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1.
Preparation and Characterization of M-Type Barium Ferrite Fibers via Aqueous Sol-Gel Process 总被引：1，自引：0，他引：1
BaFe12O19 fibers was prepared via an aqueous sol-gel process using Fe(OH)(HCOO)2 synthesized in laboratory and Ba(CH3COO)2 as the original materials and citrate as the chelate. The rheological behaviour of spinnable sol was characterized on rheometer, and the development of gel fibers to barium ferrite fibers was studied by IR, TG and XRD. Morphology observation of the fibers was given on SEM, and the diameter of the obtained fibers was between 5 and 10 μm corresponding to different additives. The additives affected the surface tension of the precursor sol which had close relation to the microstructure of fibers. Sucrose and hydroxyethylic cellulose could improve the surface tension while diethanolamine and hexadecylamine reduce that of the precursor sol. And using diethanolamine or hexadecylamine as an additive, well-structured BaFe12O19 fibers could be obtained. 相似文献
2.
This study investigated characteristics of bifurcation and critical buckling load by shape imperfection of space truss,which were sensitive to initial conditions.The critical point and buckling load were computed by the analysis of the eigenvalues and determinants of the tangential stiffness matrix.The two-free-nodes example and star dome were selected for the case study in order to examine the nodal buckling and global buckling by the sensitivity to the eigen buckling mode and the analyses of the influence,and characteristics of the parameters as defined by the load ratio of the center node and surrounding node,as well as rise-span ratio were performed.The sensitivity to the imperfection of the initial shape of the two-free-nodes example,which occurs due to snapping at the critical point,resulted in bifurcation before the limit point due to the buckling mode,and the buckling load was reduced by the increase in the amount of imperfection.The two sensitive buckling patterns of the numerical model are established by investigating the displaced position of the free nodes,and the asymmetric eigenmode greatly influenced the behavior of the imperfection shape whether it was at limit point or bifurcation.Furthermore,the sensitive mode of the two-free-nodes example was similar to the in-extensional basis mechanism of a simplified model.The star dome,which was used to examine the influence among several nodes,indicated that the influence of nodal buckling was greater than that of global buckling as the rise-span ratio was higher.Besides,global buckling is occurred with reaching bifurcation point as the value of load ratio was higher,and the buckling load level was about 50%-70% of load level at limit point. 相似文献
3.
The tectonic stress patterns were determined by a fuzzy comprehensive assessment method. Data of in-situ survey and fault information were utilized in the method. First, by making pressure and tension in the directions of along-river, cross-river, shear clockwise, and shear counterclockwise , 26 types of tectonic stress patterns were presented. And the stress vector of each pattern was obtained with FE software by taking unit displacement as boundary load. Then, by taking the 26 types of tectonic stress patterns as index set and 3 main stresses as factor set and choosing various operators, comparison of directions of computational stress vector and survey stress vector was made and the most possible tectonic stress pattern was obtained. Taking the 26 types of tectonic stress patterns as index set and strike angle as factor set, comparison of relationships between formation of fault and tectonic stress was made,and the tectonic stress patterns were assessed with known fault information. By summarizing the above assessment results, the most impossible tectonic stress pattern was obtained . Finally an engineering case was quoted to validate that the method is more feasible and reliable than traditional empirical method. 相似文献
4.
杨建中 《宿州教育学院学报》2006,9(5):98-100
IntruductionEarnest Hemingway was one of the most celebrated andmost controversial of American writers. He was seen variouslyas a sensitive and dedicated artist and as a hedonistic adven-turer, as a literary poseur and as the stylistic genius of thecentur… 相似文献
5.
Objective: To explore the characteristics of NF-κB activation in the progress of pancreatitis, the relationship with expression of TNF-α in the inflammatory reaction, and prevent the exacerbation of pancreatitis by using NAC. Method: Forty-eight rats were divided into three groups: therapy (group C), pancreatitis (group B) and control (group A). NAC served as the inhibitor of NF-κB activation. In the time intervals of 1.5, 3.0, 6.0, 12.0 hour, NF-κB activation was detected with flow cytometry (FCM) and the expression of TNF-α mRNA and protein with in situ hybridization (ISH) and enzyme-linked immuno-sorbent assay (ELISA) respectively. Meanwhile, the level of lipase and amylase in the serum was assayed and the pathological change was evaluated. Result: NF-κB activation in the pancreatitis group was higher than that in the control group (P<0.01), peaked at 3 hours, and was depressed by the inhibitor of NF-κB, NAC. The expression of TNF-α as well as the level of lipase and amylase in the serum also rose synchronously with activation of NF-κB. In contrast to group A, it was significantly different (P<0.01) in group B. After using NAC in group C, all of these values were decreased and the inflammatory reaction in the pancreas abated evidently. The pathology changes of the pancreas were shown to be alleviated in group C. Conclusion: First, NF-κB activity is intensively initiated in the course of pancreatitis and shown to have closely relationship with the release of cytokines. Second, use of NAC markedly depressed NF-κB activation. TNF-α expression is down regulated by cytokines. It is suggested that NAC probably acts as a useful agent for treatment of pancreatitis by indirectly inhibiting activation of NF-κB. 相似文献
6.
In this study, methanethiol(MT)-degradation bacteria were cultivated by using MT, methanol and trimethylamine as carbon sources under anaerobic conditions. It was found that the batch bacteria used MT and methanol as carbon sources grew faster than those used trimethylamine. The enriched bacteria used MT and methanol as the carbon sources were respectively inoculated in different biotrickling filters. The biological conversion performance of MT under anaerobic conditions was investigated in biotrickling filters. The results showed that the performance of the biotrickling filter inoculated with the bacteria enriched using MT was better than that inoculated with the bacteria enriched using methanol. When the inlet concentration of MT was 0.005vol%(50,ppm), the empty bed residence time was 50 s, p H value was 8.0, and the flow rate of the nutrient solution was 10 L/h, the removal efficiency of MT reached 95.3%. Adding methanol stimulated the growth of the biomass and the degradation of MT, but caused that some bacteria only degrading methanol outcompeted the bacteria only degrading MT. The concentration of sodium bicarbonate in the nutrient solution needed to be controlled lower than 30 g/L, otherwise, it would be harmful to the degradation of MT. 相似文献
7.
An improved test rig providing both the heat and cold source was used to perform thermal response test(TRT), and the line source model was used for data analysis. The principle of determining the temperature difference between the inlet and outlet of test well can keep the heating or cooling rate constant, along with a reduced size of test rig. Among the influencial factors of the line source model, the temperature difference was determined as the most important, which agreed with the test results. When the gravel was taken as the backfill material, the soil thermal conductivities of heating and cooling at the test place were 1.883 W/(m·K) and 1.754 W/(m·K), respectively, and the deviation of TRT between heating and cooling soil was 6.8%. In the case of fine sand, the thermal conductivities of heating and cooling were 1.541 W/(m·K) and 1.486 W/(m·K), respectively, and the corresponding deviation was 6%. It was also concluded that different velocities of water had less influence on TRT than the temperature difference. 相似文献
8.
LIGui－zhi LIUYong－ming 《上海大学学报(英文版)》2001,5(4):334-337
A study on the sorption of monocrotophos and parathion-methyl on Yellow River‘s sediments was performed.The influence of some factors,such as pH value and ionic strength,on the sorption was investigated and first order kinetics mode for the sorption of monocrophos was shown.Freundlich isotherm was suggested as the most appropriate type for monocrophos an parathion-methyl.But the sorption isotherms of monocrotophos and parathion-methyl are also in conformity with Langmuir equation.Both partition and adsorption occur to the sorption of monocrophos to Yellow River‘s sediments.but partition is the predominant for that of parathionmethyl. 相似文献
9.
Biogas from renewable sources and natural gas (NG) are both high-efficient and good-quality gaseous fuels on account of their enrichment in methane. Due to the dissimilar physical properties of biogas and NG, biogas cannot substitute NG directly without treatment and is usually used on site due to the high cost of the transportation and distribution via exclusive pipeline system. Consequently, the injection of biogas into existing NG infrastructure was proposed to address the deficiency. In this paper, the Wobbe index (WI) as well as the combustion potential (CP) were introduced for analyzing the interchangeability of an NG-biogas mixture, and a mathematical framework was put forward for modeling and simulating NG grid with a decentralized biogas injection. Results show that the maximum admissible amount of biogas in mixture was 10.5 by volume. A medium pressure network was used to interrogate the comprehensive effect of distributed biogas injection, which showed an impact on both gas quality and hydraulic regime across the grid. 相似文献
10.
Background： Endothelial and smooth muscle cells were used as seeding cells and heterogeneous acellularized matrix was used as scaffold to construct the tissue-engineered graft. Methods： A 2 weeks piglet was selected as a donor of seeding cells. Two-centimetre length of common carotid artery was dissected. Endothelial cells and smooth muscle cells were harvested by trypsin and collagenase digestion respectively. The isolated cells were cultured and expanded using routine cell culture technique. An adult sheep was used as a donor of acellularized matrix. The thoracic aorta was harvested and processed by a multi-step decellularizing technique to remove the original cells and preserve the elastic and collagen fibers. The cultured smooth muscle cells and endothelial cells were then seeded to the acellularized matrix and incubated in vitro for another 2 weeks. The cell seeded graft was then transplanted to the cell-donated piglet to substitute part of the native pulmonary artery. Results： The cultured cells from piglet were characterized as endothelial cells by the presence of specific antigens vWF and CD31, and smooth muscle cells by the presence of specific antigen a-actin on the cell surface respectively with immunohistochemical technique. After decellularizing processing for the thoracic aorta from sheep, all the cellular components were extracted and elastic and collagen fibers kept their original morphology and structure. The maximal load of acellular matrix was decreased and 20% lower than that of untreated thoracic aorta, but the maximal tensions between them were not different statistically and they had similar load-tension curves. Three months after transplantation, the animal was sacrificed and the graft was removed for observation. The results showed that the inner surfaces of the graft were smooth, without thrombosis and calcification. Under microscopy, a great number of growing cells could be seen and elastic and collagen fibers were abundant. Conclusion： Cultured self-derived endothelial and smooth muscle cells could be used as seeding cells and heterogeneous acellularized matrix could be used as scaffold in constructing tissue-engineered graft. 相似文献
11.
《天津大学学报(英文版)》2016,(3)
A Pr-doped TiO_2-NTs/SnO_2-Sb electrode was prepared by a simple method, cyclic voltammetry(CV). The methyl orange(MO)aqueous solution was selected as a simulated wastewater. The ordered microstructural TiO_2-NTs substrate was synthesized by an electrochemical method to obtain large specific surface area and high space utilization. The phase structure, electrode surface morphology and electrochemical properties of electrodes were characterized by XRD, SEM and electrochemical technology, respectively. The results showed that praseodymium oxide was successfully doped into the SnO_2-Sb film by CV method. Due to the doped Pr, the oxygen evolution potential increased from 2.25 V to 2.40 V. The degradation of MO was investigated by UV-vis. The C_t /C_0(φ)was studied as a function to obtain the optimal parameters, such as the amount of doped Pr, current density and initial dye concentration. In addition, the degradation process followed pseudo-first-order reaction kinetics and the rate constant was 0.0993 min~(-1). The result indicated that the introduction of Pr reduced the formation of oxygen vacancies or enhanced the formation of adsorbed hydroxyl radical groups on the surface, thus leading to better activity and stability. 相似文献
12.
《天津大学学报(英文版)》2016,(3)
Self-made enriched 10 B boric acid as raw material was purified by recrystallization. The effects of final crystallization temperature, crystallization time, stirring speed, crystallization frequency and other factors on the purity were investigated. The appropriate operating condition was that the final crystallization temperature and time were 5,℃ and 10 h respectively under a low-speed stirring for crystallizing twice, which would make the purity and yield of boric acid reach 99.94% and 95.36%, respectively. Taking this as foundation, recrystallization process was optimized with acetone as anti-solvent, whose amount was the most important index. The boric acid solution was added into acetone and recrystallized under the same condition, and the purity and yield of boric acid would reach 99.98% and 99.61%, respectively. The product detected by XRD was confirmed as boric acid crystal. Main ion concentration in the product was detected by ICP, which basically met the national standard of high purity. Crystal morphology of boric acid was observed by SEM. 相似文献
13.
Hydrophilic degraded gelatin was modified with hydrophobic poly(ε-caprolactone) (PCL) via a chemical grafting route.Firstly,PCL with one hydroxyl end group was prepared by the ring-opening polymerization of εcaprolactone (ε-CL) with tin (Ⅱ) 2-ethylhexanoate as catalyst and n-butyl alcohol as initiator.Secondly,the PCL reacted with isophorone diisocyanate (IPDI) to prepare PCL with isocyanate functional group (PCL-NCO).Hydroxylamine was used to degrade gelatin by the cleavage between asparagine and glycine residues of gelatin.PCL-NCO reacted with the hydroxyl/amino groups of degraded gelatin in a homogeneous system and yielded the PCL modified gelatin copolymers.The gelatin grafted PCL copolymers were measured by means of XRD,FTIR,DSC and 1 H NMR.The results confirmed the conjugation of PCL onto gelatin chains.The PCL modified gelatin can be used as biomaterials owing to their biocompatibility and biodegradation. 相似文献
14.
Ding QB Ou L Wei DZ Wei XK Xu YM Zhang CY 《Journal of Zhejiang University. Science. B》2010,11(11):880-888
Nucleoside phosphorylase is an important enzyme involved in the biosynthesis of nucleosides.In this study,purine nucleoside phosphorylase and pyrimidine nucleoside phosphorylase were co-expressed in Escherichia coli and the intact cells were used as a catalyst for the biosynthesis of nucleosides.For protein induction,lactose was used in place of isopropylβ-D-1-thiogalactopyranoside(IPTG) .When the concentration of lactose was above 0.5 mmol/L,the ability to induce protein expression was similar to that of IPTG.We determined that the reaction conditions of four bacterial strains co-expressing these genes(TUD,TAD,DUD,and DAD) were similar for the biosyntheses of 2,6-diaminopurine nucleoside and 2,6-diaminopurine deoxynucleoside.When the substrate concentration was 30 mmol/L and 0.5%of the recombinant bacterial cell volume was used as the catalyst(pH 7.5) ,a greater than 90%conversion yield was reached after a 2-h incubation at 50°C.In addition,several other nucleosides and nucleoside derivatives were efficiently synthesized using bacterial strains co-expressing these recombinant enzymes. 相似文献
15.
Black clay(BC) was used as a catalyst for the decolorization of Azure B dye by Fenton process. BC was modified by acid, alkali, distilled water, and calcination to check their changes in characterization and efficiency on decolorization of Azure B. Among three modified catalysts, maximum decolorization was obtained by acid-modified BC(AMBC) catalyst due to the highest removal of impurities, comparatively. The characterization of AMBC was done by Fourier-transform infrared spectroscopy and X-ray diffraction spectroscopy which show the presence of metal ion. The BET surface area, pore volume, pore size, and density of AMBC were calculated to be 79.402 m~2/g, 0.0608 m~3/g, 0.00306 nm, and 16 g/cm~3, respectively. The highest decolorization of 97.59% was achieved only in 10 min using AMBC at optimized calcination of 100 °C and 3 h of aging. AMBC was considered as the main catalyst for optimizing the different process parameters. Optimized conditions were obtained: pH 2, 0.2 mL of H_2O_2, catalyst dose 0.3 g, room temperature(30 °C), and stirring speed 400 r/min. The catalyst has showed excellent stability and reusability. It could remove more than 85% of color even after four cycles of run and less than negligible leaching of iron. AMBC has good recycling ability among other modified catalysts. To check the selectivity of catalyst, different dyes such as Congo red and mixed dye(mixture of Azure B and Congo red) decolorization were studied. In the present work, kinetic study was also carried out and a three-stage decolorization process was found. 相似文献
16.
The building of canals bridge, and roads was carried out by speciallytrained civil engineers as early as the middle of the 18th century. With theadvent of steam power at the beginning of the Industrial Revolution in thelast part of the 18th century, mechanical engineers started to develop en-gines, locomotives, and various other machines. The automatic knittingmachine was probably the most advanced. Originally steam was used 相似文献
17.
In this paper,a model named fictitious soil pile was introduced to solve the boundary coupled problem at the pile tip.In the model,the soil column between pile tip and bedrock was treated as a fictitious pile,which has the same properties as the local soil.The tip of the fictitious soil pile was assumed to rest on a rigid rock and no tip movement was allowed.In combination with the plane strain theory,the analytical solutions of vertical vibration response of piles in a frequency domain and the corresponding semi-analytical solutions in a time domain were obtained using the Laplace transforms and inverse Fourier transforms.A parametric study of pile response at the pile tip and head showed that the thickness and layering of the stratum between pile tip and bedrock have a significant influence on the complex impedances.Finally,two applications of the analytical model were presented.One is to identify the defects of the pile shaft,in which the proposed model was proved to be accurate to identify the location as well as the length of pile defects.Another application of the model is to identify the sediment thickness under the pile tip.The results showed that the sediment can lead to the decrease of the pile stiffness and increase of the damping,especially when the pile is under a low frequency load. 相似文献
18.
Unlike the adverse effect caused by the gelation during crystallization process, gelation of cefpiramide sodium was found to provide ideal product properties, such as a larger and more regular crystal shape. The causes of the gelation phenomenon and the mechanism of gel–crystal transition during the crystallization of cefpiramide sodium were both investigated in this work. The gel was formed due to the strapping of the solvents by the networks of cefpiramide sodium molecules. The whole gel–crystal transition process was divided into the following three stages:(1) when the temperature decreased, the system reached a metastable-state gelation;(2) the initial microcrystal in the gel grew slowly because of the low supersaturation; and(3) the gel finally disappeared, and a larger and more regular crystal was formed. The Hansen solubility parameters were used to analyze the effects of the solvents on this gelation; the analysis results can serve as guidance for solvent screening in the actual production process. 相似文献
19.
This study was undertaken to isolate and characterize the protease activity of human eye lens sample of mature and hyper mature cataract. Samples were collected just after surgery of the cataract lens and were stored at -20°C. The total protein extract was isolated from 5 samples in each case (mature and hyper mature cataract) and clear supernatant obtained after centrifugation was used as an enzyme source. The optimum pH for the proteases of mature cataract was 7.5 while the proteases of hyper mature cataract were recorded for maximum activity at pH 5.5 and 7.5. The optimum temperature for both enzyme sources was 50 °C. Effect of different metal ions such as potassium, lead, silver, zinc and borate was studied. In each case protease activity was increased. Reducing agent e.g. β mercaptoethanol also caused an increase in activity indicating the involvement of sulfhydryl groups. Protease activity was also located on agar plates. 相似文献
20.
ZHAN Liang-tong CHEN Ping NG C.W.W. 《浙江大学学报(A卷英文版)》2007,8(5):699-706
A laboratory study was carried out on both natural and compacted specimens to investigate the complex soil-water interaction in an unsaturated expansive clay. The laboratory study includes the measurement of soil-water characteristic curves, 1D free swelling tests, measurement of swelling pressure and shrinkage tests. The test results revealed that the air-entry value of the natural specimen was quite low due to cracks and fissures present. The hydraulic hysteresis of the natural specimen was relatively insignificant as compared with the compacted specimen. Within a suction range 0 to 500 kPa, a bilinear relationship between free swelling strain (or swelling pressure) and initial soil suction was observed for both the natural and compacted specimens. As a result of over-consolidation and secondary structures such as cementation and cracks, the natural specimens exhibited significant lower swelling (or swelling pressure) than the compacted specimen. The change of matric suction exerts a more significant effect on the water phase than on the soil skeleton for this expansive clay. 相似文献