bluuebunny/crossref_metadata_2025 huggingface dataset:
Transcriptome sequencing identifies ETV6–NTRK3 as a gene fusion involved in GIST
Authors: Brenca Monica , Rossi Sabrina , Polano Maurizio , Gasparotto Daniela , Zanatta Lucia , Racanelli Dominga , Valori Laura , Lamon Stefano , Dei Tos Angelo Paolo , Maestro Roberta
Published: November 2015

Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. The vast majority of GISTs are driven by oncogenic activation of KIT, PDGFRA or, less commonly, BRAF. Loss of succinate dehydrogenase complex activity has been identified in subsets of KIT/PDGFRA/BRAF‐mutation negative tumours, yet a significant fraction of GISTs are devoid of any of such alterations. To address the pathobiology of these 'quadruple‐negative' GISTs, we sought to explore the possible involvement of fusion genes. To this end we performed transcriptome sequencing on five KIT/PDGFRA/BRAF‐mutation negative, SDH‐proficient tumours. Intriguingly, the analysis unveiled the presence of an ETV6–NTRK3 gene fusion. The screening by FISH of 26 additional cases, including KIT/PDGFRA‐mutated GISTs, failed to detect other ETV6 rearrangements beside the index case. This was a 'quadruple‐negative' GIST located in the rectum, an uncommon primary site for GIST development (∼4% of all GISTs). The fusion transcript identified encompasses exon 4 of ETV6 and exon 14 of NTRK3 and therefore differs from the canonical ETV6–NTRK3 chimera of infantile fibrosarcomas. However, it retains the ability to induce IRS1 phosphorylation, activate the IGF1R downstream signalling pathway and to be targeted by IGF1R and ALK inhibitors. Thus, the ETV6–NTRK3 fusion might identify a subset of GISTs with peculiar clinicopathological characteristics which could be eligible for such therapies. Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Redox‐dependent disulfide bond formation in SAP30L corepressor protein: Implications for structure and function
Authors: Laitaoja Mikko , Tossavainen Helena , Pihlajamaa Tero , Valjakka Jarkko , Viiri Keijo , Lohi Olli , Permi Perttu , Jänis Janne
Published: November 2015

Sin3A‐associated protein 30‐like (SAP30L) is one of the key proteins in a multi‐subunit protein complex involved in transcriptional regulation via histone deacetylation. SAP30L, together with a highly homologous SAP30 as well as other SAP proteins (i.e., SAP25, SAP45, SAP130, and SAP180), is an essential component of the Sin3A corepressor complex, although its actual role has remained elusive. SAP30L is thought to function as an important stabilizing and bridging molecule in the complex and to mediate its interactions with other corepressors. SAP30L has been previously shown to contain an N‐terminal Cys3His type zinc finger (ZnF) motif, which is responsible for the key protein–protein, protein–DNA, and protein–lipid interactions. By using high‐resolution mass spectrometry, we studied a redox‐dependent disulfide bond formation in SAP30L ZnF as a regulatory mechanism for its structure and function. We showed that upon oxidative stress SAP30L undergoes the formation of two specific disulfide bonds, a vicinal Cys29‐Cys30 and Cys38‐Cys74, with a concomitant release of the coordinated zinc ion. The oxidized protein was shown to remain folded in solution and to bind signaling phospholipids. We also determined a solution NMR structure for SAP30L ZnF that showed an overall fold similar to that of SAP30, determined earlier. The NMR titration experiments with lipids and DNA showed that the binding is mediated by the C‐terminal tail as well as both α‐helices of SAP30L ZnF. The implications of these results for the structure and function of SAP30L are discussed.
Apoptotic activity and gene responses in Drosophila melanogaster S2 cells, induced by azadirachtin A
Authors: Xu Lin , Li Sheng , Ran Xueqin , Liu Chang , Lin Rutao , Wang Jiafu
Published: November 2015

BACKGROUND

Azadirachtin has been used as an antifeedant and growth disruption agent for many insect species. Previous investigations have reported the apoptotic effects of azadirachtin on some insect cells, but the molecular mechanisms are still not clear. This study investigated the underlying molecular mechanisms for the apoptotic effects induced by azadirachtin on Drosophila melanogaster S2 cells in vitro.

RESULTS

The results of the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl‐2H‐tetrazolium bromide assay demonstrated that azadirachtin exhibited significant cytotoxicity to S2 cells in a time‐ and dose‐dependent manner. The changes in cellular morphology and the DNA fragmentation demonstrated that azadirachtin induced remarkable apoptosis of S2 cells. Expression levels of 276 genes were found to be significantly changed in S2 cells after exposure to azadirachtin, as detected by Drosophila genome array. Among these genes, calmodulin (CaM) was the most highly upregulated gene. Azadirachtin was further demonstrated to trigger intracellular Ca2+ release in S2 cells. The genes related to the apoptosis pathway, determined from chip data, were validated by the real‐time quantitative polymerase chain reaction method.

CONCLUSION

The results showed that azadirachtin‐mediated intracellular Ca2+ release was the primary event that triggered apoptosis in Drosophila S2 cells through both pathways of the Ca2+‐CaM and EcR/Usp signalling cascade. © 2015 Society of Chemical Industry
AgSb(SxSe1‐x)2 thin films by rapid thermal processing of Sb2S3‐Ag‐Se thin films for photovoltaic applications
Authors: Rodriguez Vela Dorian Leonardo , Krishnan Bindu , Aguilar Martinez Josue Amilcar , Loredo Shadai Lugo , Shaji Sadasivan
Published: November 2015

Silver antimony sulfoselenide thin films have been investigated for photovoltaic applications. In the present work, we report preparation of AgSb(SxSe1‐x)2 by a rapid thermal processing of pre‐annealed Sb2S3/Ag/Se/Ag/Se layered structures. Sb2S3thin films were deposited by chemical bath deposition and Ag by thermal evaporation. Silver (Sb2S3/Ag) layered precursors were dipped in Na2SeSO3 solution followed by annealing and then rapid thermal processing. Also, photovoltaic structures were prepared using AgSb(SxSe1‐x)2 thin films as absorber and CdS as window material. The effects of rapid thermal processing on the structure, morphology and properties of these thin films were studied. Characterization of the absorber materials was done using X‐ray diffraction, X‐ray photoelectron spectroscopy, Atomic force microscopy, Optical absorption spectroscopy and Current‐voltage characteristics. Analysis of J ‐V characteristics of the photovoltaic structures under AM1.5 illumination before and after rapid thermal treatment showed Voc in a range of 457 to 473 mV and Jsc of 5.8 to 7.2 mA/cm2. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Testing multiple primary endpoints in clinical trials with sample size adaptation
Authors: Liu Yi , Hu Mingxiu
Published: November 2015

In this paper, we propose a design that uses a short‐term endpoint for accelerated approval at interim analysis and a long‐term endpoint for full approval at final analysis with sample size adaptation based on the long‐term endpoint. Two sample size adaptation rules are compared: an adaptation rule to maintain the conditional power at a prespecified level and a step function type adaptation rule to better address the bias issue. Three testing procedures are proposed: alpha splitting between the two endpoints; alpha exhaustive between the endpoints; and alpha exhaustive with improved critical value based on correlation. Family‐wise error rate is proved to be strongly controlled for the two endpoints, sample size adaptation, and two analysis time points with the proposed designs. We show that using alpha exhaustive designs greatly improve the power when both endpoints are effective, and the power difference between the two adaptation rules is minimal. The proposed design can be extended to more general settings. Copyright © 2015 John Wiley & Sons, Ltd.
Real‐time Reliability Self‐assessment in Milling Tools Operation
Authors: Liu Shujie , Hu Yawei , Liu Chi , Zhang Hongchao
Published: November 2015

To ensure reliable operations, online reliability assessment based on the system monitoring is essential, especially for the critical machineries or components with high safety requirements. The real‐time reliability of the milling cutters in practice is one of the examples that decide the total manufacturing effectiveness and the quality of products. The research on how to best estimate cutters' reliability has gained popularity in recent years due to the need in prognostics and health management. The state space model (SSM), employed to recognize the underlying degradation state as a first order Markov chain, is widely used to model the residual life and reliability evaluation. In this paper, non‐linear and non‐Gaussian SSM are established based on the tool wear condition. The degrading tendency is predicted by the particle filter algorithm, and then the conditional reliability is calculated based on the degradation state and a pre‐set threshold. The effectiveness of this approach was proven by a real case study provided. Copyright © 2015 John Wiley & Sons, Ltd.
Geographical Distribution of Total Electron Content Dependence on Geomagnetic Activity
Authors: Bertin F. , Lepine J. Papet , Vassy E.
Published: November 2015

A comparison study has been made of the distribution of the total electron content over Europe, m terms of the geomagnetic activity. When geomagnetic activity is low, the geographical distribution of the total electron content shows some irregularities which could be linked to the observation of scintillations. When geomagnetic activity is high, the total electron content is increased but the geographical distribution IS much more regular. In such a case, we notice a lack of scintillations in southwestern Europe.
Scintillation of a Radio Star at a Subauroral Latitude
Authors: Aarons Jules , Allen Richard S.
Published: November 2015

Scintillations of the radio source Cassiopeia A observed at 113 Mc/s during the period October 1961 through July 1964 were scaled to determine a semiquantitative index ofthe scintillation of source power. For fixed values of local magnetic activity mean diurnal variations were established which peaked about two hours before solar and magnetic midnight. Mean sidereal variation peaked at lower transit; this effect, attributed primarily to latitude, is compared to satellite scintillations. Both diurnal and sidereal variations showed an increase of mean scintillation activity with increase of magnetic index. Detailed examination of low magnetic index periods showed that daytime scintillations were slightly higher on the western side (towards the magnetic pole), while nighttime scintillations showed symmetry. However, with increasing magnetic activity, scintillation indices are considerably higher at night in the west while daytime scintillations are skewed to the east. A comparison of these observations with Penndorfs model of traveling and permanent maxima of spread F is attempted. The general features of the diurnal‐latitude variation of the radio star scintillation index is compared to the diurnal and latitude variation of spread F (topside and bottomside). While there is a general correlation, differences between scintillations and spread F noted in topside sounders are considerable.
Quasi‐Static Theory of a Cylindrical Impedance Probe for Magnetoplasma
Authors: Wait James R.
Published: November 2015

An expression for the fields of two parallel line charges in an anisotropic medium is derived. To facilitate the analysis, the line sources are assumed to be encased in a cylindrical dielectric r9d. The result is used to obtain a formula for the driving‐point impedance of the device. It is shown that the resonances are a well defined function of the plasma and cyclotron frequencies.
Theory of a Slotted‐Sphere Antenna Immersed in a Compressible Plasma, Part III
Authors: Wait James R. , Spies Kenneth P.
Published: November 2015

Numerical results are presented for the conductance and susceptance of a slotted‐sphere antenna which is immersed in a compressible, isotropic, and lossless electron plasma. Previous series expansions for the parameters of interest are cast in a form suitable for numerical work. The results indicate that an appreciable fraction of the power radiated is in the form of electroacoustic waves. However, this fraction may be significantly reduced if the sphere is surrounded by an electron depletion layer (i.e., a sheath) whose thickness is somewhat greater than a Debye length.
Propagation of VLF Waves Past a Coastline
Authors: Dobrott D. R.
Published: November 2015

The fundamental solution for VLF waves propagating past a shoreline in the earth‐ionosphere duct is obtained in terms of an infinite series using the Wiener‐Hopf methods. The effects of the land, sea, and ionosphere are given in terms of complex impedance boundary conditions. As a result, each mode in the series is progressively damped. At low frequencies and distances far from the shoreline where a single mode dominates, reflection and transmission coefficients are obtained. When the ionospheric impedance is small and when the source and receiver are sufficiently elevated, the effect of the shoreline is not observable. However, when either the source or receiver is near the earth, the portion of the wave reflected is proportional to the difference of sea and land impedances. At slightly higher frequencies, there exists an annular region about the shoreline where two modes propagate over the sea while, due to heavy damping, only one mode propagates over the land. The resulting increase of the field strength as the receiver passes from land, seaward is the “recovery effect.”
Approximations to the Double Knife‐Edge Attenuation Coefficient
Authors: Wilkerson Robert E.
Published: November 2015

Several approximations to the attenuation coefficient caused by double knife‐edge diffraction are given in terms of the single knife‐edge attenuation coefficient. These approximations are evaluated for several typical double knife‐edge paths and compared with the theoretical value in order to determine the best approximation in the different regions of interest.
Mountain Obstacle Diffraction Measurements at 751 Mc/s and 9.2 Gc/s
Authors: Barsis Albrecht P. , Hause L. G.
Published: November 2015

This paper contains results of a measurement program on 751 Mc/s and 9.2 Gc/s using a long mountain‐obstacle diffraction path in Colorado. Data are analyzed and evaluated in terms of long‐term and short‐term variability, correlation coefficients between carrier envelopes received on spaced antennas, and comparison of a priori predicted and measured cumulative distributions of hourly transmission loss medians. Results show beuer agreement between predictions and measurements on 751 Mc/s than on 9.2 Gc/s. Short‐term (within‐the‐hour) variations in signal level on 751 Mc/s can be characterized as prolonged space‐wave fadeouts, whereas such variations on 9.2 Gc/s very frequently show characteristics of a Rayleigh‐distributed signal.
Space and Time Correlations of Ionospheric Winds
Authors: Rosenberg N. W. , Justus C. G.
Published: November 2015

Ionospheric wind patterns between 90 and 150 km were studied by distortion of chemiluminous vapor trails released from rockets. Fifteen trails, closely paired in space or time, are reported. Profiles show well‐organized sinusoidal patterns of near‐constant wavelength, if the vertical coordinate is measured in integrated scale heights rather than kilometers. Dominant wavelength is 2–4 scale heights, similar in NS and EW components, and phase progresses downward about 1 wavelength per night. Horizontally spaced trails show vertical profile displacement corresponding to horizontal scales of 1000–4000 km in NS wind, longer in EW profiles. Viscous energy dissipation from observed waves is a significant heat source at 150 km altitude.
Theoretical Basis of the Formation of Sporadic E Due to Wind Motion in the Ionosphere
Authors: Kato S.
Published: November 2015

We discuss the mechanism producing ionization irregularities by wind motion in the ionosphere, showing that the geomagnetic field resists the production by scaloidal wind as sound waves, but induces the production by toroidal wind as turbulence. The electric polarization set up tends to impede the formation, but dissipates along high conductive field lines of the geomagnetic field, if the wind motion varies along the magnetic field. We discuss the effect of the electric field on the layer formation, illustrating its time variation when a uniform electric field and a height‐dependent horizontal wind exist.
Summary and Conclusions from the Estes Park Sporadic E Seminar; 1. Radio Measurements
Authors: Bowles Kenneth L.
Published: November 2015

In a summary of the "radio" measurements of sporadic E we cannot extricate ourselves completely from consideration of the other measurements considered in this conference. For some purposes, the radio propagation characteristics provide us with a means of diagnosing properties of the E region; for other purposes, experimental results obtained in alternative ways permit us a means of interpreting the radio propagation. In this seminar it has been possible to bring more clearly into focus the physical relationship between the various radio propagation phenomena as observed from the ground and the electron density variations which cause these phenomena. For completeness, the field of “radio” measurements of E, should also include those rocket measurements which depend upon the integrated radio path from ground to rocket. These rocket measurements are distinct from the ground‐based radio observations in that interpretation of the rocket observations yields a relatively unambiguous measure of atmospheric properties in a restricted volume centered on the rocket trajectory. The propagation phenomena which first provided us with the name “sporadic E” result from an integration of effects distributed over volumes some tens of km in extent.
Slot Admittance for Compressible Plasma Layers
Authors: Galejs Janis
Published: November 2015

The admittance of a waveguide is calculated for radiation into a general two‐layer compressible plasma which is further specialized to represent a plasma sheath and also an ion sheath in the presence of a plasma half space. The antenna admittance is related by integrals to the electric fields in the waveguide aperture, which are assumed to be a sum of the principal waveguide mode and of surface wave fields which are supported in this plasma geometry. The compressibility of plasma has the largest effect on the slot admittance when the slot width is equal to an odd number of half wavelengths of surface waves, but significant changes occur only if the relative dielectric constant of the plasma is less than 0.2, and the ratio of the free‐space velocity of electromagnetic waves to the acoustic velocity is less than 300. Plasma losses and the presence of an ion sheath tend to lessen the compressibility effects.
Wave Propagation in Plasma Waveguides
Authors: Webber J. , Sims G. D.
Published: November 2015

An experimental investigation of the propagation characteristics of longitudinal waves in plasma‐filled waveguides is described. Two distinct modes of propagation are observed, corresponding to whether the discharge is in the normal or abnormal glow region. The normal glow, or “lower mode”. exhibits completely different propagation characteristics from those of the abnormal glow or “higher mode.” The characteristics of both types of propagation are fully discussed.
The Effect of Collisions Upon the Virtual Heights of Low‐Frequency Radio Waves Reflected From the Ionosphere
Authors: Ferraro A. J. , Tou C. P.
Published: November 2015

This paper presents some results of virtual‐height computations by full‐wave and ray‐optics methods for low‐frequency radio waves reflected from a stratified ionosphere. It is concluded that ray optics without collisions included would give more accurate results than if collisions are included in the computations for both the ordinary and extraordinary modes. This has been substantiated by accurate full‐wave computations taking into account the earth's magnetic field.

The subject of a correction factor is briefly considered.
Excitation of the Whistler Mode in the Ionosphere by Leakage From VLF Guided‐Wave Modes
Authors: Capetanopoulos C. , Kieburtz R. B.
Published: November 2015

The penetration of VLF waves into the ionosphere is calculated from the mode representation of the fields in the earth‐ionosphere waveguide. This calculation is more appropriate for evaluation of leakage of VLF energy into the ionosphere at large distances from the transmitter than is the calculation based on a ray theory representation of the fields. The ratio of the amplitude of the field excited in the ionosphere to that observed on the earth is found to agree with the observations of the LOFTI I experiment.

In carrying out the analysis of the leakage of energy from the waveguide modes, it is necessary to reevaluate the modal propagation constants, employing a self‐consistent calculation requiring that the wave polarization of a modal field be preserved upon reflection at the waveguide boundaries. Upon imposing these conditions, it is found that two sets of modes result, having different polarizations. These sets of modes have been designated as quasi‐TE and quasi‐TM.by Budden, but both sets tire no1 usually used in VLF field strength calculations. Under nighttime conditions, both types of modes will be of importance, while in daytime only the quasi‐TM modes will be excited by a vertical monopole antenna on the earth. These results predict a nonreciprocal attenuation over a north‐south propagation path.
Irreversible Power and Radiation Resistance of Antennas in Magnetoionic Media
Authors: Walsh D. , Weil H.
Published: November 2015

Certain objections, based on considerations of reversible as compared with irreversible power, which have been raised against conventional computations of the radiation resistance of antennas in magnetoplasma are shown to be without foundation. The inapplicability of this concept of reversible power to steady‐state radiation is considered, and its connection with transient excitation is discussed.
On the Admittance of the Infinite Cylindrical Antenna
Authors: Fante R. L.
Published: November 2015

It is shown that, due to an incorrect asymptotic evaluation of certain integrals, the analytical results of Chen and Keller for the admittance of the infinite cylindrical antenna give an incorrect result for the conductance, although the susceptance is correct.
A Numerical Method for Interpreting D‐Region Radio Pulse Interaction Measurements
Authors: Georges T. M.
Published: November 2015

Ionospheric nonlinear wave interaction (cross modulation) experiments are conveniently and more accurately analyzed by using a computer‐oriented simulation process resembling ray tracing in the height‐time domain. Advantages of such a process over existing analytical methods are discussed, and typical experiments are simulated to illustrate its flexibility.

The technique is modified to yield a numerical method for directly synthesizing D‐region electron density and collision frequency profiles from experimental interaction measurements. Accuracy limitations inherent in the synthesis process raise doubts about the utility of the basic experiment as an accurate D‐region electron density probe.
On the Manual and Digital Computer Methods Used at Lindau for the Conversion of Multifrequency Ionograms to Electron Density‐Height Profiles
Authors: Becker W.
Published: November 2015

Real‐height analysis of multifrequency ordinary and extraordinary virtual‐height traces has been carried out at Lindau since 1956 with methods of our own design. They all take account of underlying ionization and extrapolate the real‐height profile up to the peak of the layer under discussion. This extrapolation is based on observed virtual heights rather than on deduced real heights. At least second‐order approximations of the profile are used here. All of the methods allow for analysis of monotonic and nonmonotonic virtual‐height traces. They differ only in their final accuracy. A model method is described first; only 8 min are necessary to reduce a simple F trace. The respective real‐height data have proved very useful for statistical purposes. Since 1957, very accurate and general manual methods have been in use. One and one‐half hours are necessary for a full analysis of one ionogram. While these methods rely on an estimate by eye of the critical frequency of the layer of interest, the digital computer method in general use at Lindau since 1962 deduces this value too. The accuracy of this digital computer method is much better than the technical accuracy of the present ionosondes. A complete real‐height analysis of one virtual‐height trace, showing a critical frequency of 16 MHz, amounts to about 14 min of computer time (IBM 650).

Test results on a series of theoretical ionograms of monotonic and more or less complicated non‐monotonic electron density‐height profiles, valley profiles, are also reported.
Transient TEM Wave Propagation in Unbounded Radial Line
Authors: Weiner Melvin M.
Published: November 2015

Previous analyses of transient‐wave propagation in unbounded radial lines have been restricted to excitations at the origin. This paper considers the more general case of excitations uniformly distributed about a circumference of arbitrary radius. The inverse Laplace transforms of some modified Bessel functions of the form Kn(as)Im(bs) are evaluated by means of a Green's function formulation.
Note on the Tabular Presentation of the Radio Refractive Index as a Function of Meteorological Parameters
Authors: Brady M. Michael
Published: November 2015

The different methods of presenting radio refractive‐index data currently in use are compared. It is concluded that a tabulation using the Smith and Weintraub constants for N as a function of total pressure, temperature, and dew‐point temperature best serves the needs of radiometeorologists. A tabulation using these parameters comprising 49 tables for N is described.
VLF Transmission Loss Calculated From Spectral Analyses of Atmospherics
Authors: Taylor W. L.
Published: November 2015

VLF atmospheric data recorded during four 6‐hour periods was analyzed to evaluate the feasibility of employing a new technique to determine attenuation rates over a particular path. The technique involves recording the spectral components of atmospherics arriving from within an adjustable azimuthal direction. Changes in transmission loss, deduced from the observed spectra, between day and night conditions for an approximate 3000‐km path indicate differences in total transmission loss of about 15 dB at 5 kHz, 1 or 2 dB at 10 kHz and 40 kHz, and a negative loss, or gam, between 12kHz and 30kHz.
Thermal Radiation Fields and Antenna Parameters in Magnetoplasma
Authors: Herschel Weil , Walsh D.
Published: November 2015

Spectral densities of components of the electromagnetic fields of thermal radiation in a uniform magnetoplasma are shown to be related to the radiation resistances of electrically small antennas radiating in the magne toplasma.

For antennas of arbitrary size and shape the conventional concepts used to describe antenna performance in isotropic media, i.e., gain, effective area and effective length are generalized to anisotropic media and relationships between them and radiation resistance established. A thermodynamic method is used in the derivation of the relationships.

A new derivation of the radiation resistance for an electrically small dipole in magnetoplasma is given based only on the far‐zone radiated fields.
On the Exact Theory of a Prolate Spheroidal Receiving and Scattering Antenna
Authors: Taylor Clayborne D.
Published: November 2015

An exact formula for the current distribution l(n) along an unloaded (short‐circuited terminals) prolate spheroidal receiving antenna of arbitrary eccentricity is derived when the incident field is a plane wave with the electric vector directed parallel to the major axis of the spheroid. A knowledge of the current I(0) and the input impedance Z0, derived earlier by Chu and Stratton, completely determines the receiving characteristics of the antenna when it is loaded by impedance ZL at η = 0. The current distribution along the antenna is obtained from Ampere's law by integrating the magnetic field at the surface of the spheroid around cross sections perpendicular to the major axis. This integration removes the azimuthal angular dependence providing sufficient simplification in the mathematics, so that the exact current distribution may be obtained from an equation involving a single infinite sum.

The plane‐wave scattering problem is completely formulated. It is shown that the solution for the scattered fields can be obtained only by solving simultaneous infinite matrix equations.

Numerical results are presented that compare spheroidal antenna receiving current distributions to cylindrical antenna current distributions. Also the induced center currents are compared for a number of antenna‐shape parameters. These reveal that thin cylindrical antenna theory may be extended past its theoretical limits of validity.
Traveling Waves in Relation to the Surface Fields on a Semi‐Infinite Cone
Authors: Senior T. B. A. , Wilcox P. H.
Published: November 2015

For a plane electromagnetic wave at nose‐on incidence on a semi‐infinite perfectly conducting cone expressions for the surface field components are obtained. These have been programmed for numerical computation and data are presented for the magnitudes and phases as functions of the distance from the tip for three different cone angles. Comparison with results derived from the physical optics approximation and from a simple wedge approximation shows that the differences between the exact and physical optics values are not attributable to a tip‐excited wave.
Theoretical Investigation of the Diurnal Phase and Amplitude Variations of VLF Signals
Authors: Rugg Donald E.
Published: November 2015

Multimode propagation and mode conversion at the sunrise and sunset lines must be considered to explain the diurnal variations on some VLF paths. In this investigation the model selected to represent the transition from one steady‐state ionosphere condition to the other was an abrupt change in the surface impedance and reference height of the ionosphere. Comparisons of calculated and recorded amplitude and phase variations during sunset showed that sunset could not be approximated by an abrupt ionosphere transition. Comparisons of calculated and recorded variations during sunrise, however, indicated that the simple analytical model approximated the propagation conditions during sunrise for the east‐to‐west and west‐to‐east paths that were considered.
Propagation of Electromagnetic Waves into Anisotropic Media From an External Point‐Dipole Source
Authors: Price Gary H.
Published: November 2015

A formal solution to the problem of determining the fields generated by an infinitesimal, arbitrarily oriented, electric‐dipole source located in an isotropic medium bounded by parallel plane‐stratified, anisotropic media is derived.
Groundwave Attenuation Function for Propagation Over A Highly Inductive Earth
Authors: King R. J. , Schlak Gerard A.
Published: November 2015

Propagation of an electromagnetic groundwave over a plane surface in which the argument of the surface impedance is greater than π/4 but less than π/2 is considered in some detail. The numerical distance, p, over such a surface is characterized by 0 ≤ arg p ≤ π/2. The groundwave behaves in a peculiar manner, and this is attributed to the interaction of two phasor components representing a trapped wave and a Norton surface wave. Approximate expressions are derived which determine the magnitude and phase of the groundwave attenuation function when these two waves are inphase and antiphase. A method is also given for estimating the asymptotic phase for large |p| which was previously not possible except through detailed calculations. Finally, detailed curves are presented which show the amplitude and phase of the groundwave attenuation function versus p.
Resonances of the Thin‐Shell Model of the Earth‐Ionosphere Cavity With a Dipolar Magnetic Field
Authors: Large David B. , Wait James R.
Published: November 2015

A coupled multimode analysis technique is applied to a model of the earth‐ionosphere cavity at ELF in which the ionosphere is replaced by a thin, anisotropic shell. The unique feature of the analy. sis is that it is capable of illustrating the effects of a dipolar form of geomagnetic field. Numerical values of the cavity resonant frequencies and quality factors for several values of electron density and collision frequency are presented for both a homogeneous and a dipolar magnetic field configuration. The main purpose of the paper is to demonstrate that a coupled multimode analysis is applicable to such nonsymmetrical configurations.
Utilization of the Refractive Index Surfaces to Evaluate Cerenkov Radiation in an Infinite Magnetoplasma
Authors: Sasiela R. , Freidberg J. P.
Published: November 2015

The utilization of refractive index surfaces in conjunction with the Clemmow, Mullaly, Allis (CMA) diagram greatly simplifies the determination of the regions of Cerenkov radiation and the types of waves emitted in a cold, collisionless, electron magnetoplasma. Also, the physical insight gained by this approach is used to explain the qualitative behavior of the power spectrum.
Beam Efficiency and Gain Optimization of Antenna Arrays With Nonuniform Spacings
Authors: Butler J. K. , Unz H.
Published: November 2015

A distribution of current across the elements corresponding to the optimum condition is given as a solution of the characteristic equation Ba = λCa where B and C are matrices whose elements depend on the type of sources and their spacings. The value “a” is a column matrix whose elements define the array excitation. The beam efficiency or gain of a nonunifonnly spaced array is increased over that of a uniformly spaced array. To find the element positions, one first finds the direction, known as the direction of steepest descent, of maximum change in the largest characteristic value; the direction is given as grad λ, where the partial derivatives are taken with respect to the element positions. By proceeding in the direction of steepest descent, one will arrive at the point located in the element position space that represents the optimum spacings. Perturbation methods are also used to show how the beam efficiency or gain is increased by nonunifonnly spacing the elements.
Computation of HF Ground Backscatter Amplitude
Authors: Croft Thomas A.
Published: November 2015

An HF backscatter radar system is simulated by a digital computer method which includes the detailed influence of the ionosphere through use of precomputed rays. To insure a fairly realistic simulation, allowance is made for the following factors: a spherical earth and ionosphere, electron density variations with height and range, absorption which varies with range and ray angle, antenna gain as a function of azimuth and elevation, ground scattering and specular reflection characteristics which vary with range and angle of incidence, and the transmitted pulse shape. The main approximations are (a) that ray theory is used with the assumption that most energy is distributed uniformly between closely spaced ray paths, and (b) that the effect of the geomagnetic field on ray‐path range and transit time is neglected.

This computer simulation has two main applications. First, it permits the study of idealized backscatter problems by controlled variation of one parameter at a time. For example, a localized irregularity may be inserted in the ionosphere and the backscatter can be calculated with and without it. Second, it is possible to match experimental backscatter with synthetic backscatter for the purpose of evaluating the ground‐scatter coefficient or estimating the existing ionospheric structure. This process requires carefully calibrated experimental data because the comparison must be quantitative. Some early results of this work are shown.
John Howard Dellinger Memorial Lecture
Authors: Morgan Millett G.
Published: November 2015

The viability and effectiveness of URSI, which have brought us together once again, we enjoy only because of the dedicated efforts of men such as John Howard Dellinger — men who have gone before us, seeking more effective ways to achieve our purposes, preventing us from becoming engulfed by uncontrolled growth while still being responsive to the changing needs of our science, and especially to the needs of the young men entering our field.
Reflection of Circularly Polarized Electromagnetic Waves From an Anisotropic Plasma
Authors: Bachynski M. P. , Gibbs B. W. , Graf K. A.
Published: November 2015

The reflection of both right‐hand and left‐hand circularly polarized plane electromagnetic waves normally incident along the direction of an imposed static magnetic field in an anisotropic plasma, has been investigated. Detailed measurements at a frequency of 9.2 Gc of the intensity and phase of the wave reflected from a helium afterglow plasma over wide ranges of plasma frequency and electroncyclotron frequency were carried out. The measured reflected power varied from less than 1 percent of the incident power to complete reflection, and large undulations in both intensity and phase of the reflected wave with changing electron density and magnetic field were observed. Comparison with theory based on a simple sharply bounded uniform plasma slab shows good agreement for the general nature of the dependence of the reflected wave on the plasma properties. The exact electron densities corresponding to the maxima and minima and the absolute values of the intensity and phase of the reflected wave are not accurately predicted by this simple theoretical model. In the region of the electron‐cyclotron frequency, for an incident right‐hand circularly polarized wave, the reflected signal undergoes a reduced variation in phase, and the intensity, after attaining a maximum, is observed to decrease with increasing electron density.
Estimation of the Number of Unresolvable Targets Producing a Single Radar Return
Authors: Beckmann Petr
Published: November 2015

The problem of estimating the number of unresolvable targets in a close configuration producing a single radar return is investigated by analyzing the slow fluctuations of the received signal. It is assumed that the targets have identical statistical properties. If nothing is known about the scattering cross section S of a single target, the problem is shown to have no unique solution. Solutions are given for the case when the mean of S is known, when only the type of distribution of S is known, and when the correlation function of the random process S(t) is known. Verification of the results by computer simulation is reported.
Field Theory of Depolarization of Radar Backscatter — With Application to a Distant, Slightly Rough Sphere
Authors: Erteza A. , Lenhert D. H.
Published: November 2015

This paper sets out to develop a vector field theory of time‐dependent backscatter from a large target and shows how the cross‐polarization of the return signal follows as a natural consequence of certain spatial asymmetry of the target with respect to the illuminating source. It presents an analysis of radar backscattered power from a distant, slightly rough sphere for both pulsed and sinusoidally steady‐state sources. At first, an integral expression for the received power is developed for an arbitrarily rough sphere. Then the height deviation from the mean sphere is specialized to have a bivariate Gaussian distribution and a Gaussian correlation function. The average direct‐ and cross‐polarized received powers are derived for both the pulsed and the steady‐state cases. Numerical results are computed for the case of a very slightly rough sphere for which σ/δ is of the otder of 10‒4 and presented in contrast with experimental data from a target with a much larger scale roughness, namely the moon. (In this paper σ represents the standard deviation of heights and δ is the correlation distance.)
Statistical Variations in the Apparent Specular Component of Ionospherically Reflected Radio Waves
Authors: Boys J. T.
Published: November 2015

The specular component of an ionospherically reflected radio wave giving highly correlated signals between elements of an array of antennas is measured and found to vary in a way suggesting that it is Rayleigh distributed. Examples illustrating the rate at which variations occur are given and it becomes clear why averages over different periods may give quite dissimilar results. It is inferred that there is, strictly speaking, no specular component but a group of rays all coming from very similar directions.
Predicting Ionospheric Electron Density Profiles
Authors: Haydon George W. , Lucas Donald L.
Published: November 2015

Typical measurements of the electron density in the various regions of the ionosphere are reviewed and the current availability of predictions based on these measurements is discussed. A method is suggested to combine regular ionospheric predictions such as f0F2 and f0E with estimates of electron density in the lower ionosphere and with empirical expressions for the electron density in the upper ionosphere to obtain a first approximation to the electron density versus height profile for the quiet ionosphere. Sample profile predictions based on regular ionospheric predictions are shown for ionospheric heights of most importance in the design and operation of high‐frequency communication systems.
Comparisons Between New Methods for Reduction of Ionograms to Electron Density Profiles
Authors: Shilling G. D. , Unz H.
Published: November 2015

The uniform lamination analysis method is used for the solution of the simplified integral equation which relates the electron density profiles in the ionosphere to the average measured virtual heights, taking the wave refractive index as the kernel function. The arbitrary auxiliary function is chosen to be ϕ(fN) = µ(fN), which simplifies the calculation as compared to taking ϕ(fN) = fN. Four examples are calculated for both cases and compared with the original assumed electron density profiles. Accuracy and required computer times are discussed.
Nonlinear Demodulation of an Amplitude Modulated Wave in a Plasma: Elementary Approach
Authors: Sodha M.S. , Arora A. K. , Aggarwal A. K.
Published: November 2015

A phenomenological theory for the nonlinear demodulation of an amplitude modulated wave propagating in a plasma has been developed. In contrast to the earlier work, this theory is not restricted to the cases when the frequency of modulation is much more or less than δ(δ ~ 2m/M) times the electron collision frequency. It is found that for normal operating parameters the demodulation may be significant and that it increases with decrease in electron density, modulation frequency, and initial modulation index of the propagating wave.
Random Phase Errors in End‐Fed Linear Antenna Arrays
Authors: Dudley D. G.
Published: November 2015

An analysis of linear antenna arrays containing phase errors described by a random martingale sequence is presented. The case is representative of the popular class of linear arrays of the end‐fed, traveling wave type. The expectation of the Fraunhofer power response is derived. A computer experiment is performed that shows the principal effect of the phase error is upon side‐lobe response. The complete probability distribution in the side‐lobe region is derived through the central limit theorem, which is found to apply for phase errors small enough in spite of the correlation among members of the martingale. The distribution is verified by comparison with points from the computer experiment. The results are used to relate manufacturing tolerances to side‐lobe deterioration.
Scattering of Electromagnetic Waves From a Slightly Rough Surface Moving With Uniform Velocity
Authors: Valenzuela G. R.
Published: November 2015

The scattering of electromagnetic waves from a slightly rough surface moving with uniform velocity is investigated.

Rice's generalization of Rayleigh's expansion for the scattered fields and Lorentz transformation are used to relate the fields in the moving and stationary reference frames. In the development we also use the principle of phase in variance and the covariance nature of the electromagnetic fields.
Surface‐Wave Modes in Dielectric‐Lined Coaxial Cables
Authors: Lewis J. E. , Kharadly M. M. Z.
Published: November 2015

An analysis is given for hybrid, TM, and TE surface‐wave modes in coaxial cables with homogeneous dielectric linings on either or both conductors. The characteristic equations and expressions for the group velocity are derived using the field components in the loss‐free cases. A perturbation technique is then used to derive expressions for the attenuation coefficients of all slow‐wave modes. For the dominant mode, these are shown to reduce to expressions which can be obtained by a quasi‐TEM approach.
An Approximate Synthesis of HF Backscatter Considering Ionospheric Motions
Authors: Surtees W. J.
Published: November 2015

Digital‐computer techniques have been used to synthesize ground‐backscatter records for model daytime ionospheres containing irregularities at known distances. By assuming irregularity motion at constant height and speed, approximate synthetic range‐time records are obtained. Two different methods of synthesis are described and compared. Apparent velocities of irregularity movement are derived from the slopes of the ripples on the range‐time records for various operating frequencies. For operating frequencies supporting F‐layer propagation, there appears to be little frequency‐dependence of apparent velocity when the irregularity is near reflection heights; but when the irregularity is lowered to heights near the E layer, a strong frequency‐dependence of velocity develops.
Exact Ray‐Path Solutions in a Quasi‐Linear Ionosphere
Authors: Westover Douglas E.
Published: November 2015

Exact ray solutions are helpful in determining the accuracy of general purpose ray‐tracing techniques. In this paper such solutions are presented for range, group path, phase path and reflection height of radio rays entering the ionospheric layer from the bottom and from the top. The ionospheric model used to produce the exact solutions is a function which allows closed‐form integration of the ray parameter expressions. In this ionosphere, first introduced by Muldrew, electron density is almost a linear function of height, but it does not vary in the horizontal direction. The earth's magnetic field and electron collisions are neglected but curved earth‐ionosphere geometry is included.
Signal and Noise Characteristics in Radiometric Correlation Detectors
Authors: Joseph Buck G.
Published: November 2015

In radio astronomy and other radiometric applications, correlation antenna‐receiver systems are used to measure the Fourier transform of the far‐field temperature distribution. In this paper, the effect of a finite observation bandwidth upon the measurement of the transform is determined.

The noise components in the output of the correlator‐antenna system which is observing a distributed source are calculated. The noise power present in the measurement of the real component of the Fourier transform is found to depend on the square of the sum of the integrated temperature distribution and the receiver noise, also upon the square of the real part of the Fourier transform, and the negative of the square of the imaginary part of the Fourier transform. Similar results with appropriate sign changes apply to the imaginary portion of the Fourier transform. The practical restriction on the allowable bandwidth of the correlation receiver is also apparent in these calculations.

These values of the signal and noise power can then be used for the optimum processing of the received signal.