Smart double panel with decentralised active dampers for control of sound transmission

This report presents the results of a theoretical study of active sound transmission control through a double panel. The double panel material and geometrical properties have been chosen so as to emulate section of an aircraft fuselage, or bodywork of a vehicle. It consists of two plates: an aluminium plate simply supported along all the edges and a honeycomb plate with all the edges free. The two plates, having the same length and width, are connected using elastic mounts, so that a double panel with a thin rectangular cavity between the plates is formed. Since the two plates are linked by the mounting system, and since the air is confined in the cavity between them, they form a structurally and acoustically coupled system. The sound transmission properties of the system are studied in such a way that the aluminium plate (“source panel”) is excited using a plane acoustic wave, while the honeycomb plate (“radiating panel”) radiates sound into free field.The aim of the active control is to reduce the sound transmitted in a broad frequency band, but with a particular focus on the reduction of the sound transmission at lower frequencies of the band. Decentralised velocity feedback control systems (applying active damping) are implemented, with purpose of reducing sound transmission at resonance frequencies. Control sensors and actuators are embedded into the double plate system as a regular array, so that a smart double panel is created. The theoretical study includes analysis of the passive sound transmission in terms of a parametric study, implementation of the active control using skyhook velocity sensors and skyhook force actuators, and the performance/stability analysis in case when reactive actuators and skyhook velocity sensors are used. In the latter case the actuating force is obtained using actuators located in the air cavity which can react off the two plate

Vacuum fluctuations in a supersymmetric model in FRW spacetime

We study a noninteracting supersymmetric model in an expanding FRW spacetime. A soft supersymmetry breaking induces a nonzero contribution to the vacuum energy density. A short distance cutoff of the order of Planck length provides a scale for the vacuum energy density comparable with the observed cosmological constant. Assuming the presence of a dark energy substance in addition to the vacuum fluctuations of the field an effective equation of state is derived in a selfconsistent approach. The effective equation of state is sensitive to the choice of the cut-off but no fine tuning is needed.Comment: 19 pages, accepted for publication in Phys. Rev.

Cosmological k-essence condensation

We consider a model of dark energy/matter unification based on a k-essence type of theory similar to tachyon condensate models. Using an extension of the general relativistic spherical model which incorporates the effects of both pressure and the acoustic horizon we show that an initially perturbative k-essence fluid evolves into a mixed system containing cold dark matter like gravitational condensate in significant quantities.Comment: 8 pages, 2 figures, presented by NB at the conference Beyond 2010, Cape Town, 1-6 February 201

ECONOMIC AND SOCIAL CONSEQUENCES OF BIOTECHNOLOGY: A SCENARIO ANALYSIS

Over the years agricultural technology has created remarkable commodity production growth rates and enhanced general economic growth through food production, manufactured goods and trade for most nations. Biotechnology holds the promise of continuing this remarkable record. There is a long list of potential benefits of biotechnology but unfortunately the perceived costs/risks are also many. These concerns have lead to significant consumer reluctance to accept the technology and, in some cases, outright consumer rejection of the technology. To discuss the future of biotechnology, scenario analysis is used to examine the social and economic impact of biotechnology on industrialized and emerging nations. Four scenarios are discussed in detail: biotechnology may be formally or informally banned (Scenario 1), fully accepted (Scenario 2), marketed through strict labeling (Scenario 3), or limited to non-food applications (Scenario 4). Consumer acceptance of this technology will be key to determining which scenario becomes the future for each nation. The likelihood of each scenario is different for each nation, the U.S. will most likely evolve into scenario 2 or 3, while in the EU scenarios 1 or 4 are more likely. Determining the future for emerging nations is extremely complex and dependent on several factors like malnutrition rates, environmental safety and historical trading routes. Each scenario has a major impact on small producers worldwide which ultimately influences the health of rural communities. The analysis indicates that emerging nations are the most sensitive to the timing of decisions being made about the future of biotechnology. If biotechnology becomes a reality, new data will be required to assess the social and economic impact of this technology.Research and Development/Tech Change/Emerging Technologies,