A new higher-order gravitational field equation withL =R +Ω R µvRµv / R +τR αβγδRαβγδ / R

In this paper, a new kind of higher-order gravitational theory is suggested. The field equation is obtained from a variational method. The result is a fourth-order partial differential equation for the metric, but the coefficients coupled to the higher-order terms are dimensionless. The energy momentum conservation law is discussed for the new theory. In maximally symmetric space, a de Sitter universe solution is obtained.1. Research support by the South African Foundation for Research Development.2. On leave from Fudan University, Shanghai, People's Republic of China.     

Conservation Laws and Bianchi Identities in R+R2+Q2 Theories

We investigate the conscrvalion Jaws in the class of R+R²+Q² theory with torsion. We prove that the conservation Jaws may be dcrived Born the Bianchi identities of the curvature and torsion tensors. In particular the conservation law for matter is showed to be a result of the Dianchi identities and gravitational ficld equations just as it does for T^uv=0 in general relativity.     

R170＋R23系的汽液液相平衡研究

针对PR-HV-NRTL模型对R170(乙烷) R23(三氟甲烷)系在低温下的异常计算结果,采用扩展的双液相模型对低温区进行了计算,从理论上预测出该混合物出现液相分离的可能;对185.26 K温度下的汽液液相平衡进行了初步的实验,首次证实了R170 R23系存在汽液液相平衡现象,这被认为是发现的第三种具有汽液液相平衡特性的HC HFC混合物.     

三元混合制冷剂R290+R600a+N2汽液相平衡实验研究

在氢气液化工艺中,预冷循环是重要的一环,其中混合制冷剂(mixed refrigerant,MR)预冷循环是单位能耗比较低的,故对MR性能的优化显得尤为重要.为此利用液相单相循环法搭建汽液相平衡(Vapor-liquid equilibrium,VLE)实验系统,研究了R290+R600a+N₂三元体系的VLE性质,在273.15 K～323.15 K的温度范围内,对三元混合工质R290+R600a+N₂进行实验研究,并获得18组实验数据.同时使用Peng-Pobinson-Stryjek-Vera (PRSV)状态方程结合van der Waals(vd W)混合法则对R290+R600a、R290+N₂、R600a+N₂三组二元体系的VLE文献数据进行了拟合计算,得到二元交互作用系数,拟合结果与文献数据吻合良好.以此为基础,推算该三元体系的VLE性质.最后将实验数据与计算结果对比表明,体系压力平均相对偏差AARDp为0.85%,系统组分R290、R600a和N₂的气相平均绝...     

Quantum General Relativity and the Meaning of (R + R2) Theories

It is argued that, due to the cut-off lengths arising in Quantum General Relativity, R2 corrections of Einstein's theory cannot be interpreted as quantum corrections.     

Pressure-Induced Shifts of R1 and R2 Lines of YAG:Cr3+

By means of improved ligand-field theory, the "pure electronic" pressure-induced shifts (PS's) and the PS's due to electron-phonon interaction (EPI) of R1 line and R2 line of YAG:Cr3 have been calculated, respectively.The calculated results are in very good agreement with the experimental data. It is demonstrated that the admixture of |t22(3T1)e4T2> and |t322E> bases in the wavefunction of R1 level of YAG:Cr3 and its change with pressure play a key role for the PS of R1 line. The behaviors of the "pure electronic" PS of R1 line and the PS of R1 line due to EPI are different. It is the combined effect of them that gives rise to the total PS of R1 line, which has satisfactorily explained the experimental results. The systematic analyses and comparisons between the feature of R1-line PS of YAG:Cr3 and the ones of three laser crystals (GSGG:Cr3 , GGG:Cr3 and ruby) have been made, and the origin of the difference between them has been revealed.     

Birkhoff's theorem for ghost-free,tachyon-freeR + R 2 +Q 2 theories with torsion

We investigate the conditions under which the class of ghost-free, tachyon-freeR + R ² +Q ² theories with torsion satisfy Birkhoff's theorem. We prove a weakened Birkhoff theorem requiring an additional assumption of parity invariance for two Lagrangians one of which contains torsion squared terms in addition to curvature squared terms. For another Lagrangian, also containing torsion squared terms, a weakened Birkhoff theorem requiring the additional assumptions of parity invariance and constant scalar curvature is proven. A special case of this Lagrangian is shown to satisfy a weakened Birkhoff theorem requiring only the additional assumption of constant scalar curvature. In addition the explicit dependence of torsion on parity noninvariant quantities is displayed.     

稀土-铬蓝黑R配合物体系的近红外发光研究

研究了金属指示剂铬蓝黑R对Yb3 的近红外发光的敏化作用。结果表明 ,在中性乙醇溶液中 ,铬蓝黑R和Yb3 离子可形成配比为 2∶1的配合物。配合物的形成可猝灭配体铬蓝黑R的荧光 ,同时使Yb3 离子的荧光得到显著增强。表现出配体向Yb3 离子传能的机理。在一定条件下 ,配合物体系中Yb3 离子的发光强度与Yb3 离子的浓度成正比 ,同时其他低浓度稀土离子的存在不会影响Yb3 离子的发光 ,显示出近红外发光技术在单一稀土分析中良好的应用前景。     

Derg R -Faktor des 2+-Rotationsniveaus von Er168

The rotation of the angular correlation between theγ-group at about 820 keV and the 80 keV radiation in the decay of Tm¹⁶⁸ has been observed in an external magnetic field of 20300 gauss. The result:ω _R·τ=0,485±0,051 yields for theg _R -factor of the 80 keV state of Er¹⁶⁸:g _R =+0,25±0,03. The evaluation includes a paramagnetic correction factor of:β=7,26, (B _eff=β·B _ext). The angular correlation is slightly attenuated by internal fields. For a liquid source of Tm (NO₃)₃ solved in 3 n HNO₃, a measurement of the differential angular correlation as a function of the delay time gave:λ ₂=(5,8±2,9)·10⁷sec^?1, assumingA ₂(t)=A ₂(0)·e ^?λ ₂·t. The half life of the 80 keV state was found to be:T _1/2=(1,92±0,04)·10^?9sec in agreement with earlier measurements.     

Muon level crossing resonance of the R3NMu+ ion

Observation of muon level crossing resonance with¹⁴N nuclei in frozen triethylamine is reported and assigned to the ionic species (C₂H₅)₃NMu⁺. In forming this species, the implanted positive muons mimic the chemical behaviour of protons as usual, here in a process analogous to the protonation of a base. The resultant molecular ion has the axial symmetry necessary for detection of level crossing with an integral-spin nucleus. The quadrupole coupling constant is determined to be ¦e ² qQ/h¦=0.41(4) MHz, corresponding to an electric field gradient on¹⁴N of 0.10(1) a.u. and consistent with anab initio estimate for species of the type R₃NMu⁺. The prospects for detection of the muonium-substituted ammonium ion NH₃Mu⁺ ion in ammonia are discussed.     

BaMgAl10O17:R2+(R=Eu,Mn)的真空紫外光谱特性

采用高温固相反应法合成了BaMgAl10O17:R(R＝Eu,Mn)荧光体，测量了荧光体的真空紫外激发光谱和相应的发射光谱，观察到基质吸收带位于165nm附近，Mn^2 离子的吸收位于170－240nm范围，Eu^2 离子的4f→5d吸收位于210－400nm范围。真空紫外光谱特性的研究表明基质与激活离子之间存在较好的能力传递。     

Global Regularity of Wave Maps from R 3+1 to Surfaces

 We consider Wave Maps with smooth compactly supported initial data of small -norm from R ³⁺¹ to certain 2-dimensional Riemannian manifolds and show that they stay smooth globally in time. Our methods are based on the introduction of a global Coulomb Gauge as in [17], followed by a dynamic separation as in [8]. We then rely on an adaptation of T. Tao's methods used in his recent breakthrough result [24]. Received: 16 March 2002 / Accepted: 31 January 2003 Published online: 5 May 2003 Communicated by P. Constantin     

Approximate solutions for theR +R 2 theories of gravitation: Torsion components

We search for vacuum solutions of a spherically symmetric and static field for the nineparameterR+R ² gravitational theories in a weak-field limit. In this paper approximate solutions of torsion are obtained.     

Magnetisches Verhalten heterogener Legierungen: R5Co19+RCo5 (R=Ce,Ce-La,CeMM)

Magnetic and mechanical properties of the new phase R₅Co₁₉ in the Ce-Co, Ce-La-Co and CeMM-Co systems have been investigated. The effect of this phase on the magnetic properties of RCo₅ alloys (R=Ce, CeLa and CeMM) and the influence of the variation in composition of commercial CeMM on the magnetic properties of CeMMCo₅ are presented.

     

(2 + 1)-Dimensional Solutions in F(R) Gravity

Motivated by the well-known charged BTZ black holes, we look for (2 + 1)-dimensional solutions of F(R) gravity. At first we investigate some near horizon solutions and after that we obtain asymptotically Lifshitz black hole solutions. Finally, we discuss about rotating black holes with exponential form of F(R) theory.