MHz Microwave Irradiation Research Articles

Study of 400MHz microwave conduction loss effect for a hydrolysis reaction by thermostable β-Glucosidase HT1.

Microwave irradiation at different frequencies gave molecular selective effects, namely higher frequency microwave effects for waters while lower frequency effects for ions. We already reported that 2.45GHz and 5.80GHz microwave irradiation gave different results for a hydrolysis reaction by thermostable β-Glucosidase HT1. Here, we designed and made a reactor, employed 400MHz microwave irradiation, and studied the effectiveness of 400MHz microwave for HT1 reaction, then 400MHz and 2.45GHz had the ability to accelerate HT1 reaction. In consideration of the general mechanism of enzymatic glycoside hydrolysis, our results would be reasonable if ions are key reaction species because 400MHz microwave activated ions selectively. In addition, the phenomenon that 400MHz microwave would not affect water molecules by dielectric heating might contribute the enzyme stability. This report should support that microwave is not only a tool to heat reactions efficiently but also can bring unique effects for reactions.

Degradation of trace nitrobenzene in water by microwave-enhanced H2O2-based process

To evaluate possible use of microwave-enhanced H2O2-based (MW/H2O2) process to degrade trace nitrobenzene (NB) in water, a series of batch experiments were conducted. The results showed that 2450MHz microwave irradiation significantly enhanced oxidative decomposition of nitrobenzene (NB) in a H2O2 system. About 90% NB was degraded by the MW/ H2O2 process in 30 min. Moreover, the MW/ H2O2 process could enhanced the oxidative degradation of NB even at relatively low temperature (50°C). When the initial concentration of NB was 300μg/L, the optimum ratio of H2O2 to NB and MW power were 70 and 300W respectively. The presence of humic acid significantly increased H2O2 dosage. The ultraviolet absorbance at 254 nm (UV254) indicated degradation of NB was stepwise and some intermediates were produced. The gas chromatography-mass spectrometric (GC-MS) analysis showed that main intermediates were nitrophenolic and carbonyl compounds.

Inhibition of B16 murine melanoma metastasis and enhancement of immunity by fever-range whole body hyperthermia

Purpose: Whole body hyperthermia (WBH) has been regarded as a promising alternative therapy to cure late stage cancer with metastasis. As the final biological and therapeutic effects are dependent on the specific protocol, the potential of using a microwave-based WBH approach for metastasis inhibition is established and its typical results are discussed.Materials and methods: The effectiveness of a 30-min whole body hyperthermia (WH) on animals, raised to a rectal temperature of 40.2° ± 0.3°C for 30 min followed by 84 h observation by 2450 MHz microwave irradiation, were evaluated. In an experimental lung metastasis model by injection of B16-F10 melanoma, lungs were removed from sacrificed mice 16 days after tumour implantation, and the expression of heat shock protein, inter-cellular adhesion molecule 1 (ICAM-1), proliferating cell nuclear antigen (PCNA) and cyclin D1 was examined. CD4+, CD8+ and NK cell subpopulation in peripheral blood were measured by flow cytometry before and after the last treatment.Results: The best therapeutic effect was obtained when the mice were treated with WBH in combination with the initial chemotherapy with cis-diaminodichloroplatinum (CDDP) and dacarbazine (DTIC) (p < 0.05). The WBH alone has an advantage of reduced toxicity and lower cost. Heat shock protein (HSP) expression increased in the hyperthermia groups. Reduction of PCNA and cyclin D1 was observed in the mice treated with WH alone or in combination with chemotherapy. In the hyperthermia groups, CD4+/CD8+ decreased while the NK increased slightly.Conclusions: The whole body hyperthermia protocol described in this work inhibits B16 tumour metastasis by inhibiting cell proliferation, neovascularisation and stimulating favourable immune responses. It demonstrated that WBH treatment benefits therapy of metastasis cancers.

Microwave-Assisted Preparation of TiO2/Activated Carbon Composite Photocatalyst for Removal of Methanol in Humid Air Streams

TiO2/activated carbon composite photocatalyst was prepared by a microwave-assisted impregnation method and was employed for the removal of methanol from humid air streams. A commercial microwave oven (800 W) was used as the microwave source. Under 2450 MHz microwave irradiation, titanium tetra-isopropoxide (TTIP) was quickly hydrolyzed and anatase TiO2 was formed in a short time (<20 min). As a result of the volumetric heating and selective heating of the microwave, the solvent and byproducts were quickly removed which reduced energy consumption and processing time. The formed submicrometer TiO2 particles mainly deposited on the external surface of carbon. In a packed bed reactor with an empty bed contact time of 0.35 s, the prepared materials maintained a 40% removal efficiency at an inlet methanol concentration of 39 ppm. When the TTIP conversion was complete, neither the irradiation time nor the water/TTIP ratio could further change the photocatalytic activity.

Regeneration of acid orange 7-exhausted granular activated carbons with microwave irradiation

An investigation was performed for the regeneration of three granular activated carbons (GACs) exhausted with acid orange 7 (AO7). The three GACs were made from different materials, i.e. coconut shells, almond nucleus and coal. The AO7 adsorption process was carried out in a continuous-flow adsorption column. After adsorption, the AO7-saturated GAC was dried at 120 degrees C, then regenerated in a quartz reactor by 2450 MHz microwave (MW) irradiation at 850 W for 5 min. The efficacy of this procedure was analyzed by determining the rates and amounts of AO7 adsorbed in successive adsorption-MW regeneration cycles. Effects of this regeneration on the structural properties, surface chemistry and the AO7 adsorption capacities of GAC samples were examined. It was found that after several adsorption-MW regeneration cycles, the adsorption rates and capacities of GACs could maintain relatively high levels, even higher than those of virgin GACs, as indicated by AO7 breakthrough curves and adsorption isotherms. The improvement of GAC adsorption properties resulted from the modification of pore size distribution and surface chemistry by MW irradiation.

Generation of Class A Sewage Sludges Using 2,450 MHz Microwave Irradiation

Generation of Class A Sewage Sludges Using 2,450 MHz Microwave Irradiation

Multinucleated giant cell appearance after whole body microwave irradiation of rats

Abstract Multinucleated giant cells are common for some chronic inflammatory processes in the lung. These cells are formed by fusion of macrophages, but how the process relates to the kinetics of alveolar macrophage generation is not clear. This study investigated the influence of 2450 MHz microwave irradiation on alveolar macrophage kinetics and formation of multinucleated giant cells after whole body irradiation of rats. The range of electromagnetic radiation was selected as 2450 MHz microwaves at a power density of 5 – 15mW/cm 2. A group of experimental animals was divided in four subgroups that received 2, 8, 13 and 22 irradiation treatments of two hours each. The animals were killed on experimental days 1, 8, 16, and 30. Free lung cell population was obtained by bronchoalveolar lavage. Cell response to the selected irradiation level was followed quantitatively, qualitatively and morphologically using standard laboratory methods. Total cell number retrieved by lavage slightly decreased in treated animals showing time- and dose-dependence. Cell viability did not significantly change in the irradiated animal group (G2) as compared with the control group (G1). Multinucleated cells significantly increased (p<0.01) in treated animals. The elevation of the number of nuclei per cell was time- and dose-dependent. Macrophages with two nucleoli were more common in animals treated twice or eight times. Polynucleation, that is three and more nucleoli in a single cell, was frequently observed after 13 or 22 treatments. Binucleation and multinucleation of alveolar macrophages were sensitive time- and dose-dependent morphological indicators of pulmonary stress.

Soil microbial biomass carbon and nitrogen estimates using 2450 MHz microwave irradiation or chloroform fumigation followed by direct extraction

Microwave irradiation and chloroform fumigation followed by direct extraction were compared as potential methods to estimate microbial biomass carbon and nitrogen in grassland soils. Soil amended with 700 ppm C and 70 ppm N and unamended soil were incubated at 25°C for 3 days, irradiated for various time intervals and extracted with 0.5 M K 2SO 4. An increase in microwave time resulted in an increase in extractable C in both amended and unamended soils. A 2-min irradiation time was selected as the optimal treatment because it resulted in a difference between amended and unamended soils close to what was expected and avoided excessive heating of the sample. CHCl 3 fumigation for 24 h yielded (mean±SD) 138.2±18.5 ppm extractable C and 11.6±6.7 ppm extractable N in the unamended soil and 315.5±48.3 ppm extractable C and 17.9±3.0 ppm extractable N in the amended soil. Compared to the CHCl 3 treatment, the 2-min microwave treatment resulted in 70.6% less extractable C and 79.3% less extractable N in the unamended soil and 52.2% less extractable C and 58.3% less extractable N in the amended soil. Sequential fumigation followed by irradiation produced extractable C and N values similar to fumigation alone, while fumigating twice for a total of 48 h resulted in higher extractable C in unamended soil and higher extractable N in amended soil. These results indicate that although trends of treatments are similar, microwave irradiation is not as effective as CHCl 3 fumigation for microbial biomass estimates in the soils examined.

Cerebral Blood Flow Changes During Localized Hyperthermia

Hyperthermia is becoming a potent therapeutic method for malignant brain tumors, either alone or in combination with radiation therapy. The heat response of organized tissues includes other factors besides the inherent cellular thermosensitivity, that is, tissue pH, PaO2, and nutrient supply, all of which are largely influenced by the tissue blood flow. In this study, the regional cerebral blood flow (rCBF) changes in 15 Japanese normal monkey brains during interstitial microwave hyperthermia were investigated by the hydrogen clearance method. Under general anesthesia and controlled respiration, a parieto-occipital craniectomy, 4 x 4 cm, was performed. A microwave antenna was inserted into the brain to a depth of 2.0 cm, and the brain tissue was heated with 2450 MHz microwave irradiation. The intracerebral temperatures and rCBF were measured in the white matter 1 cm from the brain surface. During hyperthermia, the rCBF linearly increased at a rate of 10% per 1 degrees C temperature rise. Heating at 42 degrees C for 180 minutes resulted in a constant increase in rCBF. The perfusion rate returned to the control levels after the termination of heating. Above 45 degrees C, the rCBF transiently increased and then started to decline during heating. No consistent results were obtained with heating at 43 degrees C. These results show that normal monkey brain tissues respond to hyperthermia by an rCBF increase as long as the threshold values of tissue temperature (43 degrees C) and exposure time (40-60 minutes) are not exceeded. Excessive heating may lead to irreversible damages to normal tissue and vasculature.

Condensation reactions in a microwave-induced acetylene plasma

The polymerization reactions induced by 2540 MHz microwave irradiation of pure acetylene and of acetylene—oxygen, acetylene—nitrogen and acetylene—argon mixtures have been directly monitored using a time-of-flight mass spectrometer, the conditions for the majority of the experiments being a flow rate of 21 h −1 and a pressure of 2 torr. Only polyacetylenes of the general formula HC(CC) n H ( n = 2, 3, 4, …) were identified in pure acetylene. In the presence of oxygen and nitrogen, oxidation products such as CO, CO 2, C 2H 2O and CH 2O, and nitrogen-containing molecular species of the general formula HC(CC) n CN, were observed in addition to polyacetylenes. The presence of argon does not significantly affect the chemical behavior of the acetylene plasma. Reaction channels are proposed for most of the products observed.

Evaluation of 2,450MHz Microwave Irradiation for Therapeutic Heating of the Brain.

Evaluation of 2,450MHz Microwave Irradiation for Therapeutic Heating of the Brain.

The effect of 2450 MHz microwave irradiation on the heart rate of embryonic quail.

Japanese quail (Coturnix coturnix japonica) embryos 8–13 days old were exposed to pulsed and CW 2450 MHz microwave radiation at specific absorption rates of 0.3–30 mW/g to investigate the effect of the radiation on heart rate. Although non-thermal effects (in particular bradycardia) caused by exposure to microwave radiation have been reported, no effects on heart rate were detected in this study which could not be attributed to temperature changes.

A mass-spectrometric investigation of polymerization processes inuced by microwave irradiation in methane, methane—argon and methane—krypton mixtures during the formation of pyrolytic carbon

The polymerization reactions induced by 2540 MHz microwave irradiation in pure methane, methane—argon and methane—krypton mixtures at pressures from 0.5 to 5 torr have been directly monitored with a time-of-flight mass spectrometer. Mainly unsaturated molecular species with 2–6 carbon atoms were identified. The more important processes are believed to be reactions of radicals and of hydrogen deficient ions, CH 2 +, CH + with methane, followed by further condensation reactions of C 2 ions, mainly C 2H 2 + and C 2H 3 + with methane and C 2 neutrals. In the presence of argon or krypton an increased rate of polymerization is observed. This is attributed to an efficient primary process, Ar* (or Kr*) + CH 4 → Ar (or Kr) + CH 2 + H 2, followed by electron impact ionization of the CH 2 radical, rather than to dissociative charge transfer Ar + + CH 4 → Ar + CH 2 + + H 2, which is not known for Kr + ions and ground state methane.

Permeability of the blood-brain barrier to mannitol in the rat following 2450 MHz microwave irradiation

The radiotracer method of Oldendorf 6,7 was used to determine if 2450 MHz continuous wave (CW) microwave energy increases blood-brain barrier permeability to [ 14C]mannitol, which is normally excluded from entering the brain. Anesthetized, adult rats were irradiated singly for 30 min in the quiet zone of an anechoic chamber, at average power densities from 0.1 to 30 mW/sq.cm. Afterwards each rat received an intracarotid bolus injection of [ 14C]mannitol/[ 3H]water mixture and was decapitated 15 sec later. Uptake of [ 14C]mannitol relative to the highly permeable reference substance, [ 3H]water, was calculated as the brain uptake index (BUI) for 4 brain regions. Mean BUI values for tissues from the microwave-irradiated rats did not differ significantly from sham-irradiated animals, and a microwave influence on barrier permeability was not evident. Irrespective of treatment, BUI values for cerebellum and medulla were much higher and more variable than values for cortex or diencephalon, and were associated with reduced absorbance or retention of [ 3H]water. Because of a compromising influence of the vertebral arterial supply on the distribution of intracarotid-injected radiotracers, BUI measurements in caudal brain regions are probably unreliable unless accompanied by data on regional radioisotope concentrations. The absence of such data in an earlier BUI study 8, suggests that increases in BUI for cerebellum and medulla attributed to microwaves were possibly misinterpreted as differences in barrier permeability to [ 14C]saccharides, when in fact changes in blood flow and [ 3H]water influx or egress were responsible.

The levels of labile intermediary metabolites in mouse brain following rapid tissue fixation with microwave irradiation.

Abstract—The levels of several labile glycolytic and organic phosphate metabolites in mouse brain were determined following rapid inactivation with 2450 MHz microwave irradiation. The levels of ATP in mouse brain following a 0·25 s exposure in a 6 kW microwave oven was found to be 2·416 ± 0·061. Whole brain levels of 8 labile intermediary metabolites in 0·4 s irradiated samples were comparable to those reported using the previously‐described methods of freeze‐blowing or whole‐animal immersion. Analysis of these same metabolites in 4 gross areas of brain did not reveal any anoxic changes betwen superficial and deeper brain areas. The advantages of the mcrowave irradiation inactivation technique for regional brain studies of labile intermediary metabolites is discussed.

The Effect of 2450 MHz Microwave Irradiation on the Growth of Mice

AbstractMany claims have been made concerning the low power density effects of microwave irradiation of living material. We herein refute one claim for the growth stimulating effect of chronic 2450 MHz irradiation and correct the record of our having confirmed experimentally a dielectric saturation effect which might cause denaturation of molecules in living material.