不同能载水平下C/C复合材料的摩擦特性

对具有粗糙层热解炭结构的针刺毡C/C复合材料在MM 1000型摩擦试验机上模拟某飞机正常着陆、超载着陆和中止起飞3种不同的能载水平进行摩擦磨损性能试验,并对磨损表面和磨屑进行扫描电镜观察.结果表明:C/C复合材料在不同能载水平下均具有高达0.31～0.32的摩擦因数,刹车力矩曲线均较平稳,磨损随能载水平的增加而增大;样件的磨损表面在正常着陆条件下形成较光滑、完整、连续的磨屑层,随着能载水平的增加,形成粗糙的磨屑层,在极高的能载水平(中止起飞条件)下又形成光滑的磨屑层;而样件的磨屑尺寸随能载水平的增加而急剧减小.表明该C/C复合材料具有极好的摩擦制动性能,尤其是在大能载水平下,摩擦性能更加优良,适用作飞机刹车材料.

能载舟,亦能煮粥

“水能载舟，亦能覆舟”是唐朝名臣魏征劝诫太宗李世民的原话。至今有一千多年。这句话被明君忠臣奉为圭臬．成为他们治理国家统治百姓的明鉴之一。

当归补血汤可作为补气之方

历版教材均认为当归补血汤具有补气生血的功效而将其作为补血方剂的代表,笔者通过查阅大量文献,从该方的功效入手,探讨"血为气之母"的理论,结合当归补血汤的源流、衍化发展及临床应用现状,提出当归补血汤补血可,补气亦可,血虚、气虚皆可应用,不必拘于补血功效。

Vermiform Ni@CNT derived from one-pot calcination of Ni-MOF precursor for improving hydrogen storage of MgH_(2)

The Ni-coated carbon nanotubes(Ni@CNT)composite was synthesized by the facile“filtration+calcination”of Ni-based metal−organic framework(MOF)precursor and the obtained composite was used as a catalyst for MgH_(2).MgH_(2)was mixed evenly with different amounts of Ni@CNT(2.5,5.0 and 7.5,wt.%)through ball milling.The MgH_(2)−5wt.%Ni@CNT can absorb 5.2 wt.%H_(2)at 423 K in 200 s and release about 3.75 wt.%H_(2)at 573 K in 1000 s.And its dehydrogenation and rehydrogenation activation energies are reduced to 87.63 and 45.28 kJ/mol(H_(2)).The in-situ generated Mg_(2)Ni/Mg_(2)NiH4 exhibits a good catalytic effect due to the provided more diffusion channels that can be used as“hydrogen pump”.And the presence of carbon nanotubes improves the properties of MgH_(2)to some extent.

Compressive properties of glue-laminated timber circular post modified by basalt fiber reinforced polymer

Glued timber structure is one of the main forms of modern wood architecture,which has gradually developed towards mid-and high-rise buildings.Glue-laminated timber(GLT)is comprised of several laminates of parallel-to-grain dimension lumber that are bonded together with durable,moisture resistant structural adhesives.GLT can be used in horizontal applications as a beam and in vertical applications as a post.So,its compressive performance has a significant impact on structural safety.Fiber reinforced polymers(FRPs)were commonly used to improve the bearing capacity of GLT components,and the structural and process parameters largely determined the reinforcement effect.This study was aimed at investigating the influence of structural and process parameters on the axial compression performance of GLT components.Three wrapping methods(middle-part,end-part and full wrapping)and three lengths(0.6,0.8,and 1.0 m)of wood post specimens were designed in this work and the axial compression performance and ductility of GLT post specimens modified by basalt fiber reinforced polymer(BFRP)were studied.The results showed that the effect of different BFRP wrapping methods on the compressive strength and elastic modulus of laminated wood was not statistically significant(P>0.05).The compressive bearing capacity of unreinforced GLT posts decreased with the increase of aspect ratio.The GLT posts with middle-part and end-part wrapping still followed this pattern,while the compressive bearing capacity of GLT posts with full wrapping showed a pattern of first decreasing and then increasing.For GLT with low aspect ratios(4.0 or 5.3),there was no correlation between the wrapping method and the compressive bearing capacity,while the compressive bearing capacity of GLT with a high aspect ratio(6.7)for middle-part,end-part and full wrapping increased by 3.5%,7.5%and 9.7%,respectively.Compared to the unreinforced group,the ultimate axial compressive strength and modulus of elasticity(MOE)of the 6-E series specimens reinforced at both ends decreased by 2.58%and 6.70%,respectively.The ultimate axial compressive strength of the 8-E specimens reinforced at both ends increased by 8.62%and the MOE decreased by 1.91%.The compressive strength of the 10-E specimens reinforced at both ends increased by 7.51%and the MOE increased by 8.14%.The failure modes of GLT with different aspects were consistent under the same BFRP wrapping,while the failure modes of GLT with the same aspect ratio were different for different BFRP wrapping methods.The ductility performance of GLT with different aspects ratio was improved by the BFRP wrapping.

Bearing mechanism of roof and rib support structure in automatically formed roadway and its support design method

Non-pillar mining technology with automatically formed roadway is a new mining method without coal pillar reservation and roadway excavation.The stability control of automatically formed roadway is the key to the successful application of the new method.In order to realize the stability control of the roadway surrounding rock,the mechanical model of the roof and rib support structure is established,and the influence mechanism of the automatically formed roadway parameters on the compound force is revealed.On this basis,the roof and rib support structure technology of confined lightweight concrete is proposed,and its mechanical tests under different eccentricity are carried out.The results show that the bearing capacity of confined lightweight concrete specimens is basically the same as that of ordinary confined concrete specimens.The bearing capacity of confined lightweight concrete specimens under different eccentricities is 1.95 times higher than those of U-shaped steel specimens.By comparing the test results with the theoretical calculated results of the confined concrete,the calculation method of the bearing capacity for the confined lightweight concrete structure is selected.The design method of confined lightweight concrete support structure is established,and is successfully applied in the extra-large mine,Ningtiaota Coal Mine,China.

Graphene-loaded nickel−vanadium bimetal oxides as hydrogen pumps to boost solid-state hydrogen storage kinetic performance of magnesium hydride

To modify the thermodynamics and kinetic performance of magnesium hydride(MgH_(2))for solid-state hydrogen storage,Ni_(3)V_(2)O_(8)-rGO(rGO represents reduced graphene oxide)and Ni_(3)V_(2)O_(8)nanocomposites were prepared by hydrothermal and subsequent heat treatment.The beginning hydrogen desorption temperature of 7 wt.%Ni_(3)V_(2)O_(8)-rGO modified MgH_(2)was reduced to 208℃,while the additive-free MgH_(2)and 7 wt.%Ni_(3)V_(2)O_(8)doped MgH_(2)appeared to discharge hydrogen at 340 and 226℃,respectively.A charging capacity of about 4.7 wt.%H_(2)for MgH_(2)+7 wt.%Ni_(3)V_(2)O_(8)-rGO was achieved at 125℃ in 10 min,while the dehydrogenated MgH_(2)took 60 min to absorb only 4.6 wt.%H_(2)at 215℃.The microstructure analysis confirmed that the in-situ generated Mg_(2)Ni/Mg_(2)N_(i)H_(4) and metallic V contributed significantly to the enhanced performance of MgH_(2).In addition,the presence of rGO in the MgH_(2)+7 wt.%Ni_(3)V_(2)O_(8)-rGO composite reduced particle aggregation tendency of Mg/MgH_(2),leading to improving the cyclic stability of MgH_(2)during 20 cycles.

N-doped ordered mesoporous carbon as a multifunctional support of ultrafine Pt nanoparticles for hydrogenation of nitroarenes

Due to the advantages of high surface areas, large pore volumes and pore sizes, abundant nitrogen content that favored the metal-support interactions, N-doped ordered mesoporous carbons are regarded as a kind of fascinating and potential support for the synthesis of effective supported cat-alysts. Here, a N-doped ordered mesoporous carbon with a high N content （9.58 wt%）, high surface area （417 m^2/g）, and three-dimensional cubic structure was synthesized successfully and used as an effective support for immobilizing Pt nanoparticles （NPs）. The positive effects of nitrogen on the metal particle size enabled ultrasmall Pt NPs （about 1.0 ± 0.5 nm） to be obtained. Moreover, most of the Pt NPs are homogeneously dispersed in the mesoporous channels. However, using the ordered mesoporous carbon without nitrogen as support, the particles were larger （4.4 ± 1.7 nm） and many Pt NPs were distributed on the external surface, demonstrating the important role of the nitrogen species. The obtained N-doped ordered mesoporous material supported catalyst showed excellent catalytic activity （conversion 100%） and selectivity （〉99%） in the hydrogenation of halogenated nitrobenzenes under mild conditions. These values are much higher than those achieved using a commercial Pt/C catalyst （conversion 89% and selectivity 90%）. This outstanding catalytic perfor-mance can be attributed to the synergetic effects of the mesoporous structure, N-functionalized support, and stabilized ultrasmall Pt NPs. Moreover, such supported catalyst also showed excellent catalytic performance in the hydrogenation of other halogenated nitrobenzenes and nitroarenes. In addition, the stability of the multifunctional catalyst was excellent and it could be reused more than 10 times without significant losses of activity and selectivity. Our results conclusively show that a N-doped carbon support enable the formation of ultrafine metal NPs and improve the reaction ac-tivity and selectivity.

The effect of functional loads on free spanning pipeline's VIV response

During the operation and installation of offshore pipelines, high axial forces and pressures are experienced, and their effects cannot be neglected. In this article, the effect of internal flow velocity and functional loads on vortex-induced vibration （VIV） response is investigated. On the basis of the Hamilton principle, a differential equation was derived to describe the motion of a pinned-pinned tensioned spanning pipeline conveying fluid. The VIV response was calculated according to DNV-RP-F105 under different functional loads. The results showed that functional loads influence free spanning pipeline VIV response by changing the natural frequency. Internal flow velocity was found less important for VIV response than other functional load factors, such as effective axial force, because the speed in reality is not high enough to be significant. The research may provide a reference for sensitivity studies of the effect of functional loads on allowable free span lengths.

新型重负荷铜基金属陶瓷摩擦材料的研究

采用粉末冶金工艺,以莫来石等陶瓷为摩擦组元,并加入较大比例的Sn、Fe、Ni、Mo等金属组元,研制出一种重负荷铜基金属陶瓷摩擦材料。研究了合金元素Ni、Mo和陶瓷相莫来石对材料性能的影响。结果表明,铜基金属陶瓷中同时加入Ni、Mo等多种合金元素,可以提高材料的摩擦系数及其稳度;莫来石则对改善材料的高温性能作用显著。其综合作用的结果使该材料的摩擦系数及其稳度有大幅提高,能够承受高于4 809J/cm2的单位面积能载,且磨损量小,是一种理想的、可广泛应用于各种高能重载工况下工作的高性能摩擦材料。

重负荷铁基粉末冶金摩擦材料的研制

采用粉末冶金工艺,以莫来石等为摩擦剂,并加入较大比例的金属组元镍、铬、钼,研制出一种重负荷铁基粉末冶金摩擦材料。研究了合金元素镍、铬、钼和摩擦组元莫来石对材料性能的影响。研究结果表明,在铁基材料中同时加入镍、铬、钼等多种合金元素,在提高材料密度和硬度的同时,可以提高摩擦系数和摩擦系数的稳度;莫来石则对改善材料的高温性能作用显著。其综合作用的结果使该材料的摩擦系数及其稳度有大幅提高,单位面积能载高达12700J/cm2,且磨损量小,是一种理想的、可广泛应用于各种高能重载工况下工作的高性能摩擦材料。该材料在国内首次应用于某型进口飞机刹车装置取得成功。

Capacity of surface warship's protective bulkhead subjected to blast loading

The protective bulkhead of the large surface warship need to be designed working in the membrane mode. In this paper, a formula is derived for calculating the plastic deformation of the protective bulkhead subjected to blast loading by the energy method, and the ultimate capability of the protective bulkhead can be calculated. The design demand of the protective bulkhead is discussed. The calculation is compared with external experiments, which indicates that the formula is of great application value.

Ecological Carrying Capacity in Beijing Mountainous Areas——Taking Fangshan District as an Example

[Objective] The aim was to investigate ecological carrying capacity of Fangshan District in Beijing. [Method] Ecological footprint and carrying capacity of Fangshan District in 2007 and 2008 were analyzed with ecological footprint model and the difference between ecological footprint and carrying capacity there was con- cluded. Furthermore, an assessment was made on relation between Fangshan de- velopment with local ecological carrying capacity to evaluate sustainable development of Fangshan District. [Result] Fangshan District is of lightly ecological deficit; ecologi- cal footprint per capita in 2007-2008 was deficit and tended to expand. Two meth- ods are available to reduce ecological ：deficit, including reduction of ecological foot- print and increase of carrying capacity. In general, supply and demand of carrying capacity in Fangshan are better, though with some problems. It is necessary to fur- ther develop related industries to final eliminate ecological deficit in order to achieve ecological conservation-orientation and sustainable development of Fangshan District. [Conclusion] The research provides theoretical references for overall evaluation on eco- logical carrying capacity of Fangshan District.

ACTUATOR OF LARGE DISPLACEMENT RAINBOW CERAMICS

A new and unique processing method for fabricating stress biased, monolithic ceramic elements for large dis placement actuators is reported. Reduced and internally bised oxide wafer (RAINBOW) ceramics show excellent properties such as high displacement under applied electric field and enhanced load bearing capabilities. The actuating mechanism, structure and properties of the RAINBOW ceramics are reviewed. Finally, the developing direction is also discussed.

Enhanced Photoelectrochemical Property of Zn Loaded TiO2 Nanotube Arrays Electrode

TiO2 nanotube arrays （TNTs） electrode loaded with Zn nanoparticles was prepared by anodization and the size of Zn nanoparticle loaded on TNTs electrode was controlled by chronoamperometry deposition time. Results of SEM and XRD analysis show that Zn nanoparticles had a diameter of about 15-25 nm when the deposition time was 3-5 s. The UV-Vis diffuse reflectance spectra show the Zn loaded harvest light with 480-780 nm more effectively than the unloaded sample. The photocurrent response of Zn loaded TNTs electrodes were studied, the results showed that TNTs electrodes loaded with Zn nanoparti-cles has 50% increased photocurrent response under high-pressure mercury lamp irradiation compared with unloaded TNTs electrode.

Finite element failure analysis of continuous prestressed concrete box girders

In order to analyze the load carrying capacity of prestressed concrete box girders, failure behaviors of in-situ deteriorated continuous prestressed concrete box girders under loading are experimentally observed and a finite failure analysis method for predicting behaviors of box girders is developed. A degenerated solid shell element is used to simulate box girders and material nonlinearity is considered. Since pre-stressed concrete box girders usually have a large number of curve prestressed tendons, a type of combined element is presented to simulate the prestressed tendons of box girders, and then the number of elements can be significantly reduced. The analytical results are compared with full-scale failure test results. The comparison shows that the presented method can be effectively applied to the failure analysis of in-situ continuous prestressed concrete box girders, and it also shows that the studied old bridge still has enough load carrying capacity.

Effect of electrical current on tribological property of Cu matrix composite reinforced by carbon nanotubes

Cu matrix composite reinforced with 10%（volume fraction） carbon nanotubes（CNTs/Cu） and pure Cu bulk were prepared by powder metallurgy techniques under the same consolidation processing condition.The effect of electrical current on tribological property of the materials was investigated by using a pin-on-disk friction and wear tester.The results show that the friction coefficient and wear rate of CNTs/Cu composite as well as those of pure Cu bulk increase with increasing the electrical current without exception,and the effect of electrical current is more obvious on tribological property of pure Cu bulk than on that of CNTs/Cu composite;the dominant wear mechanisms are arc erosion wear and plastic flow deformation,respectively;CNTs can improve tribological property of Cu matrix composites with electrical current.

Strength of circular concrete columns under concentric compression

An experimental study, in which six columns were loaded concentrically toinvestigate the behavior of reinforced normal strength and high strength circular columns underconcentric compression, is described. The concrete strengths of the columns were 30 MPa and 60 MPa.The primary variables considered were the concrete strength and the amount of transversereinforcement. Test results indicate that smaller hoop spacing provides higher column capacity andgreater strength enhancement in a confined concrete core of columns. For the same lateralconfinement, high strength concrete columns develop lower strength enhancement than normal strengthconcrete columns. Both the strength enhancement ratio (f'_(cc) /f'_(co)) and the column capacityratio (P_(test)/P_o) were observed to show linear increase variations with rho_s f_(yt)/f'_c incircular columns.

Construction of Double Cross-over Expression Vector for Chloroplast Multicistron in Brassica napus L.

[Objective] This study aimed to construct Brassica napus chloroplast multi- cistron double cross-over expression vector, to lay the foundation for the genetic engi- neering research of Brassica napus chloroplast. [Method] Two primers were designed based on the known Brassica napus chloroplast DNA sequences AF267640 and Z50868 in GenBank. By using PCR method, two Brassica napus L. chloroplast DNA fragments were obtained, which were named RbcL and ACCD. The two Brassica na- pus chloroplast DNA homologous fragments were then cloned into plasmid pMD18-T to obtain recombinant plasmid pHBM715. Tandem expression cassette harboring spectinomycin-resistant gene aadA, mannanase gene man and green fluorescent pro- tein gene gfp was cloned into the plasmid pHBM715, thereby constructing Brassica napus chloroplast multicistron double cross-over expression vector pHBM716, which was transformed into Escherichia coil for expression and identification. [Result] Plate qualitative analysis was conducted for the functional identification of expression cas- sette in the constructed Brassica napus chloroplast multicistron double cross-over ex- pression vector, results showed that the three genes of the same multicistron were all expressed in E. coil [Conclusion] This study successfully constructed Brassica napus chloroplast multicistron double cross-over expression vector, which laid the foundation for the genetic engineering of Brassica napus chloroplast.

Performance analysis of aircraft low-power thermoelectric refrigeration system

An optimal design method for an aircraft low-power thermoelectric refrigeration system（TRS）is proposed using an existing experimental model as the research platform under given aircraft flight conditions.The variation curves of the cooling capacities and the refrigeration coefficients of the system running at three flight altitudes are investigated.The performance of the system is evaluated by the minimum-entropy-generation method and the performance penalty is also calculated.The power variation curves of the cooling system are obtained by an electric power experiment.The peak values of these curves are less than the maximal electric power supply of airborne equipment,proving that the use of the low-power TRS for airborne equipment is feasible.The COP,cooling capacity and entropy generation of the system are relative to the flight altitude and the current of the TRS.Through the analyses of these data,the optimal values of the COP are obtained,and the optimization measures are proposed to maximize the use of the advantages of the TRS.