bluuebunny/crossref_metadata_2025 huggingface dataset:
An improved comparison of the LHR frequency observed by a VLF receiver and calculated from ion density measurements on the same spacecraft
Authors: Morgan M. G. , Brown P. E. , Johnson W. C. , Taylor H. A.
Published: February 2008

Comparisons are made of the LHR (lower hybrid resonance) frequency observed on a predawn and on a dusk pass of OGO 6 over Alaska by means of a VLF receiver with an electric dipole antenna, and by calculation from the ion densities measured with a sweeping ion‐mass spectrometer. An improved calibration of the spectrometer was used, taking better account of the spacecraft charge, and the change in L‐value of the spacecraft position during the sweep‐time of the spectrometer was also taken into account. Close agreement by the two methods of measurement is obtained.
Impedance characteristics of coaxial and planar magnetoplasma capacitors
Authors: Harker K. J. , Crawford F. W.
Published: February 2008

A theory has been developed for the impedance of a homogeneous magnetoplasma enclosed between two specular reflecting coaxial electrodes, with a static magnetic field parallel to the electrode axes. The parallel‐plate magnetoplasma capacitor is treated as a sub‐case. Starting with the Vlasov equation, an integral equation is derived for the electric field. Solving this equation, and integrating to obtain the voltage, gives the capacitor impedance. This includes a capacitive component, and a resistive component expressing the Landau damping associated with the open orbits of electrons reflected at the electrodes. A direct numerical solution of the field integral equation has been carried out for a range of values of magnetic field, plasma density, and signal frequency. The values of impedance so obtained are compared with the predictions of macroscopic theory, and of an approximate microscopic theory in which open orbits are ignored and solutions are obtained using finite Fourier transform methods. The mathematical relations between these theories are demonstrated.
Diffusion coefficient for turbulent plasmas
Authors: Harker K. J.
Published: February 2008

The spatial diffusion coefficient is derived for an unmagnetized, collisional plasma with a turbulent wave spectrum. The theory is applied to experimental results for ion‐acoustic turbulence in a collision dominated plasma, and also to an equilibrium plasma for comparison purposes.
Measurement of microwave radiation absorbed by biological systems: 1. Analysis of heating and cooling data
Authors: Allis John W. , Blackman Carl F. , Fromme Madeline L. , Benane Shawnee G.
Published: February 2008

In order for meaningful comparisons to be made between experiments from different laboratories, reliable dosimetry is needed for biological systems exposed to microwave radiation. We present an improved analytical method for determining energy absorption which uses heating and cooling curves. The method is demonstrated for in vitro samples that were exposed to microwave radiation in two different exposure systems. Advantages and disadvantages of the method, as well as practical considerations, are discussed.
Focal hyperthermia as induced by RF radiation of simulacra with embedded tumors and as induced by EM fields in a model of a human body
Authors: Chen Kun‐Mu , Guru B. S.
Published: February 2008

In the first of two studies distributions of rates of EM energy absorption were observed in simulated biological bodies with embedded tumors. Part‐ and whole‐body simulacra as irradiated by EM fields that ranged in frequency from 15 to 500 MHz exhibited differentially greater heating of tumors. Reduction of tumor conductivity resulted in enhancement of tumor heating. In the second study, a model of man was observed for induction of EM fields by 1 to 500‐MHz energy. Greater rates of energy absorption occurred in regions of smaller cross sections and in tissues with lower conductivities.
Losses due to the inhomogeneous sheath surrounding an antenna in a plasma
Authors: Meyer‐Vernet N. , Meyer P. , Perche C.
Published: February 2008

It is shown that, by taking into account the inhomogeneous sheath surrounding an antenna in a warm isotropic plasma, the HF input resistance may be increased by several orders of magnitude, for frequencies below the plasma frequency. This may serve to explain the “anomalous” high resistances observed in previous experiments.
Surface currents and charges on an electrically thick and long conducting tube in E‐ and H‐polarized, normally incident, plane‐wave fields
Authors: Burton R. W. , King R. W. P. , Blejer D. J.
Published: February 2008

Recent work on the theoretical and experimental determination of the distributions of surface currents and charges induced on an electrically thick tubular cylinder with the resonant electrical half‐length kh = 1.5π by an E‐polarized field is extended to electrically quite long tubes excited by both E‐ and H‐polarized plane‐wave fields. A simple approximate analytical representation of the currents and charges is described in terms of forced and resonant transverse Fourier components for cylinders with lengths not restricted to those that are axially resonant. Extensive theoretical and measured graphs and contour diagrams of the distributions of current and charge density are displayed and compared specifically for tubes with the electrical radius ka = 1 and lengths up to kh = 3.5π.
Generalization of ELF mode theory to include unequal surface impedance at the lower ionosphere boundary
Authors: Tran Anh
Published: February 2008

The mode theory for ELF wave propagation in the earth‐ionosphere cavity is generalized for the consideration of unequal surface impedances at the lower ionosphere boundary for modes with different values of νn. A mathematical expression which determines the significance of all ELF modes as compared with a designated mode is also derived. Numerical results of ∣Er∣ are obtained to show the effects due to the forementioned consideration. Although only the lowest zero‐order mode is significant whether the surface impedances are equal or not, when introducing the lowest non‐zero‐order mode, for σi = 3.8 × 10−6 mho / m and 2.0 × 10−6 mho / m, there will be a relative error, respectively, of 3.4% and 4.4% in ∣Er∣ at f = 3 kHz if the surface impedances are assumed to be equal. The relative error is independent of the source‐receiver separation and decreases with frequency. There is also an error in excitation factor caused by the assumption of equal surface impedances, which is the same as that in ∣Er∣.
Group‐delay variations at oblique incidence resulting from medium‐scale travelling ionospheric disturbances
Authors: Bartning B.
Published: February 2008

By means of a bistatic FM‐CW sounding system (transmitter‐receiver distance 565 km in central Europe), group‐delay and Doppler records at several fixed frequencies (about 4–8 MHz) were made. The daytime records show medium‐scale travelling ionospheric disturbances (TIDs). Ray‐tracing studies are presented which exhibit the influence of some ionosphere and TID parameters on the shape of the group‐path traces. Quantitative comparison between observed and calculated traces shows agreement.
On the origin of long‐period features in low‐angle sea backscatter
Authors: Wetzel Lewis
Published: February 2008

When viewed at extremely shallow grazing angles with a microwave radar, sea backscatter displays a variety of spatio‐temporal features with time scales of the order of several minutes or more. A modest body of experimental evidence accumulated from several radars looking at different oceans shows components with a period of 3–4 min sometimes imposed on a much stronger periodicity of 10–15 min, and sharply defined moving striations with speeds of the order of 15 kts and lifetimes of several minutes. The origin of these features may be sought among a wide assortment of physical phenomena, including surface effects (such as wave packets or interference patterns, illumination thresholding at extreme grazing angles, internal waves in the thermocline, shelf waves, fluctuations in the surface wind field), or propagation effects resulting from refractivity perturbations due to traveling disturbances in the atmospheric boundary layer or to water vapor perturbations in the evaporative layer. None of these hypotheses can account for all of the features observed in the data, but the more likely candidates are discussed in detail, using available data for the relevant oceanographic and atmospheric parameters. It is concluded that the behavior shown in this paper is most probably due to group effects among surface waves emphasized by illumination thresholding at low grazing angles.
Signatures of snow in the 5 to 94 GHz range
Authors: Hofer R. , Schanda E.
Published: February 2008

A long‐term observational study of the microwave emission and scattering behavior of snow under quasi‐controlled conditions was started recently on a high‐altitude Alpine test site. Results of the first set of measurements, carried out with five radiometers at frequencies of 4.9, 10.5, 21, 36, and 94 GHz, are reported and preliminary interpretations are given. The spectral reversal of the brightness temperature and its dependence on look angle and polarization provides a means to distinguish between different snow states and to estimate the wetness factors of the surface layer of the snow pack. From an electromagnetic scattering standpoint, snow cover is an excellent medium to use for studying volume scattering.
Subsurface EM transmission in tunnel waveguides
Authors: Wait J. R. , Hill D. A.
Published: February 2008

The concept that electromagnetic waves can be guided in tunnel‐like structures in the earth is now being exploited for telecommunication purposes by groups in Belgium, France, England, Canada, and the US. The relevant propagation phenomena are much more sophisticated than first envisaged. Some of the complexities are due to the complicated structure of tunnels and haulageways that were designed for ease of transportation rather than communication. Nevertheless, much progress has been made by utilizing idealized models with varying degrees of complexity. A significant aspect of this study is how an antenna interacts with the tunnel walls. For the communication problem, we wish to minimize this coupling with the environment but, for a remote sensing tool, this interaction can be used to determine the conductivity and permittivity of the external earth media. An important finding is that the input resistance of an electric dipole is approximately a constant for frequencies less than about 25 MHz for a typical tunnel radius of 2 m. In contrast, for the same conditions, the input resistance of the magnetic dipole or small loop varies approximately as the square of the frequency. Such results are shown to be in qualitative agreement with an earlier analysis of dipoles over a dissipative half space and dipoles located in insulated cavities.
Tangent‐plane aberration in aperture synthesis processing
Authors: Peterson I. R.
Published: February 2008

The transform normally used for processing the measurements of a rotational aperture synthesis radiotelescope is only approximate. When other than east‐west spacings are used, it causes a reduction in the telescope's resolution. In this paper, the magnitude of the aberration is computed and shown to be significant for high resolution instruments. A new aberration‐free transform is derived.
Wave propagation through a random medium: The random slab problem
Authors: Acquista Charles
Published: February 2008

The first‐order smoothing approximation yields integral equations for the mean and the two‐point correlation function of a wave in a random medium. A method is presented for the approximate solution of these equations that combines features of the eiconal approximation and of the Born expansion. This method is applied to the problem of reflection and transmission of a plane wave by a slab of a random medium. Both the mean wave and the covariance are calculated to determine the reflected and transmitted amplitudes and intensities.
Inversion of data from diffraction‐limited multiwavelength remote sensors: 1, Linear case
Authors: Rosenkranz P. W.
Published: February 2008

The remote sensing inverse problem is considered in which the sensor does not necessarily view the same area on the earth at each wavelength, and spatial correlations of the geophysical parameters may be present. Under the conditions of linearity and stationary statistics, the minimum mean‐square error solution to the problem of inverting such data is a spatial filter of the Wiener‐Kolmogorov class. The resulting remote‐sensing system can be characterized by an impulse response matrix in ordinary space or by a transfer matrix in frequency space. A signal‐to‐noise matrix for the geophysical parameters to be sensed is also defined; this matrix depends on the postulated a priori statistics and on the characteristics of the remote‐sensing instrument. The system transfer matrix and the signal‐to‐noise matrix are simultaneously diagonalizable. The optimum transfer matrix filters out of the estimate vector those eigenparameters for which eigenvalues of the signal‐to‐noise matrix are less than unity.
Nonlinear self‐distortion of electromagnetic waves in a magnetoplasma: Arbitrary direction of magnetic field
Authors: Tewari D. P. , Kumar Awdhesh , Tripathi V. K.
Published: February 2008

Using an elementary approach, the phenomenon of self‐distortion of an amplitude modulated EM wave (extraordinary mode) in a magnetoplasma has been studied for the general case of group velocity not aligned with the phase velocity. The nonlinearity in the plasma arises because of modulation of the temperature‐dependent collision frequency of electrons by the wave. In the case of whistlers, the fractional change in the index of modulation of the wave due to nonlinearity is shown to increase rapidly with increasing angle between the wave vector and the magnetic field. In the case of high frequency waves, the angular dependence of self‐distortion is less pronounced.
Self‐distortion of a whistler pulse in a plasma
Authors: Tripathi V. K.
Published: February 2008

Following the technique used by Akhmanov et al. to solve the nonlinear wave equation, we have investigated the propagation of temporally and spatially gaussian whistler pulses in a plasma. In the linear case the temporal width of the pulse is enhanced (due to dispersion) at a distance R ˜ τ2v3g/(∂2ω/∂k2) whereas its size is enhanced (due to diffraction) over a length Rd ∼ 2kr20/(1 + ϵ+/ϵzz); τ, r0, k, vg, ϵ+, and ϵzz are the initial time width, size, wave vector, group velocity, and the components of the dielectric tensor of the plasma. In the case of a high‐power whistler, the ponderomotive nonlinearity causes self‐focusing (for all values of ω/ωc) of the whistler and results in severe distortion of the pulse shape.
A cylindrically stratified model of the plasma wake of a dipole antenna entering a planetary atmosphere
Authors: Nordgard John D. , Papas C. H.
Published: February 2008

The radiation characteristics of a dipole antenna are calculated in a high‐velocity wind of ionized gases representing the wake region of an antenna located on the aft portion of a probe entering a planetary atmosphere. The antenna and the support structure are assumed to give rise to a cylindrically stratified plasma flow field, which is allowed to possess a radial distribution in the electron concentration and collision frequency. Each cylindrical layer of the plasma shell moves at a uniform axial velocity with respect to the antenna and is biased magnetically along the axis of the cylinder. The antenna is represented by a circularly polarized turnstile antenna mounted off‐axis a quarter wavelength above a ground plane and is oriented transverse to the axis of the cylinder. The antenna operates at frequencies near the cutoff frequency of the plasma in the wake. Integral expressions for the cylindrical components of the electric and magnetic field intensities are derived and are evaluated in the rest frame of the antenna using the techniques of asymptotic expansions. The resulting far‐field gain patterns of the antenna are given and are compared with the free‐space patterns.
Some notes on the scientific work of H. Bremmer
Authors: Stumpers F. Louis H. M.
Published: February 2008

Hendricus (Henk) Bremmer, born March 23, 1904, in the Hague, got his doctor's degree as an experimental physicist in 1934 in Leiden, the Netherlands. His thesis dealt with investigations of heat conductivity at low temperatures. This cryogenic work was carried out in the famous Kamerlingh Onnes Laboratories, where he worked as an assistant to Professor de Haas from 1927 to 1934. Eight publications[11–81], most of them in the Proceedings of the Royal Academy of the Netherlands, on the thermal conductivity of tin, indium, lead‐thallium, mercury, and superconducting alloys, treated this theme.
Source radiation in the presence of smooth convex bodies
Authors: Mittra R. , Safavi‐Naini S.
Published: February 2008

The problem of radiation from sources in the presence of smooth, convex, impenetrable objects is considered, and a brief survey of various high frequency techniques is presented. A generalization of the geometrical theory of diffraction, and two new techniques based on the spectral domain approach and an asymptotic evaluation of the radiation integral for the surface current, also are discussed. Some numerical results derived from the spectral domain formulas are presented and a comparison with available theoretical and experimental data is included.
Some properties of wave equations in inhomogeneous media
Authors: Broer L. J. F.
Published: February 2008

Inspired by the work of men like Bremmer, so many authors have developed the field of wave equations that it becomes difficult to maintain a sufficient overview of the subject. This paper attempts, therefore, to put together some of the basic notions and results in a slightly more general and systematic way than is usually employed.
Review of the theory of the irradiance distribution function in turbulent media with a particular emphasis on analytical methods
Authors: Furutsu K.
Published: February 2008

The recent theories on the irradiance distribution function of waves in turbulent media are reviewed with a particular emphasis on their physical and mathematical bases. The Rice‐Nakagami distribution is first investigated in connection with the analytical singularity of its characteristic function and the derivation of the latter. The distribution function P(I) of the irradiance I is then represented in terms of an integral over the order variable v of 〈Iv〉, v = 0, 1, 2, .... Here, the situation is rather similar to the Watson‐Sommerfeld transformation for waves diffracted by a spherical surface. It turns out that the moment of irradiance 〈Iv〉 precisely provides the characteristic function of the log‐irradiance E = log I with v as the variable of the characteristic function. This fact inevitably leads to the cumulant expansion of 〈Iv〉, and further to the distribution which is close to the log‐normal distribution with a threshold value for irradiances giving nonvanishing probability. It is then shown that the same irradiance distribution can also be derived explicitly from the moment equations of wave functions (which are essentially based on the forward scattering approximation) as the result of a cluster approximation. In the special case of a gaussian turbulence spectrum, the exact solutions of the moment equations can be obtained for all orders and they lead to the Rice‐Nakagami distribution with respect to the logarithm of irradiance; this distribution precisely describes the distribution when the wave beam is purely wandering or is in the state of “spot dancing,” as is expected from the physical model of the gaussian spectrum. Conversely, the latter fact strongly suggests that the moment equations are highly reliable for all orders to apply to various problems. The cluster approximation is also discussed with regard to its condition of applicability.
Near fields of a vector electric line source near the edge of a wedge
Authors: Pozar D. M. , Newman E. H.
Published: February 2008

Simple closed form expressions are obtained for the fields of an electric line source with transverse or longitudinal current flow parallel to and near the edge of a perfectly conducting wedge. The effect of an edge which is not perfectly sharp is investigated by considering a cylinder‐tipped half plane.
High‐frequency ionospheric ducting—A review
Authors: Toman Kurt
Published: February 2008

The observational evidence for long‐range propagation of high‐frequency radio signals began to accumulate in 1926 when transatlantic communication links were established. In 1927, signals were detected that had propagated over large distances or circled the earth with little attenuation. Long‐range and round‐the‐world (RTW) signals showed preferred periods of occurrence. Relatively high angles of incidence (20° relative to the horizontal) of such signals at the receiver paired with low attenuation ruled out conventional multihop propagation. An ionospheric refractive index boundary was postulated along which the signal propagates in a glancing incidence low‐loss mode. The transmission path of observed long‐delayed signals, originating from artificial earth satellites, was found to be located in the twilight zone. Experiments that used ground‐based transmissions confirmed the role of ionospheric absorption and tilts for the occurrence of long‐range and RTW signals. Detailed explanations for ionospheric ducting were provided by using several theoretical concepts and analyses. The μr (refractive index times geocentric distance) diagram was used for the study of ray propagation in a spherically stratified multilayered model ionosphere depicting characteristics of the ground‐detached glancing incidence mode. The potential well analysis was applied to an inhomogeneous slowly varying ionosphere. Numerical ray‐tracing computations were made by using model ionospheres with horizontal gradients. Ionospheric models were used to predict global properties of ionospheric wave channels. The role of scattering from natural and artificially induced ionospheric irregularities in long‐range ionospheric ducting was investigated.
Infrared and optical frequency standards
Authors: Chebotayev V. P.
Published: February 2008

The properties of stable lasers are discussed. Consideration is given to the methods of production of lasers with a very narrow linewidth of about 0.5 Hz and to their use in achieving high values of long‐term frequency stability and reproducibility. The results of investigations of frequency stability of a He‐Ne laser with a methane absorbant and a telescopic beam expander are presented.
Laser wavelength measurements
Authors: Rowley W. R. C.
Published: February 2008

A review is made of developments in wavelength measurement practice over the last 5 years. The rapid development of single‐frequency tunable dye lasers has led to a requirement for quick and easy wavelength measurement at accuracies of 1 part in 106 or better. This has stimulated the development of moving‐carriage interferometers and of methods of image sensing with detector arrays or vidicon tubes. There has also been progress in the attainment of very high accuracy in wavelength comparisons of stabilized lasers, now nearly matching the laser reproducibilities of a few parts in 1011. The limitations to accuracy seem to be predominantly the defects of optical surfaces and uncertainties arising from diffraction effects.
The modes of an axially slotted coaxial waveguide
Authors: Hurd R. A.
Published: February 2008

By using a quasi‐static integral equation technique a transcendental equation for the propagation constants of an axially slotted, dielectric‐filled coaxial waveguide is obtained. The equation is solved on the computer, and curves of the propagation constants versus various line parameters are presented. Also calculated are expressions for the transfer impedance and field quantities.
A numerical study of tropospheric ducting at HF
Authors: Pappert R. A. , Goodhart C. L.
Published: February 2008

In this paper, path loss calculations for frequencies between 4 and 32 MHz are compared with Hansen's recent measurements on a 235‐km over‐ocean southern California path. The calculations involve standard waveguide theory along with available radiosonde data and show convincingly that signal enhancement, relative to that expected on the basis of ground wave theory, observed on frequencies greater than 20 MHz was due to superrefractive environments.
Large‐amplitude ULF magnetic fields produced by a rapid transit system: Close‐range measurements
Authors: Ho A. M.‐H. , Fraser‐Smith A. C. , Villard O. G.
Published: February 2008

Measurements at a location close to the San Francisco Bay Area Rapid Transit (Bart) system show that Bart can produce ultra low frequency (ULF; frequencies less than 5 Hz) magnetic field fluctuations with amplitudes that are 2–3 orders of magnitude greater than the normal background level. The maximum increase in magnetic field fluctuations over the ambient background level occurs in the range 0.01–1 Hz, but significant increases occur at 0.001 and 10 Hz. Although it is generally accepted that moving trains cause magnetic field disturbances, it has not, until recently, been recognized that modern dc‐powered rapid transit systems are such powerful sources of ULF electromagnetic fields, and the existence of these sources in densely populated urban areas could have environmental implications.
A microwave exposure system for marine animals: Dosimetry and reflectometric observations
Authors: McRee Donald I. , Wachtel Howard
Published: February 2008

An aquatic system is described in which marine biota can be exposed under natural conditions for indefinite periods of time to dose‐determinate levels of microwave radiation. A source of 2450‐MHz CW energy is used to feed a standard‐gain horn that radiates a glass‐faced aquarium in the far field; source and aquarium are located in a microwave‐anechoic chamber. Seawater in the 95‐liter aquarium can be maintained at a desired temperature by a high‐capacity heat‐exchange system. By caging sets of one or more small aquatic animals at various distances from the glass face, determinate SARs at different levels can be achieved simultaneously within the aquarium. Reflectometric data on a small marine animal, the mollusc Aplysia californica, reveal that its presence in seawater does not appreciably change the load that is seen by incident RF waves. The system should prove useful in studying effects of long‐term microwave exposures in animals that are otherwise maintained in a natural environment.
Extremely‐low‐frequency fields and the slime mold Physarum polycephalum: Evidence of depressed cellular function and of internuclear interaction
Authors: Greenebaum B. , Goodman E. M. , Marron Michael T.
Published: February 2008

The acellular slime mold Physarum polycephalum has been exposed continuously to a variety of low‐level, extremely‐low‐frequency (ELF) fields for periods ranging from two months to five years. Changes in several biological parameters have been observed that are significant (P < 0.05) and reproducible. Cultures were exposed to 75‐, 60‐, and 45‐Hz CW, and 76‐Hz frequency‐modulated fields. Electric‐field intensities ranged from 0.04 to 0.7 V m−1 (rms); magnetic fields, from 0.01 to 0.2 milliteslas (rms). The observed changes are generally those of a slowing of cellular processes. A longer nuclear‐division cycle and depressed respiration rate have been seen under exposure to most CW fields and to all frequency‐modulated fields that have been tested. Additional experiments indicate that lengths of the nuclear‐division cycle of cultures formed by mixing exposed and control samples lie between those of control and exposed cultures. Indirect measurements of chromosomal numbers of this polyploid organism indicate no statistically significant difference between exposed and control nuclei.
A method for the study of retinal ganglion cell activity induced by ELF magnetic fields
Authors: Lövsund P. , Öberg P. Å. , Nilsson S. E. G.
Published: February 2008

A method is described by which the influence of time‐varying magnetic fields on excitable tissue can be studied in a reproducible way. The retina of the frog (Rana temporaria) was exposed to a time‐varying magnetic field. The field‐generated electrical activity of the ganglion cells was recorded by a microelectrode. The method opens up new possibilities for the study of effects of low‐frequency magnetic fields on excitable tissues.
Contraction of smooth muscle in a microwave field
Authors: Whitcomb Ernest R. , Blackman Carl F. , Weil Claude M.
Published: February 2008

Spontaneous contractions of smooth muscle were observed during microwave irradiation. Isolated gut segments of adult male albino rats were exposed to 1‐GHz, continuous‐wave radiation by means of a capacitive‐plate exposure system. For stabilization, the gut segment was maintained initially at 7°C for one hour and then at 36°C for one hour in a modified Ringer's solution prior to irradiation. During recording of contractions the gut segment was suspended in a 10‐ml plastic tube and was bathed by Ringer's solution (pH 7.5) at 36°C at a flow rate of 6 ml min−1 from a 500‐ml reservoir. Contractions were measured by a strain gauge. Frequency distributions of 500 contractions each were made before and during a single exposure and were displayed as interval‐histogram patterns. Four gut preparations were exposed to radiation at intensities that resulted in specific absorption rates of either 1.2, 2.3, or 6.9 mW g−1. For each absorption rate the response patterns for the four gut preparations representing a before‐exposure (control) condition were summed and compared with the summed response patterns of the same preparations during exposure. No effect of irradiation by electromagnetic energy on the rate of spontaneous contractions of smooth muscle was observed.
Classical conditioning of microwave‐induced hyperthermia in rats
Authors: Bermant Robert I. , Reeves Dennis L. , Levinson Daniel M. , Justesen Don R.
Published: February 2008

Twelve mature, experimentally naive rats, all female albinos, were randomly but equally assorted into four groups and then were subjected to classical conditioning procedures in which the conditional stimulus (CS) was a 525‐Hz auditory signal. A 30‐s CS was presented during all phases of the study (habituation, 30 trials; conditioning, 200 trials; and extinction, 100 trials) to a Tone‐Only control group. For rats of the three experimental groups, the CS antedated by 30 s and then continued until cessation of the unconditional stimulus (US) during the conditioning phase. For Tail‐Shock rats, the US was a 2‐s application of 60‐Hz ac to the tail at 300 V rms; for the 10‐s Microwave rats, 2450‐MHz sinusoidally modulated irradiation that resulted in a dose rate of 420 mW g−1 was presented for ten seconds; and for the 30‐s Microwave rats, irradiation that resulted in a dose rate of 220 mW g−1 was presented for 30 seconds. All three USs resulted in mean increments of colonie temperature (ΔTs¯) approximating 1.5°C. During habituation and extinction phases,the CS was presented without the US to all animals. A conditional response (CR or “learned” hyperthermia) of a modest sort was reliably demonstrated, was found to be highly resistant to extinction, but was also found to be a generalized reaction to the conditioning environment—although selective eliciting of CRs occurred outside the laboratory in the presence of the individual who trained the animals. The mean increments of conditionally elicited temperature were +0.37°C(2‐s Tail Shock), +0.5°C (30‐s Microwave), and +0.7°C (10‐s Microwave), but while none of these ΔTs¯ differed reliably from each other, they all departed significantly from the negative ΔTs¯ of Tone‐Only controls (−0.47)°C. Hyperthermia, whether calorically induced by microwaves or the endogenous product of an external trigger, appears to be “learnable” and could be a source of experimental confounding of any thermally sensitive assay in which noxious stimuli are repeatedly presented to the psychologically intact organism.
A comparison of patterns of stray radiation from therapeutic microwave applicators measured near tissue‐substitute models and human subjects
Authors: Lehmann Justus F. , Sfonebridge Jerry B. , Guy Arthur W.
Published: February 2008

The stray radiation produced by microwave applicators during clinical diathermy treatments creates a potential health hazard both to the patient and to the therapist. It is important to quantify levels of stray radiation so risk of excessive exposure can be minimized. In this study, tissue‐substitute models—a planelayered block, a large cylinder, a thigh‐model cylinder with one flat side, and a small cylinder—were irradiated by a 915‐MHz direct‐contact applicator, a 2450‐MHz Transco circularly polarized direct‐contact applicator with choke, and a 2450‐MHz “C” director. Power‐density measurements were made in proximity to these models to determine levels of stray radiation. Human volunteers were also irradiated by the 915‐MHz direct‐contact applicator and by the 2450‐MHz Transco applicator. The human anatomical sites irradiated were chosen for their geometric similarity to the models. Measurements made near the upper and lower areas of the dorsum were compared with those of the plane‐layered model; measurements near the thigh were compared with those near the large cylinder and the thigh model; and measurements near the biceps were compared with those made near the small cylinder. When the direct‐contact applicators were not in complete contact, levels of stray radiation above 5 mW cm−2 were measured at points 5 cm from the external surface of the applicator. The noncontacting “C” director had stray‐radiation levels above 5 mW cm−2 at 5 cm from the applicator in all directions. When the E field was perpendicular to the long axis of the muscle or the model, higher levels of stray radiation were measured. It was found that the models used were of limited value in predicting patterns of stray radiation near the human counterparts.
Experimental and numerical studies of the elevated temperatures induced in a human leg by microwave diathermy with surface cooling
Authors: Emery Ashley F. , Stonebridge Jerry B. , Sekins K. Michael , Lehmann Justus F.
Published: February 2008

A 915‐MHz microwave‐diathermy process that employs surface cooling was modeled as it applied to the treatment of the anterior portion of the human thigh. This finite‐element thermal model employed convective‐cooling conditions and microwave‐energy‐deposition patterns obtained from experiments on phantom models; the phantom model's thermal properties were first measured to improve the accuracy of values given in the literature. Numerical computations were performed for a treatment regime that included five minutes of thigh precooling before microwave heating, and a treatment schedule designed to yield the desired therapeutic temperatures in deep musculature while not creating unacceptably high temperatures in the more superficial tissues. Thigh temperatures were measured in human subjects undergoing the same diathermy process, with cooling maintained throughout the treatment period; the temperatures were compared to the computed values to evaluate the validity of the finite‐element model. It is concluded that a model of this type may be used to define the thermal response of the human thigh to this and other treatment regimes and may thus assist in optimizing the interplay of the variables under the control of the therapist—the precooling time intervals, air temperatures and flow rates, and microwave power.
Low‐frequency surface impedance measurements at some glacial areas in the United States
Authors: Arcone Steven A. , Delaney Allan J.
Published: February 2008

Measurements of apparent resistivity and phase derived from the complex surface impedance of radio waves propagating in the ground wave mode at frequencies in the radio navigational aid band (between 257 and 382 kHz) are presented. Areas encompassing between 400 and 800 km2 that covered a variety of glacial sediments, land forms, and some crystalline bedrock types were surveyed. The results show that (1) loess was commonly between 20 and 40 ohm m with phases between 50° and 60°, (2) end moraines had a wide dispersion with values generally ranging between 20 and 1000 ohm m and 40° and 80°, (3) metamorphic phyllites and schists were generally between 100 and 3000 ohm m with an average near 1000 ohm m and phases usually well below 45°, and (4) granites were the most resistive at an average value of about 2000 ohm m with the lowest phases averaging 12°. The degree of dispersion in resistivity values reflects the dispersion in grain size, while the average resistivity increases with mean grain size. Dielectric properties are suggested as one cause of the low phases observed over crystalline bedrock. The combination of apparent resistivity and phase data implies that the resistivity measurements are consistent in about 50% of the areas with previous measurements of field strength attenuation performed in the AM broadcast band.
VHF and UHF radar observations of equatorial F region ionospheric irregularities and background densities
Authors: Towle D. M.
Published: February 2008

A series of measurements of the properties of equatorial ionospheric irregularities were made at Kwajalein, Marshall Islands (M.I.) in August 1977 and July–August 1978. These measurements, sponsored by the Defense Nuclear Agency (DNA), involved coordinated ground‐based and in situ sensors. The ARPA Long‐Range Tracking and Instrumentation Radar (ALTAIR), operated by Lincoln Laboratory, obtained backscatter and transmission data during five nights in August 1977 and eight nights in July–August 1978. This report describes the ALTAIR data from the night of August 11, 1978, which yield direct quantitative measurements of 1‐m and ⅜‐m irregularities and of plasma depleted regions. These plasma depleted regions, previously predicted on the basis of theoretical analysis and in situ data, were observed during the decay phase and not the generative phase of the field‐aligned irregularities.
Refractive index profiles with a local resonance based on Heun's equation
Authors: van Duin Cornelis A. , Sluijter Frans W.
Published: February 2008

The propagation of electromagnetic waves in inhomogeneous magnetoactive plasmas is studied. In particular, the so‐called extraordinary mode is considered. The starting point is the Fuchsian equation with four singular points: Heun's equation. Transformations are developed that transform Heun's equation into a Helmholtz equation. In this way, refractive index profiles accommodating a local resonance are generated. These refractive index profiles are connected with plasma density profiles through the dispersion relation for the extraordinary mode. The thus generated plasma density profiles contain a number of adjustable parameters.
High‐latitude analytical formulas for scintillation levels
Authors: Aarons J. , MacKenzie E. , Bhavnani K.
Published: February 2008

By making measurements of the scintillations of the 137‐MHz beacon of ATS 3 at three sites along the 70°W meridian, it was possible to amass a data bank sufficient to obtain empirical analytical formulas of average scintillation at subauroral and auroral latitudes. The data base consisting of 15‐min scintillation indices of 3–7 years of observations from Sagamore Hill, Massachusetts, Goose Bay, Labrador, and Narssarssuaq, Greenland, has been presented and discussed in a companion paper. Forcing functions for the empirical formulations are time of day, day of the year, magnetic index, and solar flux. The limitations of the data are outlined including single frequency of observations and the problem of limited excursion of scintillations. Corrections are given for geometrical effects using varying irregularity configurations.
Electromagnetic surface impedance for a layered earth for general excitation
Authors: Wait James R.
Published: February 2008

An expository analysis of electromagnetic induction in an N‐layered half space is presented. The objective is to develop general expressions for the surface impedance matrix at the air/earth boundary that exhibit the dependence on the source field configuration. The justification for ignoring this dependence is given.
Foreword
Authors: Gossard Earl E. , Yeh K. C.
Published: February 2008

Radars have had a long and illustrious history in the investigation of the atmosphere. Beginning with verification of the existence of the ionosphere in the mid‐1920's [Appleton and Barnett, 1925; Breit and Tuve, 1926], radars have been operated in monostatic and bistatic modes to probe the atmosphere and have acquired names such as bottomside or topside ionosonde, meteor radar, auroral radar, meteorological radar, incoherent scatter radar, etc. It is therefore remarkable that such an old technique would warrant a special issue of Radio Science in 1980. The reason seems to be that the scientific community was slow to recognize and exploit the potential of radar for sensing the nonionized clear atmosphere.
Propagation problems connected with special source structures
Authors: Bremmer H.
Published: February 2008

In my preceding talk I treated phenomena the main characteristics of which were already apparent from effects produced by an infinitesimal point source. Let me now [Walker‐Ames Lecture at the University of Washington, June 25, 1979] consider cases in which, on the contrary, the structure of an extended source is essential for the problem in question. Having some experience in problems dealing with rather different applications, such as radio waves, optical and electron‐optical imagings, and plasma physics problems, it struck me that fundamental phenomena occurring in any of them are often discussed while overlooking results that have been obtained in one of the related fields. Today I would like to emphasize the existence of some common features in all of these problems, all having to do with sources of finite dimensions. This may be illustrated by considering a special parameter with the dimension of a length and connected with the size of the source, which plays a role in all of them. As a matter of fact, it is just the finiteness of the source which implies that some length (however, not necessarily just the size itself of the source) becomes most essential. This is at once clear in the case of the three‐dimensional source representing a transmitting antenna system. In the immediate vicinity of the latter the field depends mainly on the nearest parts of the system, but at larger distances the effects of all parts interfere, and we arrive in the so‐called ‘wave zone.’ The transition occurs at distances D at which the various parts of the source, with separations L perpendicular to the propagation direction, can reach the point of observation along path lengths differing by not more than about the operating wavelength. According to the relation
we find the expression for this critical distance. Of course, this transition distance is rather vague, since the dominating scale length L of the antenna, here introduced, is not well defined. However, it is well known that the approximations needed in order to determine radiation diagrams are only applicable in the wave zone which is just fixed, apart from the almost trivial conditions D ≫ λ and D ≫ L by the property D > Dcr = L2/λ.
On a spectral domain approach for testing Albertsen's corner diffraction coefficient
Authors: Tew M. , Mittra R.
Published: February 2008

This paper addresses the problem of evaluating the accuracy of a ray‐optical solution for the corner diffraction coefficient, which was recently derived by Albertsen. A spectral domain approach is employed to test the satisfaction of the boundary condition on an acoustically soft plate scatterer as a measure for the accuracy of the solution. The results of the test show that the corner diffraction coefficient requires improvement, and an iterative method, also based on the spectral domain approach, is employed to obtain refinements of the original solution proposed by Albertsen.
Time dispersion of electromagnetic pulses by the ionosphere
Authors: McIntosh R. E. , Malaga Alfonso
Published: February 2008

This paper reviews the temporal dispersive effects suffered by electromagnetic pulses during transmission or reflection by the ionosphere. A qualitative description of intrinsic plasma, geometrical (refractive and diffractive), and geomagnetic dispersion is presented. Also, tables that summarize previous research studies are given to indicate the variety of pulse signal formats and ionospheric conditions that have been considered.
Properties of attenuating and depolarizing atmospheric hydrometeors measured on a 19‐GHz earth‐space radio path
Authors: Cox D. C. , Arnold H. W. , Hoffman H. H. , Leck R. P.
Published: February 2008

One year of propagation data were obtained for a 19‐GHz earth‐satellite path terminating at Crawford Hill, New Jersey. These data were analyzed to determine the depolarizing and attenuating properties of liquid (rain) and solid (ice) hydrometeors along the path. The observed projections of the symmetry axes of ice and rain hydrometeors were found, generally, to lie near the horizontal and vertical planes. Ice deviates from this orientation more than rain; ice occasionally is found at any possible orientation. The observed differential attenuation and differential phase for a given copolarized signal attenuation were lower than those seen on terrestrial paths. Present terrestrial rain models do not adequately describe these results. Maximum depolarization was observed to occur for linear incident polarizations near 45°. This maximum depolarization is sufficient to significantly affect the performance of dual‐polarization satellite communications systems. Depolarization close to the minimum attainable for instantaneously optimized linear incident polarizations was observed most of the time for fixed vertical and horizontal polarizations. These minimum depolarization levels were low enough to have little effect on most dual‐polarization systems.
Numerical method for calculating the current distributions along antennas immersed in arbitrary homogeneous, isotropic media
Authors: Wong J.
Published: February 2008

A cylindrical, center‐fed antenna is placed in a homogeneous, isotropic medium with arbitrary electrical constants. A numerical technique employing digital Fourier transforms is used to solve for the current distribution along the antenna. It is found that there is an infinite set of ‘eigen‐distributions’ satisfying the differential‐integral equation describing the antenna current. These eigen‐distributions are not restricted to a finite interval; however, by superposing them in the appropriate way a limiting current distribution is formed, in which the important nonzero currents are confined to arms of the antenna. The current distributions found in this way for antennas in media with various values of α/β compare favorably with experimental and theoretical results presented in the literature.