bluuebunny/crossref_metadata_2025 huggingface dataset:
Remarks on achieving representative electron density profiles of the ionosphere: Performance and advantages of the “composite virtual height method”
Authors: Laird A. R. , Wright J. W. , Gautier T. N.
Published: February 2008

A procedure intended for obtaining representative electron density profiles of the ionosphere from groups of ionograms, without incurring the expense and uncertainties of first obtaining the constituent profiles, is examined with the evidence accumulated through more than 200 station‐years of experience with the method. Some objective comparisons of this “composite virtual height” process with other ionospheric parameters obtained by accepted standard methods, and some subjective evaluations of the composite process, are presented. It is concluded that the method performs satisfactorily in practice and that it offers the economy, lack of bias, representativeness, and internal self‐control to justify continuing its use in global ionospheric monitoring.
Observations of ion‐acoustic wave scattering over long oblique paths
Authors: Frank V. R.
Published: February 2008

An experiment was designed to look for scattering planes from plasma waves traveling parallel to the geomagnetic field lines produced by ionospheric heating. Signals were observed that appear to be due to forward scattering from irregularities associated with ion‐acoustic waves having wave numbers 1.5 to 2.0 m−1. The data, however, are ambiguous as to the orientation of the strongest scatterers. VHF scattering from this effect is very small (30 dbsm) compared to scattering from field‐aligned irregularities (80 dbsm).
Radar cross section measurements and vertical incidence effects observed with Platteville at reduced power
Authors: Utlaut W. F. , Violette E. J. , Melanson L. L.
Published: February 2008

During the past four years, experiments using high power, high frequency transmitters have demonstrated that significant modification of the F region of the ionosphere can be effected. This paper illustrates that relatively low power, creating power flux densities in the F region of the order of 1 μw m−2, can also produce significant modification in the ionosphere. Such low power illuminations create field‐aligned ionization irregularities that produce a significant scattering cross section in the modified ionosphere. It permits propagation of VHF signals over selected long distance paths that could not be used by natural means.
Nonlinear saturation and angular rotation of instabilities in the E layer
Authors: Weinstock J. , Rognlien T. D.
Published: February 2008

Two plasma instabilities have been identified as causing small‐scale irregularities in the equatorial E layer. These instabilities are referred to as the two‐stream and gradient drift instabilities. Here a unified calculation is made of the saturated density amplitudes of these instabilities. The present nonlinear saturation mechanism is referred to as perturbed orbits or diffusing orbits. The density fluctuations required for this saturation are roughly 10% for the gradient drift instability and 1% for the two‐stream instability. This agrees with rocket measurements over India. In addition, a calculation is made of the frequency shift of two‐stream waves. This shift is a nonlinear effect due to the slowing down of electrons by the unstable waves, and could be viewed as an enhanced friction. It is shown that this frequency shift will cause the angular spectrum of the two‐stream waves to be rotated upwards or downwards, depending on the direction of the electrojet. Such rotations have been observed by radar.
Radio location of a trapped miner in an anisotropic coal field
Authors: Negi Janardan G. , Saraf Padmakar D.
Published: February 2008

Low frequency communication from a trapped miner is idealized as the electromagnetic boundary value problem of two‐layered anisotropic earth energized by a buried vertical electric dipole. The shale beds form the anisotropic cover for the coal swamp. Using numerical integration techniques the field structure has been investigated on the air‐earth interface. Analysis reveals that conductivity‐anisotropy modified the electromagnetic fields quite significantly and needs to be taken into account for the precise location of the source in emergency situations.
The impedance of a dipole antenna in the ionosphere: 2. Comparison with theory
Authors: Meyer P. , Vernet N.
Published: February 2008

The interpretation of the experiment EIDI I, described in a companion paper, is undertaken. A relatively complete calculation of the impedance is done including the effect of the temperature of the plasma by using the Vlasov equation and hydrodynamic equations, the structure of the sheath using a simple model of it, the collision frequency computed for an equilibrium plasma, and an estimation of various other small effects (wake, ionospheric gradient, motion of ions, …). The result so obtained is in very good agreement with the experiment for the most part but a strong discrepancy appears in the resistance when X > 1. This indicates that the main features of the theory are correct except that a loss mechanism is missing; some hypothetical ones are discussed.
The historical development of forecasting methods for ionospheric propagation of HF waves
Authors: Rawer K.
Published: February 2008

Short wave forecasting began in the late 1930s with rather crude, more global methods. The main steps of the development until the middle of the 1950s are described. Analytical methods have now replaced the original ones.
Magnetic storms and ionospheric forecasting over Italy
Authors: Dominici Pietro
Published: February 2008

A statistical analysis of 90 selected ionospheric storms has been carried out from MUF(ZERO)F2 and MUF(3000)F2 measured in Italy from 1958 to 1972. Typical behavior with regard to season, storm intensity, and statistical dispersion is shown for forecasting purposes.
Microwave propagation and communication networks
Authors: Voge J.
Published: February 2008

Recent evolution of telecommunication networks has been strongly influenced by two main trends: an increase of radio (microwave radio links, satellite links, and mobile services) with respect to cable communication, and a rapidly progressing development of digital transmission techniques compared with analogic techniques. The first tendency leads to saturation of the frequency bands presently used for radioelectric systems and hence the need of going to higher as well as yet unused bands. Digital systems on the other hand are particularly prone to interruptions even of very short duration and such cuts can only be tolerated for extremely low time percentages. The object of this communication is to study the role of propagation conditions in the future solution of these problems, imposing a limit on the distance between repeaters or using diversity techniques.
Full‐wave analysis and coupling effects in a crossover region
Authors: Arantes D. S. , Scarabucci R. R.
Published: February 2008

The solution of the wave equation for a plane stratified medium is obtained by using a fourth‐order accurate numerical integration technique. The general solution thus obtained is described in terms of four characteristic waves, two upgoing and two downgoing. A compact expression for the coupling coefficients Γij(i ≠j), which is suitable for numerical calculation, is also derived. These techniques are then used in a quantitative study of transmission coefficients, coupling factors, and wave structures through the crossover region where the proton whistlers are generated. The negligible influence of collisions upon the transmitted energies in the two upgoing modes is discussed. The results are then compared with previous works in which the thin‐slab full‐wave method was used.
The radar cross section of the sea at 1.95 MHz: Comparison of in‐situ and radar determinations
Authors: Teague C. C. , Tyler G. L. , Stewart R. H.
Published: February 2008

The rms wave height of seven sec ocean waves determined by remote measurements using high frequency radar is compared with that determined by direct in‐situ measurements using an accelerometer buoy. The radar‐measured values vary as the buoy‐measured values for various sea and wind conditions, but the radar values are systematically low with respect to the buoy values by about 2.8 db. The radar experiment is more straightforward than conventional measurements because the same receiving antenna is used to sample both the illuminating and echo fields. Radar‐measured values for 〈σ0〉 for seven‐sec ocean waves under homogeneous sea conditions did not exceed −29.7 db.
Sensitivity of HF circuit simulations to electron density models
Authors: Rush Charles M. , Edwards Wilson R.
Published: February 2008

The dependence of HF propagation parameters on the form of the electron density model used in circuit simulation calculations is investigated. It is seen that for identical values of the F2 region critical frequency and maximum height, no one of the selected models consistently reproduces observed electron density profiles better than any other. The differences in HF circuit parameters resulting from the use of different electron density models are seen to be significantly less than the uncertainty in the simulated parameters that arises from the inability to specify or predict the ionospheric structure with perfect accuracy.
Electromagnetic wave propagation over an inhomogeneous flat earth (two‐dimensional integral equation formulation)
Authors: de Jong G.
Published: February 2008

With the aid of a two‐dimensional integral equation formulation, the ground wave propagation of electromagnetic waves transmitted by a vertical electric dipole over an inhomogeneous flat earth is investigated. For the configuration in which a ground wave is propagating across an “island” on a flat earth, the modulus and argument of the attenuation function have been computed. The results for the two‐dimensional treatment are significantly more accurate in detail than the calculations using a one‐dimensional integral equation.
Coherence properties of wideband satellite signals caused by ionospheric scintillation
Authors: Rufenach Clifford L.
Published: February 2008

Radio scintillation on satellite signals caused by small‐scale irregularities in F‐region ionospheric electron density can be an important limitation on earth‐satellite communication and navigation systems. Scintillation imposes distortion in both amplitude and phase on wideband signals. In the present work, the shallow‐modulated phase screen theory is developed in terms of coherence bandwidth including a model based on a turbulent‐like power‐law description of the irregularities. The model results usually show a greater coherence bandwidth in the signal phase than in the signal amplitude. Therefore, systems that require phase coherence over a large bandwidth should be less affected than those requiring amplitude coherence.
Covariance of irradiance fluctuations propagating through a thin turbulent slab
Authors: Furuhama Y.
Published: February 2008

Irradiance fluctuations of a plane wave propagating through a strongly refracting thin turbulent slab are treated. The parabolic wave equation of the fourth‐order moment of the field is solved by an operational method and the triple integral form of the solution is obtained. Numerical results of the variance function show the saturation effect and the values of the covariance are given for the under‐ and over‐saturation regions.
Electromagnetic waves in irregular multilayered spheroidal structures of finite conductivity—Full wave solutions
Authors: Bahar E.
Published: February 2008

The propagation of electromagnetic waves excited by electric dipoles oriented along the axis of multilayered spheroidal structures of finite conductivity is investigated. The electromagnetic parameters and the thickness of the layers of the structure are assumed to be functions of the latitude. In the analysis, electric and magnetic field transforms that constitute a discrete and a continuous spectrum of spherical waves are used to provide a suitable basis for the expansion of the electromagnetic fields at any point in the irregular spheroidal structure. For spheroidal structures with good conducting cores, the terms in the solutions associated with the continuous part of the wave spectrum vanish. In general, however, when the skin depth for the core is large compared to its dimensions or when the sources are located in the core of the structure and propagation in the core is of special interest, the contribution from the continuous part of the wave spectrum cannot be neglected. At each interface between the layers of the irregular spheroidal structure, exact boundary conditions are imposed. Since the terms of the field expansions in the irregular structure do not individually satisfy the boundary conditions, Maxwell's equations are reduced to sets of coupled ordinary first‐order differential equations for the wave amplitudes. The solutions are shown to satisfy the reciprocity relationships in electromagnetic theory. The analysis may be applied to problems of radio wave propagation in a nonuniform model of the earth‐ionosphere waveguide, particularly when focusing effects at the antipodes are important.
Determination of the in situ high frequency electrical properties of permafrost rock
Authors: Lytle R. J. , Laine E. F. , Lager D. L. , Okada J. T.
Published: February 2008

Experiments were conducted to determine the in situ relative dielectric constant ϵr and skin depth δ of hard rock in a permafrost region. In the Brooks Range in northern Alaska, measurements of transmission attenuation and transmission phase shift were done between the surface and the hole as well as from hole to hole over the frequency range of 5 to 50 MHz. Relative dielectric‐constant and skin‐depth results were in the ranges 5 to 30 and 20 to 140 m, respectively.
Microwave measurements of coal
Authors: Balanis C. A. , Rice W. S. , Smith N. S.
Published: February 2008

In this investigation dielectric constant and loss tangent values of coal samples were computed from measurements made at microwave frequencies (8.2–12.4 GHz). Two different waveguide methods were used in the measurements. One technique utilized a finite sample and two reactive terminations, and the other required the use of an infinite sample simulated in the laboratory by a very long specimen. For each of the two Pittsburgh seam coal samples, dielectric constant and loss tangent variations were also measured as a function of moisture. Typical moisture contents of 10% and 15% were examined. Electromagnetic propagation through a single layer of coal seam was then investigated analytically as a function of coal depth.
Low‐frequency scattering by a dielectric body
Authors: Senior T. B. A.
Published: February 2008

The field scattered by a homogeneous isotropic dielectric of finite extent illuminated by a low‐frequency plane electromagnetic wave is expressed in terms of a single polarizability tensor which is a function of only the geometry of the body and a parameter τ representing either the relative permittivity or permeability of the dielectric. Integral equations from which to compute the individual tensor elements are derived. Some of the properties of the tensor, including bounds on its diagonal elements, are also developed, and data are presented for the special case of a spheroidal body.
Requirements for space shuttle incoherent scatter experiments
Authors: Harker K. J.
Published: February 2008

The feasibility of carrying out incoherent scatter experiments on the space shuttle has been analyzed. Design criteria considered were the required average transmitter power, frequency resolution, spatial resolution, and statistical accuracy. Experiments analyzed were measurement of the naturally enhanced plasma line and the ion component of the incoherent scatter spectrum, and the plasma line artificially enhanced by an intense HF radio wave. The ion component measurement does not appear feasible, while the other two appear reasonable for short ranges only.
Thermal microwave emission from half‐space random media
Authors: Tsang L. , Kong J. A.
Published: February 2008

Brightness temperatures resulting from microwave thermal emission from a half‐space random medium are calculated. The random medium has a nonuniform temperature profile and is characterized by correlation functions that possess both vertical and lateral variations. Radiative transfer equations are derived. They are solved with an iterative integral equation approach for small scattering albedo and with a numerical approach for general cases. New results are illustrated, discussed, and compared with various special cases. Phenomena caused by resonant scattering, which is absent under Rayleigh approximations, are revealed. Scattering in the lateral direction contributes to the decrease of the equivalent reflectivity and the increase of the brightness temperature.
Surface currents and charges on an electrically thick conducting tube in an E‐polarized, normally incident, plane‐wave field, 2, Measurements
Authors: Burton R. W. , King R. W. P. , Blejer Dennis
Published: February 2008

The measurement of the surface densities of current and charge in both amplitude and phase over the entire surface of an electrically thick conducting tube (ka =1) when illuminated by an E‐polarized incident field is described. Use is made of a probe system consisting of a short monopole and two small mutually perpendicular shielded loops arranged to move axially as a unit along a groove in a thick‐walled aluminum tube which can be rotated through 360°. Graphs of the measured magnitude and phase of the axial and transverse components of the surface density of current and of the surface density of charge on the outside surface of the tube are displayed as functions of the axial and transverse variables. Problems of measurement and of the correlation of measured and theoretical values are discussed. It is concluded that with proper attention to detail accurate measurements can be made and the distributions of current and charge understood.
Possibility of deep crustal probing in orogenic regions by studying variations of the surface impedance parameter of natural electromagnetic fields
Authors: Negi Janardan G. , Saraf Padmakar D.
Published: February 2008

Crustal structure in orogenic regions such as the Himalayan one consists of a tilted sedimentary layer on a granitic basement which is covered by metamorphic rocks. The complex crustal problem is modeled by an almost representative three‐layer model of an anisotropic dipping layer with a substratum of a transition layer overlaying a homogeneous half space. The surface impedance of natural electromagnetic fields has been evaluated for varying anisotropy and inclinations of the sedimentary surface and thickness of the metamorphic rock regions. The following interesting conclusions can be drawn from the curves. (i) Generally, crustal electrical mappings are limited in depth by increasing anisotropy of horizontal sedimentary layers (higher longitudinal conductivity as compared to the transverse one). Fortunately, here the plane wave impedance has a better response for higher dip angles and increasing anisotropy coefficients. (ii) The thickness of inhomogeneous metamorphic regions modifies the phase of the impedance parameter quite characteristically, particularly for high anisotropy factors. The study of deeper processes in areas of intense deformation and movements may find ready application of the numerical results of the realistic model, showing promise for deeper diagnostic probing by natural electromagnetic fields.
Lightning and its radio emission
Authors: Smyth J. B. , Smyth D. C.
Published: February 2008

An exact solution of Maxwell's equations is presented which describes adequately for the first time the many observed characteristics of the lightning discharge. These include: the source of the field required to develop the discharge channel; the leader stepping with pause time between steps which continue along different directions; the large diameter halo appearance of the leader and the small diameter hot arc return stroke; the current rise time in the channel. The solution provides the electromagnetic properties (inductance, capacitance, impedance) required to describe in detail the characteristics of the radio emissions: the spatial distribution of the radio field including its relative intensity and polarization; time duration of the radio signal with aspect angle; the energy radiated by the process. The solution provides a basis for designing meaningful experiments to establish relationships between observables essential in isolating the important characteristics required for a more complete description of the nature of lightning.
A simplified inversion procedure for calculating electron density profiles from ionograms for use with minicomputers
Authors: Paul A. K.
Published: February 2008

The method presented in this paper was developed especially for use on small computers without significant loss of accuracy. It can be applied to either of the magnetoionic components and includes the option of a first‐order ‘valley’ correction.
Measurements of electromagnetic field modifications in turbulent plasma
Authors: Ghosh A. K. , Shkarofsky I. P. , Almey E. N.
Published: February 2008

An experimental technique is developed to measure the modification of an electric field in a turbulent plasma. The method is suitable for use up to near critical density of the plasma. Measurements have been performed under three plasma conditions, namely, underdense, intermediate density, and near critical density. The results show more rapid attenuation of the coherent wave than predicted by exponential decrease, which is attributed to refraction in our nonuniform plasma column. The data indicate an initial buildup of the incoherent wave (both direct and cross‐polarized components) and then a decrease to a certain level depending on the equivalent thickness as the wave penetrates into the plasma.
Theory of an insulated linear antenna in a dissipative medium
Authors: Lee K.‐M. , Wu T. T. , King R. W. P.
Published: February 2008

The theoretical model of an insulated antenna in a general ambient medium is reviewed briefly. Attention is then directed to the solution of the integral equation for the current distribution in the antenna. The properties of the kernel are discussed in detail, and approximate solutions for the complex wave number are obtained. The evaluation of the kernel and other related numerical problems are discussed and a numerical method of computation is presented. A discussion of approximate solutions is included. A comparison of the theoretical results with measured data and numerical computations is made to check the applicable range of the theory.
Radiometric recognition of coherence
Authors: Carver K. R.
Published: February 2008

The response of a radiometer to thermal radiation passing through a spatial filter is described in terms of its ability to recognize coherence effects introduced by the filter. This is illustrated by considering the response of a microwave radiometer to thermal radiation passing normally through a lossless dielectric slab, either separated from the thermal source or adjoining it. The observed degree of coherence is defined and is shown to depend in a simple manner on the slab thickness (related to spatial bandwidth) as well as the temporal bandwidth of the radiometer. Rules of thumb are given for estimating whether a given situation requires a coherent model, an incoherent model, or a partially coherent model.
Measurements of basic transmission loss for HF ground wave propagation over seawater
Authors: Hansen Peder
Published: February 2008

Experimental measurements of basic transmission loss have been made between 4 and 32 MHz on a 235 km over‐ocean path. The purpose was to verify theoretical calculations of ground wave basic transmission loss, including the effect of varying sea state as postulated by Barrick. Stepped frequency soundings were taken two times per day for a one‐month period, and hourly for one 24‐hour period. In general, the data compare well with theory. The variations in signal strength during the 24‐hour test at frequencies below 20 MHz are consistent with sea state change and somewhat correlated with the recorded winds. However, at frequencies above 20 MHz the variations in signal strength were quite different, and (at 32 MHz) gave signals at times 25 dB greater than predicted by smooth earth theory. This phenomenon was attributed to ducting.
Worldwide mapping of VLF intensities generated by a ground transmitter
Authors: Souza R. F. , Scarabucci R. R.
Published: February 2008

The prediction of the magnetic field intensity of VLF waves in the upper ionosphere generated by a ground transmitter is investigated using a latitudinally dependent model of the ionosphere that includes only electrons as charged particles. The behavior of the wave in the lower ionosphere is analyzed using a full‐wave computer program developed by Scarabucci. The attenuation in the neutral atmosphere leaky waveguide is found using the results of that program. Above the E region the WKB approximation is used to find the ray trajectories. Based on these assumptions, a mapping of the wave magnetic field intensity at an altitude of 500 km for a night transmission of the NAA station is found. The theoretical predictions are compared with some data obtained from the OGO‐4 satellite.
Satellite measurements of ionic concentrations applied to low altitude incoherent scatter interpretations
Authors: Torr M. R. , Harper R.
Published: February 2008

The determination of ion and electron temperatures and electron density from incoherent scatter radar data has in the past involved assumptions concerning the ionospheric composition below 250 km. Using a very large data base of measurements of O+, O2+, NO+, and N2+ made by the Atmosphere Explorer C satellite, we have produced a model of the ionic concentration between 130 and 300 km as a function of solar zenith angle. The results of applying this information to the interpretation of the radar observations are compared with those of earlier treatments of the same data. As the effect of the new model is to increase the radar determinations of the temperature, this may explain previous discrepancies between Langmuir probe and incoherent scatter temperatures, where the comparisons have been made at these low altitudes.
Optical fiber theory: Opportunities for advancement abound
Authors: Gloge D.
Published: February 2008

A theorist‐turned‐systems‐engineer gives his views on challenging and possibly rewarding studies left to be undertaken in the field of optical fiber theory. A short review of the present status of that theory is included.
Coupling coefficient in strongly coupled dielectric waveguides
Authors: Suematsu Yasuharu , Kishino Katsumi
Published: February 2008

The coupling properties between two strongly coupled parallel dielectric slab waveguides are investigated using an analytical method based on waveguide theory. Coupling properties between two waveguides which have different geometrical configurations are given. To specify the strongly coupled waveguides, the coupling coefficient used in this paper is defined as the power transfer ratio. As a result of the analysis, it is shown that a complete power transfer between strongly coupled waveguides cannot exist even if the phase velocities are matched, and therefore an uncoupled factor, defined here, is important. When waveguide parameters are chosen properly, the coupling coefficient becomes insensitive to the structure deviation, and therefore the tolerances in the fabrication processes of the coupled waveguides and related devices can be relaxed.
A generalized WKB approach to propagation in inhomogeneous dielectric waveguides
Authors: Bahar E. , Agrawal B. S.
Published: February 2008

A generalized WKB method is used to obtain full wave solutions for the TE (horizontally polarized) and TM (vertically polarized) waves in multimode, inhomogeneous dielectric waveguides. The results are compared with recently published solutions based on a perturbational method and on the more familiar WKB method. Solutions based on the direct numerical integration of the differential equations for the transverse field components are also obtained to determine the validity of the different solutions. It is shown that the second‐order perturbational solution provides a significant improvement to the familiar WKB solutions only for the principal mode. For the second and all the higher‐order modes the WKB method yields more accurate solutions than the second‐order perturbational approach. The generalized WKB solutions yield accurate solutions for the principal and the higher‐order modes.
Approximate solution of inverse problems with piecewise continuous solutions
Authors: Perry William L.
Published: February 2008

In some inverse problems that arise in detecting information about unknown structures we expect solutions that are piecewise continuous, for example, the problem of determining the size and shape of an orbiting satellite from backscattered far‐field measurement. Moreover, many of these problems are ill‐posed, which means among other things that accurate determination of solutions from noisy data is difficult, if not nearly impossible, unless special steps are taken. One class of methods dealing with these difficulties is regularization. In this paper, a regularization scheme is shown for finding an approximate solution of inverse problems which (a priori) possess piecewise continuous solutions. A numerical example is given.
Linear wave properties, parametric decay processes, and resulting heating in a bounded magnetized plasma
Authors: Bhatnagar V. P. , Messiaen A. M. , Vandenplas P. E. , Van Oost G.
Published: February 2008

A plasma column along a steady magnetic field is produced by a helical microwave discharge source located at one end of a linear machine. Plasma parameters are: plasma density, 8 × 109—8 × 1010 cm−3; typical electron temperature, 7 eV; magnetic field, 900–2200 Gauss. Waves in the plasma are electrostatically excited by a split‐cylindrical, slow‐wave structure. The frequency domain studied includes the Trivelpiece‐Gould (T‐G) mode (ƒLH < ƒ < ƒpe), the surface wave mode, the electrostatic ion‐cyclotron mode (ƒci < ƒ < ƒLH), and the ion‐acoustic mode (ƒ≲ ƒci). Experimentally observed resonance frequencies in the T‐G mode range and the dispersion curves of the bounded plasma system (ƒ vs. k∥) are in good agreement with the bounded plasma theory for ion‐acoustic waves, the surface wave, electrostatic ion‐cyclotron and T‐G modes. Furthermore, parametric interactions have been studied on the present plasma setup which is characterized by the presence of many normal modes. Two types of resonant parametric instabilities have been simultaneously observed above a certain threshold of the pump power at a frequency ƒp (ƒLH < ƒp « ƒpe). In both processes the electron decay product is a Trivelpiece‐Gould mode. In the first case the ion decay product is an ion‐acoustic (IA) wave (ƒ < ƒci) and electron and ion heating are observed. In the second case the ion decay mode is an ion‐cyclotron (IC) wave (ƒci < ƒ < ƒpi) which is accompanied only by electron heating.
Thermal and endocrinological effects of protracted irradiation of rats by 2450‐MHz microwaves
Authors: Lu Shin‐Tsu , Lebda Nancy , Michaelson Sol M. , Pettit Sue , Rivera Dennis
Published: February 2008

Eighty‐six male Long‐Evans rats, 63–64 days of age, were subjected to 2450‐MHz CW microwave irradiation after a two‐week “gentling” procedure and three daily sessions of sham exposure. Exposures occurred without anesthesia at power densities of 0, 1, 5, 10, or 20 mW/cm2 for 1, 2, 4, or 8 hours. Rectal temperatures of exposed rats were found to be higher than those of sham‐irradiated rats at power densities of 1 mW/cm2 for four hours, 5 mW/cm2 for one and two hours, 10 mW/cm2 for two and four hours, and 20 mW/cm2 for all of the durations of exposure. Circadian rhythmicity of rectal temperature was noted in sham‐irradiated rats. Except for rats exposed at 20 mW/cm2 for four and eight hours, none of the averaged rectal temperatures of exposed groups reliably exceeded those of sham‐irradiated rats after eight hours of exposure. We concluded that the effect of exposure to microwaves at power densities below 10 mW/cm2 accelerated the appearance of the peak rectal temperature to an earlier time of day. Serum corticosteroid (CS) levels were signficantly lower in rats exposed at 20 mW/cm2 for eight hours than in animals sham exposed for the same duration. A significant correlation between rectal temperature and CS level was observed in the sham‐irradiated rats. Certain combinations of duration of exposure and power density of incident energy could dissociate this relationship, i.e., temperature increased sometimes without corresponding elevation of CS level. Serum thyroxine levels were depressed in rats exposed to radiation at 20 mW/cm2 for four or for eight hours. A stimulatory effect of microwaves on thyroid function was noted in rats exposed at 1 mW/cm2 for four hours, but the effect was transitory. Levels of growth hormone did not change.
Insect teratogenesis in a standing‐wave irradiation system
Authors: Olsen Richard G.
Published: February 2008

Pupae of the darkling beetle, Tenebrio molitor, were irradiated in the standing wave of a CW‐microwave field such that some of the pupae were positioned in the maximum plane of the E field while others were positioned in the maximum plane of the adjacent H field. The standing wave was produced by reflecting a plane wave at normal incidence from a metal plate that was suspended in the far field of a horn‐irradiated anechoic chamber. Averaged energy dose rates for exposed pupae were determined through cooling‐curve techniques by a thermistor in a 24‐gauge hypodermic needle. Experiments were conducted at 4.0 and 5.95 GHz with calculated doses of energy of 37.8 to 1526 J/g in exposures of 5 min to 6‐hours duration. Teratogenesis was found both for E‐field and for H‐field exposures and both for parallel and for perpendicular polarizations.
Immune response of mice to 2450‐MHz microwave radiation: Overview of immunology and empirical studies of lymphoid splenic cells
Authors: Wiktor‐Jedrzejczak Wieslaw , Ahmed Aftab , Czerski Przemyslaw , Leach William M. , Sell Kenneth W.
Published: February 2008

Male CBA/J mice were exposed to 2450‐MHz microwave radiation (each exposure: 30 minutes at an averaged dose rate near 14 mW/g). The mice were tested later to determine effects of the radiation on (1) the relative frequency of T and B cells; (2) the functional capacity of spleen cells from irradiated mice to respond to T‐ and B‐cell‐specific membrane stimuli; and (3) the ability to respond to sheep red blood cells and dinitrophenyl‐lyslyl‐Ficoll. Results demonstrated that microwave radiation has weak stimulatory effects on B‐ but not T‐lymphoid cells in the spleen. Single exposures to radiation produced an increase in the incidence of cells with complement receptor on the cell's surface. Three exposures to radiation induced increases in the total number of splenic cells, in the incidence of immunoglobin‐positive cells, and in the incidence of complement receptor‐positive cells. The total number of T cells was unaffected by single or triple exposures of mice to the radiation.
Effects of a 60‐Hz magnetic field on activity levels of mice
Authors: Smith R. F. , Justesen D. R.
Published: February 2008

A total of 39 mice in groups of three was observed for 48 hours for locomotor activity and for aggression‐related vocalizations during short (120 sec) but recurrent and aperiodic presentations of a 60‐Hz field. The field was a sinusoid with a dominant magnetic component that averaged 1.7 mWb/m2 (rms) and its effects were analyzed in terms of strain of mouse, (DBA/2J pigmented versus CD/1 albinos), of nocturnal versus diurnal levels of activity and of trend. Highly reliable and persistent increases of activity of a field‐locked sort were observed. Circadian periods, as expected, and strain of mouse were also reliable sources of variation: mice of both strains were more active nocturnally than diurnally; and while the CD mice had higher baselines of activity, the DBA mice were more reactive to the magnetic field. Data from control experiments with no mice, with sham‐exposed mice and with anesthetized mice tend to exclude electrical artifact as the basis of the field‐induced increases of activity. The influence of the field on the measure of aggressive behavior is only conjectural because of low and variable rates of vocalization, both during baseline measures and during periods of exposure to the field.
The current source‐function technique solution of electromagnetic scattering from a half plane
Authors: Hanson Donald F. , Mayes Paul E.
Published: February 2008

Integral equations for electromagnetic scattering problems have usually been based on procedures attributed to Pocklington or Hallén. Integral equations for the unknown induced sources are obtained after utilizing the vector and scalar potentials as an intermediary to relate the fields and currents. This paper utilizes an alternative field‐source relationship to obtain an integral equation which retains the integral operator with the simple kernel of Hallén's equation as well as the simple forcing function of Pocklington's equation. Further benefits of this formulation are yet to be determined. The unknown function in the integral equation is called the current source‐function since it is the forcing function in an inhomogeneous differential equation for the current induced on the scatterer. The purpose of the work presented here is to develop further this new technique by applying it to a classical problem. Hence, the solution for the current induced on a perfectly conducting half‐plane by a plane‐wave H‐polarized incident field is developed.
Microwave radiometric sensing of the marine boundary layer
Authors: Beard C. I. , Martin L. U.
Published: February 2008

An experiment performed in 1975 demonstrated that 22‐GHz microwave radiometers could detect, and localize in altitude, long‐period (3–15 min) internal gravity waves on low level atmospheric inversion layers. A second experiment, in June 1976, examined atmospheric structure in finer detail by using two 3° beam width antennas. This has resulted in the first observation and correlation between radiometer beams of short‐period (i.e., 1 to 2 min), Kelvin‐Helmholtz waves. In addition, during unchanging synoptic conditions, the radiometers would follow changes in the height of the inversion base with an average sensitivity of 25 m/K. Using an atmospheric “quiet period” to determine the radiometer noise level, the resulting vertical resolution of the radiometer is shown to be approximately ±1 m, comparable to active sensors. The observed sensitivities were found to be unaffected by the presence of stratus clouds beneath the inversion. A 5.5‐hour train of 10‐ to 11‐min period waves on 19 June 1976 showed recurring internal (gravity) wave propagation from three or four directions. The corresponding radiometer undulations shifted time‐phase 180° with the microbarograph surface pressure undulations when the direction of wave propagation changed. Calculation of wave phase velocities based on meteorological soundings favor second‐mode wave propagation, in agreement with the observed wave velocities and microbarograph periodicities.
Joint statistics of rain attenuation on terrestrial and earth‐space propagation paths
Authors: Fergusson Angus , Rogers R. R.
Published: February 2008

Radar reflectivity data from the summer of 1975 were used to simulate the rain attenuation at 13 GHz on a network consisting of five earth terminals and six interconnecting terrestrial links. As rain echoes passed over the complex of terrestrial and earth‐space propagation paths, the attenuation over each of the eleven paths was calculated as a function of time with a resolution of a few minutes. Thirty‐four hours of data from twelve days were analyzed statistically to determine attenuation distributions for all paths in the network, separately and in various combinations. The five earth‐space paths were parallel, all at 18.5° elevation and 121.5° azimuth. The average attenuation distribution for these paths was essentially the same as that reported by Hodge for a network of eleven terminals located 35 km to the south of our network. Moreover, an analysis of the diversity gain achieved by using pairs of earth‐space paths revealed a dependence on terminal separation distance that was not significantly different from that of Hodge. A study of the attenuation distributions for the six terrestrial links of the network showed primarily a dependence on path length. For paths of equal length, however, moderate values of attenuation tended to occur less frequently on paths oriented perpendicular to the average direction of storm motion. Analyzed from the viewpoint of route diversity, data for the terrestrial links showed that the frequency of outages over a 40 km path could be reduced by an order of magnitude by adding a repeater along the route. Earth stations, defined as consisting of a main and an alternate earth terminal plus the terrestrial link between them, were found to have a reliability determined primarily by joint outages on the two earth‐space paths. Exceptions were cases with (1) baselines longer than about 30 km, (2) a low reference fade margin on the terrestrial link, (3) a terrestrial path leaving the main terminal in the same direction as the satellite azimuth. In these cases outages on the terrestrial link could further limit the overall system reliability.
Modal theory of long horizontal wire structures above the earth: 2, Properties of discrete modes
Authors: Olsen Robert G. , Kuester Edward F. , Chang David C.
Published: February 2008

The characteristics of the discrete propagation modes on horizontal thin‐wire structures located above a dissipative earth are investigated. In addition to the well‐known transmission line mode, a new root of the characteristic equation is found which is identified as a “surface‐attached” mode because of its close connection with the Sommerfeld pole (Zenneck wave) in some parameter ranges. Under many conditions the surface‐attached mode suffers substantially less attenuation along the propagation direction than does the transmission line mode. Numerical investigation of the propagation constants of the two modes is made, and field plots for the modes for a variety of wire parameters are presented.
Maximum‐entropy spectral analysis of radio‐auroral signals
Authors: Moorcroft D. R.
Published: February 2008

In early 1976 the Homer phased‐array radar was used to study the spectra of radio‐auroral echoes. Good temporal resolution was obtained by using very short data segments. These were analyzed by the maximum entropy method (MEM) of spectra analysis, in a form suitable for treating multiple segments of data. The use of a relatively new method of spectra analysis to obtain spectral estimates of such a short data sample raises a number of questions concerning the reliability of the results. A variety of tests using synthetic time series have demonstrated both the reliability of the spectra estimates and the superiority of MEM for the analysis of Homer radar data. In particular, line‐splitting or shifting does not seem to be a problem for spectra with sufficiently broad spectral peaks such as those of the radio aurora. Also, although the widths of the peaks in MEM spectra are highly variable, they average to give the true width. Analysis of the widths of spectral peaks in the Homer radio‐auroral data indicates that more than one scattering mechanism may be involved, and that the auroral electrojet is probably quite irregular.
Combined effects of rain and imperfect antennas on depolarization in microwave propagation
Authors: Shkarofsky I. P.
Published: February 2008

Expressions are given on cross‐polarization resulting from the combined effects of rain and imperfect antenna isolations in satellite‐to‐earth links. The calculations at 4 and 11 GHz frequencies differ from previous work in two ways, namely, that the theory adopts a worst phase relationship between receiver and transmitter antennas in clear weather, and that a more realistic expression is used for the rain extent. Sample results are illustrated on cross polarization versus misalignment angle, clear weather antenna isolations, canting angle, attenuation, and rain rate.
Angular potential patterns of electrostatic electron cyclotron waves radiated from a point source
Authors: Ohmori S. , Ohnuma T. , Adachi S.
Published: February 2008

The angular potential pattern of electrostatic electron cyclotron waves radiated from a point source in a magnetoplasma has been obtained theoretically in an analytic form. The result is generally applicable for calculating the potential patterns for all frequency regions greater than the electron cyclotron frequency. The theory has been confirmed by an experiment in a magnetoplasma.
High‐frequency surface fields excited by a point source on a concave perfectly conducting cylindrical boundary
Authors: Felsen L. B. , Ishihara T.
Published: February 2008

A previous analysis of the surface currents excited by a line source located on a perfectly conducting concave cylindrical boundary is here extended to point‐source excitation. Alternative field representations in terms of geometric optical contributions, whispering gallery modes, and canonical integrals are explored, and their utility is assessed by extensive numerical computations. As for the two‐dimensional case, it is found that a combination of rays and whispering gallery modes provides an efficient and physically appealing method for calculating the field. The results are applicable to all observation points lying outside a narrow angular region surrounding the axial direction as seen from the source point.
Wave theory for microwave remote sensing of a half‐space random medium with three‐dimensional variations
Authors: Tsang L. , Kong J. A.
Published: February 2008

The two‐variable expansion technique is used to solve for the mean Green's functions from the Dyson equation under the nonlinear approximation for a half‐space random medium with three‐dimensional correlation functions. The Bethe‐Salpeter equations are then solved under the ladder approximation. The radiative transfer equations, which have been applied extensively in the study of microwave remote sensing problems, are derived under these approximations. The limiting cases of large and small horizontal correlation lengths are discussed. It is found that there is only one propagation constant except for the case of large horizontal correlation lengths, in which there are two propagation constants. We also show that boundary layer appears in first‐order solutions and does not appear in zeroth‐order solutions.
A passive microwave technique for profiling of atmospheric water vapor
Authors: Schaerer G. , Wilheit T. T.
Published: February 2008

A technique is developed for retrieval of water vapor profiles from microwave radiometric measurements near the 183‐GHz water vapor line. Weighting functions are developed which are useful in the retrievals and which permit insight as to the information content in a given measurement. Retrievals are performed using synthetic data.
Relativity experiments with clocks
Authors: Vessot Robert F. C.
Published: February 2008

The atomic clock is the nearest approximation we have to the hypothetical proper clock of the ‘gedanken,’ or thought, experiments that are used to illustrate the new relativistic or gravitational phenomena identified in post‐Newtonian studies of gravitation. The recent decades of progress in space technology have made the whole solar system accessible as a laboratory for gravitation, and the atomic clock with stability in the 10−16 domain offers a method of measuring distance and velocity as well as being an experimental device to probe the behavior of time. Experimental gravitation, which is now nearly synonymous to experimental relativity, is reviewed in the context of modern experimental techniques, and the role of the clock is discussed in detail. A catalog of experiments, based on four classes of experiments as described by Misner et al. (1970), is used to identify the particular aspect of gravity that is being tested, and the application of the clock is discussed in each case.