886 research outputs found
Near-field light localization using subwavelength apertures incorporated with metamaterials
Cataloged from PDF version of article.We report strong near-field electromagnetic localization by using subwavelength apertures and metamaterials that operate at microwave frequencies. We designed split ring resonators with distinct configurations in order to obtain extraordinary transmission results. Furthermore, we analyzed the field localization and focusing characteristics of the transmitted evanescent waves. The employed metamaterial configurations yielded an improvement on the transmission efficiency on the order of 27 dB and 50 dB for the deep subwavelength apertures. The metamaterial loaded apertures are considered as a total system that offered spot size conversion ratios as high as 7.12 and 9.11 for the corresponding metamaterial configurations. The proposed system is shown to intensify the electric fields of the source located in the near-field. It also narrows down the electromagnetic waves such that a full width at half maximum value of λ/29 is obtained. © 2012 Elsevier B.V. All rights reserved
Sustainable development of smallholder crop-livestock farming in developing countries
Meeting the growing demand for animal-sourced food, prompted by population growth and increases in average per-capita income in low-income countries, is a major challenge. Yet, it also presents significant potential for agricultural growth, economic development, and reduction of poverty in rural areas. The main constraints to livestock producers taking advantage of growing markets include; lack of forage and feed gaps, communal land tenure, limited access to land and water resources, weak institutions, poor infrastructure and environmental degradation. To improve rural livelihood and food security in smallholder crop-livestock farming systems, concurrent work is required to address issues regarding efficiency of production, risk within systems and development of whole value chain systems. This paper provides a review of several forage basedstudies in tropical and non-tropical dry areas of the developing countries. A central tenet of this paper is that forages have an essential role in agricultural productivity, environmental sustainability and livestock nutrition in smallholder mixed farming systems
Dephasing of Mollow Triplet Sideband Emission of a Resonantly Driven Quantum Dot in a Microcavity
Detailed properties of resonance fluorescence from a single quantum dot in a
micropillar cavity are investigated, with particular focus on emission
coherence in dependence on optical driving field power and detuning.
Power-dependent series over a wide range could trace characteristic Mollow
triplet spectra with large Rabi splittings of GHz. In
particular, the effect of dephasing in terms of systematic spectral broadening
of the Mollow sidebands is observed as a strong fingerprint
of excitation-induced dephasing. Our results are in excellent agreement with
predictions of a recently presented model on phonon-dressed QD Mollow triplet
emission in the cavity-QED regime
Experimental demonstration of the enhanced transmission through circular and rectangular sub-wavelength apertures using omega-like split-ring resonators
Cataloged from PDF version of article.Enhanced transmission through circular and rectangular sub-wavelength apertures using omega-shaped split-ring resonator is
numerically and experimentally demonstrated at microwave frequencies. We report a more than 150,000-fold enhancement through
a deep sub-wavelength aperture drilled in a metallic screen. To the authors’ best knowledge, this is the highest experimentally
obtained enhancement factor reported in the literature. In the paper, we address also the origins and the physical reasons behind the
enhancement results. Moreover, we report on the differences occurring when using circular, rectangular apertures as well as doublesided
and single-sided omega-like split ring resonator structures.
(C) 2012 Elsevier B.V. All rights reserve
Climate change impact, adaptation, and mitigation in temperate grazing systems: a review
Managed temperate grasslands occupy 25% of the world, which is 70% of global agricultural land. These lands are an important source of food for the global population. This review paper examines the impacts of climate change on managed temperate grasslands and grassland-based livestock and effectiveness of adaptation and mitigation options and their interactions. The paper clarifies that moderately elevated atmospheric CO2 (eCO2) enhances photosynthesis, however it may be restiricted by variations in rainfall and temperature, shifts in plant’s growing seasons, and nutrient availability. Different responses of plant functional types and their photosynthetic pathways to the combined effects of climatic change may result in compositional changes in plant communities, while more research is required to clarify the specific responses. We have also considered how other interacting factors, such as a progressive nitrogen limitation (PNL) of soils under eCO2, may affect interactions of the animal and the environment and the associated production. In addition to observed and modelled declines in grasslands productivity, changes in forage quality are expected. The health and productivity of grassland-based livestock are expected to decline through direct and indirect effects from climate change. Livestock enterprises are also significant cause of increased global greenhouse gas (GHG) emissions (about 14.5%), so climate risk-management is partly to develop and apply effective mitigation measures. Overall, our finding indicates complex impact that will vary by region, with more negative than positive impacts. This means that both wins and losses for grassland managers can be expected in different circumstances, thus the analysis of climate change impact required with potential adaptations and mitigation strategies to be developed at local and regional levels
Analytical Model of Connected Bi-Omega: Robust Particle for the Selective Power Transmission Through Sub-Wavelength Apertures
Cataloged from PDF version of article.In this paper, we present a new analytical model of
the connected bi-omega structure consisting of two bi-omega particles
connected together through their arms. A single bi-omega
particle consists of a pair of regular equal omegas with mirror
symmetry. Assuming the individual bi-omega particle electrically
small, the equivalent circuit is derived, in order to predict its
resonant frequency. Then, two bi-omega particles are connected
together, obtaining a symmetric structure that supports two
fundamental modes, with even and odd symmetries, respectively.
The proposed analytical model, then, is used to develop a procedure
allowing the design of the particle for a desired resonant
frequency. The effectiveness of the proposed analytical model and
design guidelines is confirmed by proper comparisons to full-wave
numerical and experimental results. We also demonstrate through
a proper set of experiments that the resonant frequencies of the
connected bi-omega particle depend only on the geometrical and
electrical parameters of the omegas and are rather insensitive to
the practical scenario where the particle itself is actually used, e.g.
in free-space, rectangular waveguide or across an aperture in a
metallic screen
Catalyst for Decomposition of Nitrogen Oxides
This invention relates generally to a platinized tin oxide-based catalyst. It relates particularly to an improved platinized tin oxide-based catalyst able to decompose nitric oxide to nitrogen and oxygen without the necessity of a reducing gas
Transmission enhancement through deep subwavelength apertures using connected split ring resonators
Cataloged from PDF version of article.We report astonishingly high transmission enhancement factors through a subwavelength aperture at microwave frequencies by placing connected split ring resonators in the vicinity of the aperture. We carried out numerical simulations that are consistent with our experimental conclusions. We experimentally show higher than 70,000-fold extraordinary transmission through a deep subwavelength aperture with an electrical size of lambda/31x lambda/12 (width x length), in terms of the operational wavelength. We discuss the physical origins of the phenomenon. Our numerical results predict that even more improvements of the enhancement factors are attainable. Theoretically, the approach opens up the possibility for achieving very large enhancement factors by overcoming the physical limitations and thereby minimizes the dependence on the aperture geometries. (C) 2010 Optical Society of Americ
Numerical study of two-body correlation in a 1D lattice with perfect blockade
We compute the dynamics of excitation and two-body correlation for two-level
"pseudoatoms" in a 1D lattice. We adopt a simplified model where pair
excitation within a finite range is perfectly blocked. Each superatom is
initially in the ground state, and then subjected to an external driving laser
with Rabi frequency satisfying a Poissonian distribution, mimicking the
scenario as in Rydberg gases. We find that two-body quantum correlation drops
very fast with the distance between pseudoatoms. However, the total correlation
decays slowly even at large distance. Our results may be useful to the
understanding of Rydberg gases in the strong blockade regime
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