共查询到20条相似文献,搜索用时 234 毫秒
1.
《Radiation measurements》2007,42(4-5):719-722
Luminescence and luminescence excitation under VUV radiation of (, K, Cs; , In) double phosphates are studied. Two emission bands peaking near 330 and 420 nm are common for investigated crystals. The band structure and partial densities of electronic states of perfect , and crystals are calculated by the full-potential linear-augmented-plane-wave (FLAPW) method. It is found that the structures of the conduction bands of crystals, which have different B cations, are appreciably different. Experimental results are compared with results of calculations of the electronic structure. Assumptions concerning the origin of luminescence in double phosphates are made. 相似文献
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
《Journal of Geometry and Physics》2007,57(1):89-100
In this paper we study a generalized Darboux Halphen system given by where , , are real variables, are real constants and We prove that, for any , this system does not admit any non-constant global first integral that can be described by a formal power series. Furthermore, restricting the values of to a full Lebesgue measure set, we prove that this system does not admit any non-constant rational or Darbouxian global first integral. This is a first step toward proving that this system is chaotic. 相似文献
13.
In this paper we investigate Leibniz algebras whose quotient Lie algebra is a naturally graded filiform Lie algebra . We introduce a Fock module for the algebra and provide classification of Leibniz algebras whose corresponding Lie algebra is the algebra with condition that the ideal is a Fock -module, where is the ideal generated by squares of elements from .We also consider Leibniz algebras with corresponding Lie algebra and such that the action gives rise to a minimal faithful representation of . The classification up to isomorphism of such Leibniz algebras is given for the case of . 相似文献
14.
Rongjin Huang Laifeng Li Zhixiong Wu Xinxin Chu Xiangdong Xu Lihe Qian 《Solid State Communications》2010,150(35-36):1617-1620
Antiperovskite manganese nitrides (, 0.1, 0.15) were prepared and their negative thermal expansion, magnetic and specific heat properties were investigated. A frozen state with a freezing temperature was found at ~207 K in . This indicates that exhibits a spin glass state at low temperatures. We discussed the cause of spin glass behavior and correlated this spin glass behavior with broadening of the negative thermal expansion operation-temperature window of the manganese nitrides . 相似文献
15.
《Radiation measurements》2007,42(4-5):644-647
The tetragonal : persistent luminescence materials were prepared by a solid state reaction. The UV excited and persistent luminescence was observed in the green region centred at 535 nm. Both luminescence phenomena are due to the same ion occupying the single site in the host lattice. The codoping usually reduced the persistent luminescence of :, which differs from the : and : materials. Only the ion enhanced slightly the persistent luminescence. With the aid of synchrotron radiation, the band gap energy of : was found to be about 7 eV that is very similar to those of the : materials. Thermoluminescence results suggested that the ions might act as electron traps, but only the TL peaks created by and can be found in the temperature range accessible. Lattice defects (e.g. oxygen vacancies) are also important, since the same main thermoluminescence peak was observed at about with and without codoping. 相似文献
16.
The fundamental properties of nonlinear ion hole modes propagating in current-driven collisionless plasmas are derived. Making use of Schamel's alternative method their spatial structure and phase velocities are analyzed and found to depend crucially on the used trapped ion distribution . A regular represents a continuous spectrum, which is called privileged or perfect since it yields a definite and appears most realistic. A singular , on the other hand, involving jumps and moderate slope singularities at the separatrix, does reveal further classes of hole equilibria at the cost, however, of a well-defined . This explains why Bernstein, Greene, Kruskal (BGK)-solutions of the Vlasov–Poisson system, exhibiting a strong slope singularity of their derived trapped particle distribution, can principally not provide definite . The nonlinear dispersion relation (or ) of privileged ion holes, on the other hand, is equivalent with that of cnoidal electron holes, i.e. in addition to the ordinary ion acoustic branch there exists a correspondence to the “Langmuir” branch and to the multiple “slow electron acoustic” branches, reflecting different trapping scenarios. 相似文献
17.
《Physica A》2005,350(1):38-44
Finite size effects on the calorimetric cooperatity of the folding-unfolding transition in two-state proteins are considered using the Go lattice models with and without side chains. We show that for models without side chains a dimensionless measure of calorimetric cooperativity defined as the ratio of the van’t Hoff to calorimetric enthalpy does not depend on the number of amino acids N. The average value is lower than the experimental value . For models with side chains approaches unity as , where . Above the critical chain length these models can mimic the truly all-or-non folding–unfolding transition. 相似文献
18.
Mixed traffic flux composed of crossing pedestrians and vehicles extensively exists in cities. To study the characteristics of the interference traffic flux, we develop a pedestrian-vehicle cellular automata model to present the interaction behaviors on a simple cross road. By realizing the fundamental parameters (i.e. injecting rates , , the extracting rate β and the pedestrian arrival rate ), simulations are carried out. The vehicular traffic flux is calculated in terms of rates. The effect of the crosswalk can be regarded as a dynamic impurity. The system phase diagrams in the plane are built. It is found that the phase diagrams consist essentially of four phases namely Free Flow, Congested, Maximal Current and Gridlock. The value of the Maximal current phase depends on the extracting rate β, while the Gridlock phase is achieved only when the pedestrians generating rate is higher than a critical value. Furthermore, the effect of vehicles changing lane () and the location of the crosswalk on the dynamic characteristics of vehicles flow are investigated. It is found that traffic situation in the system is slightly enhanced if the location of the crosswalks is far from the intersection. However, when , increase, the traffic becomes congested and the Gridlock phase enlarges. 相似文献
19.
《Radiation measurements》2007,42(4-5):874-877
Ytterbium doped borate crystals are promising laser media, e.g. in (LSB) matrices large distance between ytterbium ions results in reduced concentration quenching of the ytterbium f–f luminescence [Petermann, K., Fagundes-Peters, D., Johansen, O., Mond, M., Peters, V., Romero, J.J., Kutovoi, S., Speiser, J., Giesen, A., 2005. Highly Yb-doped oxides for thin-disc lasers. J. Crystal Growth 275, 135-140]. ions in complex oxides in addition to the 4f 4f transitions often manifest fast charge transfer luminescence (CTL) in the UV-visible range. In some borates it was not observed at all, like in orthoborates of Sc, Y and La [Van Pieterson, L., Heeroma, M., de Heer, E., Meijerink, A., 2000. Charge transfer luminescence of . J. Lumin. 91, 177–193]; in haloborates , where X = Cl, Br, the UV/visible luminescence was attributed to ytterbium CTL though it looked substantially different from other matrices [Dotsenko, V.P., Berezovskaya, I.V., Pyrogenko, P.V., Efryushina, N.P., Rodniy, P.A., Eijk van, C.W.E., Sidorenko, A.V., 2002. Valence states and luminescence properties of ytterbium ions in strontium haloborates. J. Solid State Chem. 166, 271–276]; while in oxyborate “classical” CTL was observed [Jubera, V., Garcia, A., Chaminade, J.P., Guillen, F., Sablayrolles, Jean, Fouassier, C., 2007. and luminescent properties of the phase. J. Lumin. 124(1), 10–14]. In this work the luminescence properties of another borate, namely LSB doped by Yb are presented. 相似文献