The long- and finite-wavelength instabilities of weakly viscoelastic film on an oscillating inclined plane are investigated. By using the Chebyshev series solution with the Floquet theory, the combined effects of viscoelasticity and forcing amplitude on instability are described when the inclined plane oscillates in streamwise and wall-normal directions. For long-wavelength instability, the solution to the eigenvalue problem is obtained analytically by the asymptotic expansion method. Results show that the Floquet exponent is independent of the wall-normal oscillation amplitude. The effects of inclined angle, gravity and surface tension on the stability of viscoelastic liquid film are also discussed. For finite-wavelength instability, numerical results corresponding to the wall-normal oscillation disclose that with the increase of viscoelasticity, the unstable gravitational boundary moves to a higher wavenumber, and the critical amplitudes of subharmonic and harmonic instabilities are reduced. The neutral curve of gravity instability for streamwise oscillatory flow is divided into two parts, and a stable bandwidth is formed for a large value of the viscoelastic parameter. Besides, a new oscillatory mode is identified at small angles of inclination, which will be enhanced if the effect of viscoelasticity is incorporated.

Visual simultaneous localisation and mapping (vSLAM) has shown considerable promise in positioning and navigating across a variety of indoor and outdoor settings, significantly enhancing the mobility of robots employed in industrial and everyday services. Nonetheless, the prevalent reliance of vSLAM technology on the assumption of static environments has led to suboptimal performance in practical implementations, particularly in unstructured and dynamically noisy environments such as substations. Despite advancements in mitigating the influence of dynamic objects through the integration of geometric and semantic information, existing approaches have struggled to strike an equilibrium between performance and real-time responsiveness. This study introduces a lightweight, multi-modal semantic framework predicated on vSLAM, designed to enable intelligent robots to adeptly navigate the dynamic environments characteristic of substations. The framework notably enhances vSLAM performance by mitigating the impact of dynamic objects through a synergistic combination of object detection and instance segmentation techniques. Initially, an enhanced lightweight instance segmentation network is deployed to ensure both the real-time responsiveness and accuracy of the algorithm. Subsequently, the algorithm’s performance is further refined by amalgamating the outcomes of detection and segmentation processes. With a commitment to maximising performance, the framework also ensures the algorithm’s real-time capability. Assessments conducted on public datasets and through empirical experiments have demonstrated that the proposed method markedly improves both the accuracy and real-time performance of vSLAM in dynamic environments.

Written corrective feedback (WCF) is a ubiquitous pedagogical activity in second language (L2) classrooms and has become a key area of inquiry in L2 writing research. While there have been several reviews on experimental WCF research, there is not yet a synthesis of naturalistic classroom studies where the type and amount of feedback provided on students' writing performance is not manipulated or controlled. This state-of-the-art article intends to fill the gap by providing a comprehensive and critical review of naturalistic WCF studies in L2 writing, with significant implications for practice and research. A systematic search generated 50 empirical studies that met our inclusion criteria for the current review, which revealed four major themes: (1) teacher WCF practices in L2 writing classrooms, (2) L2 learner responses to WCF, (3) stakeholders’ beliefs and perspectives on WCF, and (4) WCF-related motivation and emotions. Based on the reviewed evidence, we propose pedagogical implications for enhancing teacher WCF practices and student learning, as well as potential avenues for further exploration. This article contributes to a nuanced understanding of current empirical advances in naturalistic research on WCF in L2 writing, providing insights to inform WCF pedagogy and new lines of inquiry.

This article reports on a comprehensive synthesis of the literature on the role of working memory in second language (L2) writing. It starts with an overview and clarification of the construct and measurement of working memory, followed by an elaboration of major theoretical models informing the synthesized research. The article then presents a synthesis of the methods and results of the 16 studies that have been conducted on the associations between working memory and L2 writing. The methodological synthesis encompasses research design, methods of working memory, measurement of writing performance, methods of data elicitation for writing processes, and data analysis and reporting. The results of the synthesized studies demonstrate that (1) working memory is largely unrelated to overall writing proficiency; (2) it is predictive of specific aspects of L2 composition such as complexity, accuracy, and fluency; (3) the role of working memory varies as a function of genre, proficiency, target structure, instruction type, and task demands; and (4) verbal working memory, phonological short-term memory, visual-spatial working memory, and executive functions (inhibiting, shifting, and updating) have differential associations with the process and product aspects of L2 writing. The methods and results are discussed by identifying trends, accounting for disparities, clarifying confusion, recommending solutions, and proposing new directions.

In this commentary, we summarize the findings of the seven included studies that examined implicit language aptitude from various perspectives and highlight issues to be resolved in the validation of this new construct in second language research. We start by providing an overview of the contributions of the studies. We then identify the lack of convergent validity of the measures of implicit aptitude reported in the included studies and problematize the equally varied nature of the measurement of implicit knowledge—the outcome variable of aptitude research—and related concepts. In particular, by drawing on empirical evidence and theoretical claims, we attempt to clarify the relationships between implicit and explicit knowledge, implicit and explicit learning, and implicit and explicit instruction. Next, we draw attention to the interactions reported by the included studies between aptitude and outcome measures and between aptitude and instruction type, emphasizing the value and importance of interactional research. We conclude by making recommendations for future research.

This article discusses the conceptualization, measurement, and validity of a recently emerged construct in the field of second language acquisition (SLA)—implicit language aptitude (alternatively “implicit aptitude”). Implicit aptitude is a set of cognitive abilities that enable learners to make unconscious computations of the distributional and transitional probabilities of linguistic input. Implicit aptitude is key to an accurate understanding of the cognitive foundation of language learning and contributes significantly to the advancement of SLA theory and pedagogy. The article starts by clarifying the concept and components of implicit aptitude, elaborating its role in SLA theories, identifying its attributes, and discussing its measurement. It then synthesizes the empirical evidence on its divergent, convergent, and predictive validity, which refers to whether it is distinct or separable from explicit aptitude, whether measures of implicit aptitude are correlated, and whether it is predictive of learning outcomes, respectively. Next, the article provides an overview of the seven empirical studies included in this special issue that examined implicit aptitude from various perspectives. The article concludes by identifying future directions.

This study examines the associations between implicit and explicit language aptitude and the effects of the timing of corrective feedback (CF). A total of 112 seventh-grade EFL learners were assigned to three groups: Immediate CF, Delayed CF, and Task Only. The three groups underwent three treatment sessions during which they performed six focused communicative tasks eliciting the use of the English past tense. The Immediate and Delayed CF groups received CF treatments in the first and final sessions, respectively, and the Task Only group performed the communicative tasks without receiving any feedback. Treatment effects were measured through an untimed grammaticality judgment test and an elicited imitation test. Implicit language aptitude was operationalized as procedural memory and explicit language aptitude as working memory and declarative memory. Multiple regression analysis showed that procedural memory was significantly predictive of the effectiveness of Immediate CF, declarative memory was significantly associated with Delayed CF and Task Only, and working memory was a significant predictor of Immediate CF and Delayed CF. The results were interpreted by consulting the methodological features of the treatments and the mechanisms of the three cognitive abilities.

This study investigates the validity of syntactic priming as a measure of implicit language aptitude. Syntactic priming refers to the tendency to reproduce a linguistic structure due to a previous exposure to the structure. The validity of the construct was verified by collating evidence for divergent validity—whether it is dissociable from explicit aptitude; convergent validity—whether it is correlated with other measures of implicit aptitude; and predictive validity—whether it is predictive of learning attainment. One hundred sixty-six university EFL learners completed three tests of implicit aptitude: syntactic priming, sequence learning, and LLAMA_D; three tests of explicit aptitude: LLAMA_B, _E, and _F; and three tests of L2 proficiency: untimed grammaticality judgment, metalinguistic knowledge, and elicited imitation. The results showed that syntactic priming was dissociable from explicit aptitude, but it failed to converge with the other measures of implicit aptitude, and it also failed to predict L2 proficiency. The results also showed that priming was negatively correlated with sequence learning and that sequence learning was a negative predictor of learners’ metalinguistic knowledge. On the other hand, the construct validity of explicit aptitude was strong. The results suggest the multidimensionality of implicit aptitude and the need for more research into the construct validity of syntactic priming as a cognitive ability for implicit learning.

This article provides a comprehensive and critical synthesis of the methods utilized in studies investigating the role of language aptitude in second language acquisition (SLA). The synthesis is informed by sixty-five studies generated by a thorough search of the literature, three meta-analyses (Li, 2015, 2016, 2017), and a thematic issue of Studies in Second Language Acquisition (Li & DeKeyser, in press). The synthesis starts by identifying three categories of research investigating the role of aptitude in naturalistic learning, aptitude's associations with instructed learning, and the nature of aptitude pertaining to whether it increases with age and learning experience and how it is connected to other individual difference variables. The synthesis then presents an overview and critique of major measures of aptitude and discusses the construct validity of aptitude measures based on the principles of psychometric assessments. Specifically, the measures are scrutinized along the dimensions of reliability, content validity, divergent/convergent validity, and predictive validity. The content and measurement of implicit aptitude—a newly emerged construct in SLA—are highlighted. The synthesis proceeds to summarize and vet the measures of the outcome variable of aptitude research—L2 proficiency. Throughout the synthesis, methodological features are summarized, issues are identified, and remedies are proposed.

This article reports on a study exploring the differential effects of immediate and delayed corrective feedback (CF) on the acquisition of the English past tense. One hundred and forty-five seventh-grade EFL learners were assigned to four groups: Immediate CF, Delayed CF, Task Only, and Control. Each experimental group performed six focused communicative tasks, two each in three treatment sessions, eliciting the use of the English past tense. The Immediate CF group received feedback on their erroneous use of the target structure in the first session, the Delayed CF group received feedback in the final session, and the Task Only group performed the communicative tasks without receiving any feedback. The Control group only took the achievement tests. The effects of the feedback treatments were measured through an untimed grammaticality judgment test and an elicited imitation test. Mixed-effects analyses examining the influence of both fixed and random factors demonstrated that immediate CF was more facilitative of L2 development than delayed CF. The results suggest the importance of addressing linguistic errors before they are proceduralized in the interlanguage.