Structural and Tribological Properties of Polyimide/Al2O3/SiO2 Composites in Atomic Oxygen Environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of polyimide/Al₂O₃/SiO₂ composites were investigated in a ground-based simulation facility, in which the energy of AO was about 5 eV and the flux was 7.2 × 10¹⁵ cm^?2.s^?1. The structural changes were characterized by X-ray photoelectron spectroscopy (XPS) and attenuated total-reflection FTIR (FTIR-ATR), while the tribological changes were evaluated by friction and wear tests as well as scanning electron microscopy (SEM) analysis of the worn surfaces. It was found that AO irradiation induced the oxidation and degradation of polyimide (PI) molecular chains. The destructive action of AO changed the surface chemical structure, which resulted in changes of the surface morphology and chemical composition of the samples. Friction and wear tests indicated that AO irradiation decreased the friction coefficient but increased the wear rate of both pure and Al₂O₃/SiO₂ filled PIs.     

Investigation of Pendant Group and Chain Segment Motions in P(MMA/BA) Copolymers by Thermally Stimulated Depolarization Current

Poly(methyl methacrylate/butyl acrylate) [P(MMA/BA)] copolymers (M_η ～2×10⁵) with different mass percentages of MMA were synthesized by the method of solution polymerization. Thermally stimulated depolarization current (TSDC) technique was used to investigate the effect of copolymerization on pendant group and chain segment motions. Three TSDC peaks were observed over the temperature range from 310 to 400 K. The highest temperature, ρ peak originates from the detrapping of trapped charge carriers. The lower temperature, α peak corresponds to the glass transition. The activation energy of the α relaxation decreases from 1.2 eV for PMMA to 0.98 eV for MMA(75)/BA(25). In the fitting process, another peak, β′, is separated on the low temperature side. The apparent energy barrier of the β′ for PMMA is 0.80 eV. The β′ relaxation is thought to correspond to the motion of pendant groups including intra‐ and inter‐molecular interactions. All three peaks move to lower temperatures with an increase in BA component, and the activation energy for the α and β′ relaxations also decreases with the increase of BA component in copolymers, indicating that the flexible side groups of BA have an effect of plasticization on the glass transition and motion of pendent groups. The temperatures of the α and β′ peaks of P(MMA/BA) copolymers follow the Fox equation. Fitting results gives the α peak at 238 K and β′ peak at 225 K for polybutyl acrylate (PBA).     

Synthesis of a Cationic Polymer-Bentonite Composite Utilizing a Simple and Green Process for the Adsorption of Acid Orange 7 from Aqueous Solution

A one-step, green process is reported for synthesis of poly([2-(methacryloyloxy)ethyl] trimethylammonium chloride) (PMETAC) modified bentonite (Bent-PMETAC). The Bent-PMETAC was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Zeta potential, scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA). The results indicated that large amounts of PMETAC were successfully grafted on the surface and interlayers of bentonite, and changed the Zeta potential of the sample from negative to positive. Acid Orange 7 (AO 7), as adsorbate, was used to test the anionic dye adsorption of the samples. The batch adsorption results implied that this novel Bent-PMETAC adsorbent exhibited a much higher removal (95%) of AO 7 than bentonite (10%). In addition, the adsorption process was hardly influenced by pH, which is in good agreement with the results of the Zeta potential analysis. The equilibrium adsorption isotherms and the adsorption kinetics of AO 7 fitted well to the Langmuir model and pseudo-second-order kinetic model, respectively. The maximum adsorption capacity of AO 7 onto Bent-PMETAC was 208.6?mg·g^?1 at 298?K, which is much higher than for most other materials. Overall, the results indicated the Bent-PMETAC is a low-cost, simple synthesis and highly efficient adsorbent for anionic dye removal from aqueous solutions.     

Anti de Sitter horospherical flat timelike surfaces

We investigate a special timelike surfaces in Anti de Sitter 3-space.We call such a timelike surface an Anti de Sitter horospherical flat surface which belongs to a class of surfaces given by one parameter families of Anti de Sitter horocycle.We give a generic classification of singularities and study the geometric properties of such surfaces from the viewpoint of Legendrian singularity theory.     

Numerical Radii for Tensor Products of Operators

For bounded linear operators A and B on Hilbert spaces H and K, respectively, it is known that the numerical radii of A, B and ${A\otimes B}$ are related by the inequalities ${w(A)w(B)\le w(A\otimes B)\le {\rm min}\{\|A\|w(B), w(A)\|B\|\}}$ . In this paper, we show that (1) if ${w(A\otimes B) = w(A)w(B)}$ , then w(A) = ρ(A) or w(B) = ρ(B), where ρ(·) denotes the spectral radius of an operator, and (2) if A is hyponormal, then ${w(A\otimes B) = w(A)w(B) = \|A\|w(B)}$ . Here (2) confirms a conjecture of Shiu’s and is proven via dilating the hyponormal A to a normal operator N with the spectrum of N contained in that of A. The latter is obtained from the Sz.-Nagy–Foia? dilation theory.     

Global well-posedness and stability of semilinear Mindlin–Timoshenko system

We study long-term behavior of Reissner–Mindlin–Timoshenko (RMT) plate systems, focusing on the interplay between nonlinear viscous damping and source terms. The sources may represent restoring forces, but may also be focusing thus potentially amplifying the total energy which is the primary scenario of interest. This work complements [28] which established local well-posedness of this problem, global well-posedness when damping dominates the sources (in an appropriate sense) and a blow-up in the complementary scenario assuming negative “total” initial energy. The current paper develops the potential well theory for the RMT system: it proves global existence for potential well solutions without restricting the source exponents, derives explicit energy decay rates dependent on the order of the damping exponents, and verifies a blow-up result for positive total initial energy.     

The Generalized Reflection and Transmission Matrix Method for Wave Propagation in Stratified Fluid-Saturated Porous Media

A systematic and efficient algorithm, the generalized reflection and transmission matrix method, has been developed for wave propagation in stratified fluid-saturated poroelastic half-space. The proposed method has the advantage of computational efficiency and numerical stability for high frequencies and large layer thickness. A wide class of seismic sources, ranging from a single-body force to double couples, is introduced by utilizing the moment tensor concept. In order to validate the proposed algorithm, we applied our formulation to calculate wave fields in a homogeneous poroelastic half-space. It is shown that the numerical results computed with the present approach agree well with those computed with the analytical solution. Numerical examples for a two-layer model subjected to various sources such as double couple, dipole, and explosive sources are provided. From the waveforms of surface displacements, the arrivals of transmitted and converted PS and SP waves at the interface of the two-layer model can be clearly observed. As expected, it is impossible to observe the arrivals of transmitted $S$ and transmitted and converted SP waves from the waveforms induced by fluid withdrawal.     

Small-amplitude limit cycles of polynomial Liénard systems

In this paper,we study the number of limit cycles appeared in Hopf bifurcations of a Linard system with multiple parameters.As an application to some polynomial Li’enard systems of the form x=y,y=gm(x)-fn(x)y,we obtain a new lower bound of maximal number of limit cycles which appear in Hopf bifurcation for arbitrary degrees m and n.     

硝酸镥急性毒性的体液核磁共振氢谱研究

采用现代核磁共振技术,通过分析灌胃给药0．01、0．05、0．2、2、10和100ms／kg剂量Lu(NO3)3 24h内大鼠尿液及24h后大鼠血清的核磁共振氢谱(^1HNMR),由体液中内源性代谢物浓度的变化研究了稀土化合物在动物体内急性毒性。较高剂量组体液中的氨基酸、尿囊素、柠檬酸、氮氧三甲胺和肌酸酐等重要内源性代谢物的核磁共振谱峰强度发生了明显的变化,说明动物体内的代谢物出现异常：高剂量的稀土的引入可能使动物肾脏和肝脏均受到损害,且受损程度随稀土剂量的增高而渐趋严重。