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排序方式: 共有208条查询结果,搜索用时 15 毫秒
1.
H.L. Xu A. Persson S. Svanberg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):233-236
New radiative lifetime measurements based on time-resolved laser-induced fluorescence techniques are reported for 18 even-parity
levels belonging to the 4f5d26p and 4f
25d
2 configurations of Ce I and 6 even-parity levels belonging to the 5d26s, 4f5d6p, and 4f6s6p configurations of Ce II. Free neutral and singly ionized cerium atoms were produced by laser ablation. The Ce I and Ce II
levels range in energy from 26 545 to 29 102 cm-1, and 42 573 to 48 152 cm-1, respectively.
Received 25 September 2002 Published online 4 March 2003 相似文献
2.
Many biological and medical studies have as a response of interest the time to occurrence of some event, such as the occurrence of a particular symptom or disease, remission, relapse, death due to some specific disease, or simply death. In this paper we study the problem of assessing the effect of potential risk factors on the outcome event of interest through a parametric or semi-parametric frailty model where the lifetimes have a reason to be considered dependent. This dependence may arise because of multiple endpoints within the same individual or because, when studying a single endpoint, there are natural groupings between study subjects. The objective of this paper is to extend both parametric and semi-parametric approaches to regression analysis in which the lifetimes of individuals in a group are effected by the same random frailty which follows a positive stable distribution. Some comparisons of the properties of this frailty distribution with other frailty distributions are made and an example which assesses the effect of a treatment in a litter-matched tumorigenesis study is presented. 相似文献
3.
M. D. Zipper G. P. Simon P. Cherry A. J. Hill 《Journal of Polymer Science.Polymer Physics》1994,32(7):1237-1247
Homopolymers and blends of polycarbonate/ThermX have been investigated by differential scanning calorimetry, dynamic mechanical analysis, density measurements, and positron annihilation lifetime spectroscopy. The study focuses on the chain mobility and free volume in the amorphous miscible regions of the blends and how this mobility and free volume are affected by increasing crystallinity. It is proposed that judicious annealing, which results in increasing crystallinity (while avoiding ageing or transesterification), induces a constraint on the amorphous region leading to an increase in Tg and coalescence of free volume sites. © 1994 John Wiley & Sons, Inc. 相似文献
4.
Dissociative and nondissociative electron attachment in the electron impact energy range 0–14 eV are reported for SOF2 SOF4, SO2F2, SF4, SO2, and SiF4 compounds which can be formed by electrical discharges in SF6. The electron energy dependences of the mass-identified negative ions were determined in a time-of-flight mass spectrometer. The ions studied include F– and SOF
2
–*
from SOF2; SOF
3
–
and F– from SOF4; SO2F
2
–*
, SO2F–, F
2
–
, and F– from SO2F2; SF
4
–*
and F– from SF4; O–, SO–, and S– from SO2; and SiF
3
–
and F– from SiF4. Thermochemical data have been determined from the threshold energies of some of the fragment negative ions. Lifetimes of the anions SOF
2
–*
, SO2F
2
–*
, and SF
4
–*
are also reported. 相似文献
5.
采用考虑Davidson修正的内收缩多参考组态相互作用(icMRCI+Q)方法结合相关一致基组aug-ccpV5Z和aug-cc-pV6Z计算了CF~+离子第一离解极限C~+(~2p_u)+F(~2P_u)对应的12个∧-S态(X~l∑~+,a~3∏,1~3∑~+,1~3Δ,1~1∑~-,1~1∑~-,1~3∑~-,2~1∑~+,1~1∏,2~3∏,2~1∏和2~3∑~+)所产生的23个Ω态的势能曲线.计算中考虑了旋轨耦合效应、核价相关和标量相对论修正以及将参考能和相关能分别外推至完全基组极限.基于得到的势能曲线,获得了束缚和准束缚的9个∧-S态和16个Ω态的光谱常数,并且X~1∑~+,a~3∏~(势阱一)∧-S态的光谱常数与已有的实验结果非常符合.此外,计算了CF自由基X~2∏态到CF~+离子束缚和准束缚的9个∧-S态的垂直电离势和绝热电离势,并且CF~+(X~1∑~+)←CF(X~2∏)和CF~+(a~3∏(势阱一))←CF(X~2∏)的垂直电离势和绝热电离势与相应的实验结果也非常符合.由a~3∏,1~1∏态和其他激发∧-S态势能曲线的交叉现象,借助于计算的旋轨耦合矩阵元,分析了a~3∏~(势阱一),1~1∏~(势阱一)和2~1∑~+态的预解离机理.计算的23个Ω态离解极限处的相对能量与实验结果十分吻合.最后计算了(2)0+~(势阱一)(v'=0-5),(1)1~(势阱一)(v'=0-5)和(2)1~(势阱一)(v'=0)到X0~+态跃迁的Franck-Condon因子和辐射寿命. 相似文献
6.
Mixed IR/Vis Two‐Dimensional Spectroscopy: Chemical Exchange beyond the Vibrational Lifetime and Sub‐ensemble Selective Photochemistry
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Dr. Luuk J. G. W. van Wilderen Dr. Andreas T. Messmer Prof. Dr. Jens Bredenbeck 《Angewandte Chemie (International ed. in English)》2014,53(10):2667-2672
Two‐dimensional exchange spectroscopy (2D EXSY) is a powerful method to study the interconversion (chemical exchange) of molecular species in equilibrium. This method has recently been realized in femtosecond 2D‐IR spectroscopy, dramatically increasing the time resolution. However, current implementations allow the EXSY signal (and therefore the chemical process of interest) only to be tracked during the lifetime (T1) of the observed spectroscopic transition. This is a severe limitation, as typical vibrational T1 are only a few ps. An IR/Vis pulse sequence is presented that overcomes this limit and makes the EXSY signal independent of T1. The same pulse sequence allows to collect time‐resolved IR spectra after electronic excitation of a particular chemical species in a mixture of species with strongly overlapping UV/Vis spectra. Different photoreaction pathways and dynamics of coexisting isomers or of species involved in different intermolecular interactions can thus be revealed, even if the species cannot be isolated because they are in rapid equilibrium. 相似文献
7.
Maurizio A. P. Mingardi 《光谱学快报》2013,46(6):141-147
In the past five years, a number of d6 complexes have been found to exhibit luminescence when excited by ultraviolet light. Such emission has been assigned to d-d transitions localized on the metal ion, to charge-transfer transitions, and to ligand localized transitions2,3. The specific kind of emission observed is thought to depend on which electronic level lies lowest in energy. 相似文献
8.
Considering the perturbation, the results of theoretical calculation of five Rydberg series energy levels 6s2ns^2S1/2 (n = 7 - 20), 6s^2nd^2D3/2 (n = 6 - 20), 6s^2nd^2D5/2 (n = 6 - 20), 6s^2np^2P1/2^0 (n = 7- 20), and 6s^2np^2P3/2^0 (n = 7-20) for Tl I are presented using the weakest bound electron potential model (WBEPM) theory. Furthermore, the radiative lifetimes of this five series are also calculated. The calculated values of energy levels and lifetimes are in good agreement with the experimental results. 相似文献
9.
通过激光与原子束相互作用,三步激发及时间分辨光谱术,测量了Yb原子奇宇称受扰里德堡系6snp^1,3P121个能级和两上干扰能级的自然辐射寿命,分析了各种因素对测量值的影响。 相似文献
10.
Sheldon M Ross 《Stochastic Processes and their Applications》1976,4(2):167-173
Consider an n-component reliability system having the property that at any time each of its components is either up (i.e., working) or down (i.e., being repaired). Each component acts independently and we suppose that each time the ith component goes up it remains up for an exponentially distributed time having mean μi, and each time it goes down it remains down for an exponentially distributed time having mean υi. We further suppose that whether or not the system itself is up at any time depends only on which components are up at that time. We are interested in the distribution of the time of first system failure when all components are initially up at time zero. In section 2 we show that this distribution has the NBU (i.e., new better than used) property, and in Section 3 we make use of this and other results to obtain a lower bound to the mean time until first system failure. 相似文献