Low-temperature heat capacities and standard molar enthalpy of formation of pyridine-2,6-dicarboxylic acid

This paper reports that the low-temperature heat capacities of pyridine-2,6-dicarboxylic acid were measured by a precision automatic calorimeter over a temperature range from 78~K to 380~K. A polynomial equation of heat capacities as a function of temperature was fitted by the least-squares method. Based on the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15~K were calculated and tabulated at intervals of 5~K. The constant-volume energy of combustion of the compound was determined by means of a precision rotating-bomb combustion calorimeter. The standard molar enthalpy of combustion of the compound was derived from the constant-volume energy of combustion. The standard molar enthalpy of formation of the compound was calculated from a combination of the datum of the standard molar enthalpy of combustion of the compound with other auxiliary thermodynamic quantities through a Hess thermochemical cycle.     

Low-temperature heat capacities and standard molar enthalpy of formation of N-methylnorephedrine C11H17NO（s）

This paper reports that low-temperature heat capacities of N-methylnorephedrine C11H17NO（s） have been measured by a precision automated adiabatic calorimeter over the temperature range from T=78K to T=400K. A solid to liquid phase transition of the compound was found in the heat capacity curve in the temperature range of T=342-364 K. The peak temperature, molar enthalpy and entropy of fusion of the substance were determined. The experimental values of the molar heat capacities in the temperature regions of T=78-342 K and T=364-400 K were fitted to two poly- nomial equations of heat capacities with the reduced temperatures by least squares method. The smoothed molar heat capacities and thermodynamic functions of N-methylnorephedrine C11H17NO（s） relative to the standard refer- ence temperature 298.15 K were calculated based on the fitted polynomials and tabulated with an interval of 5 K. The constant-volume energy of combustion of the compound at T=298.15 K was measured by means of an isoperibol precision oxygen-bomb combustion calorimeter. The standard molar enthalpy of combustion of the sample was calculated. The standard molar enthalpy of formation of the compound was determined from the combustion enthalpy and other auxiliary thermodynamic data through a Hess thermochemical cycle.     

Low-temperature heat capacities and standard molar enthalpy of formation of 4-（2-aminoethyl）-phenol （C8H11NO）

This paper reports that low-temperature heat capacities of 4-（2-aminoethyl）-phenol （C8H11NO） are measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 400 K. A polynomial equation of heat capacities as a function of the temperature was fitted by the least square method. Based on the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15K were calculated and tabulated at the interval of 5K. The energy equivalent, εcalor, of the oxygen-bomb combustion calorimeter has been determined from 0.68g of NIST 39i benzoic acid to be εcalor=（14674.69±17.49）J·K^-1. The constant-volume energy of combustion of the compound at T=298.15 K was measured by a precision oxygen-bomb combustion calorimeter to be ΔcU=-（32374.25±12.93）J·g^-1. The standard molar enthalpy of combustion for the compound was calculated to be ΔcHm = -（4445.47 ± 1.77） kJ·mol^-1 according to the definition of enthalpy of combustion and other thermodynamic principles. Finally, the standard molar enthalpy of formation of the compound was derived to be ΔfHm（C8H11NO, s）=-（274.68 ±2.06） kJ·mol^-1, in accordance with Hess law.     

Radiative lifetime measurements of odd-parity high-excited levels of Sn I by time-resolved laser spectroscopy

Natural radiative lifetimes of five higher-lying odd-parity levels 5p7s ³P₁^o, 5p5d ¹P₁^o, 5p6d ³F₂^o, ³D₁^o and ³F₃^o in neutral tin are measured by the time-resolved laser-induced fluorescence (TR-LIF) technique and the atomic beam method. All these lifetimes are not longer than 100 ns and they are found to be shorter than the lifetimes of even-parity levels in the same energy region. The results reported in this paper provide important transition parameters for highly-excited atomic Sn, which may be useful for theoretically calculating excited heavy atoms.     

铥原子收敛于4f13(2F7/2o)6s(7/2,1/2)4o和4f13(2F7/2o)6s(7/2,1/2)3o偶宇称里德伯系列能级的电子关联效应

本文在多通道量子亏损理论框架下,利用相对论多通道理论,计算了铥原子收敛于4f¹³（²F_7/2^o）6s（7/2,1/2）₄^o和4f¹³（²F_7/2^o）6s（7/2,1/2）₃^o的三个偶宇称里德伯系列.通过将计算结果与美国国家标准与技术研究院数据进行比较,展示了两种类型的电子关联效应：1）里德伯系列之间的相互作用,导致里德伯系列的能级出现整体偏移;2）一个孤立的干扰态镶嵌在一个里德伯系列中,破坏了该里德伯系列能级的规则性.     

钙钛矿(C6H5CH2NH3)2PbBr4拉曼光谱研究

运用激光拉曼光谱实验和密度泛函理论计算研究了450～1 700 cm-1光谱范围内有机-无机杂化钙钛矿材料(C₆H₅CH₂NH₃)₂PbBr₄的振动模式特性。对比实验所得拉曼光谱和理论计算所得拉曼光谱,发现密度泛函理论计算可以很好的模拟(C₆H₅CH₂NH₃)₂PbBr₄有机部分的分子振动模式。同时通过比较分析密度泛函理论计算和参考文献,对450～1 700 cm-1光谱范围内的拉曼峰的分子振动模式进行了初步的归属,并发现该光谱范围内的拉曼峰主要是由(C₆H₅CH₂NH₃)₂PbBr₄分子中有机部分振动所产生的。     

An investigation on the magneto-optic properties of terbium gallium garnet under high magnetic field

The superexchange interaction on a magnetic ion may be represented by an effective field H_m = $\lambda$M in some paramagnetic materials, here λ is the coefficient of effective field and M = $\chi$H_e with $\chi$ being the magnetic susceptibility and H_e being the applied field. The variation of the equivalent $\lambda_{\chi}$with the dynamic applied field is given and the crystal field-splitting levels of the excited configuration 4f⁷5d¹ of the Tb³⁺ ion are calculated in the Tb₃Ga₅O₁₂. By means of the effective field H_m and the applied field H_e, the Faraday rotation of Tb₃Ga₅O₁₂ at 6 K and 41 K, under the high magnetic field and at 0.63 μm wavelength, are presented. Our calculated results are in agreement with the experimental data.     

An Yb-fiber frequency comb phase-locked to microwave standard and optical reference

We present a fully stabilized Yb-fiber frequency comb locked to a microwave standard and an optical reference separately. The carrier-envelope offset frequency is generated by a standard f–2f interferometer with 40 dB signal-tonoise ratio. The offset frequency and the repetition rate are stabilized simultaneously to the radio frequency reference for more than 30 hours, and the fractional Allan deviation of the comb is the same as the microwave standard of 10^-12 at 1 s.Alternatively, the comb is locked to an ultra-stable optical reference at 972 nm using an intracavity electro-optic modulator,exhibiting a residual integrated phase noise of 458 mrad(1 Hz–10 MHz) and an in-loop tracking stability of 1.77× 10^-18 at 1 s, which is significantly raised by six orders comparing to the case locked to the microwave frequency standard.     

ON CORRECTION-TO-SCALING DUE TO NONLINEARITY OF SCALING FIELDS

The reliabilitu of the hynothesis that two nonlinear scaling fieles g_t and g_h satisfy F_s(g_t,g_h)=|g_t|^2-α Y_±)g_h/|g_t|^Δ) and F_s(g_t,g_h)=|g_t|^2-α/Δ Y₀)g_t/|g_h|^1/Δ),which is adopted in the theory of analytic correction to scaling due to nonlinearity of sca-ling fields, is investigated. It is shown that this hypothesis is a good one only when we take some suitable approximations under the quasi-asymptotic condition, even thou护ignore all the irrelevant variables, so that we can adopt it as a hypothe-sis in the theory with reservations. The third possible source for correction to scaling, the nonlinearity of order parameter,is also pointed out in addition to the source of the irrelevant variables and of the nonlinearitN of scaling fields.     

工作压强对射频辉光放电H2/C4H8等离子状态的影响

利用辉光放电技术采用等离子体质谱诊断的方法研究了不同工作 压强下H₂/C₄H₈混合气体等离子体中 主要正离子成分及其能量的变化规律, 并分析了压强对H₂/C₄H₈混合气体的离解机理以及主要正离子形成过程的影响. 结果表明: 随着工作压强的增加, 碳氢碎片离子的浓度和能量均逐渐减小. 当工作压强为5 Pa时, H₂/C₄H₈混合气体等离子体中C₃H₅⁺相对浓度最大; 压强为10 Pa时, C₃H₃⁺相对浓度最大; 压强为15, 20 Pa时, C₂H₅⁺相对浓度最大; 压强为25 Pa时, C₄H₉⁺相对浓度最大. 对H₂/C₄H₈等离子体中的主要组分及其能量分布所进行的定性分析, 将为H₂/C₄H₈混合气体辉光放电聚合物涂层的工艺参数优化提供参考技术基础. 关键词： 辉光放电技术 等离子体质谱诊断 工作压强     

Ohmic contacts of 4H-SiC on ion-implantation layers

The ohmic contacts of 4H-SiC are fabricated on nitrogen ion implanted layers made by performing box-like-profile implantation three and four times. Implantation parameters such as the standard deviation σ and the projection range R_p are calculated by the Monte Carlo simulator TRIM. Ni/Cr ohmic contacts on Si-face 4H-SiC implantation layers are measured by transfer length methods (TLMs). The results show that the values of sheet resistance R_sh are 30~kΩ /□ and 4.9~kΩ/□ and the values of specific contact resistance ρ_c of ohmic contacts are 7.1× 10^-4Ω.cm² and 9.5× 10^-5Ω.cm² for the implanted layers with implantation performed three and four times respectively.     

不同波长激光激发下C6H12受激拉曼散射模式竞争

发现不同波长激光激发下C₆H₁₂的受激拉曼散射模式竞争现象. 在不同波长的激光激发下，不同拉曼模式的Stokes光占优势. 短波长(404，532nm)激光激发时小频移模式ω₁(802cm^-1)为弱增益模式，大频移模式ω₂(2852—3038cm^-1)为强增益模， 主要产生ω₂模式的Stokes光. 长波长(80 关键词： 模式竞争 6H₁₂')" href="#">C₆H₁₂ 受激拉曼散射     

Isospin-conserving hadronic decay of the Ds1(2460) into Dsπ+π-

The internal structure of the charm-strange mesons D_s0^*(2317) and D_s1(2460) are the subject of intensive studies.Their widths are small because they decay dominantly through isospinbreaking hadronic channels D_s0^*(2317)⁺→D_s⁺π⁰ and D_s1(2460)⁺→D_s^*+π⁰.The D_s1(2460) can also decay into the hadronic final states D_s⁺ππ...     

Diffusion activation energy versus the favourable energy in two-order-parameter model:A molecular dynamics study of liquid Al

In the present work, we find that both diffusion activation energy E_a(D) and E_a(S^ex) increase linearly with pressure and have the same slope (0.022±0.001 eV/GPa) for liquid Al. The temperature and pressure dependence of excess entropy is well fitted by the expression -S^ex(T,P)/k_B=a(P)+b(P)T+c(P)exp(E_f/k_BT), which together with the small ratio of E_f/k_BT leads to the relationship of excess entropy to temperature and pressure, i.e. S^ex≈-cE_f/T, where c is about 12 and E_f (=Δ E-PΔV) is the favourable energy. Therefore, there exists a simple relation between E_a(S^ex) and E_f, i.e. E_a(S^ex)≈cE_f.     

The effects of Er3+ ion concentration on 2.0-μm emission performance in Ho3+/Tm3+ co-doped Na5Y9F32 single crystal under 800-nm excitation

Na₅Y₉F₃₂ single crystals doped with ~0.8-mol% Ho³⁺,~1-mol% Tm³⁺,and various Er³⁺ ion concentrations were prepared by a modified Bridgman method.The effects of Er³⁺ion concentration on 2.0-μm emission excited by an800-nm laser diode were investigated with the help of their spectroscopic properties.The intensity of 2.0-μm emission reached to maximum when the Er³⁺ ion concentration was ~1 mol%.The energy transfer mechanisms between Er³⁺,Ho³⁺,and Tm³⁺ ions were identified from the change of the absorption spectra,the emission spectra,and the measured decay curves.The maximum 2.0-μm emission cross section of the Er³⁺/Ho³⁺/Tm³⁺tri-doped Na₅Y₉F₃₂ single crystal reached 5.26 × 10^-21 cm².The gain cross section spectra were calculated according to the absorption and emission cross section spectra.The cross section for ~2.0-μm emission became a positive gain once the inversion level of population was reached 30%.The energy transfer efficiency was further increased by 11.81% through the incorporation of Er³⁺ ion into Ho³⁺/Tm³⁺ system estimated from the measured lifetimes of Ho³⁺/Tm³⁺-and Er³⁺/Ho³⁺/Tm³⁺-doped Na₅Y₉F₃₂single crystals.The present results illustrated that the Er³⁺/Ho³⁺/Tm³⁺tri-doped Na₅Y₉F₃₂ single crystals can be used as promising candidate for 2.0-μm laser.     

Semileptonic decays B/Bs→(D?,D?s)lνl in the PQCD approach with the lattice QCD input

We study the semileptonic B/Bs→(D^?,D^?s)lνl decays in the framework of the Standard Model(SM),by employing the perturbative QCD(PQCD)factorization formalism combined with the lattice QCD input for the relevant transition form factors.We calculate the branching ratios B(B(s)→D^?(s)lνl)with l=(e,μ,τ),the ratios of the branching fractions R(D^?)and R(D^?s),and the physical observables Pτ(D^?(s)),FL(D?(s))and AFB(τ).The“PQCD+Lattice”predictions for B(B→D^?lνl)and R(D^?)agree with the available experimental measurements within errors.For the ratios R(Ds)and R(D^?s),the"PQCD+Lattice"predictions agree with the other predictions.For Pτ(D^?)and FL(D^?),our theoretical predictions agree with the measured values within errors.Our theoretical predictions of the semileptonic B/Bs decays considered could be tested in the near future by the LHCb and Belle II experiments.     

KCdF3晶体中Cr3+-Li+中心局域结构研究

利用零场分裂参量与晶体结构之间的定量关系,研究了双掺杂晶体KCdF₃:Cr³⁺,Li⁺的局域结构。指出,对于KCdF₃:Cr³⁺,Li⁺晶体,四角晶场的形成包含两个方面:(1)由于电荷补偿而产生的等效电荷形成的四角对称晶场;(2)Cr³⁺的局域结构发生晶格畸变而产生的四角对称晶场。事实上,当Cr³⁺和Li⁺掺入KCdF₃晶体时,Cr³⁺代替了Cd²⁺离子;由于Cr³⁺离子与Cd²⁺离子的半径不同、电荷不同、质量不同,导致Cr³⁺的局域结构发生晶格畸变,由此而产生四角对称晶场;由于电荷补偿,Li⁺离子取代了[001]方向与Cr³⁺离子邻近的Cd²⁺离子,由此产生的等效电荷而形成的四角晶场。这样,Cr³⁺的局域结构由O_h对称变为C_4v点对称。文中建立了ZFS参量和晶体结构之间的定量关系。在考虑晶格畸变和等效电荷的基础上,研究了KCdF₃:Cr³⁺,Li⁺晶体的ZFS参量,理论结果和实验符合很好。得到了F^-离子向中心离子分别移动为ΔR₁=0.00268nm,ΔR₂=0.001nm,ΔR₃=0.00165nm。     

射频功率对辉光放电H2/C4H8等离子状态的影响

采用辉光放电技术和等离子体质谱诊断技术,研究了H₂/C₄H₈混合气体等离子体中正离子成分及主要正离子能量随射频功率的变化规律,并分析了H₂/C₄H₈混合气体主要的离解机理和形成过程.研究表明:随着射频功率的增加,碳氢碎片离子的浓度增加,在20 W时达到最大值,25 W后有所减小.当射频功率小于10 W时,H₂/C₄H₈混合气体等离子体中C₄H₉⁺相对浓度最大,当功率大于或等于10 W时,C₃H₃⁺相对浓度最大.随着射频功率的增大,碳氢碎片离子的能量逐渐增加.对H₂/C₄H₈混合气体等离子体的组成与能量进行的定性分析,将为H₂/C₄H₈混合气体辉光放电聚合物涂层工艺参数优化提供参考.     

THE STRUCTURE AND MAGNETIC PROPERTIES OF La2-2xSr1Ca2xMn2O7 (x=0.25－1.00)

In this paper, the effect of divalent cation substitution on the structure and magnetic properties in La_2-2xSr₁Ca_2xMn₂O₇ have been investigated systematically using bulk samples with a wide doping concentration range 0.25≤x≤1.00. Replacing trivalent La ions by divalent Ca ions results in the weakening and then disappearance of the long-range ferromagnetic (FM) ordering, the formation of spin canting, antiferromagnetic (AFM) ordering and low-temperature spin-glass. These results show that increasing the hole-doping concentration significantly suppresses the FM state. We suggest that this variation of magnetic properties is related to the competition of the FM and AFM interactions resulting from the change of Mn³⁺/Mn⁴⁺ ratio and Jahn-Teller-type lattice distortion of MnO₆ octahedra due to the introduction of Ca²⁺ ions.     

Broadband and efficient second harmonic generation in LiNbO3-LiTaO3 composite ridge waveguides at telecom-band

Broadband nonlinear frequency conversions of optical waves are widely employed in multiple areas of optics and photonics. However, the broadening of conversion bandwidth is often at a cost of reduction in efficiency, which may induce a limitation on practical applications. Here we theoretically propose a novel design of LiNbO₃ ridge waveguides on LiTaO₃ substrates which can be used for efficient and broadband second harmonic generation. Through group velocity engineering of the ridge waveguides, acceptance bandwidth over 20 nm with a high conversion efficiency of > 25%W^-1·cm^-2 is achieved at telecom-band.