape offering large surface area and more active sites. The CuO-NS is effective quorum sensing inhibitors, which has potential clinical applications in the management of P. aeruginosa associated infections.
The paper deals with the comparative study of nanocrystalline Lanthanum hexaboride (LaB6) thin films grown on various substrates by Pulsed laser deposition and Arc plasma method. Field emission studies were carried
out on LaB6 films deposited on various substrates show metallic behavior of the emitters. The high value of field enhancement factors,
indicating that the electron emission from LaB6 nanoscale protrusions deposited on emitter surface. The post field emission surface morphology of the emitters showed no
significant erosion of the films during continuous operation. The observed behavior indicates that it is linked with the growth
of LaB6 films on substrate crystal structure. The LaB6 nanocrystallites/nanowires films were synthesized using arc plasma method shows good emission current stability. The LaB6 micro/nanocrystallites were also obtained by picosecond laser irradiation which gives high enhancement β factor, and good emission current stability along with high current density. The results reveal that nanocrystalline LaB6 films, exhibit high resistance to ion bombardment and excellent structural stability and are more promising emitters for
practical applications in field emission based new generation devices. 相似文献
7‐Alkanoyloxy‐3,7‐dimefhyl‐7,8‐dihydro‐6H‐isochromene‐6,8‐diones 12‐15 were synthesized in 69‐16% yields from the reaction of 2,4‐dihydroxy‐3‐methyl‐6‐(2‐oxopropyl)benzaldehyde 11 with p‐toluenesulfonic acid in various carboxylic acids such as acetic acid, propionic acid, butyric acid and heptanoic acid followed by oxidation with lead tetraacetate. On the other hand, (±)‐daldinin A 5 (oleate) was not obtained using oleic acid as a medium. In the cases of heptanoic acid and oleic acid, esters 16 and 17 were produced in 23 and 9% yields, respectively. 6,8‐Dihydroxy‐3,7‐dimethyl‐2‐benzopyrylium p‐toluenesulfonate 31 is considered as the intermediate for the production of 12‐15. Overall yields of isochromenes 12‐15 were 26‐6% starting from 2‐methylresorcinol for seven steps. 相似文献
Numerical investigations on the effects of liquid superheat during solidification of a pure metal (tin) in a square cavity have been performed. Natural convection in the melt is established in a small time compared to the duration of solidification. At high degrees of superheat (ΔTsup>0.5) the average Nusselt number at the hot wall is practically invariant with time and is correlated by . Multi-cellular flow structure with peaks in the Nusselt number is predicted in the narrow melt for low values of ΔTsup. A modified superheat parameter, , suggested in the present study for the estimation of solidified volume has been found to be satisfactory. Correlations for the evolution of solid volume with time have been developed. 相似文献
Lanthanum hexaboride (LaB6) nanocrystallites/nanowires have been successfully synthesized using gas phase condensation in arc plasma. Our results show
that the LaB6 nanowires have ~20 nm diameter and length of several micrometers. The as-synthesized LaB6 nanocrystallites and nanowires are crystalline in nature. Field emission studies were carried out on as synthesized LaB6 nano-powder deposited on W and Re tips and foils, and also on Si foil substrates under ultra high vacuum. The Fowler–Nordheim
plots obtained from the current–voltage characteristics are found to be linear in accordance with the quantum mechanical tunneling
phenomenon. High value of field enhancement factor (8177) is observed for LaB6 on Re substrate, indicating that the electron emission is from the nanometric features of the LaB6. Our results show that the arc plasma synthesized LaB6 nanocrystalline film exhibits good emission stability as emitter without severe deviations from the initial set value and
also a strong ability to withstand the ion bombardment, which is useful for low operation voltage vacuum micro/nano electronic
devices. 相似文献
Field emission studies of WO2.72 nanowires synthesized by a solvothermal method have been performed in the planar diode configuration under ultra high vacuum
conditions. Fowler–Nordheim plots obtained from the current-voltage characteristics follow the quantum mechanical tunneling
process and a current density of ∼8.3×106 μA/cm2 can be drawn at an applied electric field of 2 V/μm. The field enhancement factor is 33025, while the turn-on field is only
1.4 V/μm. The emission current-time plot recorded at the pre-set value of emission current of 1 μA over a period of more than
3 h exhibits an initial increase and a subsequent stabilization of the emission current. The results reveal that the WO2.72 nanowire emitters synthesized by the solvothermal method are promising cathode materials for practical applications. 相似文献
The physicochemical properties and dissolution profile of zaleplon (ZPN) β-cyclodextrin (βCD) inclusion complex were investigated. The phase solubility profile of ZPN with β-cyclodextrin was classified as AL-type. Stability constant with 1:1 molar ratio was calculated from the phase solubility diagram and the aqueous solubility of ZPN was found to be enhanced by 714% (p < 0.001) for β-cyclodextrin. Binary systems of ZPN with βCD were prepared by kneading method. The solid-state properties of complex were characterized by differential scanning calorimetry, Fourier transformation-infrared spectroscopy and powder X-ray diffractometry. It could be concluded that ZPN could form inclusion complex with β-cyclodextrin. The dissolution profile of inclusion complex was determined and compared with those of ZPN alone and its physical mixture. The dissolution rate of ZPN was significantly increased by complexation with βCD, as compared with pure drug and physical mixture. 相似文献
Nanocrystalline ZnO thin films have been deposited on rhenium and tungsten pointed and flat substrates by pulsed laser deposition
method. An emission current of 1 nA with an onset voltage of 120 V was observed repeatedly and maximum current density ∼1.3 A/cm2 and 9.3 mA/cm2 has been drawn from ZnO/Re and ZnO/W pointed emitters at an applied voltage of 12.8 and 14 kV, respectively. In case of planar
emitters (ZnO deposited on flat substrates), the onset field required to draw 1 nA emission current is observed to be 0.87
and 1.2 V/μm for ZnO/Re and ZnO/W planar emitters, respectively. The Fowler–Nordheim plots of both the emitters show nonlinear
behaviour, typical for a semiconducting field emitter. The field enhancement factor β is estimated to be ∼2.15×105 cm−1 and 2.16×105 cm−1 for pointed and 3.2×104 and 1.74×104 for planar ZnO/Re and ZnO/W emitters, respectively. The high value of β factor suggests that the emission is from the nanometric features of the emitter surface. The emission current–time plots
exhibit good stability of emission current over a period of more than three hours. The post field emission surface morphology
studies show no significant deterioration of the emitter surface indicating that the ZnO thin film has a very strong adherence
to both the substrates and exhibits a remarkable structural stability against high-field-induced mechanical stresses and ion
bombardment. The results reveal that PLD offers unprecedented advantages in fabricating the ZnO field emitters for practical
applications in field-emission-based electron sources. 相似文献