The carbonaceous residue (coke) formed on HZSM-5 during the conversion of methanol to gasoline was studied by 13 c n.m.r. spectroscopy using cross-polarization and magic angle spinning and by e.p.r. spectroscopy. Meas...
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The carbonaceous residue (coke) formed on HZSM-5 during the conversion of methanol to gasoline was studied by 13 c n.m.r. spectroscopy using cross-polarization and magic angle spinning and by e.p.r. spectroscopy. Measurements were made on samples with different coke contents and on samples from which some external coke had been removed by treatment with an oxygen plasma. It was found that the amount of carbon visible by n.m.r. differed from that expected from the measured coke contents and that the ratio of these amounts varied with the degree of coking. We concluded that the n.m.r.-visible carbon was most probably composed of methyl-substituted polycyclic aromatic hydrocarbons, the degree of methyl substitution and ring condensation changing with the coke content. It was inferred that these methyl-substituted polycyclic aromatics were present in the channels of the zeolite whereas the coke invisible to n.m.r. could be highly condensed polycyclic aromatics or “graphitic” structures on the external surfaces of the zeolite crystals. It appears that initial coke formation is internal and that external coke forms at latter stages in the deactivation process.
In this study, an efficient HPLc method was developed and validated to determine seven polyphenols, i.e. chlorogenic acid, caffeic acid, protocatechuic acid, geniposide, rutin, quercetin and isorhamnetin, in different...
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In this study, an efficient HPLc method was developed and validated to determine seven polyphenols, i.e. chlorogenic acid, caffeic acid, protocatechuic acid, geniposide, rutin, quercetin and isorhamnetin, in different parts (leaves, barks and fruits) of Eucommia ulmoides. A Luna c-18 column (150 mm x 3.9 mm, 5.0 mu m) was applied and eluted with a gradient of acetonitrile-modified aqueous mobile phase (containing 1% acetic acid). 260 nm, 326 nm, and 360 nm were used as the detection wavelengths. With the developed method, these seven polyphenols were successfully assayed and their contents in different parts of E. ulmoides were compared. The results showed that these polyphenols displayed different distribution in the leaves, barks and fruits. chlorogenic acid, caffeic acid and rutin were their main common constituents. ABTS and DPPH free radical scavenging assay indicated that E. ulmoides displayed significant antioxidant activities in vitro. In addition, the extracts of the three parts can significantly increase the anti-oxidative stress level in wild-type c. elegans and prolong its lifespan, further demonstrating the antioxidant activity of Eucommia ulmoides.
The multi-directional laminate ccF800H/Ac631 bismaleimide composite material was exposed for a long time under the thermal-cycling environment (-60 degrees c similar to+180 degrees c), and the mass loss rate, FTIR spe...
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The multi-directional laminate ccF800H/Ac631 bismaleimide composite material was exposed for a long time under the thermal-cycling environment (-60 degrees c similar to+180 degrees c), and the mass loss rate, FTIR spectra, DMA, tensile strength were tested. The fatigue stress level was determined according to the tensile strength and the fatigue performance of the before and after the thermal-cycling environment was tested. Macroscopic visual inspection and ultrasonicc-scan were used to characterize and analyze the fatigue damage of composite materials. The results show that with the increase in the number of thermal cycles, the mass loss of the composite material started with increased rapidly and then basically flat. The c/BMI composites underwent obvious thermal oxygen aging. After thermal-cycling, it would lead to changes in dynamic mechanical properties by a certain degree of post-curing, physical aging, and local interface debonding in composite materials. With the thermal cycles increased the composite material tensile strength first increased slightly and then decreased rapidly. After 300 thermal cycles, the composite materials occurred slightly damaged, and the fatigue life was apparently reduced compared with the original state. The fatigue failure modes of composite materials are mainly fiber fracture and multi-directional laminate delamination. At high stress levels, the stiffness of the specimen after thermal-cycling are lower decrease compared with original specimens, more stress levels would lead to more II stage rate of stiffness decline, and stiffness degradation curve and hysteretic energy recovery curve had enough effect to characterize damage effect of material environment induced by thermal-cycling environment factors.
In order to improve the mechanical and ablative resistance of c/ccomposites, (Hf-Ta-Zr)c single-phase solid solution ceramics were introduced into c/ccomposites by polymer infiltration and pyrolysis (PIP) to fabrica...
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In order to improve the mechanical and ablative resistance of c/ccomposites, (Hf-Ta-Zr)c single-phase solid solution ceramics were introduced into c/ccomposites by polymer infiltration and pyrolysis (PIP) to fabricate (Hf-Ta-Zr)c modified c/ccomposites (HTZ). Their mechanical property and ablation resistance were studied. The results showed that HTZ achieved simultaneous enhancement of mechanical property and ablative resis-tance. Their flexural strength and modulus could reach 219.34 MPa and 24.82 GPa, respectively. In addition, the mass and linear ablation rate of HTZ were 0.379 mg/s and 0.667 mu m/s, respectively after the 90 s oxyacetylene ablation. A dense Hf-Ta-Zr-O multiphase oxide layer was formed on the surface of the HTZ during ablation process, which protected the interior modified c/ccomposites from ablation. Our work expands a rational design of modified c/ccomposites and broaden the application of solid solution ceramic in the field of ultra-high temperature ablation resistance for carbon or ceramic-based composites.
Due to the high speed and high pressure operating conditions, wear between the finger seal and the rotor is inevitable, and this leads to an increase of leakage clearance and becomes an important factor affecting the ...
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Due to the high speed and high pressure operating conditions, wear between the finger seal and the rotor is inevitable, and this leads to an increase of leakage clearance and becomes an important factor affecting the seal life. The theory of anisotropic elasticity was employed to describe the mechanical characteristics of the seal material. An improved Archard wear model was proposed to calculate the nodal wear rate, and the local wear direction was also determined. The wear simulation model and procedure were established based on the Arbitrary Lagrangian Eulerian adaptive mesh strategy. The effects of material density, fabric orientation, pressure differential and rotor speed on the wear characteristics of finger seal and the change of leakage clearance caused by wear loss were studied. The results show that the wear first occurs at the heel area of the finger foot bottom and gradually extends to the toe area. c/c (carbon fibre reinforced carbon matrix) composite finger seal with higher material density has smaller leakage clearance and wear depth. With the increase of fabric orientation angle, the wear depth in the heel area of finger foot is smaller, and the circumferential wear area is narrower. The average wear depth of finger seal decreases with the orientation angle. When the orientation angle is 0, the seal leakage clearance is smaller. The increase of pressure differential not only aggravates the seal wear, but also expands the wear area, and also increases the average contact pressure and leakage clearance. Increasing the rotor speed make the wear depth of the heel area of finger foot gradually increase, but the wear area becomes narrower. The average contact pressure decreases and the average leakage clearance increases. This study provides a theoretical method and basis for the prediction and evaluation of the wear life and performance of c/ccomposite finger seal.
This paper reports the temperature dependence of d.c. and a.c. conductivity in the glassy alloys of Se70Te30 and Se70Te28M2 (M = cd, Sb, Zn). The role of the cd, Sb, Zn elements as foreign atoms has been examined on t...
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This paper reports the temperature dependence of d.c. and a.c. conductivity in the glassy alloys of Se70Te30 and Se70Te28M2 (M = cd, Sb, Zn). The role of the cd, Sb, Zn elements as foreign atoms has been examined on the d.c./a.c. conduction and photoconduction in binary Se70Te30 glass. These multi-component chalcogenide glasses have been prepared by conventional, cost-effective and well-known melt-quench technique. Thermally activated a.c. conduction shows the presence of the compensation effect that is confirmed by the Meyer-Neldel relation between the associated activation energy and the pre-factor of a.c. conductivity. The metal-induced effects of cd, Sb, Zn on the photosensitivity of parent glass are also discussed.
Several leaves and shoot spot symptoms were observed on tomato (Lycopersicon esculentum Mill) plants at Zubair and Safwan farms in Basrah, Iraq. The symptomatic plant parts were collected from different varieties of t...
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Several leaves and shoot spot symptoms were observed on tomato (Lycopersicon esculentum Mill) plants at Zubair and Safwan farms in Basrah, Iraq. The symptomatic plant parts were collected from different varieties of tomato. The fungal pathogens were first isolated on PDA medium followed by a diagnosis procedure of the relevant fungi conducting phenotypiccharacterization and microscopic featuring. A molecular identification was applied by polymerase chain reaction technology using internal transcribed spacer sequences. All along an investigation on cladosporium species, three species including c. cladosporioides, c. oxysporum, and c. uredinicola were identified and recorded as new potential pathogen for the first time in Iraq causing leaf spot and lesion of tomato plant. Pathogenicity examination of each isolated pathogens was performed against of tomato plant. The importance of the current research is to investigate and identify the fungal pathogens of tomato plants to find the best protocols to restrict their growth and damage.
The reductions of cytochrome c by a series of derivatives of Fe(EDTA)2- complex have been studied by a stopped-flow technique. The reactions of cytochrome c with Fe(EDTA)2-, Fe (cDTA)2- and Fe(IDA)22- present typical ...
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The reductions of cytochrome c by a series of derivatives of Fe(EDTA)2- complex have been studied by a stopped-flow technique. The reactions of cytochrome c with Fe(EDTA)2-, Fe (cDTA)2- and Fe(IDA)22- present typical outer sphere mechanism, meanwhile the cytochrome c(III) and Fe(NTA)- system shows abnormal kinetic behavior, including the rate saturation, big negative entropy and lower overall charge and binding site charge calculated from the dependence of electron transfer rate on ionic strength. On the basis of these observations a semi-inner-sphere mechanism is proposed to illustrate the kinetics.
In order to investigate the effects of preform structures on the mechanical and ablation properties of c/Zrc-Siccomposites, 3D4X, 3D5X and 3DZcc/Zrc-Siccomposites were fabricated with the same process. The mechanic...
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In order to investigate the effects of preform structures on the mechanical and ablation properties of c/Zrc-Siccomposites, 3D4X, 3D5X and 3DZcc/Zrc-Siccomposites were fabricated with the same process. The mechanical and ablation properties of 3D4X, 3D5X, and 3DZcc/Zrc-Siccomposites were investigated. Results showed that the tensile strength (122.26 MPa) and bending strength (233.29 MPa) of 3D5X c/Zrc-Siccomposites were the largest, followed by the tensile strength (112.79 MPa) and bending strength (203.03 MPa) of 3DZccomposites and the tensile strength (86.22 MPa) and bending strength (137.59 MPa) of 3D4X composites. The mechanical properties of c/Zrc-Siccomposites were mainly related to the fiber content in the axis direction and matrix compactness. In terms of ablation properties, 3DZcc/Zrc-Siccomposites acted out the worst performance (the linear ablation rates of 0.0293 mm/s and the mass ablation rates 0.00766 g/s), followed by 3D4X composites (the linear ablation rates of 0.0276 mm/s and the mass ablation rates 0.00683 g/s) and 3D5X composites (the linear ablation rates of 0.0175 mm/s and the mass ablation rates 0.00653 g/s), respectively, which were mainly due to the specific ablation angles, thermal conductivities, and ablation oxides contents caused by fiber volume fraction, braided angles, and other forming parameters.
Fullerols of c 60 and of c 70 \ [c 60 (OH)\-\%n\%, c 70 (OH)\-\%m\%], water\|soluble fullerene derivatives, unlike some other fullerene derivatives (such as c 60 (c\-4H\-6O), c 60 (c\-3H\-7N) and c 60 [c(cOOEt)\-2]\-\...
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Fullerols of c 60 and of c 70 \ [c 60 (OH)\-\%n\%, c 70 (OH)\-\%m\%], water\|soluble fullerene derivatives, unlike some other fullerene derivatives (such as c 60 (c\-4H\-6O), c 60 (c\-3H\-7N) and c 60 [c(cOOEt)\-2]\-\%x\%), do not result in excited triplet state but in ionization via monophotonic process in aqueous solutions with 248 nm laser. The quantum yields of formation of hydrated electron ( Φ e - ) are determined to be 0.08 and 0.11 for fullerols of c 60 and of c 70 respectively at room temperature (ca. 15℃) with KI solution used as reference. By laser flash photolysis and oxidation of sulfate radical anion SO -· \-4, the fullerol radical cation or neutral radical of c 60 is confirmed to be existent and the transient absorption spectra of fullerol radical cation of c 70 are observed for the first time.
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