Damage of hybrid composites under long term hygrothermal loading and stacking sequence

The exposure of polymeric composite matrix to a cyclic moist environment produces transient residual stresses extremely important at the edges of the laminated plates, particularly at first times. In cases of critical cyclic environmental conditions, the damage of composites becomes very probable, so durability is intensively reduced. To avoid the damage probability, and to reduce the transient hygrothermal stresses, in our paper the hybrid composites with optimal stacking sequences are used. The first aim of this paper is the determination of hygrothermal characteristics for balanced stacking sequences [θ/−θ]_nS. Therefore, in order to locate the favourite directions of each stacking sequence, the polar representation method is adopted. The suitable choice of hygrothermal characteristics, allows thereafter, the reduction of transient hygrothermal stresses. By using the quadratic failure criterion in stress space, the transient strength ratio is evaluated at first ply of the hybrid plate for each sequences [θ/−θ]_nS from initial time until saturation time. Avoid the damage probability is reached by the reduction of transient hygrothermal stresses along the thickness of the hybrid plate. To locate the minimal and maximal stresses, a progressive variation of the relationship between the thicknesses h₁ and h₂ of hybrid composites constituents AS3501 and T300/5208 was carried out. In this way five cases are proposed, on which, the thickness of each material varies gradually, but the total thickness of our plate remains constant. This procedure permits us to find the best configuration which will offer favourable conditions of services, i.e., to predict a considerable reduction of hygrothermal transverse stresses at both edges of the hybrid plate.     

Detection of Oxidative Damage of Synthetic Oligonucleotides Caused by Thallium(III) Complexes

Biologically important short sequences of DNA were treated with Tl(III) complexes. The chloride complex releases the Tl(III) cation and therefore oxidizes DNA components and at concentrations higher than 50 nM cuts the strands. The cuts are well seen in the EQCM plots. The change in the strand structure is well seen at CD and UV‐Vis spectra. The chelate complexes of Tl(III) do not damage the DNA strands. The SERS spectra were particularly useful in demonstration of the chemical changes and orientation vs. the surface changes of particular groups in the strands after interaction with TlCl₄^?.     

Compensating Pulse Imperfections in Solid‐State NMR Spectroscopy: A Key to Better Reproducibility and Performance

The power and versatility of NMR spectroscopy is strongly related to the ability to manipulate NMR interactions by the application of radio‐frequency (rf) pulse sequences. Unfortunately, the rf fields seen by the spins differ from the ones programmed by the experimentalist. Pulse transients, i.e., deviations of the amplitude and phase of the rf fields from the desired values, can have a severe impact on the performance of pulse sequences and can lead to inconsistent results. Here, we demonstrate how transient‐compensated pulses can greatly improve the efficiency and reproducibility of NMR experiments. The implementation is based on a measurement of the characteristics of the resonance circuit and does not rely on an experimental optimization of the NMR signal. We show how the pulse sequence has to be modified to use it with transient‐compensated pulses. The efficiency and reproducibility of the transient‐compensated sequence is greatly superior to the original POST‐C7 sequence.     

$T_{2}(T)$的几乎可裂序列及几乎$\mathcal {D}$-可裂序列

The AR-quiver and derived equivalence are two important subjects in the representation theory of finite dimensional algebras, and for them there are two important research tools-AR-sequences and D-split sequences. So in order to study the representations of triangular matrix algebra T2 (T ) = T0TT where T is a finite dimensional algebra over a field, it is important to determine its AR-sequences and D-split sequences. The aim of this paper is to construct the right(left) almost split morphisms, irreducible morphisms, almost split sequences and D-split sequences of T2 (T) through the corresponding morphisms and sequences of T. Some interesting results are obtained.     

Complete moment convergence of pairwise NQD random variables

It is known that the dependence structure of pairwise negative quadrant dependent (NQD) random variables is weaker than those of negatively associated random variables and negatively orthant dependent random variables. In this article, we investigate the moving average process which is based on the pairwise NQD random variables. The complete moment convergence and the integrability of the supremum are presented for this moving average process. The results imply complete convergence and the Marcinkiewicz–Zygmund-type strong law of large numbers for pairwise NQD sequences.     

Some pairwise independent sequences for which the central limit theorem fails

Some simple examples are given of stationary, pairwise independent sequences of random variables for which the central limit theorem uterly fails     

Simulation of low energy displacement processes in a dilute cu-au alloy

Abstract

Research into displacement cascade processes in alloy systems has received little attention, yet is potentially of interest because issues such as the effect of solutes on the displacement threshold and the defect distribution and movement in cascades are important. As part of a wider study, we have initially considered the minor substitutional solute Au in a Cu matrix, and have used molecular dynamics to investigate the properties of point defects, the threshold displacement energy E_d, and temporal and spatial distribution of defects in low-energy (≤500 eV) displacement cascades. The results show that the influence of the solute on the properties of defects is important and that E_d is dramatically different from its form in pure copper. In comparison with pure copper, the recoil of the Au solute gives rise to a higher peak at longer times in the number of displaced atoms in the generation of a displacement cascade. The influence of this on defect density in the cascade and the final number and arrangement of defects has been investigated.