China
Africa
Explore chapters and articles related to this topic
Ultrasound-Responsive Nanomedicine
Published in Lin Zhu, Stimuli-Responsive Nanomedicine, 2021
Tyrone M. Portera, Jonathan A. Kopechek
Microbubbles coated with a stabilizing shell have been used as ultrasound contrast agents in patients for decades, primarily to image blood flow and perfusion. Contrast-enhanced ultrasound is approved for tumor detection in Asia, Europe, and other countries, but in the United States, it is currently approved only to assess left ventricular function. Microbubbles, which are generally ~1–3 microns in diameter, consist of a gas core surrounded by a surfactant such as phospholipid, protein, or polymer. The gas core typically contains a perfluorocarbon or other inert compound with low solubility in water in order to prolong stability in circulation. Antibodies or peptides can be conjugated to the shell for targeted imaging of specific tissues [17–22]. For drug and gene delivery applications, however, even in the absence of antibody conjugation ultrasound can be focused to induce microbubble destruction at a target site.
Synthesis and Characterization of Metal–Organic Frameworks
Published in T. Grant Glover, Bin Mu, Gas Adsorption in Metal-Organic Frameworks, 2018
Sonochemical synthesis is another method for the fast crystal growth of MOFs, where high-energy ultrasound is used for the reaction of the solvent mixture. The ultrasonic frequency, which is higher than the upper audible limit of human hearing, covers from 20 kHz to gigahertz. For MOF synthesis, 20–40 kHz of frequencies are often used; however, the wavelength of ultrasound is much larger than the dimension of molecules so that the ultrasound irradiation does not directly interact with reactants to form or cleave chemical bonding. During the application of high-energy ultrasound to the reaction mixture, microbubbles can be formed when acoustic pressure drops below the vapor pressure of the solvent mixture, while the contraction of the bubbles is observed when the acoustic pressure increases. These bubbles repeat the expansion and contraction processes under the irradiation of ultrasound and are collapsed violently. The collapse of microbubbles is nearly an adiabatic process; therefore, a large amount of energy is released which can result in hot spots with high transient temperature and pressure. The acoustic cavitation also forms microliquid jet when the bubbles are collapsed near the solid surface, which can activate the MOF surface and increase the mass transfer rate.47 Consequently, the increased nucleation and crystal growth rates contribute to drastically reduce the reaction time.
Microwave Hybridization for Advanced Biorefinery
Published in Veera Gnaneswar Gude, Microwave-Mediated Biofuel Production, 2017
Although microwaves provide for rapid heating of the reaction materials, mass transfer of the reaction medium is often compromised in these reactors (Martinez-Guerra, V.G. Gude 2014a). In addition, they interact with reaction materials at a higher rate which results in hot spot formation and thermal runaway. This phenomenon clearly indicates the necessity for a mixing mechanism which can ensure uniform heating of reaction materials and mass transfer promoted by the unusual heating advantage of the microwaves. In the similar context, ultrasound are capable of promoting heat and mass transfer within the reaction medium due to the intense mixing they provide as a result of the acoustic cavitations which form microbubbles with air. The formation-release-collapse of these microbubbles provides cooling and heating cycles at microscales accompanied by high thermal and pressure release. Since this energy release is at micro levels, this energy is not adequate to cause high temperature gains in the reaction medium. This clearly presents a limitation for ultrasound mediated reactions (Martinez-Guerra, V.G. Gude 2014a). These reactions require external heating to enhance the process kinetics.
Degradation of Methyl Orange by ozone microbubble process with packing in the bubble column reactor
Published in Environmental Technology, 2023
Jie Dong, Jiakang Yao, Jinliang Tao, Xiaoping Shi, Feng Wei
Microbubbles(MBs) are bubbles less than 50μm in diameter. Compared with conventional millimeter bubbles(MLBs), MBs have the advantages of smaller bubble size, larger interfacial area, lower rise velocity, higher zeta potential, and higher interior pressure[18]. Therefore, microbubble technology is applied extensively in environmental engineering, biomedical engineering, marine culture, and so on. Many researchers also found that microbubble technology can effectively improve ozone transfer and promote the degradation of organic pollutants from wastewater. In a pilot test, Ryskie et al. [19] found that it was effective to remove ammonia from synthetic wastewater and five actual mine wastewaters by using the ozone MBs. Jabesa et al. [20] used ozone MBs and ozone MLBs to degrade dimethyl sulfoxide. The results showed that the ozone MBs could completely remove dimethyl sulfoxide in a shorter time with the same other operating parameters, and the ozone utilization of ozone MBs (65 - 79%) was higher than that of conventional ozone MLBs (21 - 48%). Wang et al. [21] studied using ozone MBs to degrade concentrated leachate, and the results showed good treatment results with 76.0% and 69.9% degradation of COD and TOC, respectively. Although there are many studies on ozone MBs, the existing technology is not very mature and is mostly at the laboratory and pilot stage, which needs to be explored further. In addition, there are no literature reports on the addition of packings to the bubble column reactor of ozone MBs to improve the gas–liquid distribution and thus the treatment efficiency.
Characterization of a Doped MnO2Al2O3 Catalyst and its Application Inmicrobubble Ozonation for Quinoline Degradation
Published in Ozone: Science & Engineering, 2021
Xinwang Liu, Shutao Wang, Hao Yang, Zhisheng Liu, Ying Wang, Fucheng Meng, Jun Ma, Oksana S. Izosimova
Bubble size is a critical factor for ozonation efficiency (Azuma et al. 2019). Macrobubbles (mean bubble size of approximately 1 mm) used in the traditional ozonation process leads to poor contact area at the gas-liquid interface and low utilization efficiency. Changing the bubble size may be an effective way to improve the mass transfer efficiency, because it can enhance the solubility of ozone by improving the contact area and retention time. Generally, microbubbles are tiny bubbles with a diameter of 10–50 μm (Wu et al. 2019). Compared to normal-sized bubbles generated by aeration, microbubbles have advantages of higher density, large gas–liquid contact ratio, and high internal pressure, which can improve the mass transfer rate from gas to liquid (Surabhi et al. 2019). The high concentration of ions gathered at the interface will release accumulated chemical energy when the microbubbles rupture instantaneously, and a large amount of •OH can thus be generated. It is found that the decolorization efficiency and chemical oxygen demand (COD) removal efficiency by microbubbles of ozone is 1.2 times that of normal-sized ozone bubbles (Sun et al. 2020). The total mass transfer coefficient and the removal efficiency of TOC was 1.8 times and 1.3 times higher than those of normal-sized ozone bubbles, respectively.
Recent developments on foaming mechanical and electronic techniques for the management of varicose veins
Published in Expert Review of Medical Devices, 2019
C. Davide Critello, Salvatore A. Pullano, Thomas J. Matula, Stefano De Franciscis, Raffaele Serra, Antonino S. Fiorillo
The main cause of these adverse events lies in the ‘texture’ of foams that are injected into veins. This characteristic appears to be related to the dimension of bubbles. Since neurological adverse events are almost transients, the size of foam-derived bubbles is likely the cause of mechanical obstructions in vessels. Relatively large bubbles can behave like emboli in the blood circulation. Small bubbles, on the other hand, have been proven safe, as evidenced by the common use of ultrasound contrast agents, microbubbles with a size below 20 µm. Ultrasound contrast agents in CEUS procedures represent a clear and effective example of how it is possible to inject microbubbles safely into the bloodstream without compromising the patient’s health. Smaller bubbles also provide advantages in foam sclerotherapy: the smaller the bubbles are, the higher the foam density is, and so foam (and thus treatment) can last longer. Moreover, smaller bubbles lead to a larger contact surface area, increasing the efficacy of treatment.