A Cahn-Hilliard model in a domain with non-permeable walls

We consider in this article a Cahn-Hilliard model in a bounded domain with non-permeable walls, characterized by dynamic-type boundary conditions. Dynamic boundary conditions for the Cahn-Hilliard system have recently been proposed by physicists in order to account for the interactions with the walls in confined systems and are obtained by writing that the total bulk mass is conserved and that there is a relaxation dynamics on the boundary. However, in the case of non-permeable walls, one should also expect some mass on the boundary. It thus seems more realistic to assume that the total mass, in the bulk and on the boundary, is conserved, which leads to boundary conditions of a different type. For the resulting mathematical model, we prove the existence and uniqueness of weak solutions and study their asymptotic behavior as time goes to infinity.     

Evidence for shape coexistence at medium spin in Rb

Four previously known rotational bands in ⁷⁶Rb have been extended to moderate spins using the Gammasphere and Microball γ ray and charged particle detector arrays and the ⁴⁰Ca(⁴⁰Ca, 3pn) reaction at a beam energy of 165 MeV. The properties of two of the negative-parity bands can only readily be interpreted in terms of the highly successful Cranked Nilsson-Strutinsky model calculations if they have the same configuration in terms of the number of g9/2 particles, but they result from different nuclear shapes (one near-oblate and the other near-prolate). These data appear to constitute a unique example of shape coexisting structures at medium spins.     

退火温度对YBa2Fe3O8的结构与磁性质影响分析

YBa2Fe3O8(YBFO)是具有三方钙钛矿结构的反铁磁(AFM)体,研究它的结构和磁性质对于我们认识三方钙钛矿结构具有重要作用.目前,关于固相法制备YBFO中退火温度方面的研究并不多,而控制退火温度是这种工艺中的重要环节.为制备高含量的YBa2Fe3O8,本文分别在760℃、950℃和1100℃退火温度下,采用固相...     

Ca8Mg(SiO4)4Cl2:Eu2+,Nd3+的近红外发光

用高温固相法制备了Ca<,8>Mg(SiO<,4>)<,4>Cl<,2>:Eu<'2+>,Nd<'3+>近红外发光材料,通过X射线衍射仪,近红外,可见发射光谱和激发光谱,荧光寿命等对样品进行了测试.研究了Eu<'2+>、Nd<'3+>的掺杂浓度对近红外发光性能的影响及相对强度变化的规律,结果表明,Ca<,8>Mg(Si...     

Anilinolysis of O‐butyl phenyl phosphonochloridothioate in acetonitrile: Synthesis,characterization, kinetic study,and reaction mechanism

This paper describes a simple optimized method for the synthesis of O‐butyl phenyl phosphonochloridothioate ( 4 ) under mild conditions. The target compounds were characterized by ¹H‐nuclear magnetic resonance (NMR), ¹³C‐NMR, and ³¹P‐NMR spectroscopy, as well as mass spectroscopy. The apparent structure of 4 was confirmed by optimization using the B3LYP/6‐311 + G(d,p) level in the Gaussian 09 program in acetonitrile. The nucleophilic substitution reactions of 4 with X‐anilines (XC₆H₄NH₂) and deuterated X‐anilines (XC₆H₄ND₂) were investigated kinetically in acetonitrile at 55.0°C. The free energy relationship with X in the anilines looked biphasic concave upwards with a break region between X = H and X = 3‐MeO, giving large negative ρ_X and small positive β_X values. The deuterium kinetic isotope effects were secondary inverse (k_H/k_D < 1: 0.789‐0.995) and the magnitudes, (k_H/k_D), increased when the nucleophiles were changed from weakly basic to strongly basic anilines. A concerted S_N2 mechanism is proposed on the basis of the selectivity parameters and the variation trend of the deuterium kinetic isotope effects with X.     

Magnesium K‐edge XANES spectroscopy of geological standards

Magnesium K‐edge X‐ray absorption near‐edge structure (XANES) spectra have been investigated to develop a systematic understanding of a suite of Mg‐bearing geological materials such as silicate and carbonate minerals, sediments, rocks and chemical reagents. For the model compounds the Mg XANES was found to vary widely between compounds and to provide a fingerprint for the form of Mg involved in geologic materials. The energy positions and resonance features obtained from these spectra can be used to specify the dominant molecular host site of Mg, thus shedding light on Mg partitioning and isotope fractionation in geologic materials and providing a valuable complement to existing knowledge of Mg geochemistry.     

Effects of oxygen-containing defect complex on the electronic structures and transport properties of single-walled carbon nanotubes

The electronic structures and transport properties of (10,0)$(10,0)$ single-walled carbon nanotube ((10,0)$(10,0)$ (SWNT)) with oxygen-containing defect complex are investigated using density functional theory in combination with nonequilibrium Green?s function method. The complex delocalizes the local states of (10,0)$(10,0)$ SWNT induced by mono- and di-vacancy but strengthens the localization of the states induced by the Stone–Wales defect. As a result, the complex partially restores the transport properties of (10,0)$(10,0)$ SWNT with vacancies, but reduces the transmission of (10,0)$(10,0)$ SWNT with Stone–Wales defect. However, the oxygen-containing defect complex only slightly influences the transmission gap and threshold voltage of the system.     

Photoinduced decarboxylation of 9‐oxo‐6,9‐dihydro[1,2,5]selenadiazolo[3,4‐f]quinoline‐8‐carboxylic acid

Photoinduced reactions of 9‐oxo‐6,9‐dihydro[1,2,5]selenadiazolo[3,4‐f]quinoline‐8‐carboxylic acid (SeQCA) were investigated in alkaline media (aqueous NaOH solutions) by electron paramagnetic resonance (EPR) spectroscopy, following the in situ formation of paramagnetic species. According to UV–Vis and nuclear magnetic resonance investigations, protonation (pH ≈ 11) and deprotonation (pH ≈ 13) of the imino hydrogen of the 4‐pyridone moiety has to be considered, reflected also in the different EPR spectra observed upon irradiation. Photoinduced generation of radicals was found only for carboxylate substituted SeQCA; other studied selenadiazoloquinolone derivatives, together with those substituted at the C(8) position (R = H, COOCH₂CH₃, COOCH₃, COCH₃ or CN), did not generate paramagnetic species during exposure. Consequently, photodecarboxylation was suggested as the decisive step, accompanied by the decomposition of the selenadiazole ring, resulting in the formation of ortho‐hydroxylate anions. EPR parameters elucidated from experimental EPR spectra obtained at pH ≈ 11 and pH ≈ 13 indicate the formation of oxygen‐centered radicals at the decarboxylated 4‐pyridone ring. EPR spin trapping experiments with nitromethane confirmed a very effective photoinduced electron transfer from all the selenadiazoloquinolones investigated. Copyright © 2011 John Wiley & Sons, Ltd.     

Micro‐Raman study of exfoliated Bi2Sr2CaCu2O8+δ single crystals with different thicknesses

Exfoliated Bi₂Sr₂CaCu₂O_8+δ (Bi‐2212) single crystals were prepared by micromechanical cleavage of bulk Bi‐2212 single crystals on SiO₂/Si substrates. Room temperature micro‐Raman spectra were collected using a 532‐nm laser source. The evolutions of the spectra of A_1g (Bi), A_1g (Sr), and A_1g (O_Bi) Raman modes with different thicknesses of the samples were studied. The refractive index of Bi‐2212 single crystal was obtained by studying the intensity evolutions based on the interference effect. The observed wavenumber shifts of the A_1g (Bi), A_1g (Sr), and A_1g (O_Bi) modes were analyzed. Copyright © 2011 John Wiley & Sons, Ltd.