Difference-frequency ultrasound generation from microbubbles under dual-frequency excitation

The difference-frequency (DF) ultrasound generated by using parametric effect promises to improve detection depth owing to its low attenuation, which is beneficial for deep tissue imaging. With ultrasound contrast agents infusion, the harmonic components scattered from the microbubbles, including DF, can be generated due to the nonlinear vibration. A theoretical study on the DF generation from microbubbles under the dual-frequency excitation is proposed in formula based on the solution of the RPNNP equation. The optimisation of the DF generation is discussed associated with the applied acoustic pressure, frequency, and the microbubble size. Experiments are performed to validate the theoretical predictions by using a dual-frequency signal to excite microbubbles. Both the numerical and experimental results demonstrate that the optimised DF ultrasound can be achieved as the difference frequency is close to the resonance frequency of the microbubble and improve the contrast-to-tissue ratio in imaging.     

一道全国大学生数学竞赛试题的解法及推广

给出了一道全国大学生数学竞赛试题的三种解答,在此基础上研究了三角形三内角正弦的线性和最大值问题,从而推广了竞赛试题中的结论.最后,研究了三内角正弦的指数之积以及余弦的指数之积的上界问题.     

EPR Study on the complex formed by charge-transfer process between ground-state acceptor chloranil and nine donors

EPR study showed that the semi-quinone radical anion of chloranil (TCQ) was formed in a charge-transfer process between ground state chloranil as acceptor and each one of the following ground state donors,i.e.,N,N'-diethyl aniline (DEA),phenothiazine (PTZ),carbazole (CBZ),pyrene (PY),ferrocene (FRO),triphenylphosphine (TPP),triethylamine (TEA),anthracene (AN) and N,N-diethyl-3-aminophenyl ester of palmitic acid (DPP).Our results indicate that there is a tunneling effect for the ground-state charge-transfer process between chloranil and the donor.     

反胶束法制备直接甲醇燃料电池Pt-Sn/C催化剂及其表征

在水/AOT/环己烷反胶束体系中, 制备了Pt-Sn/C催化剂, 研究了不同ω (反胶束溶液中水与表面活性剂的物质量之比)值对Pt-Sn粒径的影响. 并采用TEM, XRD, XPS, 循环伏安等技术对其进行表征. TEM结果表明合成的Pt-Sn纳米颗粒为球形, 在碳载体表面均匀分布, 粒径分布窄, 平均粒径为2.7 nm. Pt-Sn颗粒尺寸随着ω的增加而增大. XRD结果表明该催化剂中Pt具有面心立方结构且没有与Sn形成合金. XPS结果表明在该催化剂中, Pt主要以零价态存在. 在甲醇溶液中的循环伏安扫描结果表明, 甲醇氧化峰电位和峰电流随着ω的增加而减小, 说明反胶束方法可以通过控制颗粒尺寸, 从而影响催化剂的电氧化活性. 相对于商用Pt-Ru/Vulcan XC-72 (20 wt%, E-TEK公司), 该催化剂具有较低的峰电势以及较高的I_f/I_b (循环伏安曲线中正向扫描峰电流与反向扫描峰电流的比值), 这表明用此方法制备的Pt-Sn/C催化剂具有较好的抗中毒能力.     

植物酶催化光度法测定痕量甲胺磷的初步研究

对植物酶催化酯类检测痕量有机磷农药残留量的方法进行了初步研究。在乙酸-乙酸钠的缓冲体系中,应用植物淀粉酶促进α-乙酸萘酯分解生成α-萘酚,甲胺磷农药抑制淀粉酶的活性,淀粉酶的活性随甲胺磷浓度增加而降低,α-乙酸萘酯分解生成的α-萘酚量也减少,以FeCl3指示反应,反应生成一种紫色络合物,利用该反应对甲胺磷进行定量测定。确定了反应的最佳条件,方法已应用于蔬菜表面甲胺磷残留量的分析。     

溴化锌-季(鎓)三溴盐催化二氧化碳和环氧化合物偶联反应

研究了溴化锌-季鎓三溴盐催化二氧化碳和环氧化合物偶联反应,考察了反应温度、压力和不同金属盐对反应的影响以及催化剂的循环使用性能.结果表明,在413 K和1.0 MPa条件下,以溴化锌为催化剂,苯基三甲基三溴化铵为共催化剂,无需加入任何溶剂就可以使二氧化碳和环氧化合物发生偶联反应,并以很高的收率得到环碳酸酯.     

甲基百里香酚蓝与铅的络合显色反应及其应用

目前,在化学分析方面所做的许多条件试验主要是利用全面试验法,而条件试验的全面试验法所做试验次数太多,时间长,浪费大量的药品,增加了试验费用,并且有时缺乏准确性,而利用正交试验设计进行光度试验可以克服这些缺点。为此,本法用正交试验法对甲基百里香酚蓝测定铅的光度法进行试验。光度法测定铅已有报道[1-6],但是用甲基百里香酚蓝(MTB)测定铅的光度法报道较少,本文对影响光度法测定微量铅的酸度、显色剂MTB用量、掩蔽剂(NH4F和邻二氮菲)用量、乙醇用量及稳定时间等条件进行了正交试验设计,利用了少量试验得到了比较理想的试验条件。…     

F原子与i—CH_7I反应的动力学研究

本文利用交叉分子束技术和激光诱导萤光方法,研究了F+i-C_3H_7I→IF+i-C_3H_7反应的动力学过程。获得了产物IF相对初生振动分布和相对细致反应速率常数。初生态布居接近于模型Ⅲ下的统计理论期待值,这不仅表明反应经过长寿命“配合物”,而且也说明自由基i-C_3H_7的内态是激发的。另外,确定了反应的产物IF内部能量分配和总反应截面σ,σ=(3.6±0.5)×10~(-16)cm~2.     

吡唑-3-甲酸Cu(Ⅱ)/Mn(Ⅱ)配合物的合成、表征及常压下对二氧化碳催化转化

合成和表征了2个吡唑-3-甲酸过渡金属配合物[Cu₂（pca）₂（H₂O）₆]·2H₂O（1）,[Mn（Hpca）₂（phen）]·3H₂O（2）（H₂pca=吡唑-3-甲酸;phen=菲咯啉）。X射线单晶衍射分析结果表明,配合物1属于单斜晶系P2₁/n空间群,它是一个畸变八面体的双核铜配合物;配合物2是一个畸变八面体的单核锰配合物。配合物1和2分别通过分子间的O-H…O,N-H…O氢键形成了三维网状结构。配合物1在二氧化碳的环加成反应中显示出了良好的催化效率（转化率高达97.4%;选择性高达98.9%）。     

Two Copper Complexes Based on Pyrazole-3-carboxylic Acid as Heterogeneous Catalysts for Highly Selective Oxidation of Alkylbenzenes

Two new copper complexes based on pyrazole-3-carboxylic acid(H_2pca)ligand,Cu(Hpca)_2(H_2O)_2·2H_2O(1)and Cu_2(pca)_2(H_2O)_4(2)have been synthesized and fully characterized by single-crystal X-ray diffraction(SXRD),infrared spectroscopy(IR),thermal gravity analysis(TGA),powder X-ray diffraction(PXRD)and elemental analyses.Complex 1 is mononuclear while complex 2 shows a dinuclear structure.Complex 1 crystallizes in the monoclinic system,space group P2_1/c with Z=2,a=6.5591(5),b=21.696(2),c=4.9486(2)?,V=680.94(9)?~3,F(000)=366,D_c=1.745 g/cm~3,μ=1.650 mm~(-1),the final R=0.0340 and w R=0.0792.Complex 2crystallizes in the monoclinic system,space group P2_1/n with Z=2,a=5.1935(4),b=9.6052(7),c=12.7347(9)?,V=634.44(8)?~3,F(000)=420,D_c=2.195 g/cm~3,μ=3.404 mm~(-1),the final R=0.0305 and w R=0.0653.The three-dimensional frameworks of two complexes are formed by the O-H···O and N-H···O hydrogen bonding interactions.Notably,two copper complexes are further used as catalysts in the oxidation of alkylbenzenes using t-butylhydroperoxide(TBHP)as the oxidant and they exhibit excellent catalytic performance(Conv.up to 98.9%,Sele.up to 98.7%).