bluuebunny/crossref_metadata_2025 huggingface dataset:
Results Concerning the Sunrise Effect of VLF Signals Propagated Over Long Paths
Authors: Ries G.
Published: November 2015

Periodic field strength variations which were observed during sunrise on VLF signals propagated over long paths are discussed. The stepwise phase increase and the minima of the signal amplitude may be explained by the waveguide‐mode theory; they are caused by interference between the first and the converted second mode. Owing to a weak second mode at lower frequencies, the sunrise effect at lower frequencies in general is only weakly developed. The reversed stepwise phase variation observed at higher frequencies may be explained by a strong converted second mode whose amplitude exceeds that of the first mode.
An Investigation of the Modal Interference of VLF Radio Waves
Authors: Rhoads F. J. , Garner W. E.
Published: November 2015

An experiment was carried out to study modal interference effects and the extent of agreement with theoretical results obtained previously. Field strength data for transmission from two stations in Hawaii on several frequencies between 16.6 and 26.1 kHz and from NPG on 18.6 kHz were recorded aboard an aircraft while in flight between California, Guam, Japan, and at a ground site near Washington, D.C. The experimental observations show considerable modal interference and very good agreement with the theoretical results for the isotropic case. For frequencies above 20kHz the experimental data indicate the existence of at least the first three modes for propagation to the west and to the east, out to distances greater than 3 Mm. The data at 19.8 kHz, however, indicate three‐mode effects for propagation to the east but only two modes to the west. The fading of the field strengths at Washington, D.C., during sunrise was frequently greater than 20 dB. The depth of the fades, in general, increased with frequency, whereas their time of occurrence was relatively independent of frequency over the range of 19.8 to 26.1 kHz, which was expected from theory.
Airborne Field Strength Measurements in the Region of the NPM Antipode
Authors: Rogerson J. E.
Published: November 2015

In July 1963, the Naval Research Laboratory and the Navy Electronics Laboratory conducted a joint experiment in the vicinity of the antipode of the yery low frequency transmitter NPM (19.8 kHz). An analysis of data collected by the Naval Research Laboratory during aircraft flights in the immediate vicinity of the antipode dunng this experiment is presented. A definite increase in field strength in the antipodal region was observed; inverse square root of distance variations in the field strengths over sections of the antipodal area were seen. A diurnal pattern in which highest field strengths occurred at local sunrise, lowest field strengths at local sunset, and intermediate signal levels at local noon and midnight was observed. Inferences of antipodal movement could be drawn from the data. The antipodal situation appeared to be complex, and further study is needed before a complete understanding can be obtained.
Frequency Shifts on Whistler Mode Signals from a Stabilized VLF Transmitter
Authors: McNeill F. A.
Published: November 2015

VLF signals received in New Zealand from NPG, Seattle, via the whistler mode are usually shifted in frequency during transit. They traverse a region of the magnetosphere which is bounded approximately by the magnetic longitudes of transmitter and receiver and which may vary in latitude during a single night over a range of several degrees.

In general, signals are detected only when entry and exit points of the appropriate field lines are in darkness. They are subject to a form of geomagnetic control. The roles of ionosphere and magnetosphere as frequency shifting devices are examined, and it is concluded that the chief agency is an equatorward movement of preferred paths during the night
Moment Synthesis of Array Factors With Nonuniform Spacing and Amplitude Parameters
Authors: Mafflett A. L. , Curtz T. B.
Published: November 2015

A theory of nonuniform arrays based upon the classical moment problem is developed in this paper. We suppose that a given pattern can be represented as a Fourier‐Stieltjes transform of a cumulative current distribution over a finite (normalized) aperture interval, which we then approximate by a step‐function distribution whose “treads and risers” are determined as follows. The moments of the step‐distribution are equated to the moments of the continuous distribution belonging to the given pattern, producing a set of nonlinear equations for the positions (treads) and amplitudes (risers) of the steps. The former tum out to be roots of an orthogonal polynomial, of degree equal to number of array elements, belonging to the (continuous) cumulative distribution; the latter can then be found from a resulting set of linear equations and are the so‐called Christoffel numbers. An equivalent development, which helps to illuminate the basic ideas, is to approximate the kernel of the Fourier‐Stieltjes transform by a Lagrange interpolation polynomial. Both of these approaches will produce, in general, an array factor with both nonuniform spacings and amplitudes, and will be said to be optimum in a moment sense: i.e., the original distribution and its approximation agree in their first 2M moments if M is the number of elements used for the approximation.

The equivalence of the moment and interpolation methods implies a mean‐square minimality for the polynomial factor of an error representation for the latter method. But the remaining factor of the error representation involves a parameter which cannot in general be determined explicitly; this error form is therefore of little use for large apertures (compared to the number of elements involved). Practical application of moment synthesis would therefore have to rely for an error assessment largely upon either statistical estimation or pattern computation. These facts notwithstanding, the moment method can be used to produce remarkable pattern approximations in the near main‐beam region, and, if the number of elements is sufficiently large, acceptable pattern behavior everywhere. Its chief drawback is that a large number of elements requires the computation of zeros of a orrespondingly large degree polynomial.
Ray Optics for Radiation Problems in Anisotropic Regions With Boundaries.
Authors: Felsen Leopold B. , Rosenbaum Shalom
Published: November 2015

Rigorous generic integral solutions for the fields radiated by phased‐line distributions of electric or magnetic currents in the presence of two arbitrarily anisotropic half spaces are evaluated asymptotically by the saddle‐point technique. The resulting field constituents are shown to be interpretable invariantly as geometric‐optical (incident, reflected, and refracted) and diffracted (lateral‐wave) contributions. These fields are then derived directly from ray‐optical arguments, thereby providing a justification for thls procedure without intervention of the rigorous formulation. Because of the general validity of ray‐optical concepts in connection with asymptotic solutions in the far zone, use of ray techniques is then advocated also for more complicated configurations which are not amenable to rigorous analysis.
Propagation of Oblique Electromagnetic Waves Through a Warm Plasma Slab With Normal Magnetostatic Field
Authors: Chawla B. R. , Kalluri D. , Unz H.
Published: November 2015

Reflection, transmission, and absorption coefficients for oblique electromagnetic waves with parallel polarization incident on a warm plasma slab with a static magnetic field normal to its boundary, are studied. The effect of variation in the angle of incidence, the static magnetic field, the slab width, the plasma temperature, and the collision frequency on the various coefficients is shown graphically. It is found that the transmission coefficient increases with an increase in the plasma temperature. A change in the magnetostatic field strength decreases the transmission coefficient in one frequency region while it increases it in the other. For wave frequencies greater than cyclotron frequency, a sharp cutoff phenomenon occurs in the reflection coefficient at some angle. The absorption coefficient is found to be greater for larger slab width, except at a small frequency region where it shows oscillations.
Dispersion Relation in Compressible Plasma
Authors: Wu Yung-Kuang
Published: November 2015

The Maxwell‐Euler equations are reformulated through linear operator and generalized transform techniques into an equivalent matrix integral equation. The dispersion relation is obtained from the kernel of this integral equation for a homogeneous, anistropic, and compressible electron‐fluid plasma. Some illuminating graphs showing the propagation constants as functions of the normalized plasma frequency are developed analytically to study the dispersion relation. These kinds of graphs are usually plotted from the limited amount of numerical data available in the literature (e.g., Ginzburg, 1961). Clemmow‐Mullaly‐Allis type of diagram for the compressible plasma is sketched from these graphs. Actually, dispersion curves are obtained which are inversely related to the wave normal surfaces calculated by Allis, Buchsbaum and Bers (1963). A proper terminology for the three types of waves involved in an electron plasma is also introduced.
The Admittance of Cylindrical Antennas Driven From a Coaxial Line
Authors: Otto D. V.
Published: November 2015

The situation in which the internal conductor of a coaxial transmission line projects through a ground‐plane without any change in diameter is analyzed with reference to the infinite antenna and the parallel‐plate antenna. An experimentally meaningful value of the admittance which takes into account the geometry of the antenna‐to‐coaxial line junction is obtained. This is achieved by utilizing a mathematical model in which an annular aperture or “gap” is represented by a frill of of magnetic current. The field distribution in the aperture is assumed to be of the same form as the TEM mode alone in the coaxial line. It is shown that the effect on the admittance of neglecting the TM modes in the line at the aperture, is very small. In the case of the parallel‐plate antenna, the theoretical results are shown to agree remarkably well with experiment. It is also shown how the theory may be applied to the problem of finite length cylindrical antennas.
On the Electrically Thick Cylindrical Antenna
Authors: Chang David C.
Published: November 2015

The problem of a thick cylindrical antenna driven by a delta‐function generator is investigated. Numerical solutions are obtained for two different mathematical models: one is driven by a deltafunction generator on both outside and inside surfaces of the antenna, and another is driven only on the outside surface. In both cases, the current singularity near the driven point has been taken care of and subsequently subtracted out, before the numerical solution is applied. For antennas with circumferences less than a free‐space wavelength, the results are compared with the experimental data. For antennas with larger radii, no experimental data are yet available.
The Thick Tubular Transmitting Antenna
Authors: W. P. King Ronold , Wu Tai Tsun
Published: November 2015

The growing importance of electrically thick monopole antennas has suggested a re‐examination of the model used in the derivation of the integral equation for the current in tubular antennas. It is shown that when such an antenna is driven from a coaxial line in the usual manner, which maintains a field along a narrow circumferential region on the outside surface of the tube (instead of along both the inner and outer surfaces), an additional term is required in the integral equation. This is negligible when the antenna is electrically thin, but of major importance when it is not. A quantitative comparison of conductances is provided over a wide range of thickness.
A Nomogram for Atmospheric Radio Refraction
Authors: Hudson A. C.
Published: November 2015

A six‐stage nomogram is presented for determining the refraction of a radio wave entering the earth's atmosphere in terms of surface meteorological conditions and the apparent elevation angle of the incoming wave.
On the Theory of Radiation From a Raised Electric Dipole Over an Inhomogeneous Ground Plane
Authors: Wait James R.
Published: November 2015

The influence of a finite ground plane on the field of a raised electric dipole is considered from an analytical standpoint. The method for evaluating the integrals is discussed briefly and some asymptotic results are given which illustrate the limiting behavior for ground screens of large diameter. It is shown that the resulting pattern may be crudely interpreted in terms of the direct radiation of the source dipole, its image in an infinite ground plane, and contributions from the edges of the ground screen.
Plane Wave Scattering From Modulated Corrugated Structures
Authors: Hessel A. , Hochstadt H.
Published: November 2015

A solution is presented for TM plane wave scattering from a corrugated structure with zero thickness plates and two different, alternating groove depths. Expressions for the reflection coefficients, obtainable for any number of propagating modes, are explicitly shown in the frequency range corresponding to a single (TEM) mode propagation in the plates and two diffracted spectral orders present in the free‐space region. The scattering matrix for the junction discontinuity is derived with the help of an interesting procedure. The solution has potential applications in the study of Wood anomalies of diffraction gratings and guided waves on modulated structures. The procedure may easily be generalized to an arbitrary number of different groove depths.
Simultaneous Radar Reflectivity Measurements and Refractive Index Spectra in the Clear Atmosphere
Authors: Kropfli R. A. , Katz I. , Konrad T. G. , Dobson E. B.
Published: November 2015

Simultaneous measurements of refractive index and radar reflectivity have been made in the clear atmosphere. The theoretical relationship between the refractive index spectrum and reflectivity described by Tatarski was used to compute reflectivity from the refractive index data. Excellent agreement is shown between the computed and measured reflectivity. These results indicate, (1) reflections from the clear atmosphere can be described quantitatively in terms of the refractivity spectrum, and (2) the refractivity spectrum well represents the atmosphere for these data out to limiting microscales smaller than 5 cm.
Radiation From an Oscillating Source Moving Through a Dispersive Medium With Particular Reference to the Complex Doppler Effect
Authors: Lee K. S. H.
Published: November 2015

The complex Doppler effect is analyzed from the time behavior of the radiation field of an oscillating source traversing a dispersive medium. The effect is calculated for the case where an oscillating electric dipole is moving uniformly through an ionized gas permeated by an infinitely large magnetostatic field. It is found that the radiation field can be split into a number of waves, each having characteristics of its own, and that the number of waves changes with time. The group velocity of each individual wave is shown to play an important role in the physical mechanism of the effect.
Higher Order Asymptotic Terms of the Two‐Dimensional Diffraction by a Small Aperture
Authors: Mohsen A. , Hamid M. A. K.
Published: November 2015

A modified diffraction coefficient, suitable for the computation of higher order edge‐edge interaction terms in the two‐dimensional diffraction by a narrow slit and a circular aperture, is derived. The resulting improvement in the accuracy of the transmission cross section over the usual asymptotic expressions is established. By comparison with the exact solutions for these cases, it is shown that the coefficient may be used with confidence for such apertures when Ka ⩾ 1, where K is the wave‐number and a is half the characteristic dimension of the aperture.
Relation Between Sunspot Number and the Ionospheric Index IF2
Authors: Muggleton L. M. , Kouris S. S.
Published: November 2015

A plot of the relationship (IF)12/R12. for each month of the period 1942–1967 exhibits a hysteresis characteristic in addition to a systematic change from one solar cycle to the next. A relationship based on all these data is proposed and a means is suggested of fitting this expression to the particular “half”‐cycle of mterest. In this way a conversion of parameter from R to IF2 may be made, with all the attendant advantages of the use of the latter index, in expressions relating R to ionospheric behavior based on the measured results of a particular period.
A Comment on Ray Tracing in an Anisotropic Medium
Authors: Smith R. L.
Published: November 2015

An improvement on numerical integration of Yabroff's ray‐tracing equations is suggested wherein at each step the refractive‐index vector is corrected in both magnitude and direction.
On the Diffraction by a Knife‐Edge Obstacle on a Conducting Earth
Authors: Wait James R. , Spies Kenneth P.
Published: November 2015

Some calculated results are given for influence of a knife‐edge obstacle on radio propagation over a curved surface. A special case, of a previous formulation, is employed for the calculations. It is shown that the effect of the obstacle is strongly dependent on the location relative to the path terminals. This note is an addendum to the paper “Diffraction and scattering of the electromagnetic ground wave by terrain features”, Radio Sci. 3 (New Series), No. 10, 1968.
Exact Ray Calculations in a Quasi‐Parabolic Ionosphere With No Magnetic Field
Authors: Croft Thomas A. , Hoogansian Harry
Published: November 2015

The equation of the parabolic ionosphere model is modified in a manner which introduces very slight changes in the electron‐density distribution. Using this new “quasi‐parabolic” (or QP) model, it is possible to derive exact expressions describing radio‐ray trajectories without introducing the approximations which are needed when dealing with the parabolic ionosphere, although magnetoionic effects are not included. The consequent accuracy of computed rays is useful as an aid in evaluating the accuracy of more versatile ray‐calculation methods. Also, the exact ray expressions can be of direct use in calculating slight differences between rays which are nearly identical, for in this process, small inaccuracies can become magnified.
Ray Height Computation for a Continuous Nonlinear Atmospheric Refractive‐Index Profile
Authors: Blake Lamont V.
Published: November 2015

An algorithm is described for machine computation of the height of a ray originating at or near the earth's surface, when the initial elevation angle and the ray‐path length (as measured, for example, by a radar‐antenna elevation angle and the echo signal delay time) are given, and the refractive‐index profile is specified as a continuous but nonlinear function of the height. The numerical precision of the result is limited only by the number of digits carried in the computation, although faster computation is achieved with reduced precision. The computing time is less than ls for six significant figures using the CDC‐3800 computer. The equations used (which include those for the ground range, true geometric range, and true elevation angle) have been manipulated to avoid formulations that destroy computational precision. The method requires that the refractive index be spherically symmetric with respect to the earth's center and that the height profile be representable as a piecewise continuous function. In the work described, a negative‐exponential profile was assumed. Two algorithms for higher speed computation with reduced precision, suitable for radar‐target height calculation, are also described.
Space Correlations of 35‐GHz Transmissions Over a 28‐km Path
Authors: Lee R. W. , Waterman A. T.
Published: November 2015

Experiments have been carried out in order to measure the spatial and temporal nature of amplitude fluctuations observed on a 35 GHz, 28‐km line‐of‐sight transmission path. The fluctuations are typically 1 dB in amplitude, with spectral widths of up to 1 Hz, and apparently drift horizontally past the several receiving antennas. The velocity of this drift, as determined by cross‐correlation analysis of the fluctuations at several points, correlates well with the spectral width of the fluctuations, and is also correlated with observed windspeeds, indicating that the observed drift of the amplitude fluctuations is the result of the gross motions of the atmosphere. No corresponding drift was observed for vertical antenna separation. The spatial scale length of the fluctuations remained approximately the same for all conditions encountered, in both the horizontal and vertical planes. It is concluded that the temporal characteristics of the received signal are largely the result of the horizontal drift of a relatively fixed spatial distribution of amplitude, rather than of temporal changes in this distribution.
Scattering of VLF Radio Waves in the Curved Earth‐Ionosphere Waveguide
Authors: Bahar E.
Published: November 2015

Extensive model studies have been carried out in the past to investigate the effects of ionospheric perturbations on VLF radio propagation in the earth‐ionosphere waveguide. In these model studies the surface of the earth is considered flat and the ionosphere is characterized by a finite surface impedance of variable effective height. However, the restrictions for the flat‐earth model are not satisfied for modes of near‐grazing incidence.

As shown before by Wait, a planar structure that supports the desired modes may be constructed simply by modifying the medium of propagation in the straight rectangular dual‐model waveguide.

As a result of including the earth's curvature in the model, the analysis yields an explanation for the relatively large undulations in the electric field observed at the surface of the earth.

The larger undulations in the “curved” model are a result of both the modification of the characteristic functions and a larger scattering coefficient.
Comments on “Modal Solution of a Point Source in a Strongly Focusing Medium” by E. T. Kornhauser and A. D. Yaghjian
Authors: Lang R. , Shmoys J.
Published: November 2015

A comparison is made between papers of Kornhauser and Yaghjian (1967) and Gazarian (1957). The two are found to cover many similar aspects of the same problem. Rays and caustics not considered in the above two papers are found and are plotted for some typical parameters.
Gram‐Charlier Series Distribution for foF2 and M(3000)F2
Authors: Siddiqui M. M. , Ostrow S. M.
Published: November 2015

The monthly statistical distribution of foF2 and M(3000)F2, based on 16 years of Washington data, were found to differ significantly from normal. The two‐term Gram‐Charlier series (Type A) is proposed as a statistical model for the monthly distributions, since it provides a better fit to observed data than the normal distribution.
Curvilinear Arrays
Authors: Chiang Bing , Cheng David H‐S
Published: November 2015

In a uniformly fed in‐phase curvilinear array, space phase is the only component that determines the field pattern of the array. A field pattern of the array can be found by simple proportionality techniques, employing the stationary phase principle and by‐passing tedious point‐by‐point calculations.

Field patterns and source density functions of circular‐arc arrays are shown to be linearly interdependent. The derivation is based on Poisson's sum formula and the principle of stationary phase. A simple synthesis technique is discussed; two illustrations are included.
Modified Dolph‐Chebyshev Arrays
Authors: Rao B. L. J.
Published: November 2015

A method is presented to synthesize linear array patterns in which the side lobes decay very rapidly on either side of the main beam and at the same time exhibit, very closely, the optimum property of Dolph‐Chebyshev patterns. When compared with Dolph‐Chebyshev arrays having an equal number of elements, the side lobes of the modified arrays are considerably lower, the gain is approximately the same, and there is a small increase in the width of the main beam. For larger arrays, the increase in the beam width is negligible. In the cases where it is difficult to realize practical Dolph‐Chebyshev arrays, modified arrays appear to be more practical. Some specific examples are given.
Wideband Arrays for Radio Astronomy
Authors: Klemperer W. K.
Published: November 2015

For those radioastronomical observations that involve the recording of signals from broadband noise sources, the efficiency of the antenna as well as the shape of the antenna pattern can be significantly improved by operating over as wide a frequency band as possible. The advantages become
particularly prominent for arrays that extend to spacings of thousands of wavelengths. The effect of the operating bandwidth on the far‐field pattern of interferometers and rectangular arrays is investigated. The improvements that can be expected from wideband operation in various other cases are outlined.
Pi Events With Particular Reference to Conjugate Point Phenomena
Authors: Jacobs J. A.
Published: November 2015

The morphology of irregular micropulsations Pi 2 is discussed with particular reference to their polarization, frequency spectrum, and relation with the Kp index of magnetic activity. Pi activity at the near conjugate auroral zone stations of Great Whale River and Byrd is examined in some detail. Other types of Pi activity (SIP's and IPDP's) are discussed and theories of Pi's and possible source mechanisms for Pi 2's are reviewed.
Evidence of Mode Coupling on Periodic Traveling‐Wave Dipole Arrays
Authors: Kieburtz Richard B. , Sun David F‐D.
Published: November 2015

Measurements of the distribution of electric field intensity along a periodic radiating structure consisting of a dipole array coupled to a balanced transmission line reveal a standing‐wave pattern that is formed at the driven end of the structure. We propose that this standing wave is formed by the interference of two normal modes of the coupled structure. These modes are found to possess conjugate wave functions exp [−αx±jβx], and to carry energy in opposite directions on the transmission line. They are identified with transmitting and receiving modes of the infinite, periodic structure; both are excited on a finite model to satisfy boundary conditions on both the transmission line and the dipole array at its driven end.

These conjugate normal modes arise from coupling of the TEM mode of the unloaded transmission line with the complex, radiating mode of an undriven, periodic array of dipoles. The determinantal equation of the coupled array can be cast in a form that displays the mode coupling.
Variable Notch Antenna Patterns
Authors: Biggs Albert W.
Published: November 2015

Results of antenna pattern measurements of a notch antenna are presented for variable notch lengths and different modes of notch excitation. The notch is an open slot normal to the edge of a 12° metallic wedge. Antenna patterns of the Es component are measured in perpendicular planes with the intersection line coincident with the notch axis. The Eθ component in the φ = 180° plane is compared with analytical expressions for a notch cut in a semi‐infinite conducting sheet. The excitation modes, V(x), in the analytical notch expressions are Vo cos kx, Vo sin kx, Voeikx, and Voe−ikz. The experimental verification of the assumptions in the analytical formulations is very good.
Presunrise Heating of the Ionosphere at Arecibo Due to Conjugate Point Photoelectrons
Authors: Kwei M. W. , Nisbet J. S.
Published: November 2015

In winter, as has previously been reported, the electron temperature at Arecibo starts to increase prior to local sunrise following illumination of the conjugate ionosphere. The roles played by heat conduction along the field line and by photoelectrons that traverse the field line are investigated.

Photoelectron fluxes, calculated in the manner described by Nisbet, have been used to examine the mechanism of presunrise heating at Arecibo. Detailed analyses are made of the escaping photoelectron flux from the conjugate region including the effect of elastic collisions with neutrals in confining the photoelectrons. Comparisons between the theoretical heat input and observed energy losses in ambient electrons are presented. Also the theoretical and measured heat fluxes are compared.
Spatial Extent of Geomagnetic Events Conjugate to Byrd
Authors: Walker J. K.
Published: November 2015

Five magnetometers in an east‐west line and centered on the Byrd conjugate point were operated during October 1963. The correlation of the hourly range was highest between Byrd (Antarctica) and Cape Jones (Canada), the central station, but the maximum correlation was west of the Byrd conjugate point during the morning and east after local noon. The coherency between these stations during storms or pulsations was highest for periods greater than 30 min. At periods from 1.5 to 30 min, the coherency was less than 0.5 except when pulsations occurred. The coherency was slightly higher for the amplitude of the horizontal disturbance vector than for the H component and the total force disturbance vector, while the Z component had the lowest coherency. The distribution of the Pc 5 polarization diagrams with the best fit to the Byrd diagram was centered on the Byrd conjugate point as were the pulsations with the same amplitude.
Polar Magnetic Substorms in the Conjugate Areas
Authors: Meng C.‐I. , Akasofu S.‐l.
Published: November 2015

Using simultaneous records of polar magnetic substorms from two pairs of geomagnetically conjugate stations (College‐Macquarie; Reykjavik‐Syowa), the magnitude of positive bays is shown to be mainly controlled by the ionization produced by solar wave radiation, not by the intense auroral particle bombardment which is the major factor for negative bays.

Also shown is that the pattern of the polar electrojet with respect to the dipole pole is displaced or different in the two polar caps, particularly in the solstitial months. The electrojet appears farther toward the pole in the winter polar cap than in the summer one. These results bear on the configuration of the field lines in or near the magnetospheric tail, if auroral particles originate there.
Simple Methods for Calculating LF and VLF Reflection Loss In the Disturbed Lower Ionosphere
Authors: Booker Henry G. , M. Crain Cullen
Published: November 2015

Two simple methods for estimating LF and VLF reflection loss are devised, and the procedures for applying the methods are described. The first method involves estimating the actual height of reflection, fitting an exponential profile at this height, using the wave theory answer for the fitted
exponential profile, and, if necessary, applying a correction for departure from the fitted exponential profile well below the level of reflection. The second method integrates the nondeviating region attenuation coefficient up to a level chosen, using wave theory, to give the right answer when the profile near the level of reflection is exponential.

For practical evaluations of LF and VLF transmission loss in nuclear burst environments involving highly oblique reflections in the lower D region, the methods presented can be applied with adequate accuracy for transmission frequencies at least as low as 10 kHz.
On the Calculation of Mode Conversion at a Graded Height Change in the Earth‐Ionosphere Waveguide at VLF
Authors: Wait James R. , Spies Kenneth P.
Published: November 2015

A multistep model is used to simulate the transition between the day and night portions of the earth‐ionosphere waveguide. A convenient simplification is the justified neglect of all reflected modes. On the other hand, forward mode conversion (and reconversion) is accounted for. The analytical method involves the multiplication of square matrices which correspond individually to the conversion at the various steps. The calculations are carried through for a sharply bounded ionosphere and a perfectly conducting ground. Earth curvature is allowed for but the influence of the earth's magnetic field is neglected. A calculated example for 20 kHz indicates that the transition length Δd between day and night influences the amount of mode conversion.
Ray‐Tracing Investigation of Direction of Arrival Observations of HF Radio Waves
Authors: Narayana Rao N.
Published: November 2015

A high frequency radio direction‐finding experiment involving a transmitter near Houston, Texas and a receiver near Urbana, Illinois has been under progress on a continuous basis for 1 week per month since March 1967. A network of five vertical incidence ionosondes located near and around the midpoint of the great circle path permit the evaluation of electron density gradients along the propagation path from true height analysis of ionograms recorded by this network. These gradients are used in conjunction with a three‐dimensional ray‐tracing computer program to compute the expected directions of arrival of the radio waves. Changes in bearing resulting from temporal variations in the electron density distribution and seasonal variations in the sunrise tilts are investigated. The results obtained by ray tracing are found to be in excellent agreement with the measured bearing deviations. Effective layer tilts are computed from the results of ray tracing.
A Comment on “A Note on the Mathematical Representation of the Source for Tubular Transmitting Antennas” by D. V. Otto
Authors: King Ronold W. P. , Tsun Wu Tai
Published: November 2015

It is questioned whether differences in the method used to derive the integral equation for the current in a tubular antenna are of great importance.
A Review of Scattering From Surfaces With Different Roughness Scales
Authors: Barrick Donald E. , Peake William H.
Published: November 2015

An examination and review of various theories for scattering from surfaces with different roughness scales has appeared in a recent report by Barrick and Peake. This note briefly summarizes the report by presenting some of the more important results contained therein.
Theories of Prolate Spheroidal Antennas
Authors: Wait James R.
Published: November 2015

After reviewing some of the basic properties of spheroidal wave functions, the theory of radiation from a prolate spheroid antenna is considered. Particular attention is given to the complicating inftuence of a confocal plasma sheath whose properties may be either constant or depend on the polar angle coordinate. The effects of the compressibility of the plasma and the inftuence of a d—c magnetic field are also considered, using very idealized models. Among other things, it is indicated that a spheroidal structure may be strongly resonated (in a single mode) if the surface impedance has a special form.
On the Determination of VLF Propagation Parameters by Field Strength Measurements Over Medium Distances
Authors: Frisius J.
Published: November 2015

The propagation of electromagnetic waves with a frequency of 16 kc/s is studied in the distance range 350 to 800 km from the. transmitter GBR Rugby. Field strength measurements recorded contmuously at eight stations durmg the winter of 1962/63 are compared with field strength calculations based upon the concept of the equivalent ionosphere.

The influence of the lower ionosphere on long electromagnetic waves for a specific frequency and propagation direction is nearly the same as that of a sharply bounded, homogeneously ionized isotropic equivalent ionosphere. For oblique incidence the boundary can be taken at a certain “equivalent height” h′, if the reflection coefficient is approximated by the function ‐ exp (‐ α cos ϑ), ϑ being the angie of incidence, and a a certain real positive parameter characterizing the reflection. The possible error caused by this approximation for the distance range mentioned above is considered. The two parameters h′ and a are determined from the measurements.

The possible range of parameters for nighttime and daytime propagation is first estimated by different compansons between calculated and measured field strength curves. The sunrise effect is then comsidered and evidence is found that during about 1.5 hr after sunrise the concept of the equivalent ionosphere does not satisfactorily describe the propagation.

A method is presented for finding the parameters for nighttime and daytime propagation using only the relative field strength variations as measured at the different distances.

Typical fall daytime values for h′ and ϑ are near 69 km and 4, respectively; for winter days h′ is about 73 km and a is of the order of unity, both varying in rather wide limits. For the nighttime, h′ ‐values were found to be between 81 and 89 km and a was smaller than 0.3 in most cases, corresponding to a reflection of a strong dielectric type.
Local dynamic range compensation for scanning electron microscope imaging system by sub‐blocking multiple peak HE with convolution
Authors: Sim K. S. , Teh V. , Tey Y. C. , Kho T. K.
Published: November 2015

This paper introduces new development technique to improve the Scanning Electron Microscope (SEM) image quality and we name it as sub‐blocking multiple peak histogram equalization (SUB‐B‐MPHE) with convolution operator. By using this new proposed technique, it shows that the new modified MPHE performs better than original MPHE. In addition, the sub‐blocking method consists of convolution operator which can help to remove the blocking effect for SEM images after applying this new developed technique. Hence, by using the convolution operator, it effectively removes the blocking effect by properly distributing the suitable pixel value for the whole image. Overall, the SUB‐B‐MPHE with convolution outperforms the rest of methods. SCANNING 38:492–501, 2016. © 2015 Wiley Periodicals, Inc.
Signal‐to‐noise ratio estimation using adaptive tuning on the piecewise cubic Hermite interpolation model for images
Authors: Sim K. S. , Yeap Z. X. , Tso C. P.
Published: November 2015

An improvement to the existing technique of quantifying signal‐to‐noise ratio (SNR) of scanning electron microscope (SEM) images using piecewise cubic Hermite interpolation (PCHIP) technique is proposed. The new technique uses an adaptive tuning onto the PCHIP, and is thus named as ATPCHIP. To test its accuracy, 70 images are corrupted with noise and their autocorrelation functions are then plotted. The ATPCHIP technique is applied to estimate the uncorrupted noise‐free zero offset point from a corrupted image. Three existing methods, the nearest neighborhood, first order interpolation and original PCHIP, are used to compare with the performance of the proposed ATPCHIP method, with respect to their calculated SNR values. Results show that ATPCHIP is an accurate and reliable method to estimate SNR values from SEM images. SCANNING 38:502–514, 2016. © 2015 Wiley Periodicals, Inc.
Hollow Mesoporous Silica Nanocarriers with Multifunctional Capping Agents for In Vivo Cancer Imaging and Therapy
Authors: Yang Shun , Chen Dongyun , Li Najun , Xu Qingfeng , Li Hua , Gu Frank , Xie Jianping , Lu Jianmei
Published: November 2015

Efficient drug loading and selectivity in drug delivery are two key features of a good drug‐carrier design. Here we report on such a drug carrier formed by using hollow mesoporous silica nanoparticles (HMS NPs) as the core and specifically designed multifunctional amphiphilic agents as the encapsulating shell. These nanocarriers combine the advantages of the HMS NP core (favorable physical and structural properties) and the versatility of an organic‐based shell (e.g., specificity in chemical properties and modifiability). Moreover, both the properties of the core and the shell can be independently varied. The varied core and shell could then be integrated into a single device (drug carrier) to provide efficient and specific drug delivery. In vitro and in vivo data suggests that these drug nanocarriers are biocompatible and are able to deliver hydrophobic drugs selectively to target tumor cells. After the break of the pH‐labile linkages in the shell, the drug payload can be released and the tumor cells are killed.
Effect of Varying Alkyl Chain Length on Thermal Decomposition Temperature of Zinc(II) Xanthates and its Impact on Curing of Epoxy Resin
Authors: Vagvala Tarun Chand , Pandey Shyam Sudhir , Krishnamurthy Suvratha , Hayase Shuzi
Published: November 2015

Linear and branched zinc(II) xanthates with varying alkyl chain length were synthesized and characterized by 1H NMR, 13C NMR, and IR spectroscopy, as well as elemental analysis. Zinc sulfide as the final decomposition product upon thermal annealing of zinc(II) xanthates was confirmed by XRD analysis. Cure time for epoxy resin composite at various temperatures was analyzed employing zinc(II) xanthates (5 % mass) as latent cure catalysts. XRD investigation of the cured epoxy resin including zinc(II) xanthates upon thermal annealing revealed the presence of ZnS in‐situ in the composite matrix, indicating the in‐situ thermal decomposition of zinc(II) xanthates as probable mechanism for curing. Thermogravimetric analysis was performed to investigate the thermal decomposition temperature trend of zinc(II) xanthates. A parallel trend was observed correlating the thermal decomposition temperature trend of zinc(II) xanthates and the order of curing catalytic efficiency utilizing zinc(II) xanthates. In the case of linear alkylzinc(II) xanthates with an increase in the alkyl chain length, both thermal decomposition temperature and the cure time were enhanced. In contrast, in case of branched alkyl chain zinc(II) xanthates with increasing alkyl chain length show decreasing thermal decomposition temperature as well as cure time.
Docosahexaenoic Acid Attenuates Cardiovascular Risk Factors via a Decline in Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) Plasma Levels
Authors: Rodríguez‐Pérez Celia , Ramprasath Vanu Ramkumar , Pu Shuaihua , Sabra Ali , Quirantes‐Piné Rosa , Segura‐Carretero Antonio , Jones Peter JH
Published: November 2015

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a circulating protein that regulates cholesterol metabolism by promoting LDL receptor degradation in the liver and has recently been proposed as a therapeutic target in the management of hyperlipidaemia. We investigated the impact of dietary fat on the metabolism of sterols and on plasma PCSK9 concentrations to explore likely clinical usefulness. In a post hoc analysis of a double‐blind randomised crossover controlled feeding trial, the Canola Oil Multicenter Intervention Trial (COMIT), volunteers (n = 54) with at least one condition related to metabolic syndrome consumed diets with one of the following treatment oils in beverages: (1) conventional canola oil (Canola); (2) canola oil rich in docosahexanoic acid (DHA) (CanolaDHA); and (3) high‐oleic acid canola oil (CanolaOleic). The enrichment in oleic acid resulted in lower plasma cholesterol concentration compared with diets enriched in DHA. Contrarily, DHA‐enriched oil significantly decreased plasma PCSK9 and triacylglycerols levels, but increased circulating levels of sterols. The variations in lathosterol, sitosterol, and campesterol indicate that plasma PCSK9 levels are sensitive to changes in cholesterol synthesis and/or absorption. There was a significant correlation between plasma PCSK9 levels and plasma triacylglicerol and apolipoprotein B levels, which was not affected by dietary fat. Therefore, our results suggest that the impact of dietary fats should not be discarded as complementary treatment in the management of patients with hyperlipidaemia. These findings should be considered in the analysis of ongoing studies and may represent a cautionary note in the treatment of patients with cardiovascular risk.
Mobilising the Masses: A Grass-roots Communication Strategy for Ttip
Authors: Schneider Michael
Published: November 2015

The US and the EU have set an ambitious goal of completing the negotiations on the Transatlantic Trade and Investment Partnership by the end of 2015. Because this is not a conventional trade and investment agreement, stakeholders have demanded a more open and transparent debate. This article will consider the advantages of a communication strategy which is rooted in local European communities and the role that local and regional authorities can play in bringing the message to Europe's regions and cities.
Erratum to: The current landscape of television and movies in medical education
Authors: Law Marcus , Kwong Wilson , Friesen Farah , Veinot Paula , Ng Stella L.
Published: November 2015

None
Crystal structure of the Z‐ring associated cell division protein ZapC from Escherichia coli
Authors: Ortiz Cristina , Kureisaite-Ciziene Danguole , Schmitz Florian , McLaughlin Stephen H. , Vicente Miguel , Löwe Jan
Published: November 2015

Bacterial cell division involves a contractile ring that organises downstream proteins at the division site and which contains the tubulin homologue FtsZ. ZapC has been discovered as a non‐essential regulator of FtsZ. It localises to the septal ring and deletion of zapC leads to a mild phenotype, while overexpression inhibits cell division. Interference with cell division is facilitated by an interaction with FtsZ. Here, we present the 2.9 Å crystal structure of ZapC from Escherichia coli. ZapC forms a dimer and comprises two domains that belong to the Royal superfamily of which many members bind methylated arginines or lysines. ZapC contains an N‐terminal chromo‐like domain and a Tudor‐like C‐terminal domain. We show by ITC that ZapC binds the C‐terminal tail of FtsZ.
Administration of branched‐chain amino acids alters the balance between pro‐inflammatory and anti‐inflammatory cytokines
Authors: Rosa Luciana , Scaini Giselli , Furlanetto Camila B. , Galant Leticia S. , Vuolo Francieli , Dall'Igna Dhébora M. , Schuck Patrícia F. , Ferreira Gustavo C. , Dal‐Pizzol Felipe , Streck Emilio L.
Published: November 2015

Acute leucine intoxication and neurologic deterioration can develop rapidly at any age as a result of net protein degradation precipitated by infection or psychological stress in patients with maple syrup urine disease (MSUD). Here, we investigated the effects of acute and chronic Hyper‐BCAA (H‐BCAA) administration on pro‐ and anti‐inflammatory cytokines in the brains of rats. For acute administration, Wistar rats (10 and 30 days) received three injections of BCAA pool (15.8 μL/g at 1‐h intervals) or saline, subcutaneously. For chronic administration, Wistar rats (7 days) received of BCAA pool or saline twice a day for 21 days, subcutaneously. Our results showed that acute administration of H‐BCAA increased IL‐1β (∼78%; p ≤ 0.009) and TNF‐α (∼155%; p ≤ 0.026) levels in the cerebral cortex but not in the hippocampus of infant rats. Moreover, IL‐6 levels were increased in the hippocampus (∼135%; p ≤ 0.009) and cerebral cortex (∼417%; p ≤ 0.008), whereas IL‐10 levels were decreased only in the hippocampus (∼42%; p ≤ 0.009). However, repeated administration of H‐BCAA decreased IL‐1β (∼59%; p ≤ 0.047), IL‐6 (∼70%; p ≤ 0.009) and IFN‐γ (∼70%; p ≤ 0.008) levels in the cerebral cortex, whereas the IL‐6 (∼67%; p ≤ 0.009), IL‐10 (∼58%; p ≤ 0.01) and IFN‐γ (∼67%; p ≤ 0.009) levels were decreased in the hippocampus. These findings suggest that a better understanding of the inflammatory response in MSUD patients may be useful to develop therapeutic strategies to modulate the hyperinflammatory/hypoinflammatory axis.