Excitation of multiple 2-mode parametric resonances by a single driven mode

We demonstrate autoparametric excitation of two distinct sub-harmonic mechanical modes by the same driven mechanical mode corresponding to different drive frequencies within its resonance dispersion band. This experimental observation is used to motivate a more general physical picture wherein multiple mechanical modes could be excited by the same driven primary mode within the same device as long as the frequency spacing between the sub-harmonic modes is less than half the dispersion bandwidth of the driven primary mode. The excitation of both modes is seen to be threshold-dependent and a parametric back-action is observed impacting on the response of the driven primary mode. Motivated by this experimental observation, modified dynamical equations specifying 2-mode auto-parametric excitation for such systems are presented.Comment: 8 pages, 3 figure

Piezoelectric Transformer Integration Possibility in High Power Density Applications

The contents of this work investigate the capability of integrating the PT in applications by invoking the ratio of the throughput power to volume represented by the term: power density. The fundamentals of the PT are introduced in chapter two. In chapter three, the fundamental limitations of the PT's capability of transferring power to the load are studied. There are three major limitations: temperature rise due to losses during operation, electromechanical limits of material, and interactions with output rectifier. The analysis and estimation are then verified by experiments and calculations implemented on three different PT samples fabricated from three different manufacturers. The subject of chapter four is the behavior of the PT's power amplifier. This chapter concentrates on two main amplifier topologies, optimized based on the simplicity of structure and minimization of components (passive and active): class D and class E amplifiers. The operational characteristics of these amplifiers with the PT are then comparison. Methods to track the optimum frequency and discontinuous working mode of the PT are proposed as the approaches to improve the energy transfer of the PT. In chapter five, prototypes of four devices using a PT are developed and introduced as illustrations of the integration of PTs into practical applications: an igniter for high intensity discharge (HID) lamps, high DC voltage power supplies, and electronic ballasts for LEDs, and stand-alone ionizers for food sterilizers. Some concluding statements and ideas for future works are located in the last chapter - chapter six

TRADITIONAL CULTURE CHANGES OF ETHNIC MINORITY IN THE CENTRAL HIGHLANDS IN THE PROCESS OF DEVELOPMENT AND INTERNATIONAL INTEGRATION: A STUDY OF THE BA NA ETHNIC GROUP IN KON TUM PROVINCE, VIETNAM

Kon Tum is a province located in an important geopolitical position, with 28 ethnic groups living together, of which 7 ethnic groups are local groups: Xo Dang, Ba Na, Gie Trieng, Gia rai, Brau , Ro Mam and Hre with many different cultural characteristics, [1, p.1]. A system of plentiful tangible and intangible cultural heritages bears the distinctive characteristics of the forest culture area, upland farming culture and gong culture. Mr. Koichiro Matsuura - General Director of UNESCO at the ceremony of announcing the Central Highlands Gong Culture, said: “I have enjoyed the very unique Vietnamese style of gong music and have also seen very unique musical instruments in the gong orchestra of ethnic groups in the Central Highlands. This is a very unique traditional culture of Vietnam. It's very wonderful and unique…” [5, p.1]. Nowadays, under the impact of socio-economic conditions, the exchange and integration increase; the culture of the Ba Na ethnic group is undergoing strong changes. We can easily see that, from the daily routines such as eating, clothing, accommodation, travel...to voice, customs and beliefs, as well as images, patterns... are changing. Through the process of researching and surveying ideas of artists, village elders and experts on the Ba Na ethnic group in Kon Tum province, we generalize the changes in traditional culture of the Ba Na ethnic group in Kon Tum province. Article visualizations