Dynamics characterisation of cymbal transducers for power ultrasonics applications

A class V cymbal flextensional transducer is composed of a piezoceramic disc sandwiched between two cymbal-shaped shell end-caps. Depending on the type of piezoceramic, there exists a maximum voltage that can be reached without depolarisation, but also, at higher voltage levels, amplitude saturation can occur. In addition, there is a restriction imposed by the mechanical strength of the bonding agent. The effects of input voltage level on the vibration response of two cymbal transducers are studied. The first cymbal transducer has a standard configuration of end-caps bonded to a piezoceramic disc, whereas the second cymbal transducer is a modified design which includes a metal ring to improve the mechanical coupling with the end-caps, to enable the transducer to operate at higher voltages, thereby generating higher displacement amplitudes. This would allow the transducer to be suitable for power ultrasonics applications. Furthermore, the input voltages to each transducer are increased incrementally to determine the linearity in the dynamic responses. Through a combination of numerical modelling and experiments, it is shown how the improved mechanical coupling in the modified cymbal transducer allows higher vibration amplitudes to be reached

Conservation in conflict: Illegal drugs versus habitat in the Americas

About the book: State of the Wild is a biennial series that brings together international conservation experts and writers to discuss emerging issues in the conservation of wildlife and wild places. Each volume in the series combines evocative writings with a fascinating tour of conservation news highlights and vital statistics from around the world. One-third of each volume focuses on a topic of particular concern to conservationists working to protect wildlife and our last wild places. This 2008–2009 edition considers the integration of wildlife health, ecosystem health, human health, and the health of domestic animals—a “One World–One Health” approach to disease and conservation. This focus is complemented with essays clustered into sections that address other key issues—conservation of species; conservation of wild places; people, culture, and conservation; and the art and practice of conservation. Essays cover a broad range of topics, from restoring biodiversity on the prairies to mapping the state of the oceans to the conservation impacts of lawlessness and coca cultivation in Colombia. Essay contributions come from people directly involved in on-the-ground conservation efforts and offer a unique and valuable perspective on often-overlooked topics. State of the Wild’s accessible approach educates a wide range of audiences while at the same time presenting leading-edge scientific overviews of hot topics in conservation. Uniquely structured with magazine-like features up front, conservation news in the middle, and essays from eminent authors and experienced scientists throughout, this landmark series is an essential addition to any environmental bookshelf

Optimisation of a cymbal transducer for its use in a high-power ultrasonic cutting device for bone surgery

The class V cymbal is a flextensional transducer commonly used in low-power ultrasonic applications. The resonance frequency of the transducer can be tailored by the choice of end-cap and driver materials, and the dimensions of the end-caps. The cymbal transducer has one significant limitation which restricts the operational vibration amplitude of the device. This is the limit imposed by the mechanical strength of the bonding agent between the metal end-cap and the piezoceramic driver. Therefore, when there is an increase in the input power or displacement, the stresses in the bonding layer can lead to debonding, thereby rendering the cymbal transducer ineffective for high-power ultrasonic applications. In this paper, several experimental analyses have been performed, complemented by the use of Abaqus/CAE finite element analysis, in order to develop a high-power ultrasonic cutting device for bone surgery using a new configuration of cymbal transducer, which is optimised for operation at high displacement and high input power. This new transducer uses a combination of a piezoceramic disc with a metal ring as the driver, thereby improving the mechanical coupling with the metal end-cap

Biological Effects of Dispersants and Dispersed Oil in Surface and Deep Ocean Species

Beginning with the use of industrial-strength detergents, dispersing agents have been employed in spill response for decades. The Corexit series of agents in common use today generally consist of non-ionic and/or anionic surfactants in a solvent base designed to enhance miscibility under varying temperature and salinity conditions; cationic surfactants tend to be too toxic for use. While dispersants generally serve to decrease the interfacial surface tension of oil, thus facilitating its weathering under low-energy conditions, their surface-active nature also causes their interaction with cell surfaces – those of single-celled organisms as well as the gills of vertebrates and invertebrates

General formalism for the stability of thin-shell wormholes in 2+1 dimensions

In this article we theoretically construct circular thin-shell wormholes in a 2+1 dimensional spacetime. The construction is symmetric with respect to the throat. We present a general formalism for the study of the mechanical stability under perturbations preserving the circular symmetry of the configurations, adopting a linearized equation of state for the exotic matter at the throat. We apply the formalism to several examples.Comment: 14 pages, 7 figures; v2: improved version, new references adde

Kelvin-Helmholtz versus Hall Magneto-shear instability in astrophysical flows

We study the stability of shear flows in a fully ionized plasma. Kelvin-Helmholtz is a well known, macroscopic and ideal shear-driven instability. In sufficiently low density plasmas, also the microscopic Hall magneto-shear instability can take place. We performed three-dimensional simulations of the Hall-MHD equations where these two instabilities are present, and carried out a comparative study. We find that when the shear flow is so intense that its vorticity surpasses the ion-cyclotron frequency of the plasma, the Hall magneto-shear instability is not only non-negligible, but it actually displays growth rates larger than those of the Kelvin-Helmholtz instability

Coordination and Miss-Coordination in Market Entry Games with an Application to Congestion Externalities

Marketing,

Evaluación de la planta de tratamiento de aguas residuales del municipio de Gachancipá

Trabajo de InvestigaciónSe realizó la evaluación a todas las unidades que componen la PTAR para concluir si esta cumpliendo con lo requerido por la sentencia del Río Bogotá y el cumplimiento de las resoluciones y los estándares permitidos para el vertimiento de aguas residuales.INTRODUCCIÓN 1. INTRODUCCION 2. ANTECEDENTES 3. JUSTIFICACION 4. PLANTEAMIENTO DEL PROBLEMA 5. OBJETIVOS 6. METODOLOGIA 7. MARCO DE REFERENCIA 8. CONCLUSIONES 9. RECOMENDACIONES BILBIOGRAFIA ANEXOSPregradoIngeniero Civi