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PubMed2026

Low-Carbon-Residue Multi-Principal-Element Magnetic Alloys for Excellent Microwave Absorption.

Magnetic alloy/carbon composites are promising microwave absorbers due to abundant interfaces and multiple loss mechanisms. However, reducing carbon content while maintaining uniform magnetic component distribution remains challenging. We report a spray-drying strategy to address this. By tuning nitrate precursor ratios and optimizing thermal treatment, we synthesize low-carbon alloy/oxide microspheres with uniformly distributed alloy phases. Limiting carbon content improves impedance matching, while selective nitrate precipitation creates a magnetic alloy architecture that suppresses nanoparticle agglomeration and enhances interfacial polarization. For this multiscale synergistic polarization is achieved: highly conductive Cu maximizes conduction loss, insulating Al2O3 buffers impedance, and Mn provides abundant polarization centers. The resulting microspheres exhibit tunable, exceptional performance. The attenuation-dominated FeCuMn system achieves -48.2 dB minimum reflection loss at 1.5 mm thickness. The impedance-matched FeCuAl system delivers an ultra-broad effective absorption bandwidth (EAB) of 5.12 GHz. Additionally, the FeAlMn system demonstrates superior polarization miniaturization for optimal absorption at extremely thin matching thicknesses. This work provides a practical strategy for designing electromagnetic composite structures with tunable component distribution.

customizable multicomponent↗
PubMed1978

Slow and rapid responses to CW and pulsed microwave radiation by individual Aplysia pacemakers.

Specific absorption rates (SARs) of microwave energy that altered firing rates were determined for individual pacemaker neurons in the abdominal ganglion of Aplysia californica. A stripline apparatus provided both for artifact-free recording of transmembrane potentials and for precise determination of the rate of absorption of microwave energy. Exposure for two to three minutes at an SAR of only a few mW/g was capable of changing the firing rate of some pacemakers. Two types of responses were observed. The response that was seen in all neurons developed slowly, reaching a steady state in one to three minutes. The other response was seen in a few neurons and occurred within five seconds from the onset of irradiation. Similar responses were obtained for two microwave frequencies, 1.5 and 2.45 GHz. Pulsed radiation induced rapid changes of firing rate more readily than did CW radiation at the same SAR. A convective heating scheme was used to study the effects of temperature changes on the pacemakers' firing rates. Since all of the responses are not readily explained by general heating of the preparation, alternate mechanisms are suggested for the observed effects.

Action Potentials↗
PubMed1976

Human liver alcohol dehydrogenase: purification, composition, and catalytic features.

Alcohol dehydrogenase has been purified from human liver by affinity chromatography. Ultracentrifugation, Sephadex G-200 chromatography, and amino acid analyses of multiple preparations demonstrate homogeneity of molecular weight. Sodium dodecyl sulfate disc gel electrophoresis reveals a single species of molecular weight 42 000. Based on a molecular weight of 85 000 for the dimer obtained from the amino acid composition and a molar absorptivity of A280nm0.1% = 0.58, the enzyme contains 3.6-4.2 g-atoms of zinc, as determined by emission spectrography, microwave-induced emission, and atomic absorption spectrometry. Inhibition by o-phenanthroline, (ethylenedinitrilo)tetraacetic acid, and alpha,alpha'-bipyridine demonstrates that zinc is essential to enzymatic function. Detailed kinetic analyses using primary alcohols of the homologous series CH3(CH2)nOH, n = 0-5, and the corresponding aldehydes as substrates show that KM values become smaller as n increases. This suggest that hydrophobic interactions play a role in substrate binding. The availability of well-defined preparations of human liver alcohol dehydrogenase now allows definitive genetic and functional studies of this enzyme to elucidate human ethanol metabolism.

Alcohol Oxidoreductases↗
PubMed1979

Carbon-loaded Teflon electrodes for chronic EEG recordings in microwave research.

Conventional metal electrodes can cause serious modification and intensification of the rate of energy absorption in tissues during exposure of animals to microwaves. Carbon-loaded Teflon with a conductivity close to that of tissue has been implanted and maintained for four to six months at cortical and subcortical locations in rabbits. The EEG and its spectrum as recorded from the carbon-loaded Teflon electrodes are comparable to those recorded from conventional metal electrodes. Histological examination showed good tissue compatibility. Recordings made during acute exposure of rabbits to microwave radiation (2450-MHz) at 100 mW/cm2 showed no electromagnetic interference. The results indicate that carbon-loaded Teflon electrodes can be implanted chronically to record the EEG in animals during the course of microwave radiation.

Animals↗
PubMed1979

A microwave heating system for improving temperature uniformity in heated tissue.

A microwave heating system, designed to improve temperature uniformity in heated tissue, is described. The system employs parallel-opposed waveguide applicators, operating in the TE10 mode at 2450 MHz with the tissue to be heated (i.e. mouse intestine) immersed in a liquid which is both biologically compatible with and dielectrically similar to the tissue. The liquid improves the microwave coupling and avoids shape and size dependent absorption characteristics of the irregularly shaped tissue. Also, by maintaining this liquid at a suitable temperature with respect to that required in the tissue, the thermal losses and hence temperature gradients in the tissue are reduced compared with heating in hot liquid alone.

Animals↗
PubMed1979

Preliminary studies: far-field microwave dosimetric measurements of a full-scale model of man.

Measurements of microwave heating were made in a full-size, upright human model. The 75-Kg model, composed of electrically simulated muscle, was placed in the far-zone of a standard-gain horn inside an absorber-lined chamber. Pulsed energy at 1.29 GHz was obtained from a military radar transmitter (AN/TPS-1G) and produced radiation at 6-14 mW/cm2 average power density at the location of the model. Microwave heating at the front surface was measured at nine locations on the phantom. Measurements at several depths within the phantom were also made at a central location to gain information on the depth-of-penetration of the microwave energy. Results of the frontal surface measurements and of the penetration study permitted a calculation of the approximate whole-body average specific absorption rate (SAR) when the model's long axis was parallel to the E-field vector. For a normalized power density of 1 mW/cm2 at a frequency of 1.29 GHz, the whole-body average SAR approximated 0.03 W/Kg. This result agrees well with theoretical predictions based on absorption in prolate spheroidal models of man.

Humans↗
PubMed1979

A negative test for mutagenic action of microwave radiation in Drosophila melanogaster.

Microwave radiation (2450 MHz CW) was tested for mutagenicity in Drosophila melanogaster. Embryos in water were exposed to the electromagnetic field with a mean specific absorption rate of 100 W/kg. A sensitive somatic test system was used, in which mutagenicity was measured as the frequency of somatic mutations for eye pigmentation. With the test system used, microwaves did not show any mutagenic activity.

Animals↗
PubMed1979

Quantitation of chronic microwave radiation effects on muscle cell electrical excitable properties: a temperature dependence analysis of the H-H cable and membrane current parameters of irradiated cells.

Frogs Rana pipiens maintained under constant laboratory environmental conditions were subjected daily to chronic microwave exposure with pulsed microwave (2.88 GHZ) at a power density of 10 mW/cm2, during 0.1 hour, for periods up to 100 days. The whole body Specific Absorption Rate (SAR) was of 1.5 mW/g per 1 mW/cm2. The passive and dynamic electrical parameters of sartorius muscle cells from control and irradiated frogs as a function of temperature in the range from 10 C to 30 C, have been analyzed. This temperature dependence analysis, presented in another work, was planned to be used in this paper for detecting those possible "masked" chronic microwave effects in complex membrane mechanisms highly temperature sensitive, and tightly related to the excitation and propagation of bioelectrical responses. The temperature dependence of the passive (Vr, Gm, Cm, and tau) and the active cell electrical parameters (theta, V*, Vs, VNa, Vn, V+, V-, kr, kNa, kK, tau Na, tau K, -gNa, gNa, gK, INa, and IK) was not altered by chronic microwave exposure. The striking observation reported in another work, about the presence of two groups of cell electrical parameters, characterized by their dependence with temperature, was reproduced on the irradiated muscle cells. Results have indicated that there was not muscle cell cumulative bioeffects resulting from microwave exposure to 10 mW/cm2, over a 0.1 hour period.

Action Potentials↗
PubMed1977

Rat lymphocytes in cell culture exposed to 2450 MHz (CW) microwave radiation.

Rat lymphocytes were exposed to continuous wave microwave radiation at a frequency of 2450 MHz at intensities of 5, 10 and 20 mW/cm2. The corresponding rates of absorption of energy were determined to be 0.7, 1.4 and 2.8 mW/g. The lymphocytes were exposed for 4, 24 or 44 h either with or without the addition of a mitogen (phytohemagglutinin). The transformation of lymphocytes into lyphoblasts was monitored by the addition of tritiated thymidine. No significant differences (P less than .05) were found in the uptake of tritiated thymidine between exposed and control cultures.

Animals↗
PubMed1978

Analysis of the effects of microwave energy on enzymatic activity of lactate dehydrogenase (LDH).

Interactions between microwave energy (3 GHz) and the enzyme Lactate Dehydrogenase (LDH) have been analyzed by monitoring the enzymatic activity during irradiation in steady-state or dynamic conditions, by irradiating the sample with variable power levels (up to 6 W into the sample) and, finally, by knowing accurately the true specific absorption rate. No permanent or temporary changes can be induced when the energy absorption does not cause a temperature variation. For higher energy values, effects are purely thermal in nature. Furthermore the thermal activation of the reaction velocity, caused by microwave irradiation, is in itself sufficient to give a good fit with the experimental time evolution of the enzymatic reaction.

Hot Temperature↗
PubMed1977

Effects of 2.6-4.0 GHz microwave radiation on E-coli B.

The effects of 2.6-4.0 GHz microwave radiation on living E. coli B bacteria were studied using measurement of the colony forming ability (CFA) of the cells and alterations in the molecular structure determined by comparing the infrared spectrum of irradiated and unirradiated cell cultures. At absorbed power levels of 20 mW in 1 ml of cellular suspensions (i.e., a specific absorption rate of 20 W/kg) for 10-12 hour exposures, no effects were observed on either the molecular structure or the CFA for this particular strain of E. coli.

Cell Division↗
PubMed1978

Electron spin resonance in zero magnetic field of the reaction center triplet of photosynthetic bacteria.

The decay rates kx, ky, kz of the individual spin levels of the light-induced triplet state have been accurately measured by the zero-field resonance technique under conditions of very low light intensity and a microwave sweep rate of 2.5 MHz/microseconds, which is in excess of that commonly used in optical detection magnetic resonance experiments. The rates ku found correspond well with those previously determined under somewhat different conditions (Hoff, A.J. (1976) Biochim. Biophys. Acta 440, 765--771) and with those inferred from the decay at 4.2 degrees K of the triplet-triplet absorption after picosecond excitation (Parson, W.W. and Monger, T.G. (1977) Brookhaven Symp. Biology 28, 195--212). Thus there seems no reason to doubt that PR corresponds to the triplet state detected by ESR. In a recent publication Clarke and Connors (Clarke, R.H. and Conners, R.E. (1976) Chem. Phys. Lett. 42, 69--72) published values of the rates ku which differ substantially from ours and which lead to a mean lifetime in excess of that of PR. We show that erroneous rates are obtained when the microwave sweep rate is not made fast relative to the decay of the individual spin levels. Zero-field splitting parameters for a member of photosynthetic bacteria have been measured with an accuracy of better than 0.4% for D and 1% for E. The enhanced precision as compared to conventional ESR allows one to discriminate between species of one family. Deuteration reduces the ku values by a factor of about 2, with little spin selectivity. This effect is much larger than previously observed for chlorophyll a. The present results explain the decrease in fluorescence intensity observed on microwave saturation in zero-field optical detection magnetic resonance experiments, and they also show that the simple exciton model is inadequate to derive the geometry of the reaction center dimer from the observed zerofield splitting and decay rates.

Electron Spin Resonance Spectroscopy↗
PubMed1975

Physicochemical characterization of the four-iron-four-sulphide ferredoxin from Bacillus stearothermophilus.

1. A stable ferredoxin was prepared from Bacillus stearothermophilus and purified by chromatography on DEAE-cellulose and by electrophoresis. 2. The minimum molecular weight determined from the amino acid composition was about 7900 and this was in reasonable agreement with a value of 8500 determined by polyacrylamide-gel electrophoresis. The ferredoxin contained four iron atoms and four labile sulphide groups per molecule. 3. The optical absorption, optical-rotatory-dispersion and circular-dichroism spectra are typical of ferredoxins containing 4Fe-4S clusters. 4. Oxidation-reduction titrations, combined with electron-paramagnetic-resonance (e.p.r.) spectroscopy, showed that the protein has a mid-point potential, at pH8, of -280 +/- 10mV, and that only one electron-accepting paramagnetic species is present. 5. The e.p.r. spectrum of the reduced ferredoxin is more readily saturated with microwave power at low temperatures than those of the eight-iron ferredoxins, indicating that there is another mechanism of electron-spin relaxation in the latter. 6. Mossbauer spectra of both redox states were observed over a range of temperatures and in magnetic fields. At high temperatures (77 degrees K and above) both redox states appear as quadrupole-split doublets; in the reduced state two resolved doublets are seen, suggesting appreciable localization of the additional reducing electron. 7. The average chemical shift indicates formal valences of two Fe3+ and two Fe2+ in the oxidized state and three Fe2+ and one Fe3+ in the reduced state. However, the spectra indicate that there are differing degrees of electron delocalization over the iron atoms. 8. At low temperatures (4.2 degrees K) the oxidized form shows no hyperfine magnetic interaction, even in an applied magnetic field, evidence that the oxidized ferredoxin is in a non-magnetic state as a result of antiferromagnetic coupling between the iron atoms. 9. At 4.2 degrees K the reduced form shows a broad asymmetric pattern resulting from magnetic hyperfine interaction. This contrasts with the reduced ferredoxin of Clostridium pasteurianum, which shows a doublet, suggesting that in the latter there may be interaction between the two 4Fe-4S centres. 10. In large applied magnetic fields, positive and negative hyperfine fields are seen in the Mossbauer spectra of the reduced ferredoxin, evidence for antiferromagnetic coupling between the iron atoms in the 4Fe-4S centre. The high-field spectra of the reduced ferredoxin of B. stearothermophilus are similar to those of the reduced ferredoxin of C. pasteurianum.

Amino Acids↗
PubMed1977

Induced EM fields inside human bodies irradiated by EM waves of up to 500 MHz.

In this paper, the internal EM field and the specific absorption rate of EM energy induced inside human bodies by EM waves of up to 500 MHz are theoretically quantified based on a tensor integral equation method. Numerical results for a realistic model of a man of 177 cm high irradiated by EM waves of various frequencies and of vertical and horizontal polarizations are presented. The resonance phenomenon and the effect of body heterogeneity on the induced field are studied. Some theoretical results are compared with existing experimental results.

Electromagnetic Fields↗