bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient Construction of Tri‐ and Tetracyclic Heterocycles from Linear 1,6‐Dienes by a Domino Reaction
Authors: Hu Yimin , Song Fengfa , Wu Fenghua , Cheng Dong , Wang Shaowu
Published: February 2008

Tri‐ and tetracyclic heterocycle systems were constructed by a palladium‐catalyzed domino reaction of linear 1,6‐dienes that contain acryl groups with aryl halides through C–C coupling and aromatic CH functionalization. Three different acrylamides have been shown to be very active for the reaction. The substituents on the aryl halides could be ethoxycarbonyl, ketyl, chloro, sulfonyl, cyano, etc. Thus, the ready accessibility of the starting materials, the wide range of compatibility of substrates including both dienes and aryl halides, and the generality of this process make the reaction highly valuable in view of the synthetic and medicinal importance of these kinds of heterocycles.
Altlastsanierung mit Huminstoffsystemen. Prinzipien der Natur in der Umwelttechnologie
Authors: Stottmeister Ulrich
Published: February 2008

Ein mit hochtoxischen Schwelwässern aus der Braunkohlenchemie gefülltes Tagebaurestloch (“Phenolsee”) wurde in einem interdisziplinären Projekt durch die gezielte Unterstützung der natürlichen Selbstreinigungskräfte zu einem ungefährlichen Ökosystem mit klarem Wasser. Grundlage des Erfolges war das Wissen um die Entstehung und die Eigenschaften von natürlichen Huminstoffsystemen und deren Funktionen in natürlichen Kreisläufen und Prozessen. Gealterte Deponiewässer der Carbochemie enthalten vergleichbare chaotisch strukturierte Makromoleküle.
Apoptose verhindert Osteoporose
Authors: Jacoby Petra
Published: February 2008

Neue Untersuchungen decken auf, wie Östrogen vor Knochenschwund schützt: Das Hormon stiftet knochenfressende Osteoklasten zum zellulären Selbstmord an und unterbindet dadurch einen übermäßigen Abbau von Skelettmaterial.
Ein Prosit dem Wein‐Genom
Authors: Groß Michael
Published: February 2008

Das Sequenzieren vollständiger Genome ist inzwischen so schnell und erschwinglich, dass bereits die ersten Sequenzen einzelner Personen vorliegen und die Forscher die Genomik der Taufliege Drosophila inzwischen im Dutzendpack untersuchen. Nicht ganz so schnell mithalten konnte jedoch die Pflanzengenomik. Die Weinrebe Pinot Noir, deren Genom im vergangenen Jahr entschlüsselt wurde, war erst die vierte Blütenpflanze, der diese Ehre widerfuhr.
The auxetic properties of a network of bending beams
Authors: Koenders M. A. , Gaspar N.
Published: February 2008

The mechanical response of an aggregate of bending beams in two dimensions is investigated. The special mission of this paper is to find auxetic properties (negative Poisson's ratio). A formal correspondence between a contacting granular material and a medium consisting of bending beams is established. The former has already been studied in previous papers and the results can be taken over quite readily. Among the results it is reported that networks of beams that are stubby auxetic behaviour is naturally present, even in a mean field approach. For heterogeneous materials the role of local anisotropies is highlighted as a possible mechanism underlying an overall negative Poisson ratio. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Die Seile des neuen Wembley‐Stadions
Authors: Bechtold Martin
Published: February 2008

Das Wembley‐Stadion ist das Stadion der englischen Fußballnationalmannschaft. Außerdem wird es für Pokalendspiele sowie für Musik‐ und Leichtathletikveranstaltungen genutzt. Es hat somit außerordentlich repräsentativen Charakter. Dieser Ort ist unter anderem mit einem der umstrittensten Tore des Fußballs (1966) nicht mehr aus dessen Geschichte wegzudenken. Der im März 2007 eingeweihte, imposante Neubau besitzt das Potential, die ruhmreiche Geschichte dieses bedeutenden Ortes würdevoll fortzuführen.

Die Seile des neuen Wembley‐Stadions spielen eine wichtige Rolle im Tragwerk des Daches. Zur Umsetzung des Entwurfs waren architektonisch anspruchsvolle Sonderlösungen erforderlich, die im Rahmen der Tragwerksplanung und deren Umsetzung gemeinsam mit dem Seilhersteller ausgearbeitet wurden.
Stegkrüppeln bei voll‐ und teilperforierten Trapezprofilen
Authors: Misiek Thomas , Albiez Matthias
Published: February 2008

Trapezprofile aus Stahl oder Aluminium können am Auflager oder unter Einzellasten aufgrund ihrer Dünnwandigkeit durch Stegkrüppeln versagen. Eine aus Gründen der Schalldämpfung vorgenommene Perforation der Stege reduziert den Widerstand gegen Stegkrüppeln. Der Einfluss der Perforation kann durch Abminderung der nach DIN 18807‐1 oder DIN 18807‐6 ermittelten Tragfähigkeit mit einem Faktor Cp für vollperforierte Profile oder Ctp für teilperforierte Stege ermittelt werden.
Successful field capture techniques for free‐ranging argali sheep (Ovis ammon) in Mongolia
Authors: Kenny David , DeNicola Anthony , Amgalanbaatar Sukhiin , Namshir Zundui , Wingard Ganchimeg , Reading Richard
Published: February 2008

Argali sheep (Ovis ammon) are the world's largest wild sheep and are threatened throughout their range in Mongolia. Little is known about the ecology of this highly cursorial species. This project was initiated to develop safe capture techniques in order to learn more about the ecology of argali in the Ikh Nartiin Chuluun Nature Reserve in southeastern Mongolia by using radiotelemetry. To our knowledge no one had ever successfully live‐caught a free‐ranging argali. We developed three techniques for capturing argali. From 2003 to 2007 we hand captured 65 argali lambs, losing one (our first capture) to maternal neglect because we stayed too long in the area and a second that was euthanized after being accidentally injured by a horse. Between 2000 and 2003 we captured six argali by darting, losing one ewe to an abdominal infection after a misplaced dart. Finally, between 2002 and 2007 we captured 32 argali by drive‐netting. We lost one ewe to over‐exertion after a long drive. The remaining 31 animals captured by drive‐netting did not appear to suffer any immediate effects (still alive in 30 days). This report will discuss the strengths and weaknesses for each of these capture techniques. Zoo Biol 27:137–144, 2008. © 2008 Wiley‐Liss, Inc.
Styles and regimes of orogenic thickening in the Peloritani Mountains (Sicily, Italy): new constraints on the tectono-metamorphic evolution of the Apennine belt
Authors: VIGNAROLI GIANLUCA , ROSSETTI FEDERICO , THEYE THOMAS , FACCENNA CLAUDIO
Published: February 2008

The Peloritani Mountains constitute the Sicilian portion of the Calabria–Peloritani Arc (Italy), a tectono-metamorphic edifice recording the history of the subduction–exhumation cycle during Tertiary convergence between the African and European plates. Here, we describe the kinematic and the petrological characteristics of the major shear zones bounding the lowermost continental-derived metamorphic units cropping out in the eastern portion of the Peloritani Mountains. Both meso- and micro-scale shear sense criteria indicate a top-to-the-SSE tectonic transport, during a general evolution from ductile to brittle deformation conditions. Quantitative thermobarometry on texturally equilibrated phengite–chlorite pairs crystallized along the shear bands indicates pressure of 6–8 kbar at temperatures of 360–440 °C for the structurally highest units and 3–4 kbar at 380–440 °C for the lowest ones. This documents an overall inverse-type nappe arrangement within the tectonic edifice and a transition from an Alpine- (13–18 °C km−1) to a Barrovian-type (28–36 °C km−1) geothermal gradient during the progress of the Alpine orogenic metamorphism in the Peloritani Mountains. The integration of these results allows the Peloritani Mountains to be considered as a constituent element of the Apennine orogenic domain formed during the progressive space–time transition from oceanic to continental subduction at the active convergent margin.
Lunatic fringe causes expansion and increased neurogenesis of trunk neural tube and neural crest populations
Authors: Elena De Bellard Maria , Barembaum Meyer , Arman Odette , Bronner-Fraser Marianne
Published: February 2008

Both neurons and glia of the PNS are derived from the neural crest. In this study, we have examined the potential function of lunatic fringe in neural tube and trunk neural crest development by gain-of-function analysis during early stages of nervous system formation. Normally lunatic fringe is expressed in three broad bands within the neural tube, and is most prominent in the dorsal neural tube containing neural crest precursors. Using retrovirally-mediated gene transfer, we find that excess lunatic fringe in the neural tube increases the numbers of neural crest cells in the migratory stream via an apparent increase in cell proliferation. In addition, lunatic fringe augments the numbers of neurons and upregulates Delta-1 expression. The results indicate that, by modulating Notch/Delta signaling, lunatic fringe not only increases cell division of neural crest precursors, but also increases the numbers of neurons in the trunk neural crest.
Hurst exponent derived for natural terrestrial radio noise in Schumann resonance band
Authors: Nickolaenko Alexander P. , Price Colin , Iudin Dmitry D.
Published: February 2008

We present the results of statistical R/S analysis of natural electromagnetic noise in the frequency range of Schumann resonance. The Hurst exponent was derived for the records of two horizontal magnetic antennas performed at the Negev desert, Israel. Analysis shows that ELF radio noise is an anti‐persistent random process. Temporal variations of the R/S ratio contain diurnal and slower variations probably indicating changes in the global lightning rate.
An analysis of the atmospheric processes driving the large‐scale winter sea ice variability in the Southern Ocean
Authors: Lefebvre Wouter , Goosse Hugues
Published: February 2008

The response of the sea ice in the Southern Ocean to the variability of the atmosphere on the period 1979–2004 is investigated using both model and observational data. On the one hand, our results show that in line with previous investigations, the classical modes of atmospheric variability do not explain a large part of the winter sea ice extent variability integrated over the entire Southern Ocean. On the other hand, the regression between the ice extent and the atmospheric pressure displays a pattern with low pressure areas over the South Atlantic, over the Indian Ocean, and on the southwestern part of the Pacific Ocean and a high pressure area over the Antarctic region extending toward both the southeastern Pacific and the region south of Australia. This pattern, which does not correlate significantly with any of the known modes of atmospheric variability, induces changes in the sea ice extent by influencing the air temperature, the ice production, and both the meridional and the zonal ice velocity. However, there is no clear link between the different centers of action of this pattern. Furthermore, the correlation of the sea ice extent between the different sectors is generally low. As a conclusion, we must consider that the sea ice extent in the Southern Ocean over the last 30 years does not behave as a single entity: Its variability is the result of the combination of regional sea ice changes. Each sector should thus be examined separately.
Auroral polar dawn spots: Signatures of internally driven reconnection processes at Jupiter's magnetotail
Authors: Radioti A. , Grodent D. , Gérard J.‐C. , Bonfond B. , Clarke J. T.
Published: February 2008

We report the presence of polar spots located in the dawn auroral region, based on the HST ACS 2007 campaign. We study the location of these features in the equatorial plane as well as their time scales and periodicities, based on a comprehensive series of images taken between February 21 and June 11, 2007. It is shown that the majority of polar dawn spots magnetically map to the dawn sector. Additionally, they occur quasi‐periodically every 2–3 days, a periodicity observed for the first time in auroral features. Because of their mapped location and their periodic cycle, we interpret the polar dawn spots as signatures of internally driven magnetic reconnection in the Jovian magnetotail.
Design and applications of a versatile HF radar calibration target in low Earth orbit
Authors: Bernhardt Paul A. , Siefring Carl L. , Thomason Joe F. , Rodriquez Serafin P. , Nicholas Andrew C. , Koss Steven M. , Nurnberger Mike , Hoberman Chuck , Davis Matthew , Hysell David L. , Kelley Michael C.
Published: February 2008

High frequency (HF) radars are used to detect ionospheric irregularities, meteor trails, and moving targets. The Precision Expandable Radar Calibration Sphere (PERCS) is a simple radar target in space to help determine the operational parameters of ground HF radars. PERCS will have a known radar cross section that is independent of observation direction within 0.5 dB. The PERCS satellite can be launched in a stowed configuration that has about 1 m in diameter. After launch, the PERCS will expand to a diameter of almost 10 m. Upon expansion, a stable wire frame is formed to act as a radar scatter target in the form of a polyhedral sphere. The simplest version of the sphere has 60 vertices (V60) that are joined to 90 rigid segments. Each segment is hinged so that the PERCS can be folded into a compact package for launch. Analysis of the V60 wire frame with a 10 m diameter shows that the radar cross section (RCS) is nearly independent of viewing angle up to 30 MHz. Another design with 240 vertices produces even better performance. Radar systems will be calibrated using the radar echo data and the precise knowledge of the target RCS, position, and velocity. The PERCS can reflect radar signals from natural targets such as field aligned and current driven irregularities not presently accessible from ground‐based radars. The wire frame structure has several advantages over a metalized spheroid “balloon” with (1) much less drag, (2) larger radar cross section, and (3) lower fabrication cost.
Composition and spectral characteristics of ambient aerosol at Mauna Loa Observatory
Authors: Johnson Stanley A. , Kumar Romesh
Published: February 2008

Ambient aerosol particles were sampled continuously with a time resolution of ∼4 hours for a period of 8 days at the Mauna Loa Observatory, Hawaii, in August 1986. The samples were analyzed on‐site for their chemical composition by attenuated total internal reflection infrared spectroscopy. The infrared absorption spectra of the samples also provided data on aerosol light absorbance characteristics at 9.1 and 10.6 μm— wavelengths of interest in determining aerosol backscatter coefficients for CO2 lidars. The chemical species in the ambient aerosol varied considerably during this 8‐day period. The aerosol was acidic [(NH4)3H(SO4)2, NH4HSO4, or H2SO4] rather than neutral [(NH4)2SO4] for a major fraction of the sampling time. The samples generally showed much higher absorbance at 9.1 μm than at 10.6 μm. Changes in the chemical composition between (NH4)2SO4 and the more acidic forms were accompanied by substantial changes in the sample's absorbance at 9.1 μm but lesser changes in the absorbance at 10.6 μm. These variations could have a profound effect on backscatter coefficients of atmospheric aerosol particles at CO2 wavelengths.
The bulk modulus ‐ attenuation ‐ viscosity systematics of diopside‐anorthite melts
Authors: Secco R. A. , Manghnani M. H. , Liu T.‐C.
Published: February 2008

Ultrasonic measurements of Qp−1 and Vp for An and Di.64An.36 melts are reported in the frequency range 3 – 20 MHz and in the temperature range from melting to 1934K and 1831K5 respectively. When Qp−1 and shear viscosity are normalized to their respective liquidus temperature values, they have the same linear dependence on reciprocal homologous temperature. From the Arrhenius temperature dependence of Qp−1, the activation energies calculated for An and Di.64An.36 melts are on the order of 216 and 302 kJ/mol, respectively. Although there is insufficient data for An, the activation energy of Qp−1 for Di.64An.36 is in excellent agreement with its activation energy of viscosity.

The relaxed adiabatic bulk modulus, derived from relaxed velocities, for An at 1893K is 20.4 ± 0.2 GPa and for Di.64An.36 at 1677K is 23.0 ± 0.1 GPa. These values fall into a general trend of decreasing bulk modulus with increasing Al2O3.
The structure of a tangential discontinuity: Application to the cometary ionopause
Authors: Flammer K. R. , Omidi N. , Quest K. B.
Published: February 2008

The kinetic structure of a tangential discontinuity interface separating an outflowing unmagnetized plasma from an inflowing, magnetized plasma is studied using 1‐D hybrid simulations (particle ions and fluid electrons). By including the effects of an ion‐neutral collisional force and plasma loss due to recombination, we conclude that two scale lengths control the structure of the cometary ionopause. The first is related to the ion Larmor radius of the outflowing ions which encounter the magnetic barrier, and the second is related to the balance between the ion‐neutral collisional force and the electromagnetic J × B force.
A Southern Hemisphere record of the Matuyama‐Brunhes polarity reversal
Authors: Clement Bradford M. , Kent Dennis V.
Published: February 2008

We present a record of the Matuyama‐Brunhes (0.73 Ma) polarity transition from a southern hemisphere deepsea sediment core (V16‐58; 46°S, 30°E). The transition is recorded across at least 30 cm of section and is defined by a nearly 180° change in directions which occurs during a low in the relative intensities. An increase in the 10Be/9Be ratios associated with the intensity low suggests that the relative intensities may document a decrease in the strength of the geomagnetic field. The virtual geomagnetic pole (VGP) path is neither clearly near‐ or far‐sided, but tracks approximately 120° west of the site longitude. Considered with other Matuyama‐Brunhes transition records, this southern hemisphere record supports previous interpretations that the Matuyama‐Brunhes transitional field was not dipolar. Instead, the V16‐58 transition together with other records of this reversal recently obtained from this longitudinal sector suggests that nonzonal terms which are symmetric about the equator were important during this transitional field.
Two‐station measurements of Rayleigh wave group velocity along the Hawai'ian Swell
Authors: Woods Mark T. , Lévêque Jean‐Jacques , Okal Emile A. , Cara Michel
Published: February 2008

Two‐station measurements of Rayleigh wave group velocity between Midway Atoll and O'ahu provide a useful constraint on lithospheric thickness along the Hawai'ian Swell. Comparison of the observed dispersion curve with age‐dependent, regionalized dispersion curves suggests that the swell acts as 50–110 m.y. old lithosphere, and not as 20–50 m.y. old lithosphere as is predicted by the currently favored hypothesis for the swell's formation. A preliminary isotropic shear velocity model for the swell suggests that the lithosphere may be as thick as 100 km. This value is difficult to reconcile with the lithosphere being substantially thinned during its passage over the Hawai'ian hotspot.
An olivine to beta phase transformation mechanism Mg2SiO4
Authors: Guyot François , Gwanmesia Gabriel D. , Liebermann Robert C.
Published: February 2008

Fine‐grained powder samples of Mg2SiO4 forsterite (α phase) have been partially transformed to the beta phase in a 2000‐ton uniaxial split‐sphere apparatus (USSA‐2000) at P = 15 GPa and T = 1000 °C in runs of 5 minutes duration. This technique allowed us to catch the first steps of the α ‐‐> β transformation in Mg2SiO4. A TEM study of the run products showed that a structurally disordered phase is an intermediate of the reaction. The oxygen sublattice of this intermediate phase is well ordered, but a very large density of planar faults on (010) planes destroys the long range order in the cation sublattices. A two‐steps mechanism for the α ‐‐> β transformation is therefore probable, involving first the nucleation of the structurally disordered phase, then the ordering of this phase. These two steps may be associated with low energy activation barriers and could thus explain the fast kinetics of the α ‐‐> β transformation.
The polar cusp from a particle point of view: A statistical study based on Viking data
Authors: Aparicio B. , Thelin B. , Lundin R.
Published: February 2008

We present results from the particle measurements made on board the Viking satellite. For the period of interest the Viking orbits covered at high latitudes the whole dayside sector. Data from the Viking V‐3 particle experiment acquired during the Polar Region Outer Magnetospheric International Study period (March 15 to June 15, 1986) have been used to study the extension of the cusp and cleft in magnetic local time and invariant latitude, and furthermore, their dependence on solar wind and interplanetary magnetic field parameters. The study is limited to the MLT range from 0900 to 1500 and to invariant latitudes (ILAT) from 74° to 82°. This region is divided into bins of size (15 min MLT × 0.2° ILAT). We concentrated on the region where magnetosheath solar wind plasma penetrates more directly into the magnetosphere and is measured at Viking altitudes (≈13,000 km). This region is called the “cusp proper” (Lundin et al., 1988; Newell and Meng, 1989), to be distinguished from a broader region denoted the cleft, where more energetic particles are observed. Statistically, we find the cusp proper to extend from invariant latitudes of 75° to 82° and magnetic local times from 0930 to 1400 MLT. The width in ILAT is found to be on average ≈2° and in MLT ≈ 2 hours. It is shown that a clear correlation exists between the densities in the cusp proper calculated from the Viking V‐3 experiment in the cusp proper and those in the solar wind calculated from IMP 8 measurements. It is also shown that the position of the cusp proper in MLT depends on the sense of the By component of the interplanetary magnetic field (IMF By), giving a well‐defined displacement of the region of maximum occurrence toward earlier MLTs for IMF By < 0 and a less defined displacement toward later MLTs for IMF By > 0.
Evolution of the solar wind structure over a solar cycle: Interplanetary scintillation velocity measurements compared with coronal observations
Authors: Rickett B. J. , Coles W. A.
Published: February 2008

Sixteen years of solar wind observations via the technique of interplanetary scintillation (IPS) are presented. By an ecliptic comparison with in situ spacecraft observations, these data are shown to be valuable estimates of the large‐scale slowly evolving structures in the solar wind speed, but to underestimate the speed in small‐scale or rapidly evolving structures. These IPS observations allow the large structures to be studied over solar latitudes from 60° north to 60° south over more than a solar cycle. The observations are presented as half‐yearly averages in Carrington longitude and latitude. These are compared with plots of coronal density estimated from coronameter observations and radial magnetic field estimated from solar magnetograph observations and the potential field method. In low and declining solar activity, there is the expected relationship between fast wind and low‐density open‐field regions, and between slow wind, dense corona and proximity to the neutral sheet. The dipolar field component wanders up to 30° from the rotation axis and is followed by dipolar distributions of density and velocity. Near solar maximum, average wind speeds are uniformly slow over the entire range of latitudes covered, the coronal density becomes more spherically distributed (though it retains a somewhat lower density over the solar poles), and the neutral sheet ranges over all latitudes and sometimes forms disconnected surfaces. The relationship between wind speed, density and angular separation from the neutral sheet are then broken. The results confirm the controlling influence of the coronal magnetic field in determining the three‐dimensional structure of the solar wind.
Effect of magnetic overshoot on shock drift acceleration
Authors: Giacalone J. , Armstrong T. P. , Decker R. B.
Published: February 2008

We present an investigation of the effect of magnetic overshoot (a feature of supercritical, collisionless shocks) on the shock drift acceleration (SDA) mechanism. The investigation is carried out by performing numerical simulations of ensembles of test particles (ions) to obtain reflection probabilities, energy gains, and anisotropies. We assume that the test particle approach is valid since the lowest‐energy particles studied have speeds several times the ion thermal speed in the upstream plasma frame, which corresponds to a very small percentage of the overall population. We show that the magnetic overshoot enhances particle reflection considerably when the initial gyroradius of the particle is of the order of the shock transition length. Furthermore, as compared to the no‐overshoot case, the overshoot allows initially lower energy particles to reflect. This, in turn, gives rise to more field‐aligned beams upstream of the shock. The test particle results display adiabatic‐like characteristics and indicate that the structured shock may be analytically modeled by an energy‐dependent magnetic mirror. The results presented here are in agreement with a similar study in which the electromagnetic fields were provided by a self‐consistent hybrid simulation. This investigation has applications to the regions of the outer planetary bow shocks, where curvature effects are considerably smaller than at the Earth's, and at strong interplanetary shocks ≲1 A.U., where the overshoot may still be significant.
A study of the relationship between micropulsations and solar wind properties
Authors: Yedidia B. A. , Vellante M. , Villante U. , Lazarus A. J.
Published: February 2008

A year‐long comparison between daily averages of solar wind parameters obtained from the Massachusetts Institute of Technology experiment on IMP‐8 and micropulsation measurements made by the Universita dell'Aquila has shown a correlation between solar wind speed and micropulsation power with peaks of the correlation coefficient greater than 0.8 in the period range from 20 to 40 s. Different behavior observed for different period bands suggests that the shorter period activity tends to precede the highest values of the solar wind speed while the longer period activity tends to persist for longer intervals within high velocity solar wind streams. A comparison with simultaneous interplanetary magnetic field measurements supports the upstream origin of the observed ground pulsations.
On the inversion of O+(²D‐²P) 7320 Å twilight airglow observations: A method for recovering both the ionization frequency and the thermospheric oxygen atom densities
Authors: McDade I. C. , Sharp W. E. , Richards P. G. , Torr D. G.
Published: February 2008

In this paper we demonstrate that it is possible to invert twilight observations of the O+(²D ‐²P)‐7320 Å airglow emission to obtain information about both the thermospheric atomic oxygen densities and the unattenuated O+(²P) ionization frequency. The efficacy of the proposed approach, which relies upon making twilight observations in more than one viewing direction, is illustrated using a synthetic data set and an inversion algorithm based on a simple photochemical model. The results of this study show that day‐to‐day variations in the thermospheric oxygen atom densities may be monitored from the ground without requiring complementary measurements of the solar EUV flux. The study also shows that twilight observations may be used to monitor variations in the solar flux components that are responsible for O+(²P) production and EUV heating of the upper thermosphere.
A comparison of ULF fluctuations in the solar wind, magnetosheath, and dayside magnetosphere: 1. Magnetosheath morphology
Authors: Engebretson M. J. , Lin N. , Baumjohann W. , Luehr H. , Anderson B. J. , Zanetti L. J. , Potemra T. A. , McPherron R. L. , Kivelson M. G.
Published: February 2008

“Upstream waves,” generated in the solar wind upstream of a quasi‐parallel bow shook, are believed to be a major source of the Pc 3‐4 pulsation activity observed in the dayside magnetosphere. In an attempt to better understand the means by which “upstream wave” energy is transmitted from the solar wind into the magnetosphere, we compared simultaneous data from ISEE 1 and 2 in the upstream solar wind, AMPTE IRM in the subsolar magnetosheath, and AMPTE CCE in the dayside magnetosphere. Our observations indicate that dayside magnetospheric Pc 3‐4 pulsation activity and low IMF cone angles are associated with increased turbulence in the subsolar magnetosheath magnetic field (with large amplitude fluctuations both parallel and transverse to the average field direction), and with increased and highly variable levels of energetic magnetosheath particles. Fourier analysis of the magnetic field fluctuations shows broadband increases in wave power from 0.01 Hz to at least 0.5 Hz, but with peak power at Pc 3‐4 frequencies; there is no evidence in our data set of narrow‐band magnetic field variations in the magnetosheath at these times. Purely compressional waves, which are at times observed in the subsolar magnetosheath, have a somewhat narrower frequency distribution, but are associated with neither upstream wave activity nor magnetospheric pulsations.
Observations of polar ion outflows
Authors: Chandler M. O. , Waite J. H. , Moore T. E.
Published: February 2008

The characteristics of the polar ion outflows as observed in the topside polar ionosphere by the Dynamics Explorer Retarding Ion Mass Spectrometer are reported in this study. The study is restricted to altitudes between 1000 and 4000 km in order to focus on the phenomenon of the “classical polar wind.” Except insofar as they convect into the polar cap at these altitudes, auroral and cusp/cleft outflows are specifically excluded from this study. Using a method based on the “relative wind” of ions as seen from the moving spacecraft, averages and variances of the magnetic field‐aligned ion flux and velocity, and the species densities, are derived and binned for examination of their altitudinal, seasonal, and magnetic activity dependencies. The data set used encompasses the period from autumn 1981 through 1983, the altitude range from 1000 to 4000 km, and invariant latitudes greater than 70°. Observations of H+, He+, and O+ with energies down to spacecraft potential are reported. It is found that the polar outflows are not well correlated with common indicators of solar or geomagnetic activity. The average parameters of the outflows exhibit a winter enhancement of He+ flux, a winter decrease in H+ flux, and a summer enhancement of the asymptotic outflow speeds of all species. The solar F10.7 (and hence EUV) flux is correlated with the acceleration profile of the flows, with slower flow velocities at 2500 km altitude for active solar conditions. Evidence is found that the H+ flows are, at times, subsonic in the altitude range studied, in contrast to cold polar wind models.
Semidiurnal tidal climatology of the E region
Authors: Forbes Jeffrey M. , Vial Francois
Published: February 2008

Theoretical predictions of global monthly and seasonally averaged semidiurnal temperatures and winds between 80 and 150 km are presented and compared with seasonal means from measurements at the Arecibo, Chatanika, Millstone Hill, and Sondrestrom incoherent scatter radars. The model values above 100 km are obtained by utilizing a set of tabulated ‘Hough mode extension’ functions to extrapolate the (2,2), (2,3), (2,4), and (2,5) propagating tidal modes at 100 km from a spectral model (not valid in the E region due to the way molecular dissipation is parameterized) to higher altitudes and by superimposing a component driven by in‐situ excitation (important mainly above 140 km). The monthly simulations demonstrate the close coupling that exists between seasonal and latitudinal structures and argue for an observational program emphasizing adequate seasonal and latitudinal coverage. Despite constraints imposed by the distributions of existing data with respect to month and year, comparisons with the model reveal several trends that appear to be real: (1) the model amplitudes are usually 20–50% smaller than those observed; (2) vertical wavelengths are well‐predicted by the model, but model phases generally lead the observations at middle and low latitudes by approximately 2–3 hours at all heights for both winds and temperatures; (3) semidiurnal temperatures at middle and low latitudes, in both the observations and model, indicate significant seasonal changes in the phase of the temperature oscillation, but not in the winds; and (4) the seasonal trends in the model and observations are consistent, with “summer leading winter” at Millstone Hill, while the reverse is true at Arecibo. The sources of the absolute amplitude and phase discrepancies in the model, which are probably connected with the adopted mean wind and thermal excitation specifications, need to be investigated. In addition, a concerted effort must be made within the Coupling Energetics and Dynamics of Atmospheric Regions (CEDAR) program to better delineate the seasonal‐latitudinal thermal structure and dynamics of the E region, following the example of the extensive F region observational data base which has been accumulated over the last decade.
Thermospheric tides at equinox: Simulations with coupled composition and auroral forcings: 2. Semidiurnal component
Authors: Fesen C. G. , Roble R. G. , Ridley E. C.
Published: February 2008

New simulations of semidiurnal thermospheric winds and perturbation temperatures calculated by the National Center for Atmospheric Research thermospheric general circulation model (TGCM) are presented for equinox conditions. The model now incorporates a self‐consistent calculation of neutral composition and includes high‐latitude energy and momentum sources associated with the aurora. The tidal waves propagating upward from the lower atmosphere are specified by wavelike distributions of the geopotential at the model lower boundary; the boundary geopotential is related to the other model fields through Hough mode tidal functions. The specification of the wave amplitudes and phases is based on lower atmosphere model predictions and thus represents the coupling between the upper and lower atmosphere in a more physically meaningful manner than previous calculations. In these simulations, asymmetric semidiurnal modes are also included. The revised TGCM calculations at geographic longitude 75°W are compared with observational data at low, middle, and high latitudes. In general, the agreement is reasonable, given the limited data available. The predicted solar cycle variation of the semidiurnal tides is consistent with previous works: the temperatures respond more strongly than the winds, and the solar cycle effects are most pronounced in the upper thermosphere. The lower thermosphere is dominated by the upward propagating waves from the lower atmosphere, with little contribution from solar forcing. These upward propagating waves are damped at lower altitudes as solar forcing increases. The effects of coupled composition and auroral forcings on the semidiurnal tidal components are investigated. Both processes alter the simulated solar‐driven tidal fields compared to calculations which neglected these processes: amplitudes may double or triple in restricted altitude and latitude regions, while the times of maxima may shift by a few hours. The TGCM simulations are compared with the Fourier‐decomposed exospheric temperature measured during the September 1984 Equinox Transition Study period. The semidiurnal temperature phase in particular is found to be strongly dependent on the level of geomagnetic activity. Thus the simulation of individual day observations will require careful specification of the auroral forcings which are input into the theoretical models. Simultaneous data obtained at different latitudes are vital to test and confirm the model predictions.
Cosmic ray modulation: Voyager 2 observations, 1987–1988
Authors: Burlaga L. F. , McDonald F. B. , Ness N. F. , Lazarus A. J.
Published: February 2008

We analyze the intensity profile of cosmic rays >70 MeV observed by Voyager 2 and its relation to the interplanetary magnetic field and plasma at the beginning of the new modulation cycle from day 190, 1987 to day 345, 1988 in the region from 23.3 AU to 27.8 AU. The cosmic ray intensity profile was approximately a series of four plateaus separated by three steps in which the intensity dropped abruptly. Each step was associated with a region in which the magnetic field, density, and temperature were higher than average. The plateaus were associated with regions in which the magnetic field was alternately strong and weak. To first approximation, one can picture the solar wind within 200 AU during this interval as consisting of three shells between which the flow was quasi‐periodic with a ∼26 day periodicity. This picture is an oversimplification, since the large‐scale magnetic field was approximately a multifractal. The latitudinal extent of the shells in the northern hemisphere was probably <33°, since no steps were observed by Voyager 1. Drift motions might play a role (1) during the recovery phase, just prior to the onset of the new modulation cycle, (2) in the plateau regions between the shells, (3) within the shells where drifts in various directions might mimic diffusion, and (4) close to 1 AU, where large regions of intense magnetic fields have not yet formed. However, the principal decreases in the cosmic ray intensity in the outer heliosphere during 1987 and 1988 were associated with the passage of broad regions of intense magnetic fields, consistent with the diffusion/convection model.
Resonance broadening modification of weak plasma turbulence theory
Authors: Hanssen Alfred
Published: February 2008

We examine the effects on energy spectra of weak Langmuir turbulence when we include a nonlinear damping due to the perturbation of electron orbits. The physical mechanism under consideration is usually known as a “resonance broadening” effect. Our calculations show that the inclusion of this additional damping reduces the number of cascades predicted from weak turbulence theory for waves detectable with the EISCAT UHF (933 MHz) radar in Tromsø, Norway, during RF modification of the ionospheric plasma.
Impulsive excitation of ULF waves in the three‐dimensional dipole model: The initial results
Authors: Lee Dong‐Hun , Lysak Robert L.
Published: February 2008

Impulsively excited ULF waves are studied in the three‐dimensional dipole magnetosphere. The properties of coupled compressional and transverse wave fields are found to depend on the longitudinal size of the impulse which is assumed at the magnetopause. The distribution of energy density and the wave spectra are shown for different meridians. We study how compressional waves propagate in the three‐dimensional space and excite the corresponding field line resonances, and how the impulse produces ULF waves with many azimuthal wave numbers m. The results suggest that, as the longitudinal width of the impulse becomes larger at the magnetopause, strong field line resonances are likely to be found with the lower m. On the contrary, an impulse which is narrow in longitude may excite the ULF waves with relatively high m. We examine the propagation of both compressional and transverse waves in the azimuthal direction. Our numerical results indicate that transverse waves as well as compressional waves are inclined to have harmonic structures in the azimuthal direction, even though it is well known that the Alfven shear modes become one‐dimensional modes along the field lines in the absence of coupling. The structures and coupling of global compressional and toroidal standing waves are also investigated and compared with the previous two‐dimensional results.
Latitudinal cosmic ray gradients: Their relation to solar activity asymmetry
Authors: Swinson D. B. , Humble J. E. , Shea M. A. , Smart D. F.
Published: February 2008

Data obtained by underground cosmic ray telescopes in the northern and southern hemispheres between 1965 and 1985 are analyzed as a function of the interplanetary magnetic field (IMF) sense to examine the long‐term nature of the latitudinal cosmic ray gradient, ▽Np. The nature of this gradient is inferred from the B×▽Np contribution to the solar diurnal cosmic ray anisotropy arising from the interaction between the latitudinal gradient and the IMF B. In an earlier paper we noted a correspondence between the characteristics of the latitudinal gradient and the north‐south asymmetry in activity on the Sun during the same period and attempted to explain the result in terms of a combination of two gradients: a north‐south symmetrical gradient and a north‐south asymmetrical gradient. In this paper we present results showing that asymmetry in activity on the Sun displaces the heliospheric neutral sheet either below or above the Earth (on average), according to the direction of the solar activity asymmetry. This displacement, combined with a latitudinal cosmic ray density gradient that is symmetrical in relation to the neutral sheet, produces a latitudinal cosmic ray gradient that is asymmetrical when viewed from the Earth. The cosmic ray data are consistent with a symmetric (in relation to the neutral sheet) latitudinal cosmic ray density gradient in which the density initially decreases with distance from the neutral sheet and then increases again with increasing distance from the sheet. Additional data from inclined underground cosmic ray telescopes, viewing from 60°N to 50°S, give information on latitudinal gradients further from the neutral sheet.
Monte Carlo simulation of photoelectron energization in parallel electric fields: Electroglow on Uranus
Authors: Singhal R. P. , Bhardwaj A.
Published: February 2008

A Monte Carlo simulation of photoelectron energization and energy degradation in H2 gas in the presence of parallel electric fields has been carried out. Numerical yield spectra which contain information about the electron energy degradation process and can be used to calculate the yield for any inelastic event are obtained. The variation of yield spectra with incident electron energy, electric field, pitch angle, and cutoff limit has been studied. The yield function is employed to determine the photoelectron fluxes. H2 Lyman and Werner band excitation rates and integrated column intensity are computed for three different electric field profiles taking various low‐energy cutoff limits. It is found that an electric field profile with peak value of 4 mV/m at neutral number density of 3×1010 cm−3 produces enhanced volume emission rates of H2 bands [λ < 1100 Å] explaining about 20% of the observed electroglow emission on Uranus. The effect of solar zenith angle and solar cycle variation on peak excitation rate is discussed.
Thermomechanical evolution of a thinned continental lithosphere under compression: Implications for the Pyrenees
Authors: Chery J. , Vilotte J. P. , Daignieres M.
Published: February 2008

In order to demonstrate the interactions between plate boundary forces and preexisting zones of weakness, and how those control the localization of continental deformation inside the lithosphere, the thermomechanical evolution of an initially thinned and thermally perturbed continental lithosphere in compression was analyzed within the framework of the Pyrenees. While a concensus exists as to the shallow structures, the extent and geometry of deformation at depth have been the subject of great controversy. The thermomechanical implications of recent geological hypotheses on the initial state, prior to the compression, recently derived from balanced cross‐section reconstructions are here quantified and compared to the recent ECORS deep seismic reflection profile across the Pyrenees. A thermomechanical model based on finite elastoplastic‐viscoplastic deformations has therefore been formulated using phenomenological constitutive equations derived from experimental studies. The thermally coupled problem is solved by an appropriate vertical two‐dimensional plane strain finite element approximation. In those models most of the shortening is accommodated inside a local zone of intense plastic shearing that creates a sharp wedge‐shaped root progressively sinking deep into the mantle. The main thickening takes place inside the lower crust, where it can reach a factor 2. This indentation and crustal imbrication process is controlled by a buckling instability occuring inside the uppermost part of the mantle. The evolution of the topography can be related to these phenomena. Lateral conductive heat transfer overtakes the advective transfer in the vicinity of the inflow of colder crustal material inside a warmer mantle. The deformation pattern can be explained by a three‐layer mechanical lithosphere, with a soft ductile internal layer of potential decoupling between two more competent layers characterized by a significant elastic stored energy. The overall response of this composite plate is not much influenced by smaller scale variations of crustal rheology but is very much dependent on the contrast in rates of viscous dissipation between the lower crust and the upper mantle and on the possibility of singling out a layer of significant elastic stored energy by the balance between rate of loading and rate of dissipation inside the uppermost mantle. Predicted deformation pattern is found to agree with the seismic reflection and gravity data. Even though extrapolation to other rates of shortening must be verified by appropriate numerical modelling, these physical mechanisms may be regarded as a paradigm for other crustal imbrication phenomena found in the Himalayas, Tibet, or the Alps.
Combined use of visible, reflected infrared, and thermal infrared images for mapping Hawaiian lava flows
Authors: Abrams Michael , Abbott Elsa , Kahle Anne
Published: February 2008

The weathering of Hawaiian basalts is accompanied by chemical and physical changes of the surfaces. These changes have been mapped using remote sensing data from the visible and reflected infrared and thermal infrared wavelength regions. They are related to the physical breakdown of surface chill coats, the development and erosion of silica coatings, the oxidation of mafic minerals, and the development of vegetation cover. These effects show systematic behavior with age and can be mapped using the image data and related to relative ages of pahoehoe and aa flows. The thermal data are sensitive to silica rind development and fine structure of the scene; the reflectance data show the degree of oxidation and differentiate vegetation from aa and cinders. Together, data from the two wavelength regions show more than either separately. The combined data potentially provide a powerful tool for mapping basalt flows in arid to semiarid volcanic environments.
Paleomagnetic results from Mesozoic strata in the Mérida Andes, Venezuela
Authors: Castillo Jesus , Gose Wulf A. , Perarnau Adrian
Published: February 2008

We report paleomagnetic results from Jurassic through Cretaceous sedimentary rocks (nine sites) in the Mérida Andes, Venezuela. Detailed thermal and alternating field demagnetization yielded well‐grouped directions of both polarities. The mean of the normal directions is statistically identical to the mean of the reversed directions and the site means clusters better after structural correction, both at the 95% significance level, indicating that the primary magnetization has been isolated. The mean pole position lies at 86.5°N, 151.1°E, A95 = 5.6°. Combining this pole position with 10 other poles from the southern part of cratonic South America establishes a mean pole for the Late Jurassic through Cretaceous at 87.6°N, 211.0°E, A95 = 3.3°. These results imply, within the error limit of the paleomagnetic data, that South America is indeed one rigid plate and that the motion of this plate was restricted to east‐west translation since the opening of the South Atlantic Ocean.