Effects of using different plasmonic metals in metal/dielectric/metal subwavelength waveguides on guided dispersion characteristics

The fundamental guided dispersion characteristics of guided light in a subwavelength dielectric slit channel embedded by two different plasmonic metals are investigated when varying the gap width. As a result, an overall and salient picture of the guided dispersion characteristics is obtained over a wide spectrum range below and above the plasma frequencies of the two different plasmonic metals, which is important preliminary information for analyzing this type of subwavelength waveguide. In particular, the effects of using two different metals on the guided mode dispersions are emphasized in comparison with the effects of using the same plasmonic metal cladding.Comment: 13 pages, 3 figures, typos corrected, reference added, text modifie

Students and teacher’s attitudes and perceptions toward a wiki-based collaborative process writing pedagogy in a Primary Five Chinese classroom

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Using a wiki-based collaborative process writing pedagogy to facilitate collaborative writing among Chinese primary school students

This case study explored collaborative writing in Chinese among 59 primary four Chinese students using a Wiki-based Collaborative Process Writing Pedagogy (WCPWP) in Shenzhen, China. It aimed mainly to design and orchestrate a WCPWP in order to facilitate students' Chinese writing. It investigated students' collaborative writing process and their performance on a wiki, and explored the perceptions and attitudes of the teacher and her students towards WCPWP. A wiki-based writing environment named Joyous Writing Club (JWC) was designed and developed using MediaWiki software. Data was collected from questionnaires, online wiki documents, interviews, and observations. The results illustrated students' collaborative writing process and their products on the wiki. Besides, the results showed that students perceived WCPWP was beneficial in boosting writing motivation, increasing group interactions, and extending the audience for their writing. This study may help primary educators gain a deeper understanding of the relationships between technology, pedagogy and education. It may also provide practical recommendations for primary school Chinese language teachers in the integration of Web 2.0 tools (wikis, Google Docs) as well as the use of effective pedagogical strategies in the teaching of Chinese writing.published_or_final_versio

Students and teacher’s attitudes and perceptions toward collaborative writing with WIKI in a Primary Four Chinese classroom

This case study investigated the attitudes and perceptions of primary school students and their teacher toward collaborative writing using a wiki technology in a Chinese writing class in China. An online collaborative writing environment named “Joyous Writing Club”(JWC) was designed and developed using a wiki. Participants included 59 primary four students and their Chinese language teacher. The study adopted a mixed-methods design, using quantitative and qualitative data. A writing attitude test was administered to the students using a pretest-posttest design, and JWC was used by the participants for a period of two months. After that, a questionnaire using responses on a 5-point Likert scale was administered to examine the students’ perceptions on the use of the wiki-based collaborative writing environment. A questionnaire consisting of open-ended queries was also administered to the teacher to gain her insights on using JWC with her students. The results indicated that students showed improvement in writing attitudes after engaging in collaborative writing with wiki. Students’ responses to the questionnaire revealed that they perceived the collaborative writing using a wiki as beneficial in facilitating motivation to write, heightened group interactions, and widening the reading audience of their writings. Students’ positive perceptions on the use of JWC were also found to associate positively with students’ writing attitudes in the posttest. The strongest positive correlation was found between perceptions on motivation to write and writing attitudes. The teacher reported that students expressed higher interest in writing on JWC compared relative to writing on paper. She also indicated that factors such as the topic of the Chinese composition and students’ computer skills may affect the quality of collaborative writing with wiki. This study provides information that may help teachers and researchers to understand students’ responses towards collaborative writing with a wiki environment in a Chinese writing class, and the factors that may facilitate the effective use of such wiki environment.postprin

Scaling and non-Abelian signature in fractional quantum Hall quasiparticle tunneling amplitude

We study the scaling behavior in the tunneling amplitude when quasiparticles tunnel along a straight path between the two edges of a fractional quantum Hall annulus. Such scaling behavior originates from the propagation and tunneling of charged quasielectrons and quasiholes in an effective field analysis. In the limit when the annulus deforms continuously into a quasi-one-dimensional ring, we conjecture the exact functional form of the tunneling amplitude for several cases, which reproduces the numerical results in finite systems exactly. The results for Abelian quasiparticle tunneling is consistent with the scaling anaysis; this allows for the extraction of the conformal dimensions of the quasiparticles. We analyze the scaling behavior of both Abelian and non-Abelian quasiparticles in the Read-Rezayi Z_k-parafermion states. Interestingly, the non-Abelian quasiparticle tunneling amplitudes exhibit nontrivial k-dependent corrections to the scaling exponent.Comment: 16 pages, 4 figure

Kondo physics in the algebraic spin liquid

We study Kondo physics in the algebraic spin liquid, recently proposed to describe $ZnCu_{3}(OH)_{6}Cl_{2}$ [Phys. Rev. Lett. {\bf 98}, 117205 (2007)]. Although spin dynamics of the algebraic spin liquid is described by massless Dirac fermions, this problem differs from the Pseudogap Kondo model, because the bulk physics in the algebraic spin liquid is governed by an interacting fixed point where well-defined quasiparticle excitations are not allowed. Considering an effective bulk model characterized by an anomalous critical exponent, we derive an effective impurity action in the slave-boson context. Performing the large-$N_{\sigma}$ analysis with a spin index $N_{\sigma}$, we find an impurity quantum phase transition from a decoupled local-moment state to a Kondo-screened phase. We evaluate the impurity spin susceptibility and specific heat coefficient at zero temperature, and find that such responses follow power-law dependencies due to the anomalous exponent of the algebraic spin liquid. Our main finding is that the Wilson's ratio for the magnetic impurity depends strongly on the critical exponent in the zero temperature limit. We propose that the Wilson's ratio for the magnetic impurity may be one possible probe to reveal criticality of the bulk system

Deficits in lower limb muscle reflex contraction latency and peak force are associated with impairments in postural control and gross motor skills of children with developmental coordination disorder: A cross-sectional study

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Task-Specific Balance Training Improves the Sensory Organisation of Balance Control in Children with Developmental Coordination Disorder: A Randomised Controlled Trial

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STM Spectroscopy of ultra-flat graphene on hexagonal boron nitride

Graphene has demonstrated great promise for future electronics technology as well as fundamental physics applications because of its linear energy-momentum dispersion relations which cross at the Dirac point. However, accessing the physics of the low density region at the Dirac point has been difficult because of the presence of disorder which leaves the graphene with local microscopic electron and hole puddles, resulting in a finite density of carriers even at the charge neutrality point. Efforts have been made to reduce the disorder by suspending graphene, leading to fabrication challenges and delicate devices which make local spectroscopic measurements difficult. Recently, it has been shown that placing graphene on hexagonal boron nitride (hBN) yields improved device performance. In this letter, we use scanning tunneling microscopy to show that graphene conforms to hBN, as evidenced by the presence of Moire patterns in the topographic images. However, contrary to recent predictions, this conformation does not lead to a sizable band gap due to the misalignment of the lattices. Moreover, local spectroscopy measurements demonstrate that the electron-hole charge fluctuations are reduced by two orders of magnitude as compared to those on silicon oxide. This leads to charge fluctuations which are as small as in suspended graphene, opening up Dirac point physics to more diverse experiments than are possible on freestanding devices.Comment: Nature Materials advance online publication 13/02/201

High-dimensional fractionalization and spinon deconfinement in pyrochlore antiferromagnets

The ground states of Klein type spin models on the pyrochlore and checkerboard lattice are spanned by the set of singlet dimer coverings, and thus possess an extensive ground--state degeneracy. Among the many exotic consequences is the presence of deconfined fractional excitations (spinons) which propagate through the entire system. While a realistic electronic model on the pyrochlore lattice is close to the Klein point, this point is in fact inherently unstable because any perturbation $\epsilon$ restores spinon confinement at $T = 0$. We demonstrate that deconfinement is recovered in the finite--temperature region $\epsilon \ll T \ll J$, where the deconfined phase can be characterized as a dilute Coulomb gas of thermally excited spinons. We investigate the zero--temperature phase diagram away from the Klein point by means of a variational approach based on the singlet dimer coverings of the pyrochlore lattices and taking into account their non--orthogonality. We find that in these systems, nearest neighbor exchange interactions do not lead to Rokhsar-Kivelson type processes.Comment: 19 page