bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoelectric properties of nanocarbons: Atomistic modeling
Authors: Lehmann Thomas , Ryndyk Dmitry A. , Cuniberti Gianaurelio
Published: November 2015

We present a general atomistic ab initio‐based modeling approach and numerical implementation for the calculation of thermoelectric properties of carbon nanomaterials. The approach is based on density functional theory calculations of electronic and vibrational properties in combination with quantum transport theory in the Green function formalism. It allows to calculate charge and heat transport, and therefore electrical conductance, thermopower (Seebeck coefficient), electron thermal conductance, phonon thermal conductance, and thermoelectric efficiency, i.e., figure of merit. We systematically investigated temperature, doping, and disorder dependence of the thermoelectric properties of the fundamental types of nanocarbons, such as graphene, metallic and semiconducting nanoribbons, as well as metallic and semiconducting nanotubes.
Calculating the thermal conductivity of the silicon clathrates using the quasi‐harmonic approximation
Authors: Madsen Georg K. H. , Katre Ankita , Bera Chandan
Published: November 2015

A model of the lattice thermal conductivity, based on the quasi‐harmonic approximation, is validated on a dataset of 42 rock‐salt and zinc‐blende compounds. The model reliably reproduces experimental thermal conductivities ranging over several orders of magnitude. The good performance of the model is related to the definition of the mode‐averaged Grüneisen parameter. The model is applied to the silicon‐based clathrates and found to correctly reproduce the two orders of magnitude reduction of the lattice thermal conductivity compared to Silicon in the diamond structure. It is shown how the introduction of the clathrate structure and the guest atoms lead to a reduction of approximately one order of magnitude each. The clathrate structure is found to both increase the anharmonicity and decrease the average phonon velocity, whereas the reduction due to the guest atom is almost purely due to increased anharmonicity.
Highly efficient and reliable high power InGaN/GaN LEDs with 3D patterned step‐like ITO and wavy sidewalls
Authors: Lv Jiajiang , Zheng Chenju , Zhou Shengjun , Fang Fang , Yuan Shu
Published: November 2015

Nitride‐based high power LEDs with finger‐like SiO2 current blocking layer (CBL), three‐dimensional (3D) patterned step‐like ITO double layers and wavy sidewalls were fabricated. The finger‐like SiO2 CBL beneath finger‐like p‐electrode was designed to prevent current crowding effect, thereby facilitating uniform current spreading over the entire chip. In addition, 3D patterned step‐like ITO double layers, including alternating 230 nm thick patterned upper step ITO layer and 100 nm thick lower step ITO layer, were formed by combining photolithography and aqua regia etchant. We showed that the top light extraction efficiency of high power LEDs can be significantly enhanced by taking 3D patterned step‐like ITO. The light output power of high power LEDs with 3D patterned step‐like ITO double layers is 13.9% higher than that of LEDs with smooth ITO layer. High‐power LEDs with wavy sidewalls was fabricated by an optimized mask design in conjunction with dry etching process based on Cl2/BCl3 to improve light extraction efficiency at the horizontal direction. We demonstrated that light output power of high power LEDs with wavy sidewalls can be improved by 11% as compared to LEDs with flat sidewalls.
Seasonal Variations in Occurrence of Scintillation
Authors: Munro George H.
Published: November 2015

Observations of scintillation on signals radiated on a frequency of 20.005 Mc/s from a series of satellites are used to derive diurnal variations in the appearance of scintillation. Marked seasonal changes in daytime scintillation are apparent, but it is shown that summarizing for the four conventional seasons may mask some of the more significant changes.
Influence of Solar Protons on High‐Latitude Ionospheric Disturbance
Authors: Elkins Terence J.
Published: November 2015

High‐latitude ionospheric absorption is shown to exhibit a magnetic, rather than local, time dependence. The spatial and temporal variations of absorption are compared to the same variations of impact zones for solar protons in the energy range 50 MeV to 1.0 GeV, and the agreement is shown to be good. Similar agreement is found when various other ionospheric disturbance parameters are considered. The conclusion is tentatively reached that a more or less continuous flux of solar protons is entering the earth's atmosphere, which if valid, would have important consequences in the study of the energy balance of the ionosphere as well as that of the sun itself.
Seasonal Atmospheric Attenuation Measurements at 3.27 em Wavelength
Authors: Castelli John P.
Published: November 2015

Atmospheric attenuation measurements have been made for four seasons during 1962 and 1963 at Sagamore Hill Radio Observatory, Hamilton, Mass., at a wavelength of 3.27 em. A definite seasonal trend was noted with the greatest attenuation observed during the winter when an average vertical attenuation of 0.13 dB was measured. The trend is compared with temperature and seasonal averages of surface barometric pressure. Summer attenuation in 1964 is compared with similar measurements made in 1956 in the same geographical area.
The Maximum Resolution of a Radio Telescope Imposed by Corona Scattering
Authors: Erickson W. C.
Published: November 2015

The scattering of radio waves in the solar corona will eradicate the fine structure of radio source brightness distributions. The magnitude of this effect is estimated for observations in various directions by a radio telescope situated at the earth. Even for observation in the antisolar direction, this effect may limit the resolution attainable by radio telescopes that would be otherwise technically feasible.
Further Experimental Study of Plasma Sheath Effects on Antennas
Authors: Hamm John M. , Tyras George
Published: November 2015

The plasma sheath simulation technique developed earlier has been used to investigate the effects of various types of sheath discontinuities and inhomogeneities on a slot‐antenna radiation pattern and input impedance. The results are especially applicable to re‐entry environments.

In the case of semi‐infinite and finite‐extent homogeneous plasma sheaths, the radiation pattern and the impedance characteristic are investigated with regard to the geometry of the discontinuity and its proximity to the slot antenna. It is found that the radiation pattern is unaffected by the discontinuity as long as the ratio of the distance between the source and discontinuity to the sheath thickness is of the order of 20 or greater. When the sheath is made finite in extent, with a discontinuity on each side of the slot, the resulting pattern is seen to be a superposition of the effects of each discontinuity acting separately. Investigation of the input impedance of the slot shows essentially no variation with discontinuity separation for separation‐to‐thickness ratios of at least 4. For smaller separatiOns, the impedance exhibits significant variations, strongly dependent on the geometry of the discontinuity. The effects produced by inhomogeneities are found to be similar to those of a homogeneous sheath with a certain equivalent dielectric constant.

For both the homogeneous and inhomogeneous sheaths, favorable comparisons with the available theory is obtained.
U.S.A. National Committee Report, Fifteenth URSI General Assembly, Munich, September 1966: Commission 2, Radio Propagation in Nonionized Media; Progress in Radio Propagation in Nonionized Media
Authors: Katz Isadore , Ament W. S. , Atlas David , Bean B. R. , Beard C. I. , Bolgiano Ralph , Burrows C. R. , Carroll T. J. , Chisholm J. H. , Gerks I. H. , Gordon W. E. , Herbstreit J. W. , Hogg D. C. , Katzin Martin , LaGrone A. H. , Moore R. K. , Norton K. A. , Straiton A. W. , Thompson M. C. , Wait J. R. , Waterman A. T.
Published: November 2015

In 1965 there was a strong reawakening of interest in “angel” or clear‐air radar echoes. Atlas [1965] postulated that "dot" or point‐like angles were reflections from smooth, sharp boundaries at the apex of convective thermals. Focusing from the curved surface reduced the requirement on the index gradient to 1 N unit through 1 em; however, the requirement of smoothness to a fraction of a em over the first Fresnel zone is still severe and lacks experimental confirmation. Dot angel activity at night requires another explanation. Hardy, Atlas, and Glover [1966] and Deam and LaGrone [1965] conclude that dot angel characteristics are explainable only if the targets are insects. These conclusions stem from considerations of absolute cross section and wavelength dependence.
Current Distribution and Impedance of a Cylindrical Antenna in an Isotropic Compressible Plasma
Authors: Cook K. R. , Edgar B. C.
Published: November 2015

Current distributions for cylindrical dipoles in isotropic compressible plasmas have been determmed for discrete sets of plasma temperature and densities. Coupling between the optical and plasma modes at the surface of the antenna have been accounted for, producing quite different electncallengths than experienced in incompressible plasmas.

Calculations have been made on the assumption that the normal electron velocity of the compressible plasma vanishes at the surface on the antenna. A new approximation technique has allowed simplified computer solutions for the eigenvalues determining the current distribution on the cylindncal structure. Resulting current distributions display hybrid optical‐plasma characteristics for certam frequency spectra. These results clearly point out the form of the assumed current distribution for a given structure.

Having obtained an approximation for the electroacoustic current distribution calculations for the radiation resistance of an electric dipole are easily performed. Results for the radiation resistance of various lengths of the antenna are presented, illustrating the dominance of the plasma mode for certam frequency spectra. Results have also been obtained for discrete sets of plasma temperature and densltles, as well as different length‐to‐diameter ratios of the dipole antenna. A discussion of the field structure of the optical‐plasma mode is included.
Slots in Dielectrically Loaded Waveguide
Authors: Larson R. W. , Powers V. M.
Published: November 2015

Simple modifications of formulas presented by A. A. Oliner are found to allow the determination of the impedance and resonant length of a slot in rectangular waveguide when the guide is filled with dielectric material. The modifications are justified by reference to earlier work by Oliner and others, and are verified by experimental results.

(It has been recently learned that B. R. Cheo of New York University and H. Jones have collaborated on a very similar study. Their work is in agreement and will be reported in the near future.)
Characteristics of Ionospheric Es Propagation and Calculation of Es Signal Strength
Authors: Miya K. , Sasaki T.
Published: November 2015

This report begins by describing the distribution of reflection points in the ionospheric E propagation as observed in the Far East. The ionospheric attenuation of the Es signal is statistically treated as a function of a ratio of the frequency used to the critical frequency, f0Es, at the path midpoint; and its distance dependence is compared with the so‐called secant law. The attenuation of two‐hop Es signals is discussed, utilizing the observational results. In addition, the occurrence of a noticeable deterioration in antenna gain, corresponding to “aperture‐to‐medium coupling loss” in scatter propagation, is elucidated. Three charts are presented for estimating Es signal strength up to a distance of 4,000 km. A study is also made of the receiving rate of Es signals.
Characteristics of Ionospheric Sporadic E Signals
Authors: Miya K.
Published: November 2015

Some noticeable phenomena in Es propagation are introduced, extracting from a paper entitled “Characteristics of Ionospheric Sporadic E Propagation and Calculations of Its Signal Strength,” together with new material prepared for the Es seminar.
Observed Characteristics of Ionospheric Winds
Authors: Bedinger J. F. , Knaflich H. B.
Published: November 2015

The general characteristics of ionospheric winds during twilight have been determined from observations of the motion and growth of sunlit trails of alkali vapor. Typical large shears and small features are described. Specific wind profiles are compared with nearly simultaneous measurements of electron concentration from rocket‐borne probes. Generally, the narrow regions of enhanced electron concentration measured by the probes do not occur in the low velocity region of an E‐W shear. However, the ionization peaks appear to be associated with certain other features of the wind profile.
A Rocket Experiment on the Structure of Sporadic E
Authors: Bowhill S. A.
Published: November 2015

A radio propagation experiment designed to measure very low electron densities was flown over the sunrise period on July 15, 1964. Two strong sporadic E layers were noticed during each of the three flights, with densities of the order of 105 cm‐3 The characteristics of these sporadic E layers are discussed in detail, with reference both to the characteristics of the radio signal propagated to the rocket, and to the detailed ionograms taken immediately preceding and following the flight.
The Wind‐Shear Theory of Temperate Zone Sporadic E
Authors: Axford W. I. , Cunnold D. M.
Published: November 2015

The assumptions on which the wind‐shear theory of temperate zone sporadic E is based are outlined and the formulation of the theory is described for the cases in which a single ion and many ions, both positive and negative, are present. Among the implications of the theory which agree with observations are that a zone of reduced occurrence of this type of sporadic E should occur at the geomagnetic dip equator, and elsewhere the occurrence should be roughly correlated with the horizontal component of the geomagnetic field. It is pointed out that horizontal electric polarization fields and vertical motion of the wind profile can affect the formation of layers, thus leading to difficulties in the interpretation of observations of winds and electron density profiles. The effect of the presence of many types of ion is discussed, and it is shown that if all the ions are positive, then the maximum electron density attained in a layer is determined by the ion with the smallest recombination coefficient, while the electron density outside the layer is much less depleted than it would be in the single‐ion case. Meteoritic ions in particular must react strongly to the presence of wind shears, and these may play an important part in the formation of sporadic E layers, especially at night. The effect of negative ions is also considered, and it is shown that these can lead to the formation of layers of positive ion density at apparently anomalous positions under suitable conditions.
2. Rocket Measurements
Authors: Smith L. G.
Published: November 2015

A considerable amount of data on the electron density profile of Es layers has been accumulated starting with Seddon's experiments using his CW propagation technique. More recent data have been presented at this conference. The motivation for recent observations has resulted from the wind‐shear theory. It should be pointed out that the determination of winds by the vapor‐trail technique is at present limited to night and twilight observations. Now, Es in midlatitudes, where most of these observations are being taken, is primarily a daytime phenomenon, and the basic statistical information on Es has been derived from ground‐based radio techniques. Thus the rocket data is unfortunately biased by the nighttime observations.
3. Ionospheric Wind Patterns
Authors: Rosenberg N. W.
Published: November 2015

There have been five reports at this meeting on ionospheric winds which, at first appearance, seem somewhat at variance. Further analysis shows them to be in reasonable agreement, probably because all are based on the same type of data, i.e., midlatitude winds from luminous trails.
A Note on the Influx of Extraterrestrial Dust as an Energy Source in the E Region
Authors: Fiocco Giorgio
Published: November 2015

Some connection between sporadic E layer irregularities and incoming extraterrestrial dust at heights of llO km and above has been indicated by the comparison of optical radar and ionosonde data [Fiocco, 1965]. The object of this note is primarily to point out the possible importance of the influx of extraterrestrial dust to the energy balance of the E region. Much independent evidence suggests that the average influx rate on earth of small particles of extraterrestrial origin, ranging in diameter from 0.1 µ to 100 µ, is of the order of 104 tons/day and that peaks of the order of 105 tons/day or even 106 tons/day may be possible. If these estimates are correct, and since the particles enter the earth's atmosphere at speeds of the order of 10 km/s, their influx may represent an average energy input for a vertical column in the E region of the order of 10−2 erg/cm2 sec and as high as 1 erg/cm2 sec. If it were possible to fully convert this energy into ionization, for a column of 10‐km length and a recombination coefficient α = 10−8 cm3 sec−1, electron densities of the order of 105 cm−3 and higher would be achieved, which are in excess of what is needed in a sporadic E layer. While this process may therefore in some cases supply the background ionization necessary for the formation of the layer, and other processes may be operative in organizing the distribution of charge in space, it is possible that the way by which the dust particles dissipate their energy may, by itself, directly lead to the formation of a layer. The energy of small particles characterized by a constant area‐over‐mass ratio would be dissipated in a height interval of a few tens of kilometers, the length of the interval depending upon size and angle of incidence. However, fragmentation in flight of the micrometeoroids due to mechanical, thermal, and electric effects [Fiocco and Colombo, l964] may cause the dissipation to take place in a much shorter interval of altitudes, possibly less than a scale height.
On the Effect of Heavy Ions on LF Propagation, With Special Reference to the Nuclear Environment (Digest)
Authors: Johler J. Ralph , Berry Leslie A.
Published: November 2015

A brief discussion is given of a recently published NBS Technical Note which treats propagation of low‐frequency radio waves in the vicinity of a nuclear explosion. An ionized plasma is induced in the upper atmosphere as a result of radioactive debris deposited by the nuclear event. The plasma contains a gas mixture of positive and negative heavy ions as well as electrons, all of which increase the normal ionization of the upper atmosphere and the ionosphere, and as a result cause increased attenuation of low‐frequency waves. The effective height of the upper boundary of the waveguide propagation model is deduced from a study of transmission of the wave into the plasma for any variation of the plasma properties with height. Since reflections occur at all points where the plasma is varying with height, this effective height can only be approximate, and moreover depends on the definition of the concept of effective height.
Effect of Ionospheric Reflections on the Nature of the Waveforms of Radio Atmospherics
Authors: Bhattacharya H. , Rao Manoranjan
Published: November 2015

It is well known that ionospheric reflections modify the shape of the waveforms of atmospherics. In this paper an attempt is made to deduce theoretically the shape of the waveform of the pulse radiated by a lightning discharge, after it has undergone successive reflections at the ionospheric layer. To this end, the return‐stroke current due to the lightning discharge is assumed to follow the usual double exponential formula with Kimpara's values of the constants. The ionosphere is taken to be a sharply bounded homogeneous medium and the geometric reflection is assumed to hold. Using Fresnel's reflection coefficient, an expression is obtained for the final shape of the reflected pulse. The plots of this expression for the different orders of reflection show that relative to the amplitude of the positive half of the reflected pulse waveform, the negative half increases in amplitude with the order of reflection. It is observed that there is a decrease in the quasi‐frequency of the reflected pulse waveform with the increase in the order of reflection. Some reflection types of waveforms have actually shown these features.
Radiation in a Moving Anisotropic Medium
Authors: Lee S. W. , Lo Y. T.
Published: November 2015

Starting with Minkowski's theory, the constitutive relation for a moving anisotropic medium is first derived and then the problem of radiation due to an arbitrary time‐harmonic source is formulated through an operational method. In particular, the field solution of an electric dipole in a moving, uniaxial, anisotropic medium is obtained.
Magneto‐Ionic Coupling in an Inhomogeneous Anisotropic Medium
Authors: Inoue Yuji , Horowitz Samuel
Published: November 2015

The propagation of electromagnetic waves in a horizontally stratified layer of a gyrotropic medium is discussed. Derivation of a comprehensive representation for magneto‐ionic coupling coefficients allows interpretation of the physical significance of coupling. An invariant quantity is determined which assists in locating critical levels and becomes an important guide for numerical solutions of the wave equation. Numerical results of the Booker quartic and magneto‐ionic coupling coefficients are presented for a model ionosphere. In the isotropic region the characteristic waves are linearly polarized, while for the anisotropic region they are generally elliptically polarized.
Excitation of the Lower Hybrid Resonance by an Antenna in the Ionosphere
Authors: Fejer J. A.
Published: November 2015

Ionospheric plasma oscillations near the lower hybrid resonant frequency, excited by an infinitesimally small impulsive dipole source and observed at a point moving away from the source with typical rocket or satellite velocity, are well described by cold plasma theory after a few milliseconds. The field of the oscillations at the observation point decays as the inverse 3/2 power of the time. In practice, oscillating field strengths of a few microvolts per meter should be readily attainable; the detectability of such oscillations depends on the ambient noise level, which is not well known at present.
On Frequency Variations of lonospherically Propagated HF Radio Signals
Authors: Davies Kenneth , Baker Donald M.
Published: November 2015

A technique for measuring the frequency variations of ionospherically propagated radio waves by spectrum analysis of the received signal is described, together with some theory needed to interpret such measurements. Examples of the types of variations observed with both vertical and oblique propagation are presented. On "quiet" days in middle latitudes, frequency variations of the order of ± 0.2 c/s occur, having periods of the order of 10 min. During disturbed periods the variations may be as much as 2 to 3 c/s on 5 Mc/s with vertical propagation. The frequency stability is generally greater for oblique propagation than for vertical propagation; however, the received spectrum is broader for oblique propagation. The frequency stability of E echoes is, in general, much greater than that of F2 echoes.

At night and during some geomagnetic storms, the discrete (line) spectra give way to diffuse spectra. During periods of flutter fading at low latitudes, the discrete spectra are transformed into continua with frequency spreads of up to± 5 c/s about the mean value.

Distinctive frequency deviations are caused by solar flares, geomagnetic disturbances, and traveling ionospheric disturbances. Of these, the solar flare‐induced frequency variations are the most striking. Deviations of up to 50 c/s have been observed on WWV‐10 Mc/s received at Boulder during flares. However, frequency deviations associated with solar flares have a most probable duration of about 4 min, and the majority of them have magnitudes less than 1 c/s.
The Effect of a Specular Component on the Correlation Between the Signals Received on Spaced Antennas
Authors: Whale H. A. , Gardiner C. W.
Published: November 2015

A model of a re‐entry plasma layer is analyzed by using the linearized hydrodynamic equations for a single‐fluid warm plasma medium. The model consists of a perfectly conducting plane of infinite extent covered by a warm plasma layer of uniform density. The field excited by a magnetic line source located on the conducting plane is computed by Fourier transform techniques. Expressions are obtained for the far‐zone radiation field and for the surface waves guided by the plasma layer. Numerical results are presented that show the dependence of the energy transported by these waves on frequency and electron temperature. In addition, the radiation pattern of the far‐zone field is computed for various frequencies and electron temperatures.
Infinite Helical Sheath Antenna
Authors: Chen Chin‐lin
Published: November 2015

An infinitely long helical sheath antenna driven by a ring delta‐function generator is considered. The Fourier transform technique is used to solve this problem. It is found that if βb < 2.4048, the current distribution far away from the driving point can be decomposed into a surface‐wave current and a radiating current. The former is constant in magnitude with a phase velocity less than the speed of light, the latter decays as 1/z2 and has a phase constant β. The radiation pattern of the space wave is calculated. The power radiated by the space wave, guided by the surface wave, and the efficiency of excitation of the surface wave are also determined. Numerical results are presented.
Synthesis of Nonuniformly Spaced Antenna Arrays Yielding Approximately Equal Sidelobes
Authors: Ma M. T. , Walters Lillie C.
Published: November 2015

Based on a method briefly discussed before for nonuniformly spaced symmetric antenna arrays new conclusions arising from numerical results are presented here. The results are obtained by applying Haar's theorem. where the "minimax" error criterion rather ihan the ordinary least‐mean‐square criterion 1s used. With respect to set of element spacings, the solution obtained has the following properties: (1) the maximum deviation between the synthesized and desired patterns is minimized (2) the sidelobes are approximately equal and their level can be made minimum for a specified beamwidth, (3) both the sidelobe level and the beamwidth can be improved simultaneously by adjusting each excitation and the positions of inner pairs of elements, and therefore a better performance than the Dolph‐Chebyshev array for the same number of elements and an equal overall array length is possible, (4) a minimum number of elements required to yield a pattern of approximately equal sidelobes can be determined, and (5) the solution can be unique. The method is valid for arrays consisting of either isotropic sources or directional elements.
A Normal Mode Theory of an Underwater Acoustic Duct by Means of Green's Function
Authors: Deavenport Roy L.
Published: November 2015

The resolvent Green's function technique is used to find the acoustic field due to a CW point source located in a laminar inhomogeneous medium. Results are in terms of a residue expansion (normal modes) and branch line integrals. This approach is then used to solve the wave equation for an underwater acoustic duct described by an Epstein layer. Only the residue expansion is evaluated. From the residue expansion, propagation loss is found as a function of range. Application to a realistic velocity‐depth profile indicates a pattern of beats resulting from a superposition of the normal modes. A general procedure is next described for obtaining exact solutions of the wave equation for a large variety of velocity‐depth profiles. This procedure may prove useful in developing future normal mode models.
Baseband Multipath Fading Simulator
Authors: Walker W. F.
Published: November 2015

A device is described which was built to provide representative fading multipath channel behavior for the investigation of communication system performance. The unit is based on the tapped delay line approach and operates in the band of 50 to 8000 c/s. The tap modulation functions are camgenerated with adjustable correlation. Fading bandwidths of 0 to 5 c/s are available, and 30 hr of operation are possible at a fading bandwidth of 1 c/s with no repetition of the pattern. Dual diversity output and additive noise and interference facilities are provided. In the HF mode, test results are presented showing Rayleigh amplitude fading and flat phase statistics for any input frequency between 300 and 3300 c/s. The unit is also used for underwater path simulation by substituting a tape recorder with multiple pickups as the delay device. In this mode, delay spreads of up to 10 sec may be obtained. Finally, elementary sonar path simulation is achieved by using the tape delay system for outgoing and return‐path simulation coupled with a tapped delay line for target highlight synthesis.
On Axis Far‐Field Backscattering From Flared Axially Symmetric Bodies
Authors: Weil Herschel , Raymond Joseph L.
Published: November 2015

This paper presents a physical‐optics solution for the backscattering from a concave ring singularity. The solution for a convex ring singularity has been known for some time. When taken together, the two solutions provide a simple way for estimating the backscattering from ring singularities of practically every type. Since the radar returns from rings are often dominant, the solutions should have many important applications.
Determination of the Admittance and Effective Length of Cylindrical Antennas
Authors: King R. W. P. , Aronson E. A. , Harrison C. W.
Published: November 2015

The apparent admittance of a cylindrical antenna depends critically on the structure of the conductors near the junction of the antenna and the feeding line. For thin cylinders and closely spaced lines an ideal admittance can be defined in the hypothetical limit of “zero” line spacing. The approximate theoretical equivalent is the admittance seen by a delta‐function generator with the infinite susceptance of the knife‐edge capacitance subtracted.

The iterated theoretical admittance of a cylindrical antenna with a delta‐function generator is examined for from one to 30 iterations. It is shown that for β0α ≤ 0.1 or α/λ ≤ 0.016 (where α is the radius, β0 = 2 π/λ the wave number) the conductance converges rapidly, but the susceptance increases continually with the added iterations by an amount proportional to the circumference of the antenna. The more accurate the solution, the nearer the susceptance approaches infinity. A simple empirical correction is combined with the second‐order iterated value to provide a good approximation of the ideal independent susceptance of the antenna. When β0α ≤ 0.1, the second‐order corrected admittance is essentially the same when calculated with either the exact kernel for the tubular antenna or the commonly used average kernel.

Tables of the admittance Y, impedance Z, radian effective length β0he, and directivity D are given. When combined with the terminal‐zone network for a particular transmission line, the measurable apparent admittance and impedance of a cylindrical antenna are obtained with essentially as great an accuracy as is possible in terms of an “independent” admittance for the antenna. More accurate values depend on the individual analysis of each transmission‐line‐antenna configuration.
Experimental Results of VLF Dipole Tests on the Greenland Ice Cap
Authors: Johnson T. L. , Winkler G. M. R.
Published: November 2015

Results of measurements on lung resonant dipoles installed un the Greenland ice cap are presented. The difficulties involved in laboratory modeling of VLF antennas are discussed and the full‐scale data presented show significant differences from previously reported model data. Self‐impedance, amplitude current distributions. and relative efficiency were measured using dipoles that ranged in length from 600 m to 8.000 m. Results from three 3.700‐m dipoles having different insulation diameters are (•umpared. Four‐electrude measurements of complex conductivity of the surface ice are also reported. Dipole driving point resistance at resonance is found to be higher than expected and a basic correlation of resonant length and driving point resistance with the dielectric properties of the ice is noted. The efficiency uf insulated dipoles was found to be significantly greater than that of uninsulated dipoles of equivalent length.
Investigation of the Mode Conversion at a Modeled Sunrise; Change in Ionosphere Effective Height
Authors: Hicks John J.
Published: November 2015

A simple method is given for exciting the first two propagating modes only in a waveguide model which approximates the earth‐ionosphere waveguide at VLF frequencies. A theoretical solution for the mode conversion at an assumed sunrise change in ionosphere effective height is obtained and verified experimentally.
Diffraction of Radio Waves in a Stratified Troposphere
Authors: Gerks Irvin H. , Anderson Ronald M.
Published: November 2015

The problem of diffraction around a smooth, finitely conducting earth is reexamined with the objective of obtaining an exact solution for the case of an exponential profile of refractivity. The methods employed are largely conventional. However, care is taken to avoid approximations of doubtful accuracy, and the solution is illustrated by numerical computations. It is shown that the method of using an effective earth radius and assuming a homogeneous medium is generally sound.
Survey of VLF Electric Fields in the Magnetosphere With the Polar Orbiting Spacecraft, 1964–45A
Authors: Scar F. L. , Crook G. M. , Fredricks R. W.
Published: November 2015

The VLF electrometer on the Lockheed‐Aerospace P‐11 satellite, 1964–45A, sampled ambient electric fields in the frequency range 1.7–14.5 kc/s. Tape‐recorded data for 16 full orbits were obtained between 15 August 1964 and 13 September 1964. A complete description of the experiment is given, the results for 8 of these passes are displayed and analyzed, and the remaining measurements are summarized. It is argued that the observed fields generally represent electrostatic plasma oscillations in the ambient medium, and various sources of the large nonequilibrium noise enhancements are considered. It is noted that d‐e electric fields parallel to the geomagnetic field lines (possibly associated with the flute instability) could produce the large‐amplitude plasma oscillations and related phenomena.
Sporadic E at Night
Authors: Whitehead J. D.
Published: November 2015

It is estimated that intensity of the E region source of ionization at night is required to be 0.1 percent to 1 percent of the intensity during daytime to allow the formation of sporadic E at night. Possible sources are considered.
Ionospheric Electron‐Density Profiles With Continuous Gradients and Underlying lonization Corrections. I. The Mathematical‐Physical Problem of Real‐Height Determination From lonograms
Authors: Paul Adolf K.
Published: November 2015

Any numerical method for inversion of the integral equation h'(f)= p.'(/N(z),f)dz must satisfy certain requirements in order to avoid introducing features into the true‐height profile which are not indicated by the ionogram. These requirements are first investigated by considering the equation as an integral transformation of fN(z) for several model distributions. In order to satisfy the above‐mentioned criteria a second‐order lamination process was developed; its mathematical principles are presented in this paper and its implementation at the Institute for Telecommunication Sciences and Aeronomy is discussed in the two following papers.
Tables of Virtual Heights for Models of Monotonic and Nonmonotonic Ionospheric Layers
Authors: Herbert Th.
Published: November 2015

A group of mathematical ionospheric models are defined and given numerically together with precisely calculated virtual heights. The models are intended to permit decisive tests and inter‐comparison of N(h) methods.
Results From an RF Capacity Probe Experiment in the Auroral Ionosphere
Authors: Holt O. , Lerfald G. M.
Published: November 2015

A rocket‐borne experiment, in which measurements of the RF capacity of two spherical probes of different size were taken at several frequencies, is described. The experiment was designed to measure electron density, and was performed during an auroral disturbance. Analysis shows the data agree up to 90 km with electron density measurements by a wave‐propagation experiment. Above this height the probe data indicate the presence of field‐alined enhancements in the ionization. The characteristic “thickness” of these enhancements is ≈ 400 meters. The electron temperature could be estimated from the data, and values in excess of the neutral temperature were indicated.
Results of the Two‐Frequency VLF Transmission Experiments from Criggion GBZ
Authors: Rawles A. T. , Burgees B.
Published: November 2015

During the period August–December 1965, time‐duplex transmissions in the frequency range 11.6–13.8 kHz were radiated from the VLF station GBZ at Criggion, Wales. Measurements on these transmissions were made at a few selected sites at large distances from the transmitter, and also by monitoring the signals aboard a high‐speed aircraft. A study of the rms variation of the phase delay of the difference frequencies in the range 200 to 2200 Hz, indicate that the phase‐delay fluctuations of two frequencies separated by 200 Hz are not independent The implications of this in terms of navigation requirements are discussed, it being shown that on the available experimental evidence, for rms errors of 5 nm, the use of two‐beat frequencies (200 Hz and 1.2 kHz) would be sufficient for navigation assuming a common frequency near 11 to 12 kHz. Further, the measurements of the propagation characteristics obtained by monitoring the transmissions as a function of distance in an aircraft indicated that modal interference out to distances of order 3000 km contributes an important part to the overall rms phase‐delay fluctuations throughout a 24‐hr period.
Arrays of Unequal and Unequally Spaced Dipoles
Authors: Cheong Weng‐Meng , King Ronold W. P.
Published: November 2015

The quantitative determination of the circuit and field properties of arrays of parallel, non staggered dipoles is treated theoretically and experimentally when the lengths of the elements and the distances between them may differ greatly. The simultaneous integral equations are replaced by approximately equivalent algebraic equations which are used to determine the coefficients of a simple three‐term approximation of the currents. Theoretical distributions of current. self and mutual admittances, field patterns, and other properties of simple two‐element and five‐element arrays are shown to agree well with measured values. Coupled elements ranging in length from longer than a wavelength to a small fraction of a wavelength are included in the study.
Effects of Induced Acoustic Sources on the Impedance of a Cylindrical Dipole in a Warm Plasma
Authors: Carlin J. , Mittra R.
Published: November 2015

In determining the impedance of a cylindrical dipole in intimate contact with a plasma, the effect of the induced acoustic sources (force and fluid flux distributions) on the antenna surface must be accounted for in addition to the effects of the induced current distribution. This is accomplished by the derivation of a suitable stationary formula for impedance which accounts for the effects of all the induced sources. In this variational formulation it is only necessary to know the functional form of the induced sources and not their relative magnitudes in order to obtain impedance values. In general, the effect of the acoustic sources on impedance was found to be quite small for the current and force distribution used.
Diffraction of a Dipole Field by a Perfectly Conducting Half Plane
Authors: Bowman J. J. , Senior T. B. A.
Published: November 2015

The various forms of solution for the problem of an arbitrarily oriented electric or magnetic dipole in the presence of a half plane are reviewed and presented from a unified point of view. Some new results are given and errors in the literature are corrected.
Scattering by a Two‐Dimensional Periodic Array of Narrow Plate
Authors: Ott R. H. , Kouyoumjian R. G. , Peters L.
Published: November 2015

Theoretical and experimental studies of the scattering by a two‐dimensional periodic array of narrow, perfectly‐conducting plates have been carried out. The scattering in the resonance region is treated. The present work is restricted to a normally incident plane wave; however, the approach described here can be extended to the case of oblique incidence.

The surface current on a single plate is expanded in a series of N terms. An integral equation is obtained for by enforcing the boundary condition on the tangential electric field. The N unknown coefficients of are found by satisfying the integral equation exactly at N points. The solution for the scattered field was found to be highly sensitive to the location of the N points at which the integral equation is satisfied. A set of N points is found by introducing a suitable error gauge which involves ∫ Js · ETds, where the integral is taken over a single plate and is the calculated total electric field.

Within the frequency band considered, the reflectivity of the array is seen to range from unity at its first resonance to zero at certain frequencies where Wood's anomalies occur. Also, the frequency shift of the array resonance from single element resonance is observed. Values of the reflection coefficient calculated as a function frequency compare well with experimental values.
On the Calculation of Antenna Patterns for an Inhomogeneous Spherical Earth
Authors: Spies Kenneth P. , Wait James R.
Published: November 2015

Analytical and numerical procedures are described for the evaluation of the following functions:
urn:x-wiley:00486604:media:rds19672111361:rds19672111361-math-0003
The contour Γ, for the integrals in the complex t plane, may be taken from ∞e−i2π/3 along a straight line to 0 and then out along the real axis to + ∞. In addition, and where Ai, Bi, Ai′, and Bi′ are Airy functions in the standard notation. The real quantities X and x1 and the complex factors q and q1 are the parameters of the problem. The function V′, which characterizes the pattern of a loop antenna on the earth's surface, is illustrated graphically for low radio frequencies for a mixed land/sea propagation path.
Power Flow From a Short Antenna Lossy Uniaxial Medium
Authors: Galejs Janis
Published: November 2015

The power flow from a short linear current element is computed by integrating the Poynting's vector over concentric cylindrical surfaces of various radii ρ. An effective antenna resistance is defined as the ratio between the integrated power flow and the mean square source current. In a lossless medium the integrated power flow is independent of ρ, and the conventional expression is obtained for the radiation resistance. In a slightly lossy medium, and at moderate distances ρ the effective resistance R remains unaltered for frequencies ω above the plasma frequency ωρ. For ω < ωρ, a simple asymptotic approximation shows that R which is inversely proportional to the antenna length ℓ for ρ small is gradually changed to R ∼ ℓ2/ρ3 with increasing values of ρ. There is an optimum antenna length ℓ ∼ ρ which maximizes the power flow for this value of ρ. For very large distances from the source the power flow is proportional to ℓ2/ρ4 and it remains of the same form for frequencies above and below the plasma frequency.
Admittance Dependence of the Infinite Cylindrical Antenna Upon Exciting Gap Thickness
Authors: Miller Edmund K.
Published: November 2015

The admittance of an infinite cylindrical antenna is calculated as a function of exciting frequency and exciting gap thickness. The results obtained show that an asymptotic analytical expression derived for the susceptance by Chen and Keller and also later by Fante, is strictly valid only in the limit of vanishing gap thickness. An altenate analytical form is presented for die susceptance, which removes this restriction and which gives good agreement with the correct susceptance values obtained in this study.
Scattering by Two Spheres
Authors: Liang C. , Lo Y. T.
Published: November 2015

Solutions expressed in the form of multipole expansion are presented for the electromagnetic fieids scattered by two spheres making use of the translational addition theorem for vector spherical wave functions. Some numerical computations for the backscattering cross section are compared with a few experimental results reported by other workers, and the computational problems are discussed in general.
Radiation and Scattering Problems in Compressible Plasmas. Part II. Solutions of Boundary‐Value Problems
Authors: Labianca F. M. , B. Felsen Leopold
Published: November 2015

Different two‐dimensional geometries involving bounded, homogeneous, isotropic, compressible plasma regions are considered, and exact integral representations are developed for the electromagnetic and dynamical fields due to various excitations. Specifically, the geometries include plane and cylindrical interfaces, and also a perfectly conducting half plane embedded in the plasma. Asymptotic analysis of the exact solutions by the steepest‐descent method leads to results which may be cast into a ray‐optical form. It is shown that the geometric‐optical and diffraction fields derived in this manner agree with those obtained in part I by direct application of ray‐optical procedures. This conclusion lends substance to the validity of the ray‐optical method and suggests its utility for even more general configurations which are not readily subjected to rigorous analysis.
Oblique Sweep‐Frequency Experiments Over a 2000‐km North‐South Subauroral Path
Authors: Möller Hans G.
Published: November 2015

The high‐frequency limits for radio transmission are calculated from the data of vertical sounding stations. For distances < 2000 km, only the vertical data of the station at the midpoint of the path are used. To check this rule, oblique and vertical sweep‐frequency records which were observed under normal and anomalous conditions were compared. If the distribution of ionization is nearly constant along the route, normal conditions are present, and the high‐frequency limits calculated from the midpoint station are consistent with the oblique observations.

Anomalous conditions are present during winter nights. At this time the critical frequencies may vary over a distance of 500 km by a factor of 2 or more. These steep gradients imply that the maximum observed frequency (MOF) is much higher than the calculated maximum usable frequency (MUF). Additional transmission modes are observed which are explained using rough models. The steep gradients were found to be moving southward during the night. A statistical analysis indicates that the magnitude of the gradient and the extent of this motion is increased with increased magnetic activity.