Multi-domain active sound control and noise shielding

This paper describes an active sound control methodology based on difference potentials. The main feature of this methodology is its ability to automatically preserve “wanted” sound within a domain while canceling “unwanted” noise from outside the domain. This method of preservation of the wanted sounds by active shielding control is demonstrated with various broadband and realistic sound sources such as human voice and music in multiple domains in a one-dimensional enclosure. Unlike many other conventional active control methods, the proposed approach does not require the explicit characterization of the wanted sound to be preserved. The controls are designed based on the measurements of the total field on the boundaries of the shielded domain only, which is allowed to be multiply connected. The method is tested in a variety of experimental cases. The typical attenuation of the unwanted noise is found to be about 20 dB over a large area of the shielded domain and the original wanted sound field is preserved with errors of around 1 dB and below through a broad frequency range up to 1 kHz. © 2011 Acoustical Society of Americ

Potential-based methodology for active sound control in three dimensional settings

This paper extends a potential-based approach to active noise shielding with preservation of wanted sound in three-dimensional settings. The approach, which was described in a previous publication [Lim et al., J. Acoust. Soc. Am. 129(2), 717–725 (2011)], provides several significant advantages over conventional noise control methods. Most significantly, the methodology does not require any information including the characterization of sources, impedance boundary conditions and surrounding medium, and that the methodology automatically differentiates between the wanted and unwanted sound components. The previous publication proved the concept in one-dimensional conditions. In this paper, the approach for more realistic conditions is studied by numerical simulation and experimental validation in three-dimensional cases. The results provide a guideline to the implementation of the active shielding method with practical three-dimensional conditions. Through numerical simulation it is demonstrated that while leaving the wanted sound unchanged, the developed approach offers selective volumetric noise cancellation within a targeted domain. In addition, the method is implemented in a three-dimensional experiment with a white noise source in a semi-anechoic chamber. The experimental study identifies practical difficulties and limitations in the use of the approach for real applications

Improvement of microplant establishment through in vitro and ex vitro exogenous chemical applications

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Cryopreservation of Ribes nigrum (L.) dormant buds:recovery via in vitro culture to the field

Abstract Cryopreservation of dormant buds can be a feasible method for long term preservation of clonally propagated woody plants. In the present study, dormant buds of blackcurrant (Ribes nigrum L) cultivar Mortti were cryopreserved. Twig segments from greenhouse and field grown plants were cooled at their natural moisture content at the rate of 0.17 °C min⁻¹ from zero to −38 °C, immersed in liquid nitrogen and stored in liquid nitrogen vapor. The post-cryopreservation regrowth of buds was evaluated in vitro and viability of recovered plants was tested in vivo. The estimated recovery rate for buds thawed after 1–6 days in cryostorage was 86% and 66% for outdoor and greenhouse grown buds, respectively. Microplants adequate in size and quality grew successfully in vivo and plants produced berries in field. After 4 years in cryostorage, the estimated recovery rate for outdoor buds was 58%. According to results from 1 to 6 days cryostorage, the tested dormant bud protocol turned to be applicable for cryopreservation of the blackcurrant cultivar Mortti. However, concerning the long-term preservation the decline of recovery is important to consider in the future experiments

Experimental validation of the active noise control methodology based on difference potentials

To achieve active noise cancellation over a large area, it is often necessary to get a measure of the physical properties of the noise source to devise a counter measure. This, however, is not practical in many cases. A mathematical approach, the Difference Potential Method, can provide an alternative solution for active shielding over a large area. In this approach, the cancellation of unwanted noise requires only measurements near the boundary surface but not at the source itself, and it does not require any other information. Moreover, the solution based on difference potentials applies to bounded domains in the presence of acoustic sources inside the domain to be shielded. This paper reports on the results of experimental validation. It has been demonstrated that while preserving the wanted sound, the developed approach can cancel out the unwanted noise. The volumetric noise cancellation offered by the proposed methodology along with leaving the wanted sound unchanged is a unique feature compared to other techniques available in the literature. It can be most useful in the context of applications related to civil aviation, in particular, for eliminating the exterior noise inside the passenger compartments of both current and future generation of commercial aircraft