Two-inch sized KMgF3,BaLiF3 and LiCaAlF6 (LiCAF) single crystals were grown by the Czochralski method under a CF4 atmosphere. X-ray irradiation was used to carry out a comparative study of induced optical absorption phenomena and colour centre creation in the ultra-violet and visible spectral regions. The integral of the induced absorption spectra is significantly lower in LiCAF with respect to the other studied materials. It is found that the amplitude of the F-absorption band is suppressed more than a factor of 3 by Mg-doping. For Mg-doped crystals, the optimum doping concentration is about 0.2 mol% of Mg2+. 相似文献
This paper introduces a mathematical model which makes it possible both to determine the concentration of photosynthetic herbicides and to obtain a quantitative parameter in order to compare their activity using a previously described sensing system. The working principle involves the changes in absorption properties at 860 nm of the reaction centre (RC) isolated from the bacteria Rhodobacter sphaeroides when photosynthetic herbicides are present. The method has been used for the determination and activity comparison of five photosynthetic herbicides: diuron, atrazine, terbutryn, terbuthylazine and simazine. Detection limits obtained were 2.2, 0.75, 0.046, 0.25, and 1.4 μM, respectively. The resulting order for the different herbicides according to their action on RC was: terbutryn > terbuthylazine > atrazine > simazine > diuron. 相似文献
To date, integral bases for the centre of the Iwahori-Hecke algebra of a finite Coxeter group have relied on character theoretical results and the isomorphism between the Iwahori-Hecke algebra when semisimple and the group algebra of the finite Coxeter group. In this paper, we generalize the minimal basis approach of an earlier paper, to provide a way of describing and calculating elements of the minimal basis for the centre of an Iwahori-Hecke algebra which is entirely combinatorial in nature, and independent of both the above mentioned theories.
This opens the door to further generalization of the minimal basis approach to other cases. In particular, we show that generalizing it to centralizers of parabolic subalgebras requires only certain properties in the Coxeter group. We show here that these properties hold for groups of type and , giving us the minimal basis theory for centralizers of any parabolic subalgebra in these types of Iwahori-Hecke algebra.
Tutte’s 3-Flow Conjecture suggests that every bridgeless graph with no 3-edge-cut can have its edges directed and labelled
by the numbers 1 or 2 in such a way that at each vertex the sum of incoming values equals the sum of outgoing values. In this
paper we show that Tutte’s 3-Flow Conjecture is true for Cayley graphs of groups whose Sylow 2-subgroup is a direct factor
of the group; in particular, it is true for Cayley graphs of nilpotent groups. This improves a recent result of Potočnik et al.
(Discrete Math. 297:119–127, 2005) concerning nowhere-zero 3-flows in abelian Cayley graphs. 相似文献
The classical and quantum mechanics of a system of directly interacting relativistic particles is discussed. We first discuss
the spin-zero case, where we basically follow Rohrlich in introducing a set of covariant centre of mass (CM) and relative
variables. The relation of these to the classic formulation of Bakamjian and Thomas is also discussed. We also discuss the
important case of relativistic potentials which may depend on total four-momentum squared. We then consider the quantum mechanical
case of spin-half particles. The negative energy difficulty is solved by introducing a number of first class constraints which
fix the spinor structure of physical solutions and ensure the existence of proper CM and relative variables. We derive the
form of interactions consistent with Lorentz invariance, space inversion, time reversal and charge conjugation and with the
above mentioned first class constraints and find that it is analogous to that for the non-relativistic case. Finally the relationship
of the present work with some previous work is briefly discussed. 相似文献