Quantum confinement effects on the ordering of the lowest-lying excited states in conjugated chains

The symmetrized density matrix renormalization group approach is applied within the extended Hubbard-Peierls model (with parameters U/t, V/t, and bond alternation \delta) to study the ordering of the lowest one-photon (1^{1}B^{-}_u) and two-photon (2^{1}A^{+}_g) states in one- dimensional conjugated systems with chain lengths, N, up to N=80 sites. Three different types of crossovers are studied, as a function of U/t, \delta, and N. The U-crossover emphasizes the larger ionic character of the 2A_g state compared to the lowest triplet excitation. The \delta crossover shows strong dependence on both N and U/t. The N-crossover illustrates the more localized nature of the 2A_g excitation relative to the 1B_u excitation at intermediate correlation strengths.Comment: Latex file; figures available upon request. Submitted to PR

On methods to determine bounds on the Q-factor for a given directivity

This paper revisit and extend the interesting case of bounds on the Q-factor for a given directivity for a small antenna of arbitrary shape. A higher directivity in a small antenna is closely connected with a narrow impedance bandwidth. The relation between bandwidth and a desired directivity is still not fully understood, not even for small antennas. Initial investigations in this direction has related the radius of a circumscribing sphere to the directivity, and bounds on the Q-factor has also been derived for a partial directivity in a given direction. In this paper we derive lower bounds on the Q-factor for a total desired directivity for an arbitrarily shaped antenna in a given direction as a convex problem using semi-definite relaxation techniques (SDR). We also show that the relaxed solution is also a solution of the original problem of determining the lower Q-factor bound for a total desired directivity. SDR can also be used to relax a class of other interesting non-convex constraints in antenna optimization such as tuning, losses, front-to-back ratio. We compare two different new methods to determine the lowest Q-factor for arbitrary shaped antennas for a given total directivity. We also compare our results with full EM-simulations of a parasitic element antenna with high directivity.Comment: Correct some minor typos in the previous versio

Temporal relation between top-down and bottom-up processing in lexical tone perception

Speech perception entails both top-down processing that relies primarily on language experience and bottom-up processing that depends mainly on instant auditory input. Previous models of speech perception often claim that bottom-up processing occurs in an early time window, whereas top-down processing takes place in a late time window after stimulus onset. In this paper, we evaluated the temporal relation of both types of processing in lexical tone perception. We conducted a series of event-related potential (ERP) experiments that recruited Mandarin participants and adopted three experimental paradigms, namely dichotic listening, lexical decision with phonological priming, and semantic violation. By systematically analyzing the lateralization patterns of the early and late ERP components that are observed in these experiments, we discovered that: auditory processing of pitch variations in tones, as a bottom-up effect, elicited greater right hemisphere activation; in contrast, linguistic processing of lexical tones, as a top-down effect, elicited greater left hemisphere activation. We also found that both types of processing co-occurred in both the early (around 200 ms) and late (around 300–500 ms) time windows, which supported a parallel model of lexical tone perception. Unlike the previous view that language processing is special and performed by dedicated neural circuitry, our study have elucidated that language processing can be decomposed into general cognitive functions (e.g., sensory and memory) and share neural resources with these functions.published_or_final_versio

Construction of Cross-Cultural Identity by Language Choice and Linguistic Practice: A Case-Study of Mixed Hong Kong-Mainland Identity in University Contexts

Studying relations between language and speaker’s identity is an interdisciplinary field that involves intersections among language, culture, and society. By examining the language choice and linguistic practice, especially code-mixing and code-switching, of the Mainland China students who are studying in universities of Hong Kong, we reveal a mixed Hong Kong-Mainland identity in these students: those who hold a Mainland-oriented identity tend to have a Putonghua-dominated language choice and linguistic practice, whereas those who embrace a Hong Kong-oriented identity tend to prefer a Cantonese-dominated choice and practice. This mixed identity helps better conceive the social image of Mainland immigrants in Hong Kong and discuss the cross-cultural identity formed by linguistic practice.published_or_final_versio

Review of the 9th international conference on the evolution of language (Evolang9)

published_or_final_versio

Environmental Information Disclosure in China : in the Era of Informatization and Big Data

The past decade has seen remarkable progress made in the field of environmental information disclosure in China. While the overall institutional changes and the motivation/willingness of the government to open up information are important conditions, China’s encounter with revolutionary Information and Communication Technological (ICT) advancement and rapidly emerging big data quickly changed China from an “information poor environment” to an “information complex environment.” While most previous studies centered on those drives/constraints that were recognized in established informational governance framework, recent advancement in ICTs and emerging big data posed new challenges, opportunities and research questions. When increasing information disclosure became a new game changer in environmental governance, China has had to cope with risks and pitfalls in a new technology-empowered information environment as well. This article updated previous studies on legislation/regulations/policies regarding environmental information disclosure in China and their implementation effectiveness, and paid special attention to China’s recent informatization progress and emerging big data. Information disclosure was treated as a process that includes data/information generation/collection, disclosure, functional pathways of communication, and direct/indirect impacts. Changes in environmental information disclosure should be understood in a broader context of overall changing environmental governance and informatization in China. It is important to understand ICTs and information disclosure as a double-edged sword. Normative, substantive, and instrumental benefits of disclosure as well as collection and reporting costs, the issue of targeted transparency, and the risk of unintended use should be strategically considered. Principles and guidelines need to be developed to avoid pitfalls while maximizing benefits.<br/

Ultra-brief breath counting (mindfulness) training promotes recovery from stress-induced alcohol-seeking in student drinkers

This is the final version. Available on open access from Elsevier via the DOI in this recordThe therapeutic effect of mindfulness interventions on problematic drinking is thought to be driven by increased resilience to the impact of stress on negative mood and alcohol-seeking behaviour, but this claim needs empirical support. To address this hypothesis, the current study tested whether brief training of one component of mindfulness – breath counting – would reduce drinkers’ sensitivity to the effect of noise stress on subjective mood and alcohol-seeking behaviour. Baseline alcohol-seeking was measured by choice to view alcohol versus food thumbnail pictures in 192 student drinkers. Participants then received a 6-minute audio file which either trained breath counting or recited a popular science extract, in separate groups. All participants were then stressed by a loud industrial noise and alcohol-seeking was measured again, simultaneously (to quantify the change from baseline). Subjective mood was measured after all three stages (baseline, post intervention, post stress test). The breath counting group were instructed to deploy this technique during the stress test. Results showed that the breath counting versus control intervention improved subjective mood relative to baseline, attenuated the worsening of subjective mood produced by stress induction, and accelerated recovery from a stress induced increase in alcohol-seeking behaviour. Exploratory moderation analysis showed that this accelerated recovery from stress induced alcohol-seeking by breath counting was weaker in more alcohol dependent participants. Mindfulness therapies may improve problematic drinking by increasing resilience to stress induced negative mood and alcohol-seeking, observed in this study. The weaker therapeutic effect of breath counting in more dependent drinkers may reveal limitations to this intervention strategy.Medical Research Council (MRC)Alcohol Research U

Ferromagnetic tendency at the surface of CE charge-ordered manganites

Most previous investigations have shown that the surface of a ferromagnetic material may have antiferromagnetic tendencies. However, experimentally the opposite effect has been recently observed: ferromagnetism appears in some nano-sized manganites with a composition such that the antiferromagnetic charge-ordered CE state is observed in the bulk. A possible origin is the development of ferromagnetic correlations at the surface of these small systems. To clarify these puzzling experimental observations, we have studied the two-orbital double-exchange model near half-doping n=0.5, using open boundary conditions to simulate the surface of either bulk or nano-sized manganites. Considering the enhancement of surface charge density due to a possible AO termination (A = trivalent/divalent ion composite, O = oxygen), an unexpected surface phase-separated state emerges when the model is studied using Monte Carlo techniques on small clusters. This tendency suppresses the CE charge ordering and produces a weak ferromagnetic signal that could explain the experimental observations.Comment: 8 pages, 5 figure