Adsorption effects and NMR properties: Continuous chain approach

The NMR properties of nuclei linked to long linear polymer molecules are sensitive to the influence of hard walls. In this context, the residual energy of tensorial spin-spin interactions is calculated using a path integral approach. Several thermodynamic quantities of the polymer system (free energy, equation of state,...) are also expressed, taking chain stiffness effects and the presence of two repulsive walls into consideration.     

Semi‐analytical integration of the 8‐node plane element stiffness matrix using symbolic computation

The semi‐analytical integration of an 8‐node plane strain finite element stiffness matrix is presented in this work. The element is assumed to be super‐parametric, having straight sides. Before carrying out the integration, the integral expressions are classified into several groups, thus avoiding duplication of calculations. Symbolic manipulation and integration is used to obtain the basic formulae to evaluate the stiffness matrix. Then, the resulting expressions are postprocessed, optimized, and simplified in order to reduce the computation time. Maple symbolic‐manipulation software was used to generate the closed expressions and to develop the corresponding Fortran code. Comparisons between semi‐analytical integration and numerical integration were made. It was demonstrated that semi‐analytical integration required less CPU time than conventional numerical integration (using Gaussian‐Legendre quadrature) to obtain the stiffness matrix. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006     

A numerical and experimental investigation of the interactions between a non‐uniform planar array of incompressible free jets

The interaction between multiple incompressible air jets has been studied numerically and experimentally. The numerical predictions have been first validated using experimental data for a single jet configuration. The spreading features of five unequal jets in the configuration of one larger central jet surrounded by four smaller equi‐distant jets, have been studied, for different lateral spacing ratios of 1.5, 2.0 and 2.5 and a central jet Reynolds number of 1.24×105 (corresponding to a Mach number of 0.16). Flow of five equal jets has also been simulated, for the sake of comparison. The jet interactions commence at an axial distance of about 3–4 diameters and complete by an axial distance of about 10 diameters for the lowest spacing ratio of 1.5. For larger spacing ratios, the length required for the start and completion of jet interaction increase. Peripheral jets bend more towards the central jet and merge at a smaller distance, when their sizes are smaller than that of the central jet. The entrainment ratio for multiple jets is higher than that for a single jet. Excellent agreement is observed between the experimental data and theoretical predictions for both mean flow field and turbulent quantities, at regions away from the jet inlet. The potential core length and initial jet development, however, are not predicted very accurately due to differences in the assumed and actual velocity profiles at the jet inlet. Copyright © 2004 John Wiley & Sons, Ltd.     

Load-Carrying Capacity of Circular Plates Made of a Fiber-Reinforced Composite

The load-carrying capacity of circular plates made of a fiber-reinforced composite and loaded with axisymmetric transverse forces under axisymmetric boundary conditions is investigated. The plates can be freely supported or clamped along their contour. To the known yield condition used, in the plane of main bending moments, there correspond irregular hexagons, which depend on the mechanical properties of composite constituents and some characteristic geometrical parameters. It is shown that, depending on the ratio of ultimate radial and circumferential bending moments, in the plastic state, the circular plates (the central part of the clamped plates) take the form of a cone or a frustum of cone. For each of the cases, the limit load is found, which is a function of the above-mentioned mechanical parameters. The statically allowable fields of bending moments and the corresponding allowable fields of deflection rates are determined. The solutions found are exact. Special cases for the freely supported plates are analyzed, and the results obtained are presented in the form of graphs.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 177–192, March–April, 2005.     

平台框架部件刚度的简化计算

利用卡氏定理,对惯性平台框架部件的刚度进行简化计算。通过微机编程获得数据,为结构设计初期合理选取结构参数提供参考。     

Bending loss measurement using a fiber cavity ringdown scheme

A novel sensitive technique for the determination of losses in fiber cavities is presented. The method is based on the cavity ringdown scheme implemented in silica-based single-mode fibers. Bending losses of fiber cavities of different lengths have been measured showing all an oscillating behavior with respect to the curvature radius of the fiber as predicted by a theoretical model. The best minimum detectable absorbance per cavity pass achieved by this new method is 1.72×10⁻³ dB within a 10 m-long cavity. This limit suffices well for an accurate determination of optical bending losses even in bend-insensitive fibers. Furthermore, the comparison of the measured bending losses with a theoretical model allows the extraction of different fiber parameters. Good agreement has been found between the experimentally derived parameters and literature data.     

Plastic multipliers as driving variables of numerical simulation in elastoplasticity

Statics of elasto-plastic media is stated in terms of eigenstrains acting upon a background elastic problem with fixed (initial) stiffness. In order to minimize the number of unknowns and to provide computationally cheap algorithms plastic multipliers are used as main driving variables. Fixed-point type iterations are suggested for computing plastic multipliers within the load increment. Numerical experiments results are shown to be in good correlation with other software results. A range of problems is outlined where the usage of the proposed algorithms can be advantageous.     

Glass transition measurements of asphalts by DSC

The glass transition temperature (T_g), measured by Modulated Differential Scanning Calorimetry (MDSC), is related to the flow characteristics of asphalt at low temperatures as is the rate of change of the creep stiffnessm. This study compared the glass transition temperature of different asphalts (neat, chemically modified, and crumb rubber modified asphalts) with the creep stiffness, the rate of change of creep stiffness, and the low specification temperature of the continuous PG grading of those asphalts.From the rheological data (BBR) and the thermal data (MDSC) for the virgin and the modified asphalts, the modified products had the same variations of values ofm, S, and T_g at lower temperatures as those of their corresponding virgin asphalts. A correlation between the T_g andm value was observed for both the modified and unmodified asphalts. Since DSC measurements for asphalt low temperature properties use less operator time, less sample, and have less measurement and operator error than rheological methods, T_g has promise to be considered as a fast and easy laboratory method to obtain the low temperature useful range of asphalts in pavements.The authors would like to acknowledge Susan P. Needham for her work in conducting rheological testing for the modified and unmodified asphalts.     

Preferential Uniplanar Orientation of Cellulose Microfibrils Reinvestigated by the FTIR Technique

A simple detection method to observe the uniplanar orientation behavior of native cellulose microfibrils to the cell wall surface by using Fourier transform infrared (FTIR) spectroscopy in the transmission mode is reported. Four bands at 1372, 1355, 1337, and 1317 cm⁻¹ (the latter two have been mentioned previously by Liang and Marchessault (1960, J. Polym. Sci. 43: 85–100)) were found to be sensitive to such orientation: the two middle bands at 1355 and 1337 cm⁻¹ increase remarkably when the 0.60–61 nm lattice planes lie parallel to the cell wall surfaces. The reverse was true when the 0.53–54 nm lattice planes oriented preferentially. Polarization of the two bands at 1372 and 1355 cm⁻¹ was parallel, while that of the other two bands at lower wavenumbers, i.e., at 1337 and 1317 cm⁻¹, was perpendicular to the molecular axis of cellulose. These bands were assigned to OH-related motion, probably to in-plane OH bending, as reported by Maréchal and Chanzy (2000, J. Mol. Spectrosc. 523: 183–196).     

Conformation of Tax-response elements in the human T-cell leukemia virus type I promoter

Background: HTLV I Tax is believed to activate viral gene expression by binding bZIP proteins (such as CRIB) and increasing their affinities for proviral THE target sites. Each 21 by THE target site contains an imperfect copy of the intrinsically bent CRE target site (the TRE core) surrounded by highly conserved flanking sequences. These flanking sequences are essential for maximal increases in DNA affinity and transactivation, but they are not, apparently, contacted by protein. Here we employ non-denaturing gel electrophoresis to evaluate TRE conformation in the presence and absence of bZIP proteins, and to explore the role of DNA conformation in viral transactivation.Results: Our results show that the TRE-1 flanking sequences modulate the structure and modestly increase the affinity of a CREB bZIP peptide for the TRE-1 core recognition sequence. These flanking sequences are also essential for a maximal increase in stability of the CREB-DNA complex in the presence of Tax.Conclusions: The CRE-like TRE core and the TRE flanking sequences are both essential for formation of stable CRIB-TRE-1 and Tax-CREB-TRE-1 complexes. These two DNA segments may have co-evolved into a unique structure capable of recognizing Tax and a bZIP protein.