The present study investigated the effects of microwave (MW) radiation applied under a sublethal temperature on Escherichia coli. The experiments were conducted at a frequency of 18 GHz and at a temperature below 40°C to avoid the thermal degradation of bacterial cells during exposure. The absorbed power was calculated to be 1,500 kW/m 3 , and the electric field was determined to be 300 V/m. Both values were theoretically confirmed using CST Microwave Studio 3D Electromagnetic Simulation Software. As a negative control, E. coli cells were also thermally heated to temperatures up to 40°C using Peltier plate heating. Scanning electron microscopy (SEM) analysis performed immediately after MW exposure revealed that the E. coli cells exhibited a cell morphology significantly different from that of the negative controls. This MW effect, however, appeared to be temporary, as following a further 10-min elapsed period, the cell morphology appeared to revert to a state that was identical to that of the untreated controls. Confocal laser scanning microscopy (CLSM) revealed that fluorescein isothiocyanate (FITC)-conjugated dextran (150 kDa) was taken up by the MW-treated cells, suggesting that pores had formed within the cell membrane. Cell viability experiments revealed that the MW treatment was not bactericidal, since 88% of the cells were recovered after radiation. It is proposed that one of the effects of exposing E. coli cells to MW radiation under sublethal temperature conditions is that the cell surface undergoes a modification that is electrokinetic in nature, resulting in a reversible MW-induced poration of the cell membrane.The effects of MW radiation on microorganisms have been studied and debated for more than half a century (3,4,10,12,17,20,28,29,35). The nature of the debate surrounding this interaction has often referred to the existence of so-called specific microwave (MW) effects that are nonthermal in nature (4,10,13,17,20,28,29). Much has been published supporting the notion that a range of specific MW effects exist and can be identified in terms of their manifestations on cell physiology (2,4,10,13,27,28). For example, Dreyfuss and Chipley examined the effects of MW radiation (2.45 GHz) at sublethal temperatures on the metabolic activities of a range of enzymes expressed by the bacterium Staphylococcus aureus (10). These results suggested that MW radiation affected S. aureus cells in a way that could not have been explained solely by thermaleffect theories. It has also been found that Burkholderia cepacia bacteria could be wholly inactivated using MW radiation at sublethal temperatures at a frequency of 20 GHz (2). Samarketu et al. (25) examined the effects of MW radiation at a frequency of 9.575 GHz on the physiological behavior of Cyanobacterium dolium (Anabaena dolium). The authors suggested that MW radiation nonthermally induced different biological effects by changing the protein structures by differentially partitioning the ions and altering the rates and/or directions of biochemical reactions (25)...
Microstructural characterization of hot work tool steel processed by selective laser melting was carried out. The findings shed light on the interrelationship between processing parameters and the microstructural evolution. It was found that the microstructure after layerwise processing partially consists of metastable-retained austenite which transforms to martensite in a subsequent tensile test. This improves the mechanical properties of the hot work tool steel enabling direct application.
Microwave processing of materials is a relatively new technology advancement alternative that provides new approaches for enhancing material properties as well as economic advantages through energy savings and accelerated product development. This paper presents a state-of-theart review of microwave technologies, processing methods and industrial applications. The characteristics of microwave interactions with materials are outlined together with the challenges that difficult to process materials present. To fully realise the potential benefits of microwave and hybrid processes, it is essential to scale-up process and system designs to large batch or continuous processes. This necessitates computational modelling and simulation, system design and integration and a critical assessment of the costs and benefit analysis. Impediments to industrial applications are identified and development opportunities that take advantage of unique performance characteristics of microwaves are discussed. Clearly, advantages in utilising microwave technologies for processing materials include penetrating radiation, controlled electric field distribution and selective and volumetric heating.The aim of the work presented in this paper is to help guide those interested in using microwaves to improve current materials processing. Microwave fundamentals are described to provide a brief awareness of the advantages and limitations of microwaves in the processing of materials. Furthermore, the limitations in current understanding are included as a guide for potential users and for future research and development activities. Examples of successful applications are given to illustrate the characteristics of materials, equipment and processing methods applicable to industrial microwaves. Economic considerations are described and costs are provided as guidelines in determining the viability of using microwaves for processing materials.
FeMn‐Ag alloys as potential bioresorbable implant materials were prepared by selective laser melting (SLM) from mixed powders of FeMn and Ag. The microstructure of the samples is characterized by presence of few micrometers to several tens of micrometer large Ag‐phases within the FeMn matrix. The microstructure dependent corrosion and biomineralization processes in simulated body fluid (SBF) were studied in‐situ by means of electrochemical impedance spectroscopy (EIS). The microstructure and local surface film formation were analyzed by electron microscopy (FE‐SEM) and Raman microscopy. The results clearly show that the Ag‐phase acts as a local cathode within the FeMn matrix. However, surface film formation is observed both for the Ag‐ and the FeMn‐phases, which potentially lowers the self‐corrosion as well as the galvanic coupling of the two phases. The formation of AgCl on the Ag‐phases and mixed metal phosphates on the FeMn‐phases can be observed by local Raman spectroscopic analysis in combination with FE‐SEM characterization.
The aim of the present review was to evaluate the literature suggesting that consideration be given to the existence of specific microwave (MW) effects on prokaryotic microorganisms; that is, effects on organisms that cannot be explained by virtue of temperature increases alone. This review considered a range of the reported effects on cellular components; including membranes, proteins, enzyme activity as well as cell death. It is concluded that the attribution of such effects to non-thermal mechanisms is not justified due to poor control protocols and because of the possibility that an unmeasurable thermal force, relating to instantaneous temperature (T (i)) that occurs during MW processing, has not been taken into account. However, due to this lack of control over T (i), it also follows that it cannot be concluded that these effects are not 'non-thermal'. Due to this ambiguity, it is proposed that internal 'micro'-thermal effects may occur that are specific to MW radiation, given its inherent unusual energy deposition patterning.
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