EXPERIMENTAL STUDY OF NONLINEARITY IN FREE PROGRESSIVE ACOUSTIC WAVES IN AIR AT 20 kHz

On a étudié expérimentalement la propagation d'ondes d'amplitude finie dans l'air à 20 kHz. La source utilisée est un générateur aérien de puissance d'un type nouveau, capable d'atteindre avec une grande directivité des niveaux quasi-monochromatiques de l'ordre de 160 dB. Les expériences en ondes entretenues ont été conduites dans une chambre de dimensions 7,4 x 5,5 x 5,5 m3. Les mesures essentielles ont porté sur les amplitudes du fondamental et des trois premiers harmoniques pour différents niveaux d'émission et à des distances variables dans le champ éloigné. Les formes d'ondes et les diagrammes de directivités correspondants ont été également enregistrés. Les résultats obtenus confirment la limitation d'amplitude transmissible par propagation non linéaire. On a pu mettre clairement en évidence le phénomène de saturation acoustique. L'évolution des formes d'ondes et des diagrammes de directivité illustrent également ce comportement non linéaire.This paper describes an experimental investigation of the propagation of periodic waves of finite amplitude in air at 20 kHz. The acoustic source used in our experimental work is a new high-power ultrasonic transducer for use in air. This transducer, which emits a directive radiation, is able to generate a nearly pure sinusoïdal wave up to sound pressure levels over 160 dB. The experiments were done in a 7.4 m long, 5.5 m wide and 5.5 m high anechoic chamber, using cw mode. They consisted essentially of measuring the amplitude of the fundamental component of the wave and its first three harmonics for different source pressure levels and at different distances in the farfield. In addition, oscillograms and directivity patterns were recorded. The obtained results confirm the strong limitations in the transmission of intense waves due to nonlinear distortion. The phenomenon of acoustic saturation at high source levels is clearly observed. Also the evolution of waveforms and the changes in the radiation patterns show the effect of nonlinear behaviour

Development of deliquoring method enhanced by electric and acoustic fields

A method developed uses acoustic and electric force fields to enhance filtration by increasing filtration capacity and by reducing production costs and consumption of energy.In both laboratory and pilot scale filtration the application of an electric field significantly increases the cake capacity of a vacuum disc filter.When constant DC electric field was applied across the ceramic capillary filter (CERAMEC), about 3.5-fold cake capacity values (with electric field: 250 kg D.S./m2h) were recorded during the filtration of titanium dioxide suspension using laboratory scale filter.Using continuous operation pilot scale filter values with and without electric field as its best were 60 kg D.S./m2h amd 10 kg D.S./m2h respectively.When an ultrasonic field was used during cake drying it was possible to obtain a rapid dewatering effect, up to 6% decrease in the cake moisture content, from 24 wt-% to 18 wt-%, using laboratore scale filter.In continuous operating pilot-scale filter the decrease in cake moisture content was about 3% from 24 to 21 wt-%.This research has revealed that the use of ultrasound is an effective way to increase the dewatering efficiency of the cake filtration process.The most important advantages of this process are obtained in the filtration of suspensions with very fine particles, whehe conventional systems are inefficient

Exigência de treonina, com base no conceito de proteína ideal, de alevinos de tilápia-do-nilo Digestible threonine requirement of Nile tilapia fingerlings using ideal protein concept

Avaliou-se o efeito dos níveis de treonina digestível, com base no conceito de proteína ideal, em rações com 1,35% de lisina digestível sobre o desempenho de alevinos de tilápia-do-nilo (Oreochromis niloticus). Utilizaram-se 432 alevinos revertidos de tilápia, linhagem tailandesa, com peso inicial de 1,64 ± 0,03 g, em delineamento inteiramente ao acaso, com seis tratamentos, cada um com seis repetições, e doze peixes por unidade experimental. Os tratamentos consistiram de cinco rações com diversas relações treonina:lisina digestível (69,0; 74,0; 79,0; 84,0 e 89,0%) e relação metionina + cistina:lisina digestível de 70,0% e uma ração com relação treonina:lisina digestível de 84,0% e de metionina + cistina:lisina digestível de 75,0%, todas isoenergéticas e isoprotéicas. Os peixes foram mantidos em 36 aquários de 130 L, dotados de abastecimento de água, temperatura controlada e aeração individuais, e alimentados à vontade, seis vezes ao dia, durante 30 dias. Avaliaram-se o desempenho, a composição corporal, as deposições de proteína e gordura e a eficiência de retenção de nitrogênio dos peixes. O consumo de ração, o teor de proteína corporal e a deposição de proteína corporal aumentaram de forma linear de acordo com a relação treonina:lisina na ração, contudo, não foram influenciados pelo aumento da relação metionina + cistina:lisina da ração. Os níveis de treonina total ou digestível que proporcionaram os melhores resultados de desempenho em alevinos de tilápia-do-nilo foram de 1,11 e 0,99%, enquanto os níveis que promoveram melhor deposição de proteína corporal foram de 1,43 e 1,28%, que correspondem às relações treonina:lisina total de 71,0 e 69,0% e treonina:lisina digestível de 90,0 e 89,0%.<br>The effects of digestible threonine levels, based on ideal protein concept in diets with 1.35% of digestible lysine on Nile tilapia (Oreochromis niloticus) fingerlings performance. Four hundred thirty two reverted Nile tilapia, Thailand strain, with initial weight of 1.64 ± 0.03 g, were allotted to completely randomized design, with six diets and six replications with twelve fishes each. The five diets, isoenergetic isoproteic, consisted of various threonine:digestible lysine ratio (69.0, 74.0, 79.0, 84.0, and 89.0%) and methionine + cystine:digestible lysine ratio of 70.0% and one diet with threonine:digestible lysine of 84.0% and methionine + cystine:digestible lysine of 75.0%. The fish were kept in 36 aquariums of 130 L, equipped with water supply, controlled temperature and individual aeration, and ad libitum fed six times a day for 30 days. Performance, body composition, protein and fat depositions and nitrogen retention efficiency of fishes were evaluated. Consumption of feed, body protein content and body protein deposition increased in a linear fashion in accordance to threonine:digestible lysine in the diet, however, was not affected by the increase of dietary methionine + cystine:digestible lysine. Total or digestible threonine levels that provided the best results of performance of Nile tilapia fingerlings were 1.11 and 0.99%, while the levels that promoted better body protein deposition were 1.43 and 1.28%, which correspond to threonine:total lysine ratio of 71.0 and 69.0% and threonine:digestible lysine of 90.0 and 89.0%