The effects of cognitive styles on naive impetus theory application degrees of pre-service science teachers

Cataloged from PDF version of article.The purpose of this study was to determine whether there is a relationship between pre-service science teachers’ Field Dependent or Field Independent (FD/FI) cognitive styles and the application of degrees of naive impetus theory. The sample consisted of 122 preservice science teachers (97 females and 25 males) who were enrolled in the Introductory Physics course required by the Science Education program. Data were collected in two successive years, after the completion of the required Introductory Physics undergraduate courses, in 2008 and 2009. The Group Embedded Figure Test and Impetus Theory Application Test (a two-tier-type test) were administered to assess the FD/FI tendency of students and to determine the degree students applied the naïve impetus theory, respectively. Initial results showed that a majority of students had made use of the native impetus theory repeatedly. The results also indicated that the degree to which students applied the naïve impetus theory was statistically related to their FD/FI cognitive styles. The findings of this research showed that there existed a statistically significant difference between the FI and FD students’ degree of applying the naïve impetus theory in favor of FI students. However, the test score gap between FI and FD students remained almost constant regardless of the testing instruments utilized in this study

Quantum phases in mixtures of fermionic atoms

A mixture of spin-polarized light and heavy fermionic atoms on a finite size 2D optical lattice is considered at various temperatures and values of the coupling between the two atomic species. In the case, where the heavy atoms are immobile in comparison to the light atoms, this system can be seen as a correlated binary alloy related to the Falicov-Kimball model. The heavy atoms represent a scattering environment for the light atoms. The distributions of the binary alloy are discussed in terms of strong- and weak-coupling expansions. We further present numerical results for the intermediate interaction regime and for the density of states of the light particles. The numerical approach is based on a combination of a Monte-Carlo simulation and an exact diagonalization method. We find that the scattering by the correlated heavy atoms can open a gap in the spectrum of the light atoms, either for strong interaction or small temperatures.Comment: 15 pages, 8 figure

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

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

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

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

Boosting up quantum key distribution by learning statistics of practical single photon sources

We propose a simple quantum-key-distribution (QKD) scheme for practical single photon sources (SPSs), which works even with a moderate suppression of the second-order correlation $g^{(2)}$ of the source. The scheme utilizes a passive preparation of a decoy state by monitoring a fraction of the signal via an additional beam splitter and a detector at the sender's side to monitor photon number splitting attacks. We show that the achievable distance increases with the precision with which the sub-Poissonian tendency is confirmed in higher photon number distribution of the source, rather than with actual suppression of the multi-photon emission events. We present an example of the secure key generation rate in the case of a poor SPS with $g^{(2)} = 0.19$, in which no secure key is produced with the conventional QKD scheme, and show that learning the photon-number distribution up to several numbers is sufficient for achieving almost the same achievable distance as that of an ideal SPS.Comment: 11 pages, 3 figures; published version in New J. Phy

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

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