bluuebunny/crossref_metadata_2025_split huggingface dataset:
Axial‐Radar Cross Section of Finite Cones by the Equivalent‐Current Concept with Higher‐Order Diffraction
Authors: Burnside W. D. , Peters L. 
Published: February 2008

In a recent paper, Senior and Uslenghi [1971] further developed the radar cross section of a finite cone. For the axial radar cross section, they evaluated the fields on the axial caustic using the first‐ and second‐order solution of Keller [1960]. It is the intent of this paper to show that the equivalent‐current method of Ryan and Peters [1969, 1970] yields the same results as those of Senior and Uslenghi. The equivalent‐current technique is, however, a more straightforward procedure to implement for the treatment of the scattered fields in the vicinity of the caustic and should be included in the collection of diffraction solutions.The equivalent‐current technique is required only in the vicinity of the axial caustic. The results merge with the more conventional procedures as the observation point moves away from the axial caustic region. Thus, the numerical results discussed in this paper are concerned with the axial backscattered fields.In our development, the second‐order diffracted ray across the base of the cone includes a factor of one‐half not included in the Senior‐Uslenghi solution. The reason for this factor is discussed in detail. The solution to a simpler wedge problem with and without this factor is compared to an integral equation solution in the Appendix.The experimental and theoretical results for the cone differ consistently by approximately 2 db for a wide range of cone‐base radii and indicate that an additional mechanism contributes significantly to the scattered fields. One is suggested and indeed is required in the similar wedge solution of the Appendix.The equivalent‐current technique is seen to be applicable to cones which have base radii as small as 0.3λ.
Commission 8. Radio noise of terrestrial origin
Authors: Hagn G. H. 
Published: February 2008

The review paper, given by E. L. Maxwell (USA), concentrated on recent developments in three areas: (a) prediction of atmospheric noise levels and characteristics, (b) calculation of system performance in the presence of atmospheric noise, and (c) measurement of atmospheric noise.The development of a digital‐computer model for predicting the characteristics of VLF atmospheric‐noise characteristics was described. The model provides for the calculation of (a) mean values of vertical electric‐field intensity which can be converted to mean noise power available from an ideal short vertical antenna, Fa, (b) the standard deviation from the mean values, (c) mean values of voltage deviation Vd) and (d) the direction of arrival of the noise energy. It uses both thunderstorm and lightning distributions derived from thunderstorm‐day observations at more than 7000 locations and lightning characteristics to calculate the noise energy radiated per square kilometer over the entire earth surface. An earth‐ionosphere waveguide model is used to calculate the noise energy propagated to any location. Statistical characteristics of noise are calculated from those of thunderstorms and lightning and from propagation parameters. It was emphasized that measured VLF noise data were not used to generate the model. The accuracy of the noise model was good when compared with atmospheric radio‐noise (ARN‐2) data but not better than that of the empirical model of CCIR Report 322 [1964] when compared with data from the 16 locations used for that model. For very high latitudes and other remote locations the results from the current model differ from those of CCIR Report 322 by up to 20 db. It seemed desirable to update the report for VLF by using the results from the noise‐prediction model and all the noise data collected by the NBS/NOAA network. It was suggested that a separate map for VLF for three‐month periods for the world might be preferable to the presentation in CCIR Report 322. Some continuing measurements with ARN‐2 equipment were remommended.
Incoherent scatter observations of the ionospheric response to a large solar flare
Authors: Mendillo Michael , Evans John V. 
Published: February 2008

Incoherent scatter observations at Millstone Hill were made during the importance 3B solar flare which occurred at 15:00 UT on 7 August 1972. Measurements were obtained of the electron density profile over the height range 125 to 1200 km, together with observations of the electron temperature, ion temperature, and vertical drift velociy above 225 km. The Ne(h) results showed electron density enhancements of nearly 100% at 125 km and 60% at 200 km; Ne enhancements were also observed throughout the topside, with the percentage enhancement increasing with height above 400 km. The total electron content up to 1200 km showed an increase of 3.8 × 1016 el m−2 (≃30%).The temperature and drift data represent the first Thomson scatter measurements of these parameters during flare conditions. While the electron temperature results showed substantial increases at all altitudes examined, the ion temperatures were only slightly perturbed. The drift data provided the most interesting results. In response to the flare, a dramatic upward surge was observed in which the drifts increased nearly linearly with height over the height range 300 to 750 km.In discussing the overall results obtained during this event, estimates are made of the flare‐induced electrodynamic and thermal processes which contribute to the observed effects.
A new wideband, fully steerable, decametric array at Clark Lake
Authors: Erickson William C. , Fisher J. Richard 
Published: February 2008

A new, fully steerable, decametric array for radio astronomy is under construction at the Clark Lake Radio Observatory near Borrego Springs, California. This array will be a “T” of 720 conical spiral antennas (teepee‐shaped antennas, hence the array is called the TPT), 3.0 by 1.8 km capable of operating between 15 and 125 MHz. Both its operating frequency and beam position will be adjustable in less than one msec, and the TPT will provide a 49‐element picture around the central beam position for extended‐source observations.Considerable experience has been gained in the operation of completed portions of the array, and successful operation of the final array is assured. This paper describes the results of the tests which have been conducted with the conical spirals and outlines the planned electronics.
Ionospheric heating by powerful radio waves
Authors: Meltz G. , Holway L. H. , Tomljanovich N. M. 
Published: February 2008

In addition to the communication applications that stem from the generation of field‐aligned irregularities, ionospheric heating by powerful HF waves also holds promise for establishing new techniques in D‐, E‐, and F‐region aeronomy. This paper concentrates on the application of the theory of plasma heating by ohmic and nonlinear dissipation to the special conditions of the lower ionosphere where the electron collision and disturbing wave frequencies are comparable and the upper ionosphere where electron thermal transport is large and restricted by the earth's magnetic field. We predict the magnitude and distribution of large‐scale changes in the electron temperature and density in both the D and F layers under a variety of conditions. These results are compared with direct measurements or inferred changes whenever possible.We also examine the effects of specular‐height mismatch, multiple frequency operation involving heater‐power sharing, and antenna beam tilt on the total cross section for field‐aligned scattering. The analysis is based on the concept that the energy‐density distribution on the heater reflectrix computed by means of a ray‐tracing technique can be related directly to the density‐fluctuation intensity through an appropriate scattering model. Lastly, potential applications to aeronomy are discussed, particularly in regard to D‐region measurements of the effective recombination coefficient magnitude and temperature dependence and the relative water cluster ion concentration.
Nighttime and sunrise variations of absorption
Authors: Ganguly S. 
Published: February 2008

The average behavior of the MF A1 absorption data at night and sunrise times at Calcutta has been described with a view to understanding the maintenance of the nighttime absorbing region. The nighttime variation of absorption which attains a minimum around one hour after local midnight could easily be accounted for in terms of the scattered UV fluxes.A small decrease in absorption before sunrise is evidenced. The analysis using the partially reflecting Es echo suggests this is caused by a decrease in deviative loss at F‐region heights. The onset time for a further increase in absorption agrees very well with that observed from other techniques.
Electric field spectrum and intensity covariance of a wave in a random medium
Authors: Fante Ronald L. 
Published: February 2008

Numerical results are presented for the effect of the strength of turbulence on the temporal frequency spectrum of a focussed beam propagating in a random medium having a von Karman spectrum for the index of refraction fluctuations.We also present a new theory for the normalized covariance BI(z, r) in the intensity fluctuations of a plane wave and find that forσ12 ≡ 1.23 k07/6 Cn2z11/6 » 1,B1 (z, R) ≃ (−11.2σ12R5/3) + (σ12)−2/5ƒ[R/(σ12)3/5]where k0 is the signal wave number, Cn2 is the refractive index structure constant, z is the path length, R = (k0/2πz)1/2r, and f3(···) is a function given in section 3. Note that the first term is sharply peaked about R = 0 and corresponds to the rapid drop‐off in BI(R) observed experimentally. The second term varies very slowly with R and corresponds to the long tail of BI(R) seen in experiments. Unlike other theories this theory is completely self‐contained, and does not involve the introduction of any arbitrary cut‐off parameters.
Marconi, radio waves, and the ionosphere
Authors: Beynon W. J. G. 
Published: February 2008

The life story of Marconi is too well documented to need detailed repetition, but there are certain facts about his early years which bear directly upon his quite remarkable success and indeed which relate to the early development of the subject of wireless telegraphy.Anyone looking at the early history of radio wave propagation and of Marconi's major role in it, cannot fail to be impressed with certain facts. Thus it is surely remarkable that in February 1896 when he first took his black wireless boxes to England, Marconi was only 21 years old and it is to be remembered that not only was he a very young man but he had had very little formal training in science. The second remarkable fact is that on 2 June 1896, i.e., within a few weeks of arriving in England (he was now just 22) he filed with the British Patent Office a provisional patent specification (the first of many) to safeguard his commercial interests in wireless communication. The third striking fact is that just one year later, in the summer of 1897, at the age of 23 he and his friends formed the Wireless Telegraph and Signal Company Limited (soon to be renamed the Marconi Wireless Telegraph Company) with an initial capital of £100,000. The shares in the new company were quickly subscribed; Marconi himself received £15,000 in cash and also held a large number of the shares.
Introduction
Authors: Hunsucker Robert D. , Greenwald Raymond A. 
Published: February 2008

This special issue of Radio Science contains papers presented at the URSI International Symposium on Radio Probing of the High‐Latitude Ionosphere and Atmosphere: New Techniques and New Results held in Fairbanks, Alaska, August 9–13, 1982. This symposium was sponsored by the International Union of Radio Science, Commissions G and H, the University of Alaska, USNC/URSI, U.S. Air Force Geophysics Laboratory, the National Science Foundation and Alascom, Inc.Ninety‐seven papers were presented at the symposium, of which some were already in the publication process and some were not submitted for publication in this issue of Radio Science. The papers were submitted to Radio Science following announcements in the symposium brochure, EOS, and Radio Science.
Cocorp seismic reflection profiling in the Ouachita Mountains of western Arkansas: Geometry and geologic interpretation
Authors: Nelson K. Douglas , Lillie Robert J. , de Voogd Beatrice , Brewer Jonathan A. , Oliver Jack E. , Kaufman Sidney , Brown Larry , Viele George W. 
Published: February 2008

COCORP seismic reflection profiling in the Ouachita Mountains of western Arkansas indicates that (1) Carboniferous foreland basin deposits within the Arkoma Basin thicken dramatically toward the south, reaching an aggregate thickness in excess of 12 km (4.5 s two‐way travel time) beneath the southern edge of the Frontal Thrust Zone, (2) evidence for northward directed low‐angle thrusting within this clastic sequence is prominent, with a probable decollement surface lying at or near the contact with underlying Early Paleozoic shelf carbonates, (3) beneath the Benton Uplift a sequence of discontinuous events defines a broad antiform cresting at approximately 7 km (2.8 s); this structure appears to mimic the anticlinorial shape of the Benton Uplift indicated by the surface outcrop pattern, (4) beneath the Southern Ouachitas, south dipping stratified events are observed to depths in excess of 14 km (5.0 s), (5) deeper in the section a prominent, gently north dipping reflection occurs at approximately 22 km depth (7.6 s) beneath the northern Coastal Plain/Southern Ouachitas.Extrapolation of data along strike in the Ouachita belt, and consideration of large‐scale structure observed in other collisional orogenic belts, suggest that the reflection events observed beneath the Benton Uplift represent Early Paleozoic shelf carbonates correlative with those that floor the Arkoma Basin to the north. This interpretation requires that the Early Paleozoic deep‐water sediments exposed in the core of the Ouachitas be allochthonous, and also implies significant basement uplift beneath the core zone. To the south, the prominent package of layered reflections occurring beneath the Southern Ouachitas and northern Coastal Plain indicates that a significant portion of the crust in that region is composed of imbricate sedimentary and/or metasedimentary strata. At relatively ‘shallow’ levels these strata are correlative with the Carboniferous flysch cropping out in the Southern Ouachitas, and at somewhat deeper levels, they are correlative with the Early to Middle Paleozoic deep‐water sediments exposed on the Benton Uplift.
Structural discordance between neogene detachments and frontal sevier thrusts, central Mormon Mountains, southern Nevada
Authors: Wernicke Brian , Walker J. Douglas , Beaufait Mark S. 
Published: February 2008

Detailed geologic mapping in the Mormon Mountains of southern Nevada provides significant insight into processes of extensional tectonics developed within older compressional orogens. A newly discovered, WSW‐directed low‐angle normal fault, the Mormon Peak detachment, juxtaposes the highest levels of the frontal most part of the east‐vergent, Mesozoic Sevier thrust belt with autochthonous crystalline basement. Palinspastic analysis suggests that the detachment initially dipped 20–25° to the west and cut discordantly across thrust faults. Nearly complete lateral removal of the hanging wall from the area has exposed a 5 km thick longitudinal cross‐section through the thrust belt in the footwall, while highly attenuated remnants of the hanging wall (nowhere more than a few hundred meters thick) structurally veneer the range. The present arched configuration of the detachment resulted in part from progressive “domino‐style” rotation of a few degrees while it was active, but is largely due to rotation on younger, structurally lower, basement‐penetrating normal faults that initiated at high‐angle.The geometry and kinematics of normal faulting in the Mormon Mountains suggest that pre‐existing thrust planes are not required for the initiation of low‐angle normal faults, and even where closely overlapped by extensional tectonism, need not function as a primary control of detachment geometry. Caution must thus be exercised in interpreting low‐angle normal faults of uncertain tectonic heritage such as those seen in the COCORP west‐central Utah and BIRP's MOIST deep‐reflection profiles. Although thrust fault reactivation has reasonably been shown to be the origin of a very few low‐angle normal faults, our results indicate that it may not be as fundamental a component of orogenic architecture as it is now widely perceived to be. We conclude that while in many instances thrust fault reactivation may be both a plausible and attractive hypothesis, it may never be assumed.
Orogeny and metamorphism: A model for deformation and pressure‐temperature‐time paths with applications to the central and southern Appalachians
Authors: Jamieson R. A. , Beaumont C. 
Published: February 2008

A model is presented for deformation, uplift, and exhumation in convergent orogens based on the following premises: (1) foreland basin subsidence monitors the distribution in time and space of overthrust loads added to an orogen; (2) the presence of an inherited rifted margin plays an important role in the subsequent history of an orogen by forming a basement ramp or buttress that must be surmounted in order for thrusts to advance on the craton; on the seaward side of this transition, up to 20 km of overthrusts can be accumulated without creating topography; (3) critical shape theory can be applied to orogens as a whole, allowing predictions to be made concerning dynamic balance between mass addition and loss, uplift, exhumation, and growth of topography; and (4) pressure‐temperature‐time (P‐T‐t) data can be used to reconstruct particle paths within the deforming orogen.Three states of overthrust orogens can be defined based on the relative rates of mass loss and mass addition, as monitored by the foreland. Rapid exhumation of metamorphic terranes is most likely in the ‘steady state’ where erosion balances accretion; a ‘constructive state,’ where mass addition is greater than mass loss, results in crustal thickening and initially little exhumation; a ‘destructive state,’ where mass loss outweighs mass addition, results in slow exhumation or subsidence of metamorphic rocks in the orogen depending on whether mass is removed by erosion or by extension. P‐T‐t data on peak metamorphism, pluton emplacement, uplift, exhumation, and cooling can be used in conjunction with data from the foreland to distinguish among these various states. The topography and strength of the inherited rifted margin play an important role in localizing zones of exhumation and uplift within the orogen. Application of this model to the central and southern Appalachians suggests that during the constructive phases of the Taconian and Acadian orogenies, overthrust loads accumulated mainly on the seaward side of the ocean‐continent transition as marked by the Bouguer gravity gradient. Between the Acadian and Alleghanian orogenies, the Appalachian orogen was probably in a steady state with uplift and exhumation of rocks in the orogen but little subsidence of the foreland or advance of thrusts toward the craton. The constructive stage of the Alleghanian orogeny achieved the critical topography necessary to drive crystalline thrust sheets over the craton; this resulted in widespread uplift and westward transport of older metamorphic rocks. Post‐orogenic unroofing of the southern Appalachians is compatible with the predictions of flexural models; the post‐orogenic unroofing history of the central Appalachians and Ouachitas probably reflects Mesozoic extension in these areas.
Constraints on uplift in the Franciscan Subduction Complex from apatite fission track analysis
Authors: Dumitru Trevor A. 
Published: February 2008

The Franciscan accretionary prism of California contains large belts of sediments that were subducted to depths of 10 to 30 km, metamorphosed there under high‐pressure, low‐temperature conditions, and later uplifted back to the surface. Reconnaissance apatite fission track data (40 samples) place constraints on the uplift histories of these and related lower‐pressure rocks. Franciscan metagreywackes from a few areas (parts of the Diablo Range, parts of the northern Coast Ranges' Eastern and Central belts) retain imprecise fission track evidence of cooling in the middle or Late Cretaceous(?). Using annealing temperatures of fission tracks in apatite and assuming 9°C/km subduction‐period geothermal gradients (estimated from blueschist mineralogy, paleogeothermal gradients in the Great Valley forearc basin, plate motion reconstructions, and other data), these rocks were uplifted through about the 12 km depth level at that time. Since some of these rocks were probably metamorphosed at depths of 15–25 km, substantial uplift had occurred by the middle or Late Cretaceous(?). Rocks from several areas retain fission track evidence of cooling in the early to middle Tertiary, including the Diablo Range (roughly 32 Ma), San Francisco (about 43 Ma), Chiles Creek in Napa County (about 45 Ma), and parts of the northern Coast Ranges' Eastern and Central belts (early to middle Tertiary). Great Valley forearc basin sandstones in the Clear Lake outlier retain evidence of cooling at roughly 35 Ma. Assuming 8.5°–10.5°C/km gradients, rocks from these areas were buried at least 8–10 km in the early or middle Tertiary and experienced at least a few kilometers of uplift at that time. In the northern Coast Ranges, two areas retain evidence of cooling in the late Tertiary (Coastal belt at roughly 20–10 Ma; Yolla Bolly Mountains in Eastern belt at roughly 20 Ma). Assuming 12°C/km gradients, they were buried at least 7 km in the late Tertiary and were uplifted at least a few kilometers at that time. The data thus suggest in general that uplift was occurring in various areas of the Franciscan forearc more or less continuously thoughout much of the period that subduction was occurring. This progressive uplift is most compatible with models where uplift is driven by synsubduction underplating of subducted sediments at the base of the accretionary prism, because those models predict continuing, long‐term uplift throughout the period of subduction but also allow episodicity in uplift as underplating rates and locations vary.Modern geothermal gradients in most Franciscan outcrop areas are moderately high (about 28°–35°C/km), a consequence of latest Cenozoic termination of subduction and development of the San Andreas transform margin. Franciscan and Great Valley samples show no fission track evidence of latest Cenozoic exposure to high temperatures (>100°C). Therefore they were only shallowly buried during the postsubduction period, and postsubduction uplift has been relatively minor (maximum of about 3.2 km).
Is the principal source of the secular variation of the Earth's magnetism within or without the Earth's crust?
Authors: Bauer L. A. 
Published: February 2008

In the papers on the “Distribution and the Secular Variation of the Earth's Magnetism,” presented before the Washington Philosophical Society in May, 1895, I showed that certain laws pertaining to the distribution of the magnetic elements over the earth's surface are similar to those pertaining to the secular variation as derived thus far. I shall refer to four of the deductions then made, as they will be found interesting in connection with some of the conclusions reached in this paper. These laws2 are:I. The minimum range in declination along a parallel of latitude occurs near the equator, generally increasing upon leaving the equator. II. The maximum range in inclination along a parallel of latitude occurs near the equator, generally diminishing upon leaving the equator. III. The minimum average secular change in declination along a parallel of latitude from 1780 to 1885 occurred near the equator, the values generally increasing upon leaving the equator. IV. The maximum average secular change in inclination along a parallel of latitude from 1780 to 1885 occurred near the equator, the values generally diminishing upon leaving the equator.