三嵌段共聚物SEBS中自由体积行为的温度及e+辐照时间依赖性的研究

利用正电子湮没寿命谱实验手段研究了²²Na放射源的e⁺自辐射对三 嵌段共聚物SEBS的正电子湮没参数的影响，而后结合Eldrup的经典模型，研究了SEBS的自由体积孔尺寸和自由体积分数随着温度的变化关系，给出了自由体积分数在T_g以上和在Tg以下各自区域内分别与温度呈线性关系，最后结合Williams-Landel-Ferry(WLF)自由体积理论和Eldrup的经典模型讨论了热膨胀系数和自由体积分数中的A常数. 关键词： 正电子湮没技术 嵌段共聚物 自辐射 热膨胀     

60Co的γ辐照对SB的自由体积和微结构的影响的PALS和FT-IR的研究

利用正电子湮没技术和傅里叶红外分析研究手段，基于Eldrup的自由体积孔经典模型，分别研究了⁶⁰Co的γ辐照剂量对聚苯乙烯-丁二烯二嵌段共聚物(SB)的自由体积和微结构变化的影响，并关联两种测试结果，确定了⁶⁰Co的γ辐照对SB的辐照交联和降解模型.而后用热重分析(TGA)研究了辐照前后的SB的热稳定，给出了自由体积参数变化与热稳定的关联. 关键词： 正电子湮没技术 正电子素 嵌段共聚物 γ辐射     

超高分子量聚乙烯退火处理自由体积研究

本文用正电子湮没技术对超高分子量聚乙烯退火处理后的结构进行了研究。用ＰＡＴＦＩＴ－８８软件件分析了正电子湮没谱，给出了在１００℃条件下，样品的结晶度。自由体积和自由体积分数随退火的变化。实验证明，结晶度．自由体积和自由体积分数在退火初期变化最快，随着退火时间增加变化趋于平缓。这一结果与Ｗｕｎｄｅｒｌｉｃｈ提出的理论相一致。     

用正电子湮没研究高聚物聚甲基丙烯酸甲脂的结构转变与自由体积特性

在20—150℃温度范围内,测量了高聚物聚甲基丙烯酸甲酯(PMMA)中的正电子湮没寿命谱和湮没辐射多普勒展宽谱随温度的变化。两种正电子湮没参数的温度关系均一致反映了高聚物PMMA中的结构变化。108℃和48℃处的变化与玻璃化转变和β相交有关,而本实验发现正电子湮没特征在84℃处出现异常,这可能是此温度下少量自由体积孔洞的连通所致。由实验测得的o-Ps寿命及其相对强度计算了PMMA中自由体积孔洞的尺寸及自由体积分数随温度的变化。     

SMMA/SMA共聚物共混物的自由体积的热动态特性与相分离行为的PALS研究

基于自由体积理论，利用正电子湮灭寿命谱仪(PALS)分别研究在不同升温速率条件下，聚苯乙烯-甲基丙烯酸甲酯共聚物(SMMA)和聚苯乙烯-马来酸酐共聚物(SMA)混合物(30/70)的自由体积参数的温度依赖性，探索相容共混物相行为的热动态特性.在PALS实验中，在玻璃化转变温度T_g以上，当结构松弛的弛豫时间与等温停留时间相当，发现在某一段温度范围内，共混物的自由体积参数随着温度的变化明显地偏离线性关系.从自由体积孔的浓度I₃值在该段的变化趋势，初步推断共混物在该温 关键词： 正电子湮没 正电子素 聚合物共混物 相分离     

导电聚合物聚醚聚氨酯的结构与导电性能的正电子湮没研究

用正电子湮设方法研究了高分子固体电解质聚醚聚氨酯（ＰＥＵ）在与ＬｉＣlＯ₄络合前后的结构变化及导电性能．实验结果表明，当ＰＥＵ与ＬｉＣlＯ₄络合后，正电子素（o－Ｐｓ）的寿命及其强度均减少，而中间寿命分量的湮没参数基本不变．这表明Ｌｉ杂质主要扩散在无序的非晶区．掺杂前后样品的温度实验表明，在玻璃化转变温度Ｔ_g之下，络合前后的自由体积分数的变化很小，这与自由体积理论预言的结果一致．在Ｔ_g之上，络合后的自由体积空洞的浓度和自由体积分数均减小．此外，ＰＥＵ－ＬｉＣlＯ₄络合物的电导率随温度和Ｌｉ杂质浓度的变化可以用自由体积理论解释． 关键词：     

用正电子湮没探测高聚物的自由体积特性

简要介绍了用正电子湮没谱探测高聚物的微观结构的方法，给出了几种具有简单链结构的高聚物的玻璃化转变，自由体移浓度的标度行为，自由体积形成能的直接测量等方面的最新应用结果，由此表明，正电子湮没谱学在高分子物理研究领域具有十分广阔的应用前景。     

元素周期表中元素单晶基于局域密度理论的正电子寿命计算

在局域密度近似理论（LDA）的基础上用中性原子叠加模型和有限插分方法（SNA-FD）计算了元素周期表中各种元素单晶的正电子体寿命和单空位寿命.分析了不同结构的单晶中自由正电子的分布信息和湮没信息.元素单晶的正电子寿命计算值与文献中的实验测量值相符合,表明LDA基础上的SNA-FD方法可以作为单晶中正电子湮没理论计算的有效研究手段. 关键词： 局域密度近似理论 正电子寿命     

聚乙烯的多重弛豫与正电子湮没寿命谱

在143～373K用正电子湮没寿命谱(PALS)方法研究了高密度聚乙烯(HDPE)中的自由体积与温度 的关系.对实验谱分别进行了三寿命成分和四寿命成分分析,并对实验拟合结果作了微分的尝试.发现经这种方 法处理后的结果对温度变化十分灵敏,并且从四寿命分析的微分曲线可以完整地观察到HDPE在该温度区间的 三重α弛豫和表观双玻璃化转变过程,而用三寿命分析的微分曲线将难以解释这些转变.这说明对部分结晶的 聚合物而言,用四寿命拟合比三寿命拟合更符合实际的物理过程;讨论了正电子在HDPE中的湮没机制,证实正 电子在HDPE的结晶区和非晶区都可能形成电子偶素(Ps),而且正电子所处的空间大小对Ps产额有影响;最后 根据PALS实验的结果直接估算了HDPE在不同温度下的热膨胀系数.     

包含逃逸过程的正电子位错捕获模型

本文给出一个包含逃逸过程的正电子位错捕获模型,附带讨论割阶通过位错捕获正电子的温度依赖性,并找出正电子主要湮没在位错线上的起始温度.     

Parameter dependence and outcome dependence in dynamical models for state vector reduction

We apply the distinction between parameter independence and outcome independence to the linear and nonlinear models of a recent nonrelativistic theory of continuous state vector reduction. We show that in the nonlinear model there is a set of realizations of the stochastic process that drives the state vector reduction for which parameter independence is violated for parallel spin components in the EPR-Bohm setup. Such a set has an appreciable probability of occurrence ( 1/2). On the other hand, the linear model exhibits only extremely small parameter dependence effects. We investigate some specific features of the models and we recall that, as has been pointed out recently, if one wants to be able to speak of definite outcomes (or equivalently of possessed objective elements of reality) at finite times, one has to slightly change the criteria for their attribution to physical systems. The concluding section is devoted to a detailed discussion of the difficulties which one meets when one tries to take, as a starting point for the formulation of a relativistic theory, a nonrelativistic scheme which exhibits parameter dependence. Here we derive a theorem which identifies the precise sense in which the occurrence of parameter dependence forbids a genuinely relativistic generalization. Finally we show how the appreciable parameter dependence of the nonlinear model gives rise to problems with relativity, while the extremely weak parameter dependence of the linear model does not give rise to any difficulty, provided one takes into account the appropriate criteria for the attribution of definite outcomes.Work supported in part by the Trieste Section of the INFN.     

Soil radon depth dependence

The knowledge of the soil radon levels is important for the planning and construction of new buildings in order to estimate the radon risk and to classify the ground for construction purposes.

The purpose of this investigation was to study in situ the radon levels at various depths 0–2 m in terrain where the geology is comparatively uniform. The data from the measurements was fitted to simple functions in order to facilitate future extrapolations of radon levels from various depths to 1 m at measurements anywhere.

The plastic film Kodak LR 115 was used as the detector of the radon levels at four different depths in the interval 0–2 m. The measurements were made along a 2200 m long profile at 16 different points.     

Temperature dependence in sputtering

We have obtained the result on the temperature dependence in sputtering of silver which is contrary to the current believes by taking steps to eliminate spurious effects due to changes of residual gas pressure and target temperature, and by determining the relevant energy range for thermal sputtering. The result i3 thought to be due basically to the thermal spike effect, and agreement is shown with a postulated thermal spike model, in which the instantaneous variation of spike temperature against thermal diffusivity is treated on the basis of Carslaw's solution of the normal heat conduction equation. The thermal diffusivity is shown to be proportionate to the thermal conductivity subject to a constant metal density in the temperature range 300–500K and a heat capacity that obeys the Dulong-Petit law which holds good for most metals at high temperatures (> θ_D). The thermal conductivity versus preheat target temperature curve matches the Makinson electronic thermal conductivity curve for metals.     

Temperature dependence of viscosity

A correction to the simple exponential temperature dependence of viscosity arises because of a difference between the real and ideal conditions for a viscous fluid flow. This correction is similar to those to pressure and volume in the real gas law. As a result, the expression for viscosity takes the form

Spatial dependence of dispersion

The use of Pulsed Gradient Spin Echo (PGSE) NMR to investigate flow in porous media is well established. Using two pairs of position-encoding pulses in the PGSE experiment gives the possibility of examining velocity fluctuations, by comparing displacements, during the two encoding intervals. This method may be used to measure the asymptotic dispersion coefficient as well as the Velocity Auto-Correlation Function (VACF) in porous media flow. Some examples of two-dimensional maps of density and velocity distributions are accompanied by the first attempt to perform localized measurements of flow dispersion in porous media.     

Density dependence and composition dependence of the viscosity of neon-helium and neon-argon mixtures

In this paper we present a detailed experimental study of the density dependence of the viscosity of HeNe and NeAr mixtures at various compositions. The data are analyzed in terms of a density expansion including a logarithmic contribution whose presence is predicted by the kinetic theory of gases. The composition dependence of the viscosity of the dense gas mixtures is compared with estimated values predicted on the basis of the Enskog-Thorne theory for dense mixtures of gases of hard spheres.     

Velocity dependence of atomic friction

Sliding friction between the tip of a friction force microscope and NaCl(100) was studied to deduce the velocity dependence of friction forces on the atomic scale. A logarithmic dependence of the mean friction force is revealed at low velocities. The experimental data are interpreted in terms of a modified Tomlinson model which is based on reaction rate theory.     

Temperature dependence of infrared spectra

A simple form of cell for the study of infrared absorption spectra at low and high temperatures is described. Preliminary results of a study of the temperature-phase dependence of fluorobenzene and m-toluic acid spectra are reported.