赤泥的固硫特性及其机理研究

燃烧固硫技术作为洁净煤技术的一个重要发展方向,一直受到研究者的关注.其中,对固硫剂的研究也是热点之一.     

小题大作——记一堂高效轻负的研究性学习课

在学习圆锥曲线时,教师一般都会向学生介绍它们的光学性质,学生对这一内容也很感兴趣.有一次下课后,学生问我:老师,这些性质怎样证明呢?我当时随口回答说:当然能,但这要用到圆锥曲线的切线知识,而圆锥曲线的切线教材不作要求,所以我们也就不学这些性质的证明.     

Tuning field emission properties of boron nanocones with catalyst concentration

Single crystalline boron nanocones are prepared by using a simple spin spread method in which Fe 3 O 4 nanoparticles are pre-manipulated on Si(111) to form catalyst patterns of different densities.The density of boron nanocones can be tuned by changing the concentration of catalyst nanoparticles.High-resolution transmission electron microscopy analysis shows that the boron nanocone has a β-tetragonal structure with good crystallization.The field emission behaviour is optimal when the spacing distance is close to the nanocone length,which indicates that this simple spin spread method has great potential applications in electron emission nanodevices.     

Surface-enhanced Raman scattering properties of highly ordered self-assemblies of gold nanorods with different aspect ratios

Gold nanorods with aspect ratios of from 1 (particles) to 31.6 were synthesized by the seed-mediated method and packed in a highly ordered structure on a large scale on silicon substrates through capillary force induced self-assembly behaviour during solvent evaporation.The gold nanorod surface exhibits a strong enhancing effect on Raman scattering spectroscopy.The enhancement of Raman scattering for two model molecules (2-naphthalenethiol and rhodamine 6G) is about 5-6 orders of magnitude.By changing the aspect ratio of the Au nanorods,we found that the enhancement factors decreased with the increase of aspect ratios.The observed Raman scattering enhancement is strong and should be ascribed to the surface plasmon coupling between closely packed nanorods,which may result in huge local electromagnetic field enhancements in those confined junctions.     

Selective formation of ultrathin PbSe on Ag(111)

Two-dimensional (2D) semiconductors, such as lead selenide (PbSe), locate at the key position of next-generation devices. However, the ultrathin PbSe is still rarely reported experimentally, particularly on metal substrates. Here, we report the ultrathin PbSe synthesized via sequential molecular beam epitaxy on Ag(111). The scanning tunneling microscopy is used to resolve the atomic structure and confirms the selective formation of ultrathin PbSe through the reaction between Ag₅Se₂ and Pb, as further evidenced by the theoretical calculation. It is also found that the increased accumulation of Pb leads to the improved quality of PbSe with larger and more uniform films. The detailed analysis demonstrates the bilayer structure of synthesized PbSe, which could be deemed to achieve the 2D limit. The differential conductance spectrum reveals a metallic feature of the PbSe film, indicating a certain interaction between PbSe and Ag(111). Moreover, the moiré pattern originated from the lattice mismatch between PbSe and Ag(111) is observed, and this moiré system provides the opportunity for studying physics under periodical modulation and for device applications. Our work illustrates a pathway to selectively synthesize ultrathin PbSe on metal surfaces and suggests a 2D experimental platform to explore PbSe-based opto-electronic and thermoelectric phenomena.     

Synthesis and photoluminescence property of boron carbide nanowires

Large scale, high density boron carbide nanowires have been synthesized by using an improved carbothermal reduction method with B/B203/C powder precursors under an argon flow at 1100℃. The boron carbide nanowires are 5-10 μm in length and 80-100 nm in diameter. Transmission electron microscopy （TEM） and selected area electron diffraction （SAED） characterizations show that the boron carbide nanowire has a B4C rhombohedral structure with good crystallization. The Raman spectrum of the as-grown boron carbide nanowires is consistent with that of a B4C structure consisting of B11C icosahedra and C-B-C chains. The room temperature photoluminescence spectrum of the boron carbide nanowires exhibits a visible range of emission centred at 638 nm.     

四种材料超晶格的价带自旋劈裂的研究

自从Esaki和Tau[1]发现量子阱和超晶格以来,人们已对由两种材料构成的量子阱及超晶格的能带结构进行了大量的研究.陈维友等人[2]已研究了三种材料构成的超晶格的能带结构.本文将利用文献[2]报道的计算方法,对由四种材料构成的超晶格价带自旋劈裂的变化规律进行研究.     

地基高分辨率傅里叶变换红外光谱反演环境大气中的CH4浓度变化

CH₄在大气中的浓度较低(～1.8 ppmv)且混合较为均匀, 不同区域浓度差较小, 其在大气中微量变化的精确观测对反演技术提出了很高要求. 基于高分辨率(0.02 cm^-1)傅里叶变换直射太阳光谱, 研究一种高精度、大尺度的CH₄浓度反演方法, 高灵敏地观测CH₄在大气强背景下的浓度变化. 先利用先验参数实现测量光谱的准确建模, 再采用非线性最小二乘光谱拟合和非线性逐次迭代相结合的方法反演CH₄的垂直柱浓度(vertical column density, VCD), 并以7885 cm^-1 O₂ 吸收窗口为参考, 反演CH₄的柱平均干空气混合比浓度(column-averaged dry air mixing ratios) XCH₄. CH₄ VCD和XCH₄拟合误差均小于1%, 且绝大多数XCH₄反演值均位于Total Carbon Column Observing Network (TCCON)规定的<0.5%区间内. 基于典型的日观测值, 研究了CH₄浓度的日变化规律, CH₄ VCD随时间变化而减少, XCH₄的日变化量小于0.02 ppmv.     

Signatures of strong interlayer coupling in γ-InSe revealed by local differential conductivity

Interlayer coupling in layered semiconductors can significantly affect their optoelectronic properties. However, understanding the mechanisms behind the interlayer coupling at the atomic level is not straightforward. Here, we study modulations of the electronic structure induced by the interlayer coupling in the γ-phase of indium selenide (γ-InSe) using scanning probe techniques. We observe a strong dependence of the energy gap on the sample thickness and a small effective mass along the stacking direction, which are attributed to strong interlayer coupling. In addition, the moiré patterns observed in γ-InSe display a small band-gap variation and nearly constant local differential conductivity along the patterns. This suggests that modulation of the electronic structure induced by the moiré potential is smeared out, indicating the presence of a significant interlayer coupling. Our theoretical calculations confirm that the interlayer coupling in γ-InSe is not only of the van der Waals origin, but also exhibits some degree of hybridization between the layers. Strong interlayer coupling might play an important role in the performance of γ-InSe-based devices.     

A STRATEGY FOR ISOLATING DIFFERENTIATIONINDUCING COMPLEMENTARY DNAs FROM HUMAN ESOPHAGEAL CANCER CELL LINE TREATED WITH RETINOIC ACID

Treatment of the human esophageal cancer cell line EC8712 with retinoic acid (RA) stopped the cell growth significantly and gave rise to terminal differentiation of the cells characterized by increased expression of involucrin gene. Two cDNA libraries were constructed from the parental and RA-treated cells respectively. Repeated subtractive hybridization of single-stranded plasmid DNA prepared from pooled colonies of cDNA library of the parental cells with cDNA probe generated from the RA-treated cells exhausted sequences common to both libraries of the cell. The unhybridized cDNA probe represented, therefore, the genes activated after RA-treatment. By using these enriched cDNAs as probe to screen the cDNA library constructed from the RA-treated cells thirty-nine positive colonies were obtained, of which two were specifically due to RA-induction. One of these two cDNA clones, designated as pRA538, has undergone further analysis and shown differentiation-inducing effect on parental cancer cells. A novel