六方相TbPO_4·nH_2O的控制合成及发光性能研究

通过控制PO3-4/Tb3+的量比,在低温水热条件下合成了不同形貌的TbPO4·nH2O纳米晶体。采用X射线衍射仪(XRD)、场发射扫描电镜(FE-SEM)及光致发光光谱(PL)等分析手段对所制备的样品进行了表征。研究了溶液中PO3-4/Tb3+比值变化对产物晶型结构、形貌、晶粒尺寸及发光性能的影响,给出了TbPO4·nH2O纳米粉体的生长机理。实验发现,当PO3-4/Tb3+比值达到60∶1时,产物在过量的磷酸根体系中生长成直径为100~200 nm的TbPO4·nH2O茧状微球,且产物的发光强度最大。PO3-4/Tb3+比值对TbPO4·nH2O形貌和发光性能有重要影响。     

Analysis of bending and buckling of pre-twisted beams: A bioinspired study

Twisting chirality is widely observed in artificial and natural materials and structures at different length scales. In this paper, we theoretically investigate the effect of twisting chiral morphology on the mechanical properties of elas- tic beams by using the Timoshenko beam model. Particular attention is paid to the transverse bending and axial buckling of a pre-twisted rectangular beam. The analytical solution is first derived for the deflection of a clamped-free beam under a uniformly or periodically distributed transverse force. The critical buckling condition of the beam subjected to its self- weight and an axial compressive force is further solved. The results show that the twisting morphology can significantly improve the resistance of beams to both transverse bending and axial buckling. This study helps understand some phenomena associated with twisting chirality in nature and provides inspirations for the design of novel devices and structures.     

高速逆流色谱法分离紫锥菊花色苷及其抗氧化性研究

建立了高速逆流色谱(HSCCC)分离制备紫锥菊花色苷类化合物的方法,并对所获得的2个花色苷单体进行了体外抗氧化性实验。以新鲜紫锥菊花瓣为原料,含0.1%HCl的60%乙醇为溶剂避光冷浸提取,经乙酸乙酯萃取和D101大孔吸附树脂(100 mL,2 cm×30 cm)纯化后,得2.1 g紫锥菊花色苷提取物干粉样品。以水-正丁醇-甲基叔丁基甲醚-乙腈-三氟乙酸(6∶3∶2∶1∶0.001)为HSCCC分离溶剂系统,上相为固定相,下相为流动相,流速2.0 mL/min,进样量160 mg,通过一次分离得到2种花色苷单体化合物,经HPLC检测其纯度分别达95.1%(9.8 mg)、98.2%(14.3 mg),MS及NMR技术鉴定其结构分别为矢车菊素-3-O-β-D葡萄糖苷(化合物1)和矢车菊素-3-O-(6″-O-丙二酰-β-D葡萄糖苷)(化合物2)。以Vc为对照组,对所获得的2种花色苷单体化合物进行了1,1-二苯基-2苦肼基(DPPH.)体外抗氧化性能评价,结果显示2种花色苷对DPPH.的半清除率(EC50)均小于10 mg/L,小于对照样Vc,表明2种花色苷均具有较强的自由基清除作用,且化合物1的清除能力强于化合物2。     

Dawson型磷钨钼杂多酸的制备及其对H2O2氧化环己酮制己二酸的催化

采用水热法制备了新型H6P2W9Mo9O62.24H2O催化剂,并用UV-Vis、FT-IR和TG-DTA等测试技术对催化剂进行了表征。以微波促进30%过氧化氢氧化环己酮制备己二酸合成反应为探针,考察了催化剂的催化性能。通过正交实验探讨了几种因素对反应的影响,确定了优化工艺条件为:n(环己酮)∶n(过氧化氢)∶n(草酸)∶n(催化剂)=100∶400∶1.25∶0.25,反应温度100℃,微波辐射功率400 W,反应时间3.5 h,己二酸产品的收率达87.33%,纯度可达99.7%。反应结束后,将反应后含催化剂的溶液浓缩至一定浓度,催化产率降低,重复使用5次收率降低为45.89%。     

Nb2O5·nH2O-PtRu/C的制备及其对甲醇氧化的催化作用

采用沉淀法制备了甲醇氧化电催化剂10%Nb2O5 nH2O-20%Pt10%Ru/C,并在Ar气氛下对它进行了热处理.用X射线衍射(XRD),透射电子显微镜(TEM)和X射线光电子谱(XPS)研究了热处理对催化剂的结构和形貌的影响,用循环伏安法和计时电流法研究了热处理对催化剂的电化学性能的影响.结果表明:催化剂中看不到Ru的衍射峰存在,Pt晶粒以面心立方体结构存在,Nb2O5 nH2O对Pt的结合能基本无影响;与20%Pt10%Ru/C相比,同温度热处理的条件下,10%Nb2O5 nH2O-20%Pt10%Ru/C催化剂中Pt,Ru合金化程度较差,活性组分颗粒较小、分散均匀,而且催化甲醇氧化性能和抗"CO"毒化性能较好,700℃热处理的10%Nb2O5 nH2O-20%Pt10%Ru/C的性能最好.Nb2O5 nH2O不仅能抑制热处理过程中活性颗粒的长大和Pt,Ru的合金化,还能促进氢离子的传递,提供活性"-OH",使甲醇及其氧化中间体更容易吸附-脱附.     

含铕配合物荧光纳米纤维的制备及光学性质的研究

通过静电纺丝技术,将发光良好的稀土配合物Eu(DBM)₃·H₂O和Eu(DBM)₄·CPC纳米微粒复合到水溶性的聚乙烯基吡咯烷酮中,制备了具有稀土铕离子红色特性荧光的聚合物纳米纤维。通过对稀土配合物以及聚合物纳米纤维样品扫描电镜和透射电镜的测试,发现当稀土配合物复合到聚合物纳米纤维中后,由于与聚乙烯基吡咯烷酮乙醇溶解性良好,其微观结构发生了变化,得到了50～100 nm左右的比较均匀的线状结构。同时,通过对稀土配合物以及聚合物纳米纤维样品的荧光激发、发射光谱及荧光寿命进行研究,表明稀土配合物在聚合物纳米纤维中比其在粉末状有更高的发光强度及更长的荧光寿命,其原因在于高分子纳米纤维为稀土配合物提供了较稳定的化学环境。     

Nanoparticle nucleation and coagulation in a mixing layer

Numerical simulation of nanoparticle nucleation and coagulation in a mixing layer with sulfuric acid vapor binary system is performed using the large eddy simulation and the direct quadrature method of moment. The distributions of number concentration, volume concentration, and average diameter of nanoparticles are obtained. The results show that the coherent structures have an important effect on the distributions of number concentration, volume concentration and average diameter of nanoparticles via continuously transporting and diffusing the nanoparticles to the area of low particle concentration. In the streamwise direction, the number concentration of nanoparticles decreases, while the volume concentration and the average diameter increase. The distributions of number concentration, volume concentration and average diameter of nanoparticles are spatially inhomogeneous. The characteristic time of nucleation is shorter than that of coagulation. The nucleation takes place more easily in the area of low temperature because where the number concentration of nanoparticles is high, while the intensity of coagulation is mainly affected by the number concentration. Both nucleation and coagulation result in the variation of average diameter of nanoparticles.     

Experimental study on correlation between turbulence and sound in a subsonic wind tunnel

In this paper, the effects of turbulence on sound generation and velocity fluctuations due to pressure waves in a large subsonic wind tunnel are studied. A trip strip located at different positions in the contraction part or at one position in the diffuser of a large wind tunnel is used to investigate the aforementioned phenomenon, and the results indicate that the trip strip has significant effects on sound reduction. The lowest turbulence intensity and sound are obtained from a trip strip with a diameter of 0.91 mm located either at X/L = 0.79 or at X/L = 0.115 in the wide portion of the contraction. Furthermore, the effect of monopole, dipole and quadrupole sources of aerodynamic noise at different velocities is investigated, and it is demonstrated that the contribution of the monopole is dominant, while the shares due to the dipole and quadrupole remain less important. In addition, it is found that the sound waves have a modest impact on the measured longitudinal turbulence and are generated essentially by eddies.     

Effects of tip perturbation and wing locations on rolling oscillation induced by forebody vortices

The wing rock motion is frequently suffered by a wing-body configuration with low swept wing at high angle of attack. It is found from our experimental study that the tip perturbation and wing longitudinal locations affect significantly the wing rock motion of a wing-body. The natural tip perturbation would make the wing rock motion of a nondeterministic nature and an artificial mini-tip perturbation would make the wing rock motion deterministic. The artificial tip perturbation would, as its circumferential location is varied, generate three different types of motion patterns： （1） limit cycle oscillation, （2） irregular oscillation, （3） equilibrium state with tiny oscillation. The amplitude of rolling oscillation corresponding to the limit cycle oscillatory motion pattern is decreased with the wing location shifting downstream along the body axis.     

Dynamic behaviour of axially moving nanobeams based on nonlocal elasticity approach

In this article, transverse free vibrations of axially moving nanobeams subjected to axial tension are studied based on nonlocal stress elasticity theory. A new higher-order differential equation of motion is derived from the variational principle with corresponding higher-order, non-classical boundary conditions. Two supporting conditions are investigated, i.e. simple supports and clamped supports. Effects of nonlocal nanoscale, dimensionless axial velocity, density and axial tension on natural frequencies are presented and discussed through numerical examples. It is found that these factors have great influence on the dynamic behaviour of an axially moving nanobeam. In particular, the nonlocal effect tends to induce higher vibration frequencies as compared to the results obtained from classical vibration theory. Analytical solutions for critical velocity of these nanobeams when the frequency vanishes are also derived and the influences of nonlocal nanoscale and axial tension on the critical velocity are discussed.