bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic Force Microscopic Observations of Diamond-like Carbon (DLC)
Films Produced by Plasma Immersion and Fibroblasts Cultured on DLC
Authors: Uzumaki E. T. , Lambert C. S. , Santos Jr. A. R. , Zavaglia C. A. C.
Published: May 2007

Diamond-like carbon (DLC) films have been intensively studied with a
view to improving orthopaedic implants. Studies have indicated
smoothness of the surface, low friction, high wear resistance, corrosion
resistance and biocompatibility [1-4]. DLC coatings can be deposited
using various techniques, such as plasma assisted chemical vapour
deposition (PACVD), magnetron sputtering, laser ablation, and others
[5]. However it has proved difficult to obtain films which exhibit good
adhesion. The plasma immersion process, unlike the conventional
techniques, allows the deposition of DLC on three-dimensional
workpieces, even without moving the sample, without an intermediate
layer, and with high adhesion [6], an important aspect for orthopaedic
articulations. In our previous work, DLC coatings were deposited on
silicon and Ti-13Nb-13Zr alloy substrates using the plasma immersion
process for the characterization of microstructure, mechanical
properties and corrosion behaviour [7-9]. Hardness, measured by a
nanoindenter, ranged from 16.4-17.6 GPa, the pull test results indicate
the good adhesion of DLC coatings to Ti-13Nb-13Zr, and electrochemical
assays (polarization test and electrochemical impedance spectroscopy)
indicate that DLC coatings produced by plasma immersion can improve the
corrosion resistance [9].
Characterization of Ultrathin Films of Cellulose Esters
Authors: Kosaka P. M. , Kawano Y. , Salvadori M. C. , Petri D. F. S.
Published: May 2007

The adsorption of polysaccharides onto solid substrates provides an
environment for the immobilization of biomolecules [1] giving rise to
conditions for the development of biosensors [2] and kits for
immunoassays. One can find in the literature reports about the adhesion
of proteins on cellulose ester membranes [3]. However, studies about the
formation of cellulose ester ultrathin films have been seldom reported.
Cellulose esters are nontoxic materials largely used as coating layers,
fibers, inks and films.
Characterization of Thin Films Using Different Scanning Probe
Microscopy (SPM) Modes
Authors: Marulanda D. M. , Arias D. F. , Devia A.
Published: May 2007

Scanning probe microscopy (SPM) is unique among the imaging
techniques in which it provides three-dimensional (3-D) real-space
images and among surface analysis techniques in which it allows
spatially localized measurements of structure and properties. Under
optimum conditions, subatomic spatial resolution is achieved. The
development given has not been only because of its ability to obtain
topographic and structural images of the surface at micro and nano
scale, but also for the possibility of performing analysis of
superficial properties such as local adhesion properties, chemical
heterogeneity, and local mechanical properties [1]. The SPM has
different variations depending on the interaction between the tip and
the sample surface, such as AFM, which has the ability of showing
topographic characteristics at atomic scale, LFM, which measures local
friction differences, FMM and PDM that measure differences of local
elasticity. The instrument counts with the spectroscopy mode and with
this it is possible to obtain Force — distance (F-d) curves that give
information about the local elastic properties of the sample surface. In
this work, TiN and ZrN thin films grown by the PAPVD by pulsed arc
technique were studied, using the AFM, LFM, FMM, PDM and spectroscopy F
vs. d techniques.
Fabrication of Selective Metal Contacts on Single-Walled Carbon
Nanotubes for Device Applications
Authors: Maciel I. O. , Neves B. R. A. , Santos A. P. , Furtado C. A. , Ferlauto A. S. , Plentz F.
Published: May 2007

Silicon based devices are expected to achieve the limit of possible
downscaling in 10 to 15 years. Thus, the search of new materials to
construct smaller, faster and more energy efficient devices has been a
very active research area. Carbon nanotubes (CNTs) are very good
candidates to construct nanoelectronic and nanophotonic devices [1,2,3]
due to unique physical properties, such as its metallic or
semiconducting characteristics depending only its diameter and chirality
[4,5] and capability of caring high current densities (up to 1010A/cm2).
In this work we develop nanofabrication techniques of single-walled
carbon nanotubes (SWNTs) based devices using a combination of electron
beam and optical lithography with Atomic Force Microscopy (AFM). We used
both CVD-grown nanotubes [6] and HipCO-NTs [7] suspended on aqueous
solution and deposited on the substrate. Atomic Force Microscopy (AFM)
in tapping mode (Multimode Nanoscope IV, Digital Instruments) was used
to CVD sample characterization, study of CNT deposition and to localize
and index the nanotubes on substrate using lithography patterns as
references, making possible to selectively construct metallic contacts
on the CNTs.
Mechanical Measurements of Multilayer Thin Films Obtained by a
PAPVD System
Authors: Arroyave M. , Perez W. , Quintero J. , Casanova S. , Devia A.
Published: May 2007

The need of techniques for determining the mechanical properties of
thin films, e.g. hardness coatings on ion beam treated surfaces has
prompted a study of the microindentation hardness technique. The present
interest is driven to a good understanding of the adhesion, friction,
wear, and indentation processes. In most of the solid-solid interfaces
of technological relevance, it occurs contact in many asperities, and
this is why the study of fundamental properties of micro-mechanic and
tribology of surfaces and interfaces is very important. The recent
developments of different microscopic techniques based on tips and force
surface devices (i.e. AFM, FM, LFM) allowed investigations of
interfacial problems with high resolution and have led to the nanoscale
regime the mechanical properties study for a wide spectrum of materials.
In this work a method for Young's modulus determination of hard coatings
multilayers of TiN/ZrN is evaluated. This method is based on AFM and
spectroscopy-force modes [1-2].
Grains and Sub Grains Identification in AISI 430 Stainless Steel
with Atomic and Magnetic Force Microscopies
Authors: Vilela J. M. C. , de Oliveira N. J. L. , Talarico M. L. , Andrade M. S. , Barbosa R. A. N. M. , Goncalves I. N. , Oliveira T. R.
Published: May 2007

Cold rolled sheets of AISI 430 ferritic stainless steel have been
widely used in kitchen utensils, ornamental articles, among other
products due to their corrosion resistance and good formability.
However, a localized increase of the surface roughness, known as
ridging, develops during ferritic stainless steel forming [1]. The
ridging is caused by anisotropic plastic flow of the material containing
alternated bands of different crystallographic textures. These bands, or
grain colonies, are formed during hot rolling fabrication step. During
this step, the deformed grains can undergo dynamic recrystallization
and/or recovery. In the regions where recovery takes place these texture
bands are formed. In order to study ridging, it is necessary to identify
the recovered regions (regions containing sub grains with nearly the
same crystal orientation) and recrystallized regions (regions containing
grains with different crystal orientations). Two well established
techniques are applied to the characterization of recrystallized and
recovered grains: the optical microscopy with polarized light, normally
done in samples prepared with colored etching, and the electron
backscatter diffraction (EBSD). In this work, atomic force microscopy
(AFM) and magnetic force microscopy (MFM) were used to study the
recrystallization and the recovery of the deformed specimens.
Silver Nanoparticles Self Assembled on HOPG: Unusual Behavior as
Probed by Scanning Tunneling Microscopy
Authors: Andrade J. E. , Aquiar H. B. , Cunha F.
Published: May 2007

The controlled construction of nanostructures on solid surfaces for
technological applications depends primarily on a deep understanding of
the physical chemistry of the interface. Several methods have been
devised to grow metallic nanostructures on solid surfaces, notably
physical vapor deposition and electrodeposition. The electrochemical
method led to the creation of a very promising technology called
Electrochemical Step Edge Decoration (ESED) by the Penner group in
Irvine, Ca. In this method, metallic nano and mesowires are built
through electrochemical deposition on the step edges of the basal plane
of Highly Oriented Pyrolytic Graphite (HOPG) [1]. The proposed growth
mechanism is based on the Terrace-Ledge-Kink (TLK) model [2], in which
the foreign adatoms nucleate the electrochemically induced growth of
nanoparticles in the lower plane of step edges. White and collaborators
[3], while studying the stability of gold nanoparticles electrodeposited
on HOPG, noticed the preferential nucleation on the upper plane of step
edges in stark opposition to the TLK model. They proposed that this
preferential deposition is associated with a slippage of the atomic
layer near the edge. This proposition indicates that the surface in the
upper plane near the edge will present a decrease in the atomic distance
in the plane, disrupting the registry with the underlying plane. To
further assess this proposition we have devised another experimental
approach where, instead of electrodepositing foreign adatoms for
nucleation and growth, we deposited fully formed silver nanoparticles on
HOPG through a Self Assembly mechanism and studied its spatial
distribution. Through this approach, we intend to study the surface
mobility of nanoparticles, as opposed to atomic species as studied in
electrochemical deposition.
The 2004 Parkfield earthquake: Test of the electromagnetic precursor hypothesis
Authors: Park Stephen K. , Dalrymple William , Larsen Jimmy C.
Published: May 2007

A controversy has existed for 30 years concerning the possibility of earthquake prediction using electromagnetic precursors. Long‐term electromagnetic monitoring prior to, during, and after the M6.0 earthquake at Parkfield, California, on 28 September 2004 now provides a definitive test of this hypothesis. During the earthquake our instruments recorded clearly documented electrical signals from an earthquake: impulsive changes of up to +2.5 mV at an electrode located 250 m from the rupture zone followed by a transient decay lasting at least 3 1/4 hours. Similar signals (−1.5 mV) were recorded with the only two M > 5 aftershocks, but their transient decays lasted for only ∼17 min. These signals are unambiguously a result of the earthquake and can be useful in studies of fluid flow in faults, a major current topic in earthquake physics. Patterns in the distribution of transient voltages differ from static stress changes, but are consistent with a small coseismic pressure drop on the fault and fluid flow inward. Signals at a distance of 1 km from the fault are less than 1 mV and are statistically no different from zero in our analysis. Transient voltages for the aftershocks have opposite polarity from those recorded with the main shock and are again maximal close to the fault, suggesting subsequent outward flow from the fault. Finally, there is no evidence of any precursory signal, strongly calling into question previously suggested signals preceding smaller or more distant earthquakes.
Coccolith δ18O and alkenone records in middle Pliocene orbitally controlled deposits: High‐frequency temperature and salinity variations of sea surface water
Authors: Beltran Catherine , de Rafélis Marc , Minoletti Fabrice , Renard Maurice , Sicre Marie Alexandrine , Ezat Ullah
Published: May 2007

The calcareous nannoplankton flora is strongly controlled by water masses and is sensitive to ambient nutrient levels. In consequence, fossil remains of calcareous nannoplankton are useful tools for paleoceanography. Although they are the major producers of carbonates in the pelagic realm, their use as a seawater δ18O recorder is not easy due to their small size and the difficulty in isolating them from the bulk carbonate. Using a granulometric separation technique (Minoletti et al., 2001), it is now possible to concentrate coccoliths in monospecific fractions. We applied this method on three precession cycles (insolation cycles i‐288 to i‐282) from the mid‐Pliocene Punta Piccola section (South Sicily), which led to an almost pure Pseudoemiliana lacunosa fraction. It was then possible to measure the isotopic signatures (δ18O and δ13C) and alkenone unsaturation ratio on the same recorder: P. lacunosa. This permits a precise reconstruction of environmental conditions (temperature and salinity) that prevailed in the upper photic zone during the cyclic deposition of these sediments. Our data provide a clear confirmation that sapropelic marl formation occurred during a wetter climate compared to the deposition of the marly limestones. Moreover, these results point out that salinity variations are not, as previously thought, always the primary factor that controlled the deposition of these cyclic events. This study is a step forward in the utilization of calcareous nannoplankton isotopic records in paleoenvironmental reconstructions.
Oceanic climate and circulation changes during the past four centuries from radiocarbon in corals
Authors: Druffel Ellen R. M. , Griffin Sheila , Beaupré Steven R. , Dunbar Robert B.
Published: May 2007

We analyzed radiocarbon in annual coral bands from the Galápagos Islands in the tropical east Pacific to understand natural variability of past ocean circulation associated with climate change. Variability was observed on El Niño timescales (3–7 years) as well as at decadal and multi‐decadal periods. Low radiocarbon levels persisted for ten years during the early 1600s and for sixteen years during the early 1800s, both coincident with periods of high volcanic aerosol loading in the atmosphere from massive eruptions. Intensification of tropical circulation at this time may be linked to climatically‐controlled changes in the structure of the tropical thermocline that is responsible for delivering cool, upwelled waters to the tropical east Pacific.
Transequatorial magnetic flux loops on the Sun as a possible new source of geomagnetic storms
Authors: Saito Takao , Sun W. , Deehr C. S. , Akasofu S.‐I.
Published: May 2007

Some intense geomagnetic storms have no clear solar activity several days prior to their onset (SSC). On the other hand, some of such storms are associated with an unmistakable indication of magnetic flux ropes in interplanetary space. We found that some of such SSC geomagnetic storms occurred several days after the passage of transequatorial loops on the central part of the solar disk; transequatorial magnetic loops connect sunspot groups between the northern and southern hemispheres and at times show some brightening activity for a day or so. Since transequatorial loops must have the IMFBzcomponent, we examined them as a new possible source of geomagnetic storms, in addition to solar flares and filament disappearances.
Slow initial phase and nucleation process of microearthquakes in western Nagano, central Japan
Authors: Ito Shinobu , Ito Hisao
Published: May 2007

We investigated the slow initial phase of small earthquakes (M 0.0–3.6) in western Nagano, central Japan, by deconvolution with causal attenuation operators and empirical Green's functions. To determine whether the slow initial phase is caused by propagation effects along the raypath or source effects, we investigated whether all earthquakes begin as shear cracks with a constant stress drop and rupture velocity, whether the path effect can be represented by a constant attenuation operator, and whether the seismograms of the smallest earthquakes are empirical Green's functions for the path effect of larger earthquakes. We found that the larger earthquakes (M ≥ 1.9) have complicated source processes in combination with linear growth, while smaller earthquakes show simple linear increases in moment accelerations. It is possible that the larger earthquakes are fundamentally different from the smaller earthquakes. It also appears that the complex waveforms observed in the larger earthquakes can be explained by multiple rupture processes, although the slow initial phase of M ≥ 1.9 events, at the very least, must be explained as a source effect.
Transport properties of pyroclastic rocks from Montagne Pelée volcano (Martinique, Lesser Antilles)
Authors: Bernard Marie‐Lise , Zamora Maria , Géraud Yves , Boudon Georges
Published: May 2007

The hydraulic and electrical properties of pyroclastic rocks have been investigated in laboratory on a representative sampling of Montagne Pelée (Martinique, France) deposits with renewed interest in geophysical applications. This sampling covers all the lithologic units of this volcano: lava dome and lava flows, pumices from ash‐and‐pumice fall and flow deposits, lava blocks from block‐and‐ash flow and Peléean “nuées ardentes” deposits, scoriae from scoria flow deposits. The connected porosity varies over a wide range from 3 to 62%. The unconnected porosity is important only on pumices where it can reach 15%. The permeability covers more than 5 orders of magnitude, ranging from 10−16 to 35 × 10−12 m2. The higher values are obtained on lava blocks and the scoriae, even if these rocks are less porous than the pumices. The formation factor ranges from 7 to 1139. The transport properties of these rocks are slightly correlated with porosity. This indicates that these properties are not only controlled by the connected porosity. To connect the transport properties to the textural characteristics of the pore network of pyroclastic rocks, different models, based on geometrical considerations or percolation theory, were tested. The pore access radius distribution and the tortuosity control the transport properties of pyroclastic rocks. Consequently, the models (electric and hydraulic) based on the concept of percolation (e.g., the models of Katz and Thompson), apply better than the equivalent channel model of Kozeny‐Carman. In addition, the difference in transport properties observed on lava blocks and pumices confirms that the mechanisms of degassing and vesiculation are different for these two types of rock.
North Luzon and the Philippine Sea Plate motion model: Insights following paleomagnetic, structural, and age‐dating investigations
Authors: Queano Karlo L. , Ali Jason R. , Milsom John , Aitchison Jonathan C. , Pubellier Manuel
Published: May 2007

Results of one of the most comprehensive paleomagnetic and supporting geological programs ever carried out in offshore SE Asia on North Luzon, northern Philippines, are reported. Six new results, based on 66 sites, are reported from a total collection of 243 individual sites. Declinations in the data subset are sometimes scattered, likely reflecting combinations of major plate and local rotations in both clockwise and counterclockwise directions, and thus have a somewhat limited value for tectonic modeling. The inclination data are, however, much more valuable and can be best explained if North Luzon traveled as part of the Philippine Sea Plate for most of its history, a scenario which is compatible with the known geology of the eastern Philippines and broader region. In the proposed model, for all of its Eocene‐Pliocene history, North Luzon is placed on the western edge of the Philippine Sea Plate, effectively always just to the west of the site where the Benham Plateau formed ∼40 Ma. The paleomagnetic data indicate a substantial northward migration of the area since the start of the Neogene, with an earlier interval stretching back to at least the mid‐Early Cretaceous when this part of the plate occupied equatorial latitudes. Post‐15 Ma motion of the plate has involved the indentation of the Palawan microcontinental block into the western side of the Philippine Archipelago. Deformations induced by this process offer the most likely explanation for the scattered declinations observed in North Luzon and areas a short distance to the south.
A new strategy for discrete element numerical models: 1. Theory
Authors: Egholm David Lundbek
Published: May 2007

A new derivative of the particle‐based discrete element method (DEM) for computationally modeling the mechanics of granular materials is suggested. In contrast to the conventional DEM, the new stress‐based discrete element method (SDEM) presented here is formulated using a macroscopic parameterization, lending itself well for structural geomodeling for which the Mohr‐Coulomb constitutive relation is the underlying model assumption. In SDEM, consistency exists between the macroscopic properties of a particle assembly and the microscopic parameters specified for each particle, unlike for the standard DEM for which microscopic and macroscopic properties can at best be calibrated through troublesome testing experiments. Importantly, this consistency allows for modeling realistically unforced formation and growth of faults and shear zones, with orientations as predicted by Mohr‐Coulomb theory and in agreement with general observations. By measuring the virtual deformation of spherical elastic particles rather than just virtual particle overlaps, this new formulation introduces strain rate and stress tensors at the particle level. Strain rates are obtained by adopting interpolation techniques from the methodology of meshless continuum methods like smoothed particle hydrodynamics, while the appealing discrete kinematic of DEM, including inherent dilatation effects and stick‐slip instabilities, is preserved as particles interact by finite contact forces. The SDEM theory, the computational strategy, and test examples are presented here. In the companion paper, SDEM computational “sandbox‐type” models illustrate the method's potential for contributing insight into the dynamics and kinematics of more advanced geomechanical processes.
Experimental study of air bubbles and turbulence characteristics in the surf zone
Authors: Mori Nobuhito , Suzuki Takuma , Kakuno Shohachi
Published: May 2007

A set of laboratory experiments of free‐surface elevation, water velocity, void fraction, and bubble distribution was conducted simultaneously for regular wave breaking on a plane slope. The data were collected by using a measurement array of wave gages, a dual‐tip resistivity void fraction probe, and an acoustic Doppler velocimeter. The measurements were conducted in two different wave flumes to check the scale effects of air entrainment into the water on the wave breaking. The power law scaling of bubble size distribution was measured, and it was found that the bubble size has a power law of d−1.5∼−1.7 independent of the location and water depth. The relationship between void fraction and turbulent intensity shows a linear relationship between the void fraction and turbulent intensity.
Alongshore currents and mesoscale variability near the shelf edge off northwestern Australia
Authors: Brink K. H. , Bahr F. , Shearman R. K.
Published: May 2007

Shelf break conditions and alongshore flow off northwestern Australia are studied during the strongly evaporative conditions of austral winter 2003. Present results, along with those of previous authors, confirm that a poleward, fresh Leeuwin current core is normally found near the shelf break. Salinity increases alongshore toward the southwest. Although there is no obvious shelf break front, there is a persistent offshore upward tilting of isopycnals in the depth range of 100–150 m. Repeated mesoscale surveys were made at the shelf edge during 8 days when the shelf break flow was equatorward. Waters offshore of the shelf break contain a rich baroclinic ageostrophic eddy field, with typically 10 km length scales, and the eddy patterns in the upper 60 m are uncorrelated with those below 90 m. The two depth horizons yield energy transfers from mean to eddy potential energy and appear to represent distinct finite amplitude instabilities on upper ocean and 180 m mean velocity cores, respectively. A linear stability model supports the existence of the two vertically separated instability types.
Dust absorption over the “Great Indian Desert” inferred using ground‐based and satellite remote sensing
Authors: Moorthy K. Krishna , Babu S. Suresh , Satheesh S. K. , Srinivasan J. , Dutt C. B. S.
Published: May 2007

Mineral dust is the single largest contributor of natural aerosols over land. Dust aerosols exhibit high variability in their radiative effects because their composition varies locally. This arises because of the regional distinctiveness of the soil characteristics as well as the accumulation of other aerosol species, such as black carbon, on dust while airborne. To accurately estimate the climate impact of dust, spatial and temporal distribution of its radiative properties are essential. However, this is poorly understood over many regions of the world, including the Indian region. In this paper, infrared (IR) radiance (10.5–12.5 μm) acquired from METEOSAT‐5 satellite (∼5‐km resolution) is used to retrieve dust aerosol characteristics over the “Great Indian Desert” and adjacent regions. The infrared radiance depression on account of the presence of dust in the atmosphere has been used as an index of dust load, called the Infrared Difference Dust Index (IDDI). Simultaneous, ground‐based spectral optical depths estimated at visible and near‐infrared wavelengths (using a multiwavelength solar radiometer) are used along with the IDDI to infer the dust absorption. The inferred single scattering albedo of dust was in the range of 0.88–0.94. We infer that dust over the Indian desert is of more absorbing nature (compared with African dust). Seasonally, the absorption is least in summer and most in winter. The large dust absorption leads to lower atmospheric warming of 0.7–1.2 K day−1.
Spike‐like change of the vertical E × B drift in the equatorial region during very large geomagnetic storms
Authors: Kil H. , Oh S.‐J. , Paxton L. J. , Zhang Y. , Su S.‐Y. , Min K.‐W.
Published: May 2007

We investigate the characteristics of the storm‐time disturbance electric fields in the equatorial region using the measurements of the vertical ion velocity from the Defense Meteorological Satellite Program F13 and the first Republic of China Satellite during the selected 43 geomagnetic storms of Dst <−100 nT in 2000–2004. The distinguishing feature in both observations is the occurrence of the spike‐like vertical E × B drift during the main phase of very large storms (Dst <−150 nT). The spikes occur simultaneously at different local times but the direction of the spikes shows a dependence on the local time. The spikes are upward on the dayside and downward on the nightside. The observed characteristics of the spikes can be explained by the penetration of the dawn‐to‐dusk polar cap electric field to low latitude.
On recent interannual variability of the Arctic winter mesosphere: Implications for tracer descent
Authors: Siskind David E. , Eckermann Stephen D. , Coy Lawrence , McCormack John P. , Randall Cora E.
Published: May 2007

Observations from the Sounding of the Atmosphere with Broadband Emission Radiometry (SABER) experiment on the NASA/Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite show an unusual vertical displacement of the winter Arctic stratopause in 2006 with zonal mean temperatures at 0.01 hPa (∼78 km) exceeding 250 K. By contrast, at the conventional stratopause location near 0.7 hPa (∼50 km), temperatures were unusually cold. Simulations with the NOGAPS‐ALPHA model suggest that these are coupled to an unusually warm and disturbed lower stratosphere that filtered out many of the gravity waves that normally break at and above 50 km. The model also shows that downward transport in the 2006 Arctic vortex was enhanced relative to 2005. These results might explain observations of enhanced upper atmospheric NO descending to the upper stratosphere in 2006 and highlights the importance of gravity waves in modulating the coupling of the upper atmosphere with the stratosphere.
A regional model of the geomagnetic field over the Pacific Ocean for epoch 2002
Authors: Toh Hiroaki , Kanezaki Hironori , Ichiki Masahiro
Published: May 2007

The Pacific region has been geomagnetically less surveyed in the sense that there are a very limited number of ground stations that continuously measure the Earth's vector magnetic field. Recently, however, long‐term vector geomagnetic observation has started at several stations, mostly on oceanic islands but including one seafloor station, which presently reinforces monitoring the geomagnetic field by the land‐based observation network. The new geomagnetic data together with those collected by Intermagnet Magnetic Observatories (IMOs) being operated in the Pacific and its rim were combined to give a regional geomagnetic reference field over the western Pacific (RGRF‐P) for epoch 2002 using spherical cap harmonics (SCHs). The resultant snapshot of the regional geomagnetic field was found to coincide well with existing global models, e.g., the 10th generation of International Geomagnetic Reference Field (IGRF‐10). This implies that the regionally denser geomagnetic network still sees small contribution of non‐dipole components over the Pacific.
Improving land‐surface model hydrology: Is an explicit aquifer model better than a deeper soil profile?
Authors: Gulden Lindsey E. , Rosero Enrique , Yang Zong‐Liang , Rodell Matthew , Jackson Charles S. , Niu Guo‐Yue , Yeh Pat J.‐F. , Famiglietti James
Published: May 2007

We use Monte Carlo analysis to show that explicit representation of an aquifer within a land‐surface model (LSM) decreases the dependence of model performance on accurate selection of subsurface hydrologic parameters. Within the National Center for Atmospheric Research Community Land Model (CLM) we evaluate three parameterizations of vertical water flow: (1) a shallow soil profile that is characteristic of standard LSMs; (2) an extended soil profile that allows for greater variation in terrestrial water storage; and (3) a lumped, unconfined aquifer model coupled to the shallow soil profile. North American Land Data Assimilation System meteorological forcing data (1997–2005) drive the models as a single column representing Illinois, USA. The three versions of CLM are each run 22,500 times using a random sample of the parameter space for soil texture and key hydrologic parameters. Other parameters remain constant. Observation‐based monthly changes in state‐averaged terrestrial water storage (dTWS) are used to evaluate the model simulations. After single‐criteria parameter exploration, the schemes are equivalently adept at simulating dTWS. However, explicit representation of groundwater considerably decreases the sensitivity of modeled dTWS to errant parameter choices. We show that approximate knowledge of parameter values is not sufficient to guarantee realistic model performance: because interaction among parameters is significant, they must be prescribed as a congruent set.
A transition of interlayer coupling from antiferromagnetic to ferromagnetic observed at low temperatures in CoFe∕Bi∕Co trilayers
Authors: Hsu Jen-Hwa , Xue Zhi-Long , Sahu D.
Published: May 2007

The temperature variation of interlayer coupling on the sandwiches with semimetal bismuth as spacer is reported. The thermal behavior of the coupling between two ferromagnetic layers has been studied in the 25–300K temperature range. The exchange interaction oscillates as a function of spacer thickness between ferromagnetic and antiferromagnetic couplings at room temperature. Besides, the oscillation periods as well as the phase remain the same as the temperature declines from room temperature. However, a strong increase of the coupling strength is found when the temperature is below 150K. Besides, influence of temperature is quite different for ferromagnetic and antiferromagnetic interlayer couplings at low temperatures. The transition from the antiferromagnetic to ferromagnetic coupling causes the disappearance of the oscillation of interlayer coupling. This is because the antiferromagnetic interlayer coupling is suppressed by stronger ferromagnetic interaction.
FePt films fabricated by electrodeposition
Authors: Thongmee S. , Ding J. , Lin J. Y. , Blackwood D. J. , Yi J. B. , Yin J. H.
Published: May 2007

In this work, we have fabricated FePt films with a thickness in the range of 0.1–1μm using the combination of electrodeposition and postannealing. FePt films with a composition around Fe50Pt50 were formed by electrodeposition onto the Si (100) substrates with an underlayer of Au, Ag, or Cu, and subsequently annealed at a temperature in the range of 200–900°C for 20min. From our x-ray diffraction analysis, the L10 FePt phase started to form after annealing at 400°C for the film deposited on the Au underlayer. The highest coercivity (10kOe) was found after annealing at 600°C. When the FePt was deposited on the Ag underlayer, a high coercivity over 15kOe with an out-of-plane anisotropy has been achieved after annealing at 700–800°C. The magnetic anisotropy was associated with the crystallographic texture. The magnetic properties of FePt films deposited on the Cu underlayer were relatively poor with lower values of coercivity (4–5kOe as the maximum coercivity), probably due to the large grain size.
Room temperature ferromagnetism in transition metal (V, Cr, Ti) doped In2O3
Authors: Gupta Amita , Cao Hongtao , Parekh Kinnari , Rao K. V. , Raju A. R. , Waghmare Umesh V.
Published: May 2007

Indium oxide is chosen as the host material for doping Ti, V, and Cr transition metal ions. Theoretical calculations based on density functional theory within a local spin density approximation show that V–V separation of 5.6Å is more stable with a strong ferromagnetic coupling. Our calculations clearly predict that substitution of vanadium for indium should yield ferromagnetism in In2O3. Experimentally, (In0.95TM0.05)O3 (TM=Ti,V,Cr) were prepared using sol-gel as well as solid state reaction methods. Superconducting quantum interference device magnetization measurements as a function of field and temperature clearly showed that the V and Cr doped samples are ferromagnetic with Curie temperature well above room temperature. Thin films deposited by pulsed laser ablation using these materials on sapphire substrates exhibit a preferred 222 orientation normal to the plane of the film. The magnetic moment for (In0.95V0.05)O3 film deposited in 0.1mbar oxygen pressure was estimated to be 1.7μB∕V and is comparable to the theoretical value of 2μB∕V.
Effect of ion irradiation on a Co-based amorphous ribbon
Authors: Park D. G. , Kim C. G. , Lee J. H. , Kim W. W. , Hong J. H.
Published: May 2007

The effects of ion irradiation on a giant magnetoimpedance (GMI) have been investigated for a Co-based amorphous ribbon with various kinds of ions such as Xe, Ar, and N. The GMI ratio and M-H loop parameters were used to characterize the samples before and after the ion irradiation. The GMI ratio increased considerably in the ion irradiated samples and the GMI response showed a strong dependence on the irradiated ion species and driving frequencies. It was shown that the ion irradiations lead to a substantial modification of the magnetic properties including a large coercivity and shearing of the in-plane magnetization loops, thus suggesting the reduction of an exchange coupling.
Thermally activated magnetization reversal behavior of uniaxial ferromagnetic thin films in the microsecond to second time regime
Authors: Ryu Kwang-Su , Lee Kyeong-Dong , Shin Sung-Chul , Choe Sug-Bong
Published: May 2007

We investigate the thermally activated magnetization reversal of Co∕Pd multilayers with uniaxial perpendicular anisotropy using a magneto-optical Kerr effect microscope capable of direct domain observation in a wide time range of microsecond to second. It is found that the energy barrier in the thermally activated process is nonlinearly dependent on the applied field, irrespective of the difference in the domain evolution processes of wall motion, dendrite growth, and nucleation. These results are well explained by a theoretical model considering a ferromagnetic thin film with uniaxial perpendicular anisotropy.
Element specific investigation of ultrathin Co2MnGa∕GaAs heterostructures
Authors: Claydon Jill S. , Hassan Sameh , Damsgaard Christian D. , Bindslev Hansen Jørn , Jacobsen Claus S. , Xu Yongbing B. , van der Laan Gerrit
Published: May 2007

We have used x-ray magnetic circular dichroism to study the element specific magnetic properties of ultrathin films of the Heusler alloy Co2MnGa at room temperature. Nine films were grown by molecular beam epitaxy on GaAs substrates and engineered to vary in stoichiometry as Co1.86Mn0.99Ga1, Co1.95Mn0.98Ga1, and Co1.97Mn0.96Ga1, with thicknesses of 5.3, 7.6, and 9.7nm, and were capped with Al to prevent oxidization. Sum rule analysis revealed magnetic moments significantly lower than the values predicted theoretically, especially in the case of the Mn total magnetic moment. The results do not support the hypothesis that a large magnetic moment is transferred from Co to Mn, and may suggest that diffusion and reacted layers at ultrathin thicknesses can effect the establishment of a full Heusler structure.
Broken spin-Hall accumulation symmetry by magnetic field and coexisted Rashba and Dresselhaus interactions
Authors: Chen Son-Hsien , Liu Ming-Hao , Chen Kuo-Wei , Chang Ching-Ray
Published: May 2007

The spin-Hall effect in the two-dimensional electron gas (2DEG) generates symmetric out-of-plane spin Sz accumulation about the current axis in the absence of external magnetic field. Here we employ the real space Landauer-Keldysh formalism [B. K. Nikolić et al., Phys. Rev. Lett. 95, 046601 (2005); Phys. Rev. B 73, 075303 (2006)] by considering a four-terminal setup to investigate the circumstances in which this symmetry is broken. For the absence of Dresselhaus interaction, starting from the applied out-of-plane B corresponding to Zeeman splitting energy Δ=0–0.5 times the Rashba hopping energy tSOR, the breaking process is clearly seen. The influence of the Rashba interaction on the magnetization of the 2DEG is studied herein. For coexisted Rashba tSOR and Dresselhaus tSOD spin-orbit couplings in the absence of B, interchanging tSOR and tSOD reverses the entire accumulation pattern.
Effects of cation distribution for AFeO3 (A=Ga,Al)
Authors: Kim Woochul , We Jee Hoon , Kim Sam Jin , Kim Chul Sung
Published: May 2007

Piezoelectric and ferrimagnetic AFeO3 (A=Ga,Al) samples have been prepared by various annealing conditions and then their hyperfine structures have been investigated by x-ray diffraction and Mössbauer spectroscopy. From the analysis of the x-ray diffraction patterns by Rietveld refinement method, the crystal structure of samples was found to be an orthorhombic structure (Pc21n,Pna21) with four different cation sites which are labeled A1 and A2 (predominantly occupied by gallium and aluminum ions) and Fe1 and Fe2 (predominantly occupied by Fe ion). The crystal structure is not changed between the samples, but the occupancies of Fe ions in four cationic sites show slight difference. We notice that the occupancies of Fe ion in A1 tetrahedral site of the samples have an effect on the magnetic properties. From the x-ray diffraction results, the ratios of occupied Fe ions in A1 site were determined to be 9.0%, 9.5%, and 7.8% for slow-cooled GaFeO3, quenched GaFeO3, and AlFeO3, respectively, which accord with the result of Mössbauer spectroscopy. We found that the Néel temperature range decreases from 265to250K, with decreasing the Fe–O–Fe bond angles between GaFeO3 and AlFeO3. Also, external field dependence of magnetic moment curve shows a several-stepped shape which is similar with the exchange-spring magnet. It could be explained distinctly by an effect of Fe ion distribution in hyperfine structure.
Determination of the anisotropy of (111) textured IrMn films at low thickness
Authors: Steenbeck K. , Mattheis R. , Diegel M.
Published: May 2007

The anisotropy constant K of antiferromagnetic (111) textured IrMn films was determined from the blocking temperature TB of the high field rotational losses of NiFe∕IrMn(t) film systems of low thickness t⩽2.5nm. The losses are measured by torquemetry as a function of t and temperature T. TB has been calculated using a Stoner-Wohlfarth model adapted to the experiments. From TB=(0.04∕kB)Ktϕ2 (ϕ=grain size), we estimate a constant value of K=(3±1)×105J∕m3 for T=10–400K. The method is applicable also to other measurements of TB(t) and can be modified for other film systems.
Magnetic reversal phenomena in pseudo-spin-valve films with perpendicular anisotropy
Authors: Ilievski Filip , Perkinson Joy C. , Ross Caroline A.
Published: May 2007

Perpendicular pseudo-spin-valve films with structure Ti∕CoCrPt∕Ti∕CoCrPt were fabricated by UHV sputtering. The Ti serves both as a seed layer, to promote a perpendicular c-axis orientation, and as a spacer between the magnetic layers. The films show characteristic two-step switching with a wide plateau corresponding to antiparallel alignments of the magnetic layers. For a 5nm Ti∕5nm CoCrPt∕5nm Ti∕20nm CoCrPt, antiparallel alignment exists between 70 and 345Oe. Minor loops demonstrate switching of the thin layer, in addition to time-dependent magnetization reversal attributed to creep in the magnetization as a result of growth of reversed domains. Magnetic force microscopy and time-dependent magnetization measurements suggest that the domain propagation field is lower than the field necessary for domain nucleation.
Influence of the Oersted field in the dynamics of spin-transfer microwave oscillators
Authors: Consolo G. , Azzerboni B. , Finocchio G. , Lopez-Diaz L. , Torres L.
Published: May 2007

This paper focuses on the magnetization dynamics induced by the balance between the physical positive damping and the negative induced by spin-transfer torque in point-contact devices. We consider an applied field perpendicular to the device plane which both saturates the magnetization of the free layer and tilts the one of the pinned layer about 30° out-of-the-film plane. The influence of the nonuniform current-induced magnetic (Oersted or Ampere) field on the magnetization dynamics of such oscillators has been taken into account within a micromagnetic framework. Results of micromagnetic calculations show that the Oersted field yields spatial asymmetries in the magnetization configuration, which do not introduce any modifications in the frequency domain. Finally, Slonczewski’s analytical formulation [J. Magn. Magn. Mater. 159, L1 (1996)] about the spatial geometry of the current-excited spin-wave modes has been validated numerically.
On the influence of loading profile upon the tensile failure of stainless steel
Authors: Gray G. T. (Rusty) , Bourne N. K. , Henrie B. L.
Published: May 2007

A material placed in direct contact with a high explosive experiences a Taylor wave (triangular-shaped) shock loading profile. While a large number of studies have probed the structure, properties, and tensile response of materials subjected to square-topped shock loading pulses histories, few studies have systematically quantified the influence of shock-wave profile shape on material response. Samples of 316L stainless steel were shock loaded to peak stresses of 6.6, 10.2, and 14.5 GPa to examine the influence of square-topped and triangular (Taylor wave)-shaped pulse loading on the dynamic tensile behavior (spallation). The 316L SS samples were loaded with a square-topped pulse to each peak shock stress, using a pulse duration of 0.9 μs. They displayed increasing incipient spallation damage with increasing peak stress. Samples loaded to the peak shock stresses of 6.6 and 10.2 GPa with a Taylor-wave loading pulse (which immediately unloads the sample after the peak Hugoniot stress is achieved) exhibited no damage. Only the 14.5 GPa Taylor pulse shocked sample exhibited both a pull-back signal and incipient damage following tensile loading. The damage evolution in the square-topped shocked samples was found to be a mixture of void and strain localization damage, the void fraction increasing with peak shock amplitude. With the Taylor-wave loading profile of amplitude 14.5 GPa, a high incidence of shear localization and low incidence of void formation was observed. Detailed analysis of the damage evolution as a function of shock pulse shape revealed that a nominally equivalent level of incipient damage was obtained using a Taylor-wave or square-topped loading pulse when a similar rear sample surface stress-time total impulse was applied. In order to induce equivalent damage with the two pulse shapes, the impulse applied needed to be nominally matched. For this to occur, the Taylor-wave profile required twice the amplitude of the square one and the durations of each pulse needed to be appropriately scaled. Detailed metallographic, microtextural, and void shape and size analyses of the damage evolution are presented as a function of the inferred loading pulse shape and the peak Hugoniot stress.
Single pulse excimer laser nanostructuring of thin silicon films: Nanosharp cones formation and a heat transfer problem
Authors: Eizenkop Julia , Avrutsky Ivan , Auner Gregory , Georgiev Daniel G. , Chaudhary Vipin
Published: May 2007

We present analytical and computer modeling along with an experiment on the formation of sharp conical tips on monocrystalline silicon thin films, silicon-on-insulator, subjected to irradiation by single 25 ns pulses from a KrF excimer laser focused into a spot several micrometers in diameter. These fabricated structures have heights of about 1 μm and apical radii of curvature of several tens of nanometers. We offer a simplified analytical model for the formation of these structures. The computer simulation includes two-dimensional time-dependant heat transfer and phase transformations in Si films on SiO2 substrates that result from the laser irradiation (the Stefan problem). It is shown that upon irradiation and initial melting, the liquid/solid interface remains mainly parallel to the surface of the film. After the laser pulse, the molten material self-cools and resolidifies. The solid/liquid interface moves predominately laterally toward the center of the irradiated spot, forming an almost vertical front. We discuss the relation between the dynamics of the melting/freezing front movement and the displacement of material in the irradiated spot.
Experimental determination of the thermal conductivity of liquid UO2 near the melting point
Authors: Sheindlin M. , Staicu D. , Ronchi C. , Game-Arnaud L. , Remy B. , Degiovanni A.
Published: May 2007

The article gives an account of measurements of the thermal conductivity of liquid UO2. The sample was heated up to above the melting point by a laser pulse of a controlled shape, and the produced thermogram of temperature history was measured by a fast and accurate pyrometer with a time resolution of 10 μs. The experiment shows that the rate of temperature increase during the ascending part of the pulse changes moderately across the melting point. Due to the high power input, this effect cannot be explained in terms of the sole intake of latent heat of fusion. By solving the related heat transfer equation with a 2D-axisymmetric numerical model, it is demonstrated that this feature depends principally on heat conduction in the sample, and proves that the thermal conductivities of solid and liquid are not very different. A theoretical sensitivity study assessing the influence of the liquid thermal conductivity on the pulse temperature evolution showed that the conductivity of the liquid can be deduced from the fitting of the thermograms with a numerical precision of the order of 1%. The analysis reveals that the thermal conductivity is weakly correlated with the effective heat losses during the pulse and to the melting enthalpy, so that the uncertainty in its evaluation by fitting the experimental thermograms with model predictions is satisfactory. The value of the thermal conductivity of liquid UO2 near the melting point resulted to be 2.6±0.35 W m−1 K−1, where the magnitude of the uncertainty is much lower than the scatter of the previously published, discordant measurements.