Investigation of structural changes of paint-and-varnish copolymers under influence of ageing

Paintwork materials applied as coatings protecting from rust and corrosion suffer with time structural changes leading to worsening of their physical and mechanical characteristics. We study by X-ray diffraction technique the inner structure of a new modified silicate coating depending on its ageing. It is shown that new crystalline formations appear with ageing in samples worsening significantly their service properties.     

Investigation of ageing effects on the electrical properties of polyaniline/silver nanocomposites

Polyaniline(PANI)/Ag nanocomposites, synthesized by incorporation of separately prepared silver nanoparticles in 1-methyl-2-pyrrolidinone(NMP) solution of PANI, have been aged at the accelerated temperature of 120 oC to simulate a storage period of 2 years at 25 oC. The accelerated ageing of these materials is done by using the activation energy calculated from data collected using heat flow calorimetry (HFC). The impedance spectroscopic studies of NMP plasticized aged nanocomposite films suggest a microphase separation into reduced and oxidized repeat units. There is crosslinking of the PANI films during ageing thereby obstructing the charge transfer between PANI chains and silver nanoparticles. As a result, the resistivity is increased.     

Investigation of ageing characteristics and identification of surface chemical changes on SrGa2S4:Ce display phosphor under electron beam bombardment

Cathodoluminescent ageing characteristics of SrGa₂S₄:Ce³⁺ under prolonged electron beam bombardment was studied and the data are presented. The cathodoluminescent intensity with an increasing Coulomb loading was observed to degrade under different primary electron beam voltages. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to monitor the surface chemical changes during electron beam bombardment and after the degradation process. Auger peak to peak heights monitored during the ageing process suggest a loss in S and C and an initial increase in oxygen concentration on the surface. XPS results indicate the formation of a SrO overlayer due to electron stimulated surface chemical reactions (ESSCRs).     

Investigation of structural changes in phlogopites on heating

It was shown experimentally that there are three types of curve for the temperature variation of d/d (001) for phlogopites. The relationship is linear for hard phlogopites while the soft phlogopites have negative expansion coefficients over the range of 160–250 °C. The curves for phlogopites of average hardness occupy intermediate positions. This effect is explained by the existence of layers which are capable of being dehydrated due to the presence of interstitial water.     

Euclidean nonlinear classical field equations with unique vacuum

We study the real, Euclidean, classical field equation $$(\mu ^2 + \Delta )\varphi + \lambda F(\varphi ) = f,\mu ^2 > 0$$ where φ: ? ^d →? is suitably small at infinity. We study existence and regularity assuming that λ≧0,F∈C ^∞(?), andaF(a)≧0?a∈∝. These hypotheses allow strongly nonlinearF and nonunique solutions forf≠0. WhenF′≧0, we prove uniqueness, various contractivity properties, analytic dependence on the coupling constant λ, and differentiability in the external sourcef. For applications in the loop expansion in quantum field theory, it is useful to know that φ is in the Schwartz classL wheneverf is, and we provide a proof of this fact. The technical innovations of the problem lie in treating the noncompactness of R ^d , the strong nonlinearity ofF, and the polynomial weights in the seminorms definingL.     

Effect of corona ageing on the structure changes of polyimide and polyimide/Al2O3 nanocomposite films

In order to investigate the corona ageing mechanism of polyimide and polyimide/Al₂O₃ nanocomposites, effects of corona ageing on the structure changes of the two polymers were studied. The physical and chemical changes were studied by Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectroscope (FTIR) respectively. Modified isothermal discharge current method (MIDC) was used to investigate the trap level distribution before and after corona ageing. AFM images showed that there are large amounts of nano-clusters on the surface of polyimide nanocomposite before corona ageing. The surface roughness parameters of the nanocomposite is much larger than that of the pure polyimide, and that is slightly decreased for polyimide nanocomposite and largely increased for pure polyimide after corona ageing. FTIR spectra analysis showed that possible chemical changes due to the decomposition of C–O–C bond and C–N bond occurred during corona ageing for both polyimide and its nanocomposite. Pulse corona ageing can introduce even larger structure changes than the AC corona ageing for 100HN, while 100CR was just the opposite. IDC measurements showed that the trap level density was increased evidently after corona ageing and become larger for longer ageing time in 100HN film, whereas for 100CR, the trap level density was decreased with ageing time extended. Thus conclusions can be drawn that, corona ageing is a combined process leading to physical and chemical degradation of PI film. The more serious ageing the specimen suffers, the more changes of the trap level density and the surface roughness occurs. The deposition of inorganic nanoparticles on the surface of nanocomposite can form a flat block layer for corona ageing, which can decrease both the surface roughness and the physical trap level density.     

Long-term low-temperature ageing of amorphous alloys

Long term stability of the coercivity and⁵⁷Fe Mössbauer parameters (magnitude and average orientation of hyperfine induction) at ca 150 °C was tested at three TM-M type amorphous alloys (Fe₈₃B₁₇, Fe₄₀Ni₄₀B₂₀ and Co₆₆Fe₅Cr₇Si₈B₁₄) up to 5000 hrs. Correlations between the Mössbauer and magnetic quantities were found and their possible causes are discussed.     

A two-dimensional isotropic quantum antiferromagnet with unique disordered ground state

We continue the study of valence-bond solid antiferromagnetic quantum Hamiltonians. These Hamiltonians are invariant under rotations in spin space. We prove that a particular two-dimensional model from this class (the spin-3/2 model on the hexagonal lattice) has a unique ground state in the infinite-volume limit and hence no Néel order. Moreover, all truncated correlation functions decay exponentially in this ground state. We also characterize all the finite-volume ground states of these models (in every dimension), and prove that the two-point correlation function of the spin-2 square lattice model with periodic boundary conditions has exponential decay.     

Investigation of the compositional changes of a Y-Ba-Cu-O HTSC target under ion sputtering

An Auger electron spectroscopy study is reported of the elemental depth profile of Y-Ba-Cu-O HTSC targets subjected to ion-plasma sputtering in a magnetron deposition system and ion-beam sputtering in the Auger spectrometer chamber. It has been established that the process consists in all cases of predominant copper sputtering accompanied by the formation of a modified surface layer and of a copper-depleted region. This region is assumed to originate from intense copper diffusion from the bulk to the modified surface layer driven by a concentration gradient.     

On non-local representations of the ageing algebra

The ageing algebra is a local dynamical symmetry of many ageing systems, far from equilibrium, and with a dynamical exponent z=2$z=2$. Here, new representations for an integer dynamical exponent z=n$z=n$ are constructed, which act non-locally on the physical scaling operators. The new mathematical mechanism which makes the infinitesimal generators of the ageing algebra dynamical symmetries, is explicitly discussed for an n-dependent family of linear equations of motion for the order-parameter. Finite transformations are derived through the exponentiation of the infinitesimal generators and it is proposed to interpret them in terms of the transformation of distributions of spatio-temporal coordinates. The two-point functions which transform co-variantly under the new representations are computed, which quite distinct forms for n even and n odd. Depending on the sign of the dimensionful mass parameter, the two-point scaling functions either decay monotonously or in an oscillatory way towards zero.     

Investigation of microstructural changes in M250 grade maraging steel using positron annihilation

Microstructural evolution of M250 grade maraging steel subjected to various thermal-aging treatments has been investigated using positron annihilation, X-ray diffraction, hardness and electron microscopy studies. Isochronal aging treatment in the range of 600–900 K, in steps of 100 K, was carried out and positron lifetime, austenite volume fraction and hardness values have been measured. The stages corresponding to point defect dynamics and formation of intermetallics have been clearly identified. Based on these results, measurements were performed on specimens isothermally aged at 755 K from 0.1 to 100 h to elucidate the time evolution of microstructural changes, and the results are discussed.     

Intermolecular double-quantum coherence MR microimaging of pig tail with unique image contrast

Image contrast in intermolecular double-quantum coherence (iDQC) imaging of a pig tail was investigated on a 7.05-T microimaging scanner. In addition to TR (repetition time) and TE (echo time), the time interval tau between radio frequency pulses during iDQC evolution and the areas under the iDQC-encode gradients in the iDQC imaging sequence were also used to manipulate image contrast. When suitable imaging parameters were selected, images with unique contrast, such as those with certain regions of the sample highlighted, were obtained without using contrast agents. The effects of iDQC-encode gradient on image contrast were studied quantitatively, and the unique contrast imposed by the related diffusion weighting was also shown. Experimental results demonstrated that the iDQC images have contrast fundamentally different from the conventional single-quantum coherence images.     

Investigation of changes in properties of water under the action of a magnetic field

The properties of water and their changes under the action of a magnetic field were gathered by the spectrum techniques of infrared, Raman, visible, ultraviolet and X-ray lights, which may give an insight into molecular and atomic structures of water. It was found that some properties of water were changed, and a lot of new and strange phenomena were discovered after magnetization. Magnetized water really has magnetism, which has been verified by a peak shift of X-ray diffraction of magnetized water + Fe₃O₄ hybrid relative to that of pure water + Fe₃O₄ hybrid, that is a saturation and memory effect. The properties of infrared and ultraviolet absorptions, Raman scattering and X-ray diffraction of magnetized water were greatly changed relative to those of pure water; their strengths of peaks were all increased, the frequencies of some peaks did also shift, and some new peaks, for example, at 5198, 8050 and 9340 cm⁻¹, occurred at 25°C after water was magnetized. In the meanwhile, the magnetized effects of water are related to the magnetized time, the intensity of an externally applied magnetic field, and the temperature of water, but they are not a linear relationship. The study also showed a lot of new and unusual properties of magnetized water, for example, the six peaks in 3000–3800 cm⁻¹ in infrared absorption, the exponential increase of ultraviolet absorption of wave with the decreasing wavelength of light of 200–300 nm, the frequency-shifts of peaks, a strange irreversible effect in the increasing and decreasing processes, as well as a stronger peak of absorption occurring at 50°C, 70°C and 80°C, the existence of many models of motion from 85°C to 95°C in 8000–10000 cm⁻¹, and so on. These results show that the molecular structure of water is very complicated, which needs further study. Furthermore, the macroscopic feature of mechanics, for instance, surface tension force of magnetized water, was also measured. Experiments discovered that the size in contact angles of magnetized water on the surface of hydrophobic materials decreases, thus the surface tension force of magnetized water decreases relative to that of pure water. It is seen from the above results that the clustering structure of hydrogen-bonded chains and polarization effects of water molecules are enhanced after magnetization. These results are helpful in revealing the mechanism of magnetization of water. Supported by the National Basic Research Program of China (Grant No. 2007CB936103)     

A unique continuation principle for steady symmetric water waves with vorticity

Abstract

We consider a symmetric, steady, and periodic water wave. It is shown that a locally vanishing vertical velocity component implies a flat or oscillating surface profile.     

SUPERLUMI: A unique setup for luminescence spectroscopy with synchrotron radiation

Twenty-five years ago, the SUPERLUMI setup at HASYLAB went into operation. In the meantime, the setup is used as a facility by many groups from Europe. In the present paper, history, continuous improvements, performance and scientific output of SUPERLUMI are described.     

Initial stage of physical ageing in network glasses

An atomistic view on Johari–Goldstein secondary β-relaxation processes responsible for structural relaxation far below the glass transition temperature (T_g ) in network glasses is developed for the archetypal chalcogenide glass, As₂₀Se₈₀, using positron annihilation lifetime, differential scanning calorimetry, Raman scattering and nuclear magnetic resonance techniques. Increased density fluctuations are shown to be responsible for the initial stage of physical ageing in these materials at the temperatures below T_g . They are correlated with changes in thermodynamic parameters of structural relaxation through the glass-to-supercooled liquid transition interval. General shrinkage, occurred during the next stage of physical ageing, is shown to be determined by the ability of system to release these redundant open volumes from the glass bulk through the densification process of glass network.