Cr4+∶YAG固体激光器效率的理论分析

对Cr4+∶YAG固体激光器的吸收效率、量子效率、储存效率和提取效率等本征效率进行了分析.Cr4+∶YAG晶体的吸收截面、发射截面、上能级寿命和激活离子浓度等对激光器的本征效率有很大的影响.提高Cr4+∶YAG晶体的光学品质和激活离子的掺杂浓度,优化泵浦源的运转波长和激光腔的设计都能显著改善Cr4+∶YAG固体激光器的本征效率.     

Orbital-selective Mott-insulator transition in Ca 2 - x Sr x RuO 4

The electronic structures of the metallic and insulating phases of the alloy series Ca_2-xSr_xRuO₄ ( 0 ? x ? 2) are calculated using LDA, LDA+U and Dynamical Mean-Field Approximation methods. In the end members the groundstate respectively is an orbitally non-degenerate antiferromagnetic insulator (x = 0) and a good metal (x = 2). For x > 0.5 the observed Curie-Weiss paramagnetic metallic state which possesses a local moment with the unexpected spin S = 1/2, is explained by the coexistence of localized and itinerant Ru-4d-orbitals. For 0.2 < x < 0.5 we propose a state with partial orbital and spin ordering. An effective model for the localized orbital and spin degrees of freedom is discussed. The metal-insulator transition at x = 0.2 is attributed to a switch in the orbital occupation associated with a structural change of the crystal. Received 27 July 2001     

Molecular dynamic studies of the solubility of sodium chloride: fast calculations using seed crystalline cluster probe

Theoretical predictions of solubility, typically accomplished by comparing the chemical potential of pure solid and solution, currently suffer from a lack of accuracy. We suggest an alternative method for predicting solubility based on molecular dynamics simulations of the behaviour of a small seed crystalline cluster probe in solutions of varying concentrations. The size dynamics of a properly chosen seed cluster that dissolves in unsaturated solutions and grows in size in supersaturated solutions is indicative of the saturation point. This approach is illustrated by its application to NaCl in water.     

A New Equation between Surface Tensions and Solubility Parameters without Molar Volume Parameters Simultaneously Fitting Polymers and Solvents

Both surface tension and solubility parameter are decided by molecular interactions. There are several empirical equations describing their connection. However, at least two limitations exist for them: polymers cannot be treated and only apolar or weakly polar solvents can be fitted. We found when only the dispersive properties were considered, for 37 solvents and 22 polymers, a linear relationship exists between γ ^d and γ/δ^2/3 _d , fitted by a new equation. Compared with the previous equations, the value of the new equation is that most solvents and common polymers could be treated simultaneously. This equation will be of value for estimating the accuracy of reported surface tension data or solubility parameters of polymers.     

The water‐promoted Diels–Alder reaction in quaternary ammonium salts

Prevailing classification of salts based on their effect in solubility and stability of proteins in aqueous solution predicts that tetraalkylammonium salts, guanidinium chloride (GnCl), LiClO₄ act as salting‐in (S/I) and LiCl, NaCl act as salting‐out (S/O) in aqueous conditions. In the same context the behaviour of GnCl, LiClO₄ and LiCl are contradictory in polar solvents like ethylene glycol and formamide. In these solvents, expected salt effect shows just opposite nature from their usual expectation. However, in the aqueous solution salts like tetraalkylammonium halide (R₄NX, R = alkyl group, X = Br group) behave like salting‐in salts. The physicochemical origin of the salting in effect of R₄NX type of salts has been discussed elaborately in the present work. The role of cations in terms of substitution of various alkyl groups on R₄NX has been systematically presented here on the basis of experimental kinetic and thermodynamic studies. The abnormal behaviour of R₄NX salts in aqueous solution has also been explained by the Setschenov equation (k_s) and Δμ_solvation values, which highlights their individual nature out of common properties of R₄NX. Copyright © 2015 John Wiley & Sons, Ltd.     

Investigation on Three-Dimensional Solubility Parameters for Explanation and Prediction of Swelling Degree of Polydimethylsiloxane Pervaporation Membranes

Using polydimethylsiloxane (PDMS) as a basic matrix to prepare ethanol and butanol permselective pervaporation membranes is a vibrant field. Many studies have verified that the three-dimensional Hansen solubility parameters (HSP) theory offers a valid explanation for the swelling performance of ethanol and butanol in PDMS. Five parameters (δ_D, δ_P, δ_H, δ_t, and R_a) are defined in HSP theory which can be individually used to explain the interaction strength between a solvent and a polymer. However, for the above five parameters, which one is the most effective parameter for deciding the swelling degree still needs to be determined. In this study, a commonly used hydroxy-terminated PDMS precursor was adopted to prepare the PDMS network. The HSP of the chosen PDMS precursor was measured by an advanced “solubility-rating” method. The special software package HSPiP (4.1.03), purchased from the HSPiP team, was used to process the “solubility-rating” results. The equilibrium swelling degree (Q value) of the PDMS network in water, ethanol, butanol, and toluene was measured and the relationships between the five HSP parameters of the solvents and the logarithmic equilibrium swelling degree, log(Q), were discussed. It was found that the measured polar parameter, δ_P, of PDMS was 0.12 MPa^0.5. The measured hydrogen bonding parameter, δ_H, was larger than δ_P, attaining a value of 8.6 MPa^0.5, because the hydroxy groups directly contributed to the hydrogen bonding solubility parameter, δ_H. With respect to the relationships between log(Q) and δ_D, δ_P, δ_H, δ_t, and R_a, linear relationships existed after plotting log(Q) vs. δ_P and log(Q) vs. δ_H. The linear relation degree of the fitted lines was 0.995 and 0.989, respectively. Their standard deviations were 0.149 and 0.232, respectively. Therefore, a better linear relationship existed between log(Q) and δ_P than the other solubility parameters. This indicated that the polar interaction was the main effect for deciding the swelling degree of the PDMS network in water and alcohol systems.     

VUV spectroscopy of pure and Tm-doped LicaAlF6 crystals

Nominally pure and Tm³⁺-doped LiCaAlF₆ crystals were grown by the Czochralski technique in a reducing atmosphere. The optical properties of transparent single crystals were studied using absorption and time-resolved luminescence spectroscopy in the VUV spectral range (330-100 nm). The strongest VUV emission peaking at 60 800 cm⁻¹ with a decay time of 5.6 μs (7 μs) at 300 K (7.4 K) was assigned to the spin-forbidden 4f¹¹5d-4f¹² transition of Tm³⁺. The fine structure observed in the VUV emission and corresponding excitation spectra indicate intermediate strength of electron-phonon coupling in this system. The efficient excitation of f-f emissions above 72 000 cm⁻¹, higher than the onset of f-d absorption at 63 000 cm⁻¹, is mainly caused by the F⁻ to Tm³⁺ charge transfer absorption. The nature of various host-related excitation processes in the energy transfer to the Tm³⁺ ions is discussed.     

Synthesis and Characterization of Soluble Cardo Poly(ester-imide)s Derived from 9,9-Bis[4-(3,4-dicarboxybenzoyloxy)phenyl]fluorene

A novel fluorenyl cardo dianhydride-9,9-bis[4-(3,4-dicarboxybenzoyloxy)phenyl]fluorene (BDPF) was synthesized and characterized. A series of fluorenyl cardo poly(ester-imide)s (FCPEIs) were prepared by the polycondensation of BDPF with m-phenylene diamine, 4,4′-oxydianiline (4,4′-ODA), 3,4′-oxydianiline (3,4′-ODA), 2,2-bis[4-(4-amino -phenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, and 1,6-hexamethylenediamine. Most of the FCPEIs exhibited excellent solubility in common organic solvents such as 1,2-dichlorobenzene (o-DCB), chloroform, tetrahydrofuran, N,N-dimethylacetamide (DMAc), dimethyl sulfoxide, N-methyl-2-pyrrolidinone, etc. Intrinsic viscosities of FCPEIs in DMAc, for instance, ranged from 0.29–0.52 dL/g. The glass transition temperature of these polymers was between 199°C and 283°C by differential scanning calorimentry, and the 5% weight loss temperature of all polymers exceeded 400°C in air.     

基于经验模式分解的拖曳式声纳拖船噪声抵消研究

拖曳式线列阵声纳的拖船噪声具有多途角扩展等特点，并且是一个非平稳过程，使得对该噪声的消除或抑制是一大难点。经验模式分解是一种用于分析非线性非平稳信号的新方法，该方法自适应地将嵌于数据内部的多个固有模式函数逐一分解开来。本文尝试利用经验模式分解方法分离出水听器接收信号中的拖船干扰噪声，从而达到消除干扰的目的。海上试验数据的处理结果充分验证了这种方法的可行性。