Let be a -periodic potential such that . The classical Lyapunov criterion to stability of Hill's equation is , where is the negative part of . In this paper, we will use a relation between the (anti-)periodic and the Dirichlet eigenvalues to establish some lower bounds for the first anti-periodic eigenvalue. As a result, we will find the best Lyapunov-type stability criterion using norms of , . The numerical simulation to Mathieu's equation shows that the new criterion approximates the first stability region very well.
A cationic water‐soluble polyfluorene (P2) containing a high density of tetraalkylammonium side chains in polymer backbone was synthesized and characterized. The polymer shows excellent water solubility up to 100 mg · mL−1 as well as high photoluminescence (PL) quantum yield of 44% in water. The relatively high cationic density and appropriate side chain length of the polymer are the key factors to achieve such high water solubility. The reduction potential of P2 is decreased as compared with its neutral polymer, reflecting the enhanced electron injection abilities. The standard NPB/Alq3 device using such a polymer as the electron injection layer shows nearly three‐fold enhancement in the electroluminescence (EL) efficiency.
We study the Lyapunov stability of periodic motion of an atom in the vicinity of an infinite straight wire with an oscillating uniform charge, which serves as a mechanism for trapping cold neutral atoms. It is proved by King and Leséniewski that the system has classical periodic motion for a certain range of parameters. In this Letter, we will prove, using the Birkhoff Normal Forms and Morse Twist Theorem, that such a periodic state is of twist type. As a result, besides the stability of the periodic state in the sense of Lyapunov, the system has infinitely many interesting bound states such as subharmonics and quasi-periodic states. 相似文献
In this paper, we determine the infimum and the supremum of the Dirich-let eigenvalues λn(p) (n = 1,2,…)of the problem t∈ ?[0,T], where 1 < p < ∞, and the weights p are nonnegative and are subject to conditions p(t)dt = M and max(e[0,T] p(t) = H. It is also explained for whatweights p the infimum and the supremum will be attained. 相似文献
The photophysical properties, such as the UV-vis absorption spectra, triplet transient difference absorption spectra, triplet excited-state extinction coefficients, quantum yields of the triplet excited state, and lifetimes of the triplet excited state, of 10 novel zinc phthalocyanine derivatives with mono- or tetraperipheral substituents have been systematically investigated in DMSO solution. All these complexes exhibit a wide optical window in the visible spectral range and display long triplet excited-state lifetimes (140-240 mus). It has been found that the complexes with tetrasubstituents at the alpha-positions exhibit a bathochromic shift in their UV-vis absorption spectra, fluorescence spectra, and triplet transient difference absorption spectra and have larger triplet excited-state absorption coefficients. The nonlinear absorption of these complexes has been investigated using the Z-scan technique. It is revealed that all complexes exhibit a strong reverse saturable absorption at 532 nm for nanosecond and picosecond laser pulses. The excited-state absorption cross sections were determined through a theoretical fitting of the experimental data using a five-band model. The complexes with tetrasubstituents at the alpha-positions exhibit larger ratios of triplet excited-state absorption to ground-state absorption cross sections (sigma T/sigma g) than the other complexes. In addition, the wavelength-dependent nonlinear absorption of these complexes was studied in the range of 470-550 nm with picosecond laser pulses. All complexes exhibit reverse saturable absorption in a broad visible spectral range for picosecond laser pulses. Finally, the nonlinear transmission behavior of these complexes for nanosecond laser pulses was demonstrated at 532 nm. All complexes, and especially the four alpha-tetrasubstituted complexes, exhibit stronger reverse saturable absorption than unsubstituted zinc phthalocyanines due to the larger ratio of their excited-state absorption cross sections to their respective ground-state absorption cross sections. 相似文献