Interaction of markedness and transfer of /r/ in L1 Thai learners acquiring L1 Thai and L2 English

PhD ThesisIn Thai, prevocalic /r/ shows a range of possible variants. The two standard variants are the prestigious trill [r] and the flap [ɾ], but some speakers may also use the lateral [l], or, in an initial cluster, /r/-cluster deletion [Ø]. In this dissertation, I argue that the phonological modification of rhotics in favour of lateral [l] and deletion [Ø] can be explained by considering the preference for the unmarkedness. Features or structures are distinguished as marked or unmarked features. The lateral [l] and deleted [Ø] variants are considered relatively unmarked features in comparison with rhotics. The primary aim of the dissertation is to investigate which variable strategies Thai speakers employ when speaking English, alongside their native language. The rhotics in these two languages differ and, in terms of markedness, the English approximant [ɹ] is comparatively more marked than the rhotics in Thai. This study is an overview of L2 phonology in Thai liquids, and this is supplemented by a variationist analysis. It examines the speech production of prevocalic English /r/ by L2 Thai leaners of English from the perspectives of markedness and transfer. It investigates if the Markedness Differential Hypothesis (MDH) proposed by Eckman (1977) is able to explain the errors subjects make in learning L2 English. In the variationist analysis, the quantitative paradigm was adopted to specify which linguistic and extralinguistic factors were of statistical significance in relation to the merger of /r/ and /l/ in L1 Thai and L2 English. Speech data were subjected to mixed logistic regression analysis with syllable stress, preceding segment, age, gender, speech style, and proficiency as based on IELTS speaking score as independent variables along with speakers and words as random effects. Data were collected from ten native speakers of Thai. The results show that the MDH could predict difficulties in L2 acquisition and which features were more likely to be transferred to L2 English, the results in terms of the relationship between the degrees of difficulty and degrees of markedness did not support the MDH. In the variationist analysis, the best-fit model shows that preceding segment, age group, and speech style influence the choice of variants in terms of the merger of /r/ and /l/ in both the L1 and L2. Gender is a significant factor in L1 Thai but is found to be insignificant in L2 English. With /r/-/l/ merger in Thai, the declining use of the standard Thai flap [ɾ] and trill [r] in formal speech in the present study seems to follow the trend indicated in previous studies, ii but the decline of /r/-/l/ merger in informal context is unexpected, given that the existing literature suggests that the frequency of /r/-/l/ merger in Thai is increasing.Suratthani Rajabhat Universit

Study of transmission properties for waveguide bends by use of a circular photonic crystal

We study the transmission properties for the waveguide bends composed by a circular photonic crystal. Two types (Y and U type) of the waveguide bends utilizing the circular photonic crystal are studied. It has been shown, compared with the conventional photonic crystal waveguide bends, transmission properties for these bends can be significantly improved. Over a 6.4% bandwidth, less than 1-dB loss/bend are observed. U bent waveguide, i.e., $180^o$ bend, can be easily realized with low loss using the circular photonic crystal.Comment: 9 pages, 6 figure

Woodpile and diamond structures by optical interference holography

We report the use of an optical interference holographic setup with a five-beam configuration, consisting of four side beams and one central beam from the same half space, to fabricate woodpile and diamond structures for the use as photonic bandgap materials in which electromagnetic waves are forbidden in the bandgap. By exploiting the advantage of the binarization of the interference pattern, using intensity cut-off, either linear or circular central beam can be used. More importantly, the beam configurations can be easily implemented experimentally as compared to other configurations in which the interfering beams are counter-propagating from both half spaces.Comment: 11 pages, 3 figures, and one tabl

Guiding and reflecting light by boundary material

We study effects of finite height and surrounding material on photonic crystal slabs of one- and two-dimensional photonic crystals with a pseudo-spectral method and finite difference time domain simulation methods. The band gap is shown to be strongly modified by the boundary material. As an application we suggest reflection and guiding of light by patterning the material on top/below the slab.Comment: 12 pages, 7 figure

Simulation-based reachability analysis for nonlinear systems using componentwise contraction properties

A shortcoming of existing reachability approaches for nonlinear systems is the poor scalability with the number of continuous state variables. To mitigate this problem we present a simulation-based approach where we first sample a number of trajectories of the system and next establish bounds on the convergence or divergence between the samples and neighboring trajectories. We compute these bounds using contraction theory and reduce the conservatism by partitioning the state vector into several components and analyzing contraction properties separately in each direction. Among other benefits this allows us to analyze the effect of constant but uncertain parameters by treating them as state variables and partitioning them into a separate direction. We next present a numerical procedure to search for weighted norms that yield a prescribed contraction rate, which can be incorporated in the reachability algorithm to adjust the weights to minimize the growth of the reachable set

Design of Optomechanical Cavities and Waveguides on a Simultaneous Bandgap Phononic-Photonic Crystal Slab

In this paper we study and design quasi-2D optomechanical crystals, waveguides, and resonant cavities formed from patterned slabs. Two-dimensional periodicity allows for in-plane pseudo-bandgaps in frequency where resonant optical and mechanical excitations localized to the slab are forbidden. By tailoring the unit cell geometry, we show that it is possible to have a slab crystal with simultaneous optical and mechanical pseudo-bandgaps, and for which optical waveguiding is not compromised. We then use these crystals to design optomechanical cavities in which strongly interacting, co-localized photonic-phononic resonances occur. A resonant cavity structure formed by perturbing a "linear defect" waveguide of optical and acoustic waves in a silicon optomechanical crystal slab is shown to support an optical resonance at wavelength 1.5 micron and a mechanical resonance of frequency 9.5 GHz. These resonances, due to the simultaneous pseudo-bandgap of the waveguide structure, are simulated to have optical and mechanical radiation-limited Q-factors greater than 10^7. The optomechanical coupling of the optical and acoustic resonances in this cavity due to radiation pressure is also studied, with a quantum conversion rate, corresponding to the scattering rate of a single cavity photon via a single cavity phonon, calculated to be 292 kHz.Comment: 18 pages, 10 figures. minor revisions; version accepted for publicatio

Immittance Matching for Multi-dimensional Open-system Photonic Crystals

An electromagnetic (EM) Bloch wave propagating in a photonic crystal (PC) is characterized by the immittance (impedance and admittance) of the wave. The immittance is used to investigate transmission and reflection at a surface or an interface of the PC. In particular, the general properties of immittance are useful for clarifying the wave propagation characteristics. We give a general proof that the immittance of EM Bloch waves on a plane in infinite one- and two-dimensional (2D) PCs is real when the plane is a reflection plane of the PC and the Bloch wavevector is perpendicular to the plane. We also show that the pure-real feature of immittance on a reflection plane for an infinite three-dimensional PC is good approximation based on the numerical calculations. The analytical proof indicates that the method used for immittance matching is extremely simplified since only the real part of the immittance function is needed for analysis without numerical verification. As an application of the proof, we describe a method based on immittance matching for qualitatively evaluating the reflection at the surface of a semi-infinite 2D PC, at the interface between a semi-infinite slab waveguide (WG) and a semi-infinite 2D PC line-defect WG, and at the interface between a semi-infinite channel WG and a semi-infinite 2D PC slab line-defect WG.Comment: 8 pages, 6 figure