Shielding of a moving test charge in a quantum plasma

The linearized potential of a moving test charge in a one-component fully degenerate fermion plasma is studied using the Lindhard dielectric function. The motion is found to greatly enhance the Friedel oscillations behind the charge, especially for velocities larger than a half of the Fermi velocity, in which case the asymptotic behavior of their amplitude changes from 1/r^3 to 1/r^2.5. In the absence of the quantum recoil (tunneling) the potential reduces to a form similar to that in a classical Maxwellian plasma, with a difference being that the plasma oscillations behind the charge at velocities larger than the Fermi velocity are not Landau-damped.Comment: 9 pages, 11 figures. v3: Fixed typo, updated abstrac

Vowel reduction in word-final position by early and late Spanish-English bilinguals

Vowel reduction is a prominent feature of American English, as well as other stress-timed languages. As a phonological process, vowel reduction neutralizes multiple vowel quality contrasts in unstressed syllables. For bilinguals whose native language is not characterized by large spectral and durational differences between tonic and atonic vowels, systematically reducing unstressed vowels to the central vowel space can be problematic. Failure to maintain this pattern of stressed-unstressed syllables in American English is one key element that contributes to a ?foreign accent? in second language speakers. Reduced vowels, or ?schwas,? have also been identified as particularly vulnerable to the co-articulatory effects of adjacent consonants. The current study examined the effects of adjacent sounds on the spectral and temporal qualities of schwa in word-final position. Three groups of English-speaking adults were tested: Miami-based monolingual English speakers, early Spanish-English bilinguals, and late Spanish-English bilinguals. Subjects performed a reading task to examine their schwa productions in fluent speech when schwas were preceded by consonants from various points of articulation. Results indicated that monolingual English and late Spanish-English bilingual groups produced targeted vowel qualities for schwa, whereas early Spanish-English bilinguals lacked homogeneity in their vowel productions. This extends prior claims that schwa is targetless for F2 position for native speakers to highly-proficient bilingual speakers. Though spectral qualities lacked homogeneity for early Spanish-English bilinguals, early bilinguals produced schwas with near native-like vowel duration. In contrast, late bilinguals produced schwas with significantly longer durations than English monolinguals or early Spanish-English bilinguals. Our results suggest that the temporal properties of a language are better integrated into second language phonologies than spectral qualities. Finally, we examined the role of nonstructural variables (e.g. linguistic history measures) in predicting native-like vowel duration. These factors included: Age of L2 learning, amount of L1 use, and self-reported bilingual dominance. Our results suggested that different sociolinguistic factors predicted native-like reduced vowel duration than predicted native-like vowel qualities across multiple phonetic environments

Oral corrective feedback: Pre-service English as a second language teachers’ beliefs and practices

This study investigated the relationship between pre-service English-as-a-second-language (ESL) teachers’ pedagogical beliefs and their actual teaching practices. To determine the nature of this relationship, 99 teachers-in-training with little or no teaching experience were asked to complete a questionnaire seeking information about their teaching beliefs, particularly about oral corrective feedback (i.e. teachers’ responses to students’ language errors). The teachers’ responses were subjected to an exploratory factor analysis which revealed several dimensions underlying their beliefs. To examine how these beliefs affect classroom performance, 10 of the teachers were first asked to indicate how they would correct language errors illustrated in hypothetical (videotaped) classroom scenarios and were then observed teaching an authentic ESL class. The classes were video-recorded and 30-minute teacher-fronted communicative segments from the lessons were analysed for the number and type of errors learners made and the teachers addressed. Results indicate a multifarious relationship between stated beliefs and actual teaching practices in that while the teachers corrected fewer errors than they believed they would, they preferred the same corrective techniques in both hypothetical and actual teaching situations. Most notably, the study suggests that the complexities of the language classroom and the pre-service teachers’ lack of experience at integrating theoretical knowledge and practical skills, lead them to behave overall as native-speaking interlocutors, not as language teachers. Implications for teacher training are discussed