圆盘锯齿型石墨烯量子点的电子结构研究

通过数值求解Dirac方程,研究了在垂直磁场下锯齿型（zigzag）石墨烯（graphene）量子点的能谱结构。无磁场时,量子点能谱没有带隙,并存在能量为零的边界态。当外加磁场时,能谱中出现朗道能级,最低朗道能级能量为零且与磁场大小无关,随着磁场的增加,朗道能级简并度会随之增加。同时发现,磁场对K点与K’点的能谱结构有不同的影响,导致谷（valley）间简并被破坏。     

Ce和S共掺杂SnO2材料导电性能的第一性原理研究

本文利用密度泛函理论的第一性原理平面波超软赝势法计算了Ce和不同浓度S元素共掺杂后SnO₂的电子结构，定性分析了各掺杂模型的晶体结构、能带结构、态密度和电荷布局，定量计算了相对电导率。分析结果表明：随着S原子掺杂浓度的增大，掺杂体系的形成能不断增大，稳定性也随之降低；与Ce单掺相比，共掺后能带整体向费米能级方向移动，能带曲线更紧密，禁带宽度进一步减小，载流子跃迁所需的能量进一步降低；共掺后费米能级附近的态密度有所增大，这是因为S原子轨道和Sn和Ce原子轨道发生杂化，电子转移加剧，价带顶部被S-3p轨道占据，提供了更多载流子；同时共掺使材料的电荷密度分布改变，共价性减弱，离子性增强；共掺后，自由电子浓度明显增大，电子迁移率明显提高，电导率也明显优于单掺体系；与Ce-2S掺杂结构相比，Ce-S掺杂结构的自由电子迁移率更高，电导率也更高，说明Ce-S共掺结构的导电性能更佳。     

爆炸固结法制备MoSi2p/Nb复合材料的铸态组织研究

主要通过扫描电镜研究了爆炸固结法制备的MoSi2p／Nb复合材料铸态组织。结果表明，爆炸固结瞬间，由于冲击波能量汇聚产生铸态组织。爆炸固结过程中，冲击波能量在粉末颗粒中分布不平衡，造成爆炸固结过程中形成液相数量不同，导致在最终爆炸固结试样中形成不同的微观组织形貌。粉末在冲击波作用下表现出粉末颗粒效应。由于爆炸固结后熔融液体的冷却速度极快，MoSi2p／Nb复合材料中存在轻微偏析现象，并存在枝晶结构。     

富Al的Al—Ti系的机械合金化

本文研究了富Ａｌ的Ａｌ－Ｔｉ混合粉末在球磨过程中的结构演变过程。研究结果表明球磨机的类型即球磨输入能量对混合粉末的结构变化有很大影响，球磨输入能量决定最终球磨态粉末的畸变程度和晶粒大小。输入能量高的球磨方式能导致Ｔｉ完全地过饱和固溶于Ａｌ中，甚至有部分非晶相和ＬＩ_２有序相的形成。中等输入能量只能形成过饱和固溶体，而输入能量较低就不能使Ａｌ－Ｔｉ完全过饱和固溶，更不能形成非晶相。利用ＧＮ－２型球磨机制备的机械合金化Ａｌ－Ｔｉ粉末的畸变明显高于另外两种球磨机制备的粉末，旦晶粒最细。高的畸变和细的晶粒可能是合金部分非晶化的原因之一。     

SO2-4,NO-3,Cl-对ZnS,CdS纳米粉末晶型的影响

考察了采用均相沉淀法制备单分散ZnS和CdS纳米微粒时，溶液中SO4^2-、NO3^-和Cl^-对粉末晶型的影响。结果表明，SO4^2-、NO3^-和Cl^-对ZnS粉末晶型基本上没有影响；而在NO3^-、SO4^2-体系中得到闪锌矿型CdS粉末，在Cl^-体系中，得到纤维锌矿结构CdS粉末。这是因为在Cl^-体系中，Cl^-和Cd^2 的络合作用不仅改变了溶液中沉淀离子的过饱和度，更重要的是改变了溶液中生长基元的存在形式及其连接方式，从而生成了结构更稳定的纤维锌矿型CdS晶体。     

氩气氛NTDFZ－Si中的空位型缺陷

用正电子湮没技术研究了生长态、总注入量分别为５．８×１０￣（１６）和３．６×１０￣（１７）ｃｍ￣（－２）的中子辐照氩气氛区熔单晶硅中空位型缺陷的退火行为，发现未辐照单晶硅在从室温到高温的退火过程中始终存在着分量强度为１０％～１８％的单空位型缺陷；低注入量中子辐照的主要缺陷是单空位型，较高注入量中子辐照时单空位和双空位型缺陷浓度均较高。     

CaMn1-xWxO3(0.05≤x≤0.20)体系电荷有序的建立与消失

通过对样品磁化强度-温度（M-T）曲线、磁化强度-磁场强度（M-H）曲线、电阻率-温度（ρ-T）曲线及部分样品ESR谱的测量，研究了Mn位w掺杂对Cabin1-x，WxO3（x=0．05，0．07，0．10，0．12，0．14，0．16，0．20）体系磁结构的影响。结果表明，随着W掺杂量的增加，体系磁结构发生了复杂的变化过程。当掺杂量x≤0．07时，体系为铁磁（FM），反铁磁（AFM）和顺磁（PM）态的共存，随掺杂量增加，FM态减弱，AFM态增强；当x=0．10，0．12时，体系建立电荷有序（charge ordering，CO）态，AFM／CO态共存于相变温度以下，且电荷有序温度TCO随掺杂量增加而增加；当x≥0．14时，体系电荷有序（CO）态减弱并消失。     

选区激光熔化FGH4096高温合金的组织与性能

以等离子旋转电极法制备的FGH4096粉末为原材料,利用选区激光熔化(selective laser melting,SLM)技术制备了FGH4096合金,合金致密度达99. 3%。研究了SLM沉积态、直接时效态、固溶+时效态的组织和拉伸性能。SLM沉积态FGH4096合金由柱状晶构成,垂直熔池边界生长,柱状晶内排列着精细的树枝结构或等轴结构,以奥氏体γ相为主,少量的γ′相和碳化物沿树枝结构和等轴结构边界析出;直接时效处理后,大量三次γ′相析出,树枝结构或等轴结构边界粗化;固溶+时效后,回复和再结晶的发生,合金晶粒呈不规则形状,树枝结构和等轴结构消失,少量一次γ′相和碳化物在晶界析出,晶内分布少量二次γ′和大量均匀的三次γ′相。SLM沉积态FGH4096室温拉伸塑性好,热处理后强度明显提高,塑性下降,直接时效态屈服强度和拉伸强度最高,接近锻造状态。3种状态拉伸断口呈穿晶断裂,随着强度的提高,直接时效态拉伸断口出现数量较多的沿晶断裂区域。     

Sm2O3对Ba0.5Sr0.5Co0.75Fe0.25O3-δ体系电子结构及氧空位影响的理论研究

采用第一性原理对掺杂Sm2O3的Ba0.5Sr0.5Co0.75Fe0.25O3-δ体系的电子结构和空位形成能进行了研究。研究结果表明,Co和Sm的态密度在费米能级附近有较大的态,而Fe则很小,这使得Co和Sm离子易于变价,而Fe离子的化合价则基本保持不变。空位形成能随空位数的增多而增大,Sm的掺杂有利于氧空位的形成,且CoVFe比CoVCo型氧空位形成能稍大,这些源于体系的电子结构和局域几何结构。     

爆炸焊接边界效应的力学-能量原理

在爆炸焊接工艺中，存在一种称为边界效应的物理现象。即在一般情况下，在爆炸焊接后的复合材料中，会出现雷管区不复、其余周边被打伤、打裂和变形严重等问题。这些问题严重地影响着这类材料的质量。该文从传统的和经典的力学及能量原理出发，探讨了边界效应产生的力学－能量原理，并且提出了预防的措施。     

Lipid bilayer electrostatic energy, curvature stress, and assembly of gramicidin channels

Hydrophobic interactions between lipid bilayers and imbedded membrane proteins couple protein conformation to the mechanical properties of the bilayer. This coupling is widely assumed to account for the regulation of membrane protein function by the membrane lipids' propensity to form nonbilayer phases, which will produce a curvature stress in the bilayer. Nevertheless, there is only limited experimental evidence for an effect of bilayer curvature stress on membrane protein structure. We show that alterations in curvature stress, due to alterations in the electrostatic energy of dioleoylphosphatidylserine bilayers, modulate the structurally well-defined gramicidin A monomer <--> dimer reaction. Maneuvers that decrease the electrostatic energy of the unperturbed bilayer promote channel dissociation; we measure the change in interaction energy. The bilayer electrostatic energy thus can affect membrane protein structure by a mechanism that does not involve the electrostatic field across the bilayer, but rather electrostatic interactions among the phospholipid head groups in each monolayer which affect the bilayer curvature stress. These results provide further evidence for the importance of mechanical interactions between a bilayer and its imbedded proteins for protein structure and function.     

Properties of calcium spikes revealed during GABAA receptor antagonism in hippocampal CA1 neurons from guinea pigs

A potential energy function for unsaturated hydrocarbons is proposed and is shown to agree well with experiment, using molecular dynamics simulations of a water/octene interface and a dioleoyl phosphatidylcholine (DOPC) bilayer. The simulation results verify most of the assumptions used in interpreting the DOPC experiments, but suggest a few that should be reconsidered. Comparisons with recent results of a simulation of a dipalmitoyl phosphatidylcholine (DPPC) lipid bilayer show that disorder is comparable, even though the temperature, hydration level, and surface area/lipid for DOPC are lower. These observations highlight the dramatic effects of unsaturation on bilayer structure.     

The formation and annealing of structural defects in lipid bilayer vesicles

It is shown that sonication of phospholipid-water dispersions below the crystalline leads to liquid crystalline phase transition temperature (Tc) produces bilayer vesicles with structural defects within the bilayer membrane, which permit rapid permeation of ions and catalyze vesicle-vesicle fusion. These structural defects are annihilated simply by annealing the vesicle suspension above Tc. The rate of annealing was found to be slow, of the order of an hour for T = 3 degrees C above Tc, but annealing is complete within 10 min for T = 10 degrees C above Tc. It is proposed that these structural defects are fault-dislocations in the bilayer structure, which arise from a population defect in the distribution of the lipid molecules between the outer and inner monolayers, when small bilayer fragments reassemble to form the small bilayer vesicles during the sonication procedure. Such a population defect can only be remedied by lipid transport via the inside in equilibrium outside flip-flop mechanism, which would account for the slow kinetics of annealing observed even at 3 degrees C above the phase transition.     

The structure and morphology of the abnormal serum lipoprotein-X

The structure and morphology of an abnormal lipoprotein particle present in the serum of patients with obstructive jaundice has been investigated by gel filtration, electron microscopy and NMR spectroscopy. Lipoprotein-X is a spherical lipoprotein particle with an average Stokes diameter of approximately 40 nm and a wide size distribution ranging from 20 to 70 nm. Different from all lipoprotein structures known so far lipoprotein-X is a hollow particle (= vesicle) with a water-filled internal cavity surrounded by a continuous, single bilayer which is impermeable to cations and K3Fe(CN)6. The packing of the bilayer is tighter and the segmental motion of both the polar group and the hydrocarbon chains are significantly reduced relative to typical phosphatidylcholine bilayers. In terms of segmental motion and anisotropy of packing the lipoprotein-X bilayer closely resembles a model bilayer system consisting of phosphatidylcholine, lysophosphatidylcholine, sphingomyelin and cholesterol mixed in the same molar ratio as in lipoprotein-X. In that model system the phospholipid distribution between the two layers of the bilayer is asymmetric with (sphingomyelin + lysophosphatidylcholine) being preferentially located on the inner layer and phosphatidylcholine preferentially on the outer layer of the bilayer. By analogy with the model system the phospholipid distribution in lipoprotein-X bilayers is proposed to be also asymmetric.     

Energetics of inclusion-induced bilayer deformations

The material properties of lipid bilayers can affect membrane protein function whenever conformational changes in the membrane-spanning proteins perturb the structure of the surrounding bilayer. This coupling between the protein and the bilayer arises from hydrophobic interactions between the protein and the bilayer. We analyze the free energy cost associated with a hydrophobic mismatch, i.e., a difference between the length of the protein's hydrophobic exterior surface and the average thickness of the bilayer's hydrophobic core, using a (liquid-crystal) elastic model of bilayer deformations. The free energy of the deformation is described as the sum of three contributions: compression-expansion, splay-distortion, and surface tension. When evaluating the interdependence among the energy components, one modulus renormalizes the other: e.g., a change in the compression-expansion modulus affects not only the compression-expansion energy but also the splay-distortion energy. The surface tension contribution always is negligible in thin solvent-free bilayers. When evaluating the energy per unit distance (away from the inclusion), the splay-distortion component dominates close to the bilayer/inclusion boundary, whereas the compression-expansion component is more prominent further away from the boundary. Despite this complexity, the bilayer deformation energy in many cases can be described by a linear spring formalism. The results show that, for a protein embedded in a membrane with an initial hydrophobic mismatch of only 1 A, an increase in hydrophobic mismatch to 1.3 A can increase the Boltzmann factor (the equilibrium distribution for protein conformation) 10-fold due to the elastic properties of the bilayer.     

Complications of sedation with midazolam in the intensive care unit and a comparison with other sedative regimens

Small angle X-ray diffraction was used to examine arterial smooth muscle cell (SMC) plasma membranes isolated from control and cholesterol-fed (2%) atherosclerotic rabbits. A microsomal membrane enriched with plasma membrane obtained from animals fed cholesterol for up to 13 weeks showed a progressive elevation in the membrane unesterified (free) cholesterol:phospholipid (C/PL) mole ratio. Beyond 9 weeks of cholesterol feeding, X-ray diffraction patterns demonstrated a lateral immiscible cholesterol domain at 37 degrees C with a unit cell periodicity of 34 A coexisting within the liquid crystalline lipid bilayer. On warming, the immiscible cholesterol domain disappeared, and on cooling it reappeared, indicating that the immiscible cholesterol domain was fully reversible. These effects were reproduced in a model C/PL binary lipid system. In rabbits fed cholesterol for less than 9 weeks, lesser increases in membrane C/PL mole ratio were observed. X-ray diffraction analysis demonstrated an increase in membrane bilayer width that correlated with the C/PL mole ratio. This effect was also reproduced in a C/PL binary lipid system. Taken together, these findings demonstrate that in vivo, feeding of cholesterol causes cholesterol-phospholipid interactions in the membrane bilayer that alter bilayer structure and organization. This interaction results in an increase in bilayer width peaking at a saturating membrane cholesterol concentration, beyond which lateral phase separation occurs resulting in the formation of separate cholesterol bilayer domains. These alterations in structure and organization in SMC plasma membranes may have significance in phenotypic modulation or aortic SMC during early atherogenesis.     

Simultaneous measurement of spectroscopic and physiological signals from a planar bilayer system: detecting voltage-dependent movement of a membrane-incorporated peptide

We developed an experimental system that can measure spectroscopic and physiological signals simultaneously from ion channels in a planar lipid bilayer, to study the relationship between the structure and function of the ion channels. While the membrane potential was clamped, fluorescent emission and ionic currents were measured simultaneously. The fluorescent emissions from a planar bilayer constructed in a specially designed chamber were monitored exclusively, and the signal intensity was measured with a photon-counting system. The intensity of fluorescence and spectral shape were measured successfully from the planar bilayer, with a high signal-to-noise ratio. The system can measure the intensity of fluorescence from a restricted area of the planar bilayer, with a diameter of 70 micrometer and a focal depth of 15 micrometer. The low background signal was achieved by optimizing the optical system. More than 95% of the measured fluorescence comes from the planar lipid bilayer. A 22-mer peptide with a sequence identical to that of the S4 segment of the electric eel sodium channel domain IV was synthesized and fluorescence-labeled. This peptide formed a voltage-dependent ion channel in a planar bilayer. The changes in the intensity of the fluorescence accompanying ionic currents generated by a voltage clamp suggest that voltage gating involves the insertion of the N-terminal of the peptide into the membrane. The electrical and optical signals were measured with a gate time of 10 ms. This measurement enabled the detection of movement of the membrane-incorporated peptides with channel opening.     

Structure and properties of an R6M5K5 high-speed steel-titanium carbide composite in the form of a hot-forged bilayer product

The structure of a bilayer powder composite consisting of a working wear-resistant layer (carbidosteel) based on R6M5K5 high-speed steel with disperse titanium carbide inclusions and of a substrate made of a plain carbon steel is studied. This carbidosteel is fabricated by hot forging of powder workpieces. The structures of the hot-forged and sintered steels in the zone of steel-titanium carbide interaction are compared. The physicomechanical properties and wear resistance of a bilayer product with a wear-resistant carbidosteel layer produced by hot forging are estimated and compared to carbidosteels produced by other methods.     

Definition of conditions for the detection of genotoxic chemicals in the adult rat-liver epithelial cell/hypoxanthine-guanine phosphoribosyl transferase (ARL/HGRPT) mutagenesis assay

1. Fresh human erythrocytes were treated with lytic and non-lytic combinations of phospholipases A2, C and sphingomyelinase. The 31P-NMR spectra of ghosts derived from such erythrocytes show that, in all cases, the residual phospholipids and lysophospholipids remain organized in a bilayer configuration. 2. A bilayer configuration of the (lyso)phospholipids was also observed after treatment of erythrocyte ghosts with various phospholipases even in the case that 98% of the phospholipid was converted into lysophospholipid (72%) and ceramides (26%). 3. A slightly decreased order of the phosphate group of phospholipid molecules, seen as reduced effective chemical shift anisotropy in the 31P-NMR spectra, was found following the formation of diacyglycerols and ceramides in the membrane of intact erythrocytes. Treatment of ghosts always resulted in an extensive decrease in the order of the phosphate groups. 4. The results allow the following conclusions to made: a. Hydrolysis of phospholipids in intact red cells and ghosts does not result in the formation of non-bilayer configuration of residual phospholipids and lysophospholipids. b. Haemolysis, which is obtained by subsequent treatment of intact cells with sphingomyelinase and phospholipase A2, or with phospholipase C, cannot be ascribed to the formation of non-bilayer configuration of phosphate-containing lipids. c. Preservation of bilayer structure, even after hydrolysis of all phospholipid, shows that other membrane constitutents, e.g. cholesterol and/or membrane proteins play an important role in stabilizing the structure of the erythrocyte membrane. d. A major prerequisite for the application of phospholipases in lipid localization studies, the preservation of a bilayer configuration during phospholipid hydrolysis, is met for the erythrocyte membrane.     

Structural studies of polymer-cushioned lipid bilayers

The structure of softly supported polymer-cushioned lipid bilayers, prepared in two different ways at the quartz-solution interface, were determined using neutron reflectometry. The polymer cushion consisted of a thin layer of branched, cationic polyethyleneimine (PEI), and the bilayers were formed by adsorption of small unilamellar dimyristoylphosphatidylcholine (DMPC) vesicles. When vesicles were first allowed to adsorb to a bare quartz substrate, an almost perfect bilayer formed. When the polymer was then added to the aqueous solution, it appeared to diffuse beneath this bilayer, effectively lifting it from the substrate. In contrast, if the polymer layer is adsorbed first to the bare quartz substrate followed by addition of vesicles to the solution, there is very little interaction of the vesicles with the polymer layer, and the result is a complex structure most likely consisting of patchy multilayers or adsorbed vesicles.