单壁碳纳米管吸附色氨酸的机理研究

用近边X射线吸收精细结构谱(NEXAFS)和同步辐射电子能谱(SRPES)技术,研究了单壁碳纳米管(SWCNTs)吸附色氨酸(Trp)的机理.对比Trp吸附于SWCNTs前后样品C-K边NEXAFS谱,发现SWCNTs与吸附的Trp之间存在明显的界面相互作用.吸附前后N-K边NEXAFS谱的峰形和峰位的变化可忽略,这表...     

单壁碳纳米管的纯化过程研究

用X射线吸收谱(XAS)和光电子能谱(PES)对化学气相沉积(CVD)方法制备的单壁碳纳米管纯化过程进行了研究。实验表明对碳纳米管进行盐酸处理纯化,可以大大减少残留在碳纳米管中的催化剂颗粒,但也发现盐酸中的部分氯离子与碳纳米管成键。这种成键作用可能会对碳纳米管形成修饰。     

单壁碳纳米管的γ辐射剪切与光声效应

系统研究了在硫酸溶液中用γ辐射法剪切单壁碳纳米管,初步探索了在激光以及γ射线照射下的水溶液中单壁碳纳米管的光声效应,并对辐射剪切单壁碳纳米管的机制进行了讨论。用透射电子显微镜（TEM）、傅里叶变换红外光谱（FT-IR）以及拉曼光谱对短单壁碳纳米管进行分析和表征。结果表明：γ辐射和硫酸氧化作用在剪切碳管的过程中存在协同效应,得到的短碳纳米管的平均长度为200～400nm,在水中可稳定分散1周;辐射剪切在碳纳米管外侧及端帽处引进—OH、—COOH等官能团。另外,Q开关脉冲激光照射下的单壁碳纳米管在溶液中会发生强光声效应,相比而言,当照射碳管的光子能量达到γ光子能量时碳管的光声效应非常微弱。     

十八胺在碳钢表面吸附和成膜的分子动力学研究

华龙一号机组主给水系统大量使用P280GH碳钢管道,并应用十八胺（ODA）在管道内壁吸附形成缓蚀膜,ODA可高效抑制腐蚀,避免管道失效和蒸汽发生器（SG）严重结垢。但ODA在碳钢表面的吸附和成膜机理目前仍不明确,严重制约了ODA的性能优化和推广应用,针对该问题,采用分子动力学（MD）模拟开展研究。结果表明,ODA分子头部的氮原子与碳钢表面铁原子形成配位键,促使ODA分子吸附“锚定”。所形成缓蚀膜的微观构型与ODA浓度相关。浓度较低时,缓蚀膜呈ODA分子尾链间交织较差的单层构型,随着浓度增加,缓蚀膜逐渐演变为ODA分子尾链间紧密交织的复杂双层构型。在ODA浓度超过一定阈值后,缓蚀膜的构型不再显著变化,未吸附成膜的ODA分子最终积聚形成胶体微团。     

单壁碳纳米管在LB培养基及生理盐水中的抗菌性研究

测定了单壁碳纳米管(SWNTs)在生理盐水及LB培养基中对革兰氏阳性菌枯草芽孢杆菌(B.subtilis)的抑菌率,探讨了SWNTs的抑菌机理及培养基对SWNTs抑菌性的影响。用扫描电镜(SEM)、透射电镜(TEM)对有无LB(Luria-Bertani)培养基的SWNTs进行了表征。结果表明:SWNTs的抑菌性受环境影响,在生理盐水及LB培养基中,抑菌性能表现迥异。     

内嵌金属的多壁碳纳米管辐射损伤研究

辐射损伤性能是制约核电池效能和使用寿命的重要因素。美国研究者Popa-Simil提出基于碳纳米管、金属复合结构材料的概念核电池,可实现核能到电能的高效转换,其设计中利用了碳纳米管的抗辐射损伤特性。本文通过建立包覆金属铜的多壁碳纳米管模型,采用分子动力学方法,对内嵌金属的多壁碳纳米管体系进行了辐射损伤的模拟研究。从配位缺陷数、溅射原子数、完美结构缺陷(Perfect structure defect,PST)原子数以及总的辐射损伤量等方面,与无内嵌金属的碳纳米管体系进行了分析对比。发现在有金属铜内嵌的情况下,溅射原子产额与无金属内嵌情况差别不大,但配位数缺陷和PST缺陷减小。表明内嵌金属起到支撑的效果,降低多壁碳纳米管在辐照下的形变,增强了其自修复能力,从而使得辐照耐受性能有所增强。     

脉冲激光沉积薄膜生长机制的计算机模拟研究

建立了一个分子动力学模型以研究脉冲激光沉积金属薄膜的成膜过程，探讨激光沉积中极主的瞬时沉积率和载能粒子轰击对成模机制的影响，以能量为１０ｅＶ的Ｃｕ原子入射到Ｃｕ（１００）表面为例，进行了分子动力学模拟的计算，结果表明，激光成膜过程中载能粒子的瞬时高能量沉积极大地增加了外延表面的原子扩散活性，促使薄膜能在低温下以原子层尺度逐层生长。     

碳纳米管-环糊精复合材料对Eu(Ⅲ)的吸附

在等离子体条件下用有机大分子材料环糊精对碳纳米管进行功能化处理,制备出一种新的放射性核素吸附材料,即碳纳米管-环糊精复合材料。实验研究了pH、时间、离子强度对该材料吸附Eu(Ⅲ)的影响。该材料对废水中Eu(Ⅲ)的吸附速率快,吸附率在95%以上,通过吸附方程推算得到对Eu(Ⅲ)的最大吸附量可达约80mg/g,废水中其它离子及浓度对Eu(Ⅲ)的吸附无明显影响。     

气相纯化处理对碳纳米管修饰的XANES和XPS谱学研究

结合X射线近边吸收谱和光电子能谱对经过一系列纯化过程处理后的单壁碳纳米管进行系统的表征.这些纯化过程包括空气氧化、盐酸浸泡以及退火处理.从实验结果发现单壁碳纳米管的表面修饰程度在纯化过程中逐渐增强,经过Ar气保护下的高温退火后,这些表面修饰明显减少.同时还发现单壁碳纳米管能与氯原子成键,这种简单的修饰方法可能对单壁碳纳米管的应用具有重要意义.     

基于分子动力学计算流体临界点预测方法研究

使用分子动力学(MD)方法计算了CO₂分子和H₂O分子的临界点,通过对气液平衡状态下的物性参数外推获得较为精确的临界点结果。对于CO₂分子,使用TraPPE模型和粗粒度模型SAFT进行了模拟,TraPPE模型计算结果更加接近美国国家标准与技术研究院(NIST)实验数据。对于H₂O分子,使用SPC/E和TIP4P/2005模型进行计算,结果表明TIP4P/2005模型的预测值与NIST实验数据最接近,同时对于分子水体系的饱和蒸汽压精确预测仍然存在挑战。     

Molecular dynamics study on carbon film deposition

Hydrogen-free carbon film deposition is studied through molecular dynamics (MD) simulation. MD simulation is performed for low-energy carbon particle impacts on carbon surfaces at room temperature. Deposition energy is considered up to E = 100 eV per carbon atom. Deposited surface is set into amorphous, and (1 1 1) surface of diamond crystal is considered in order to compare. For (1 1 1) surface, we found three characteristic regions. The deposition frequently results in the shallow trapping in E ? 20 eV. In E ? 30 eV, the deep trapping occurs about normal incidence, and the reflection appears about grazing incidence. For the amorphous surface, however, the reflection and the deep trapping are suppressed.     

Theoretical study on the carbon nanotube used ashard x—radiation source

Calculations and analyses are made on the interaction between the carbon nanotube and the incident positron of high energy.The results obtained show that it is possible to use carbon nanotube as hard X-radiation source with high intensity and good monochromaticity.     

Combined quantum-mechanics/molecular-mechanics dynamics simulation of A-DNA double strands irradiated by ultra-low-energy carbon ions

In order to promote understanding of the fundamentals of ultra-low-energy ion interaction with DNA, molecular dynamics simulations using combined quantum-mechanics/molecular-mechanics of poly-AT and poly-GC A-DNA double strands irradiated by <200 eV carbon ions were performed to investigate the molecular implications of mutation bias. The simulations were focused on the responses of the DNA backbones and nitrogenous bases to irradiation. Analyses of the root mean square displacements of the backbones and non-hydrogen atoms of base rings of the simulated DNA structure after irradiation revealed a potential preference of DNA double strand separation, dependent on the irradiating energy. The results show that for the backbones, the large difference in the displacement between poly-GC and poly-AT in the initial time period could be the reason for the backbone breakage; for the nitrogenous base pairs, A-T is 30% more sensitive or vulnerable to ion irradiation than G-C, demonstrating a preferential, instead of random, effect of irradiation-induced mutation.     

Effect of different ion beam energy on properties of amorphous carbon film fabricated by ion beam sputtering deposition (IBSD)

Amorphous carbon (a-C) films were fabricated by ion beam sputtering technique. The influence of sputtering ion beam energy on bonding structure, morphologic, mechanical properties, tribological properties and corrosion resistance of a-C films are investigated systematically. Morphology study shows that lowest surface roughness exists for mid-ion beam energy. Improved adhesion is observed for the films that are prepared under high ion beam energy, attributed to film graphitization, low residual stress and mixed interface. Relatively, a-C films prepared with ion beam energy of 2 keV exhibits optimum sp³ bond content, mechanical properties and corrosion resistance. It is found that the wear rate of DLC films decrease with increased ion beam energy in general, consistent with the varied trend of the H/E value which has been regarded as a suitable parameter for predicting wear resistance of the coatings. The correlation of the sp³ bond fraction in the films estimated from Raman spectroscopy with residual stress, nanohardness and corrosion resistance has been established.     

图像仿真在数字辐射成像系统指标估算中的应用

通过计算机模拟的方法改进了^60Co集装箱检测系统的指标估算的方法，结果CI和IQI指标估算值与实测值较好地吻合。     

CARR上的应力测量中子衍射谱仪概念设计和模拟研究

中子衍射法是迄今为止可直接测量材料或工程部件内部深处应力场分布的唯一非破坏性方法，在工程上具有重要的应用。中国先进研究堆（CARR)中子散射工程拟建造一台应力测量中子衍射谱仪，其主要功能是测量材料中的残余应力和载荷应力。本文介绍了该谱仪的概念设计方案，并应用蒙特卡罗模拟软件MCSTAS对设计方案进行了模拟研究，对部分中子部件参数进行了优化设计。     

Preparation of potassium iron(III) hexacyanoferrate(II) supported on activated carbon and Cs uptake performance of the adsorbent

Synthesis of potassium iron(III) hexacyanoferrate(II) (K/Fe-Fe(CN)₆) in the pores of activated carbon (AC) was attempted by impregnating AC with K₄[Fe(CN)₆] and FeCl₃, and the Cs uptake performance of the resulting adsorbent was examined. K/Fe-Fe(CN)₆ supported on AC was prepared by varying the reaction conditions such as the supplied amounts and molar ratios of the reagents, and the Cs uptake performance was optimized. The impregnated product was characterized by XRD, EPMA, and porosimetry to elucidate the condition to which Fe₄[Fe(CN)₆]₃ was filled in the AC pores. The K/Fe-Fe(CN)₆-on-AC was immersed in seawater containing 0.075 mmol · dm^?3 Cs and agitated for 1 day to obtain the Cs uptake. The Cs uptake was large at pH < 10 but decreased abruptly at pH > 10.5. The maximum Cs uptake was 10.4 μmol · g^?1 at the equilibrium Cs concentration of 49 μmol · dm^?3 and the distribution coefficient was 45.5 dm³ · g^?1 at the equilibrium concentration of 0.015 μmol · dm^?3, respectively. When K/Fe-Fe(CN)₆-on-AC was immersed in Cs-containing seawater, K⁺ ions in the adsorbent were completely exchanged for Na⁺ ions in seawater, and the added Cs⁺ ions were then substituted for the Na⁺ ions in the adsorbent.     

Formation of amorphous carbon on the surface of poly(ethylene terephthalate) by helium plasma based ion implantation

The surface modification of poly(ethylene terephthalate) (PET) by helium plasma based ion implantation (He PBII) was studied. The effect of the main process parameters (acceleration voltage, fluence and fluence rate) on the alterations of the surface chemical composition and structure were investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy.According to SRIM calculations, at ion energies above 2 keV the stopping power of PET for He⁺ ions is dominated by the electronic component and the contribution of the nuclear component is relatively small. Degradation of the ester group and carbonisation were observed by XPS due to elimination of O-rich fragments. The total C-content of the modified layer increased with the increase of fluence rate and acceleration voltage of particles, enabling the purposeful alteration of the surface composition. A strong broadening was detected in the Raman spectrum between 1000 and 1700 cm⁻¹, testifying to the intense formation of amorphous carbon. The area ratio of the D (∼1410 cm⁻¹) to G (∼1570 cm⁻¹) band increased with the increase of particle fluence and the increase of acceleration voltage, offering the possibility of tailoring the chemical structure of the amorphous carbon layer created by the He PBII treatment.     

肺密度变化对组织吸收剂量影响的模拟研究北大核心CSCD

为探究由呼吸运动引起的肺组织物理特性变化对肺组织及肿瘤组织吸收剂量的影响,基于蒙特卡罗方法进行模拟计算,使用EGSnrc(electron gamma shower software toolkit)程序将收集的不同密度肺组织数据转换成对应模体材料,建立不同呼吸状态下的组织模型,计算在不同射野照射下的百分深度剂量与离轴比差异,并探讨对目前常见照射技术的影响。结果表明,射野越小不同呼吸状态下组织吸收剂量差异越明显,在10 cm×10 cm射野下肺组织模体吸收剂量无明显差异,肿瘤模体吸收剂量最大降低3.86%;当射野小于5 cm×5 cm时上游肺组织模体吸收剂量随深度增加呈先增大后减小的趋势;在1 cm×1 cm时肺组织体膜吸收剂量差异最大达46.87%,肿瘤模体吸收剂量在1 cm×1 cm时差异最大达6.97%。同时在小野照射下低密度组织中存在明显的电子不平衡现象。在三维适形技术下呼吸运动引发的组织剂量差异小于调强及立体定向放射治疗,在呼吸门控技术下临床医生可结合TPS(treatment planning system)算法在吸气末进行靶区勾画,可降低正常肺组织剂量同时提高靶区剂量。     

Anisotropic rearrangement of the substrate atoms during Ar bombardment on Pd(0 0 1) surface

Using a three-dimensional molecular dynamics (MD) simulation, we investigated the atomic scale rearrangement that occurs on a Pd(0 0 1) surface after energetic bombardment by Ar at room temperature. High energy Ar bombardment provoked the significant rearrangement of Pd atoms in a ballistic manner with a fourfold symmetric lateral distribution aligned along the 〈1 1 0〉 direction. The MD simulation of uniform Ar bombardment at normal incidence on a Pd surface reproduced the experimentally observed fourfold symmetric nano-scale surface structure. The present result supports that the ballistic rearrangement of the substrate atoms plays an important role in the ion induced surface structure evolution.