3,578 research outputs found
General calculation of transition rates for rare-earth ions using many-body perturbation theory
The transition rates for rare-earth ions in crystals can be
calculated with an effective transition operator acting between model
and states calculated with effective Hamiltonian, such as
semi-empirical crystal Hamiltonian. The difference of the effective transition
operator from the original transition operator is the corrections due to mixing
in transition initial and final states of excited configurations from both the
center ion and the ligand ions. These corrections are calculated using
many-body perturbation theory. For free ions, there are important one-body and
two-body corrections. The one-body correction is proportional to the original
electric dipole operator with magnitude of approximately 40% of the uncorrected
electric dipole moment. Its effect is equivalent to scaling down the radial
integral \ME {5d} r {4f}, to about 60% of the uncorrected HF value. The
two-body correction has magnitude of approximately 25% relative to the
uncorrected electric dipole moment. For ions in crystals, there is an
additional one-body correction due to ligand polarization, whose magnitude is
shown to be about 10% of the uncorrected electric dipole moment.Comment: 10 pages, 1 figur
Numerical analysis of four-wave mixing between 2 ps mode-locked laser pulses in a tensile-strained bulk SOA
A numerical model of four-wave mixing between 2-ps pulses in a tensile-strained bulk semiconductor optical amplifier is presented. The model utilizes a modified Schrodinger equation to model the pulse propagation. The Schrodinger equation parameters such as the material gain first and second order dispersion, linewidth enhancement factors and optical loss coefficient are obtained using a previously developed steady-state model. The predicted four-wave mixing pulse characteristics show reasonably good agreement with experimental pulse characteristics obtained using frequency resolved optical gating
Opportunities for Public Aquariums to Increase the Sustainability of the Aquatic Animal Trade
The global aquatic pet trade encompasses a wide diversity of freshwater and marine organisms. While relying on a continual supply of healthy, vibrant aquatic animals, few sustainability initiatives exist within this sector. Public aquariums overlap this industry by acquiring many of the same species through the same sources. End users are also similar, as many aquarium visitors are home aquarists. Here we posit that this overlap with the pet trade gives aquariums significant opportunity to increase the sustainability of the trade in aquarium fishes and invertebrates. Improving the sustainability ethos and practices of the aquatic pet trade can carry a conservation benefit in terms of less waste, and protection of intact functioning ecosystems, at the same time as maintaining its economic and educational benefits and impacts. The relationship would also move forward the goal of public aquariums to advance aquatic conservation in a broad sense. For example, many public aquariums in North America have been instrumental in working with the seafood industry to enact positive change toward increased sustainability. The actions include being good consumers themselves, providing technical knowledge, and providing educational and outreach opportunities. These same opportunities exist for public aquariums to partner with the ornamental fish trade, which will serve to improve business, create new, more ethical and more dependable sources of aquatic animals for public aquariums, and perhaps most important, possibly transform the home aquarium industry from a threat, into a positive force for aquatic conservation. Zoo Biol. 32:1-12, 2013. © 2012 Wiley Periodicals, Inc
Common mechanisms in intelligence and development: a study of ability profiles in mental age-matched primary school children
BACKGROUND AND AIMS: We examine the relationship between individual differences and cognitive development in order to address the question of whether variability in each might be due to common mechanisms. In two experiments, we compare the cognitive profiles of groups of younger and older children matched on overall mental age (MA) using standard tests of intelligence (British Abilities Scales-II; BAS-II, and Wechsler Intelligence Scale for Children, 3rd edition; WISC-III).
RESULTS: In both experiments, MANOVAs revealed few differences in the profiles of younger and older MA-matched children. In Experiment 1, no reliable differences were found on the six BAS-II core scales, and only one group difference was found on the supplementary, Speed of Processing diagnostic test, where the older children outperformed the younger children. In Experiment 2, analyses of the 10 core scales of the WISC-III revealed two group differences. These were on Coding, where the younger children's performance was superior to the older children, and on Arithmetic, where the older children outperformed the younger children.
CONCLUSIONS: The degree of similarity between cognitive profiles of younger and older MA-matched groups suggests that a common mechanism may indeed underlie variability in individual differences and development. The findings further suggest that children of different ages, who are of the same overall ability level, are at the same developmental and intellectual level. However, further research is needed to determine just how similar ability-matched children remain over the course of development
A Summary on Progress in Materials Development for Advanced Lithium-Ion Cells for NASA's Exploration Missions
No abstract availabl
Conservation of connectivity of model-space effective interactions under a class of similarity transformation
Effective interaction operators usually act on a restricted model space and
give the same energies (for Hamiltonian) and matrix elements (for transition
operators etc.) as those of the original operators between the corresponding
true eigenstates. Various types of effective operators are possible. Those well
defined effective operators have been shown being related to each other by
similarity transformation. Some of the effective operators have been shown to
have connected-diagram expansions. It is shown in this paper that under a class
of very general similarity transformations, the connectivity is conserved. The
similarity transformation between hermitian and non-hermitian
Rayleigh-Schr\"{o}dinger perturbative effective operators is one of such
transformation and hence the connectivity can be deducted from each other.Comment: 12 preprint page
Extending Phenomenological Crystal-Field Methods to Point-Group Symmetry: Characterization of the Optically-Excited Hyperfine Structure of Er:YSiO
We show that crystal-field calculations for point-group symmetry are
possible, and that such calculations can be performed with sufficient accuracy
to have substantial utility for rare-earth based quantum information
applications. In particular, we perform crystal-field fitting for a
C-symmetry site in Er:YSiO. The calculation
simultaneously includes site-selective spectroscopic data up to 20,000
cm, rotational Zeeman data, and ground- and excited-state hyperfine
structure determined from high-resolution Raman-heterodyne spectroscopy on the
1.5 m telecom transition. We achieve an agreement of better than 50 MHz
for assigned hyperfine transitions. The success of this analysis opens the
possibility of systematically evaluating the coherence properties, as well as
transition energies and intensities, of any rare-earth ion doped into
YSiO .Comment: 6 pages, plus 5 pages in supplementary information, 4 figures tota
Calculation of single-beam two-photon absorption transition rate of rare-earth ions using effective operator and diagrammatic representation
Effective operators needed in single-beam two-photon transition calculations
have been represented with modified Goldstone diagrams similar to the type
suggested by Duan and co-workers [J. Chem. Phys. 121, 5071 (2004) ]. The rules
to evaluate these diagrams are different from those for effective Hamiltonian
and one-photon transition operators. It is verified that the perturbation terms
considered contain only connected diagrams and the evaluation rules are
simplified and given explicitly.Comment: 10 preprint pages, to appear in Journal of Alloys and Compound
Local Field effects on the radiative lifetime of emitters in surrounding media: virtual- or real-cavity model?
For emitters embedded in media of various refractive indices, different
macroscopic or microscopic theoretical models predict different dependencies of
the spontaneous emission lifetime on refractive index. Among those models are
the two most promising models: the virtual-cavity model and the real-cavity
model. It is a priori not clear which model is more relevant for a given
situation. By close analysis of the available experimental results and
examining the assumptions underlying the two models, we reach a consistent
interpretation of the experimental results and give the criteria which model
should apply for a given situation.Comment: 12 pages with 4 figure
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