bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Antenna Height for Protection Against Microwave Diffraction Fading
Authors: Dougherty Harold T. , Wilkerson Robert E.
Published: November 2015

The wide variations in refractive index gradients that may be encountered for nominally line‐of‐sight microwave maritime paths can cause severe fading. A common type is known as k‐type fading which includes phase‐interference fading and also diffraction fading as the refractive index gradient varies over a wide range. Lewin (1962) was the first to provide an engineering design procedure that roughly approximated: (a), the required terminal antenna heights to reduce diffraction fading, and (b), the required diversity separations (frequency or space) to provide a dynamic reduction of phase‐interference fading. The diversity design procedures, (b) above, have since been derived in a more accurate manner although they presuppose that item (a) has been provided for. The present paper meets this requirement. It provides a more accurate design procedure for determining the requirements, (a) above, to reduce diffraction fading. As an aid for the procedure, a new computer‐derived curve is presented for the attenuation by a spherical earth at grazing conditions.
Corona Currents After the Return Stroke and the Emission of ELF Waves in a Lightning Flash to Earth
Authors: Rao Manoranjan
Published: November 2015

In this paper an attempt is made to show that the lateral corona currents that flow between the leader sheath and the core of the first return stroke radiate ELF waves whose spectral peak amplitude is of the same order as the spectral peak amplitude of VLF waves emitted by the return. The total energies radiated by the corona and the return are also estimated, and the difference in their magnitudes in relation to the spectral peak amplitudes explained.

The corona current mechanism is, however, not the only source of ELF energy. The long continuing currents involving large quantities of charge transfer (as reported by Kitagawa and others) cannot be explained by the corona mechanism, but they are capable of emitting ELF waves.
Propagation of Electromagnetic Waves Near a Coastline on a Flat Earth
Authors: Millar R. F.
Published: November 2015

A magnetic line source is placed parallel to and possibly near a land‐sea boundary on a flat earth. The problem is two dimensional, but its solution may be employed to examine the corresponding three‐dimensional configuration which involves a vertical electric dipole. The mathematical model consists of a perfectly conducting half plane (sea) in the interface between free space and an imperfectly conducting dielectric (land). The far field, over both sea and land, is required.

The method employed is to evaluate the rigorous, contour integral solution of Clemmow (1953), under the assumption that the complex refractive index n of the land is large. This integral is evaluated first for points not too near, but not necessarily far from the coastline. A second field representation (useful very near the shoreline) as a Bessel‐function series is derived.

Analytical comparison is made with recent work of Wait (1963) and Bach Andersen (1963). Good agreement is found except in the immediate neighborhood of the coastline. The onset of the "recovery effect" over the sea and the associated rapid phase variations near the coastline, are found for a wave incident from over the land; the corresponding effects for a wave incident from over the sea are also noted. These are in qualitative agreement with experiment. Numerical results are exhibited for a frequency of 10 MHz and n=3.91−i 2.30.
Transmission and Reception Properties of an Equatorial Slot Antenna on a Reentry Sphere
Authors: Harrison Charles W. , Taylor Clayborne D.
Published: November 2015

The reentry vehicle model employed in this study consists of a plasma‐clad sphere with a narrow circumferential slot cut at the equator. The slot is excited by a biconical transmission line driven at its center by a coaxial cable. The homogeneous plasma is assumed to be in contact with the sphere.

The driving‐point impedance referred to the input terminals and the radiation field in terms of the input current are determined. The efficiency of transmission is calculated by taking the ratio of the power obtained by integrating the Poynting vector over the surface of a great sphere to the power supplied the linearly tapered radial transmission line by the coaxial cable. The voltage appearing across an impedance connected to the terminals of the biconical transmission line is evaluated in terms of the amplitude of an incident plane‐wave electromagnetic field.

Numerical results are presented exhibiting the transmission and reception qualities of the equatorial slot antenna on the reentry sphere for a range of frequencies and plasma properties.
On the Coupling of Modal Waves in a Plasma‐Filled Parallel‐Plate Waveguide
Authors: Lee S. W. , Liang C. , Lo Y. T.
Published: November 2015

The modal wave solutions of an isotropic, plasma‐filled, parallel‐plate waveguide are examined in detail using both the cold‐ and the warm‐plasma models without collision. It is found that three types of modal waves‐optical, acoustic, and slow‐wave modes‐mav exist in the guide filled with warm plasma. In the zero‐temperature limit, both the propagating characteristics and the field solutions are studied for the purpose of comparing with the results obtained in a cold‐plasma waveguide.
Wave Propagation in a One‐Dimensional Random Medium
Authors: Bassanini Piero
Published: November 2015

A simple one‐dimensional model for wave propagation in a random medium is considered. A few approximate methods of solution are investigated and compared with the exact solution. In particular, Tatarskii and Gertsenshtein's “renormalization” method is applied and shown to give results which, under certain assumptions, coincide with the exact solution.
On the Problem of the Infinite Antenna in an Anisotropic Plasma
Authors: Cook K. R. , Johnson G. L.
Published: November 2015

An integral expression is derived for the current distribution on an infinite, perfectly conducting antenna alined with the magnetic field in an anisotropic incompressible plasma. Use is made of the Wilcox radiation condition and the notion of generalized eigenfunctions. An asymptotic evaluation of the integral is presented, and it is shown that the current distribution contains the wave numbers of the two plane waves possible in this medium.
A Note on the Potential of a Vertical Electric Dipole Over the Interface Between Two Lossy Media
Authors: Cacavas P. C. , Tyras G.
Published: November 2015

The method of steepest descents has been used to evaluate solutions for the potential of a vertical electric dipole over an interface, wherein the characteristics of both media have been expressed in generalized (nonmagnetic) terms. The nature of the propagation is found to depend upon the relative loss tangents of the two media, and to consist of spherical waves and (in the more lossy region) two additional waves with surface bound properties, independently of the location of the dipole.
Propagation of VLF Waves Below an Anisotropic Stratified Ionosphere With a Transverse Static Magnetic Field
Authors: Galejs Janis
Published: November 2015

The surface impedance of a cylindrically stratified anisotropic ionosphere has been computed in the presence of a transverse static magnetic field without requiring explicit representations of the individual cylindrical wave functions in the lower ionospheric layers. The propagation parameters are determined from the usual transcendental modal equation which is solved starting out with an initial real solution dependent on the reactive part of the ionospheric surface impedance. The surface impedance computations are continued below the ionospheric boundary height, and the impedance reflected to the ground level by the ionosphere is compared with the ground impedance. The accuracy of the computations is shown to be comparable to a few percent uncertainty of the ground impedance for low conductivity ground.

The propagation parameters of the first three waveguide modes are calculated for a number of ionosphere models which include the recent D region models of Deeks (1966). For propagation in the east‐to‐west direction, the phase velocity of the second mode is shown to be discontinuous when the real part of the ionospheric reflection coefficient undergoes a sign change. This condition is characterized by an absorption peak and for ionosphere models of lower anisotropy (lower values of ωH/v, where ωH is the gyrofrequency and v is the effective collision frequency) the interference distance D of the two lowest modes is increased for propagation in the east‐to‐west direction relative to the West‐to‐east direction. but it is decreased for larger ωH/v ratios which are representative of available models of stratified ionosphere.
Transmission of VLF Radio Waves Through the Ionosphere
Authors: Wieder Bernard
Published: November 2015

The fields of 10‐kHz radio waves propagating into and through the lower ionosphere are calculated by numerical methods, and the attenuation, polarization, and power flow characteristics are examined as a function of height for daytime and nighttime ionospheric electron density profiles with varying angles of incidence, directions of propagation relative to the earth's magnetic field, and dip angle. The conclusions are that virtually all the attenuation of the wave occurs in the lower D region of the ionosphere, that the transmitted wave is nearly circularly polarized, and that the energy of the transmitted wave is traveling nearly along the magnetic lines of force in agreement with the predictions of “ray theory.” The analysis also shows the strong variation in transmission with dip angle and with change from day to night ionosphere in agreement with observed variations in intensity and in frequency of occurrence of “whistlers.”
Five Years of VLF Worldwide Comparison of Atomic Frequency Standards
Authors: B. E. Blair , E. L. Crow , A. H. Morgan
Published: November 2015

The VLF radio broadcasts of GBR(16.0 kHz), NBA(18.0 or 24.0 kHz), and NSS(21.4 kHz) have enabled worldwide comparisons of atomic frequency standards to parts in 1010 when received over varied paths and at distances up to 9000 or more kilometers. This paper summarizes a statistical analysis of such comparison data from laboratories in England, France, Switzerland, Sweden, Russia, Japan, Canada, and the United States during the 5‐year period 1961–1965. The basic data are differences in 24‐hr average frequencies between the local atomic standard and the received VLF radio signal expressed as parts in 1010. The analysis of the more recent data finds the receiving laboratory standard deviations, âi;, and the transmission standard deviation, τ, to be a few parts in 1011. Averaging frequencies over an increasing number of days has the effect of reducing âi and τ to some extent. The variation of the âi; with propagation distance is studied. The VLF‐LF long‐term mean differences between standards are compared with the recent portable clock tests, and they agree to parts in 1011.
Atmospheric Noise From 20 Hz to 30 kHz
Authors: Maxwell Eugene L.
Published: November 2015

This paper discusses measurements of atmospheric noise which have been made at various times during the past two years in Malta, G.C.; Point Barrow, Alaska; Boulder, Colorado; Tokyo, Japan; Hawaii; Miami, Florida; and at various locations throughout Central and South America. Most of the measurements were average measurements of the vertical electric field intensity and amplitude probability distributions of the vertical electric fields. The atmospheric noise spectra obtained at these widely spaced locations over this large frequency range provide a good basis for rough estimates of noise field intensities at any global location. The results correlate well with lightning spectra and propagation attenuation coefficients. The amplitude probability distributions provide interesting and useful information regarding the characteristics of the noise and are used to convert the average measurements to rms values. These are some of the first amplitude probability distributions obtained throughout this frequency range. Subsurface noise spectra have been computed for several earth models as an aid to subsurface communicators.
Radiation From Dipoles in an Idealized Jungle Environment
Authors: Wait James R.
Published: November 2015

A method is presented for computing the field of a vertical electric dipole over a homogeneous conducting half space coated with an anisotropic conducting slab. The asymptotic form of the solution indicates that the field varies essentially as an inverse square of the horizontal range. The results have application to HF radio propagation over smooth terrain with dense vegetation.
Radiation of an Antenna in a Compressible Magnetoplasma
Authors: Deschamps Georges A. , Kesler Oren B.
Published: November 2015

The far field produced by an arbitrary monofrequency source in a compressible magnetoplasma is expressed in terms of the modal plane waves in that medium.
DiHraction by a Cylinder in a Locally Uniaxial Medium With Azimuthal Optic Axis
Authors: Stalzer Henry J. , Shmoys Jerry
Published: November 2015

An exact solution of Maxwell's equations is given for the problem of a magnetic line source parallel to the axis of a perfectly conducting cylinder in an inhomogeneous uniaxial medium of infinite extent. The inhomogeneity is due to the curvature of the lines of force of the static magnetic field responsible for the anistropy of the medium. These lines of force are taken to be concentric with the cylinder. The exact solution is transformed, for frequencies above the plasma frequency and for large cylinder radius, to a more rapidly convergent form which is given a geometric interpretation. This geometric interpretation can then be used to obtain approximate solutions when the magnetic field and the scatterer are more complicated and do not admit an exact solution of Maxwell's equations.
Graphical Attenuation Calculations for Irregular Terrain (A Digest)
Authors: Hartmann Raymond F.
Published: November 2015

This digest presents, in part, graphical solutions for the electric field in the far‐diffraction region when radio waves are diffracted over a homogeneous spherical earth with a ridge or a cliff in the radio path. More complete details for this method of calculation were recently published by this author.
Electromagnetic Induction in a Small Conducting Sphere Above a Resistive Half Space
Authors: Wait James R.
Published: November 2015

The limitations of detection of a small metallic sphere by the electromagnetic induction method are discussed. Particular attention is given to the masking effect of a conductive half space located beneath the scatterer. The results indicate that a dual frequency operation should provide the required discrimination.
Measurements of the Coherence Ratio of Ionospherically Propagated Radio Waves
Authors: Whale H. A. , Boys J. T.
Published: November 2015

Phase difference measurements made with an accuracy of 5° between pairs of antennas separated by up to 150 yards in three directions (N, E, and SW) show that radio waves reflected from the ionosphere are generally not sufficiently stable in direction for any particular component to be regarded as being specular in the usual sense. It is concluded that the coherence ratio should be regarded as equal to zero except in very special one‐hop cases. The equipment used for the measurements is described in general form.
Diffraction and Scattering of the Electromagnetic Groundwave by Terrain Features
Authors: Wait James R.
Published: November 2015

A class of two‐dimensional diffraction and scattering problems is considered for evaluating the influence of idealized terrain features in groundwave propagation. The analysis makes extensive use of the orthogonality properties of the Airy type wave functions which characterize the height dependence of the modes. The procedure is quite straightforward when reflected modes are small. Also, multiple obstacles may be treated without difficulty. Finally, it is indicated that the results may be applied to three‐dimensional configurations if certain minor modifications are introduced.
Subsurface Radio Propagation Experiments
Authors: Tsao Carson K. H. , deBettencourt J. T.
Published: November 2015

Propagation experiments were conducted on Cape Cod, the Adirondack region of New York State, and in Cheyenne Mountain in Colorado to determine the feasibility of communication between vertical linear antennas located in drill holes in the rock below overburden, and similar antennas located on the surface of the ground.

The bulk conductivity of the propagation media, i.e., the average conductivity along the path between the antennas, must be determined by measurements of propagation loss and transmission delay, because of the lack of homogeneity in the rock media. High values of bulk conductivity limited experiments to the VLF relation on Cape Cod and the Adirondacks, which involved ranges of 1.6 km and 5 km. respectively. Distances up to 48 km in the LF region were achieved by up‐and‐over transmissions from inside Cheyenne Mountain.

Analysis of the experimental results and theoretical considerations indicate that the usefulness of the through‐the‐rock mechanism is severely limited by the bulk conductivity. For shallow antenna depths, particularly if the overburden is thin or absent, substantial transmission ranges can be achieved by using up‐over‐down propagation.
Fourier Transform Method in Cylindrical Antenna Theory
Authors: Otto D. V.
Published: November 2015

A technique is developed in this paper which greatly reduces the numerical labor involved in the Fourier Transform solution for cylindrical antennas of exbitrary length. This method is then applied to solid antennas with two commonly used excitation geometries. It is also applied to the case of an antenna in a homogeneous conducting media. In all cases it is shown that the numerical results compare very well with the available experimental results.
Latitude Variation in VLF Modal Interference
Authors: Kaiser A. B.
Published: November 2015

Sunrise modal interference patterns are analyzed to reveal the variation with latitude of VLF propagation parameters. For VLF transmissions from NLK/NPG and WWVL received in New Zealand, the sunrise interference observations confirm Lynn's result that anomalies in the phase and. magnitude of mode conversion occur when the sunrise line is near the geomagnetic equator. A smaller anomalous effect is observed during sunset. Analyzing data for many paths in the frequency range 18–20 kHz, it is found that D (the interference wavelength of the first and second modes in the nighttime waveguide) differs little from the theoretically expected value (about 2 Mm) between geomagnetic latitudes 30° and 60°. At smaller geomagnetic latituds, however, values of D up to 3 Mm are observed for westward propagation. This large increase in D explains anomalous observations of nighttime amplitude.
Bearing Deviation in HF Transionospheric Propagation. II. Applications of Exact Computations
Authors: Rao N. Narayana
Published: November 2015

This paper deals with two applications of the exact computations of the ray‐path parameters and in particular, the bearing deviations for an eccentric model ionosphere with no magnetic field derived in a companion paper. These are (a) evaluation of the ITSA three‐dimensional ray‐tracing computer program and (b) investigation of direction‐of‐arrival observations of HF radio waves. In both cases, very good agreement has been found between the two sets of results.
A Ray‐Tracing Program and its Application to the Computation of Frequency Deviations in a High‐Frequency Signal
Authors: Inston H. H. , Curtis A. R.
Published: November 2015

A two‐dimensional formulation based on Fermat's principle is used to compute electromagnetic rays in the ionosphere in geocentric polar coordinates. The geomagnetic field and electron collisions are omitted. Digital and analogue computers are used. The accuracy of the digital program is sufficient to compute frequency deviations due to ionospheric disturbances by a direct method.
MUF Calculations Including the Effect of the Earth's Magnetic Field
Authors: Kopka Helmut , Möller Hans G.
Published: November 2015

To investigate the influence of the earth's magnetic field on ionospheric propagation, P'(f) curves were calculated by means of a ray‐tracing program. The calculations were made for a path length of 2000 km. The geomagnetic latitude of the midpoint of the path and the angle between the magnetic meridian and the path are varied in steps of 15°. Corrections to the no‐field MUF, as functions of the above parameters, are obtained.
An Evaluation of the ITSA 3‐D Ray‐Trace Program
Authors: Lemanski Theodore J.
Published: November 2015

A three‐dimensional ray‐trace program developed by ITSA, Boulder, Colorado is compared for range accuracy with theoretically calculated values of range. Ray tracings were made through two quasi‐parabolic ionospheres of different heights and thicknesses with no magnetic field or electronic collisions involved. For the case where the maximum allowable single step error was a minimum (corresponding to longer computer running time), the maximum range error encountered was 26.3 km at a zero‐degree launch angle. However, for launch angles equal to or greater than 0.5°, the typical range errors were less than 1.0 km.
A ConductingߚSlab Model for Electromagnetic Propagation Within A Jungle Medium
Authors: Sachs David L. , Wyatt Philip J.
Published: November 2015

A theoretical determination of the path loss in radio propagation through jungle is obtained by considering the jungle as a homogeneous conducting dielectric slab on a flat earth. An exact integral is obtained for the vertical component of the electric field within the jungle due to a vertical electric dipole within the jungle. An analytic evaluation of the integral leads to an approximate expression for the field and an estimate of the error. When this accuracy is insufficient, a numerical evaluation of the integral is performed. The combination of analytic and numerical techniques leads to the evaluation of the electric field and thereby path loss to any accuracy desired. Experimental measurements of path loss in a Thailand jungle are compared with the calculations. The results agree within a standard deviation of 6 dB when the jungle conductivity is taken as 0.15 mmho/m.
Generalization of Abel's Solution for Both Magnetoionic Components in the Real‐Height Problem
Authors: Paul Adolf K. , Smith G. H.
Published: November 2015

Modern methods of calculating the electron density distribution from virtual heights include joint use of both magnetoionic components since, in certain ranges, one component alone does not provide sufficient information to obtain a unique solution of the integral equation involved. Experience shows, however, that joint use of both components does not always give satisfactory results. We therefore consider in this paper whether sufficient information is provided by two components, used together, to remove ambiguities in the problem. A solution formula is first developed for each component, in a form similar to the Abel (1823) solution valid for an isotropic ionosphere. Application of these generalized solution formulas to each component and a combination of the two resulting expressions leads to a new integral equation in which only the distribution of the underlying ionization or the distribution in the valley between two layers is involved. Consideration of this new integral equation leads to the result that in general only a first or second‐order approximation to the distribution in those parts can be obtained.
Radiation From an Oscillating Magnetic Dipole in a Streaming Plasma
Authors: Bergeson John E.
Published: November 2015

The electromagnetic field of an oscillating magnetic dipole is calculated, assuming that the dipole is immersed in a cold, streaming plasma. The amplitude of the magnetic dipole moment is assumed to be sufficiently weak that the linearized cold‐plasma equations may be used to describe the response of the plasma.

The resulting field of the dipole is rather different from the field that would result if the plasma were not streaming. In particular, a longitudinal electrostatic field appears as a consequence of the plasma's motion. The far field of the dipole is such that the Poynting vector is not purely radial, but is tilted against the direction of the zeroth‐order plasma flow.

An outward flow of mechanical energy is associated with the electrostatic field. However the mechanical energy flow is negligible for streaming velocities small compared with the velocity of light. The force necessary to hold the dipole in place is also calculated. This force vanishes when the dipole axis is parallel to the streaming direction, as does the longitudinal electric field.
Theorem Concerning Reflection From a Plane Stratified Medium
Authors: Booker Henry G. , Fejer Jules A. , Lee Kai Fong
Published: November 2015

Let a plane electromagnetic wave of wavelength λ be incident in free space at an angle of incidence i upon a medium that is stratified in horizontal planes. Let the squared complex refractive index be an analytic function of height, and consider height as a complex variable. By sliding the contour map of the analytic function parallel to the imaginary height axis a family of refractive index profiles is obtained along the real height axis. Let one member of the family correspond to a nonabsorbing medium, and let another typical member of the family be obtained by displacing the contour map of the analytic function a distance b in the direction of the negative imaginary height axis. Then the amplitude reflection coefficient of the stratified medium is exp and the phase change on reflection is independent of b. This is true regardless of the precise form of the analytic function specifying the refractive index profiles. A function with singularities may be used, provided that the range of b is restricted to use only a region of the complex plane where the function is analytic.
Whistler Precursors
Authors: Laaspere T. , Wang C. Y.
Published: November 2015

A study has been made of the whistler precursor events that have been observed at the “Whistlers‐East” network of Dartmouth College in the period from IGY through IQSY. The results confirm the earlier reports that precursors are associated only with two‐hop whistlers. Other results are presented to illustrate some of the common features of precursor events, such as the absence of one‐hop hybrid components, the relatively high intensity of precursors, and the repeatability of the patterns of precursor events over time periods as long as a day. It is concluded that while the exact nature of the mechanism of precursor generation is not yet clear, we are probably dealing with triggering involving an instability process in a fairly limited region of space. The mechanism must, however, differ in some significant respect from the type of forward‐triggering that has been discussed in some detail in the literature.
Guidance in the Magnetosphere Along Field‐Alined Irregularities
Authors: Gothard Nicholas
Published: November 2015

A study is made of guidance of waves along an inhomogeneous field‐alined plasma stratum. A time invariant model of the ionosphere imbedded in the earth's dipole field is postulated. Along the lines of flux of the earth's magnetic field bell shaped plasma strata are alined. The theory presented here is based on the mode of theory of propagation in an inhomogeneous medium and is modified to account for anisotrophy. The two‐dimensional problem is reduced to a one‐dimensional integral equation, the modal condition, by using Booker's q parameter.

The numerical results are calculated for the locked modes only, although the theory is capable of handling the leaky modes as well.

The numerical results indicate the existence of total guidance between the conjugate points for some frequencies, but only partial guidance for other frequencies.
Waveguide Excitation of Dielectric and Plasma Slabs
Authors: Bates C. P. , Mittra R.
Published: November 2015

Time‐harmonic analyses are presented for the excitation of a dielectric slab and for the excitation of an isotropic, incompressible, plasma slab by means of a parallel‐plate waveguide with one plate truncated. Both TE and TM polarizations are considered in these open‐region problems.

The principal contribution of the paper is the development of a procedure for factoring the function of a complex variable which appears in the formulation of each of these Wiener‐Hopf type boundary value problems. The technique obtains the factorization for the open‐region problem by a limiting procedure on a function and its factorization associated with a related closed‐region problem. The latter factorization is usually trivial. The technique is quite general and should find application to a wide range of Wiener‐Hopf problems involving open regions.

Details of the investigation including the results of numerical computations are presented for the excitation problems. These include the average power reflected in the waveguide, radiated in the space wave, and transmitted by the surface waves. The radiation pattern of the space wave is also given.
A Modified Reflection Coefficient for Layered Media
Authors: Adams Roy N.
Published: November 2015

The energy leaving an antenna is considered as a series of rays reflected to a distant antenna. Each ray forms many reflected rays at each layer and invariant imbedding is used to study those rays of interest (i.e., rays forming a triangular zone connecting the antennas) and all others are considered lost.

The modified reflection coefficient differs by several dB in some cases from the conventional plane‐wave reflection coefficient.
Differential Microwave Phase Shifter
Authors: Keys J. E.
Published: November 2015

A waveguide phase shifter has been designed which is capable of providing extremely small, accurately controlled phase shifts. Three prototypes have been constructed and operate as predicted.
Oblique Wave Propagation in Drifting Isotropic Warm Plasma
Authors: Unz H.
Published: November 2015

The electromagneto‐plasma‐gas‐dynamics equations for small signal theory are summarized for the warm, isotropic, drifting electron gas plasma, by using tensor notation. Taking oblique plasma wave propagation, we derive a detenninantal equation for the corresponding refractive index. This is an extension for oblique incidence of a previous paper (Unz, 1966).
Crossed‐Dipole Method of Measuring Wave Tilt
Authors: King R. J.
Published: November 2015

Techniques for measuring the wave tilt for parallel and perpendicular polarization are reviewed and an extensive bibliography is included. An additional measurement technique is proposed which should be useful for the HF, MF, and LF range, and has potential application in the VLF band. Measurement of the phase difference between the signals induced in crossed dipoles lying in the plane of incidence allows determination of the ground constants.
Surface Wave Propagation Over a Thin Plasma Layer on a Ground Plane
Authors: Lee W. C.‐Y. , Walter C. H.
Published: November 2015

A theoretical study is made of the propagation of surface waves along an infinite, perfectly conducting plane surface that is coated with a layer of plasma and subjected to an applied d‐c magnetic field perpendicular to the layer. The electric and magnetic fields are computed for the separate media and the relations arising from boundary conditions are expressed as transcendental equations.

In the limiting case of small plasma layer thickness the fields and propagation constants may be expressed in simple forms. Curves of phase velocity versus plasma thickness are illustrated with different plasma frequencies and cyclotron frequencies. It is found that a backward wave occurs for a certain range of plasma frequencies.

The thin slab approximation used in this paper is checked by comparing both exact solution and approximate solution in the case of no applied d‐c magnetic field. The error is found to be very small.
Theoretical Study of Dipole Array of N Parallel Elements
Authors: Chang V. W. H. , King R. W. P.
Published: November 2015

The five‐term method developed for two arbitrarily located parallel antennas (Chang, 1967) has been successfully extended to a general antenna array of N parallel elements. The method can be applied to either planar array or three‐dimensional array. The array is characterized either by specifying driving voltages or input currents. Arrays of both half‐wave and full‐wave elements are discussed. The results reveal that the phase of the current along the antenna does not stay constant, as is generally assumed, even for arrays of half‐wave elements. As a consequence, differences between the actual computed field patterns and the ideal patterns computed by assuming sinusoidal currents are not negligible even in the main beam region. The input admittances of the elements vary widely from element to element. For the arrays of half‐wave elements, a complete analysis is also carried out with the conventional emf method. The results reveal the inadequacy of the emf method in dealing with these arrays.
Rough Surface Scattering on a Communication Link
Authors: Staras Harold
Published: November 2015

On a communication link between two terminals using essentially isotropic antennas, where at least one of the terminals is in the general vicinity of an extended rough surface, scattering from that surface introduces multipath fading which must be taken into account in assessing the performance of the link. Fading, of course, occurs only if the terminal or the surface changes position with time. This paper discusses the characteristics of fading under the assumption that the surface is rigid but the terminal is moving relative to the rough surface. The important systems parameters, including the depth and rapidity of fading, associated with a given communication link are evaluated. The extension to other links is indicated.
A Note on the Theory of End‐Corrections for Thick Monopoles
Authors: Chang David C. , Tsun Wu Tai
Published: November 2015

The apparent input admittance of an infinitely long, thick monopole driven from a low‐impedance coaxial line is found. The so‐called “capacitive end‐correction” of an antenna driven either by an external delta‐function generator or by an assumed TEM‐mode excitation is then expressed in a very simple form. The theoretical results thus found agree very well with the experimental measurements.
Scintillation Observations at Medium Latitude Geomagnetically Conjugate Stations
Authors: Yeh K. C. , Simonich D. , Mawdsley J. , Preddey G. F.
Published: November 2015

The present investigation is concerned with scintillation observations of radio signals at 40 MHz from satellite BE‐B recorded at Adak, Alaska, and at Wellington, New Zealand. The point conjugate to Adak is approximately 1000 km west of Wellington along a constant L shell. The nigttime irregularity patches that cause scintillation have a dimension 500 km in the north‐outh direction and much larger in the east‐west direction. Therefore, Adak and Wellington are sufficiently close to being a conjugate pair to permit a meaningful correlation of scintillation study.

One year's data have been studied, extending from October 1964, through October 1965. The nighttime scintillation shows a semiannual variation especially equatorward of Adak and Wellington.

Cross‐correlation studies indicate that the conjugate effect is statistically significant at night, but not in daytime. There is also an indication of slight asymmetry with respect to L shells. When the time difference of observations at the two stations is reduced from 2 ½ hr to ½ hr, the correlation coefficient is increased from 0.46 to 0.56. This suggests the time variability of the phenomenon under study.
Balloon Observations of Electron Precipitation in Conjugate Regions of the Auroral Zone
Authors: Brown R. R.
Published: November 2015

A summary of balloon observations of electron bremsstrahlung bearing on conjugate relationships, with particular consideration given to temporal and spatial features of electron precipitation that offer the best means of exploring the problem for energetic particles.
Dielectric Theory of E‐M Waves in Turbulent Med
Authors: Frank Taylor Leonard S.
Published: November 2015

Mathematical solutions of the wave equation in turbulent dielectrics are based upon the use of a “locally defined” permittivity ∊(r). However, in a random medium this definition is ambiguous except in the limit ℓ ≫ λ where ℓ is the scale of the turbulence. The difficulty is resolved by using a method in which the effective permittivity is determined in a manner related to the derivation of the Lorentz‐Lorenz formula for uniform gases. It is found that an additional term exists for the effective permittivity which has not been included in previous results. For λ ≫ ℓ the presence of this term effectively modifies the formulas that describe the propagation of coherent waves in turbulent dielectrics.
Analysis of Spectra of Atmospheric Refractive Index Differences
Authors: Straiton A. W. , Deam A. P. , Dodd J. L. , Fannin B. M.
Published: November 2015

When atmospheric refractive index is observed by measuring the index differences between two points, a filtering action is introduced in the fluctuation spectra. A filter function is obtained when the refractive index difference spectra frequency component is divided by the corresponding frequency component of the index spectra for a single‐point data. Test results of this filter function are compared with theoretical models.

The measured filter functions for 12 data samples obtained with four refractometers on top of an 85‐m tower, are presented. These 12 cases are arranged in the order of increasing wind variability; that is, of increasing ratio of rms wind‐speed variation to the mean‐wind speed.

The measured data are compared with theoretical filter functions derived assuming a “frozen‐atmosphere” model; a statistically homogeneous and isotropic invariant structure being assumed to be carried along at the mean‐wind velocity. A single mean‐wind velocity is assumed for those periods for which the measured wind data indicate a nearly constant flow. For more variable situations an integration over a range of mean‐wind speeds and wind directions is performed.

Though there are numerous marked differences between the measured and calculated filter functions (as would be expected whenever a crude model is used to predict results for a truly complex situation), the model assumed does provide satisfactory explanations for many of the observed features.

An unexplained anomaly, which appears in the measured filter function for many of the cases, is that at the high‐frequency end, the functions are lower than predicted.
Near Fields of a Cylindrical Antenna
Authors: Galejs Janis
Published: November 2015

The near fields of a cylindrical transmitting antenna have been computed in free space by modifying a variational impedance formulation. Current distributions that decay linearly with distance from the ends of the antenna excite strong tangential and parallel electric fields near the antenna
ends. Such fields are avoided by choosing the axial antenna current to vary in proportion to the square root of the distance from the antenna ends. The electric fields parallel to the antenna surface decrease with increasing distance ρ from the antenna axis near the driving point and the antenna ends, but are found to increase in an intermediate range. The magnetic fields exhibit an approximately inversedistance dependence, but the deviations from this inverse ρ dependence are significant for establishing a correlation with the variations of the electric fields.
VLF Electromagnetic Radiation in a Magnetoionic Medium
Authors: Snyder Martin Avery , Weitzner Harold
Published: November 2015

We examine VLF electromagnetic radiation through an ionized gas in a permanent magnetic field (magnetoionic medium). Such a medium can be taken as a model of the ionosphere. We work from the Fourier transform of the dyadic Green's function which relates the current density and the electric field. Asymptotic expansions of the function are obtained for both small and large separation. The expansions for small separation can be used to discuss the power radiated by a current distribution (antenna). Special attention is given to the power radiated by a Hertzian dipole, and a conflict in the literature (Staras, 1964; Lee and Papas, 1965) is resolved. The expansion for large separation can be used to discuss the far field. The radiated far field is shown to propagate most strongly along the field lines of the permanent magnetic field. The far field radiated by a Hertzian dipole is considered.
A Sensitive Technique for Detecting Late‐Time Absorption Following High‐Altitude Nuclear Explosions
Authors: Herman John R.
Published: November 2015

Variations in atmospheric radio noise intensity measured at Kekaha, Hawaii, are used to detect long‐lasting ionospheric absorption produced by late‐time, radioactive debris deposited in the upper atmosphere by the high‐altitude nuclear explosions Star Fisli and King Fish. Variations in noise source intensity and location, combined with variations in radio propagation conditions between the source and receiver, describe the observed variations in received noise power at a distant station. At Kekaha, the noise level on frequencies between 0.5 and 5.0 MHz was depressed for about four nights following each explosion. The depression is explained by the existence of a low‐intensity absorbing region occupying a wide geographic area that effectively fills a major portion of the omnidirectional antenna beam employed at the noise receiving station.
Simultaneous or Sequential Orthogonal Gradient Formation in a 3D Cell Culture Microfluidic Platform
Authors: Uzel Sebastien G. M. , Amadi Ovid C. , Pearl Taylor M. , Lee Richard T. , So Peter T. C. , Kamm Roger D.
Published: November 2015

Biochemical gradients are ubiquitous in biology. At the tissue level, they dictate differentiation patterning or cell migration. Recapitulating in vitro the complexity of such concentration profiles with great spatial and dynamic control is crucial in order to understand the underlying mechanisms of biological phenomena. Here, a microfluidic design capable of generating diffusion‐driven, simultaneous or sequential, orthogonal linear concentration gradients in a 3D cell‐embedded scaffold is described. Formation and stability of the orthogonal gradients are demonstrated by computational and fluorescent dextran‐based characterizations. Then, system utility is explored in two biological systems. First, stem cells are subjected to orthogonal gradients of morphogens in order to mimic the localized differentiation of motor neurons in the neural tube. Similarly to in vivo, motor neurons preferentially differentiate in regions of high concentration of retinoic acid and smoothened agonist (acting as sonic hedgehog), in a concentration‐dependent fashion. Then, a rotating gradient is applied to HT1080 cancer cells and the change in migration direction is investigated as the cells adapt to a new chemical environment. The response time of ≈4 h is reported. These two examples demonstrate the versatility of this new design that can also prove useful in many applications including tissue engineering and drug screening.
Wide‐Range Tunable Fluorescence Lifetime and Ultrabright Luminescence of Eu‐Grafted Plasmonic Core–Shell Nanoparticles for Multiplexing
Authors: Zhang Jun , Song Feng , He Zhubing , Liu Yanling , Chen Zhanyao , Lin Shangxin , Huang Ling , Huang Wei
Published: November 2015

Wide‐range, well‐separated, and tunable lifetime nanocomposites with ultrabright fluorescence are highly desirable for applications in optical multiplexing such as multiplexed biological detection, data storage, and security printing. Here, a synthesis of tunable fluorescence lifetime nanocomposites is reported featuring europium chelate grafted onto the surface of plasmonic core–shell nanoparticles, and systematically investigated their optical performance. In a single red color emission channel, more than 12 distinct fluorescence lifetime populations with high fluorescence efficiency (up to 73%) are reported. The fluorescence lifetime of Eu‐grafted core–shell nanoparticles exhibits a wider tunable range, possesses larger lifetime interval and is more sensitive to separation distance than that of ordinary Eu‐doping core–shell type. These superior performances are attributed to the unique nanostructure of Eu‐grafed type. In addition, these as‐prepared nanocomposites are used for security printing to demonstrate optical multiplexing applications. The optical multiplexing experiments show an interesting pseudo‐information “a rabbit in a well” and conceal the real message “NKU.”
Modulation of Immune Response Using Engineered Nanoparticle Surfaces
Authors: Moyano Daniel F. , Liu Yuanchang , Peer Dan , Rotello Vincent M.
Published: November 2015

Nanoparticles (NPs) coated with a monolayer of ligands can be recognized by different components of the immune system, opening new doors for the modulation ofimmunological responses. By the use of different physical or chemical properties at the NP surface (such as charge, functional groups, and ligand density), NPs can be designed to have distinct cellular uptake, cytokine secretion, and immunogenicity, factors that influence the distribution and clearance of these particles. Understanding these immunological responses is critical for the development of new NP‐based carriers for the delivery of therapeutic molecules, and as such several studies have been performed to understand the relationships between immune responses and NP surface functionality. In this review, we will discuss recent reports of these structure‐activity relationships, and explore how these motifs can be controlled to elicit therapeutically useful immune responses.
Efficient production of gamma-aminobutyric acid using Escherichia coli by co-localization of glutamate synthase, glutamate decarboxylase, and GABA transporter
Authors: Dung Pham Van , Somasundaram Sivachandiran , Lee Seung Hwan , Park Si Jae , Hong Soon Ho
Published: November 2015

Gamma-aminobutyric acid (GABA) is an important bio-product, which is used in pharmaceutical formulations, nutritional supplements, and biopolymer monomer. The traditional GABA process involves the decarboxylation of glutamate. However, the direct production of GABA from glucose is a more efficient process. To construct the recombinant strains of Escherichia coli, a novel synthetic scaffold was introduced. By carrying out the co-localization of glutamate synthase, glutamate decarboxylase, and GABA transporter, we redirected the TCA cycle flux to GABA pathway. The genetically engineered E. coli strain produced 1.08 g/L of GABA from 10 g/L of initial glucose. Thus, with the introduction of a synthetic scaffold, we increased GABA production by 2.2-fold. The final GABA concentration was increased by 21.8 % by inactivating competing pathways.
Diagnosing Septic Arthritis in the Synovial White Cell Count “Gray Zone”
Authors: Ruzbarsky Joseph J. , Gladnick Brian P. , Dodwell Emily
Published: November 2015

Differentiating septic arthritis of the pediatric hip from other causes of hip pain and effusion continues to present a diagnostic challenge for the clinician. Although septic arthritis traditionally has been reported to have a synovial white blood cell count of 75, 000 cells/mm3 or greater, lower counts can be seen in this condition. In cases where a synovial sample has been obtained and the cell count falls in the intermediate range between 25, 000 and 75, 000 cells/mm3, it is unclear what proportion of these cases may be truly septic hips. In this evidence-based review, we examine Heyworth et al's study focusing on the predictive value of this intermediate white cell count range in a Lyme-endemic region.