How definite are we about the English article system? Chinese learners, L1 interference and the teaching of articles in English for academic purposes programmes.

Omission and overspecification of the/a/an/Ø are among the most frequently occurring grammatical errors made in English academic writing by Chinese first language (L1) university students (Chuang & Nesi, 2006; Lee & Chen, 2009). However, in the context of competing demands in the English for academic purposes (EAP) syllabus and conflicting evidence about the effectiveness of error correction, EAP tutors are often unsure about whether article use should or could be a focus and whether such errors should be corrected or ignored. With the aim of informing pedagogy, this study investigates: whether explicit teaching or correction improves accuracy; which article uses present the most challenges for Chinese students; the causes of error and whether a focus on article form can be integrated within a modern genre based/student centred approach in EAP. First, a questionnaire survey investigates how EAP teachers in higher education explicitly teach or correct English article use. Second, the effect of explicit teaching and correction on English article accuracy is investigated in a longitudinal experiment with a control group. Analysis of this study’s post-study measures raise questions about the sustained benefits of written correction or decontextualised rule-based approaches. Third, findings are presented from a corpus-based study which includes an inductive and deductive analysis of the errors made by Chinese students. Finally, in a fourth study hypotheses are tested using a multiple-choice test (n=455) and the main findings are presented: 1) that general referential article accuracy is significantly affected by proficiency level, genre and students’ familiarity with the topic; 2) Chinese students are most challenged by generic and non-referential contexts of use which may be partly attributable to the lack of positive L1 transfer effects; 3) overspecification of definite articles is a frequent problem that sometimes gives Chinese B2 level students’ writing an ‘informal tone’; and 4) higher nominal density of pre-qualified noun phrases in academic writing is significantly associated with higher error rates. Several practical recommendations are presented which integrate an occasional focus on article form with whole text teaching, autonomous proofreading skills, register awareness, and genre-based approaches to EAP pedagogy

Analytical time-like geodesics

Time-like orbits in Schwarzschild space-time are presented and classified in a very transparent and straightforward way into four types. The analytical solutions to orbit, time, and proper time equations are given for all orbit types in the form r=r(\lambda), t=t(\chi), and \tau=\tau(\chi), where \lambda\ is the true anomaly and \chi\ is a parameter along the orbit. A very simple relation between \lambda\ and \chi\ is also shown. These solutions are very useful for modeling temporal evolution of transient phenomena near black holes since they are expressed with Jacobi elliptic functions and elliptic integrals, which can be calculated very efficiently and accurately.Comment: 15 pages, 10 figures, accepted by General Relativity and Gravitatio

Setting up tunneling conditions by means of Bohmian mechanics

Usually tunneling is established after imposing some matching conditions on the (time-independent) wave function and its first derivative at the boundaries of a barrier. Here an alternative scheme is proposed to determine tunneling and estimate transmission probabilities in time-dependent problems, which takes advantage of the trajectory picture provided by Bohmian mechanics. From this theory a general functional expression for the transmission probability in terms of the system initial state can be reached. This expression is used here to analyze tunneling properties and estimate transmissions in the case of initial Gaussian wave packets colliding with ramp-like barriers.Comment: 18 pages, 4 figure

Causality in AdS/CFT and Lovelock theory

We explore the constraints imposed on higher curvature corrections of the Lovelock type due to causality restrictions in the boundary of asymptotically AdS space-time. In the framework of AdS/CFT, this is related to positivity of the energy constraints that arise in conformal collider physics. We present explicit analytic results that fully address these issues for cubic Lovelock gravity in arbitrary dimensions and give the formal analytic results that comprehend general Lovelock theory. The computations can be performed in two ways, both by considering a thermal setup in a black hole background and by studying the scattering of gravitons with a shock wave in AdS. We show that both computations coincide in Lovelock theory. The different helicities, as expected, provide the boundaries defining the region of allowed couplings. We generalize these results to arbitrary higher dimensions and discuss their consequences on the shear viscosity to energy density ratio of CFT plasmas, the possible existence of Boulware-Deser instabilities in Lovelock theory and the extent to which the AdS/CFT correspondence might be valid for arbitrary dimensions.Comment: 35 pages, 20 figures; v2: minor amendments and clarifications include

Microlensing Evidence for Super-Eddington Disc Accretion in Quasars

Microlensing by the stellar population of lensing galaxies provides an important opportunity to spatially resolve the accretion disc structure in strongly lensed quasars. Disc sizes estimated this way are on average larger than the predictions of the standard Shakura-Sunyaev accretion disk model. Analysing the observational data on microlensing variability allows to suggest that some fraction of lensed quasars (primarily, smaller-mass objects) are accreting in super-Eddington regime. Super-Eddington accretion leads to formation of an optically-thick envelope scattering the radiation formed in the disc. This makes the apparent disc size larger and practically independent of wavelength. In the framework of our model, it is possible to make self-consistent estimates of mass accretion rates and black hole masses for the cases when both amplification-corrected fluxes and radii are available.Comment: 11 pages, 5 figures; typo corrected in formula 1