Universality in eight-arm star polystyrene and methylcyclohexane mixtures near the critical point

Measurements of the coexistence curve and turbidity were made on different molecular mass samples of the branched polymer-solvent system eight-arm star polystyrene in methylcyclohexane near its critical point. We confirmed that these systems belong in the Ising universality class. The location of the critical temperature and composition as well as the correlation length, susceptibility, and coexistence curve amplitudes were found to depend on molecular mass and the degree of branching. The coexistence curve diameter had an asymmetry that followed a "complete scaling" approach. All the coexistence curve data could be scaled onto a common curve with one adjustable parameter. We found the coexistence curve amplitude to be about 12% larger for branched than linear polystyrenes of the same molecular mass in either solvent cyclohexane or methylcyclohexane. The two-scale-factor universality ratio R was found to be independent of molecular mass or degree of branching.     

共聚物平均组成曲线软件的开发

利用高级编程语言Vc 6.0为工具,制作了高分子化学课程中的共聚物平均组成曲线的动态曲线图.曲线显示窗口主要有以下功能,即重画坐标系功能、清除当前曲线功能、清除全部曲线功能、绘制曲线功能、输入参数功能、返回登陆窗口功能.采用控件编程技术,实现了参数的随机录入、曲线的动态形成、坐标系和曲线的变色绘制、线体和线宽的重新设置以及序列显示曲线相关参数等诸多功能.它不仅可以作为高分子化学课程课堂教学使用,又可作为本专业学生有效地进行课后复习.该教学系统针对性强,操作简单,使用方便,是一种较实用的计算机辅助教学工具.     

Time-strain rate superposition for relaxation behavior of polyethylene pressure pipes

A new superposition principle based on time and strain rate is suggested as an alternative approach to construct a master curve of relaxation modulus versus time for polyethylene (PE) pressure pipe. The new approach uses results from a series of relaxation tests that reach the same relaxation strain at different strain rates (by varying the crosshead speed). Construction of the master curve for the relaxation modulus is first through horizontal shift using an expression similar to that for the time–temperature superposition principle. Then, a vertical shift is applied to generate a smooth curve profile. Such a time-strain rate superposition principle can serve as an alternative approach to construct a master curve for the long-term behavior of PE. The master curve shows two transitions for the rate of decrease of the relaxation modulus, instead of one transition reported before. The additional transition occurs within a short period after the relaxation strain is reached, and is detectable only if the initial strain rate is sufficiently low. Discovery of the new transition offers an additional perspective for studying mechanisms involved in the PE deformation.     

Polymer analysis by fractionation with on-line light scattering detectors

Summary The classical method for the determination of the molecular weight distribution (MWD) curve of a polymer requires fractionation according to the molecular weight and prior calibration of the separator. It is shown that the use of a dual detection system which includes a molecular mass sensitive detector eliminates the need for prior calibration. The principles of operation of a low-angle light scattering photometer, working as such a detector, are presented, as well as the basic equations for determination of the MWD curve from the elution curve and of the average molecular weights. Then the performances of the light scattering photometer are discussed with special emphasis on the various sources of errors and unaccuracies in these determinations.     

Modulated temperature DSC measurements relating to the cold crystallization process of poly(ethylene terephtalate)

The modulated temperature differential scanning calorimetric method (MT-DSC) yields three temperature dependent signals, an underlying heat capacity curve from the underlying heat flow rate (corresponding to the conventional DSC signal), and a complex heat capacity curve with a real part (storage heat capacity) and an imaginary part (loss heat capacity). These curves have been measured in the cold crystallization region for poly(ethylene terephtalate) with a modified Perkin-Elmer DSC-7. The underlying curve shows the well known large exothermic crystallization peak. The storage heat capacity shows a step change which reproduces the change in heat capacity during crystallization. This curve may be used as baseline, to separate the crystallization heat flow rate from the underlying heat flow rate curve. The loss heat capacity curve exhibits a small exothermic peak at the temperature of the step change of the storage curve. It could be caused by changes of the molecular mobility during crystallization.Dedicated to Professor Wunderlich on the occasion of his 65th birthday     

Quantum mechanical guides to the potential energy curves of some simple molecules

The molecular orbital expression for the bond energy of a chemical bond is used to obtain some insight into the factors which produce the potential energy curves of a number of simple bonds. The resulting picture of bond formation and the potential energy curve is an electrostatic one and it depicts the potential energy curve as the sum of a long range attractive curve and a short range repulsive one. Broadly speaking, that part of the curve to the long bond length side of the minimum is determined essentially by the two electrons which form the bond and, in particular, by the `binding energy' of these two electrons. The position of the minimum and the shape of the short bond length side of the curve do depend in general on the other valence electrons of the two atoms. The long range attractive curve is easily calculated but it is difficult to get the short range repulsive curve accurately. The results may prove useful in the construction of potential energy surfaces where the long bond length side of the potential energy curve is the important part.     

Program in BASIC for Ferguson plot analysis, using a personal computer: application to gel electrophoresis in a continuous buffer

A program in BASIC suitable for personal computers is described which is applicable to gel electrophoresis conducted in a single (continuous) buffer. The curve fitting is to a polynomial function, allowing for an objective selection of the most appropriate curve type and order--linear, convex or concave--in the particular application. Results do not differ significantly from previous programs for evaluation of linear Ferguson plots or of curve fitting to an exponential function for evaluating convex plots, executed on mainframe computers such as the DEC-10 (Digital) and IBM 370 computers. Thus, the program combines original versatility with, for the first time, the possibility for widespread application of Ferguson plot analysis on personal computers.     

The effect of input pulse duration on the elution curve profile

Numerical simulation and new analytical solutions have been used to study the effect of the duration of the input pulse of an adsorbate on the development of the elution curve profile in the adsorption dynamics. Elution curves calculated with regard to finite input pulse duration have been compared with those determined for the instantaneous injection of an adsorbate in the absence of extracolumn broadening. Quantitative regularities of variations in curve parameters measured as the time corresponding to the maximum of the curve and its width at a fixed height as depending on the length of an adsorbent layer have been estimated. The influence of the input pulse duration on the statistical moments of the elution curve has been determined, with the obtained moments being in agreement with the published solution that was previously found using the Laplace transformations. Correspondence between the theoretical and experimental data has been revealed for argon elution from a helium flowing through an activated carbon layer.     

A new approach to data reduction and evaluation in high-resolution time-of-flight mass spectrometry using a time-to-digital convertor data-recording system

A new effective and robust approach to the detection of incompletely resolved peaks, and evaluation of their parameters in high-resolution time-of-flight mass spectra for time-to-digital convertor (TDC) data acquisition mode, is described. The method is based on fast construction of a smoothed continuous curve that approximates the initial data (transformed to a constant relative width of time intervals for ion counting) with respect to precision of measurements. The first derivative of this curve is used for correction of skewness of the peak shape as far as possible. A contribution of the second derivative is subtracted from the smoothed curve for better resolution of partially resolved peaks. The comparison of local maxima of this resulting final curve with those for the initial smoothed curve allows reliable detection of the peaks and to test whether or not they are spoiled by overlapping. Ion counting performed by TDC gives an opportunity to estimate standard deviations of peak locations and their intensities. These values proved to be close to theoretically minimal standard deviations for these parameters for single fully resolved peaks. Thus, estimates of the main parameters of mass peaks by the described method are close to statistically efficient estimators for these parameters.     

AVERAGE LATITUDINAL VARIATION IN ULTRAVIOLET RADIATION AT THE EARTH''S SURFACE

Abstract— Tabulated values are presented for ultraviolet radiation at the earth's surface as a function of wavelength, latitude, and season, for clear sky and seasonally and latitudinally averaged ozone amounts. These tabulations can be combined with any biological sensitivity function in order to obtain the seasonal and latitudinal variation of the corresponding effective doses. The integrated dosages, based on the erythemal sensitivity curve and on the Robertson-Berger sunburn-meter sensitivity curve, have also been calculated, and these are found to vary with latitude and season in very nearly the same way as 307 and 314 nm radiation, respectively.     

Creep behavior and lifetime prediction of PMMA immersed in liquid scintillator

The creep behavior of PMMA immersed in liquid scintillator at room temperature was experimentally studied with a new type of creep test machine. Both short-term and creep-rupture tensile tests at eight stress levels were performed. A master curve of creep compliance at a reference stress was obtained according to the Time-Stress Superposition Principle. The master curve was compared with the actual long-term creep curve. It demonstrates that the two curves coincide well at short times. However, the actual creep data shows a higher creep rate as time goes on. The actual lifetime is much shorter than that predicted by the master curve. Furthermore, the relationship between long-term creep limited strength and service life was determined. The results can be used to guide the safety design of PMMA vessels for application in a neutrino observatory.     

Wesslau分布和Lansing-Kraemer分布在给定区间内的平均分子量

由于Wesslau公式不够精确,用于计算分布较宽的正态GPC曲线将导致较大的误差。这一问题以往尚未为人们所觉察,本文推导出Wesslau分布及Lansins-Kraemer分布在给定区间内M的计算公式,不但可提高函数法计算M的准确度,而且对分布曲线的性质得出了一些新的结论。还指出了提高GPC法测定宽分布试样M准确度的途径。     

A free-electron theory of optical activity

The Schrödinger equation is derived for an electron moving in the field of a potential supported by a space curve, and an approximate solution is found which becomes exact as the potential binds the electron more and more tightly to the curve but otherwise does not restrict the electron's motion along the curve. These so-called free-electron wavefunctions and energy levels are used to obtain a general expression for the optical rotatory power associated with an arbitrary space curve. Calculations of the specific rotatory power are carried out for three different curves.     

Direct current conductivity and ion motions in poly(vinyl chloride)‐poly‐1,4‐cis butadiene blends by electrical relaxation method

Ionic conduction in poly(vinyl chloride) (PVC)‐poly‐1,4‐cis butadiene blends has been studied using the electrical relaxation method. Temperature dependence of direct current (dc) conductivity does not change at the glass transition of PVC but does change at higher temperatures. The shape of the frequency dispersion curve of the electric modulus in a frequency range from 0.01 to 100 Hz depends on temperature. At low temperatures, the shape of the dispersion curve is reproduced by calculation assuming the Debye decay function, whereas this is not reproduced at high temperatures. Two kinds of analysis of the dispersion curve are discussed for this complicated change in the shape of the dispersion. One is that the dispersion curve is regarded as a single process expressed by the Kohlrausch decay function, and the other is that the curve is regarded as two processes expressed by the Debye and the Kohlrausch decay functions. The observed dispersion of the electric modulus is not expressed by the single process but by the two processes. One of the two processes is characterized by the Debye decay function, and the other is characterized by the Kohlrausch decay function. The parameter of the Kohlrausch decay function for one of these processes has a value of 0.82, and this value does not depend on temperature. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 226–235, 2002     

Cloud-Point Curve for the System Copoly(Ethylene-Vinyl Acetate) Plus Methyl Acetate. Measurement and Prediction by Continuous Thermodynamics

The cloud-point curve for the system copoly(ethylene-vinyl acetate) plus methyl acetate has been measured by a simple visual method. The critical point was determined by using the phase volume ratio method. The method of continuous thermodynamics was applied for thermodynamic treatment. The composition of the copolymer is described by a divariate distribution function assumed as a generalized Stockmayer distribution. The activity coefficients were obtained with the aid of the Huggins Chi -parameter concept assuming Chi to be a quadratic polynomial with respect to the weight-average chemical composition of the copolymer. The three model parameters were calculated from the critical point and the slope of the cloud-point curve at the critical point. The cloud-point curve and the shadow curve were predicted from these parameters. The cloud-point curve shows qualitative agreement with experimental data.     

Properties of the square-root derivative type curve

The conventional way to analyse well test data is by a combination of type curve analysis and special analysis for specific flow periods. In many cases, these flow periods, radial, linear, spherical, etc., are identified by inspection of type curves. Once identified, the pressure versus some time function may be plotted as a straight line. Then, reservoir and well properties may be computed from the slope of the lien and its position in the coordinate system. In this work, we propose a new type curve based on derivatives with respect to the square-root of time. The resulting type curve is useful for identifying linear flow regimes. Linear flow periods may appear in many cases, for example: flow towards horizontal wells, vertically fractured wells, etc.     

Development of a fitting model suitable for the isothermal titration calorimetric curve of DNA with cationic ligands

A novel curve fitting model was developed for the isothermal titration calorimetry (ITC) of a cationic ligand binding to DNA. The ligand binding often generates a DNA conformational change from an elongated random coil into a compact collapsed form that is referred to as "DNA condensation". The ligand binding can be classified into two regimes having different binding constants Ki, i.e., the binding to an elongated DNA chain with a binding constant K1 and with K2 that occurred during the conformational transition. The two-variable curve fitting models are usually bound by a strict regulation on the difference in the values of the binding constants K1 > K2. For the DNA condensation, however, the relationships for K1 and K2 are still unclear. The novel curve fitting model developed in this study takes into account this uncertainty on the relationship of the binding constants and is highly flexible for the two-variable binding constant system.     

The relation between faraday and two-layer impedances

The impedance of an electrode as a function of the potential for lowfrequency ac corresponds to the derivative of the polarization curve, while for high-frequency ac it corresponds to the electrocapillarity curve. Medium frequencies give an intermediate result.     

Determination of carbonate alkalinity and apparent dissociation constants in a multiprotolytic system

A method for analysing the carbonate system in a multicomponent solultion is presented, which does not need knowledge of the total composition of the system. It is based on two titrations with acid, starting at the same pH, one of the original solution and the other after removal of carbonate species as carbon dioxide and restoration of the pH to the value for the original solution by addition of carbonate-free base. The differential titration curve, obtained by subtracting one titration curve from the other, is associated with the carbonate system. A procedure is proposed for calculating from the differential titration curve the apparent first and second dissociation constants of carbonic acid, total CO(2) and the carbonate alkalinity at the original pH of the solution.