Frank S. Barnes

TEMPORALLY-SPECIFIC MODIFICATION OF MYELINATED AXON EXCITABILITY IN VITRO FOLLOWING A SINGLE ULTRASOUND PULSE

Single, short-duration, low-energy pulses of ultrasound were found to elicit distinct modifications of the electrical excitability of myelinated frog sciatic nerve in vitro in a window extending 40-50 ms after pulse termination. These modifications include both enhancement and suppression of relative excitability, the sequence of which generally follows one of two distinct temporal response patterns. The ultrasound pulses were focused, 2-7 MHz, of 500-microseconds duration, and of peak intensities of 100-800 W/cm2. Total absorbed pulse energies were generally less than 100 mJ/g, corresponding to local temperature rises of the nerve trunk of no more than 0.025 degrees C per pulse, thereby precluding bulk heating as a basis of this effect. The observed effects cannot be elicited using either a subthreshold square wave or RF electrical prestimulus, suggesting a unique form of receptivity of the nerve trunk to mechanical perturbation. We present evidence that the low-frequency radiation pressure transient accompanying the envelope of the acoustic pulse is the active parameter in this phenomenon, and postulate that it may act by the gating of stretch-sensitive channels, which have been recently reported in a variety of cell membranes. These results may demonstrate that stretch-sensitive channels in neural membrane can serve to functionally modulate neuro-electric signals normally mediated by voltage-dependent channels, a finding which could suggest new clinical applications of high peak-power, low-total-energy pulsed ultrasound.

Combined action of static and alternating magnetic fields on ionic current in aqueous glutamic acid solution

Combined parallel static and alternating magnetic fields cause a rapid change in the ionic current flowing through an aqueous glutamic acid solution when the alternating field frequency is equal to the cyclotron frequency. The current peak is 20-30% of the background direct current. The peak is observed with slow sweep in the alternating magnetic field frequency from 1 Hz-10 Hz. Only one resonance peak in the current is observed in this frequency range. The frequency corresponding to the peak is directly proportional to the static magnetic field. The above effect only arises at very small alternating field amplitude in the range from 0.02 microT-0.08 microT.

Doped Ba0.6Sr0.4TiO3 thin films for microwave device applications at room temperature

Abstract The dielectric property comparison between laser-ablated Mn-doped and undoped Ba0.6Sr0.4TiO3 (BST) thin films at low frequency (100 kHz) and at microwave frequencies has been demonstrated. The dielectric properties were characterized at low frequency using interdigital capacitors, and at microwave frequencies with coplanar waveguide (CPW) meander-line phase shifters. With 1% Mn-doped BST films, results to date gave a dielectric constant as high as 2100, a tunability of 85% with DC bias field of 88 kV/cm, and a loss tangent without DC bias as low as 0.0033 at 100 kHz and room temperature. At 10 GHz, our best result to date was also obtained with 1% Mn-doped BST film deposited on MgO substrate, which at room temperature possess a dielectric constant of 1820 with a tunability of 56% at 40 kV/cm DC electric field, and a loss tangent of 0.006 at zero bias.

Microlenses on the end of single-mode optical fibers for laser applications

Various microlenses are fabricated on the end of single-mode fibers using a photolithographic technique. The radii of these lenses are in the 2.6–20-μm range. The beam waist and beam waist position of these lenses are measured and compared to theoretical values derived for Gaussian beams under a paraxial ray approximation. Beam spot sizes of <0.75 μm have been achieved at 830 nm.

Bioengineering and biophysical aspects of electromagnetic fields

BIOENGINEERING AND BIOPHYSICAL ASPECTS OF ELECTROMAGNETIC FIELDS Environmental and Occupationally Encountered Electromagnetic Fields K.H. Mild and B. Greenebaum Endogenous Electric Fields in Animals R. Nuccitelli Dielectric and Magnetic Properties of Biological Materials C. Gabriel Magnetic Properties of Biological Material J. Dobson Interaction of Direct Current and Extremely Low Frequency Electric Fields with Biological Materials and Systems F. Barnes Magnetic Field Effects on Free Radical Reactions in Biology S. Engstrom Signals, Noise, and Thresholds J.C. Weaver and M. Bier Biological Effects of Static Magnetic Field S. Ueno and T. Shigemitsu The Ion Cyclotron Resonance Hypothesis A.R. Liboff Computational Methods for Predicting Field Intensity and Temperature Change J.C. Lin and P. Bernardi Experimental EMF Exposure Assessment S. Kuhn and N. Kuster Electromagnetic Imaging of Biological Systems W.T. Joines, Q.H. Liu, and G. Ybarra

Model for Some Nonthermal Effects of Radio and Microwave Fields on Biological Membranes

A model is presented for mechanisms by which non-thermal effects could take place in biological materials as a result of microwave, radio-frequency fields. Both shifts in ion concentrations across a membrane and the orientation of long chain molecules are shown to be possible.

Voltage tunable capacitors using high temperature superconductors and ferroelectrics

In this paper we report the construction of both slot capacitors on bulk substrate and thin film interdigital capacitors using YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) and Ba/sub x/Sr/sub 1-x/TiO/sub 3/. Slot capacitors made on bulk Ba/sub x/Sr/sub 1-x/TiO/sub 3/ (BST) yielded variations in capacitance of more than 6 to 1 at 86 K with a peak electric field strength of 25 kV/cm. With a metal organic deposition (MOD) grown Ba/sub x/Sr/sub 1-x/TiO/sub 3/ 300-nm overcoat on a YBCO thin film, an interdigital capacitor on LaAlO/sub 3/ substrate yielded an approximate tuning range of 10% for peak field of 66 kV/cm over temperatures ranging from 50 K to 120 K.<<ETX>>

The Thermal-Chemical Damage in Biological Material under Laser Irradiation

A mathematical model for thermal-chemical damage to biological materials excited by laser irradiation is described. The chemical rate equations for protein denaturization are used to predict radii of damage for cases where the input-laser-energy distribution results in the uniform heating of a small sphere or a disk. These rate equations are limited to a single-hit process. Experimental checks on this model are presented for ruby-laser irradiation of small carbon particles in egg albumin and for CO 2 ?laser surface heating of egg albumin.

Reduction of the Earth's magnetic field inhibits growth rates of model cancer cell lines.

Small alterations in static magnetic fields have been shown to affect certain chemical reaction rates ex vivo. In this manuscript, we present data demonstrating that similar small changes in static magnetic fields between individual cell culture incubators results in significantly altered cell cycle rates for multiple cancer-derived cell lines. This change as assessed by cell number is not a result of apoptosis, necrosis, or cell cycle alterations. While the underlying mechanism is unclear, the implications for all cell culture experiments are clear; static magnetic field conditions within incubators must be considered and/or controlled just as one does for temperature, humidity, and carbon dioxide concentration.

Short microwave pulses cause ultrastructural membrane damage in neuroblastoma cells

Investigations on the biological hazards of microwave radiation (MWR) have become necessary because of the increasing domestic and industrial use of microwave equipment and the need to establish meaningful and realistic safety standards. Ultrastructural changes in mouse neuroblastoma cells, grown in vitro and exposed to MWR and to heat, are reported. Cells were exposed to 1- μ sec pulses at 330 pulses/sec at field strengths from 1.7 to 3.9 kV/cm at 2.7 GHz. The most striking damage occurs in the form of breaks in the cell and mitochondrial membranes. Parts of the cell membrane are expelled and appear as membrane-bound sacs outside the cell surface. Cristae lose their normal pattern and form myelinated figures inside mitochondria. It is suggested that these effects may be of a nonthermal nature: (1) because cells exposed to heat alone at temperatures equivalent or considerably higher than the calculated temperature-rise in microwave exposed cells do not show similar changes, and (2) because of the differential heating, the membranes are expected to undergo thermal relaxation too rapidly to allow a significant temperature differential between the membranes and the surrounding material. The observed changes in the cell membrane may explain the increase in cell membrane permeability after MWR exposure.