The effects of synchronous text-based computer-mediated communication tasks on the development of L2 and academic literacy: A mixed methods study

ABSTRACT The dissertation examines how synchronous text-based computer-mediated communication (SCMC) tasks may affect English as a Second Language (ESL) learners\u27 development of second language (L2) and academic literacy. The study is motivated by two issues concerning the use of SCMC tasks in L2 writing classes. First, although some of the alleged benefits of SCMC, including its visual saliency and the possibility of slower processing speed, have been supported by theories of Second Language Acquisition (SLA), more evidence is still needed since empirical studies have not yet produced enough consistent findings. Second, most studies on SCMC have focused on its influence on learners\u27 development of basic communicative competence while it has been suggested that SCMC may hold great potential for the development of advanced academic literacy (Luo, 2005; Mohan & Luo, 2005) that is considered as an essential goal for L2 writing classes. Therefore, the dissertation addresses these issues using mixed methods research completed in two phases. A quasi-experiment was conducted in the first phase among forty-four international students enrolled in two sections of an ESL academic writing course to examine the differential effects of SCMC and face-to-face tasks. The differential effects were assessed by comparing the students\u27 improvement on measures of L2 grammatical and lexical complexity, accuracy, and fluency (Wolfe-Quintero, Inagaki, & Kim, 1998) from a pre-test to a post-test. The results of the quasi-experiment were also used to help select representative focal students for the multiple case studies in the second phase where the SCMC discourse of the focal students was examined for the details of L2 learning and the development of academic literacy. In analyzing the SCMC discourse of different triads, instances of L2 learning opportunities based on the Interaction approach and sociocultural theory of L2 learning were identified and classified, and the patterns of learning for each triad and between triads were discussed. The SCMC discourse was then re-analyzed to examine how the focal students developed their ability to construct effective arguments by participating in the back-and-forth rhetoric and by learning to use meta-discourse devices appropriately. The patterns of learning observed in the SCMC discourse of the focal students were also compared with the patterns observed from their writing samples. The quasi-experiment and the multiple case studies were connected by a mixed methods research design (Creswell & Plano Clark, 2007, p. 73) whose aim was to understand how SCMC tasks might affect both the outcome and the processes of the development of L2 and academic literacy. The results largely confirmed the benefits of SCMC tasks on L2 written accuracy and fluency, and suggested that SCMC tasks had great positive potential in engaging students in the processes of arguments to help them learn to incorporate discussions of opposing views in building effective arguments. Future research may further examine the differences of learning between pairs, triads, or small groups working on the same SCMC task. Research on the use of SCMC tasks and the learning of meta-discourse devices can also inform pedagogical decisions

Turnitin and peer review in ESL academic writing classrooms

Despite the benefits of peer review, there are still challenges that need to be addressed to make it more effective for L2 students. With the development of technology, computer-mediated peer review has captured increasing attention from L2 writing researchers and instructors. While Turnitin is known for its use in detecting plagiarism, its newly developed module, PeerMark, aims to facilitate peer review. In this article, we share our experience of using Turnitin for peer review in an ESL academic writing course and discuss its advantages, its limitations, and how different features of PeerMark may be used to address some of the challenges identified in previous research on peer review in the L2 writing classroom. Throughout a semester, the students were required to complete three peer review tasks through Turnitin. Based on the instructor’s experience and the students’ reports, we found that Turnitin could help shift students’ attention from local to global issues in writing, scaffold students in their effort to provide more helpful comments and to make connections between specific suggestions and holistic advice for writing, and facilitate classroom management during peer review

Quenching depends on morphologies: implications from the ultraviolet-optical radial color distributions in Green Valley Galaxies

In this Letter, we analyse the radial UV-optical color distributions in a sample of low redshift green valley (GV) galaxies, with the Galaxy Evolution Explorer (GALEX)+Sloan Digital Sky Survey (SDSS) images, to investigate how the residual recent star formation distribute in these galaxies. We find that the dust-corrected $u-r$ colors of early-type galaxies (ETGs) are flat out to $R_{90}$, while the colors turn blue monotonously when $r>0.5R_{50}$ for late-type galaxies (LTGs). More than a half of the ETGs are blue-cored and have remarkable positive NUV$-r$ color gradients, suggesting that their star formation are centrally concentrated; the rest have flat color distributions out to $R_{90}$. The centrally concentrated star formation activity in a large portion of ETGs is confirmed by the SDSS spectroscopy, showing that $\sim$50 % ETGs have EW(H$\rm \alpha$)$>6.0$ \AA. For the LTGs, 95% of them show uniform radial color profiles, which can be interpreted as a red bulge plus an extended blue disk. The links between the two kinds of ETGs, e.g., those objects having remarkable "blue-cored" and those having flat color gradients, are less known and require future investigations. It is suggested that the LTGs follow a general picture that quenching first occur in the core regions, and then finally extend to the rest of the galaxy. Our results can be re-examined and have important implications for the IFU surveys, such as MaNGA and SAMI.Comment: ApJ Letter, accepted. Five figure

From outside-in to inside-out: galaxy assembly mode depends on stellar mass

In this Letter, we investigate how galaxy mass assembly mode depends on stellar mass $M_{\ast}$, using a large sample of $\sim$10, 000 low redshift galaxies. Our galaxy sample is selected to have SDSS R_{90}>5\arcsec.0, which allows the measures of both the integrated and the central NUV$-r$ color indices. We find that: in the $M_{\ast}-($ NUV$-r$) green valley, the M_{\ast}<10^{10}~M_{\sun} galaxies mostly have positive or flat color gradients, while most of the M_{\ast}>10^{10.5}~M_{\sun} galaxies have negative color gradients. When their central $D_{n}4000$ index values exceed 1.6, the M_{\ast}<10^{10.0}~M_{\sun} galaxies have moved to the UV red sequence, whereas a large fraction of the M_{\ast}>10^{10.5}~M_{\sun} galaxies still lie on the UV blue cloud or the green valley region. We conclude that the main galaxy assembly mode is transiting from "the outside-in" mode to "the inside-out" mode at M_{\ast} 10^{10.5}~M_{\sun}. We argue that the physical origin of this is the compromise between the internal and the external process that driving the star formation quenching in galaxies. These results can be checked with the upcoming large data produced by the on-going IFS survey projects, such as CALIFA, MaNGA and SAMI in the near future.Comment: Accepted for publication in ApJL,6 pages, 5 figure

Structure and morphology of X-ray selected AGN hosts at 1<z<3 in CANDELS-COSMOS field

We analyze morphologies of the host galaxies of 35 X-ray selected active galactic nucleus (AGNs) at $z\sim2$ in the Cosmic Evolution Survey (COSMOS) field using Hubble Space Telescope/WFC3 imaging taken from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). We build a control sample of 350 galaxies in total, by selecting ten non-active galaxies drawn from the same field with the similar stellar mass and redshift for each AGN host. By performing two dimensional fitting with GALFIT on the surface brightness profile, we find that the distribution of S$\`e$rsic index (n) of AGN hosts does not show a statistical difference from that of the control sample. We measure the nonparametric morphological parameters (the asymmetry index A, the Gini coefficient G, the concentration index C and the M20 index) based on point source subtracted images. All the distributions of these morphological parameters of AGN hosts are consistent with those of the control sample. We finally investigate the fraction of distorted morphologies in both samples by visual classification. Only $\sim$15% of the AGN hosts have highly distorted morphologies, possibly due to a major merger or interaction. We find there is no significant difference in the distortion fractions between the AGN host sample and control sample. We conclude that the morphologies of X-ray selected AGN hosts are similar to those of nonactive galaxies and most AGN activity is not triggered by major merger.Comment: 5 pages, 3 figures, accepted for publication in The Astrophysical Journal Letter