435 research outputs found
Scattering mechanism in a step-modulated subwavelength metal slit: a multi-mode multi-reflection analysis
In this paper, the scattering/transmission inside a step-modulated
subwavelength metal slit is investigated in detail. We firstly investigate the
scattering in a junction structure by two types of structural changes. The
variation of transmission and reflection coefficients depending on structural
parameters are analyzed. Then a multi-mode multi-reflection model based on ray
theory is proposed to illustrate the transmission in the step-modulated slit
explicitly. The key parts of this model are the multi-mode excitation and the
superposition procedure of the scatterings from all possible modes, which
represent the interference and energy transfer happened at interfaces. The
method we use is an improved modal expansion method (MEM), which is a more
practical and efficient version compared with the previous one [Opt. Express
19, 10073 (2011)]. In addition, some commonly used methods, FDTD, scattering
matrix method, and improved characteristic impedance method, are compared with
MEM to highlight the preciseness of these methods.Comment: 25 pages, 9 figure
Graph Invariants of Vassiliev Type and Application to 4D Quantum Gravity
We consider a special class of Kauffman's graph invariants of rigid vertex
isotopy (graph invariants of Vassiliev type). They are given by a functor from
a category of colored and oriented graphs embedded into a 3-space to a category
of representations of the quasi-triangular ribbon Hopf algebra . Coefficients in expansions of them with respect to () are
known as the Vassiliev invariants of finite type. In the present paper, we
construct two types of tangle operators of vertices. One of them corresponds to
a Casimir operator insertion at a transverse double point of Wilson loops. This
paper proposes a non-perturbative generalization of Kauffman's recent result
based on a perturbative analysis of the Chern-Simons quantum field theory. As a
result, a quantum group analog of Penrose's spin network is established taking
into account of the orientation. We also deal with the 4-dimensional canonical
quantum gravity of Ashtekar. It is verified that the graph invariants of
Vassiliev type are compatible with constraints of the quantum gravity in the
loop space representation of Rovelli and Smolin.Comment: 34 pages, AMS-LaTeX, no figures,The proof of thm.5.1 has been
improve
Self-assembled Ni/NiO/RGO heterostructures for high-performance supercapacitors
A nano-sized nickel/nickel oxide/RGO (Ni/NiO/RGO) nano-hybrid was generated successfully by using a facile and green sol-gel approach, with the reduced graphene oxide as an effective component, for developing a high-efficiency electrode material with super-capacitance. In the novel hierarchical nano-composite, the combination of metallic nickel interfaced with the nickel oxide was created by the reduction of a nickel nitrate precursor with the carbon of the reduced graphene oxide surface, during the thermal treatment in nitrogen. The electrochemical performances of the Ni/NiO/RGO composite were measured through cyclic voltammetry tests and galvanostatic charge-discharges, as a supercapacitor material. Due to the higher conductivity and synergistic effect, the new hybrid delivered a high specific capacitance of 1027.27 F g-1 at the charge/discharge current density of 2 A g-1, and 720 F g-1 at 20 A g-1. After 1000 uninterrupted cycles at 5 A g-1, the high specific capacitance value can be still stabilized, and kept at 92.95% of the initial value of the specific capacitance for Ni/NiO/RGO. This new nano composite with RGO and Ni/NiO exhibits great promise as an electrode material for supercapacitors
Energy levels and far-infrared spectroscopy for two electrons in a semiconductor nanoring
The effects of electron-electron interaction of a two-electron nanoring on
the energy levels and far-infrared (FIR) spectroscopy have been investigated
based on a model calculation which is performed within the exactly numerical
diagonalization. It is found that the interaction changes the energy spectra
dramatically, and also shows significant influence on the FIR spectroscopy. The
crossings between the lowest spin-singlet and triplet states induced by the
coulomb interaction are clearly revealed. Our results are related to the
experiment recently carried out by A. Lorke et al. [Phys. Rev. Lett. 84, 2223
(2000)].Comment: 17 pages, 6 figures, revised and accepted by Phys. Rev. B (Dec. 15
A minimum single-band model for low-energy excitations in superconducting KFeSe
We propose a minimum single-band model for the newly discovered iron-based
superconducting KFeSe. Our model is found to be numerically
consistent with the five-orbital model at low energies. Based on our model and
the random phase approximation, we study the spin fluctuation and the pairing
symmetry of superconducting gap function. The spin excitation
and the pairing symmetry are revealed. All of the results can
well be understood in terms of the interplay between the Fermi surface topology
and the local spin interaction, providing a sound picture to explain why the
superconducting transition temperature is as high as to be comparable to those
in pnictides and some cuprates. A common origin of superconductivity is
elucidated for this compound and other high-T materials.Comment: 5 pages, 4 figure
Risk Theory with Affine Dividend Payment Strategies
We consider a classical compound Poisson risk model with affine dividend payments. We illustrate how both by analytical and probabilistic techniques closed-form expressions for the expected discounted dividends until ruin and the Laplace transform of the time to ruin can be derived for exponentially distributed claim amounts. Moreover, numerical examples are given which compare the performance of the proposed strategy to classical barrier strategies and illustrate that such affine strategies can be a noteworthy compromise between profitability and safety in collective risk theory
J/psi production in relativistic heavy ion collisions from a multi-phase transport model
Using A Multi-Phase Transport (AMPT) model, we study J/psi production from
interactions between charm and anti-charm quarks in initial parton phase and
between D and Dbar mesons in final hadron phase of relativistic heavy ion
collisions at the Relativistic Heavy Ion Collider (RHIC). Including also the
inverse reactions of J/psi absorption by gluons and light mesons, we find that
the net number of J/psi from the parton and hadron phases is smaller than that
expected from the superposition of initial nucleon-nucleon collisions, contrary
to the J/psi enhancement predicted by the kinetic formation model. The
production of J/psi is further suppressed if one includes the color screening
effect in the parton phase. We have also studied the dependence of J/psi
production on the charm quark mass and the effective charm meson mass.Comment: Figures redone with better statistic
Caste development and reproduction: a genome-wide analysis of hallmarks of insect eusociality
The honey bee queen and worker castes are a model system for developmental plasticity. We used established expressed sequence tag information for a Gene Ontology based annotation of genes that are differentially expressed during caste development. Metabolic regulation emerged as a major theme, with a caste-specific difference in the expression of oxidoreductases vs. hydrolases. Motif searches in upstream regions revealed group-specific motifs, providing an entry point to cis-regulatory network studies on caste genes. For genes putatively involved in reproduction, meiosis-associated factors came out as highly conserved, whereas some determinants of embryonic axes either do not have clear orthologs (bag of marbles, gurken, torso), or appear to be lacking (trunk) in the bee genome. Our results are the outcome of a first genome-based initiative to provide an annotated framework for trends in gene regulation during female caste differentiation (representing developmental plasticity) and reproduction
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