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The demand for foreign teachers of English as a Foreign Language (EFL) has been high in non-English speaking countries, including Thailand. As foreigners have resided in the country for several years, they picked up students’ first language (L1) competence. Several foreign teachers, to some extent, utilized this mastery of L1 to assist the English instruction. This research aimed to explore how students with different Common European Framework of Reference for Languages (CEFR) levels perceive foreign English teachers’ use of L1. Three hundred twenty students from Walailak University participated in the survey. A quantitative survey and qualitative interview were used to collect data. Descriptive and inferential statistics were performed to analyze quantitative data, while content analysis was administered to investigate the qualitative data. The quantitative findings revealed a significant difference in students’ perceptions, Welch’s F(2,68.42)=11.304, p .05. The qualitative findings exposed that students in level A1 had significantly different perceptions compared to those in levels A2 and B1. Students who supported L1 integration disclosed that it ameliorated communication, enhanced learning motivation, and improved academic achievement. Additionally, students who opposed L1 expressed that English’s full usage developed their learning motivation and academic accomplishment.

The problem of ensuring the sustainability of the processing process is directly related to the energy efficiency of the entire processing process. Virtually any machine the control of motion of which is considered interacts with the environment (technological, aerodynamic, trybologic, etc.). If one sticks to the synergetic analytical concept, the influence of the environment is described by a model of forces in state coordinates. The interaction is also characterized by the irreversible transformation capacity trajectory on the work. As a result, the system parameters are change causing additional strain displacements changing the trajectory. This transformation characterizes internal control and they are defined not by external action but by internal self-organization and defines the evolutionary trajectory. The properties of the system along the evolutionary trajectory change and the trajectory can lose its stability. The article considers the process of mathematical simulation of the evolutionary trajectory forming by the example of metalwork by cutting at turning machines and analyzes its stability. The evolution is presented as the parameters of the system depending on the capacity and work trajectory and presented by the Volterra integral equation of the second kind. When the trajectory loses its stability, irreversible changes can be formed in the system which may cause a complete system breakdown. In addition, the loss of stability leads to an increase in the oscillation amplitude of the tool and, as a consequence, an increase in energy costs for processing.

The problem of ensuring stability of movements of the tool about workpiece taking into account parametric self-excitation is considered. The factors causing periodic changes of parameters in dynamic system when cutting are analyzed. They are connected with spatial anisotropy of properties of elasticity in a subsystem of the processed workpiece with allowance variations on workpiece rotation perimeter, with kinematic perturbation from mechanical part of drives of executive elements of the machine, with periodic processes in a cutting zone. The generalized dynamic model of system with periodically changing parameters is given. Influence of periodically changing parameters on stability of trajectories is studied. The features of loss of stability specific to dynamic systems of cutting are disclosed. In particular, it is shown that due to parametrical effects with increasing cutting speed at increase of rotational frequency of spindle there is always a critical frequency at which the system loses stability.