bluuebunny/crossref_metadata_2025 huggingface dataset:
Long runout landslides: The role of frictional heating and hydraulic diffusivity
Authors: Goren L. , Aharonov E.
Published: April 2007

Natural landslides often exhibit surprisingly large travel distances, and an unexplained decrease in apparent friction coefficient H/L (where H is the drop height and L the travel distance) with increasing slide volume, V. This manuscript investigates a thermo‐poro‐elastic mechanism operating at the base of landslides that may explain this curious behavior. Simulation results indicate that frictional heating at the shear zone at the base of a landslide, elevates pore fluid pressure and reduces friction, resulting in large sliding velocities and distances. Depth‐dependent permeability controls pore pressure diffusion rates from the shear zone, allowing larger slides to maintain high pore pressure for longer times, thus resulting in lower H/L. The numerically obtained relation between V and H/L, agrees with field data of subaerial landslides.
Strong influence of lowermost stratospheric ozone on lower tropospheric background ozone changes over Europe
Authors: Ordóñez C. , Brunner D. , Staehelin J. , Hadjinicolaou P. , Pyle J. A. , Jonas M. , Wernli H. , Prévôt A. S. H.
Published: April 2007

Using ozone measurements from two sounding sites and two high‐altitude stations in Central Europe, we show evidence for a dominant influence of changes in lowermost stratospheric ozone on the variability and overall upward trend of background ozone in the lower troposphere (3000–3500 m asl) during the 1992–2004 period. Numerical simulations with a stratospheric chemistry transport model suggest that changes in lower stratospheric ozone were driven by dynamics rather than by changes in stratospheric chlorine loading. In addition, Lagrangian model simulations indicate that changes in downward transport of ozone from the stratosphere into the troposphere were dominated by changes in lowermost stratospheric ozone concentrations rather than by variations of cross‐tropopause air mass transport. This suggests that the positive ozone trends and concentration anomalies in the lower free troposphere over Europe during the 1990s were likely to a large extent due to enhanced stratospheric ozone contributions, particularly in winter–spring.
Extraordinary dust event over Beijing, China, during April 2006: Lidar, Sun photometric, satellite observations and model validation
Authors: Papayannis A. , Zhang H. Q. , Amiridis V. , Ju H. B. , Chourdakis G. , Georgoussis G. , Pérez C. , Chen H. B. , Goloub P. , Mamouri R. E. , Kazadzis S. , Paronis D. , Tsaknakis G. , Baldasano J. M.
Published: April 2007

An extraordinary dust event over Beijing (April 2006) was followed by a synergy of lidar, Sun photometric and satellite measurements. Extreme aerosol optical depth (AOD) values (1–4) were measured by AERONET and MODIS over Beijing. The size distribution of the particles remained close to 2.5 μm and the single scattering albedo was around 0.92 ± 0.5 (440 nm). Coarse particles contributed to more than 60–80% to the AOD values, indicating the presence of very large particles (Ångström exponent <0.3). Coarse particle contribution to total AOD is associated with the free‐tropospheric aerosols calculated by lidar profiles (65%). Lidar vertical profiles with AOD values from AERONET were used to estimate a typical lidar ratio for the dust particles (84 sr) during the most intense dust period. The DREAM forecast model was applied for the accurate description of the dust event evolution. Ground‐truth data were used for the validation of DREAM over the Beijing area.
Modulation of the growth of auroral kilometric radiation by electromagnetic ion cyclotron waves
Authors: Xin L. , Menietti J. D.
Published: April 2007

The role of electromagnetic ion cyclotron (EMIC) waves in the stimulation of auroral kilometric radiation is addressed in this study. Observations of the modulation of electron flux and energy due to EMIC/electrostatic ion cyclotron waves within the auroral kilometric radiation (AKR) source region have been reported in the past. These modulations produce in turn oscillations of the electron phase space density and therefore lead to fluctuations of AKR growth rate that may translate along the magnetic field line at the group velocity of the stimulating waves. For a model electron “horseshoe” distribution function, we use the theory of the cyclotron maser instability to investigate how this process might influence the AKR wave spectrum and fine structure.
Crust‐mantle boundary in the central Fennoscandian shield: Constraints from wide‐angle P and S wave velocity models and new results of reflection profiling in Finland
Authors: Janik Tomasz , Kozlovskaya Elena , Yliniemi Jukka
Published: April 2007

Our paper presents analysis of the crust‐mantle boundary in the central Fennoscandian shield based on new P and S wave two‐dimensional velocity models of the SVEKA'81, SVEKA'91 and FENNIA wide‐angle reflection and refraction profiles and on results of a new seismic reflection experiment in Finland (Finnish Reflection Experiment (FIRE)). In this area, the crust is extremely thick (50–60 km), and the Moho boundary is difficult to detect using methods based on interpretation of P waves only (near vertical profiling and wide‐angle experiments). However, the S wave reflections from the Moho boundary (SmS) are frequently more pronounced in wide‐angle data than the P wave reflections (PmP). In order to infer the crust‐mantle transition, we developed new P and S wave velocity models using reprocessing of the old data and compared them to record sections of collocated reflection profiles and to published values of Vp and Vp/Vs for the main types of lower crustal and upper mantle rocks. On the basis of the lateral variations of Vp, Vp/Vs, and reflectivity in the lower crust and upper mantle, three main types of the crust‐mantle boundary were distinguished. The first type corresponds to eclogitized lower crust that overlies peridotitic upper mantle. In this case, the Moho coincides with the lithological crust‐mantle boundary. The second type corresponds to lower crust composed of mafic garnet granulites overlying the peridotitic upper mantle, for which the Moho and the lithologic crust‐mantle boundary coincide as well. The third type corresponds to the mafic garnet granulites underlain by a layer of eclogitic upper mantle. In the latter case, the lithological crust‐mantle boundary is deeper than the Moho.
Insights into the magmatic architecture of the Oslo Graben by petrophysically constrained analysis of the gravity and magnetic field
Authors: Ebbing Jörg , Skilbrei Jan Reidar , Olesen Odleiv
Published: April 2007

A new model of the crustal structure of the Oslo Graben with a special emphasis on the location of magmatic intrusions is presented based on the interpretation of gravity and magnetic data constrained by petrophysical data, seismics, and surface geology. Three‐dimensional modeling shows that the gravity high above the Oslo Rift is caused by a combination of crustal thinning and the presence of a high‐density body in the upper crust, related to Precambrian gneiss complexes at the western flank of the rift. The short‐wavelength gravity anomalies are correlated with the outcropping low‐density magmatic rocks of Permian age that extend to the depths of 1.5–4 km. In addition, simultaneous modeling of aeromagnetic data sets collected at two flight altitudes (50 and 3400 m) using susceptibility and remanence within a range of reasonable magnetic properties suggests an underlying intrusion with a depth extent up to 15 km. Magnetization and density of the intrusion are increasing with depth, leading to a small density contrast but a large contrast in magnetization with the surrounding rocks. Therefore only modeling of the magnetic field can resolve the nature of the deep intrusions. The three‐dimensional model provides a new estimate of the volume of magmatic material in the Oslo Graben system (∼63,000 km3); this is only two‐thirds of the values proposed earlier (>95,000 km3) as we disregard high‐volume magmatic underplating. Correlation with structural data, surface geology, and deep lithospheric features shows that the distribution of extrusive rocks in the Oslo Rift can be related to the timing and onset of rifting.
Assessment of interannual variations in the surface mass balance of 18 Svalbard glaciers from the Moderate Resolution Imaging Spectroradiometer/Terra albedo product
Authors: Greuell Wouter , Kohler Jack , Obleitner Friedrich , Glowacki Piotr , Melvold Kjetil , Bernsen Erik , Oerlemans Johannes
Published: April 2007

We estimate annual anomalies of the surface mass balance of glaciers on Svalbard for the period 2000–2005 (six years), by calculating the so‐called “satellite‐derived mass balance” (Bsat) from time series of satellite‐derived surface albedos. The method needs no other input variables. Surface albedos are extracted from the Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra albedo product. We validate the MODIS albedos by comparing them with in situ measurements on Kongsvegen, and we find a low root‐mean‐square error of 0.04 for higher‐quality MODIS data. Confidence in the MODIS product is also provided by realistic profiles of albedo along glacier centerlines. We apply the method to 18 glaciers that are evenly distributed over the archipelago. Correlation coefficients of time series of Bsat and direct measurements of the annual mass balance on Kongsvegen and Hansbreen are highly significant (0.94 and 0.82, respectively). Moreover, spatial distributions of the anomalies for individual years are coherent. Disadvantages of the method are that absolute values of the mass balance cannot be determined and that the interannual variability is underestimated. The latter might be corrected by equations to be established with mass balance models.
North Atlantic cloud cover response to the North Atlantic oscillation and relationship to surface temperature changes
Authors: Previdi Michael , Veron Dana E.
Published: April 2007

Cloud cover changes over the high‐latitude North Atlantic during January associated with the North Atlantic oscillation (NAO) are studied using the Polar MM5 regional climate model. The cloud response to the NAO is marked by an increase in cloudiness during the high phase over much of the North Atlantic east of Greenland and an overall decrease in cloudiness west of Greenland. These cloud changes are accompanied by surface cloud radiative forcing anomalies that are of the same sign as the model‐simulated surface air temperature (SAT) anomalies in most areas. NAO‐related cloud cover changes in January are therefore likely to represent a positive feedback on the SAT changes induced by anomalous atmospheric advection.
Relationship between Amazon and high Andes rainfall
Authors: Vizy Edward K. , Cook Kerry H.
Published: April 2007

A regional climate model is used to study the connections between Amazon and high Andes rainfall. The modeling effort focuses on understanding the rainfall response during the Last Glacial Maximum (LGM) (∼21,000 years ago), as paleoproxy evidence generally suggests that the high Andes were wet during this period, while conditions over the Amazon were drier, although there is more uncertainty about the latter. Analysis of the yearlong present‐day and full LGM integrations reveals that the delayed onset of Amazon convection in the LGM during austral spring is associated with an enhancement of rainfall over the high Andes. In the absence of convection over the Amazon in the austral spring, zonal geopotential height gradients over the Amazon strengthen, resulting in anomalous easterly flow between the Amazon and the high Andes. Instead of the low‐level flow paralleling the Andes (e.g., northwesterly), the flow impinges more directly onto the eastern slopes of the Andes during the LGM, where it rises and transports moisture from the Amazon up into the mountains, enhancing convection over the Andes. This circulation mechanism explains how the moisture and rainfall over the high Andes of Peru and Bolivia can increase (such as the case for the LGM) despite large‐scale drying over South America. Present‐day observations are then explored for 1984, 2002, and 2003 to identify whether mechanisms identified in the paleoclimate modeling are observable in the present‐day climate. Comparison of these particular springs reveals a response analogous to the LGM model response, suggesting that this mechanism that connects tropical Atlantic sea surface temperatures/Amazon convection and high Andes rainfall is operating in the present climate.
Particle fluxes over forests: Analyses of flux methods and functional dependencies
Authors: Pryor S. C. , Larsen S. E. , Sørensen L. L. , Barthelmie R. J. , Grönholm T. , Kulmala M. , Launiainen S. , Rannik Ü. , Vesala T.
Published: April 2007

Particle number fluxes at two forests are computed using data from condensation particle counters and both the eddy covariance (EC) and relaxed eddy accumulation (REA) methods applied offline, post data collection. The results indicate that a 30‐min integration period for flux calculation frequently applied for other scalars is also appropriate for particle number fluxes. Half‐hour average particle number fluxes computed using REA and EC are statistically indistinguishable. Less than 1% of all fluxes derived using EC and REA differ by more than the mutual uncertainty bounds, and the average ratio of fluxes computed using the two approaches is 1.00 ± 0.01. This finding tends to support assertions that, for the size of particles under study (with diameters <100 nm), the assumption of similarity with heat transfer is likely robust. Data from both sites indicate higher particle deposition velocities (vd) for particle ensembles with lower number geometric mean diameter (GMD), for GMD of 10 to 100 nm, although the decrease with increasing GMD is less marked than is predicted by the deposition models such as that of Slinn. The relationships between median and mean vd conditionally sampled by GMD are well described by power law fits. Particle vd exhibits a linear dependence on friction velocity for the range of conditions studied and also enhancement under unstable conditions. Similarities between average particle vd conditionally sampled by number GMD, friction velocity, and stability from the two forest sites point to the generalizability of the empirical fits derived herein.
Predictions of the electrical conductivity and charging of the aerosols in Titan's nighttime atmosphere
Authors: Whitten R. C. , Borucki W. J. , Tripathi S.
Published: April 2007

The electrical conductivity and electrical charge on Titan's atmosphere are computed for altitudes between 0 and 400 km on the nightside for which the main source of ionization is galactic cosmic rays (GCR). Unlike the dayside, electrical charging of the aerosol particles at night is not only negative but also time‐dependent. Hence a time‐dependent model must be employed for computations of electron and ion densities as well as aerosol charging over the night hemisphere. After developing a method for computing the time‐dependent charge states of the aerosol particles, we found that that at altitudes above about 60 km (the effusion range) the charging of the aerosols at the antisolar point is quite close to that at steady state; however, at lower altitudes where (the slow) diffusion of the electrons and ions prevails, the electron density is larger (and the charging of the aerosol particles is smaller) than at steady state. Because polycyclic aromatic hydrocarbons (PAHs) are expected in Titan's atmosphere and have been observed in the laboratory and found to be electrophillic, we have included the formation of negative ions in the aerosol charging model. Such ions are of major importance at night between about 170 and 360 km where they capture most of the negative charge. As a result they greatly reduce the electron density and thus the electrical conductivity in that altitude range. The charge distributions at 50 km (diffusion range), 150 km (effusion range with few negative ions), and 250 km (effusion range) are presented.
Earthquake early warning for Bucharest, Romania: Novel and revised scaling relations
Authors: Böse M. , Ionescu C. , Wenzel F.
Published: April 2007

The accumulation of strong earthquakes with resembling source mechanisms in the Romanian Vrancea zone, SE Carpathians, allows for designing a simple, cheep and robust earthquake early warning (EEW) system for Bucharest with leading times of about 25 s. A previously established scaling relation for EEW predicts in the range from 1–2 s a ten times higher ground motion amplitude in Bucharest than the maximum P‐wave acceleration measured in the epicentral area. Using additional weak and strong motion data, we find that ground shaking in Bucharest is generally overestimated by this relation by a factor of two. However, the predicted amplitudes are within the 95% confidence interval of our revised relation. Additional predictive laws for EEW are determined for different ground motion parameters. The application of our scaling relations to the October 27, 2004 Vrancea earthquake (Mw = 6.0) supports the feasibility of the approach for EEW in Romania.
The possible role in the ocean heat budget of eddy‐induced mixing due to air‐sea interaction
Authors: Greatbatch Richard J. , Zhai Xiaoming , Eden Carsten , Olbers Dirk
Published: April 2007

The traditional point of view is that in the ocean, the meridional transport of heat is achieved by the wind‐driven and meridional overturning circulations. Here we point out the fundamental role played by ocean mixing processes. We argue that mixing (i.e., water mass conversion) associated with eddies, especially in the surface mixed layer, can play an important role in closing the ocean heat budget. Our results argue that the lateral mixing applied at the surface of ocean/climate models should be playing an important role in the heat balance of these models, indicating the need for physically‐based parameterizations to represent this mixing.
Observation of a P-associated defect in HfO2 nanolayers on (100)Si by electron spin resonance
Authors: Clémer K. , Stesmans A. , Afanas’ev V. V.
Published: April 2007

Electron spin resonance analysis has detected a P-donor related point defect in nanometer-thick HfO2 films on (100)Si after annealing in the range of 500–900°C. Based on the principal g matrix (axial; g‖=1.9965; g⊥=1.9975) and hyperfine tensor values (A1=1425±10G, A2=1245±10G, and A3=1160±10G) inferred from consistent K- and Q-band spectrum simulations, the center is assigned to a P2-type defect—a P substituting a Hf atom—similar to P2 in silica, where the unpaired spin is strongly localized on the P atom. The annealing impact is linked to the onset of crystallization enabling substitutional positioning of the P impurities. The centers may act as detrimental charge trapping sites.
Quantitative and qualitative characterization of zigzag spatiotemporal chaos in a system of amplitude equations for nematic electroconvection
Authors: Oprea Iuliana , Triandaf Ioana , Dangelmayr Gerhard , Schwartz Ira B.
Published: April 2007

It has been suggested by experimentalists that a weakly nonlinear analysis of the recently introduced equations of motion for the nematic electroconvection by M. Treiber and L. Kramer [Phys. Rev. E 58, 1973 (1998)] has the potential to reproduce the dynamics of the zigzag-type extended spatiotemporal chaos and localized solutions observed near onset in experiments [M. Dennin, D. S. Cannell, and G. Ahlers, Phys. Rev. E 57, 638 (1998); J. T. Gleeson (private communication)]. In this paper, we study a complex spatiotemporal pattern, identified as spatiotemporal chaos, that bifurcates at the onset from a spatially uniform solution of a system of globally coupled complex Ginzburg-Landau equations governing the weakly nonlinear evolution of four traveling wave envelopes. The Ginzburg-Landau system can be derived directly from the weak electrolyte model for electroconvection in nematic liquid crystals when the primary instability is a Hopf bifurcation to oblique traveling rolls. The chaotic nature of the pattern and the resemblance to the observed experimental spatiotemporal chaos in the electroconvection of nematic liquid crystals are confirmed through a combination of techniques including the Karhunen-Loève decomposition, time-series analysis of the amplitudes of the dominant modes, statistical descriptions, and normal form theory, showing good agreement between theory and experiments.
Chaotic spatial bifurcation by complex coupling
Authors: Shalfeev Vladimir D. , Ivanchenko Mikhail V. , Forti Gian L.
Published: April 2007

A spatial bifurcation (a transition from stationary to oscillatory regime) in a chain of unidirectionally coupled phase systems is studied. It is shown that complication of coupling terms can make this bifurcation spatially chaotic in contrast to the previously observed “regular” and “predictable” type. It is demonstrated that the found type of spatial bifurcation corresponds to a smooth (predictable) manifold in the parameter space, while its spatial location gets actually unpredictable being governed by regularities of chaotic behavior. We infer that complex collective dynamics may arise in networks with plain architecture and simple dynamics of individual elements if nontrivial coupling is realized.
Systematic investigation of Permalloy nanostructures for magnetologic applications
Authors: Engel-Herbert R. , Haque S. A. , Hesjedal T.
Published: April 2007

Magnetic logic gates based on magnetostatically coupled ferromagnetic structures show a great promise for future information processing. The absolute size and shape of the elementary structures determine their intrinsic and interaction properties and thus have to be chosen appropriately in order to allow for binary logic operations. Here, we present a systematic study of the switching behavior, stray field, and coupling of Permalloy nanostructures as a function of geometrical parameters using micromagnetic simulations. We show that bow-tie shaped elements are promising for magnetic logic gates.
Experiments on bubble pinch-off
Authors: Thoroddsen S. T. , Etoh T. G. , Takehara K.
Published: April 2007

A bubble is slowly grown from a vertical nozzle until it becomes unstable and pinches off. We use ultra-high-speed video imaging, at frame-rates up to 1millionfps, to study the dynamics and shape of the pinch-off neck region. For bubbles in water (Bo≃1.0) the radius of the neck reduces with a power law behavior R∼tα, over more than 2 decades, with an exponent in the range α=0.57±0.03, in good agreement with other available studies, but which is slightly larger than 1∕2 predicted by Rayleigh-Plesset theory. The vertical curvature in the neck increases more slowly than the azimuthal curvature, making the neck profiles more slender as pinch-off is approached. Self-similar shapes are recovered by normalizing the axial coordinate by a separate length scale which follows a different power law, Lz∼tγ, where γ=0.49±0.03. Results for air, He, and SF6 gas are identical, suggesting that the gas density plays a minimal role in the dynamics. The pinch-off in water leaves behind a tiny satellite bubble, around 5μm in diameter and the flow-field inside the liquid is shown to be consistent with simple sink flow. The effects of liquid viscosity on the pinch-off speed and neck shapes, are also characterized. The speed starts to slow down at a viscosity of about 10 times that of water, which corresponds to Reμ≃2000. This also changes the power law, increasing the exponent to α≃1 for viscosities above 70cP (Reμ≃40). For surrounding liquid of viscosity above 10cP, we observe just before pinch-off, that the neck is stretched into a thin filament of air, which then breaks into a stream of microbubbles. In some cases we observe a cascade of bubble sizes. While some of the details differ, our results are in overall agreement with those of Burton, Waldrep, and Taborek [Phys. Rev. Lett. 94, 184502 (2005)], except we do not observe the rupture of the air cylinder as it reduces to 50μm size. For water we observe a continuous necking down to the pixel-resolution of our optical system, which at the largest frame-rates is ∼10μm.
Microstructure and possible strain relaxation mechanisms of La2CuO4+δ thin films grown on LaSrAlO4 and SrTiO3 substrates
Authors: He Jiaqing , Klie Robert F. , Logvenov Gennady , Bozovic Ivan , Zhu Yimei
Published: April 2007

Layered perovskite La2CuO4+δ (LCO) thin films were epitaxially grown on SrTiO3 (STO) and LaSrAlO4 substrates by atomic-layer-by-layer molecular beam epitaxy. The lattice defects and residual strain in these films were investigated by means of transmission electron microscopy and electron energy loss spectroscopy. The LCO films showed a high epitaxial quality with flat interfaces and top surfaces. Misfit dislocations with Burgers vector a⟨010⟩ and shear defects were frequently observed at or near the film/substrate interfaces and in the films, respectively. In one LCO film, grown on STO at the highest temperature, 700°C, we observed a two layered structure with the top layer being rhombohedral CuLaO2. In addition, stacking faults were observed in the plane views of one LCO film grown on the STO substrate. The residual strains were evaluated from the associated splitting of Bragg reflection. Possible mechanisms of strain relaxations are discussed based on the observed defects.
Fluid simulations of turbulent impurity transport
Authors: Dubuit N. , Garbet X. , Parisot T. , Guirlet R. , Bourdelle C.
Published: April 2007

Impurity transport in tokamak plasmas is studied with a fluid turbulence code, which has been upgraded to implement two ion species and electrons. The (fixed-flux) simulations are compared to the predictions of a quasilinear model. These simulations mostly agree with quasilinear estimates; they indicate that a turbulent impurity pinch exists. Moreover, this pinch is found to be dominated by curvature terms, as thermodiffusion pinches are found to decrease as 1∕Z and observed parallel velocity effects remain weak. The sign of the pinch is also investigated.
Influence of low temperature thermal annealing on the performance of microcrystalline silicon thin-film transistors
Authors: Chan Kah-Yoong , Bunte Eerke , Stiebig Helmut , Knipp Dietmar
Published: April 2007

Top-gate staggered microcrystalline silicon thin-film transistors (μc-Si:H TFTs) were prepared by plasma enhanced chemical vapor deposition at temperatures below 200°C. The μc-Si:H TFTs exhibit high effective electron mobilities (device mobilities) of up to 35cm2∕Vs for long channel devices. Due to the high carrier mobility μc-Si:H TFTs are promising devices for large area electronics such as organic light-emitting diode displays or radio frequency identification devices. The fabrication process of the μc-Si:H TFTs is similar to the fabrication process of amorphous silicon thin-film transistors, which facilitates an easy transfer of the technology to industry. In this paper, the influence of postfabrication low temperature thermal annealing (150°C) on the device properties of top-gate staggered μc-Si:H TFTs is investigated. Low temperature thermal annealing reduces the device threshold voltage and subthreshold slope. Furthermore, the annealing step results in an increase of the effective mobility for long channel transistors, whereas the effective mobility for short channel transistors is reduced. The influence of the postfabrication low temperature thermal annealing on the device performances will be discussed in detail.
Finite-difference time-domain simulation of fusion plasmas at radiofrequency time scales
Authors: Smithe David N.
Published: April 2007

Simulation of dense plasmas in the radiofrequency range are typically performed in the frequency domain, i.e., by solving Laplace-transformed Maxwell’s equations. This technique is well-suited for the study of linear heating and quasilinear evolution, but does not generalize well to the study of nonlinear phenomena. Conversely, time-domain simulation in this range is difficult because the time scale is long compared to the electron plasma wave period, and in addition, the various cutoff and resonance behaviors within the plasma insure that any explicit finite-difference scheme would be numerically unstable. To resolve this dilemma, explicit finite-difference Maxwell terms are maintained, but a carefully time-centered locally implicit method is introduced to treat the plasma current, such that all linear plasma dispersion behavior is faithfully reproduced at the available temporal and spatial resolution, despite the fact that the simulation time step may exceed the electron gyro and electron plasma time scales by orders of magnitude. Demonstrations are presented of the method for several classical benchmarks, including mode conversion to ion cyclotron wave, cyclotron resonance, propagation into a plasma-wave cutoff, and tunneling through low-density edge plasma.
Effect of pressure on the itinerant ferromagnet CoS2: A first-principles study
Authors: Liu X. B. , Altounian Z.
Published: April 2007

Electronic structure and magnetic properties of CoS2 with a cubic-pyrite-type structure have been studied by a first-principles density functional theory (DFT) calculation using a linear muffin-tin orbital method within the framework of the generalized gradient approximation for the treatment of exchange-correlation effects. The total energy and magnetic moments are calculated as a function of lattice constant. The calculated lattice constant and magnetic moments are in good agreement with the experimental results. The pressure-volume relationship is obtained by fitting the calculated total energy to the universal equation of state. The derived bulk modulus is 137GPa and the equilibrium volume is 42.16Å3∕f.u. The calculated Co magnetic moment decreases at a rate of −0.0055μB∕GPa as the external pressure less than 3.6GPa, in agreement with the experimental value of −0.005μB∕GPa. The DFT calculations predict the occurrence of a first order pressure induced magnetic transition in CoS2 at a high pressure (12GPa), which is qualitatively consistent with the experimental data which show that the ferromagnetic state in CoS2 is unstable at external pressures higher than 6GPa.
Large tunneling magnetoresistance effect at high voltage drop for Co-based Heusler alloy∕MgO∕CoFe junctions
Authors: Rata A. D. , Braak H. , Bürgler D. E. , Schneider C. M.
Published: April 2007

Growth and magnetic characterization of thin films of Co2Cr0.6Fe0.4Al and Co2MnSi full-Heusler compounds are investigated. Thin films were deposited by magnetron sputtering at room temperature directly onto oxidized Si wafers. These Heusler films are magnetically very soft and ferromagnetic with Curie temperatures well above room temperature. Polycrystalline Co2Cr0.6Fe0.4Al Heusler films combined with MgO barriers and CoFe counter electrodes are structured to magnetic tunnel junctions and yield almost 50% magnetoresistance at room temperature. The magnetoresistance shows a strong bias dependence with the maximum occurring at a voltage drop well above 1V. This special feature is accompanied by only a moderate temperature dependence of the tunnel magnetoresistance.
Alfvénic phenomena triggered by resonant absorption of an O-mode pulse
Authors: Tsung F. S. , Morales G. J. , Tonge J.
Published: April 2007

A simulation and modeling study is made of the nonlinear interaction of an electromagnetic pulse, in the O-mode polarization, with a magnetized plasma having a cross-field density gradient. For small amplitudes, the pulse propagates up to the cutoff layer where an Airy pattern develops. Beyond a certain power level, the ponderomotive force produced by the standing electromagnetic fields carves density cavities. The excess density piled up on the side of the cavities causes secondary, field-aligned plasma resonances to arise. Strong electron acceleration occurs due to the short scale of the secondary resonant fields. The fast electrons exiting the new resonant layers induce a return current system in the background plasma. This generates a packet of shear Alfvén waves of small transverse scale and increasing frequency. The results provide insight into microscopic processes associated with a recent laboratory investigation in which large-amplitude Alfvén waves have been generated upon application of high-power microwaves [B. Van Compernolle et al., Phys. Plasmas 13, 092112 (2006)].
Enhanced spin-dependent tunneling magnetoresistance in magnetite films coated by polystyrene
Authors: Wang Wendong , Malkinski Leszek , Tang Jinke
Published: April 2007

Hematite films were deposited by magnetron sputtering. A phase transformation from hematite to magnetite occurred when polystyrene (PS) coated hematite films were annealed above 200°C in hydrogen flow. Giant negative magnetoresistance (MR) was observed with the best MR ratio of over 8% (at room temperature and in a field of 5.5T) found in samples annealed at 230°C. The temperature dependence of the resistivity is characteristic of intergranular tunneling. After the PS layer was removed and the films annealed again at 230°C in hydrogen flow, the resistivity increased by about one order of magnitude and the MR ratio decreased to 4.3%. These data show that PS coating layer can protect magnetite films from oxidation and enhance interganular spin-dependent tunneling magnetoresistance.
Equation of state for expanded fluid mercury: Variational theory with many-body interaction
Authors: Kitamura Hikaru
Published: April 2007

A variational associating fluid theory is proposed to describe equations of state for expanded fluid mercury. The theory is based on the soft-sphere variational theory, incorporating an ab initio diatomic potential and an attractive many-body potential; the latter is evaluated with quatnum chemical methods and expressed as a function of the local atomic coordination number and the nearest-neighbor distance. The resultant equation of state can reproduce the observed gas-liquid coexistence curve with good accuracy, without introducing phenomenological effective pair potentials. Various thermodynamic quantities such as pressure, isochoric thermal pressure coefficient, adiabatic sound velocity, and specific heat are calculated over a wide density-temperature range and compared with available experimental data.
Information-theoretic measures of hyperspherical harmonics
Authors: Dehesa J. S. , López-Rosa S. , Yáñez R. J.
Published: April 2007

The multidimensional spreading of the hyperspherical harmonics can be measured in a different and complementary manner by means of the following information-theoretic quantities: the Fisher information, the average density or first-order entropic moment, and the Shannon entropy. They give measures of the volume anisotropy of the eigenfunctions of any central potential in the hyperspace. Contrary to the Fisher information, which is a local measure because of its gradient-functional form, the other two quantities have a global character because they are powerlike (average density) and logarithmic (Shannon’s entropy) functionals of the hyperspherical harmonics. In this paper we obtain the explicit expression of the first two measures and a lower bound to the Shannon entropy in terms of the labeling indices of the hyperspherical harmonics.
Infrared absorption of C6H5SO2 detected with time-resolved Fourier-transform spectroscopy
Authors: Chu Li-Kang , Lee Yuan-Pern
Published: April 2007

C 6 H 5 S O 2 radicals were produced upon irradiation of three flowing mixtures: C6H5SO2Cl in N2, C6H5Cl and SO2 in CO2, and C6H5Br and SO2 in CO2, with a KrF excimer laser at 248nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record the time-resolved infrared (IR) absorption spectra of reaction intermediates. Two transient bands with origins at 1087.7 and 1278.2cm−1 are assigned to the SO2-symmetric and SO2-antisymmetric stretching modes, respectively, of C6H5SO2. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predict the geometry and vibrational wave numbers of C6H5SO2 and C6H5OSO. The vibrational wave numbers and IR intensities of C6H5SO2 agree satisfactorily with the observed new features. Rotational contours of IR spectra of C6H5SO2 simulated based on predicted molecular parameters agree satisfactorily with experimental results for both bands. The SO2-symmetric stretching band is dominated by a- and c-type rotational structures and the SO2-antisymmetric stretching band is dominated by a b-type rotational structure. When C6H5SO2Cl was used as a precursor of C6H5SO2, C6H5SO2Cl was slowly reproduced at the expense of C6H5SO2, indicating that the reaction Cl+C6H5SO2 takes place. When C6H5Br∕SO2∕CO2 was used as a precursor of C6H5SO2, features at 1186 and 1396cm−1 ascribable to C6H5SO2Br were observed at a later period due to secondary reaction of C6H5SO2 with Br. Corresponding kinetics based on temporal profiles of observed IR absorption are discussed.
Defect induced low temperature ferromagnetism in Zn1−xCoxO films
Authors: Biegger E. , Fonin M. , Rüdiger U. , Janßen N. , Beyer M. , Thomay T. , Bratschitsch R. , Dedkov Yu. S.
Published: April 2007

We present a detailed study on the structural, magnetic, and optical properties, as well as the electronic structure of epitaxial Co-doped ZnO films prepared by magnetron sputtering. Different preparation conditions were implemented in order to control the concentration of oxygen vacancies in the ZnO host lattice. Magnetization measurements indicate ferromagnetic behavior at low temperature for samples prepared at oxygen-poor conditions whereas the samples prepared at oxygen-rich conditions show extremely small ferromagnetic signal corroborating that ferromagnetism in Zn1−xCoxO correlates with the presence of the oxygen-related defects. X-ray absorption spectroscopy (XAS) at the Co L2, 3 edge together with optical transmittance measurements show that Co ions are present in the high-spin Co2+ (d7) state under tetrahedral symmetry indicating a proper incorporation in the ZnO host lattice. Comparison of the O K edge XAS spectra of the samples prepared at different conditions show substantial changes in the spectral line shape which are attributed to the presence of lattice defects such as oxygen vacancies in the ferromagnetic oxygen-poor Co-doped ZnO samples. Our findings indicate that the ferromagnetic properties of Co-doped ZnO samples are strongly correlated with the presence of oxygen vacancies in the ZnO lattice supporting the spin-split impurity band model.
Field dependent alternating current susceptibility of metalorganically deposited YBa2Cu3O7−δ films
Authors: Chen D.-X. , Pardo E. , Sanchez A. , Iliev M. N. , Wang S.-S. , Han Z.-H.
Published: April 2007

The field amplitude and frequency dependent complex alternating current susceptibility χ(Hm, f) of YBa2Cu3O7−δ films metalorganically deposited on different substrates with different processes has been measured at 77 K and studied in relation with their microstructures and some modeling results. It is shown that χ(Hm) for films with well aligned grains and a high Jc is of Bean type with a characteristic f dependence for a power-law E(J), so that thermally activated collective flux creep is the dominant dissipation mechanism. The Jc of these films may be well determined by χ(Hm, f) measurements. For films with misaligned grains and intermediate values of Jc, χ(Hm, f) is anomalous and able to be roughly simulated by a linear-exponential E(J). This phenomenon should be related to the presence of weak links and Josephson vortices, but to look for its physical mechanism is still challenging.
Photonic bands in two-dimensional microplasma arrays. II. Band gaps observed in millimeter and subterahertz ranges
Authors: Sakaguchi Takui , Sakai Osamu , Tachibana Kunihide
Published: April 2007

Plasma photonic band gaps have been observed in a two-dimensional microplasma array, and we have characterized their properties by both experimental and theoretical results. Microplasma columns ignited in helium near atmospheric pressure formed crystal-like structures in a square lattice with a lattice constant from 1.5to2.5mm. Microwaves in the millimeter range transmitting through the array region attenuated at frequencies of photonic band gap in the Γ-X direction, as predicted by the modified plane-wave expansion method. Frequency dependence around the band gap was clarified in the numerical analysis of electromagnetic wave propagation and agreed with experimental results. Electron density in microplasmas was estimated to be 1×1013cm−3 from the attenuation rate at the band gap in the Γ-X direction. Variation of the lattice constant induced frequency shift of the band gap in the millimeter and subterahertz regions, and so plasma photonic crystal can perform as a dynamically controllable band-stop filter.
Anisotropy of the thermal expansion of the Ni(Si1−xGex) phases investigated by high-temperature x-ray diffraction
Authors: Perrin C. , Nemouchi F. , Clugnet G. , Mangelinck D.
Published: April 2007

Thin films of Ni(Si1−xGex) are of interest for their applications in metal-oxide semiconductor transistors as contacts and interconnections. In this work, the lattice parameters and the coefficients of linear thermal expansion (γa, γb, and γc) of the orthorhombic Ni(Si1−xGex) alloys, with 0⩽x⩽1, were determined from high-temperature x-ray diffraction data (298–1073K). A negative thermal expansion along the b axis of Ni(Si1−xGex) is observed for all x values of the Ge concentration: the magnitude of the thermal expansion coefficient decreases with increasing Ge concentration. The anisotropy of the thermal expansion is potentially important for the integration of Ni(Si1−xGex) in microelectronic devices.
Measurements of metal gate effective work function by x-ray photoelectron spectroscopy
Authors: Lebedinskii Yuri , Zenkevich Andrei , Gusev Evgeni P.
Published: April 2007

We developed a method to measure effective work function of metal gate in contact with high-k dielectric. The method was based on the deposition of ultrathin (1–5nm) continuous and very uniform layers of metal on high-k gate stack (HfO2) by pulsed laser deposition and in situ measurements by x-ray photoelectron spectroscopy. This approach was applied to investigate the evolution of work function during silicidation reaction between Ni overlayer and thin Si∕HfO2∕Si(100). The effect of dopants on fully silicided gate formation and work function modulation was also explored. The effective work function of NiSi, Ni2Si, and Sb-doped Si gate electrodes on HfO2 dielectric was found to be 4.4, 4.5–4.7, and 4.2eV, respectively. Ge interlayer at the NiSi∕HfO2 interface showed no significant effect. These values were in a good agreement with C-V measurements performed ex situ on metal-oxide-semiconductor capacitors.
Separation of electrostrictive and absorptive stimulated Brillouin spectra
Authors: Sonehara Toshiaki , Kaminaga Hitomi , Tatsu Eriko , Saikan Seishiro , Ohno Seigo
Published: April 2007

From the symmetry analysis of frequency modulated (FM) stimulated Brillouin spectrum in As40Se60 glass, we demonstrate a separate detection of electrostrictive and absorptive FM Brillouin spectra as well as the detection of real and imaginary parts of Brillouin spectrum due to FM spectroscopy.
Optical characterization of liquid crystals by combined ellipsometry and half-leaky-guided-mode spectroscopy in the visible-near infrared range
Authors: Abbate G. , Tkachenko V. , Marino A. , Vita F. , Giocondo M. , Mazzulla A. , De Stefano L.
Published: April 2007

In this paper, we present our results for the anisotropic refractive index measurements of commonly used liquid crystal (LC) materials (E7 and 5CB) in the whole visible–near infrared range. In order to achieve a high accuracy in the obtained values, we have employed a combination of two techniques, namely, Mueller matrix spectroscopic ellipsometry in transmission and half-leaky-guided-mode (HLGM). Measurements with the HLGM technique are usually performed at a single wavelength. In order to obtain a spectroscopic measurement based on the HLGM technique in a wide wavelength range, we modified our commercial VASE® ellipsometer. In particular, we designed a sample holder by means of which measurements in guiding structures are also possible. Thus, we take advantage of the wide-spectrum light, emitted from a standard Xe lamp of the ellipsometer, also in the HLGM setup. The complementary and in-one-setup utilization of both techniques has allowed us to overcome most of the problems previously encountered in applying spectroscopic ellipsometry to the determination of the optical parameters of LC materials and eventually to achieve an accuracy in the obtained results of the order of 10−4. We discuss how individual elements of the Mueller matrix can be used to this aim. Finally, we compare the dispersion curves for the refractive indices and the birefringence of E7 and 5CB with the data already existing in the literature.
Influence of plasma decay on emission of 147-nm ultraviolet light from discharge cells in the plasma display panel
Authors: Uhm Han S. , Yoo Naleum , Choi Eun H.
Published: April 2007

The time profile of 147-nm light emission from a cell discharge of the plasma display panel is investigated in terms of the xenon mole fraction χ and the gas pressure p, including the important influences of the diffusion loss of the plasma and the three-body collisions of excited xenon atoms in the resonance state. The light emission profile dY∕dt in time is analytically expressed in terms of the gas pressure and xenon mole fraction. The theoretical analysis indicates that the emission intensity increases from zero, reaches its peak, and then decreases, as time goes by. The peak emission intensity (dY∕dt)p and the corresponding emission time tp are obtained analytically in terms of the gas pressure p and xenon mole fraction χ. The total emission Y of 147-nm light during each discharge in the cells is proportional to the plasma decay time τ. The experimental data are remarkably consistent with the theoretical predictions.
Embedding procedure for ab initio correlation calculations in group II metals
Authors: Voloshina Elena , Gaston Nicola , Paulus Beate
Published: April 2007

In order to apply ab initio wave-function-based correlation methods to metals, it is desirable to split the calculation into a mean-field part and a correlation part. Whereas the mean-field part (here Hartree-Fock) is performed in the extended periodic system, it is necessary to use for the correlation part local wave-function-based correlation methods in finite fragments of the solid. For these finite entities it is necessary to construct an embedding. The authors suggest an embedding scheme which has itself no metallic character but can mimic the metal in the internal region, where the atoms are correlated. With this embedding it is also possible to localize the metallic orbitals in the central part. The long-range nonadditive contributions of metallicity and correlation are treated with the method of increments. In this paper they present different ways to construct such an embedding and discuss the influence of the embedding on the correlation energy of the solid.
Accurate measurement of longitudinal cross-relaxation rates in nuclear magnetic resonance
Authors: Pelupessy Philippe , Ferrage Fabien , Bodenhausen Geoffrey
Published: April 2007

The accuracy of the determination of longitudinal cross-relaxation rates in NMR can be improved by combining symmetrical reconversion with suitable operator swapping methods that lead to the averaging of differences in autorelaxation rates and eliminate the effects of cross relaxation with the environment. The principles are first discussed for an isolated two-spin system comprising a pair of N15 and HN1 nuclei subjected to chemical shift anisotropy and dipole-dipole relaxation, and then extended to include further protons. The gains in accuracy are demonstrated experimentally for the protein ubiquitin.