RESUMO
The current study examined the use of electronic textbooks designed as mobile applications for learning vocabulary in English among Iranian university students. To this end, 95 university students in an experimental (N = 50) and a control group (N = 45) participated in the study. An explanatory sequential mixed methods design was employed and over an academic semester, the participants used either traditional materials or mobile-based electronic textbooks for learning 600 words in English. To assess the outcomes from different learning conditions, receptive knowledge of the target vocabulary items was tested in three junctures of time (i.e. pre-, post-, and delayed post-test). Additionally, open-ended questionnaires and interviews were used to collect qualitative data from the experimental group to further investigate their perceptions of using mobile-based electronic textbooks for vocabulary learning. The findings revealed a significant main effect for time and both groups significantly improved their vocabulary knowledge from pre-test to post-test. Moreover, a significant main effect was found for using electronic textbooks on mobile devices, and the experimental group outperformed the control group on the post- and delayed post-tests. The qualitative findings revealed three perceived benefits, namely episodic learning, easy access to materials, and enhanced enjoyment for mobile assisted vocabulary learning through electronic textbooks. The perceived challenges were related to health concerns, distractions associated with mobile environments, and external pressure resulting from excessive mobile use among the participants. In general, the findings of the study shed light on the potential offered by mobile-based textbooks for learning English vocabulary, with implications for teachers and materials developers in language teaching programs.
RESUMO
We experimentally demonstrate an order of magnitude enhancement in the quasi-continuous-wave radiated power from a photomixer with plasmonic contact electrodes in comparison with an analogous conventional photomixer without plasmonic contact electrodes in the 0.25-2.5 THz frequency range when pumped at an optical wavelength of 1550 nm. The significant efficiency enhancement results from the unique capability of the plasmonic contact electrodes to reduce the average transport path of photocarriers to the device contact electrodes, increasing the ultrafast photocurrent that drives the terahertz antenna.
RESUMO
A photoconductive terahertz detector based on plasmonic contact electrodes is presented. The use of plasmonic electrodes mitigates the inherent tradeoff between high quantum efficiency and ultrafast operation of the employed photoconductor, enabling significantly higher detection sensitivities compared to conventional photoconductive terahertz detectors. Prototypes of comparable photoconductive detectors with and without plasmonic contact electrode gratings were fabricated and characterized in a time-domain terahertz spectroscopy setup under the same operation conditions. The experimental results show that the plasmonic photoconductive detector offers more than 30 times higher terahertz detection sensitivities compared to the comparable conventional photoconductive detector without plasmonic contact electrodes over 0.1-1.5 THz frequency band.
