Evidence for, and an understanding of, the initial nucleation of carbon nanotubes produced by a floating catalyst method

An understanding of the growth mechanism of carbon nanotubes (CNTs) is very important for the control of their structures, which in turn will be the basis for their further theoretical studies and applications. On the basis of high-resolution transmission electron microscopy observations of the initial nucleation of CNTs, the following deductions are made: (1) the nucleation of single-walled carbon nanotubes (SWNTs) and double-walled carbon nanotubes (DWNTs) starts at a low-temperature zone in front of the reaction zone; (2) the addition of sulfur results in localized liquid zones on the surface of big catalyst particles as the initial nucleation sites; (3) a temperature gradient is necessary to realize the role of sulfur in the structure of CNTs; and (4) the shell number of CNTs can be changed at the nucleation and growth stages. On the basis of the above, a growth model for the formation of SWNTs and DWNTs is proposed, which might open up the possibility of controlling the structure of CNTs.     

Visible light photocatalyst: iodine-doped mesoporous titania with a bicrystalline framework

Iodine-doped (I-doped) mesoporous titania with a bicrystalline (anatase and rutile) framework was synthesized by a two-step template hydrothermal synthesis route. I-doped titania with anatase structure was also synthesized without the use of a block copolymer as a template. The resultant titania samples were characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared, nitrogen adsorption, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-visible absorption spectroscopy. Both I-doped titania samples, with and without template, show much better photocatalytic activity than commercial P25 titania in the photodegradation of methylene blue under the irradiation of visible light (>420 nm) and UV-visible light. Furthermore, I-doped mesoporous titania with a bicrystalline framework exhibits better activity than I-doped titania with anatase structure. The effect of rutile phase in titania on the adsorptive capacity of water and surface hydroxyl, and photocatalytic activity was investigated in detail. The excellent performance of I-doped mesoporous titania under both visible light and UV-visible light can be attributed to the combined effects of bicrystalline framework, high crystallinity, large surface area, mesoporous structure, and high visible light absorption induced by I-doping.     

Ginsenoside Rg8, a new dammarane-type triterpenoid saponin from roots of Panax quinquefolium

A new dammarane-type triterpenoid saponin, ginsenoside Rg(8) (1), was isolated from the roots of Panax quinquefolium, along with five known saponins, (20E)-ginsenoside F(4) (2), ginsenosides Rh(1) (3), Rg(2) (4), F(1) (5), and (20R)-ginsenoside Rh(1) (6). The structure of ginsenoside Rg(8) (1) was determined to be (3beta,6alpha,12beta,20E)-24,25-epoxy-3,12,23-trihydroxydammar-20(22)-en-6-O-alpha-L-rhamnopyranosyl(1-->2)-beta-D-glucopyranoside by various spectroscopic analyses. Among the known saponins, (20E)-ginsenoside F(4) (2) and ginsenoside F(1) (5) were first reported from the title plant.     

Surface Corrugation in Rotational and Diffractive Scattering of O2 from LiF （001）

A quantum dynamic calculation on a five-dimensional O2/LiF （001） model system is performed using the multi-configuration time-dependent Hartree method. The obtained results show that the mechanism of rotational and diffractive excitation in details： Comparison with the rotational excited state, the initially non-rotational state is seen to favor the inelastic scattering in the rotational excitation process. The surface corrugation can damp the quantum interferences and produce a greater amount of rotational inelastic scattering at the expense of the elastic process in the rotational excitation process. The diffraction process and the average energy transferred into the rotational and diffractive mode are also discussed.     

Magnetocaloric effect in antiferromagnetic Dy3Co compound

Magnetic properties and magnetocaloric effects (MCEs) of the Dy₃Co compound are studied. Two successive magnetic transitions: the antiferromagnetic (AFM)-to-AFM transition at T _AF =29 K and the AFM-to-paramagnetic (PM) transition with increasing temperature at the Néel temperature T _N =44 K are observed. Dy₃Co undergoes a field-induced metamagnetic transition from the AFM to the ferromagnetic (FM) state below T _N , giving rise to a large MCE. The maximal value of magnetic entropy change ΔS _m is −13.9 J/kg K with a refrigerant capacity (RC) of 498 J/kg around T _N for a field change of 0–5 T. A sign change of MCE in Dy₃Co with magnetic field and temperature is observed near the critical field where the metamagnetic transition occurs.     

基于准连续介质方法模拟纳米多晶体Ni中裂纹的扩展

通过准连续介质方法模拟了纳米多晶体Ni中裂纹的扩展过程.模拟结果显示:裂纹尖端的应力场可以导致晶界分解、层错和变形孪晶的形成等塑性形变,在距离裂纹尖端越远的位置,变形孪晶越少,在裂纹尖端附近相同距离处,层错要远多于变形孪晶.这反映了局部应力的变化以及广义平面层错能对变形孪晶的影响.计算了裂纹尖端附近区域原子级局部静水应力的分布.计算结果表明:裂纹前端晶界处容易产生细微空洞,这些空洞附近为张应力集中区,并可能促使裂纹沿着晶界扩展.模拟结果定性地反映了纳米多晶体Ni中的裂纹扩展过程,并与相关实验结果符合得很好     

相位一致性图像及其在目标跟踪中的应用(英文)

针对传统实时相关跟踪方法对照度变化敏感的问题,提出了一种基于相位一致性图像的相关跟踪方法.利用相位一致性函数值在[0,1]区间内且无量纲、对图像的亮度和对比度具有不变性等特点,首先对原始图像进行相位一致性检测,得到相位一致性图像,再利用MAD(Minimum Absolute Difference)等相关跟踪算法在相位一致性图像中对目标进行跟踪运算.对可见光和红外图像的实验表明,在图像的亮度和对比度发生剧烈变化的情况下,算法仍能保持对目标的稳定跟踪.该方法可用于解决传统实时相关跟踪方法普遍存在的因照度变化导致跟踪点漂移甚至跟踪失败的问题.     

比卡鲁胺片的相对生物利用度及生物等效性评价

采用同体交叉试验方法,对天津新新制药厂提供的比卡鲁胺片(受试制剂)与德国AstraZeneca公司进口的比卡鲁胺片(参比制剂)在健康人体内的生物等效性进行评价。18名健康志愿者分别单剂量口服受试制剂和参比制剂,应用高效液相色谱法测定血浆中比卡鲁胺药物浓度,绘制药时曲线,计算受试制剂和参比制剂的主要药代动力学参数,2种制剂的达峰时间Tmax分别为(4.94±0.24)h和(3.11±0.32)h,达峰时血中药物浓度Cmax分别为(3885.19±1924.55)ng/mL和(4319.88±2250.15)ng/mL,2种制剂的消除相半衰期t1/2分别为(12.59±3.31)h和(13.45±3.90)h,药时曲线下面积AUC0→48分别为(37966.35±9228.13)ng.h.mL-1和(36552.52±9591.71)ng.h.mL-1,AUC0→∞分别为(41451.43±10326.81)ng.h.mL-1和(40286.27±11573.62)ng.h.mL-1,相对生物利用度F为(104.85±9.62)%。研究结果表明受试制剂的AUC0→48、AUC0→∞的90%可信限落在参比制剂80%—125%范围内,Cmax落在70%—143%范围内。虽然受试制剂较参比制剂达峰慢,但2种制剂的Cmax、AUC0→48和AUC0→∞一致,可以认为受试制剂与参比制剂2种制剂生物等效。     

First-principles study of cobalt silicide nanosheet and nanotubes: Stability and electronic properties

We perform first-principle calculations to study the geometric and electronic structures of cobalt silicide (CoSi₂) nanosheet and nanotubes. The structure of layered CoSi₂ is characterized by a CoSi₂ nanosheet, analogous to the (1 1 1) surface of CoSi₂ crystal. The strain energy involved in rolling up a CoSi₂ nanosheet to CoSi₂ nanotubes is very low. Both the CoSi₂ nanosheet and nanotubes are energetically stable. CoSi₂ nanotubes prefer to form bundles to further release strain energy. All CoSi₂ nanotubes exhibit uniformly metallicity and steady work functions, independent of tube chirality.     

Coalescence between Cu57 and Cu58 clusters at a room temperature: molecular dynamics simulations

Three coalescence processes of Cu57-Cu57,Cu57-Cu58,and Cu58-Cu58 clusters at 300 K are investigated by employing molecular dynamics simulations.According to the evolutions of mean square displacement and local atom packing,the coalescence process can be separated into three stages including an approaching stage,a coalescing stage,and a coalesced stage.The simulations show that the coalescence processes and the formed products are sensitive to the respective initial structures of,and the relative configuration between,the two coalescing icosahedron-based clusters.