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At least 361 records · Page 20Linked to original sources
PubMed1999

Heat transfer analysis of staphylococcus aureus on stainless steel with microwave radiation.

Staphylococcus aureus (NCTC 6571; Oxford strain) on stainless steel discs was exposed to microwave radiation at 2450 MHz and up to 800 W. Cell viability was reduced as the exposure time increased, with complete bacterial inactivation at 110 s, attaining a temperature of 61.4 degrees C. The low rate of temperature rise, RT, of the bacterial suspension as compared with sterile distilled water or nutrient broth suggests a significant influence of the microwave sterilization efficacy on the thermal properties of the micro-organisms. The heat transfer kinetics of thermal microwave irradiation suggest that the micro-organism has a power density at least 51-fold more than its surrounding liquid suspension. When the inoculum on the stainless steel disc was subjected to microwave radiation, heat conduction from the stainless steel to the inoculum was the cause of bacteriostasis with power absorbed at 23.8 W for stainless steel and 0.16 W for the bacteria-liquid medium. This report shows that the microwave killing pattern of Staph. aureus on stainless steel was mainly due to heat transfer from the stainless steel substrate and very little direct energy was absorbed from the microwaves.

Hot Temperature↗
PubMed1996

Microwave-enhanced fixation of rabbit articular cartilage.

Cartilage, being highly aqueous, is difficult to preserve for electron microscopy without artefacts. Microwave-enhanced fixation is suggested as a standard method for block samples of this material, with dimensions of up to 12 x 7 x 3 mm. Cartilage samples from the tibial plateau of adult rabbits were fixed by conventional, cryo- or microwave-enhanced fixation. Constant or cyclical microwave irradiation of samples, immersed in fixatives, was carried out to varying final solution temperatures. Microwave-enhanced fixation and staining is shown to be both rapid and reproducible, giving fine structural preservation. Below 323 K microwave fixation always gave excellent preservation of the fine structure within seconds. At higher temperatures thermal artefacts were introduced. In this study the microwave-enhanced fixation is equal in quality to the test conventional immersion fixation and is nearly as fast as cryo-preservation. It provides a standardized, reproducible fixation for morphological studies on cartilage with good process control.

Animals↗
PubMed2000

Effects of microwave irradiation and chemical fixation on the localization of perisinusoidal cells in rat liver by gold impregnation.

Modified gold impregnation is one of the methods that are used in light microscopical demonstration of hepatic perisinusoidal cells. This method has some disadvantages, such as restriction of fixation time to 16 h, which allows limited time for processing the tissues, especially when dealing with a large amount of material, and a long impregnation time (16-24 h). We investigated the effect of prolonged fixation on the staining of sections, to shorten the time needed for gold impregnation by using microwave irradiation. Liver specimens were fixed in Baker's calcium-formalin for different periods of time. After fixation, frozen sections were impregnated in gold chloride solution either at room temperature or in a microwave oven. The staining quality of the sections which had been impregnated in the microwave oven for a much shorter time were equal to or even superior to the ones impregnated at room temperature. Prolonging the fixation time up to 7 days did not affect the staining results by microwave irradiation, whereas satisfactory results were not obtained from sections stained at room temperature and fixed for more than 3 days. We conclude that microwave irradiation can be used to shorten the impregnation time in gold chloride solution and the duration of fixation can be prolonged up to 3 days in the original method and up to 7 days when microwave irradiation is used during impregnation.

Animals↗
PubMed2003

Microwave cell death: Immunohistochemical and enzyme histochemical evaluation.

In Japan, microwave coagulation therapy (MCT) has been used for the management of primary and metastatic liver cancer. Needle biopsy examination from the lesion has frequently shown the presence of nucleated cancer cells in histopathological examinations, prompting the conclusion that cancer cells are not completely eliminated by microwave therapy, whereas computed tomography and ultrasonography examinations show tumor regression. To determine whether microwave-treated tissue contains functionally viable cells, an examination of the Na+-K+-ATPase protein and its activity using immunohistochemical and enzyme histochemical methods were carried out in microwave-treated rat liver. Four concentric, morphologically identifiable zones around the microwave probe needle appeared 2 days after treatment. Zone A, which was between the innermost spongy zone and the outer necrotic zone, contained only slight morphological alterations in the hepatocytes, which had slightly hyperchromatic nuclei and mildly eosinophilic cytoplasm. The hepatocytes in zone A were found to be positive for the Na+-K+-ATPase antigenicity but negative for enzyme activity, indicating that zone A was undergoing cell death, although morphologically this was not discernible. This type of cell death caused by microwave treatment is morphologically different from previously known types of cell death, either oncosis or apoptosis.

Animals↗
PubMed2001

Transpapillary microwave coagulation therapy for recanalizing self-expandable metallic stents occluded by tumor ingrowth: initial experience.

Percutaneous microwave coagulation for recanalizing stents occluded by tumor ingrowth has been reported. With this technique, however, the percutaneous drain diminishes the quality of life in patients with unresectable tumors and a limited prognosis. Transpapillary microwave ablation was attempted in three patients with occluded stents. After a sheath had been inserted into the proximal hepatic duct across the occluded region, a microwave electrode was introduced into the intrahepatic duct via the sheath. We used microwave therapy with an output power of 40 W, based on our previous in vitro study. Except in one patient, the stents were successfully recanalized with one or two attempts. In one patient who underwent ablation in the intrahepatic duct, a 1.8-mm electrode enabled recanalization of the stent. In another who underwent ablation in the extrahepatic duct, however, a larger electrode was required. There were no procedure-related complications. Transpapillary microwave coagulation of occluded stents appears to be an alternative to percutaneous microwave coagulation with an electrode fitting the stent size. The technique might be easier with the use of a redesigned electrode with a guide wire lumen.

Aged↗
PubMed2004

Investigation of the thermal and tissue injury behaviour in microwave thermal therapy using a porcine kidney model.

Minimally invasive microwave thermal therapies are being developed for the treatment of small renal cell carcinomas (RCC, d<3 cm). This study assessed the thermal history and corresponding tissue injury patterns resulting from microwave treatment of the porcine renal cortex. Three groups of kidneys were evaluated: (1) in vitro treated, (2) in vivo with 2-h post-treatment perfusion (acute) and (3) in vivo with 7-day post-treatment perfusion (chronic). The kidneys were treated with an interstitial water-cooled microwave probe (Urologix, Plymouth, MN) that created a lesion centered in the renal cortex (50 W for 10 min). The thermal histories were recorded at 0.5 cm radial intervals from the probe axis for correlation with the histologic cellular and vascular injury. The kidneys showed a reproducible 2 cm chronic lesion with distinct histologic injury zones identified. The thermal histories at the edge of these zones were found using Lagrangian interpolation. The threshold thermal histories for microvascular injury and stasis appeared to be lower than that for renal epithelial cell injury. The Arrhenius kinetic injury models were fit to the thermal histories and injury data to determine the kinetic parameters (i.e. activation energy and frequency factor) for the thermal injury processes. The resultant activation energies are consistent in magnitude with those for thermally induced protein denaturation. A 3-D finite element thermal model based on the Pennes bioheat equation was developed and solved using ANSYS (V7.0). The real geometry of the kidneys studied and temperature dependent thermal properties were used in this model. The specific absorption rate (SAR) of the microwave probe required for the thermal modelling was experimentally determined. The results from the thermal modelling suggest that the complicated change of local renal blood perfusion with temperature and time during microwave thermal therapy can be predicted, although a first order kinetic model may be insufficient to capture blood flow changes. The local blood perfusion was found to be a complicated function of temperature and time. A non-linear model based on the degree of vascular stasis was introduced to predict the blood perfusion. In conclusion, interstitial microwave thermal therapy in the normal porcine kidney results in predictable thermal and tissue injury behaviour. Future work in human kidney tissue will be necessary to confirm the clinical significance of these results.

Algorithms↗
PubMed2001

TLM simulation of microwave sintering of ceramics using SiC stimulus.

Microwave heating technology is becoming a successful technique used for sintering ceramic materials. However, various aspects of sintering experiments, such as the use of process stimulus and the preparation of sample arrangements, depend mainly on human expertise. The Transmission Line Matrix (TLM) method is first used to solve the combined electromagnetic and thermal equations modeling microwave heating of dielectric materials. It is then used to simulate microwave sintering of a low-loss ceramic material in a multimode microwave cavity. To enhance the microwave sintering process, Silicon Carbid (SiC) was first used as a susceptor and in a picket fence arrangement. As multiple samples may be processed in a microwave oven, the TLM was used to model such a process, and the introduction of SiC as a stimulus was also examined. Results show the importance of the stimulus thickness and configuration on the uniformity and density of the electromagnetic field distribution and, therefore, on the power dissipation within the ceramic load.

Aluminum Oxide↗
PubMed2003

A review of microwave-assisted polymer chemistry (MAPC).

As a relatively new source of processing energy, microwave energy offers many compelling advantages in materials processing over conventional heat sources. These advantages include greater flexibility, greater speed and energy savings, improved product quality and properties, and synthesis of new materials that cannot be produced by other heating methods. Studies of microwave processing of polymeric materials in the early 1960s led to a successful industrial application in the rubber industry. Since the mid-1980's, there has been a great deal of interest in microwave processing of polymeric materials worldwide. The discipline can be categorized in two major fields: microwave-assisted polymer physics (MAPP) and microwave assisted polymer chemistry (MAPC). This paper offers an overview of the state-of-the-art research on the field of MAPC, including polymer processing (curing of thermosets, processing of thermoplastics, and joining), polymer synthesis, plasma modification of polymer surfaces, plasma polymerization, polymer degradation, and production of nanomaterials. Most of these studies have focused on laboratory-scale, exploratory efforts. Challenges and possible future directions for the commercialization of microwave processing technologies are discussed.

Biocompatible Materials↗
PubMed2003

Microwave sintering process model.

In order to simulate and optimize the microwave sintering of a silicon nitride and tungsten carbide/cobalt toolbits process, a microwave sintering process model has been built. A cylindrical sintering furnace was used containing a heat insulating layer, a susceptor layer, and an alumina tube containing the green toolbit parts between parallel, electrically conductive, graphite plates. Dielectric and absorption properties of the silicon nitride green parts, the tungsten carbide/cobalt green parts, and an oxidizable susceptor material were measured using perturbation and waveguide transmission methods. Microwave absorption data were measured over a temperature range from 20 degrees C to 800 degrees C. These data were then used in the microwave process model which assumed plane wave propagation along the radial direction and included the microwave reflection at each interface between the materials and the microwave absorption in the bulk materials. Heat transfer between the components inside the cylindrical sintering furnace was also included in the model. The simulated heating process data for both silicon nitride and tungsten carbide/cobalt samples closely follow the experimental data. By varying the physical parameters of the sintering furnace model, such as the thickness of the susceptor layer, the thickness of the allumina tube wall, the sample load volume and the graphite plate mass, the model data predicts their effects which are helpful in optimizing those parameters in the industrial sintering process.

Ceramics↗
PubMed2004

Measurement of DNA damage after acute exposure to pulsed-wave 2450 MHz microwaves in rat brain cells by two alkaline comet assay methods.

PURPOSE: To investigate the effect of 2450 MHz pulsed-wave microwaves on the induction of DNA damage in brain cells of exposed rats and to discover whether proteinase K is needed to detect DNA damage in the brain cells of rats exposed to 2450 MHz microwaves. MATERIALS AND METHODS: Sprague-Dawley rats were exposed to 2450 MHz pulsed-wave microwaves and sacrificed 4 h after a 2-h exposure. Rats irradiated whole-body with 1 Gy (137)Cs were included as positive controls. DNA damage was assayed by two variants of the alkaline comet assay on separate aliquots of the same cell preparation. RESULTS: Significant DNA damage was observed in the rat brain cells of rats exposed to gamma-rays using both versions of the alkaline comet assay independent of the presence or absence of proteinase K. However, neither version of the assay could detect any difference in comet length and/or normalized comet moment between sham- and 2450 MHz pulsed-wave microwave-exposed rats, regardless of the inclusion or omission of proteinase K in the comet assay. CONCLUSIONS: No DNA damage in brain cells was detected following exposure of rats to 2450 MHz microwaves pulsed-wave at a specific absorption rate of 1.2 W kg(-1) regardless of whether or not proteinase K was included in the assay. Thus, the results support the conclusion that low-level 2450 MHz pulsed-wave microwave exposures do not induce DNA damage detectable by the alkaline comet assay.

Animals↗
PubMed2004

Repeated exposure to low-level extremely low frequency-modulated microwaves affects baseline and scopolamine-modified electroencephalograms in freely moving rats.

PURPOSE: To compare in the electroencephalogram of rats the effects of scopolamine (an acetylcholine receptor antagonist) alone and after repeated exposure to low-level microwaves modulated at extremely low frequency. MATERIALS AND METHODS: Averaged frequency spectra (0.5-30 Hz) of the electroencephalogram were studied in freely moving rats with carbon electrodes implanted into the somatosensory cortex. The rats were repeatedly (3 days, 30 min day(-1)) exposed to low-intensity (approximately = 0.3 mW cm(-2)) microwaves (915 MHz, 20-ms pulse duration), amplitude modulated (square-wave) at extremely low frequency (4 Hz). RESULTS: The exposure to extremely low frequency microwaves alone significantly enhanced the fast electroencephalographic rhythms (18-30 Hz). This effect was observed neither in subsequent sham-exposure experiment nor in radiation-naïve animals. In the microwave-exposed rats, scopolamine (0.1 mg kg(-1), subcutaneously) did not cause a slowing in the electroencephalogram that was shown in non-exposed rats. A similarity between the scopolamine-induced electroencephalogram effect in the microwave-exposed rats and that of physostigmine (enhancing the acetylcholine level in the brain) in radiation-naïve animals was noted. This paradoxical phenomenon stimulates new experimentation for understanding its mechanism(s). CONCLUSIONS: The data obtained provide additional evidence that repeated low-level exposure to extremely low frequency microwaves can modify an activity of cholinergic system in the brain.

Animals↗
PubMed1985

Thermal aspects of biological effects of microwaves in Saccharomyces cerevisiae.

The formation of zygotes between two haploid strains of yeast (Saccharomyces cerevisiae) was determined under treatment with microwaves of 9.4 and 17 GHz at power levels up to 50 and 60 mW/cm2 and a specific absorption rate below 24 mW/g, or with conventional heating. Microwave treatments at 9.4 GHz or 17 GHz at a power density of 10 mW/cm2 produced an increase in zygote formation equivalent to that produced by conventional heating in an incubator, i.e. equivalent to a rise in temperature of 0.5 or 1 degrees C. At higher power densities zygote formation was slightly increased by microwaves at 17 GHz as compared to microwaves at 9.4 GHz probably due to the higher absorption of microwaves at 17 GHz by intracellular water molecules. Under these conditions, microwaves had no effect on cell survival or the induction of cytoplasmic 'petite' mutations.

Hot Temperature↗
PubMed2001

Microwave process for volatile organic compound abatement.

The CHA Corporation has completed the U.S. Air Force Phase II Small Business Innovation Research program to investigate the feasibility of using a novel microwave-based process for the removal and destruction of volatile organic compounds (VOCs) in effluents from noncombustion sources, such as paint booth ventilation streams. Removal of solvents by adsorption, followed by the regeneration of saturated granular activated carbon (GAC) by microwave energy, was achieved in a single fixed-bed reactor. Microwave regeneration of the fixed-bed-saturated carbon restored the original GAC adsorption capacity. After 20 adsorption/regeneration cycles, the adsorption capacity dropped from 13.5 g methyl ethyl ketone (MEK)/100 g GAC to 12.5 g MEK/100 g GAC. During microwave regeneration of the GAC fixed bed, the concentrated desorbed paint solvent was oxidized by passing the solvent mixture through a fixed bed of an oxidation catalyst mixed with silicon carbide in a microwave reactor. A 98% oxidation efficiency was consistently achieved from the oxidation of VOCs in the microwave catalytic reactor.

Adsorption↗
PubMedDate not supplied

A simple and rapid microwave-assisted hematoxylin and eosin staining method using 1,1,1 trichloroethane as a dewaxing and a clearing agent.

The use and practicability of microwave-assisted staining procedures in routine histopathology has been well established for more than 17 years. In the study reported here, we aimed to examine an alternative approach that would shorten the duration of dewaxing and clearing steps of hematoxylin and eosin (H & E) staining of paraffin sections by using a microwave oven. Although xylene is one of the most popular dewaxing and clearing agents, its flammability restricts its use in a microwave oven; thus we preferred 1,1,1 trichloroethane, which is not flammable, as the dewaxing and clearing agent in the present study. In Group I and Group II (control groups), intestine was processed with xylene and 1,1,1 trichloroethane, respectively. The sections were then stained with H & E according to the conventional staining protocol at room temperature and subdivided into two groups according to the duration of dewaxing and clearing in xylene. In Groups III and IV (experimental groups) similar tissues were processed with xylene and 1,1,1 trichloroethane, respectively; however, sections from these groups were divided into four subgroups to study the period required for dewaxing and clearing in 1,1,1 trichloroethane, then stained with H & E in the microwave oven at 360 W for 30 sec. Our conventional H & E staining procedure, which includes dewaxing, staining and clearing of sections, requires approximately 90 min, while our method using 1,1,1 trichloroethane and microwave heating required only 2 min. Our alternative method for H & E staining not only reduced the procedure time significantly, but also yielded staining quality equal or superior to those stained the conventional way. Our results suggest that 1,1,1 trichloroethane can be used effectively and safely as a dewaxing and clearing agent for H & E staining in a microwave oven.

Eosine Yellowish-(YS)↗
PubMed1979

Determination of a thermal equivalent of millimeter microwaves in living cells.

Recent microwave experiments have shown frequency dependent influences on the growth rate of bacteria. To determine whether microwaves are able to affect growth (or to induce lesions in cellular DNA of yeast cells), experiments were performed with millimeter microwaves at frequencies between 70 and 75 GHz. Saccharomyces cerevisiae cells were irradiated on millipore filter discs placed on agar plates in open petri dishes. A diploid strain of yeast (D5, Zimmerman), that is sensitive to genetic insult was used to study the effects of temperature and of microwave irradiation on cell survival, induction of mitotic recombination, and induction of cytoplasmic "petite" mutations. No evidence of altered survival, impaired function, or structural injury was seen at either frequency, even at power densities as high as 60 mW/cm2. Conventional heating had no deleterious effects until temperatures of specimens exceeded 50 degrees C. In addition, two haploid strains of yeast of opposite mating type were compared with respect to temperature and microwave treatment for formation of zygotes. The elevation of temperature due to the microwave treatment at 60 mW/cm2 and 2 mm distance was estimated to correspond to 3 degrees C.

DNA, Fungal↗
PubMed1979

Microwave irradiation and ambient temperature interact to alter rat behavior following overnight exposure.

Each of twelve male hooded rats was trained to insert its head into a food cup for food pellets on a random-interval schedule of reinforcement. After performances stabilized, the rats were assorted into 3 groups of 4 animals. Groups were matched for response rates. Animals were exposed in groups of 4 for 15.5 h to CW 2450-MHz microwaves once every 6 nights. Animals of each group were exposed to microwaves at only one power density, either 5, 10, or 15 mW/cm2; they were exposed three times at an ambient temperature of 22 degrees C, then three times at 28 degrees C, and then once more at 22 degrees C. The relative humidity was 50% during all exposures. Rats were sham irradiated (at 0 mW/cm2) the night before each microwave exposure. Behavior was tested daily after termination of microwave irradiation or after sham exposures. None of the exposures to microwaves at 22 degrees C altered rates or durations of responding. Exposures at 28 degrees C reduced response rates and increased response durations in direct relation to the power density. The results are interpreted as the transient debilitation of behavior produced by the interaction of a mild elevation of ambient temperature and microwave irradiation.

Animals↗
PubMed1980

Cook/chill foodservice system with a microwave oven: aerobic plate counts from beef loaf, potatoes and frozen green beans.

The purpose was to evaluate microbiological quality and end temperature (ET) of portioned food after heating in a microwave oven as used in a hospital cook/chill foodservice system. Beef loaf (15 kg), potatoes (6 kg), and green beans (5 kg) were prepared in a laboratory. After initial cooking to 60 degrees C, and storage (7 degrees C for 24 h), beef loaf (100 g) was microwave heated: 20, 50, 80 or 110 s. Potatoes were reconstituted, stored (7 degrees C for 24 h), portioned (100 g/portion), and microwave-heated: 25, 45, 65 or 84 s. Beans were thawed (7 degrees C for 24 h), portioned (100 g/portion), and microwave-heated: 20, 50, 80 or 110 s. Aerobic plate counts (APC) for foods were obtained throughout product flow. Wide ranges of Et and of APC in foods indicates that research is needed, for greater control of microwave-heating through advanced microwave engineering and food technology, to produce food with constant microbiological quality.

Animals↗
PubMed1985

Data analysis reveals significant microwave-induced eye damage in humans.

Appleton and McCrossan undertook a study for the U.S. Army at Ft. Monmouth to determine if microwave exposure would cause cataracts. They concluded: "The comparison showed the groups (microwave exposed vs. not exposed ) to be essentially the same and did not support the hypothesis that human cataracts are being caused by chronic exposure to microwaves in the military environment in this country." There are three major flaws in Appleton and McCrossan's work. First, the exposed group likely included people with little or no exposure. This would tend to minimize the possibility of finding microwave effects. Secondly, their control group consisted of people working with equipment known to cause eye damage. This also would tend to minimize the possibility of finding microwave effects. Thirdly, and most important, they did not do a statistical analysis on their data. When the writer did one, it was found that Appleton and McCrossan have a statistically significant difference between groups, with the microwave exposed showing more lens opacities than would be expected by chance. Thus, their conclusion should have been the opposite of what they stated. It is the uncritical acceptance of negative biological studies of non-ionizing radiation, such as this, that has contributed to the distortion of science in this area of research and has stimulated public opposition to the installation of such energy sources.

Adult↗