kHz Ultrasounds Research Articles

Comparative Study of Different Production Methods of Activated Carbon Cathodic Electrodes in Single Chamber MFC Treating Municipal Landfill Leachate

The treatment of real waste extracts with simultaneous energy production is currently under research. One method of addressing this dual task is using biochemical reactors named microbial fuel cells (MFCs). MFCs consist of a bioanode and a cathode where the oxygen reduction reaction (ORR) occurs. Cathodes are currently under optimization regarding the nature of their support, their catalytic efficiency and their configurations. In this work, we present facile preparation methods for the production of activated carbon ceramic-supported cathodic electrodes produced with three different techniques (wash-coat, brush-coat, and ultrasound-assisted deposition/infiltration). The produced cathodic electrodes were tested in a single-chamber MFC, filled with the concentrated liquid residue, after the reverse osmosis (RO-CLR) treatment of leachate from a municipal waste landfill, in order to exploit their electrochemical potential for simultaneous waste treatment and energy production. The electrode produced utilizing 20 kHz ultrasounds proved to be more effective in terms of energy harvesting (10.7 mW/g·L of leachate) and wastewater treatment (COD removal 85%). Internal resistances of the ultrasound-produced electrodes are lower, as compared to the other two methods, opening new exploitation pathways in the use of ultrasound as a means in producing electrodes for microbial fuel cells.

Energy-sustained reversible nanoscale order and conductivity increase in polymer thin films

When treated with 30 kHz ultrasounds in isothermal conditions, poly-3-hexylthiophene (P3HT) thin films show a marked increase of their nanoscale order. This structural transition is fully reversible, as the system returns to its initial structure when ultrasounds are turned off. The increase of nanoscale order is shown to consists of a more efficient packing and/or alignment of amorphous fragments along pre-existing nano-crystals. Additionally, owing to the reduced structural disorder, the ultrasound treatment leads to the marked increase (up to 100%) of the film conductivity. The effect, being dependent on the thickness and degree of crystallinity of the polymer films, is discussed in terms of ultrasound-induced packing of P3HT chain segments and the subsequent strain-driven relaxation to restore the initial order when sonication is switched off. These results open the way to a new field of study dealing with energy-sustained ordering processes of randomly oriented soft molecular moieties, as a new path to sample quasi-equilibrium states in partially crystalline systems. This novel approach promises new paths to reversible modification and control of polymeric materials and devices.

Acoustic field and convection pattern within liquid material during ultrasonic processing

When ultrasound propagates in a liquid alloy, nonlinear effect takes place such as cavitation effect and acoustic streaming, which accelerates the solute and thermal transportation during alloy solidification, and consequently, improves the solidification microstructures and mechanical properties of the metallic alloy. Therefore, it is significant to investigate the ultrasound propagation characteristics in liquid. Here, by choosing water as a model transparent material, the acoustic fields and flow fields induced by 20 and 490 kHz ultrasounds are investigated by numerical simulation, and the effects of frequency and ultrasonic horn radius are studied. Firstly, the simulation results demonstrate that the sound pressure under 20 kHz ultrasound decreases obviously along the ultrasonic propagation direction, and the maximum of sound pressure value is equal to the initial pressure. In this case, the cavitation effect only occurs in the region close to the ultrasonic horn. By contrast, when the ultrasonic frequency increases to 490 kHz, the sound pressure is higher than that of 20 kHz ultrasound, and displays periodical vibration characteristic along the wave propagation direction. The cavitation volume correspondingly expands to a large extent with a regular striped distribution. It can also be found that increasing the ultrasonic horn radius under 20 and 490 kHz ultrasounds can effectively promote the sound pressure level in water, and hence leads to the remarkable enlargement of cavitation volume. Secondly, the calculated results of flow field indicate that the streamlines in water are similar under the two ultrasounds with different frequencies. A jet produced by the center of horn spreads down and divergences to both sides after reaching the bottom. For both frequencies as the horn radius increases, the radius of jet increases and the average velocity in water first increases and then decreases, whose maximum value appears when the horn radius is 40 mm. Meanwhile, the average velocity under 20 kHz ultrasound is larger than that under 490 kHz ultrasound for each horn radius. Finally, particle image velocimetry method is employed to measure the velocity field in water. Both the positions of eddy and the velocity distribution are the same as the simulation results, which verifies the reliability of the present theoretical calculation model. The scenario in this work is analogous to the acoustic field and the flow field in liquid alloy, which is beneficial for the design of parameter optimization during ultrasonic processing in alloy solidification.

Potential of high-frequency ultrasounds to improve sludge anaerobic conversion and surfactants removal at different food/inoculum ratio

High-frequency ultrasounds have recently gained interest as oxidative technique for sonochemical degradation of organic contaminants in water. In this study an innovative approach applying 200 kHz ultrasounds to improve both sludge anaerobic biodegradability and decontamination is proposed. Digestion tests were performed on batch reactors fed either with untreated or sonicated sludge, at different food/inoculum (F/I) ratio, in the range 0.3-0.9. First order kinetic highlighted a decreasing trend of the hydrolysis rate by increasing F/I, both for untreated and sonicated sludge. Positive effect of ultrasounds on specific biogas production was evident, but the conversion rate for pretreated sludge was strongly affected by F/I, and decreased by increasing F/I. Anionic surfactants anaerobic removal occurred in all tests, but the effect of ultrasounds was significant only at F/I=0.3. By pretreating sludge with high frequency ultrasounds, low F/I was the ideal ratio improving both sludge anaerobic digestion and decontamination.

Acid-induced gelation behavior of sonicated casein solutions

Casein gels were made from solutions sonicated by 24 and 130 kHz ultrasounds for 0, 60 and 120 min, followed by acidification with glucono-δ-lactone at 30 °C. The dynamics of gel formation were studied using rheological methods and microstructure of gels was monitored using scanning electron microscopy. Sonication postponed the gelation point to a lower pH value and increased the elasticity of freshly formed gels. It also resulted in gels with a more interconnected structure and smaller non-distinguishable particulates. This structure was especially dominant for the gel made from the solution already sonicated for 120 min.

Comparison of pH-dependent sonodisruption of re-assembled casein micelles by 35 and 130 kHz ultrasounds

Sonodisruption behavior of re-assembled casein micelles was compared at two ultrasound frequencies (35 and 130 kHz) by turbidity measurement and laser-diffraction based particle size analysis. Sonochemical ultrasound (130 kHz) was more effective than power ultrasound (35 kHz) in micelle disruption. This was attributed to the higher strain rates generated upon implosion of cavities, as well as the liberation of more free radicals to the surrounding medium. The higher the pH of solution, the more effective was the ultrasonic disruption due to a looser expanded assembly of particles at higher pH values. Sonochemical ultrasound decreased the consistency coefficient of casein solutions and increased their flow index except at a pH value of 6.35, while power ultrasound did not affect the flow behavior of solutions across the whole pH range.

C-section birth per se or followed by acute global asphyxia altered emotional behaviour in neonate and adult rats

Birth complications such as perinatal asphyxia are considered risk factors for later neurobehavioural disorders. Behavioural analysis of animal models may help to clarify the contribution of particular patterns of early hypoxia and their combination to psychiatric morbidity. Wistar rats underwent caesarean section (c-section) alone or c-section followed by asphyxia, the latter induced by placing pups still in uterus horns into a water bath at 37 °C for 20 min. Vaginally delivered pups were used as controls. Frequency of ultrasound emissions was analysed following isolation at a lower temperature than that of the home nest (23 ± 0.5 °C) and reunion with their mother (3 min) on postnatal day (PND) 13 (maternal potentiation test). A sex-dependent effect of hypoxia was observed, with higher production of ultrasounds in hypoxic males. Caesarean-delivered pups produced significantly more ultrasounds than those vaginally delivered. At adolescence (PND 35) rats underwent a 25 min social interaction test with a conspecific of the same sex and age. Significant alterations in investigative behaviour (inclusive of: nose, anogenital, body sniffing, and following) were evident in caesarean-delivered rats of both sexes, but not in rats experiencing perinatal asphyxia. At adulthood, auditory, and context conditioned responses, analysed in a fear conditioning test, were not markedly affected either by c-section or c-section plus hypoxia. However, hypoxic rats emitted significantly more 22 kHz ultrasounds than c-section or vaginally delivered rats during the training session. In conclusion, differential effects appear to be brought about by c-section and by hypoxia mainly related to emotional/anxious responses.

Ultrasonically elaborated Au/PTFE composite coatings

The deposition of finely dispersed particles in a metal matrix by electrolytic co-deposition process led to new generated composite coatings. Previous works have been devoted to the characterisation of gold - PTFE composite coatings performed by electrolysis. The aim of the present work is to develop a new process for the electrolytic co-deposition of PTFE particles in an Au - Ni matrix, which consists in using an ultrasonic stirring. This study shows that the use of 500 kHz ultrasounds improves both the coating deposition rate and the inclusion rate of PTFE particles, leading to a significant improvement of wear resistance.

Fatty acids methyl esters from vegetable oil by means of ultrasonic energy

The transesterification of vegetable oil with short-chain alcohols, in the presence of base-catalyst, by means of low frequency ultrasound (28 and 40 kHz) in order to obtain biodiesel fuel was studied. By using ultrasounds the reaction time is much shorter (10–40 min) than for mechanical stirring. The quantity of required catalyst is 2 or 3 times lower. The molar ratio of alcohol/oil used is only 6:1. Normal chain alcohols react fast, while secondary and tertiary alcohols show some or no conversion after 60 min of reaction. Surprisingly, 40 kHz ultrasounds are much more effective in the reduction of the reaction time (10–20 min). Twenty eight kilohertz give slightly better yields (98–99%), but longer reaction time, while higher frequencies are not useful at all for the transesterification of fatty acids.

99/00533 Kinetics of the non-catalytic transesterification of soybean oil

The transesterification of vegetable oil with short-chain alcohols, in the presence of base-catalyst, by means of low frequency ultrasound (28 and 40 kHz) in order to obtain biodiesel fuel was studied. By using ultrasounds the reaction time is much shorter (10–40 min) than for mechanical stirring. The quantity of required catalyst is 2 or 3 times lower. The molar ratio of alcohol/oil used is only 6:1. Normal chain alcohols react fast, while secondary and tertiary alcohols show some or no conversion after 60 min of reaction. Surprisingly, 40 kHz ultrasounds are much more effective in the reduction of the reaction time (10–20 min). Twenty eight kilohertz give slightly better yields (98–99%), but longer reaction time, while higher frequencies are not useful at all for the transesterification of fatty acids.

The effects of idazoxan and 8-OH-DPAT on sexual behaviour and associated ultrasonic vocalizations in the rat

Two experiments were performed studying the effects of 8-OH-DPAT and idazoxan on sexual behaviour and ultrasonic communication of male rats. In addition, the reactions of the females towards drug-treated males were studied. 8-OH-DPAT (a very specific 5-HT1A agonist) and idazoxan (an alpha 2-adrenergic antagonist) differentially affected sexual behaviour: 8-OH-DPAT (0.1 and 0.4 mg/kg IP) markedly facilitated ejaculations, a feature indicated by decreased numbers of mounts and intromissions preceding ejaculation and a reduction in ejaculation latency. This drug concomitantly reduced the postejaculatory refractory period. Idazoxan reduced the number of intromissions before ejaculation only at the highest dose (10 mg/kg IP), but did not markedly facilitate other parameters. Both drugs markedly and dose-dependently suppressed the postejaculatory 22 kHz ultrasounds normally recorded during the postejaculatory refractory period. Ultrasound frequencies above 30 kHz first appear at the end of the absolute refractory period, even when the refractory period is shortened by 8-OH-DPAT. Idazoxan increased the number of these 30 kHz ultrasounds, whereas 8-OH-DPAT had no effect on them. No effects were observed on ultrasound production (either 22 kHz or above 30 kHz) before an ejaculation. The behaviour of the females towards 8-OH-DPAT-treated males was also affected, with the females showing more darting and lordosis before and after ejaculation, but less sitting after ejaculation. Idazoxan treatment of the males resulted in more hopping and earwiggling of the females before ejaculation. Following ejaculation, females treated with the antagonist showed more darting, hopping, earwiggling and lordosis, but sitting was decreased. It has been suggested in the rat that the emergence of ultrasounds higher than 30 kHz indicates the end of the absolute refractory period and signals to the female that the male is capable of resuming sexual activity. The significance of 22 kHz ultrasound in sexual behaviour remains puzzling because these vocalizations could be easily uncoupled from the refractory period by drugs acting via different receptor mechanisms without disturbing sexual behaviour per se. A failure to produce postejaculatory sounds appears to disinhibit (proceptive) behaviour by the females.

Twenty-two kHz alarm cries to presentation of a predator, by laboratory rats living in visible burrow systems

When a cat was presented to groups of 3 male and 2 female laboratory rats in the open area of a visible burrow system, the rats retreated to the burrow system and showed high levels of 18–24 kHz ultrasonic cries during the cat presentation and for 30 min following removal of the cat. Latency to make ultrasonic vocalizations, durations of these vocalizations, and duration in the burrow systems were all strikingly and reliably different during and after cat exposure in comparison to similar periods with a control (stuffed cat toy) stimulus. However, when individual rats were exposed to a cat in an open area of similar size, ultrasonic cry production was minimal. Also rats exposed individually to a cat in an apparatus providing an escape chamber similarly showed no ultrasonic cries, indicating that concealment per se is not a sufficient condition for their appearance. These results suggest that the production of ultrasonic vocalizations during and after exposure to a predator is greatly facilitated by the presence of familiar conspecifics, and may serve as alarm cries. While the alarm cry hypothesis also suggests a possible function for 18–24 kHz ultrasounds in the context of copulation and intraspecies aggression, the sonographic and functional relationships among the cries emitted in these different situations remain to be analyzed.

Temporal patterning of ultrasonic distress calls in the adult rat: effects of morphine and benzodiazepines

Opioids and benzodiazepines modulate the ultrasounds that rats emit before being presented with aversive stimulation. Mild, intermittent 10 s electrical tail stimulation induces rats to emit 20-30 kHz ultrasounds before and after the stimulation. Analysis of the temporal parameters of the sounds via a customized computer system reveals them to be emitted in bouts of about five sounds, each sound being separated from the next by 0.2-0.35 s pauses. Morphine decreases the per cent time vocalizing during the pre-stimulation period, with 6 mg/kg being fully suppressive. This effect is reversed by 1 mg/kg naloxone pre-treatment. Chlordiazepoxide and morphine have opposite effects on the temporal structure of the pre-stimulation calls; chlordiazepoxide induces longer bouts with more pulses, and morphine dissolves the bout structure into a series of single pulses. These differential and selective effects of morphine and benzodiazepines on the occurrence and temporal structure of ultrasounds may be relevant to characteristics of different affective expressions.

Female behavior is affected by male ultrasonic vocalizations in house mice

The effects of male-mouse ultrasonic vocalizations on female preference behavior were investigated using Swiss-Webster mice. Intact females spent more time with an intact tethered male than with a devocalized tethered male during 3-min preference tests. Female preference behavior was similar during estrus and diestrus; but, a preference for the vocalizing male was absent after ovariectomy, and returned following replacement treatment with ovarian hormones. Similar effects on female behavior were obtained using synthetic 70 kHz ultrasounds presented behind one of two devocalized tethered males during preference tests. The results indicate that ultrasounds maintain the female close to the vocalizing male and may facilitate copulation.