bluuebunny/crossref_metadata_2025_split huggingface dataset:
Groundwave Propagation Across Semi‐Infinite Strips and Islands on a Flat Earth
Authors: King R. J. , Tsukamoto W. I. 
Published: November 2015

An electromagnetic groundwave propagating along the surface of the earth will be partially transmitted and partially reflected at an abrupt electrical discontinuity such as a coastline, lake, island, peninsula, river, certain types of mineral deposits, etc. The theoretical work of Wait is extended to yield a solution which can be applied to semi‐infinite or finite ground plane inhomogeneities of arbitrary shape. Calculations were made for two special cases: perpendicular propagation near a semiinfinite strip (e.g., a peninsula), and near a small rectangular island.The theoretical solution was experimentally verified to a good order of accuracy through the use of microwave‐frequency (4.3 Gc/s) laboratory models on which both amplitude and phase measurements were made. In these models, water was used to simulate imperfectly conducting media, while aluminum plates simulated perfectly conducting media. It is shown that the position of a semiinfinite strip or island transverse to the direction of propagation has considerable influence on the phase of the transmitted signal.
Radiation and Propagation of Electromagnetic Waves from Moving Sources
Authors: Lewis Robert M. , Pressman Walter 
Published: November 2015

The electromagnetic field produced by a general point source moving on an arbitrary trajectory an infinite homogeneous medium is obtained by solving an initial value problem for Maxwell's equations. The solution is expressed parametrically with the aid of bicharacteristics or space‐time rays. This representation, which is equivalent to the more common “retarded time” representation is used because it clarifies the space‐time geometry of the solution. For the case of a moving charge, the solution reduces to a standard result.In a sequel, the results obtained will be applied to the problem of radiation and propagation of electromagnetic waves produced by point sources moving in an inhomogeneous medium.
Electromagnetic Radiation in a Moving Lossy Medium
Authors: Fujioka H. , Kumagai N. 
Published: November 2015

This paper treats electromagnetic radiation from sources immersed in an isotropic lossy nondispersive medium moving at nonrelativistic uniform velocity. The inhomogeneous wave equations for the radiated fields are derived and are solved by means of a suitable transformation of the dependent variables. The well‐known radiation phenomena are found to be modified when the moving medium is lossy. The results show that, in general,(1) the far‐zone field is elliptically polarized,(2) the far‐zone electric and magnetic fields are not mutually perpendicular,(3) the far‐zone Poyntinjl: vector is not purely radial.As an illustrative example, the case in which the source is an oscillating dipole is worked out in detail.
Waves in a Partially Ionized Paramagnetic Gas
Authors: Hodges R. R. 
Published: November 2015

The nature of electromagnetic wave propagation in a partially ionized paramagnetic gas in a static magnetic field is explored. It is necessary to characterize such a medium by second‐order tensor expressions for both the permittivity and permeability, the former being that characteristic of an ordinary magnetoplasma, and the latter that for a magnetized paramagnetic medium. Employing linearized forms of these and Maxwell's equations leads to a general dispersion relation. For lossless conditions it is shown that the resonances and cutoffs associated with the free electrons and those due to the paramagnetic constituents are independent. This leads to some interesting, hypothetical propagation conditions that may exist in planetary or stellar atmospheres.Application of this theory is made to the ionosphere, in which atomic oxygen is the major para‐magnetic constituent. Accounting for collisional losses, it is shown that the upper limit of the absorption at the peak of the atomic oxygen electron spin resonance line in the ionosphere is only 5 × 10ߚ4 times the background absorption due to the free electrons; the effect of Doppler broadening would be to decrease this number. The minute nature of this absorption line is supported by the apparently complete lack of experimental evidence of electron spin resonance effects on radio wave propagation in the terrestrial ionosphere. It is also shown that the internal radiation (noise) in the ionosphere must exhibit a similarly weak absorption line at the electron spin resonance, due to the nonequilibrium nature of the energy distribution of the free electrons.
A Numerical Investigation of Classical Approximations Used in VLF Propagation
Authors: Pappert Richard A. , Gossard Earl E. , Rothmuller Ilan J. 
Published: November 2015

A computer program based on formalism developed by Budden will be used to evaluate the adequacy of some approximations that have been used in VLF waveguide propagation studies. The program makes allowance for the inhomogeneity and anisotropy of the lowest part of the ionosphere, allows for earth curvature, and may be used for arbitrary direction of propagation at any latitude.The results of this program will be compared with calculations of Wait and Spies who used a model ionosphere consisting of an exponential variation for both electron density and collision frequency. This comparison will allow us to demonstrate a close numerical equivalence between the modified refractive index formulation and the spherical coordinate formulation as implemented by Wait and Spies. Also, it will be shown that an approximation introduced by Wait and Spies during the course of applying the effective surface impedance concept, though quite valid for first‐order mode calculations, is inadequate for daytime second‐order mode calculations.
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.
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.
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.
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.
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.
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 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

SummaryThis 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

SummaryAn 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.
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

AbstractLinear 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

AbstractProprotein 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.