221 research outputs found
Study of left-handed materials
Left handed materials (LHMs) are artificial materials that have negative electrical permittivity, negative magnetic permeability, and negative index of refraction across a common frequency band. They possess electromagnetic (EM) properties not found in nature. LHMs have attracted tremendous attention because of their potential applications to build the perfect lens and cloaking devices. In the past few years there has been ample proof for the existence of LHMs in the microwave frequency range. Recently, researchers are trying hard to push the operating frequency of LHMs into terahertz and the optical regime.;In this thesis, we start with the theoretical prediction of left handed materials made by Veselago 40 years ago, introducing the unique electromagnetic properties of the left handed materials. After discussing the realization of LHMs by the split ring resonators (SRRs) and wire designs, we briefly review the development of LHMs from microwave frequency to the optical regime. We discuss the chiral metamaterial, which provides an alternative approach to realize negative refractive index.;In Chapter 2, we discuss the electromagnetic properties of the SRRs and the breakdown of linear scaling properties of SRRs at infrared and optical frequencies. By discussing the current modes, and the electric and magnetic moments, we study three resonance modes of SRR with respect to different polarizations of EM waves. Through numerical simulations, we find the breakdown of linear scaling, due to the free electron kinetic energy for frequencies above 100 THz. This result is important. It proves that researchers cannot push metamaterials into the optical regime by just scaling down the geometrical size of metamaterial designs used at low frequency.;Due to the breakdown of the linear scaling property, a much smaller structure size of LHMs design is required in the optical regime, so new designs with simpler topology are needed.;In Chapter 3, we discuss a short wire pair design, which has a distinct advantage over conventional SRRs. We systemically study the electromagnetic properties of the short wire pair design. We determine the criteria overlaps the electric and magnetic resonances of short wire pairs. Using an H-shaped short wire pairs design, we demonstrate negative refractive index experimentally.;In Chapter 4, we introduce a LHM design using short wire pairs with long wires, which avoid the difficulty of overlapping the electric and magnetic resonances. We also discussed the relationship between three important LHM designs suitable for the optical regime: double gap SRRs, the short wire pairs, and the fishnet structure.;Compared to LHMs at microwave frequencies, the current designs at optical frequencies suffer from high losses which limit their potential applications in the area requiring low losses, such as the perfect lens. In Chapter 5, we investigate the role of losses of the short wire pairs and the fishnet structures. We find the losses can be reduced substantially by increasing the effective inductance to capacitance ratio, L/C, especially at THz frequencies and in the optical regime
Magnetic and Electric Excitations in Split Ring Resonators
We studied the electric and magnetic resonance of U-shaped SRRs. We showed
that higher order excitation modes exist in both of the electric and magnetic
resonances. The nodes in the current distribution were found for all the
resonance modes. It turns out that the magnetic resonances are the modes with
odd-number of half-wavelength of the current wave, i.e. 1/2, 3/2 and 5/2
wavelengths modes, and the electric resonances are modes with integer number of
whole-wavelength of current wave, i.e. 1, 2 and 3 wavelengths modes. We
discussed the electric moment and magnetic moment of the electric and magnetic
resonances, and their dependence to the length of two parallel side arms. We
show that the magnetic moment of magnetic resonance vanishes as the length side
arms of the SRR reduces to zero, i.e. a rod does not give any magnetic moment
or magnetic resonance.Comment: Journal-ref and DOI link adde
Specific genetic modifications of domestic animals by gene targeting and animal cloning
The technology of gene targeting through homologous recombination has been extremely useful for elucidating gene functions in mice. The application of this technology was thought impossible in the large livestock species until the successful creation of the first mammalian clone "Dolly" the sheep. The combination of the technologies for gene targeting of somatic cells with those of animal cloning made it possible to introduce specific genetic mutations into domestic animals. In this review, the principles of gene targeting in somatic cells and the challenges of nuclear transfer using gene-targeted cells are discussed. The relevance of gene targeting in domestic animals for applications in bio-medicine and agriculture are also examined
Polaron dynamics with a multitude of Davydov D trial states
We propose an extension to the Davydov D Ansatz in the dynamics study of
the Holstein molecular crystal model with diagonal and off-diagonal
exciton-phonon coupling using the Dirac-Frenkel time-dependent variational
principle. The new trial state by the name of the "multi-D Ansatz" is a
linear combination of Davydov D trial states, and its validity is carefully
examined by quantifying how faithfully it follows the Schr\"odinger equation.
Considerable improvements in accuracy have been demonstrated in comparison with
the usual Davydov trial states, i.e., the single D and D Ans\"atze.
With an increase in the number of the Davydov D trial states in the
multi-D Ansatz, deviation from the exact Schr\"odinger dynamics is
gradually diminished, leading to a numerically exact solution to the
Schr\"odinger equation.Comment: 14 pages, 15 figure
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