Biosurfactants for microbubble preparation and application

Biosurfactants can be classified by their chemical composition and their origin. This review briefly describes various classes of biosurfactants based on their origin and introduces a few of the most widely used biosurfactants. The current status and future trends in biosurfactant production are discussed, with an emphasis on those derived from plants. Following a brief introduction of the properties of microbubbles, recent progress in the application of microbubble technology to molecular imaging, wastewater treatment, and aerobic fermentation are presented. Several studies on the preparation, characterization and applications of biosurfactant-based microbubbles are reviewed.     

Development of a high temperature-atmospheric pressure environmental cell for high-resolution TEM

An environmental cell for high-temperature, high-resolution transmission electron microscopy of nanomaterials in near atmospheric pressures is developed. The developed environmental cell is a side-entry type with built-in specimen-heating element and micropressure gauge. The relationship between the cell condition and the quality of the transmission electron microscopic (TEM) image and the diffraction pattern was examined experimentally and theoretically. By using the cell consisting of two electron-transparent silicon nitride thin films as the window material, the gas pressure inside the environmental cell is continuously controlled from 10(-5)?Pa to the atmospheric pressure in a high-vacuum TEM specimen chamber. TEM image resolutions of 0.23 and 0.31?nm were obtained using 15-nm-thick silicon nitride film windows with the pressure inside the cell being around 5?×?10(-5) and 1?×?10(4)?Pa, respectively.     

A comparative study of microbubble generation by mechanical agitation and sonication

As focus on the potential applications of microbubbles increases, information about the efficiency of generation methods and their effects on the properties and stability of microbubbles is crucial in the selection of an appropriate method to generate microbubbles with the desired properties. This paper evaluates the generation efficiencies of two commonly used methods, mechanical agitation and sonication, in two surfactant systems. The results demonstrated that sonication was more effective than mechanical agitation in the generation of microbubbles in terms of higher gas hold-up, smaller bubble size, and larger interfacial area. Analysis of the changes in bubble size over time revealed that the existence of a critical diameter for the shrinkage of microbubbles. The behavior of microbubbles and the critical diameter depended on the generation method employed and the surfactant used.

Industrial relevance

Microbubble technology has gradually become accepted as a cost-effective and environmentally friendly technology with great potential within almost every field of the food industry. Selection of a suitable method to generate microbubbles with the desired properties is crucial. Mechanical agitation and sonication are two commonly used methods for microbubble generation. However, systematic information on their generation efficiency and effects on the properties of microbubbles is not available. Thus, a comparative study was conducted in this paper.     

Precision die-casting of optical MU/SC conversion sleeve

The performance of MU/SC conversion sleeve produced by bulk metallic glass (Zr₅₅Al₁₀Ni₅Cu₃₀) was examined. A precision die-casting method was applied to improve size accuracy. The size accuracy of the conversion sleeve produced by the precision die-casting method was ±1 μm, and optical insertion loss (Li) was less than 0.3 dB for a standard value. The wear resistance of metallic glass is improved by surface oxidation treatment in air at 673 K. The MU/SC conversion sleeve produced from bulk metallic glass has superior characteristics for optical parts.     

Photostability of Isovaline and its Precursor 5-Ethyl-5- methylhydantoin Exposed to Simulated Space Radiations

Aqueous solutions of isovaline and its precursor molecule, 5-ethyl-5-methylhydantoin, were irradiated with ultraviolet and γ-ray photons, to evaluate their structural stability against space radiation. The degree of photolysis was measured and irradiation products were identified using chiral, reversed-phase and ion-exchange high-performance liquid chromatography. The experimental results show that the degree of photolysis of 5-ethyl-5-methylhydantoin is more significant than that of isovaline under ultraviolet light irradiation, while the results under γ-ray irradiation are the opposite. As the products of isovaline photolysis, aspartic acid, serine, glutamic acid and alanine were dominantly detected.     

Non‐Enzymatic Geometry‐Selective Acylation of Tri‐ and Tetrasubstituted α,α′‐Alkenediols

A highly geometry‐selective organocatalytic acylation of tri‐ and tetra‐substituted 2‐alkylidene‐1,3‐propanediols has been developed. The highly E‐selective acylation of various tetrasubstituted 2‐alkylidene‐1,3‐propanediols was achieved in 96 to >99% selectivity for the first time by a non‐enzymatic protocol.     

A New Form of Rolling Contact Damage in Grease-Lubricated,Deep-Groove Ball Bearings

A new form of rolling contact damage was discovered in the fatigue tests of series 6206 deep groove ball bearings under pure radial load with grease lubrication. The appearance of the damage reveals a few cracks at right angles to the rolling direction of the ball, along with the formation of a dent about 20 μ m deep in the raceway surface. This is found to occur only on the stationary outer ring raceway and the ball surface and is distributed widely within the load zone. Furthermore, under the raceway surface several cracks propagating into the substrate at an angle of about 60-80 degrees relative to the raceway surface are observed not only under the damage site but also in other nearby locations. Only the cracks at the damage position open up to the surface. The grease used for the test contained a lithium complex thickener with mineral oil as the base oil with a kinematic viscosity of 141 mm²/s at 40°C. On the test bearings two pure radial load levels of 9.14 and 12.13 kN were applied. In order to prevent the occurrence of seizure at each load, the speed of the inner ring of the test bearing was maintained at 1800-2500 min^{? 1} and 600-800 min^{? 1}, respectively, to keep the outer ring circumference temperature below 65°C. It is suggested that the damage is caused by metal-to-metal contacts due to lubricant starvation under grease lubrication and to a decrease in oil film thickness due to local increases in temperature.     

Spectrum sharing method for secondary systems using frequency priority table to reduce inter-secondary interference

Because of the rapid development of cognitive radio technologies, research on sharing frequency resources allocated to primary users with secondary users has attracted much attention. If a frequency band is unused by the primary users, multiple secondary users are expected to share the spectrum in a future wireless communication network. To efficiently share the spectrum among secondary systems, we propose a novel channel allocation method that uses a frequency priority table generated based on the location of the secondary system. By using this method, the interference with other systems is autonomously reduced by selecting channels. Moreover, a power control method is also proposed for protecting the secondary systems that are allocated to the channels with higher priority.