bluuebunny/crossref_metadata_2025 huggingface dataset:
Late Miocene vegetation and palaeoenvironments of the Drygalski Formation, Heard Island, Indian Ocean: evidence from palynology
Authors: TRUSWELL ELIZABETH M. , QUILTY PATRICK G. , MCMINN A. , MACPHAIL M.K. , WHELLER G.E.
Published: August 2005

Well sorted, fine lithic sandstone within the Drygalski Formation at Cape Lockyer on the southern tip of Heard Island, preserves a diverse terrestrial palynoflora as well as marine diatoms and a few foraminifera. A combination of these elements suggests a Late Miocene age (10–5 Ma). The palaeovegetation was markedly different from that presently on the island, and appears to comprise at least two ecologically distinct communities: open heath or herbfield dominated by grasses and Asteraceae, and a more mesophytic community dominated by ferns but also including lycopods and angiosperms such as Gunnera. This may have represented a coastal flora similar to the ‘fern-bush’ community that exists now on Southern Ocean islands north of the Antarctic Polar Frontal Zone, and in Tierra del Fuego; however, there is no evidence of tree species in the local flora and trace amounts of tree pollen present may have blown in from other landmasses in the region.
Age and tectonic significance of the Lassiter Coast Intrusive Suite, Eastern Ellsworth Land, Antarctic Peninsula
Authors: FLOWERDEW M.J. , MILLAR I.L. , VAUGHAN A.P.M. , PANKHURST R.J.
Published: August 2005

Depleted mantle model ages derived from granitoids of the Lassiter Coast Intrusive Suite, sampled over a wide geographical area in eastern Ellsworth Land, Antarctica, cluster between 1000 Ma and 1200 Ma and suggest involvement of Proterozoic crust in the petrogenesis of the suite. Ion-microprobe U–Pb zircon analyses from a small intrusion at Mount Harry, situated at the English Coast, yield a concordant age of 105.2 ± 1.1 Ma, consistent with published ages from other parts of the Lassiter Coast Intrusive Suite. Significant variation in the Sr and Nd isotope composition of the granitoids, along the extrapolation of the Eastern Palmer Land Shear Zone (a proposed terrane boundary) located close to the English Coast, is not evident. However, the isotope signature at the English Coast is more homogeneous than the Lassiter Coast; this variation may relate to geographical proximity to the Pacific margin during intrusion, may reflect subtle changes in basement with a broadly similar character across the proposed terrane boundary, or suggest that any major fault structure is located further to the north, with implications for the kinematics of regional mid-Cretaceous transpression.
A revised inventory of Antarctic subglacial lakes
Authors: SIEGERT MARTIN J. , CARTER SASHA , TABACCO IGNAZIO , POPOV SERGEY , BLANKENSHIP DONALD D.
Published: August 2005

The locations and details of 145 Antarctic subglacial lakes are presented. The inventory is based on a former catalogue of lake-type features, which has been subsequently reanalysed, and on the results from three additional datasets. The first is from Italian radio-echo sounding (RES) of the Dome C region of East Antarctica, from which 14 new lakes are identified. These data also show that, in a number of occasions, multiple lake-type reflectors thought previously to be individual lakes are in fact reflections from the same relatively large lake. This reduces the former total of lake-type reflectors by six, but also adds a significant level of information to these particular lakes. The second dataset is from a Russian survey of the Dome A and Dome F regions of East Antarctica, which provides evidence of 18 new lakes and extends the coverage of the inventory considerably. The third dataset comprises three airborne RES surveys undertaken by the US in East Antarctica over the last five years, from which forty three new lakes have been identified. Reference to information on Lake Vostok, from Italian and US surveys taken in the last few years, is now included.
Baroclinic and barotropic tides in the Weddell Sea
Authors: ROBERTSON ROBIN
Published: August 2005

Barotropic and baroclinic tides were simulated for the Weddell Sea using ROMS. The model estimates for both tidal elevations and velocities showed good agreement with existing observations. The rms differences were 9 cm for elevations and 1.2–1.7 cm s−1 for the major axes of the tidal ellipses for the semidiurnal constituents and 6–8 cm and 4.5 cm s−1 for the diurnal constituents, respectively. Most of the discrepancies occurred deep under the ice shelf for the semidiurnal tides and along the continental slope for the diurnal tides. Along the continental slope, the model overestimated the generation of diurnal continental shelf waves. The diurnal tides were barotropic throughout the basin. However, internal tides were generated at semidiurnal frequencies over rough topography. Over the continental slope, semidiurnal baroclinic tidal generation was enhanced by the existence of continental shelf waves, through their harmonics. Baroclinic tides generated over rough topography in the northern Weddell Sea incited inertial oscillations as they propagated south. These inertial oscillations varied with depth since they were incited at different depths at different times as the internal tide progressed. Both the baroclinic tides and inertial oscillations induced vertical shear in the water column and increased the divergence of the horizontal surface velocities.
A new global average model of the coupled thermosphere and ionosphere
Authors: Smithtro C. G. , Sojka J. J.
Published: August 2005

A model representing the global average ionosphere and thermosphere (GAIT) is developed as a tool to explore the response of the coupled system to changes in the input solar irradiance between 3 and 360 nm. The GAIT model self‐consistently solves the coupled continuity, momentum, and energy equations for the three major neutral species, N2, O2, and O, as well as minor neutral constituents important to the global energy budget. In the ionosphere the model includes five different ion species and two excited states of O+. The GAIT model also includes an approximate treatment of photoelectrons, in order to calculate secondary ionization and thermal electron volume heating rates. After examining the sensitivity of the GAIT model to uncertainties in key reaction rates and inputs, we consider its response to four different extreme ultraviolet irradiance models. With three of the irradiance models we reproduce the expected variation in exospheric temperature to within 2%; however, the dynamic range of the fourth is deemed to be too small. We conclude with an analysis of the model's wavelength‐dependent sensitivity to input solar photons.
Behavior of the ionosphere and thermosphere subject to extreme solar cycle conditions
Authors: Smithtro C. G. , Sojka J. J.
Published: August 2005

A 1‐D global average ionosphere and thermosphere (GAIT) model is used to examine the climatological behavior of the upper atmosphere, subject to both extremely low and high solar flux. These extremes are justified, in part, by the Maunder Minimum and Grand Maximum epochs described by J. A. Eddy, as well as other studies involving cosmogenic isotopes and Sun‐like stars. As the irradiance falls below normal solar minimum levels, the concentration of O+ decreases rapidly relative to the molecular ions, such that the ratio foF2/foF1 approaches unity. When subject to exceptionally high solar fluxes, the ionospheric peak electron density (NmF2) unexpectedly plateaus, remaining relatively constant even as the photon flux continues to increase. In both cases, the state of the underlying thermosphere, particularly the neutral gas temperature, is found to be largely responsible. Model trends are discussed in relation to ionospheric observations, specifically the preponderance of so‐called ionospheric G conditions at solar minimum and foF2 saturation at solar maximum, as well as the problem of Earth's global helium budget.
Toward magnetic field dissipation during the 23 July 2002 solar flare measured with Solar and Heliospheric Observatory/Michelson Doppler Imager (SOHO/MDI) and Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
Authors: Zharkova Valentina V. , Zharkov Sergey I. , Ipson Stanley S. , Benkhalil Ali K.
Published: August 2005

We analyze the SOHO/MDI high‐cadence magnetic field variations that occurred in a bipolar area around the apparent neutral line (ANL) prior to and during the 2B/X4.8 flare on 23 July 2002 and their association with the hard X‐ray (HXR) and Hα emission observed with RHESSI and BBSO. Magnetic field changes started 6 min prior to the hard X‐ray emission onset in 0.3–2 MeV band or 7 min in the 12–25 keV band and finished 20 min later. Before the flare, there are nine preexisting sources of a strong magnetic field of the positive and negative polarities, and six new magnetic sources associated with the hard X‐ray foot points emerged 2 min before the flare maximum: two negative and four positive ones. The difference magnetograms show a steady movement with a speed of 250 km/s of the magnetic field changes toward the northeast, or a ‘negative magnetic field discharge’ associated with the magnetic energy release in this flare. The magnetic field changes in the whole flaring area are irreversible, showing an increase of the magnetic flux from 6.7 × 1021 Mx up to 7.9 × 1021 Mx lasting for 6 min and returning after to noise fluctuations about the new magnitude. There is an irreversible increase by −120 G of an absolute magnitude of the negative magnetic field component. The rate of magnetic field changes deduced from the total area around the ANL and from the areas of the hard X‐ray foot point with the irreversible changes is about 3.1 × 1018 Mx/s, and the average Poynting flux is (5–20) × 1011 erg/cm2/s. The LOS fraction of a magnetic energy released for the whole flare duration is estimated as ∼(2.3–10) × 1031 erg. The possible scenarios of particle acceleration in this flare are proposed based on HXR and γ‐ray emission.
Ionospheric signatures of plasma injections in the cusp triggered by solar wind pressure pulses
Authors: Cerisier Jean‐Claude , Marchaudon Aurélie , Bosqued Jean‐Michel , McWilliams Kathryn , Frey Harald U. , Bouhram Mehdi , Laakso Harri , Dunlop Malcolm , Förster Matthias , Fazakerley Andrew
Published: August 2005

We describe coordinated observations made on 14 July 2001 simultaneously in the midaltitude cusp by Cluster and at the cusp's ionospheric magnetic footprint by Super Dual Auroral Radar Network (SuperDARN) and Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) during a period of three successive solar wind dynamic pressure pulses. In association with each of these pulses, Cluster observes plasma injections while auroral images from the IMAGE spacecraft show enhanced precipitation in the cusp. Following these plasma injections, channels of fast convection flows are observed in the ionosphere by the SuperDARN radars. On the basis of the spatial and temporal relationships between these various signatures, we analyze the response of the dayside magnetosphere and ionosphere to the pressure pulses as follows: (1) the solar wind dynamic pressure pulses are the drivers of plasma injections from the magnetosheath into the cusp; (2) the ionospheric convection bursts start shortly after the auroral intensifications and their duration is much longer (10 min versus 4–6 min for the auroral intensifications); (3) the convection bursts occur on the poleward side of the cusp precipitation; and (4) the Alfvén waves that are responsible of the transmission of the magnetic stress from the reconnection site to the ionosphere are strongly reflected in the upper ionosphere. This, in addition to possible parallel potential drops, may explain the imperfect mapping of the magnetospheric electric field into the ionosphere during the injections. These observations demonstrate that the convection bursts are “fossil” signatures of the compression–injection process, which is also a signature of reconnection at the dayside magnetopause driven by the interplanetary magnetic field alone.
Spatial and temporal variability in active layer thickness over the Russian Arctic drainage basin
Authors: Zhang Tingjun , Frauenfeld Oliver W. , Serreze Mark C. , Etringer Andrew , Oelke Christoph , McCreight James , Barry Roger G. , Gilichinsky David , Yang Daqing , Ye Hengchun , Ling Feng , Chudinova Svetlana
Published: August 2005

Changes in active layer thickness (ALT) over northern high‐latitude permafrost regions have important impacts on the surface energy balance, hydrologic cycle, carbon exchange between the atmosphere and the land surface, plant growth, and ecosystems as a whole. This study examines the 20th century variations of ALT for the Ob, Yenisey, and Lena River basins. ALT is estimated from historical soil temperature measurements from 17 stations (1956–1990, Lena basin only), an annual thawing index based on both surface air temperature data (1901–2002) and numerical modeling (1980–2002). The latter two provide spatial fields. Based on the thawing index, the long‐term average (1961–1990) ALT is about 1.87 m in the Ob, 1.67 in the Yenisey, and 1.69 m in the Lena basin. Over the past several decades, ALT over the three basins shows positive trends, but with different magnitudes. Based on the 17 stations, ALT increased about 0.32 m between 1956 and 1990 in the Lena. To the extent that results based on the soil temperatures represent ground “truth,” ALT obtained from both the thawing index and numerical modeling is underestimated. It is widely believed that ALT will increase with global warming. However, this hypothesis needs further refinement since ALT responds primarily to summer air temperature while observed warming has occurred mainly in winter and spring. It is also shown that ALT exhibits complex and inconsistent responses to variations in snow cover.
Evaluation of a new cloud droplet activation parameterization with in situ data from CRYSTAL‐FACE and CSTRIPE
Authors: Meskhidze Nicholas , Nenes Athanasios , Conant William C. , Seinfeld John H.
Published: August 2005

The accuracy of the 2003 prognostic, physically based aerosol activation parameterization of A. Nenes and J. H. Seinfeld (NS) with modifications introduced by C. Fountoukis and A. Nenes in 2005 (modified NS) is evaluated against extensive microphysical data sets collected on board the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft for cumuliform and stratiform clouds of marine and continental origin. The cumuliform cloud data were collected during NASA's Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL‐FACE, Key West, Florida, July 2002), while the stratiform cloud data were gathered during Coastal Stratocumulus Imposed Perturbation Experiment (CSTRIPE, Monterey, California, July 2003). In situ data sets of aerosol size distribution, chemical composition, and updraft velocities are used as input for the NS parameterization, and the evaluation is carried out by comparing predicted cloud droplet number concentrations (CDNC) with observations. This is the first known study in which a prognostic cloud droplet activation parameterization has been evaluated against a wide range of observations. On average, predicted droplet concentration in adiabatic regions is within ∼20% of observations at the base of cumuliform clouds and ∼30% of observations at different altitudes throughout the stratiform clouds, all within experimental uncertainty. Furthermore, CDNC is well parameterized using either a single mean updraft velocity or by weighting droplet nucleation rates with a Gaussian probability density function of w. This study suggests that for nonprecipitating warm clouds of variable microphysics, aerosol composition, and size distribution the modified NS parameterization can accurately predict cloud droplet activation and can be successfully implemented for describing the aerosol activation process in global climate models.
Fluviodeltaic response to sea level perturbations: Amplitude and timing of shoreline translation and coastal onlap
Authors: Swenson John B.
Published: August 2005

Alluvial river systems respond to changing sea level by adjusting channel length through shoreline translation and coastal onlap/offlap at the alluvial basement transition. The magnitude and timing of shoreline translation and coastal onlap/offlap relative to the driving sea level signal depend on the dynamics of the fluvial system and have important implications for interpreting ancient fluviodeltaic deposits. I obtain analytical solutions to a diffusive geometric model of fluviodeltaic response to sea level perturbations that treats the shoreline and alluvial basement transition as moving boundaries. Fluviodeltaic behavior is most sensitive to the ratio of the period of eustatic cycling to the fluvial response time, which varies with the length and water discharge of the fluvial system. The square root of this ratio provides a first‐order estimate of the fraction of the fluvial long profile affected by eustatic forcing. The fluviodeltaic system behaves as a low‐pass filter with respect to eustatic cycling: The amplitude of both shoreline translation and coastal onlap/offlap increase with increasing cycle period within a relatively narrow bandwidth in which the fluvial response time is comparable to the cycle period. Only small time lags develop between shoreline response and eustatic forcing. The time lag between maximum coastal onlap and maximum sea level increases without bound as the forcing period decreases relative to the fluvial response time. Model predictions agree with experimental data and differ considerably from the model predictions of Pitman (1978) and Angevine (1989), which suggest that fluviodeltaic systems are strong high‐pass filters to sea level cycling.
Channelized lava flows at the East Pacific Rise crest 9°–10°N: The importance of off‐axis lava transport in developing the architecture of young oceanic crust
Authors: Soule S. A. , Fornari D. J. , Perfit M. R. , Tivey M. A. , Ridley W. I. , Schouten H.
Published: August 2005

Submarine lava flows are the building blocks of young oceanic crust. Lava erupted at the ridge axis is transported across the ridge crest in a manner dictated by the rheology of the lava, the characteristics of the eruption, and the topography it encounters. The resulting lava flows can vary dramatically in form and consequently in their impact on the physical characteristics of the seafloor and the architecture of the upper 50–500 m of the oceanic crust. We have mapped and measured numerous submarine channelized lava flows at the East Pacific Rise (EPR) crest 9°–10°N that reflect the high‐effusion‐rate and high‐flow‐velocity end‐member of lava eruption and transport at mid‐ocean ridges. Channel systems composed of identifiable segments 50–1000 m in length extend up to 3 km from the axial summit trough (AST) and have widths of 10–50 m and depths of 2–3 m. Samples collected within the channels are N‐MORB with Mg# indicating eruption from the AST. We produce detailed maps of lava surface morphology across the channel surface from mosaics of digital images that show lineated or flat sheets at the channel center bounded by brecciated lava at the channel margins. Modeled velocity profiles across the channel surface allow us to determine flux through the channels from 0.4 to 4.7 × 103 m3/s, and modeled shear rates help explain the surface morphology variation. We suggest that channelized lava flows are a primary mechanism by which lava accumulates in the off‐axis region (1–3 km) and produces the layer 2A thickening that is observed at fast and superfast spreading ridges. In addition, the rapid, high‐volume‐flux eruptions necessary to produce channelized flows may act as an indicator of the local magma budget along the EPR. We find that high concentrations of channelized lava flows correlate with local, across‐axis ridge morphology indicative of an elevated magma budget. Additionally, in locations where channelized flows are located dominantly to the east or west of the AST, the ridge crest is asymmetric, and layer 2A appears to thicken over a greater distance from the AST toward the side of the ridge crest where the channels are located.
Cosmogenic helium and neon in 11 Myr old ultramafic xenoliths: Consequences for mantle signatures in old samples
Authors: Moreira Manuel , Madureira Pedro
Published: August 2005

The helium and neon isotopic compositions of olivines coming from a 11 Myr old xenolith sampled at Mt. Hampton (West Antarctica) were analyzed by crushing. The helium isotopic ratio varies between 1340 and 6300 (R/Ra between 115 and 539) with 4He content around 3–8 10−10 ccSTP/g, confirming that cosmogenic helium can be extracted by crushing. The neon also shows a clear cosmogenic origin (20Ne/22Ne down to 7.7 and 21Ne/22Ne > 0.32), indicating that the cosmogenic neon can also be extracted by crushing out of the olivines. Melting of the powder left after the crushing experiment gives a 4He/3He ratio as low as 42 ± 8 (R/Ra = 17,300) and 21Ne/22Ne as high as 0.78, close to the cosmogenic production end‐member. This study shows that up to ∼0.5% of cosmogenic helium and neon can be extracted by crushing. In this way, for samples that had been exposed to cosmic rays for a long time (e.g., a few Myr), a crushing procedure may not give the mantle ratios without ambiguity, and measurement of neon can help to discriminate between cosmogenic and mantle origin of the 3He.
Continental recycling: The oxygen isotope point of view
Authors: Simon L. , Lécuyer C.
Published: August 2005

Mass balance calculations based on a data compilation lead us to estimate a δ18O value of 8.9 ± 0.7‰ for the continental crust. This isotopic composition is the product of two competing processes, namely, the erosion and growth of continental masses. Erosion tends to enrich the continental crust in 18O through low‐temperature isotopic exchange with the hydrosphere, whereas continental growth maintains the composition of the crust close to its mantle‐derived precursor (δ18O = 5.7‰). Box modeling of the oxygen isotope exchange between the continents, mantle, and seawater leads us to calculate a flux of subducted sediments averaged over the Earth's history of 0.4 km3 yr−1, significantly lower than most other recent estimates.
Explaining the dielectric properties of firn as a density‐and‐conductivity mixed permittivity (DECOMP)
Authors: Wilhelms F.
Published: August 2005

The relative dielectric permittivity (RP) of mixtures can be calculated to good approximation by composing its constituents' cubic roots of RP by volume fraction (VF). This is even true for RP's complex continuation, which also treats the conductivity of the material. Firn is a mixture of ice and air. The DECOMP formula links the RP of the ice and its VF, with the RP of the firn. The inversion of the formula is, for most practical applications, possible; the density of firn as well as the ice's RP can then be determined with high spatial resolution from dielectric profiling measurements (DEP) alone. If the ice phase's density and the real component of RP are a constant material property the inversion is feasible. This paper gives an example for numerical inversion of complex‐valued dielectric mixing formulae for some known material properties, which is applicable to other composites as well.
Competitive oxidation in atmospheric aerosols: The case for relative kinetics
Authors: Donahue N. M. , Robinson A. L. , Hartz K. E. Huff , Sage A. M. , Weitkamp E. A.
Published: August 2005

We develop relative kinetics for heterogeneous oxidation of multi‐component organic aerosols. Common accommodation, diffusion, and deposition terms cancel in this formulation, and rate constants may be determined for many compounds simultaneously within an aerosol with a realistic composition. Finally, cross‐phase relative rate constants with a gas‐phase reference compound and a condensed‐phase target compound provide effective rate constants for use in atmospheric models.
Relationship between western North Pacific typhoon activity and Tibetan Plateau winter and spring snow cover
Authors: Xie Lian , Yan Tingzhuang , Pietrafesa Leonard J. , Karl Thomas , Xu Xiangde
Published: August 2005

The annual frequency of western North Pacific (WNP) typhoons and the number of landfall typhoons in China are shown to negatively correlate with the Tibetan Plateau snow cover (TP‐SC) during the preceding winter and spring. When TP‐SC was above normal, fewer typhoons formed in the WNP and made landfall in China, and vice versa. The observed seasonal lag correlation between the TP‐SC and the WNP typhoon activity suggests the existence of a seasonal memory of the East Asia – West Pacific regional climate system which provides a means for the seasonal prediction of WNP typhoon activity and typhoon landfall frequency in China.
Ionospheric characteristics above Martian crustal magnetic anomalies
Authors: Withers Paul , Mendillo M. , Rishbeth H. , Hinson D. P. , Arkani‐Hamed J.
Published: August 2005

We studied several thousand electron density profiles from the Mars Global Surveyor Radio Science experiment. Electron densities in some of these profiles change significantly over vertical distances as short as 1–2 km, often causing localized “bite‐outs”. These “anomalous” profiles are preferentially located above crustal magnetic anomalies. Anomalous features and their association with strong magnetic fields are also seen in profiles from Mariner 9. The probability of a profile being anomalous depends on the orientation of the magnetic field, suggesting localized electrodynamic effects upon otherwise global photochemical ionospheric processes. On Mars, unlike most other planets, the magnetic field has a short characteristic lengthscale, so its effects on the ionosphere will vary over short horizontal distances. We discuss possible ionospheric dynamo processes and encourage additional ionospheric observations over regions of strong crustal magnetic field.
Regional NO3− events in the northeastern United States related to seasonal climate anomalies
Authors: Fischer Emily , Talbot Robert
Published: August 2005

We demonstrate a direct connection between anomalously high levels of NO3− in aerosols over the northeastern U.S. with transport of air masses from south of the Great Lakes during periods of unseasonably warm climatic conditions in that area. Previous studies document the predominant and pervasive role of SO42− and organic matter in regional aerosol composition over the Northeast. Here we characterize multi‐day episodic events where NO3− exceeded SO42− by up to 3‐fold at Mount Washington and increased from the seasonal median of about 1 nmol m−3 to 60–100 nmol m−3. These events take place in the colder seasons, with the three most significant ones in the last 6 years occurring in November 2001, January 2002, and March 2004. We propose that large amounts of NH3 are volatilized in the Midwest under these conditions, which exceeds available SO42− and allows high levels of NH4NO3 aerosol to form. The occurrence of these events, which completely changes the character of aerosols over the Northeast and may lead to enhanced NO3− deposition to ecosystems, could increase with continued warming over North America.
The dual source region for the 2004 Sumatra tsunami
Authors: Fine Isaac V. , Rabinovich Alexander B. , Thomson Richard E.
Published: August 2005

Wave arrival times obtained from coastal tide gage and satellite altimetry records for the Indian Ocean are used to delineate the source region for the December 26, 2004 Sumatra tsunami. Findings define a curved, 250‐km wide, 1000‐km long tsunami source region centered over the Sunda Subduction Zone, which closely matches the seismic source estimated from broadband geophysical data. Imbedded in this general region are “hot spots” associated with the southern fast‐slip and northern slow‐slip domains which served as distinct source areas for the destructive waves that inundated the coast of the Indian Ocean.
Fe3+ and Al solubilities in MgSiO3 perovskite: implication of the Fe3+AlO3 substitution in MgSiO3 perovskite at the lower mantle condition
Authors: Nishio‐Hamane Daisuke , Nagai Takaya , Fujino Kiyoshi , Seto Yusuke , Takafuji Naoto
Published: August 2005

Perovskite in the starting composition of Mg3Fe3+AlSi3O12 was investigated at 24 and 51 GPa and 2100 K using a laser‐heated diamond anvil cell (LHDAC) and an analytical transmission electron microscopy (ATEM) to understand the solubilities of Fe3+ and Al into MgSiO3‐dominated perovskite. A single phase of orthorhombic perovskite was formed at 51 GPa and 2100 K and the Fe3+AlO3 bearing perovskite showed no structural change during decompression. The samples synthesized at 24 GPa and 2100 K showed minor amounts of magnesioferrite and stishovite phases in spaces along the perovskite grain boundaries. These results indicate that the solubility of ferric iron incorporated as the Fe3+AlO3 component in MgSiO3‐based perovskite is higher and slightly lower than 25 mole % at 51 and 24 GPa, respectively.
Slow slip on the northern Hikurangi subduction interface, New Zealand
Authors: Douglas A. , Beavan J. , Wallace L. , Townend J.
Published: August 2005

In October 2002, a surface displacement episode of 20–30 mm magnitude was observed over a ∼10 day period on two continuous Global Positioning System (GPS) instruments near Gisborne, North Island, New Zealand. We interpret this to result from slow slip on the northern Hikurangi subduction interface. Using ten years of regional campaign GPS (1995–2004) and recent continuous GPS data, we estimate the recurrence interval for similar events to be 2–3 yrs. In November 2004, a similar slow slip event occurred within this recurrence period. The 2002 event can be modeled by ∼18 cm of slow slip near the down‐dip end of the seismogenic zone on the subduction interface offshore of Gisborne. The campaign GPS data show that the 2002 slow slip event had little effect on regional strain patterns.
Linear trends of zonally averaged thermosteric, halosteric, and total steric sea level for individual ocean basins and the world ocean, (1955–1959)–(1994–1998)
Authors: Levitus S. , Antonov J. I. , Boyer T. P. , Garcia H. E. , Locarnini R. A.
Published: August 2005

We present estimates of the linear trends of zonally averaged fields of thermosteric, halosteric, and steric sea level by pentads (1955–1959)–(1994–1998) for individual ocean basins and the world ocean. The Atlantic is characterized by density compensating linear trends in the thermosteric and halosteric components of steric sea level change. Northward of approximately 45°N the halosteric trend acts to increase steric sea level and the thermosteric trend acts to decrease sea level. Southward of 45°N these two terms are reversed in sign. Similar to the Atlantic, the Indian Ocean is characterized by density compensating trends at most latitudes, a major exception being 28°S–38°S. The Pacific is different from the Atlantic and Indian oceans. The two components act in concert to change sea level in the same way with the exception of the 34°N–45°N and 22°S–38°S regions.
Importance of aerosol variations for surface UV‐B level: Analysis of ground‐based data taken at Belsk, Poland, 1992–2004
Authors: Jarosławski Janusz P. , Krzyścin Janusz W.
Published: August 2005

We compare various optical characteristics of atmospheric aerosols derived from ground‐based measurements (by Brewer spectrophotometer and Cimel Sun photometer and horizontal visibility from standard observations of the visual range) and satellite measurements (Moderate‐Resolution Imaging Spectroradiometer (MODIS) instrument on board the Terra satellite) over Belsk (51°84°N, 20°79°E), Poland. It is shown that aerosol forcing on the erythemally weighted UV at the Earth's surface is as important for the clear‐sky radiation level as that due to changes in the columnar ozone amount both on long‐term (trend) and short‐term (day‐to‐day) timescales. Real characteristics of aerosols in the UV‐B range appear important for estimating of the erythemally weighted irradiance and actinic flux during cloudless conditions. This is demonstrated by a comparison of the results of a radiative transfer model (libRadtran) using input from various measurements carried out at Belsk and the results using restricted input (possible for many other stations). Frequently, the irradiance and actinic flux in the UV‐B range cannot be modeled using the aerosols characteristics extrapolated directly from those measured in the visible range. A weak correspondence between the horizontal visibility and aerosol optical depth in the UV range is also found. Thus corrections to the results from the radiative transfer model incorporating restricted input are proposed to account for the specific aerosol properties in the UV range.
Shielding Space Explorers From Cosmic Rays
Authors: Parker Eugene N.
Published: August 2005

Expert opinions are split on the most promising strategies for protecting astronauts from the dangers of cancer‐inducing radiation in space.
Put the “Living” Back Into “Living With a Star”
Authors: Kintner P. M.
Published: August 2005

NASA needs to put the “living” back into the Living With a Star (LWS) program by moving ahead with the Ionosphere‐Thermosphere Storm Probes and Imager. For the U.S. taxpayer and the other 6.5 billion inhabitants of the Earth, there are significant space weather impacts driven by the Sun and mediated by the magnetosphere and the ionosphere‐thermosphere systems. On the basis of these impacts, Congress approved the LWS program and the National Academy Decadal Survey of Solar and Space Physics recommended that the Ionosphere‐Thermosphere Storm Probes (ITSP) and the Radiation Belt Storm Probes (RBSP) be implemented following the Solar Dynamics Observatory (SDO). This synergistic sequence of missions was designed to overlap in order to advance our understanding and subsequently enable specification and forecasting. Now a new wave of budgetary constraints demands that NASA reconsider the content and timing of the LWS missions.
Permanent Focal Brain Ischemia Induces Isoform-Dependent Changes in the Pattern of Na+/Ca2+ Exchanger Gene Expression in the Ischemic Core, Periinfarct Area, and Intact Brain Regions
Authors: Boscia Francesca , Gala Rosaria , Pignataro Giuseppe , de Bartolomeis Andrea , Cicale Maria , Ambesi-Impiombato Alberto , Di Renzo Gianfranco , Annunziato Lucio
Published: August 2005

Dysregulation of sodium [Na+]i and calcium [Ca2+]i homeostasis plays a pivotal role in the pathophysiology of cerebral ischemia. Three gene products of the sodium–calcium exchanger family NCX1, NCX2, and NCX3 couple, in a bidirectional way, the movement of these ions across the cell membrane during cerebral ischemia. Each isoform displays a selective distribution in the rat brain. To determine whether NCX gene expression can be regulated after cerebral ischemia, we used NCX isoform-specific antisense radiolabeled probes to analyze, by radioactive in situ hybridization histochemistry, the pattern of NCX1, NCX2, and NCX3 transcripts in the ischemic core, periinfarct area, as well as in nonischemic brain regions, after 6 and 24 h of permanent middle cerebral artery occlusion (pMCAO) in rats. We found that in the focal region, comprising divisions of the prefrontal, somatosensory, and insular cortices, all three NCX transcripts were downregulated. In the periinfarct area, comprising part of the motor cortex and the lateral compartments of the caudate-putamen, NCX2 messenger ribonucleic acid (mRNA) was downregulated, whereas NCX3 mRNA was significantly upregulated. In remote nonischemic brain regions such as the prelimbic and infralimbic cortices, and tenia tecta, both NCX1 and NCX3 transcripts were upregulated, whereas in the medial caudate-putamen only NCX3 transcripts increased. In all these intact regions, NCX2 signal strongly decreased. These results indicate that NCX gene expression is regulated after pMCAO in a differential manner, depending on the exchanger isoform and region involved in the insult. These data may provide a better understanding of each NCX subtype's pathophysiologic role and may allow researchers to design appropriate pharmacological strategies to treat brain ischemia.
Memantine Reduces Hematoma Expansion in Experimental Intracerebral Hemorrhage, Resulting in Functional Improvement
Authors: Lee Soon-Tae , Chu Kon , Jung Keun-Hwa , Kim Juhyun , Kim Eun-Hee , Kim Se-Jeong , Sinn Dong-In , Ko Song-Yi , Kim Manho , Roh Jae-Kyu
Published: August 2005

Glutamate is accumulated in abundance during the early period of experimental hematoma, and the activation of N-methyl-D-aspartate (NMDA) receptors by glutamate can result in an influx of calcium and neuronal death in cases of intracerebral hemorrhage (ICH). Memantine, which is known to be a moderate-affinity, uncompetitive, NMDA receptor antagonist, was investigated with regard to its ability to block the glutamate overstimulation and tissue plasminogen activator (tPA)/urokinase plasminogen activator (uPA)/matrix metalloproteinase (MMP)-9 modulation in experimental ICH. Intracerebral hemorrhage was induced via the infusion of collagenase into the left basal ganglia of adult rats. Either memantine (20 mg/kg/day) or PBS was intraperitoneally administered 30 min after the induction of ICH, and, at daily intervals afterwards, for either 3 or 14 days. Hemorrhage volume decreased by 47% in the memantine group, as compared with the ICH-only group. In the memantine group, the numbers of TUNEL+, myeloperoxidase (MPO)+, and OX42+ cells decreased in the periphery of the hematoma. Memantine resulted in an upregulation of bcl-2 expression and an inhibition of caspase-3 activation. Memantine also exerted a profound inhibitory effect on the upregulation of tPA/uPA mRNA, and finally decreased the MMP-9 level in the hemorrhagic brain. In modified limbplacing test, the memantine-treated rats exhibited lower scores initially, and recovered more quickly and thoroughly throughout the 35 days of the study. Here, we show that memantine causes a reduction of hematoma expansion, coupled with an inhibitory effect on the tPA/uPA and MMP-9 level. Subsequently, memantine was found to reduce inflammatory infiltration and apoptosis, and was also determined to induce functional recovery after ICH.
Organic solid-state lasers based on sexiphenyl as active chromophore
Authors: Schneider D. , Rabe T. , Riedl T. , Dobbertin T. , Kröger M. , Becker E. , Johannes H.-H. , Kowalsky W. , Weimann T. , Wang J. , Hinze P.
Published: August 2005

We report on various sexiphenyl derivatives as gain media in organic solid-state lasers. The molecules involved in this research are simple p-sexiphenyl, the laser dye molecule 2,5,2””’,5””’-tetra-t-butyl-p-sexiphenyl (TBS) and the spirolinked sexiphenyl-derivative 2,7-bis(biphenyl-4-yl)-2’,7’-di-tert-butyl-9,9’-spirobifluorene. It appears that the morphology of vacuum-deposited thin films is highly dependent on the sterical dimensions of the respective molecules. Whereas thin films based on simple p-sexiphenyl comprise large clusters which significantly deteriorate their waveguiding properties; films formed by TBS, and the spiroderivative show a dramatically improved morphology with reduced surface roughness. Therefore amplified spontaneous emission (ASE) and lasing are demonstrated in both of the last but not in films based on p-sexiphenyl. Second-order distributed-feedback lasers with TBS as the active medium have been prepared with an emission between 390 and 435 nm depending on the grating period of the Bragg reflector. While the ASE characteristics are similar in films formed by TBS and the spiroderivative, TBS exhibits even superior laser threshold densities which are as low as 45μJ∕cm2 at a wavelength of 396 nm.
Efficient upconversion fluorescence in a blue-emitting spirobifluorene-anthracene copolymer doped with low concentrations of Pt(II)octaethylporphyrin
Authors: Laquai Frédéric , Wegner Gerhard , Im Chan , Büsing Arne , Heun Susanne
Published: August 2005

Upconversion-induced fluorescence in platinum-octaethylporphyrin (PtOEP)-doped thin films of a spirobifluorene-anthracene copolymer has been investigated. Upon exciting in the range of the absorption band (2.31 eV, 537 nm) of the guest molecules, blue fluorescence (2.75 eV, 450 nm) from the spirobifluorene host was observed. The intensity of the upconverted emission was found to be one order of magnitude higher than from a PtOEP doped but anthracene-free spirobifluorene copolymer and than previously reported for metallated porphyrin-doped polyfluorene samples. It is argued that the efficient upconversion originates from the triplet energy transfer from the phosphorescent dopant to the sensitive unit of the host polymer, followed by triplet-triplet annihilation and finally blue emission from the spirobifluorene host polymer backbone.
Magnetic and optical properties of the InCrN system
Authors: Anderson P. A. , Kinsey R. J. , Durbin S. M. , Markwitz A. , Kennedy V. J. , Asadov A. , Gao W. , Reeves R. J.
Published: August 2005

Room-temperature ferromagnetic In1−xCrxN films with x ranging from 0.0005 to 0.04 and antiferromagnetic CrN films have been grown by plasma-assisted molecular-beam epitaxy. Electron and x-ray-diffraction techniques could find no evidence for precipitates or phase segregation within the films. Ferromagnetism was observed in the In1−xCrxN layers over a wide range of Cr concentrations, with the magnitude of the ferromagnetism found to correlate with the background carrier concentration. Higher n-type carrier concentrations were found to lead enhanced ferromagnetism, with maximum saturation and remnant moments of 7 and 0.7emu∕cm3, respectively. The addition of Cr to the InN matrix led to reduced photoluminescence intensity and a shift of the peak to higher energy. These observations along with a band-gap-like optical transmission feature at 0.7 eV suggest that CrN has an indirect gap of approximately 0.7 eV and a direct Γ-valley gap greater than 1.2 eV.
Change in soft magnetic properties of Fe-based metallic glasses during hydrogen absorption and desorption
Authors: Novák L. , Lovas A. , Kiss L. F.
Published: August 2005

The stress level can be altered in soft magnetic amorphous alloys by hydrogen absorption. The resulting changes in the soft magnetic parameters are reversible or irreversible, depending on the chemical composition. Some of these effects are demonstrated in Fe–B, Fe–W–B, and Fe–V–B glassy ribbons, in which various magnetic parameters are measured mainly during hydrogen desorption. The rate of hydrogen desorption is also monitored by measuring the pressure change in a hermetically closed bomb. The observed phenomena are interpreted on the basis of induced stresses and chemical interactions between the solute metal and hydrogen.
Competition between tensile and compressive stress mechanisms during Volmer-Weber growth of aluminum nitride films
Authors: Sheldon Brian W. , Rajamani Ashok , Bhandari Abhinav , Chason Eric , Hong S. K. , Beresford R.
Published: August 2005

Stress evolution during molecular-beam epitaxy of AIN films was monitored with in situ curvature measurements. Changes in the growth rate produced large stress variations, with more tensile stress observed at higher growth rates. For example, at a growth temperature of 750°C the instantaneous steady-state stress in films with similar grain sizes varied from −0.15GPa at a growth rate of 90nm∕h, to approximately 1.0GPa at a growth rate of 300nm∕h. To explain these results, we develop a kinetic model of stress evolution that describes both tensile and compressive mechanisms. The tensile component is based on a mechanism which is proposed here as an inherent feature of grain-boundary formation. The compressive component is based on our recent model of atom insertion, driven by the excess chemical potential of surface adatoms that is created by the growth flux. The combined model predicts that the stress is largely governed by the competition between tensile and compressive mechanisms, which can be conveniently described with a single parameter, α. The limiting values α→0 and α→+∞ correspond to previous models of compressive and tensile stresses, respectively.
Competition between cation-π interactions and intermolecular hydrogen bonds in alkali metal ion-phenol clusters. I. Phenol dimer
Authors: Vaden Timothy D. , Lisy James M.
Published: August 2005

The competition between ion-molecule and molecule-molecule interactions was investigated in M+(phenol)2 cluster ions for M=Li, Na, K, and Cs. Infrared predissociation spectroscopy in the O–H stretch region was used to characterize the structure of the cluster ions. By adjusting the experimental conditions, it was possible to generate species where argon was additionally bound in order to investigate cold cluster ions. The spectra showed the presence of hydrogen bonding in the colder M+(phenol)2Ar cluster ions but the absence of hydrogen bonding in the warmer M+(phenol)2 species. For the cold species, the IR spectra were compared with minimum-energy ab initio calculations to elucidate the hydrogen-bonded structures. In the dominant hydrogen-bonded configurations observed experimentally, the phenol molecules form hydrogen-bonded dimers and the alkali-metal ions bind to the phenol via a cation-π interaction with the aromatic ring. Increasing the strength of the cation-π interaction by decreasing the ion size forces the distance between the phenol O–H groups to increase, thus weakening the intermolecular hydrogen bond. Free-energy differences of different configurations relative to the ground state demonstrate that hydrogen-bonded structures are enthalpically favored, while non-hydrogen-bonded structures are entropically favored and are thus observed in the warm cluster ions.
Light emission and degradation of single-walled carbon nanotube filament
Authors: Zhao Z. G. , Li F. , Liu C. , Cheng H. M.
Published: August 2005

Household light bulbs were fabricated using macroscopically long and aligned single-walled carbon nanotube (SWNT) ropes as filaments. It was found that the SWNT filament could emit bright light when an electric current was passed through it. The light spectrum from the SWNT filament showed a nonblackbody characteristic of the thermal emission, and its infrared emission was almost completely suppressed possibly due to the “photonic band-gap” effect that originates in the loose fibrous bundle structure of the SWNT filament. The electrical resistance of the SWNT filament was found to first increase, and then continually decrease during light emission. It was also found that an electric current could cause degradation and burnout of the SWNT filament and result in complete amorphization, and that an interesting mushroomlike carbon structure was formed due to the carbon evaporation of the nanotube filament during light emission.
Large coercivity and low-temperature magnetic reorientation in ε-Fe2O3 nanoparticles
Authors: Gich M. , Roig A. , Frontera C. , Molins E. , Sort J. , Popovici M. , Chouteau G. , Martín y Marero D. , Nogués J.
Published: August 2005

A large coercive field, HC=20kOe, is obtained at room temperature in ε-Fe2O3 nanoparticles embedded in a silica matrix, produced by sol-gel chemistry. The combination of a relatively high magnetic anisotropy together with the small saturation magnetization are responsible for this large HC. Upon cooling, a strong reduction of HC is observed at T∼100K, which is accompanied by a drastic reduction of the squareness ratio MR∕MS. Neutron-diffraction measurements reveal the existence of a low-temperature magnetic transition to which the softening of this material can be ascribed.