掺杂Eu~(3+)的Na_(24)As_2Mo_(22)O_(83)的合成及其发光特性

本文在固相合成掺杂稀土离子的单钨酸盐、混合碱土金属钨酸盐[1～ 3 ] 等体系的系统研究基础上 ,采用固相反应法合成掺杂Ｅｕ3 + 离子的Ｎａ2 4Ａｓ2 Ｍｏ2 2 Ｏ83 荧光体结晶粉末 ,并经元素分析 ,ＩＲ和Ｘ射线粉末衍射等分析手段确定了它的结构 ,探讨了Ｅｕ3 + 离子在Ｎａ2 4 Ａｓ2 Ｍｏ2 2 Ｏ83 中的发光和能量传递机理。1　实验部分1 1　试剂及样品的制备先将Ｎａ3 ＡｓＯ4 ·1 2Ｈ2 Ｏ (分析纯 )和Ｎａ2 ＭｏＯ4 ·2Ｈ2 Ｏ(分析纯 )在 2 5 0℃下灼烧 30ｍｉｎ脱水制得Ｎａ3 ＡｓＯ4 和Ｎａ2 ＭｏＯ4 结晶粉末 ,再按一定物质的量比 ( 9…     

A Double Bounded Version of Schur's Partition Theorem

Dedicated to the memory of Paul Erdős Schur's partition theorem states that the number of partitions of n into distinct parts (mod 3) equals the number of partitions of n into parts which differ by 3, where the inequality is strict if a part is a multiple of 3. We establish a double bounded refined version of this theorem by imposing one bound on the parts (mod 3) and another on the parts (mod 3), and by keeping track of the number of parts in each of the residue classes (mod 3). Despite the long history of Schur's theorem, our result is new, and extends earlier work of Andrews, Alladi-Gordon and Bressoud. We give combinatorial and q-theoretic proofs of our result. The special case L=M leads to a representation of the generating function of the underlying partitions in terms of the q-trinomial coefficients extending a similar previous representation of Andrews. Received November 18, 1999 Research of the first author supported in part by NSF Grant DMS-0088975.     

The structure of naked singularity in self-similar gravitational collapse: II

Generalizing the results of Joshi and Dwivedi inComm. Math. Phys. 146, 333 (1992), it is pointed out that strong curvature naked singularities could occur in the self-similar gravitational collapse of any form of matter satisfying the weak energy condition for the positivity of mass-energy density.     

Soliton geometry and the vacuum gravitational field equations

A soliton geometry is introduced on manifolds with arbitrary dimensions. The usual soliton connection 1-form defined by Crampin et al. is recovered when the soldering form is a 0-form. It is shown that Einstein's vacuum field equations admit a soliton connection and a soldering 1-form. An associated linear equation with a spectral parameter of Einstein's vacuum field equations are found and some properties of this equation are explored. An example of a Bäcklund transformation is also given.     

Experimental boundaries of the quantum rotor induced polarization (QRIP) in liquid state NMR

The Haupt‐effect is a rather seldom used hyperpolarization method. It is based on the interdependence between nuclear spin states and rotational states of nearly free rotating methyl groups having C₃ symmetry. A sudden change in temperature from 4.2 K to room temperature by fast dissolution yields considerably enhanced ¹³C and ¹H resonance signals. This phenomenon is now termed quantum rotor induced polarization. More than 40 substances have been studied by this approach in order to identify them as polarizable by the ‘Haupt‐effect in the liquid state’. Influencing factors have been analyzed systematically. It could be concluded that substances having a high tunneling frequency, which is due to a small and narrow potential barrier, are most likely to feature quantum rotor induced polarization‐enhanced signals. Copyright © 2013 John Wiley & Sons, Ltd.     

Lorentzian geometry of globally framed manifolds

A new class of globally framed manifolds (carrying a Lorentz metric) is introduced to establish a relation between the spacetime geometry and framed structures. We show that strongly causal (in particular, globally hyperbolic) spacetimes can carry a regular framed structure. As examples, we present a class of spacetimes of general relativity, having an electromagnetic field, endowed with a framed structure and a causal spacetime with a nonregular contact structure. This paper opens a few new problems, of geometric/physical significance, for further study.     

Source-free electromagnetic fields in the Einstein-Gödel universe

A metric containing a parameter (² = 1) has been derived which represents axially symmetric source-free electromagnetic fields in a static Einstein universe when is put equal to 1. The same metric represents the source-free electromagnetic fields in a Gödel rotating universe when is put equal to-1. Many known solutions are obtained as particular cases.     

Defects in hexagonal vanadium fluoride bronzes: A high resolution electron microscope study

Observations of hexagonal vanadium fluoride bronzes, A_xVF₃, (A = K, Rb, Cs, and Tl; 0.18 ≤ x ≤ 0.32 by high resolution electron imaging showed the presence of several kinds of defects, including stacking faults, overlays, twin boundaries, and different types of antiphase boundaries. These defects were modeled, and the structures confirmed by comparison of calculated and observed images where necessary. The presence of disorder was interpreted as supporting evidence for the tentative phase diagram.     

N-(η5-Cyclopentadienylvanadium)benzenesulfonamide

N-(⁵-Cyclopentadienylvanadium)benzenesulfonamide has been synthesized for the first time by treating benzenesulfonamide orN-(tributylstannyl)benzenesulfonamide with vanadocene.Deceased.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2107–2109, December, 1993.     

Lifetime of Parahydrogen in Aqueous Solutions and Human Blood

Molecular hydrogen has unique nuclear spin properties. Its nuclear spin isomer, parahydrogen (pH₂), was instrumental in the early days of quantum mechanics and allows to boost the NMR signal by several orders of magnitude. pH_2-induced polarization (PHIP) is based on the survival of pH₂ spin order in solution, yet its lifetime has not been investigated in aqueous or biological media required for in vivo applications. Herein, we report longitudinal relaxation times (T₁) and lifetimes of pH₂ ( ) in methanol and water, with or without O₂, NaCl, rhodium-catalyst or human blood. Furthermore, we present a relaxation model that uses T₁ and for more precise theoretical predictions of the H₂ spin state in PHIP experiments. All measured T₁ values were in the range of 1.4–2 s and values were of the order of 10–300 minutes. These relatively long lifetimes hold great promise for emerging in vivo implementations and applications of PHIP.