bluuebunny/crossref_metadata_2025 huggingface dataset:
Stellenwert von gegen TNF-α und CD20 gerichteten Biologika in der Therapie der Vaskulitis und des systemischen Lupus erythematodes
Authors: Walker Ulrich A. , Hasler Paul
Published: April 2008

Während die Hemmung von TNF-α bei Vaskulitis sowohl in vitro und in Tiermodellen Wirkung gezeigt hat, basiert die klinische Evidenz für die Effektivität der TNF-α Blockade bei den meisten Vaskulitiden im Wesentlichen auf Fallberichten und Fallserien. Randomisierte kontrollierte Studien haben bisher keine Überlegenheit eines anti-TNF-α Präparates beim M. Wegener und der Riesenzellarteritis gezeigt. Vielmehr ist im Kontext eines M. Wegener mit häufigeren und schweren Infektionen zu rechnen. Beim M. Behçet ist in refraktären Fällen die Behandlung der Uveitis und anderer Organmanifestationen mit einem TNF-α Hemmer aussichtsreich. Rituximab hat in einzelnen Fallberichten bei Vaskulitis eine gute Wirkung erzielt, Ergebnisse aus kontrollierten Studien sind bisher nicht verfügbar. Beobachtungsstudien lassen annehmen, dass bei refraktärem systemischem Lupus erythematodes und möglicherweise auch bei manchen Kleingefäßvaskulitiden mit Rituximab gute Ergebnisse erzielt werden können. Die unter TNF-α Blockade häufiger auftretenden schweren Infektionen setzen eine strenge multidisziplinäre Indikationsstellung und Risikoabwägung sowie eine Analyse der Verlaufsparameter voraus. Eine eingehende Information der Patienten über die Zeichen einer möglichen Infektion, sowie die Notwendigkeit einer umgehenden Abklärung und gegebenenfalls Therapie des Erregers ist notwendig. Wegen der Komplexität der Fragestellung und der Gefahr der Morbidität durch die Vaskulitis oder des systemischen Lupus erythematodes einerseits und deren Therapie andererseits sollten Biologika in der Therapie dieser Erkrankungen nur in dafür umfassend ausgestatteten Institutionen angewendet werden.
Irritable Bowel Syndrome - eine Standortbestimmung
Authors: Gschossmann J.M.
Published: April 2008

Das Reizdarmsyndrom (Irritable Bowel Syndrome IBS) stellt durch seine hohe Prävalenz und seinen chronischen Krankheitsverlauf ein bedeutendes Krankheitsbild für den niedergelassenen Arzt dar. Gekennzeichnet ist das IBS vor allem durch chronisch rezidivierende Abdominalschmerzen und Stuhlgangsunregelmässigkeiten, ohne dass in der Routinediagnostik eine dafür erklärende Pathologie gefunden werden kann. Die Ursachen für die Entstehung eines IBS scheinen multifaktoriell und sowohl intrinsischer als auch extrinsischer Natur zu sein. Im Zentrum der pathophysiologischen Alterationen stehen Veränderungen der gastrointestinalen Motilität sowie der viszeralen Schmerzperzeption und -verarbeitung. Die therapeutischen Optionen sind bis dato immer noch primär symptomatischer Natur. Nicht zuletzt bedingt durch potentielle Nebenwirkungen kausal ansetzender Therapiestrategien sind diese aktuell noch deutlich limitiert.
Onkologische Notfälle
Authors: Winterhalder R.C. , Müller B.
Published: April 2008

Das Wissen um die Ursachen und die Behandlung der wichtigsten onkologischen Notfallsituationen ist in der Praxis unerlässlich. Die obere Einflussstauung wird mit Chemo- oder Radiotherapie und Stenteinlage behandelt. Bei der Hyperkalzämie sind die intravenöse Rehydratation und die Gabe von Bisphosphonaten entscheidend. Die febrile Neutropenie ist ein hämatologischer Notfall und erfordert meist eine Hospitalisation und breite antibiotische Therapie. Die Rückenmarkskompression sollte frühestmöglich erkannt, mit Steroiden, Radiotherapie oder Chirurgie behandelt werden
ArcheoInt: An upgraded compilation of geomagnetic field intensity data for the past ten millennia and its application to the recovery of the past dipole moment
Authors: Genevey A. , Gallet Y. , Constable C. G. , Korte M. , Hulot G.
Published: April 2008

This paper presents a compilation of intensity data covering the past 10 millennia (ArcheoInt). This compilation, which upgrades the one of Korte et al. (2005), contains 3648 data and incorporates additional intensity and directional data sets. A large majority of these data (∼87%) were acquired on archeological artifacts, and the remaining ∼13% correspond to data obtained from volcanic products. The present compilation also includes important metadata for evaluating the intensity data quality and providing a foundation to guide improved selection criteria. We show that ∼50% of the data set fulfill reasonable reliability standards which take into account the anisotropic nature of most studied objects (potsherds), the stability of the magnetization, and the data dispersion. The temporal and geographical distributions of this sub–data set are similar to those of the main data set, with ∼72% of the data dated from the past three millennia and ∼76% obtained from western Eurasia. Approximately half of the selected intensity data are associated with at least an inclination value. To constrain the axial and full dipole evolution over the past three millennia requires that we avoid any overrepresentation of the western Eurasian data. We introduce a first‐order regional weighting scheme based on the definition of eight widely distributed regions of 30° width within which the selected data are numerous enough. The regional curves of virtual axial dipole moments (VADM) and of mixed VADM‐virtual dipole moments (VDM) averaged over sliding windows of 200 years and 500 years testify for strong contributions from either equatorial dipole or nondipole components. The computation of global VADM and mixed VADM/VDM variation curves, assuming an equal weight for each region, yields a dipole evolution marked by a distinct minimum around 0 B.C./A.D. followed by a maximum around the third‐fourth century A.D. A second minimum is present around the eighth century A.D. This variation pattern is compatible with the one deduced from earlier, more sophisticated analysis based on the inversion of both intensity and directional data. In particular, there is a good agreement among all VADMs and dipole moment estimates over the historical period, which further strengthens the validity of our weighting scheme.
Controls on temporal patterns in phytoplankton community structure in the Santa Barbara Channel, California
Authors: Anderson Clarissa R. , Siegel David A. , Brzezinski Mark A. , Guillocheau Nathalie
Published: April 2008

Characterizing phytoplankton succession in the context of physical and chemical processes is important for understanding the mechanisms driving phytoplankton species composition and succession. An understanding of these processes ultimately influences the ability to predict the contribution of phytoplankton to carbon cycling, the initiation and persistence of harmful algal blooms, and the ability to use satellites for the remote sensing of specific phytoplankton taxa important for biogeochemistry. A statistical analysis of 5 years (1998−2003) of phytoplankton pigment concentrations from the Santa Barbara Channel using empirical orthogonal functions reveals four dominant modes of variability that explain 80% of the variance in the pigment data set. The annual cycle is characterized by a switching from a mixed‐phytoplankton assemblage mode to modes dominated by either diatoms, dinoflagellates, or a combination of nano‐ and pico‐phytoplankton. The dominant two modes correspond to a prebloom condition that precedes upwelling conditions, with all identified phytoplankton groups present in low abundance and a diatom‐dominated upwelling state that develops following spring upwelling. In 2001, the EOF analysis indicated a transition toward more intense diatom blooms in spring and summer and fewer, large dinoflagellate blooms. This trend was corroborated by analyses of diagnostic pigments and CHEMTAX analysis and may be linked to an increase in local upwelling intensity between 2001 and 2003. Both spring diatom blooms occurring after 2001 were dominated by toxicPseudo‐nitzschiaspecies and led to significant marine mammal deaths in the channel in 2003.
Characterizing evapotranspiration over a meadow ecosystem on the Qinghai‐Tibetan Plateau
Authors: Gu Song , Tang Yanhong , Cui Xiaoyong , Du Mingyuan , Zhao Liang , Li Yingnian , Xu Shixiao , Zhou Huakun , Kato Tomomichi , Qi Peitong , Zhao Xinquan
Published: April 2008

To characterize evapotranspiration (ET) over grasslands on the Qinghai‐Tibetan Plateau, we examined ET and its relevant environmental variables in a Kobresia meadow from 2002 to 2004 using the eddy covariance method. The annual precipitation changed greatly, with 554, 706, and 666 mm a−1 for the three consecutive calendar years. The annual ET varied correspondingly to the annual precipitation with 341, 407, and 426 mm a−1. The annual ET was, however, constant at about 60% of the annual precipitation. About 85% annual ET occurred during the growing season from May to September, and the averaged ET for this period was 1.90, 2.23, and 2.22 mm/d, respectively for the three consecutive years. The averaged ET was, however, very low (<0.40 mm/d) during the nongrowing season from October to April. The annual canopy conductance (gc) and the Priestley‐Taylor coefficient (α) showed the lowest values in the year with the lowest precipitation. This study first demonstrates that the alpine meadow ecosystem is characterized by a low ratio of annual ET to precipitation and that the interannual variation of ET is determined by annual precipitation.
A new method for in situ soil gas diffusivity measurement and applications in the monitoring of subsurface CO2 production
Authors: Risk David , Kellman Lisa , Beltrami Hugo
Published: April 2008

Subsurface approaches to soil CO2 monitoring are becoming increasingly important for process studies in terrestrial carbon research. When used in conjunction with a diffusion model to determine CO2 production, subsurface methods require good estimates of effective soil gas diffusivity (De). Outlined here is a novel membrane probe and continuous flow system for in situ soil gas diffusivity measurements. Laboratory tests confirm performance across the range of CO2 diffusivities found in natural soils. Field tests were performed across a range of soil moisture contents by artificially hydrating eight soils over a period of three to seven days. These soils were representative of a range of textural classes in eastern Nova Scotia, Canada. The absolute values of diffusivity, and also the rate at which diffusivity decreased with increasing soil moisture content were typically quite different from model predictions. When applied to subsurface CO2 monitoring at two sites, the site‐specific diffusivity measurements greatly improved the accuracy of CO2 production estimates. We observed a consistent and close correspondence between calculated profile CO2 production and (independently measured) soil CO2 surface flux. The subsurface CO2 production estimates acquired using in situ gas diffusivity measurements allows detailed vertical profile resolution to be constructed over time. The majority of CO2 was generated at shallow depths, but periodic contributions from deeper depths were important, particularly towards the end of the growing season.
O2, Ar, N2, and 222Rn in surface waters of the subarctic Ocean: Net biological O2 production
Authors: Emerson Steven , Quay Paul , Stump Charles , Wilbur David , Knox Molly
Published: April 2008

Distributions of oxygen, argon, nitrogen, and radon in the upper ocean of the subarctic Pacific distinguish the fluxes controlling the oxygen mass balance during the summers of 1987 and 1988. The difference between the net O2 flux (in mmol m−2 d−1) to the atmosphere via gas exchange (32) and the integrated decrease with time (−14) is balanced by biological production (13‐17), air injection by bubble entrainment (5), and O2 flux to the thermocline −(0‐4). Nitrogen/argon and oxygen/argon ratios reveal that ˜15% of the oxygen supersaturation in summer is produced by air injection and ˜40% by biological production, with the rest induced by surface water warming. Our estimate of biologically induced oxygen production when translated stoichiometrically to nitrogen uptake agrees to within error estimates with both the particulate and dissolved nitrogen mass balances for the upper ocean determined in the SUPER program during the same time period. The oxygen mass balance requires a net carbon production in the euphotic zone of ˜140 mg C m−2 d−1 (PQ=1.5), which is 20–30% of the level of 14C primary production determined by SUPER investigators.
Field theory analysis of electrical networks
Authors: Popović B. D.
Published: April 2008

The paper describes an integral equation method for analysis of electrical networks as electromagnetic boundary value problems. This means that it is necessary to specify exact geometrical form of the network and the interconnecting conductors, as opposed to the classical network analysis, in which topological properties of the network are of sole interest. The network elements can be in the form of point (i.e., very small) generators, resistors, capacitors, inductors, and their combinations, or in the form of cylinders with distributed resistive and/or capacitive or inductive loading. Numerical results are in excellent agreement with experimental results far above the classical network theory frequency limit.
Complex source pulsed beams: Properties and applications
Authors: Heyman Ehud
Published: April 2008

Complex source pulsed beams (CSPB) are exact solutions of the wave equation which can be modeled by a time‐dependent source located at a complex coordinate point. With a proper choice of parameters, these wave fields are confined in beamlike fashion in transverse planes perpendicular to the propagation axis while confinement along the axis is due to temporal windowing. Because they have these properties, CSPBs are useful wave objects for generating and synthesizing highly focused transient fields and for local probing of a medium. Furthermore, CSPBs form a complete set of basis functions for a new exact angular spectrum expansion of source‐excited time‐dependent fields. This paper reviews the techniques pertaining to these applications and research directions.
Numerical study of scattering by rough surfaces with intermediate and large scale roughness
Authors: Ivanova K. , Michalev M. A. , Yordanov O. I.
Published: April 2008

The phase perturbation technique (PPT) and the Lynch variational method (LVM) are compared in the case of scalar waves scattered by one‐dimensional Dirichlet‐type Gaussian random rough surfaces at normal incidence. The attention is focused on surfaces whose irregularities are comparable to or larger than the wavelength. For this purpose, expressions representing the coherent scattering coefficient and the incoherent scattering cross section within the framework of the LVM are derived with no resort to the high‐frequency limit. The results show that the LVM curve lies between the PPT and the Kirchhoff approximation ones and under certain circumstances the PPT and the LVM coincide for all scattering angles. It is concluded from this evidence that a considerable part of the shadowing of the scattered field is due to diffraction from irregularities which cannot be considered flat over the wavelength scale.
A general formulation of applied potential tomography.
Authors: Berntsen Svend , Andersen J. Bach , Gross Eugene
Published: April 2008

Reconstruction of the conductivity of a medium from a set of known values of the boundary potential and boundary normal current is described. The geometry is general, two or three dimensional. The method is applied to two cases, a circular medium and an infinite medium under a plane. In both cases the conductivity is found as an expansion on a system of orthogonal functions. In a linear approximation the conductivity may explicitly be reconstructed. The problem is an ill posed one, the condition numbers are found. Some numerical examples are included.
Dominant mode power leakage from printed‐circuit waveguides
Authors: Shigesawa H. , Tsuji M. , Oliner A. A.
Published: April 2008

This study is concerned with a new type of dominant mode power leakage from uniform lengths of printed‐circuit waveguides, such as microstrip line, slot line, and coplanar waveguide. These leakage effects, which are presently not recognized and can therefore be unexpected as well as undesired, occur at higher frequencies, and are therefore important for millimeter‐wave integrated circuits and high‐speed circuits. The cross talk and coupling that result can ruin the performance of a complex, high‐density circuit unless the leakage effects are understood and controlled. The leakage effects reported here occur on uniform lengths of printed‐circuit waveguide on which the dominant mode is purely bound at ordinary microwave frequencies but becomes leaky at higher frequencies; they appear in addition to the leakage produced by conversion into surface waves at various discontinuities. The nature of the leakage is described, and numerical results are presented for several structures as illustrations of the variety of ways this type of leakage can arise.
Direct determination of the underlying Lie algebra in nonlinear optics
Authors: Arnold J. M.
Published: April 2008

It is shown that the equations of resonant nonlinear optics can be studied entirely within the framework of an underlying Lie algebra, in which the 2x2 su(2) Hamiltonian and density matrices of the quantum mechanical description of the atomic system transform directly to the 2x2 sl(2,R) matrices of the Ablowitz‐Kaup‐Newell‐Segur (AKNS) scheme, and the AKNS eigenvalue is introduced naturally as a free parameter. The Lie algebra sl(2,R) is also the symmetry algebra of transformations between equivalence classes of AKNS systems under SL(2,R) gauge transformations. The Lie algebra formalism condenses much algebraic manipulation, and provides a natural basis for the perturbation theory of “nearly integrable” nonlinear wave systems.
Phase space methods for radiation from large apertures
Authors: Steinberg B. Z. , Heyman Ehud , Felsen L. B.
Published: April 2008

Coping with complex wave phenomena, especially at high frequencies, requires detailed understanding of the spectral as well as the configurational behavior of the fundamental wave constituents employed in field synthesis. These aspects can be treated in a phase space that covers simultaneously the configurational and spatial wave number variables for the time harmonic regime, with the addition of time and frequency variables for the transient regime. Although it represents the most general format, the full phase space constructed in this manner may not be the most convenient for tracking physical observables. Better suited may be reduced or partial phase space representations based on the spectral decomposition of only some of the space‐time variables. Various choices in the reduction lead to alternative representations with different physical content, and to corresponding alternative parametrizations of the radiation and propagation process. As part of a general study in both the frequency and time domains, the present paper concentrates on time harmonic spatial and spectral representations that contain sampling windows. Such sampling, either discrete or continuous, formalizes the localization that plays an important role in high frequency wave phenomena. The analytical machinery, together with asymptotic constructs that provide physical interpretation in terms of beams, is developed here for radiation from plane aperture sources.
Proton cyclotron echoes at 3ƒH and 4ƒH resonances
Authors: Chen G. M. , Horita R. E.
Published: April 2008

A new class of proton cyclotron echoes observed on topside sounder ionograms is presented; these echoes occur at frequencies above the electron plasma frequency and at the third and fourth harmonics of the electron cyclotron frequency, 3ƒH and 4ƒH. Some features are noted such as the dependence on low dip angle values. It is suggested that the 3ƒH and 4ƒH proton cyclotron echoes may be generated by wave‐particle interaction between the electrostatic waves and the protons that are both energized by the dipole antenna on Alouette II, ISIS I, or ISIS II.
HF multipath dispersion measurements using cepstral signal processing
Authors: Eken Faik , Atmaca Fikri , Hepsaydir Erol
Published: April 2008

A technique for measuring ionospheric echo arrival times and strengths is described. The technique uses ordinary HF‐SSB transceivers and an easy to generate probe signal. It is based on the cepstral signal processing tool for deconvolution. Identification of ionospheric echoes in a received sky wave signal was viewed as a deconvolution problem, and the cepstral transformation was used to obtain information about the multipath profile of the channel. Field tests were carried out where multipath characteristics of the ionospheric channel was measured using this technique.
Test functions for the moment method which yield the minimum mean square error
Authors: Shamansky H. , Yang C.
Published: April 2008

The method of moments has found extensive applications in the solution of a wide class of electromagnetic problems. Additionally, there are a number of basis functions which have found favor and with them different types of testing methods. This work examines the selection of test functions, given a selected set of basis functions, which serve to minimize the mean square error. These test functions will guarantee equal or lesser error compared with any other test function. Additionally, these test functions provide a monotonic improvement of the approximation as the increase in the order of the system. Hence while these test functions require the application of the differential or integral operator one additional time, they provide an absolute lower bound to the mean square error in the approximation and a means to systematically improve accuracy with each increase in the order of the unknowns.
Ground radiation scattered from feed support struts: A significant source of noise in paraboloidal antennas
Authors: Landecker T. L. , Anderson M. D. , Routledge D. , Smegal R. J. , Trikha P. , Vaneldik J. F.
Published: April 2008

The struts supporting the feed or subreflector of a symmetrical paraboloidal antenna generate sidelobes around cones of wide opening angle by scattering energy from the plane wave leaving the reflector. On the basis of simple assumptions about these “scatter cone” sidelobes, an approximate formula is derived to predict their level relative to the main beam; it is tested against published measurements. The noise added to the antenna when the scatter cone sidelobes receive radiation from the ground is calculated, and this mechanism is seen as a significant contributor to antenna noise. The use of struts of triangular cross section in place of circular ones redirects sidelobe energy away from the back hemisphere of the radiation pattern to the front hemisphere. For most antenna pointings these sidelobes will not strike the ground, and antenna noise temperature is likely to be reduced. Radiometric measurements at 1420 MHz have been made using a 9‐m antenna equipped with struts of various cross sections and sizes. These measurements have been used to isolate the strut contribution to antenna noise, and have verified that this contribution can be reduced by using triangular struts. The strut contribution to antenna noise is calculated as a function of zenith angle of the main beam of the antenna. Triangular struts are superior to circular ones at all main‐beam zenith angles. When three struts are used, the upright Y configuration of the tripod is better than the inverted Y.
Millimeter‐wave radar scattering from snow: 2. Comparison of theory with experimental observations
Authors: Ulaby Fawwaz T. , Haddock Thomas F. , Austin Richard T. , Kuga Yasuo
Published: April 2008

Using a truck‐mounted platform, backscatter measurements were made at 35, 95, and 140 GHz for a variety of snow conditions to evaluate the radar response to incidence angle, surface roughness, and liquid water content. Good agreement was obtained between the experimental observations and theoretical calculations based on the numerical solution of the radiative transfer equation presented in the preceding paper. A notable exception is when the snowpack is in the refreezing phase of the diurnal cycle, during which the snowpack is characterized by a dry surface boundary with wet layers underneath. To accommodate this type of condition, a hybrid first‐order numerical solution is proposed. The hybrid approach provides excellent agreement between theory and experiment.
Packets of cyclotron waves induced by electron beam injection from the space shuttle 1. Linear theory
Authors: Mourenas D. , Béghin C.
Published: April 2008

Measurements of high‐frequency wave emissions were made on board Spacelab 1 during artificial electron beam injection from the shuttle bay. The most unusual kind of spectrum is considered here, i.e., packets of electron cyclotron waves occurring at successive harmonics of the plasma frequency. Using a linear theory, it is shown that the emissions consist of the well‐known electronic Bernstein modes, which are thought to be generated by an interaction between the neutralization return current and the ambient ionospheric plasma, and not directly by the primary beam. A simplified model of the electron velocity distribution function of the return current is developed. Then, a numerical resolution of the dispersion equation is undertaken, with the experimental constraint that the waves have to fit the “rendezvous” condition with the instruments flying on board the orbiter. The observed electron cyclotron emissions, as well as their amplitude modulation around the fundamental of the plasma frequency, are found to be easily explained by such a linear theory. A companion paper [Mourenas and Béghin, this issue] will propose a nonlinear treatment of the same mechanism, which is thought to be responsible for the production of upper harmonic packets.
Ionospheric equivalent slab thickness and its modeling applications
Authors: Fox Matthew W. , Mendillo Michael , Klobuchar John A.
Published: April 2008

A data base of equivalent slab thickness observations covering nearly two complete solar cycles has been obtained at a mid‐latitude site (Hamilton, Massachusetts). The mean variations are described both qualitatively, in terms of changes to profile shapes, and quantitatively, in terms of a simple numerical model. A number of currently available ionospheric models have also been used to predict values of slab thickness (τ = total electron content/Nmax) over Hamilton, Massachusetts, and comparisons of these values with those observed provided validation of the models. Adjustments to the model profiles were suggested in a couple of cases.
Comments on the role of oceanic biota as a sink for anthropogenic CO2 emissions
Authors: Smith S. V. , Mackenzie F. T.
Published: April 2008

In a letter published in Issues in Science and Technology, Revelle [1990] comments that one of the principal sinks for atmospheric carbon is probably phytoplankton production in the ocean. Revellegoes on to state (p. 21‐22).

This process (that of phytoplankton growth and death, followed by settling of organic carbon out of the surface ocean to depth; the so‐called “biological pump”) could account for the sequestration of at least a billion tons of carbon of the total of five billion or six billion produced annually by fossil fuel consumption and biological activity.
Methane emission from rice fields as influenced by solar radiation, temperature, and straw incorporation
Authors: Sass R. L. , Fisher F. M. , Turner F. T. , Jund M. F.
Published: April 2008

Since rice fields emit methane, an important contributor to the increasing greenhouse effect, one of our goals is to characterize factors that influence this emission. To create a range in plant and soil temperature, solar radiation, and microbial substrate, rice fields were planted on April 13, May 18 and June 18 of 1990 on silty clay soils near Beaumont, Texas. Immediately prior to planting, one half of each field was supplemented with 6000 kg ha−1 of disc‐incorporated grass straw (Paspalum spp.). Methane emission rates were measured throughout the cultivation period. Methane emission rates varied markedly with planting date and straw addition. The highest emission rate originated from the earliest planted straw‐supplemented field. In general, methane emission decreased with the later plantings that received less solar radiation. Annual emission rates of methane and rice grain yield from individual fields were positively correlated with accumulated solar radiation for both straw‐incorporated and control plots. Straw incorporation resulted in decreased grain yield and increased methane emission in all three fields. Diel variation of methane emission strongly correlated with temperature. The activation energies for methane production, obtained from laboratory soil incubations, and methane emission, obtained from diel field measurements, were approximately the same: 88–98 kJ mol−1 for production and 87 kJ mol−1 for emission.
A general channel model for RF propagation through structured ionization
Authors: Dana Roger A. , Wittwer Leon A.
Published: April 2008

The second‐order statistics of transionospheric RF scintillation are described by the two position, two‐frequency, two‐time mutual coherence function of the received signal. The derivation of the mutual coherence function from Maxwell's equations requires a model for the temporal and spatial variations of the electron density fluctuations in the ionosphere. Under Taylor's frozen‐in hypothesis the electron density fluctuations are described as a rigid structure that drifts past the line of sight. There is then a deterministic relationship between spatial and temporal fluctuations in the electron density. This model is accurate when the ionization has formed a thin layer of striations aligned with the geomagnetic field lines. Before striations have formed or when there are multiple scattering layers in the ionosphere with different relative velocities, a turbulent model may be more appropriate. In the fully turbulent case the spatial and temporal fluctuations of the electron density are uncorrelated. Reality should lie somewhere between these two limiting models. This paper describes a general model which varies smoothly between the frozen‐in and turbulent models. Examples are given which illustrate the effects on the received signal as the channel varies from the turbulent to frozen‐in models.
The role of the ring current in the generation or inhibition of equatorial F layer irregularities during magnetic storms
Authors: Aarons J.
Published: April 2008

For the equatorial ionosphere in years of high solar flux the F layer parameters are such that irregularities are produced almost every night in specific months. The question that has emerged is why are there nights in these months without irregularities. The hypothesis advanced is that for this period, one must look not for external seeding mechanisms but for inhibiting factors. The ring current during magnetic storms appears to play a leading role directly or indirectly in establishing the conditions necessary for equatorial F layer irregularity generation and inhibition. The hypothesis advanced is that for a particular ionospheric propagation intersection, the local time when the peak excursion of the ring current occurs (its decay from maximum negative values), affects the equatorial electric field and therefore the height of the F layer. Using data from a number of magnetic storms with dates ranging from December 1971 to November 1981 primarily in years of high solar flux, the following categories were found. If the maximum ring current energy as shown by Dst occurred during the midnight to postmidnight time period, irregularities were generated. If the maximum Dst, the period before recovery set in, occurred in the early afternoon, irregularities were inhibited. If the maximum occurred around sunset or shortly after sunset, then there was no effect on the generation of irregularities that night. While the ideas on positive and negative correlation with magnetic indices have been shown in many early references, the importance of local time and its relationship with the maximum ring current energy have not been emphasized. The use of widely spaced equatorial data from Manila and Huancayo allowed for contrasting reactions for the same storm and for validation of the hypothesis for the months and solar conditions stated. For other periods, when occurrence of irregularities is lower, the effect on layer height may be only one factor in setting conditions for the generation of irregularities.
Upgrades for efficient three‐dimensional ionospheric ray tracing: Investigation of HF near vertical incidence sky wave effects
Authors: Reilly Michael H.
Published: April 2008

An earlier, three‐dimensional ray‐tracing program has been upgraded to include magnetic field effects, variable step sizes, improved propagation loss computation, and efficient homing and focusing computation algorithms. A combination of fourth‐order Runge‐Kutta and Adams methods, with error control and extension to variable step size, has been included. The program is applied to an investigation of high‐frequency near vertical incidence sky wave (NVIS) effects. Model simulations of oblique ionograms are found to be consistent with experiment. Implications for NVIS geolocation are discussed.
Applications for high‐accuracy digital ionosonde data
Authors: Paul Adolf K.
Published: April 2008

Most of the information about the near‐Earth's environment up to the height of the F region maximum is obtained by ionosondes. The height range in question is below the altitude of long‐lasting satellites. In addition, satellite measurements cannot provide the temporal and spatial resolution for an unambiguous sampling of the dynamic phenomena of the ionosphere, unless a large number of satellites with identical equipment are placed in proper orbits. Similar remarks apply to balloon and rocket observations. The advance of digital ionosondes permits the measurement of new quantities (for example, echo phase) and of classical parameters (for example, delay time and signal strength of an echo) with much improved precision. The analysis of such data in turn provides more details and higher accuracy of properties of the ionosphere. This will be demonstrated here for electron density profile parameters, Doppler frequencies, angle of arrival measurements, and other quantities.
Ionospheric slab thickness in middle and low latitudes
Authors: Davies K. , Liu X. M.
Published: April 2008

The equivalent slab thickness of the ionosphere at 15 stations in middle and low latitudes was studied to determine its dependence on solar cycle and location. The data were grouped by season. The following are the major conclusions. There appears to be little or no geographical, or geomagnetic, dependence. The slab thickness varies approximately linearly with the 12‐month smoothed values of the 10.7‐cm solar radio flux. In middle latitudes the winter midnight thickness is essentially independent of the flux, whereas in summer and equinox the midnight thickness increases with increase of solar flux. The noon thickness increases with increase of solar flux in all seasons. The zero‐order Fourier coefficients for the diurnal curves at all 15 stations were expressed as linear functions of the 10.7‐cm flux. The higher harmonic coefficients showed no appreciable dependence on solar flux. The pronounced predawn increase in slab thickness is caused by low values of the maximum electron density, not by increase of total electron content.
Double diffraction at a coplanar skewed edge configuration
Authors: Ivrissimtzis Leonidas P. , Marhefka Ronald J.
Published: April 2008

The problem of double edge diffraction in the near‐field region of a coplanar skewed edge geometry, illuminated by a plane wave, is studied asymptotically via an extended spectral theory of diffraction approach. The resulting uniform dyadic double edge diffraction coefficient is expressed in terms of a universal integral (the generalized Fresnel integral) and remains valid when any one of the edges is within the transition region of a singly diffracted wave, while it asymptotically reduces to the ordinary geometrical theory of diffraction double diffraction coefficient elsewhere. Comparisons with method of moments computations for radiation patterns of sources in the vicinity of flat plate structures demonstrate the validity of the asymptotic approximation.
High‐frequency scattering by a smooth coated cylinder simulated with generalized impedance boundary conditions
Authors: Syed Hasnain H. , Volakis John L.
Published: April 2008

Rigorous uniform geometrical theory of diffraction (UTD) diffraction coefficients are presented for a convex coated cylinder simulated with generalized impedance boundary conditions. In particular, ray solutions are obtained which remain valid in the transition region and reduce uniformly to those in the deep lit and shadow regions. These involve new transition functions in place of the usual Fock‐type integrals, characteristic to the impedance cylinder. A uniform asymptotic solution is also presented for observations in the close vicinity of the cylinder. As usual, the diffraction coefficients for the convex cylinder are obtained via a generalization of the corresponding ones for the circular cylinder.
Improved asymptotic expansions of time domain antenna current
Authors: Chen Kenneth C. , Warne Larry K.
Published: April 2008

An improved asymptotic series for an integral representing transient current on an infinite cylindrical antenna caused by a step voltage source, applied at the gap, is given. A generating function for obtaining the general coefficient is derived. The method is applicable to types of integrals whose integrands consist of a product of a slowly varying function and a rapidly varying function. A simple accurate formula obtained before, by the averaging method, is shown to be the leading term of this infinite series. The averaging used in evaluating integrals is shown to improve the accuracy of the leading term.
Error analysis of image reconstruction by a synthetic aperture interferometric radiometer
Authors: Ruf Christopher S.
Published: April 2008

An error analysis is presented for the image reconstruction algorithm currently employed by the electronically steered thinned array radiometer aircraft instrument. This instrument samples components of the Fourier transform of the brightness temperature distribution at 1.4 GHz. Sources of error are identified, including systematic offsets and stochastic noise in the measurements, errors in the interference pattern antenna calibration, multipath scattering from the antenna support structure, mutual coupling between nearby array elements, and variations in the antenna patterns of the array elements. These errors are shown to produce artifacts in the image which appear as “streaks” running along the instrument flight line. Possible hardware corrections are discussed. These include a reduction in the profile of the antenna support structure and a decoupling of adjacent and other nearby array elements using corrugated “skirts.” Also discussed are several image enhancement techniques which detect and correct for some of the streaking. These techniques include a renormalization of the interference patterns based on the measured element patterns, a perturbation based interpretation of image contrast, and a covariance analysis of noise present in the image.
Denitrification in continental shelf sediments has major impact on the oceanic nitrogen budget
Authors: Christensen John P. , Murray James W. , Devol Allan H. , Codispoti Louis A.
Published: April 2008

Denitrification rates in sediments within the oxygen deficient waters off Mexico and from the Gulf of Maine were investigated on the basis of interstitial nutrient profiles. Nitrate fluxes into the sediments were calculated from gradients across the sediment‐water interface and vertical molecular diffusion coefficients and averaged 0.151 (Mexico) and 0.0920 (Gulf of Maine) pmol NO−3 cm−2 s−1. These are minimum values, since these gradients may have been underestimated. In the Gulf of Maine, bottom water irrigation by macrobenthos increases the nitrate supply well above this estimate. In addition, only 15‐22% of the expected ammonium is present in Gulf of Maine sediments perhaps because of removal by a rapid coupling of nitrification with denitrification. This large apparent loss of the regenerated ammonium appears to be ubiquitous in shelf sediments with oxygenated bottom water. The global denitrification rate in continental shelf sediments was reassessed to be >50 Tg N yr−1 (1 Tg = 1012 g), demonstrating that sediments are an important sink for oceanic nitrogen. Globally, current nitrogen losses from the oceans may exceed inputs by 60‐90 Tg N yr−1. Over the glacial‐interglacial cycle the global sedimentary denitrification rate probably varied commensurately with the changing continental shelf area. An oscillating oceanic nitrogen budget over these time scales could occur given the sequence of (1) scouring and dumping of terrestrial nitrogen into the oceans during glacial advance, (2) removal of oceanic combined nitrogen to the atmosphere by denitrification following glacial retreat, and (3) reincorporation of this N into terrestrial biomass during the interglacial period.
C/P ratios in marine detritus
Authors: Peng Tsung‐Hung , Broecker Wallace S.
Published: April 2008

Until reliable procedures have been developed to preserve the phosphorus contained in particulate matter captured by in situ pumps and sediment traps and until these procedures are applied over a wide range of locations and depths in the sea, indirect methods will have to be used to determine the C/P ratio in marine detritus. We have taken two such approaches: (1) the use of C/N ratios for particulates captured in the upper thermocline in conjunction with 02/P and N/P ratios obtained from deconvolutions of ocean chemical data and (2) regression along isopycnals in the deep‐sea waters free of fossil fuel CO2. While neither approach yields a definitive answer, both suggest that a value of 127 carbon atoms per phosphorus atom would be a more appropriate interim value than that of 106 adopted long ago by A. C. Redfield and his associates.
Radiolarian flux and seasonality: Climatic and El Nino response in the subarctic Pacific, 1982–1984
Authors: Takahashi Kozo
Published: April 2008

Seasonal flux distributions of numerically dominant radiolarian species were studied using Particle Flux (PARFLUX) 1982‐1984 high‐resolution, time series sediment trap samples recovered from the eastern subarctic Pacific Station Papa (water depth: 4,200 m) in the Gulf of Alaska. Flux patterns of several major radiolarian species showed more temporally restricted seasonal maxima than those of siliceous phytoplankton groups, suggesting more confined seasonal flux signals than those of siliceous phytoplankton. These species showed significant flux reduction from year 1 to year 2 associated with an El Nino event, as did siliceous phytoplankton. On the other hand, fluxes of three major radiolarian subgroups and some other radiolarian species showed little change in timing or amplitude of seasonal flux patterns from year 1 to year 2 except for the presence/absence of summer maxima. This type of radiolarian flux signal is a reflection of recurring large changes in seasonal environmental conditions and, to a lesser extent, of response to the deviations of interannual amplitudes. Two generic pairs of radiolarian fluxes showed temporal niches which may have evolved due to dietary preferences. Biological competition may take place among species from different genera but not within a genus. Fluxes of juvenile and adult forms of two Pterocanium species were compared in order to understand their reproductive cycles. Reproduction appears to occur sporadically throughout most of the year and nonsynchronously among population members. The longevity of Pterocanium species was estimated to be several weeks. There are two separate radiolarian sinking processes; accelerated sinking via aggregates and discrete sinking. Smaller‐sized species tend to sink faster due to aggregate incorporation than larger ones. Radiolarians are considered a good measure of productivity. The contribution of phaeodarians can be as high as 10% or more in total opal flux. Large‐sized phaeodarian specimens are involved in this high percentage and play a significant role in silica redistribution within the water column since they dissolve quickly.
The occurrence of peroxyacetyl nitrate over the Atlantic Ocean east of North America during WATOX‐86
Authors: Bottenheim Jan W. , Gallant Alan J.
Published: April 2008

Measurements of PAN (peroxyacetyl nitrate) over the western Atlantic Ocean, collected during four aircraft missions in January 1986, are reported. The observed concentrations at circa 150‐200 km off the coast while the general airflow was directly from the coast to the sampling location were surprisingly low, ranging from 20‐510 ppt in the planetary boundary layer (PBL) and 25‐230 ppt in the free troposphere (FT). Most PAN was found in pollution plumes in the PBL. With the exception of one small plume, the level in the FT appeared to be indicative of a continental background air mass. It is speculated that the low average PAN level in the PBL was due to efficient dilution of the air, transported over the open ocean, thereby preventing extensive oxidation of NOx into PAN and inorganic nitrates, or alternatively to the preferential production of other not identified organic nitrates. Averaged over the total data set the PAN mixing ratio was determined at 184 ± 115 ppt and 94 ± 48 ppt for the PBL and FT, respectively. Comparison with NOx data suggests that for flux calculations most of the N flux in the PBL can be assumed to be in the form of NOx (≡ NO + NO2), but a similar assumption for FT flow would lead to an underestimation of total N flux.
The P wave velocity structure near the base of the mantle
Authors: Wright C. , Muirhead K. J. , Dixon A. E.
Published: April 2008

Travel times from 16 events recorded at two temporary networks of short‐period seismometers deployed across Australia have been used to study the P wave velocity structure of the mantle below depths of 1700 km. The slowness‐distance curve derived from these times shows small deviations from the slownesses predicted from the preliminary reference earth model of Dziewonski and Anderson [1981] that may be significant. The most important feature is a rapid decrease of more than 0.5 s/degree between distances of 85° and 88°. Velocity filtering of seismograms from 5 nuclear explosions in Kazakh recorded at these Australian networks indicates the presence of two arrival branches at distances between 83° and 91° whose slownesses differ by 0.40 to 0.55 s/degree and which intersect at a distance of 87°. Processed P wave seismograms from the Yellowknife array in Canada also indicate the presence of a similar phenomenon in the same distance range in two separate regions. The results can be explained by a widespread rapid or sharp increase in velocity of 2.5 to 3.0% about 200 km above the core mantle boundary.
The distribution of geothermal fields on the Juan de Fuca Ridge
Authors: Crane Kathleen , Aikman Frank , Embley Robert , Hammond Steve , Malahoff Alexander , Lupton John
Published: April 2008

Near bottom water temperatures were mapped along 400 km of the strike of the Juan de Fuca Ridge as part of a combined Sea MARC/Seabeam experiment to image the variability of morphology and structure along a spreading center segment. The water temperature data collected by a continuously towed thermistor chain, in addition to salinity data, indicate that there are four geothermal areas spaced at distances of 100 km from each other south of the Cobb propagator and one field just to the north of the propagator on the Endeavor Ridge segment. Each thermal region is located above a morphological dome on the spreading center. These domes are an average of 100–200 m shallower than the rest of the axis. The structure of bottom water suggests that the geothermal regions are on average 20 km long and that the heat from these fields raises the temperature in the water column by a minimum of 0.06°C up to 300 m above the bottom. Two simple models are used to estimate the heat flux associated with these features.