bluuebunny/crossref_metadata_2025 huggingface dataset:
Induction of calcium‐ion efflux from brain tissue by radio‐frequency radiation: Effects of modulation frequency and field strength
Authors: Blackman C. F. , Elder J. A. , Weil C. M. , Benane S. G. , Eichinger D. C. , House D. E.
Published: February 2008

Bawin and her coworkers have reported changes in binding of calcium after exposure of avian brain tissue to nonionizing electromagnetic radiation. Because calcium is intimately involved in the electrical activity of the brain, their results reveal a heretofore unrecognized potential for nonionizing radio‐frequency radiation to affect biological function. We have verified and extended their findings. The forebrains of newly hatched chickens, separated at the midline to provide treatment‐control pairs, were labeled in vitro with radioactive calcium. Samples of tissue were exposed for 20 minutes in a Crawford irradiation chamber to 147‐MHz radiation, which was amplitude modulated sinusoidally at selected frequencies between 3 and 30 Hz. Power densities of incident radiation ranged between 0.5 and 2 mW cm−2. Compared with nonirradiated samples, a statistically significant increase in efflux of calcium ions (P < 0.01) was observed in irradiated samples at a modulation frequency of 16 Hz and at a power density of 0.75 mW cm−2. Our data confirm the existence of the frequency “window” reported by Bawin et al., as well as a narrow power‐density “window” within which efflux of calcium ions is enhanced.
Microwave irradiation and lipid metabolism in mice
Authors: Deficis A. , Dumas J. C. , Laurens S. , Plurien G.
Published: February 2008

A total of 154 male mice of the DBA strain was exposed during a three‐day period for nearly 60 hours to 2.45‐GHz microwaves in multimode cavities or in an electrically anechoic chamber. The estimated effective CW power density in the cavities was 3.3 (±2) mW cm−2; that in the chamber, 4 (±2) mW cm−2. Sham‐irradiated controls numbered 126. Two hours after termination of treatments, mean serum levels of triglycérides were elevated by 30% and 55%, respectively, in cavity‐ and chamber‐irradiated mice. Commensurate elevations of β‐lipoproteins were also observed. While rectal temperatures were not reliably elevated during the exposures, the absence of dosimetric data coupled with the likelihood that resonant absorption took place requires circumspection in interpreting the generality of the data for exposure of man.
Models of long‐range order in cerebral macromolecules: Effects of sub‐ELF and of modulated VHF and UHF fields
Authors: Sheppard A. R. , Bawin S. M. , Adey W. R.
Published: February 2008

Weak RF fields (450 MHz) that were sinusoidally modulated at 16 Hz increased the efflux of calcium ion from freshly isolated chick brain. The data demonstrate upper and lower bounds for power levels of incident fields at which the change of efflux is observed. These bounds, > 0.05 mW cm−2 and < 2.0 mW cm−2, constitute an amplitude window for the calcium‐efflux effect, which is also characterized by a frequency window demonstrated in previous experiments. The mechanisms by which weak low‐frequency fields—or weak high‐frequency fields modulated at sub‐ELF rates—interact with biological tissue derive from the properties of the biological components of neuronal membrane and from the unique dielectric properties of biological tissues in fields that oscillate at brain‐wave frequencies.
The effect of low‐level 2450‐MHz CW microwave radiation and body temperature on early embryonic development in chickens
Authors: Fisher Paul D. , Lauber J. K. , Voss W. A. G.
Published: February 2008

The effects of 2450‐MHz irradiation (3.5 mW cm−2) on cranial length and wet mass of four‐ and five‐day embryos at different incubation temperatures (32 to 36°C) were investigated. A temperature‐dependent effect on growth rate was observed. At 36°C, final cranial lengths and wet mass of experimental embryos were found to be below those of controls after four and after five days of incubation; however, the rate of growth was higher than that of controls. At 32°C, the final values of cranial length and wet masses were higher than the control values after four and after five days of incubation while the rate of growth was lower. It is concluded, after comparing wet‐mass data with cranial‐length data, that the developmental rate of the whole embryo was affected, and that the effect was a result of some mechanism not associated with an incremented temperature of the embryo.
Developmental effects of microwaves on Tenebno: Influences of culturing protocol and of carrier frequency
Authors: Pickard William F. , Olsen Richard G.
Published: February 2008

First‐day pupae of the darkling beetle Tenebno molitor were exposed to CW microwaves in the far field of a horn‐irradiated, temperature‐controlled, anechoic chamber. They and controls were allowed to develop to the adult stage and were then examined for the presence of gross morphological abnormalities. Control pupae from an in‐house colony developed significantly fewer developmental abnormalities than control pupae purchased from an outside supplier. The following experiments were performed at 5.95 GHz: (1) Pupae were held parallel to the electric‐field vector for two hours at an E‐field maximum (91 V m−1 RMS) of a standing‐wave distribution; at a nominal dose rate of 130 W kg−1, no effect was observed in either sample of pupae. (2) Pupae were held parallel to the magnetic‐field vector for two hours at an H‐field maximum ‐1.53 A m−1 RMS) of a standing‐wave distribution; at a nominal dose rate of 54 W kg−1, no effect was seen in colony pupae but significant effects were observed in cultures of the other pupae. (3) Pupae were held parallel to the electric‐field vector in a traveling‐wave distribution at 110 W m−2; only outside pupae were used, but no effect was detected for 13‐hour exposures. Another experiment was performed at 10.025 GHz: Pupae were held antiparallel to Poynting's vector for four hours in a traveling‐wave field at 50 W m−2; no effect was detected in colony pupae but a marginally significant effect was observed in the outside pupae. It was also demonstrated in samples of both pupal types that the condition under which they were maintained during development within the pupal stage could significantly affect the incidence of abnormalities in the adults.
Behavior of chicks exposed to low‐power 450‐MHz fields sinusoidally modulated at EEG frequencies
Authors: Sagan P. M. , Medici R. G.
Published: February 2008

As part of an integrated series of experiments designed to provide a comprehensive picture of the behavior chicks exposed to 450‐MHz fields that are modulated at EEG frequencies, a total of 24, 23‐hour‐water‐deprived chicks, ∼ 12‐day post‐hatch at the beginning of the experiment, were exposed to 3‐ and 16‐Hz amplitude‐modulated fields at a power density of 1 or 5 mW cm−2 (n = 12) while performing on a fixed‐time 30‐second (FT‐30) schedule of water reinforcement. Reinforcments were in no way dependent on the subject's behavior and were delivered every 30 s for a 2‐s period. (Training on an FT schedule leads to an increase in the amount and temporal regularity of motor activity that occurs between successive reinforcements.) Sessions were divided into three 40‐reinforcment epochs: the first and third epochs were used as control periods (the field was never presented), while the middle epoch was that during which sham exposures or exposures to the field occurred. Computer analyses of the recorded interim behavior revealed possible differences in the temporal distributions of motor activity as a function of the exposure condition, but an analysis of variance performed on the mean latencies of activity counts showed that the differences were not statistically significant.
Problems of quantifying effects of microwave irradiation on the blood‐brain barrier
Authors: Blasberg Ronald G.
Published: February 2008

The question of whether microwave irradiation in the absence of gross or focal heating has any effect on normal function of the blood‐brain barrier has not been clearly answered. Two reasons for this ambiguity relate to the unknown magnitudes of microwave‐induced effects and to the sensitivity and quantitative accuracy of measurement. Histological and physiological methods are compared. Seven different physiological methods that involve four different tracer‐input modalities, which are currently being used to study and quantify the blood‐brain‐barrier permeability, are discussed; their advantages and disadvan‐tages are presented and their applicability to the study of effects of microwaves on normal blood‐brain‐barrier function are compared.
VHF radar measurements during a jet stream passage
Authors: Rüster R. , Czechowsky P.
Published: February 2008

During April 11–13, 1978, a jet stream passed over Germany. A synopsis of this event, deduced from radiosonde data taken every 6 hours at five German weather stations, is given. During the maximum overhead passage the jet stream has been observed continuously using the SOUSY (sounding system) VHF radar facility. With an eastward pointing antenna beam, one component of the horizontal velocity was derived. Height profiles of the eastward jet stream velocity for a period of 11 hours are presented for the altitude range 3.3–10.65 km with a spatial resolution of about 150 m. These profiles show a pronounced maximum at the jet stream altitude which agrees well with measurements of the nearest radiosonde ascent. A shear instability generated by the strong vertical gradients of the horizontal velocity at the bottom of the jet stream is observed. The results clearly indicate that the spatial scales of such processes are of the order of 100 m. A height resolution of 150 m, as is used here, is necessary to resolve these processes.
Remote sensing of the sea surface using one‐ and two‐frequency microwave techniques
Authors: Plant W. J. , Schuler D. L.
Published: February 2008

The capabilities of one‐ and two‐frequency, coherent, pulsed, microwave radars for the remote sensing of the sea surface have been investigated both theoretically and experimentally. A combined instrument recording data independently in both modes is a compact and versatile probe for the study of two‐scale wave systems. An expression for the output of a dual‐frequency microwave system operated at intermediate grazing angles has been developed and quantitatively confirmed. This expression predicts that, for large illuminated areas, the dual‐frequency signal/background ratio will be inversely proportional to the area of the scattering cell, a dependence which has been confirmed experimentally. Furthermore, it has been shown that if a scattering cell of radial dimension small in comparison with the dominant ocean wavelength and an azimuthal dimension large in comparison with the dominant ocean wavelength is used, frequency demodulation of coherent single‐frequency microwave backscatter yields a signal proportional to the orbital velocity of those long waves which are propagating radially. This directional discrimination has been verified experimentally, and directional waveheight spectra have been shown to compare favorably with those measured by an array of pressure sensors. Finally, a double‐modulation technique has been conceived and tested experimentally. This technique allows measurement of interactions between waves with lengths of a few meters and much longer waves. Representative modulation transfer functions for these wave‐wave interactions have been obtained by using the technique.
On the asymptotic theory of inhomogeneous wave tracking
Authors: Einziger P. , Raz S.
Published: February 2008

This work presents alternative formulations of the asymptotic, inhomogeneous wave tracking theory (IWT) proposed by Choudhary and Felsen and investigates the basic analytical features of the ensuing operators. The outstanding deviations from classical ray theory are traceable to the fact that the generalized system of equations is of the quasi‐linear, elliptical type. Consequently, representation via an initial value formulation, standardly posed by geometrical optics (and in the quasi‐homogeneous limit, by IWT) must be approached with caution, and an appropriate boundary value formulation should be considered. Questions of existence, uniqueness, stability, and locality are discussed. The following alternative, but by no means equivalent, formulations are considered: (1) first‐order, quasi‐linear system of equations cast into a canonical form, the existence and uniqueness (but not the stability) of whose solution is ensured by the Cauchy‐Kowalewsky conditions, (2) a quasi‐linear, second‐order, elliptical differential equation subject to Dirichlet boundary conditions and to the requirements of elliptical uniformity, (3) same as formulation 2, but posed as a two‐dimensional variational problem, and (4) quasi‐linear, second‐order, phase trajectory equation obtained from formulation 2 via the so‐called hodograph transformation.
Methods for the extraction of long‐period ocean wave parameters from narrow beam HF radar sea echo
Authors: Lipa Belinda , Barrick Donald
Published: February 2008

This paper describes inversion methods for HF radar sea echo Doppler spectra, giving parameters of the ocean wave spectrum in the important long‐wavelength region. Radar spectra exhibiting very narrow spikes in the higher‐order structure adjacent to the first‐order lines are indicative of ocean wave components with a single dominant wavelength. In the simplest method of interpretation these components are assumed to be unidirectional; in this case we show how to extract wave period, direction, and rms wave height. If this simple model does not provide a good fit to the data or if the radar side bands have the form of broad peaks, we use a model for the wave spectrum with a cardioid distribution in direction and a Gaussian distribution in wave frequency. Parameters identifiable from this model include the rms wave height, dominant direction and period, and the angular spread in the direction and frequency distributions. In normal surface wave experiments the major source of error or noise is the random surface height of the sea; we describe the resulting statistics of the radar spectrum and trace the propagation of uncertainty to the derived ocean parameters.
Accurate determination of ionospheric effects on satellite‐based positioning systems in terms of residual range error
Authors: Ajayi G. O. , Hedberg A. , Hamberg G.
Published: February 2008

Positioning systems using artificial satellites like Navsat or Navstar systems offer facilities for accurate three‐dimensional position fixes for both navigational and geodetic purposes. The signals from these satellites, when propagated through the ionosphere, are subjected to phase delay, refraction, and dispersion. The ionospheric effects consequently lead to some degree of uncertainty in the position determination. Various approximations have been made to the complex refractive index of the ionosphere in order to evaluate these uncertainties. The dual‐frequency compensation eliminates the first‐order ionospheric effects. The higher‐order terms in the refractive index and the bending of the optical path give rise to a residual range error (RRE). The complete Appleton‐Hartree formula for the refractive index without any approximation has been utilized in the investigation. Consequently, a three‐dimensional ray‐tracing program, modified to give ‘homing’ facilities, has been used to study the variation of the RRE with the angle of elevation. The computed RRE values for the Navsat system, operating on 150 MHz and 400 MHz, are compared with the results of earlier approximate methods. The effect of the magnetic field on the RRE has been evaluated for both the Navsat and the Navstar (GPS) systems. The magnetic field can be completely neglected in the Navstar system operating on 1200 MHz and 1600 MHz. The RRE has also been computed for various electron density profiles for a constant total electron content (TEC). The RRE can be obtained for all practical profiles by using a simple Chapman profile with the same TEC and almost the same slab thickness as the experimental profile. The accuracy in RRE obtained by using the simple Chapman profile is high enough for geodetic applications.
A probabilistic theory of electromagnetic wave scattering from a slightly random surface 2. Vertical polarization
Authors: Nakayama J. , Sakata M. , Ogura H.
Published: February 2008

The scattering of an electromagnetic wave from an infinite random surface is studied by the probabilistic method developed in a previous paper. For a vertical polarized plane wave incident on a slightly random and perfectly conductive surface a new stochastic wave solution involving multiple scattering is obtained. The stochastic solution is free from the divergence difficulty as in the small perturbation method but gives an anomaly such that for a grazing angle of incidence the coherent scattering almost disappears and instead the incoherent scattering becomes dominant. In terms of the stochastic solution, a number of statistical properties of the scattering are calculated concretely for a perfectly conductive surface, such as the complex amplitude of the coherent scattering, the variance of the electric field, the optical theorem describing the power relation between the coherent and the incoherent scattering, the angular distribution of the incoherent scattering, the scattering cross section per unit area, and the surface wave flow, which are all illustrated in the figures.
Distortion of model subsurface radar pulses in complex dielectrics
Authors: Arcone Steven A.
Published: February 2008

The propagation of subsurface radar pulses in complex dielectric media is studied numerically. The model waveform is a 10‐ns sinusoidal cycle, and the media properties are similar to those of moist ground or sea ice. When the real part of the dielectric permittivity is frequency independent and the imaginary part is dominated by the dc resistivity, amplitudes of the positive and negative half cycles unbalance, and the sinusoidal zero crossing is delayed from its normal position. In these cases, if reflector depth is known, the dielectric constant can be measured from the time delay of the leading edge of the signal, and the dc resistivity can be estimated from a comparison of the input and output pulse power spectra. When dielectric permittivity is frequency dependent through a simple relaxation process, waveform distortion depends on relaxation frequency. In addition, if reflector depth is known, the dielectric relaxation parameters εs and ε∞ may be estimated when the medium relaxation frequency lies above and below the major portion of the pulse bandwidth, respectively.
Augmented electric‐ and magnetic‐field integral equations
Authors: Yaghjian Arthur D.
Published: February 2008

Augmented electric‐ and magnetic‐field integral equations, which preserve the basic simplicity, solution capability, and pure electric‐ and magnetic‐field character of Maue's original integral equations, are introduced to eliminate the spurious resonances from the exterior solution of the original integral equations. The exact dependence of the original and augmented integral equations on the geometry of the principal area (self patch) which excludes the singularity of their kernels is also determined, and alternate forms for the integral equations are provided that avoid integrals dependent upon the geometry of the principal area. Numerical results obtained for scattering from the perfectly conducting cube, sphere, and infinite circular cylinder confirm the theoretically predicted result that the augmented integral equations eliminate the spurious resonances for all perfectly conducting scatterers except the sphere.
Scan performance of dual offset reflector antennas for satellite communications
Authors: Rahmat‐Samii Y. , Galindo‐Israel V.
Published: February 2008

This paper summarizes the basic numerical steps employed to analyze dual offset reflector antennas. The technique is based on the application of the geometrical theory of diffraction from the subreflector and physical optics (PO) scattering from the main reflector. The PO integral is evaluated by using the Jacobi‐Bessel series expansion. Numerical results are presented for the off‐axis (scan) performance of an offset (clear aperture) Cassegrain antenna and comparison is made between a Cassegrain antenna and its equivalent paraboloid.
Equivalent network analysis of dielectric thin‐film waveguides for optical integrated circuits and its applications
Authors: Koshiba Masanori , Suzuki Michio
Published: February 2008

The equivalent network approach has been applied to the guided wave problems in the dielectric thin‐film waveguides for optical integrated circuits. This approach utilizes transmission lines and equivalent networks which furnish physical insight, and application of the so‐called transverse resonance technique yields, in very simple fashion, approximate but fairly accurate analytical expressions for the dispersion relations of the dielectric thin‐film waveguides. The results computed from these relations for the optical strip waveguide and the rib waveguide which have recently received considerable attention agree well with the results of the numerical approaches.
Turbulence in planetary occultations: A strong scattering formulation including an inhomogeneous background
Authors: Haugstad Bjarne S.
Published: February 2008

We show, from a Huygens‐Fresnel integral formulation of the scattered electromagnetic field, that the wave equation for a thin turbulent medium with nonconstant mean characteristics can be reformulated as a problem involving turbulence on a constant background. This is accomplished by a set of simultaneous transformations, which, when reversed and applied to known solutions of the simpler problem involving a constant background, yield results that correctly account for the inhomogeneous ambient atmosphere upon which the turbulence is superimposed. When applied to the mutual coherence function it is found that this quantity is unaltered if the separation of the two field points in the plane of the receiver is replaced by the corresponding separation obtained by projecting these points along the average refracted rays back to the ray periapsis. For the associated spectral broadening function this implies that spectra corresponding to different occultation depths and geometries may be obtained by simple translation of a shape‐invariant spectrum along the frequency axis. We also find that the scintillation index approaches asymptotically unity in strong scattering in precisely the same way as if the ambient background were strictly homogeneous, consistent with recent numerical simulations of a one‐dimensional scattering model.
Surface wind speed extraction from HF sky wave radar Doppler spectra
Authors: Dexter P. E. , Theodoridis S.
Published: February 2008

The ability to obtain sea surface wind speeds from HF sky wave radar backscatter spectra is important if such a radar is to make a meaningful contribution to a meteorological or oceanographic observation network. Since the radar measures wave parameters only, wind vectors must be inferred from the wave measurements in the light of what knowledge we have concerning the processes of wave generation. Previous attempts to extract wind speeds have proved unsatisfactory for a variety of reasons. We present here a new technique to enable such a derivation, which uses sea state parameters obtained with an appropriate inversion technique, together with relevant empirical/theoretical relationships on the growth of a wind‐generated sea. The procedure is illustrated with a Doppler spectrum obtained during the JASIN experiment, and some comparisons made with other JASIN surface data.
Interplanetary plasma concentration measurements by use of dual frequencies from separated sites
Authors: Croft Thomas A. , Edson William A.
Published: February 2008

Since 1965 the dual‐frequency method has been used for measuring densities of plasmas near planets and in interplanetary space. Signals at two frequencies are sent from an antenna on the earth to a spacecraft, or vice versa. The speed of the higher‐frequency signal is less affected by plasma than that of the lower‐frequency signal. The difference of delays provides a measure of the integrated effect of plasma along the radio path. In essence, the higher‐frequency signal serves as a benchmark against which the lower‐frequency effect is measured. Two markedly different sets of equipment have thus far been used to perform dual‐frequency observations; their strengths and weaknesses are reviewed, and it shown that many of the weaknesses could be overcome by using separate sites on the earth from which to transmit the low and high frequencies. A survey of the expected error in measurements using separated sites suggests that the critical element is time synchronization between them. The best available device for performing this function is the cesium beam clock; six such clocks were tested under conditions that accurately simulate an operational system. The test results are related to errors that would arise in plasma densities derived by this method. While the feasibility of site separation is dependent upon the specific mission to be accomplished, it appears practicable at the present state of the art for many planetary, solar wind, and comet applications.
Electromagnetic scattering from geophysical targets by means of the T matrix approach: A review of some recent results
Authors: Kristensson Gerhard , Ström Staffan
Published: February 2008

In the present contribution we review some recent work on scattering of electromagnetic waves from various geophysical targets, by means of P. C. Waterman's approach. As an introduction to the specific applications to be described, a general outline is given of the basic features of this approach, as applied to electromagnetic waves. The algebraic structure of the resulting equations for single and multiple scattering situations is discussed with special emphasis on the case of an infinite interface and an adjacent finite inhomogeneity in one of the half spaces. We review a number of applications relevant for electromagnetic prospecting. The bedrock is modeled as a lossy half space, and various configurations of ore bodies in this half space are considered. The measurements are assumed to be made on the surface or along a borehole into the ground, and the radiation source is again either on the ground or in the borehole. The behavior of the field in the vicinity of the inhomogeneity and interference effects are discussed. Actual ore bodies are often rather thin plates, and the influence of a layered structure of the half space may be of importance. Therefore in other applications the half space is taken to be layered, and the inhomogeneity is taken to be a perfectly conducting spheroid or a perfectly conducting disc.
Review of electromagnetic field calculations by digital linear filtering
Authors: Verma Rajni K.
Published: February 2008

The determination of electromagnetic fields over layered earth structures involves evaluation of the Hankel transform integrals. The classical method of numerical integration is very tedious, as it involves evaluating infinite integrals containing product functions with Bessel functions that are oscillatory and thus time consuming even on high‐speed digital computers. In contrast, the digital linear filter (convolution) method, which avoids Bessel function evaluations, is extremely rapid with regard to the ease with which it can be applied and to speed of calculations, and it provides accurate (five or more decimal accuracy) results. The speed of calculations can be further significantly increased while maintaining the same accuracy using a variable convolution approach. In some cases, the digital linear filter method has proved to be more rapid in calculations than the fast Fourier transform method.
Computer modeling of multipath propagation: Review of ray‐tracing techniques
Authors: Shkarofsky I. P. , Nickerson S. B.
Published: February 2008

The field of ray tracing and related differential equations are reviewed in reference to multipath propagation. Past efforts are limited in that analytical approaches require simple refractive index profiles and computer ray tracing usually does not include the crucial boundary condition that rays have to hit the receiver with adequate accuracy. We describe a three‐dimensional computer program that finds all the important rays converging on the receiver within 2 × 10−6m. We obtain the angles of launch and arrival, the ray trajectories, and the divergence or convergence factor of each ray intensity. A complex vector differential equation is also solved for the electric field polarization components from which we calculate the attenuation and depolarization. We include antenna amplitude and phase copolar and cross‐polar patterns. The potentiality of the computer program is illustrated for two refractive index profiles and varying receiver height assuming zero earth curvature. The first profile has a transition in refractive index at an elevated layer of about 300 m. Angles of arrival approaching ± 1° off boresight and time delays up to 19 ns are possible. The second profile has a transition in the refractive index gradient at a low‐altitude layer of 70 m. As the receiver height is changed from 40 to 80 m, rays appear, disappear, and coalesce. When rays coalesce, they also converge, and this leads to enhanced fields. We find that the depolarization is strongly dependent on the ground‐reflected rays for circular polarization and on the antenna patterns for all polarizations. Interference due to other rays is consequential. The divergence factor and the phases of the antennas are also important parameters.
Radar observations of polarization characteristics and lightning‐induced realignment of atmospheric ice crystals
Authors: Hendry A. , Antar Y. M. M.
Published: February 2008

The reflectivity and polarization characteristics of ice crystals as measured with a 1.8‐cm radar are reported. Included are measurements on stratiform ice crystal clouds, showing cancelation ratios of 16 to 20 dB and reflectivities of 7 to 28 dBZ. The degree of preferred orientation was approximately 40 to 50%. Some vertical soundings in snow appear to show changes in the snow crystal form with height. Observations of the rapid changes in polarization characteristics in the upper levels of thunderstorms show some cases for which the depolarizing particles are not the same as those which are responsible for the radar backscatter.
Radiation patterns of interfacial dipole antennas
Authors: Engheta N. , Papas C. H. , Elachi C.
Published: February 2008

The radiation pattern of an infinitesimal electric dipole is calculated for the case where the dipole is vertically located on the plane interface of two dielectric half spaces and for the case where the dipole is lying horizontally along the interface. For the vertical case, it is found that the radiation pattern has nulls at the interface and along the dipole axis. For the horizontal case, it is found that the pattern has a null at the interface; that the pattern in the upper half space, whose index of refraction is taken to be less than that of the lower half space, has a single lobe whose maximum is normal to the interface; and that in the lower half space, in the plane normal to the interface and containing the dipole, the pattern has three lobes, whereas in the plane normal to the interface and normally bisecting the dipole, the pattern has two maxima located symmetrically about a minimum. Interpretation of these results in terms of the Cerenkov effect is given.
VHF parabolic cylinder antenna for incoherent scatter radar research
Authors: Hagfors T. , Kildal P. S. , Kärcher H. J. , Liesenkötter B. , Schröer G.
Published: February 2008

A parabolic cylinder reflector antenna has been designed for high‐power radar observations of signals scattered from the ionospheric plasma at a frequency of 224 MHz. The antenna is constructed with an offset feed system to reduce aperture blockage. Efficient illumination for circular polarization using crossed dipoles is achieved by means of primary beam forming, which amounts to the construction of a polarization sensitive corner reflector. The measured aperture efficiency is 64%, and the gain 43.6 dB. The antenna can be mechanically steered through 90° in the meridian plane, and the beam can be offset from this plane by ±21.3° by manual phase steering of the 128‐element line feed. The width of the aperture is 40 m, and the length 120 m. The reflector is constructed in four 30‐m‐long sections which can be individually steered. The RF distribution system is such that the two antenna halves can be operated and pointed completely independently. The paper describes the design considerations, the construction, and the testing of the performance of the completed antenna.
Effects of high‐intensity microwave pulse exposure of rat brain
Authors: Guy Arthur W. , Chou Chung‐Kwang
Published: February 2008

Previous studies have indicated that auditory responses could be evoked in the head of animals exposed to 500‐μs‐wide or less microwave pulses of relatively small absorbed energies (5–180 mJ/kg). These studies were extended using an exposure system capable of locally exposing the head and especially the brain of the animal to a single 915‐MHz pulsed magnetic field with sufficient intensity to produce a specific absorption rate level as high as 4×105 W/kg for any pulse width. When the animal was exposed to various pulse widths (1μs to 360 ms) and power levels (2–10 kW), the animal displayed no reaction other than that due to the hearing effect until the peak absorbed energy density in the brain exceeded 28 kJ/kg, or an absorbed energy in the head of 680 J, regardless of peak power or pulse width. Thermographic and thermocouple measurements indicated a maximum temperature rise of 8°C or final maximum brain temperature of 46° −46.5°C at the reaction level. The reaction consisted of petit or grand mal seizures lasting for 1 min after exposure, followed by a 4‐ to 5‐min unconscious state during which normal reflexes were displayed. There was a decrease in heartbeat rate in the exposed unanesthetized animals. After the period of unconsciousness the rats recovered without apparent effect from the exposure. Measurements indicated that the brain temperature returned to baseline level within 5 min after exposure and the animals began moving when the brain temperature returned to within 1°C of their normal values. These results would indicate that the thresholds for convulsions induced by short exposures of the brain to high energy pulses are dependent only on the deposited energy and temperature rise. Histological examinations of some of the animal brains indicated some demyelination of neurons 1 day after exposure and some microfocal glial nodules in the brain 1 month after exposure.
Improving ionospheric maps using theoretically derived values of f0F2
Authors: Rush C. M. , PoKempner M. , Anderson D. N. , Stewart F. G. , Perry J.
Published: February 2008

The results of a study to improve the global maps of monthly median values of the F2 region critical frequency, f0 F2, using values determined from a theoretical model are presented. Values of the midlatitude F2 region critical frequency that could be used to improve the prediction of f0 F2 in regions of the earth inaccessible to ground‐based measurements were obtained. This was accomplished by including in the theoretical calculations realistic physical processes along with a realistic geomagnetic field model. Parameters were adjusted so that agreement was achieved between calculated and observed f0 F2 values as a function of local time at different stations, and then these same input parameters (i.e., neutral wind field, and neutral atmospheric model) were assumed valid at all regions of interest where the major difference is the geomagnetic field line configuration. Coefficients that yield global representations of f0 F2 were then determined using the theoretically derived f0 F2 values, and the predicted critical frequencies were compared with observed values to estimate the degree of improvement.
Electromagnetic scattering from subterranean obstacles in a stratified ground
Authors: Karlsson Anders , Kristensson Gerhard
Published: February 2008

In this paper we give a general three‐dimensional treatment of electromagnetic scattering from a finite obstacle in a stratified half space. The two generic cases of an obstacle either below all layers or inside one of the layers are treated. The results are an extension of earlier works on scattering in related geometries, treated by means of the T matrix method. Numerical results are presented for subterranean inhomogeneities of various shapes in a lossy one‐layered half space with plane interfaces.
Modeling of spaced‐receiver scintillation measurements
Authors: Wernik A. W. , Liu C. H. , Yeh K. C.
Published: February 2008

Spaced‐receiver scintillation measurements are modeled applying scintillation theory together with model spectral representations of nonfrozen turbulent media. The effects of velocity distribution of scatterers, diffusion of irregularities and velocity gradient across the scattering layer on parameters derived from spaced‐receiver scintillation experiments are studied. Both correlation and dispersion analyses are considered. The results from modeling are compared with observational data from the equatorial region. It will be demonstrated that self‐consistent models can be constructed in interpreting the data and information about the drift velocity field in the ionosphere can be obtained from spaced‐receiver experiments.
Structure and dynamics of the winter polar cap F region
Authors: Buchau J. , Reinisch B. W. , Weber E. J. , Moore J. G.
Published: February 2008

All‐sky imaging photometer measurements and ionospheric soundings taken at Thule, Greenland (86° corrected geomagnetic latitude), in December 1979 and January 1982 reveal the large‐scale organization of the winter polar cap ionosphere. Three groups of forms have been identified: (1) The most predominant features are sun‐aligned, generally unstructured, subvisual, F region arcs, extending for more than 1000 km (limit of all‐sky field of view) across the polar cap. In general, these arcs drift from dawn to dusk at speeds between 100 and 250 m s−1; however, stagnation of arc drift and drift reversals have been observed. The arcs are produced by soft particle precipitation. (2) During a magnetically disturbed period the arcs disappeared, and large patches of enhanced F region ionization drifted at speeds of 250 to 700 m s−1 across the field of view in the antisunward direction. Although arcs are produced by soft particle precipitation, preliminary results from the Dynamics Explorer satellite do not indicate any localized soft electron precipitation into the patches. (3) On a few occasions both forms were observed simultaneously. Between F region sun‐aligned arcs, which were drifting from dawn to dusk, small patches of ionization were observed moving at much higher speed in the antisunward direction. Both the arcs and the patches appear as strong localized irregularities in the ionospheric soundings. The Doppler information provided by the aircraft's Digisonde 128PS was used to relate backscatter traces to individual arcs or patches and to track individual features over more than 1500 km. For a large number of observations the time variation of measured Doppler velocities suggests specular reflection from electron density enhancements associated with the optical forms, rather than scatter from field‐aligned irregularities imbedded in the arcs or patches. A simple velocity filter applied to the ionogram data permitted the generation of range‐time characteristics for selected ionization drift velocities. A tendency for high velocities to occur during magnetically active periods was found. The ionospheric soundings showed that the F region arcs are bands of enhanced ionization, imbedded in a background ionosphere with a base height (h′F) of approximately 250 km and a critical frequency of approximately 4 MHz (∼2 × 105 el cm−3). The virtual heights in the ionograms did not change during transit of the arcs through the zenith. During the active periods, when the antisunward moving patches were observed, the background ionization dropped to less than 3 MHz (105 el cm−3) while the base height (h′F) moved up to heights above 400 km. The strongly ionized patches (f0 F2 > 8 MHz), however, were observed to reach a minimum virtual range of ∼250 km during the zenith transit, leading during their passage through the zenith to rapid h′F fluctuations of the order of 200 km within minutes.
Locating TID sources with a north‐south chain of rapid‐run ionosondes in western Québec
Authors: Morgan M. G.
Published: February 2008

Three rapid‐run ionosondes placed mutually 150 km apart for determination of the vector motion of traveling ionospheric disturbances, near L = 3.3 in northern New Hampshire and Vermont, were augmented with three more ionosondes laid out northward near L = 4.0. 4.5, and 6.0 in western Québec along the predominant direction (north‐northwest) from which daytime TID's arrive at the New Hampshire‐Vermont network. Observations were made for the 3‐month period March, April, May 1982. In a preliminary analysis, records have been reduced by our “slit‐scanner” technique to produce continuous displays of virtual height at selected frequencies moderately below the F layer critical. These isofrequency waveforms show a high degree of correlation among the three network stations, with propagation time delays from which speed and direction of TID travel can be deduced. An example, from 1980 observations, is shown of remarkable correlation over many daytime hours of the waveforms obtained by the network stations with that obtained by a sounder placed 1500 km downstream in the predominant direction (south‐southeast) toward which the TID's go. On the other hand, sources have now been found to be located as little as 200 km upstream from the network. TID's and their causative gravity waves propagate northward from these sources as well as southward. The sources are evidently narrow in north‐south extent for they frequently exist between the stations, spaced some 275 km apart, without causing absorption of ionosonde signals at either adjacent station. However, when they are located at an ionosonde station, they cause complete loss of echoes, thereby confirming that they are zones of energetic particle precipitation. They are believed to be due to precipitation from the outer radiation belt.
Relationship between scattered power and correlation time in VHF radar signals
Authors: Røyrvik O.
Published: February 2008

Equations describing the wave number spectra of wind shear‐generated turbulent velocities and refractive index irregularities are discussed, and relations between radar echo power and signal correlation time are derived. If the radar backscatter wave‐length is within the inertial subrange of the spectrum, a positive correlation between the scattered power and the signal correlation time is expected. For radar Bragg wavelengths within the dissipative subrange of turbulence, the correlation between scattered power and signal correlation time will be negative as usually expected in turbulence.
Ionospheric structures in the polar cap: Their origin and relation to 250‐MHz scintillation
Authors: Buchau J. , Weber E. J. , Anderson D. N. , Carlson H. C. , Moore J. G. , Reinisch B. W. , Livingston R. C.
Published: February 2008

An investigation of the polar cap ionosphere near the peak of the last solar cycle identified polar cap F layer arcs and ionization patches as unique features of the polar cap ionosphere, and as sources of severe scintillations observed on 250‐MHz satellite beacon signals. The continuing investigations in January and December 1983 and January 1984 have shown that arcs and patches persist as the dominant features of the winter polar cap ionosphere during periods of low sunspot numbers. Improved ionospheric soundings made at Thule, Greenland (86°CGL), showed a clear diurnal variation for the occurrence of the patch‐type ionization. Discussion of various possible mechanisms producing the observed ionization patches leads to the conclusion that the solar produced ionosphere equatorward of the dayside cusp is the source region of the ionization patches. Polar plasma convection transports this ionization across the cusp and the central polar cap. The local time dependence of the occurrence of the patches at Thule is shown to be a manifestation of the well‐known universal time control of the polar cap F region. A strong positive solar cycle dependence of the scintillations was measured during three extended campaigns and confirms earlier measurements. The diurnal variation of scintillations is almost flat at solar maximum and has a local time variation very similar to that of the patch type ionization at solar minimum. Both arcs and patches contribute to substantial scintillations around solar maximum, while only the patches are responsible for the considerably weaker scintillations during solar minimum.
Ionospheric scintillation measurements at 1.5 GHz in mid‐latitude region
Authors: Karasawa Yoshio , Yasukawa Koji , Yamada Matsuichi
Published: February 2008

Anomalous signal fluctuations due to ionospheric scintillation at 1.5 GHz appear occasionally on earth‐space paths in maritime satellite communication. With regard to the characteristics of ionospheric scintillations at gigahertz frequencies, few data are available in the middle latitude region. This paper describes the results of 1.5‐GHz scintillation measurements at Yamaguchi, Japan. Measurements were carried out by receiving a 1.5‐GHz beacon signal from the MARISAT satellite over the Indian Ocean with an elevation angle of 17.3°. In 13 months of measurements, very severe scintillation with peak‐to‐peak fluctuations exceeding 30 dB was observed in the equinoctial month, and a number of spike‐type scintillations were also observed, particularly at night. Scintillation characteristics, such as diurnal and seasonal variations, amplitude distribution, spectrum, and depolarization are discussed.
A statistical study of magnetic aspect effects associated with VHF auroral backscatter
Authors: Koehler J. A. , Sofko G. J. , Mehta V.
Published: February 2008

VHF auroral backscatter is usually assumed to show an aspect angle dependence on backscatter cross section of about −10 dB/deg. In the summer of 1981, an experiment was performed in northern Saskatchewan to measure, explicitly, this dependence at 50 MHz. The technique used was to simultaneously observe the same scattering volume from a number of receiving and transmitting locations. The data showed that the aspect sensitivity was highly variable and not obviously correlated with other geophysical phenomena. The spectral characteristics of the received backscatter showed a strong but also variable dependence on aspect angle. These observations, supported by some other previous experiments, suggest that there are important unexplained areas which cannot be accounted for by present theories of coherent backscatter.
Statistics of 1‐m wavelength plasma irregularities and convection in the auroral E Region
Authors: Waldock J. A. , Jones T. B. , Nielsen E.
Published: February 2008

Data from the Sweden and Britain Radar Auroral Experiment have been utilized in a statistical study of auroral backscatter due to 1‐m‐scale plasma irregularities and of plasma convection in the auroral E layer. An examination of approximately 15000 hours of backscatter amplitude data indicates that (1) the strongest backscatter is invariably associated with the main electrojets, between 1300–1900 UT and 2300–0300 UT, (2) only weak backscatter occurs in the vicinity of the convection reversals, particularly in the morning sector, and (3) the backscatter intensity can exhibit an aspect angle attenuation of between 0 and 10 dB/deg depending on the absolute intensity measured. Average convection patterns obtained from approximately 1400 hours of two‐station measurements reveal a well‐defined two‐cell structure for all magnetic conditions. As magnetic activity increases the Harang discontinuity moves toward earlier local times, the flow speed increases and the morning convection cell expands relative to the evening cell.