bluuebunny/crossref_metadata_2025 huggingface dataset:
Interannual stability of grid cell snow depletion curves as estimated from MODIS images
Authors: Kolberg Sjur , Gottschalk Lars
Published: November 2010

The effect of calibrating spatially distributed snow model parameters using satellite data is evaluated by a cross‐validation approach in a 26,000 km2 mountainous region in Norway. From 6 years of data and 13 to 15 Moderate Resolution Imaging Spectroradiometer (MODIS) images per melt season, parameters of local snow depletion curves are estimated annually for each grid cell. The estimated values are averaged over 5 years and evaluated by the sixth year, using each year in turn for validation. The parameters are the subgrid snow storage coefficient of variation cv, the premelt snow‐covered fraction A0, the premelt snow storage m, and the time sequence of accumulated melt depth {λ}. The likelihood is formulated in terms of the Normalized Difference Snow Index (NDSI), rather than fractional snow‐covered area, in order to avoid highly skewed distributions for values close to 0 or 1. The 5 year averaged values for cv, A0, and a bias‐correcting snow storage multiplier mcorr were applied in rerunning the precipitation‐runoff model. For 22 subcatchments within the region, validation‐year standard error in snow melt runoff volume was reduced from 21% to 13%. Standard error in NDSI on the grid cell level was reduced from 0.34 to 0.27. The stationarity of individual parameters was also evaluated, comparing the 5 year calibrated values for each of cv, A0, and mcorr to the validation‐year estimates, after normalizing for the prior information. On average, the calibrated maps for cv, A0, and mcorr predicted 32%, 46%, and 56%, respectively, of the spatial variance in the validation year's change from prior to posterior estimates.
Simulation of aeolian sand saltation with rotational motion
Authors: Huang Ning , Wang Cong , Pan Xiying
Published: November 2010

In this work, we propose a theoretical model based on the distribution functions of initial liftoff velocity and angular velocity of sand grains to describe a sand saltation process in which both wind field–sand grain coupling and the Magnus force experienced by saltating sand grains have been incorporated. The computation results showed that the Magnus force had significant effects on sand grain saltation. In particular, when the Magnus force was incorporated, the calculated sand transport fluxes and sand transport rate per unit width were closer to the experimental value than when this force was excluded. The sand transport flux is enhanced because the Magnus force owing to particle rotation causes the particles to have higher and longer trajectories, so the particles can get more speed and energy from the wind, which leads to a larger sand transport flux. In addition, it was found that when taking the Magnus force into account, the probability density of the impact velocity and angular velocity of saltating sand grains followed an exponential distribution and a unimodal asymmetric distribution, respectively. Moreover, the sand energy flux increased with the height above the sand surface until the energy flux reached its maximum and then decreased. Furthermore, the energy flux near the ground surface decreased as the grain diameter increased, but beyond a specific height the energy flux increased with the grain diameter. Finally, for the same sand grain diameter, the energy flux increased with the friction velocity.
Estimates of past and future ozone trends from multimodel simulations using a flexible smoothing spline methodology
Authors: Scinocca John. F. , Stephenson David B. , Bailey Trevor C. , Austin John
Published: November 2010

A novel additive model analysis of multimodel trends is presented. The approach is motivated by, and particularly suited to, the analysis of multimodel time series of varying length. This Time series Additive Model (TSAM) approach consists of three distinct steps: estimation of individual model trends, baseline adjustment of the trends, and the weighted combination of the individual model trends to produce a multimodel trend (MMT) estimate. The baseline adjustment step is not an essential ingredient of the TSAM but is included to reduce model spread. The association of the TSAM approach with a probabilistic model allows trend estimates to be used to make formal inference (e.g., calculation of confidence and prediction intervals). The method is applied to the analysis of multimodel ozone time series of varying lengths as were considered for the 2006 Scientific Assessment of Ozone Depletion. The advantages of the TSAM approach are demonstrated to include the production of smooth trend estimates out to the ends of the time series, the ability to model explicitly interannual variability about the trend estimate, and the ability to make rigorous probability statements. Calculated ozone return dates are consistent with previous qualitative estimates, but the more quantitative analysis provided by the MMT is expected to allow such data sets to be better utilized by the community and policy makers.
Spatial and temporal controls on watershed ecohydrology in the northern Rocky Mountains
Authors: Emanuel Ryan E. , Epstein Howard E. , McGlynn Brian L. , Welsch Daniel L. , Muth Daniel J. , D'Odorico Paolo
Published: November 2010

Vegetation water stress plays an important role in the movement of water through the soil‐plant‐atmosphere continuum. However, the effects of water stress on evapotranspiration (ET) and other hydrological processes at the watershed scale remain poorly understood due in part to spatially and temporally heterogeneous conditions within the watershed, especially in areas of mountainous terrain. We used a spatially distributed model to understand and evaluate the relationship between water stress and ET in a forested mountain watershed during the snow‐free growing season. Vegetation water stress increased as the growing season progressed, due to continued drying of soils, and persisted late into the growing season, even as vapor pressure deficit decreased with lower temperatures. As a result, ET became decoupled from vapor pressure deficit and became increasingly dependent on soil moisture later in the growing season, shifting from demand limitation to supply limitation. We found water stress and total growing season ET to be distributed nonuniformly across the watershed due to interactions between topography and vegetation. Areas having tall vegetation and low topographic index experienced the greatest water stress, yet they had some of the highest evapotranspiration rates in the watershed.
Salinity dynamics of discharge lakes in dune environments: Conceptual model
Authors: Zlotnik Vitaly A. , Robinson Neville I. , Simmons Craig T.
Published: November 2010

Lakes of varying salinity are ubiquitous in dune environments with semiarid climates. Often these lakes become solute traps due to specific groundwater flow conditions. Over geological time after emergence of such lakes, the groundwater flow and mass transport processes lead to accumulation of solutes. This salinity increase can result in mineral deposition and free convection from lakes. However, high solute concentrations in these lakes are often not observed. We propose a conceptual model that estimates the lake salinity dynamics and yields concentration profiles beneath the lakes over centennial and millennial scales. Unlike previous approaches, a simple mathematical model is proposed based on coupling the lake solute mass balance with the advection‐dispersion equation. We discuss limitations of the model and apply it to conditions of the Nebraska Sand Hills, USA. We show that the lake salinity concentration is consistent with the regional paleoclimate data. The proposed model can be used to constrain hydrologic paleoclimate reconstructions, which is a significant challenge for lakes in dune environments.
Convective dissolution of carbon dioxide in saline aquifers
Authors: Neufeld Jerome A. , Hesse Marc A. , Riaz Amir , Hallworth Mark A. , Tchelepi Hamdi A. , Huppert Herbert E.
Published: November 2010

Geological carbon dioxide (CO2) storage is a means of reducing anthropogenic emissions. Dissolution of CO2 into the brine, resulting in stable stratification, increases storage security. The dissolution rate is determined by convection in the brine driven by the increase of brine density with CO2 saturation. We present a new analogue fluid system that reproduces the convective behaviour of CO2‐enriched brine. Laboratory experiments and high‐resolution numerical simulations show that the convective flux scales with the Rayleigh number to the 4/5 power, in contrast with a classical linear relationship. A scaling argument for the convective flux incorporating lateral diffusion from downwelling plumes explains this nonlinear relationship for the convective flux, provides a physical picture of high Rayleigh number convection in a porous medium, and predicts the CO2 dissolution rates in CO2 accumulations. These estimates of the dissolution rate show that convective dissolution can play an important role in enhancing storage security.
Radiation belt dynamics: The importance of wave‐particle interactions
Authors: Thorne Richard Mansergh
Published: November 2010

The flux of energetic electrons in the Earth's outer radiation belt can vary by several orders of magnitude over time scales less than a day, in response to changes in properties of the solar wind instigated by solar activity. Variability in the radiation belts is due to an imbalance between the dominant source and loss processes, caused by a violation of one or more of the adiabatic invariants. For radiation belt electrons, non‐adiabatic behavior is primarily associated with energy and momentum transfer during interactions with various magnetospheric waves. A review is presented here of recent advances in both our understanding and global modeling of such wave‐particle interactions, which have led to a paradigm shift in our understanding of electron acceleration in the radiation belts; internal local acceleration, rather than radial diffusion now appears to be the dominant acceleration process during the recovery phase of magnetic storms.
Space observations of inland water bodies show rapid surface warming since 1985
Authors: Schneider Philipp , Hook Simon J.
Published: November 2010

Surface temperatures were extracted from nighttime thermal infrared imagery of 167 large inland water bodies distributed worldwide beginning in 1985 for the months July through September and January through March. Results indicate that the mean nighttime surface water temperature has been rapidly warming for the period 1985–2009 with an average rate of 0.045 ± 0.011°C yr−1 and rates as high as 0.10 ± 0.01°C yr−1. Worldwide the data show far greater warming in the mid‐ and high latitudes of the northern hemisphere than in low latitudes and the southern hemisphere. The analysis provides a new independent data source for assessing the impact of climate change throughout the world and indicates that water bodies in some regions warm faster than regional air temperature. The data have not been homogenized into a single unified inland water surface temperature dataset, instead the data from each satellite instrument have been treated separately and cross compared. Future work will focus on developing a single unified dataset which may improve uncertainties from any inter‐satellite biases.
High particle export over the continental shelf of the west Antarctic Peninsula
Authors: Buesseler Ken O. , McDonnell Andrew M. P. , Schofield Oscar M. E. , Steinberg Deborah K. , Ducklow Hugh W.
Published: November 2010

Drifting cylindrical traps and the flux proxy 234Th indicate more than an order of magnitude higher sinking fluxes of particulate carbon and 234Th in January 2009 than measured by a time‐series conical trap used regularly on the shelf of the west Antarctic Peninsula (WAP). The higher fluxes measured in this study have several implications for our understanding of the WAP ecosystem. Larger sinking fluxes result in a revised export efficiency of at least 10% (C flux/net primary production) and a requisite lower regeneration efficiency in surface waters. High fluxes also result in a large supply of sinking organic matter to support subsurface and benthic food webs on the continental shelf. These new findings call into question the magnitude of seasonal and interannual variability in particle flux and reaffirm the difficulty of using moored conical traps as a quantitative flux collector in shallow waters.
Effects of solar wind dynamic pressure on the ionospheric O+ fluence during the 31 August 2005 storm
Authors: Damiano P. A. , Brambles O. J. , Lotko W. , Zhang B. , Wiltberger M. , Lyon J.
Published: November 2010

The Multifluid‐Lyon‐Fedder‐Mobarry (MFLFM) global simulation model incorporating an ionospheric cusp O+ outflow model based on an empirical relation between downward DC Poynting flux and O+ outflow flux regulated by the precipitating electron number flux (Fen) is used to simulate the 31 August 2005 storm. A baseline run incorporating the original solar wind data is contrasted against a case where the solar wind dynamic pressure (Pdyn) is artificially adjusted to see what effects this variable has on the O+ fluence generated in the model. Consistent with data, it is found that both the fluence and O+ outflow flux have a positive correlation with the solar wind dynamic pressure. Additionally, changes in Pdyn affect the downward Poynting flux only marginally and regulates both outflow flux and cusp outflow area via Fen. Increases in Pdyn lead to increased cusp electron precipitation, which has the physical effect of enhancing the upwelling O+ population available for outflow.
Anomalous behavior of the thermosphere during solar minimum observed by CHAMP and GRACE
Authors: Bruinsma Sean L. , Forbes Jeffrey M.
Published: November 2010

High‐resolution density observations inferred from accelerometer measurements on the Challenging Mini‐Satellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellites for the period 11–17 December 2008 during the solar minimum are analyzed and compared to reference model predictions. The density distribution as a function of altitude can be studied because the satellites were in the same 8.4/20.4 hour (0824/2024) local solar time plane, CHAMP at a mean altitude of 332 km and GRACE 144 km higher. The mean observed and model density profiles at 476 km reveal considerable differences, which, except for a 25% bias, is not the case at an altitude of 332 km. These differences result from the fact that during this solar minimum the transition from predominantly O to He occurs at a much lower altitude in connection with the winter helium bulge than is predicted by the model. When averaged over the 1 week period, striking wave‐3 structures are revealed with respect to longitude that are remarkably consistent between CHAMP and GRACE. We interpret these as the manifestations of nonmigrating tides propagating upward from the lower atmosphere. Comparisons are made with similar data from August 2008, which reveal a wave‐4 structure. However, whereas previous results and conventional wisdom would suggest that these features are produced by the eastward propagating diurnal tides with zonal wave numbers s = −2 (DE2) and s = −3 (DE3), respectively, the asymmetries and day‐night phase differences that are present suggest the predominance of semidiurnal tides SE1 and SE2, respectively, along with the aforementioned diurnal tides as well as tides SW5 and SW6.
Global simulation of magnetosonic wave instability in the storm time magnetosphere
Authors: Chen Lunjin , Thorne Richard M. , Jordanova Vania K. , Horne Richard B.
Published: November 2010

Coupling between the Rice Convection Model and Ring Current–Atmospheric Interactions Model codes is used to simulate the dynamical evolution of ring current ion phase space density and the thermal electron density distribution for the 22 April 2001 storm. The simulation demonstrates that proton ring distributions (df⊥/dv⊥ > 0) develop over a broad spatial region during the storm main phase, leading to the instability of equatorial magnetosonic waves. Calculations of the convective growth rate of magnetosonic waves for multiples of the proton gyrofrequency from 2 to 42 are performed globally. We find that the ratio between the perpendicular ring velocity and the equatorial Alfven speed determines the frequency range of unstable magnetosonic waves. Low harmonic waves (ω < 10 tend to be excited in the high‐density nightside plasmasphere and within the duskside plume, whereas higher‐frequency waves (ω > 20 are excited over a broad spatial region of low density outside the morningside plasmasphere.
Enhanced transport across entire length of plasma sheet boundary field lines leading to substorm onset
Authors: Lyons L. R. , Nishimura Y. , Xing X. , Angelopoulos V. , Zou S. , Larson D. , McFadden J. , Runov A. , Mende S. , Fornacon K.‐H.
Published: November 2010

Recently, images from the THEMIS all‐sky imager array were used to suggest that longitudinally localized enhanced plasma transport across the nightside open‐closed boundary (separatrix) ∼5.5 min before substorm onset leads to intrusion of new plasma toward the near‐Earth plasma sheet and to substorm onset via near‐Earth instability. If such reconnection‐related flow enhancements precede substorm onsets, they should be seen along the entire length of separatrix field lines within the appropriate longitudinal region as perpendicular flow before onset. Evidence for such flows has been previously reported for four events over a limited radial extent. Based on 13 substorm events with at least one of the THEMIS spacecraft near the outer boundary of the plasma sheet in the premidnight region and simultaneous auroral images, we find here that enhanced flows toward the plasma sheet center are often seen (11 of 13 events) in the premidnight sector a few minutes prior to onset from X ∼ −11 to −26 RE. Previous radar observations within the ionosphere have also shown that such enhanced flows bringing new plasma into the auroral zone from polar cap field lines prior to onset are common. Assuming that the outer boundary of the plasma sheet approximately demarcates the open‐closed field line boundary, these results indicate that reconnection‐related flow enhancements do indeed precede substorm onset along the entire radial extent of the plasma sheet outer boundary. Consistent with longitudinal localization, enhanced flows toward the plasma sheet center were not observed on all spacecraft for five events where there were more than one spacecraft near the plasma sheet boundary.
Wind‐enhanced resuspension in the shallow waters of South San Francisco Bay: Mechanisms and potential implications for cohesive sediment transport
Authors: Brand Andreas , Lacy Jessica R. , Hsu Kevin , Hoover Daniel , Gladding Steve , Stacey Mark T.
Published: November 2010

We investigated the driving forces of sediment dynamics at the shoals in South San Francisco Bay. Two stations were deployed along a line perpendicular to a 14 m deep channel, 1000 and 2000 m from the middle of the channel. Station depths were 2.59 and 2.19 m below mean lower low water, respectively. We used acoustic Doppler velocimeters for the simultaneous determination of current velocities, turbulence, sediment concentration and fluxes. Maximum current shear velocities were 0.015 m s−1 at the station further from the channel (closer to the shore) and 0.02 m s−1 at the station closer to the channel. Peak wave‐induced shear velocities exceeded 0.015 m s−1 at both stations. Maximum sediment concentrations were around 30 g m−3 during calm periods (root mean square wave height <0.15 m). During wavy periods, sediment concentrations increased to 100 g m−3 and sediment fluxes were 5 times higher than in calm conditions (0.02 g m−2 s−1 versus >0.10 g m−2 s−1) at the station further from the channel 0.36 m above the bed. Closer to the channel, sediment concentrations and vertical fluxes due to wind wave resuspension were persistently lower (maximum concentrations around 50 g m−3 and maximum fluxes around 0.04 g m−2 s−1). Most resuspension events occurred during flood tides that followed wave events during low water. Although wave motions are able to resuspend sediment into the wave boundary layer at low tide, the observed large increases in sediment fluxes are due to the nonlinear interaction of wind waves and the tidal currents.
Spatial and temporal variation of in‐reach suspended sediment dynamics along the mainstem of Changjiang (Yangtze River), China
Authors: Hassan Marwan A. , Church Michael , Yan Yunxia , Slaymaker Olav
Published: November 2010

Four major reaches of Chiangjang (Yangtze River) were analyzed for the period 1956–2007 in terms of long‐term trends in suspended sediment gain and loss in each reach, the relation of input and output to within‐reach sediment fluxes, and the impacts of dam construction on reach sediment dynamics. The temporal and spatial patterns of within‐reach sediment dynamics correspond closely with river morphology and also reflect basin conditions over the past few decades; thus they are conditioned by coeval trends in climate, hydrology, and land use. The study period encompasses both unusually wet years (e.g., 1998) and unusually dry periods (e.g., 2006). There are suggestive coincidences between changes in the suspended sediment regime and innovations in land use, sediment mining, and dams. The relatively strong statistical relation between sediment input and output for each of the four study reaches, and weak relations between storage and output, imply that most sediment supplied to each reach is delivered from upstream and that relatively small amounts of sediment are recruited within each reach. Cumulative departure plots reveal epicycles of sediment exchange varying from 15 to 40 years, implying a characteristic fine sediment storage time on the order of decades. Shorter epicycles (5–8 years) are commonly related to sediment influx associated with major floods.
Recognition of cellular implants by the brain's innate immune system
Authors: Bergwerf Irene , Tambuyzer Bart , De Vocht Nathalie , Reekmans Kristien , Praet Jelle , Daans Jasmijn , Chatterjee Shyama , Pauwels Patrick , van der Linden Annemie , Berneman Zwi N , Ponsaerts Peter
Published: November 2010

Currently, much attention is given to the development of cellular therapies for treatment of central nervous system (CNS) injuries. Diverse cell implantation strategies, either to directly replace damaged neural tissue or to create a neuroregenerative environment, are proposed to restore impaired brain function. However, because of the complexity of the CNS, it is now becoming clear that the contribution of cell implantation into the brain will mainly act in a supportive manner. In addition, given the time dependence of neural development during embryonic and post‐natal life, cellular implants, either self or non‐self, will most likely have to interact for a sustained period of time with both healthy and injured neural tissue. The latter also implies potential recognition of cellular implants by the innate immune system of the brain. In this review, we will emphasize on preclinical observations in rodents, regarding the recognition and immunogenicity of autologous, allogeneic and xenogeneic cellular implants in the CNS of immune‐competent hosts. Taken together, we here suggest that a profound study of the interaction between cellular grafts and the brain's innate immune system will be inevitable before clinical cell transplantation in the CNS can be performed successfully.
Mechanistic Approaches To The Prevention Of Mutation And Cancer
Authors: De Flora Silvio
Published: November 2010

Cancer and other mutation-related diseases can be prevented at three levels: primary prevention, which is addressed to healthy individuals in order to prevent occurrence of the disease; secondary prevention, which is addressed to early stage patients in order to prevent progression of the disease; and tertiary prevention, which is addressed to patients after therapy in order to prevent relapses of the disease. Although the most obvious approach to prevention is to minimize exposures to recognized risk factors, a complementary strategy is represented by chemoprevention, using dietary and pharmacological agents that reinforce the host defence machinery. Since 1988, I proposed detailed classifications of mechanisms of inhibitors of mutagenesis and carcinogenesis. They may apply not only to cancer but also to other degenerative diseases that have replaced infectious diseases as the leading causes of death in the population. In fact, certain mechanisms, such as damage to nuclear DNA and mtDNA, oxidative stress, chronic inflammation, signal transduction alterations and epigenetic changes may be involved in the pathogenesis of different diseases. Studies performed in our laboratory have shown that certain genomic alterations that are usually investigated in cancer research may also be detected in other chronic diseases, such as atherosclerosis, degenerative heart diseases, chronic obstructive pulmonary diseases, neurological disorders, eye diseases, skin ageing, and alopecia. Similar alterations were investigated in critical periods of life, such as birth and ageing. The nucleotide alterations occurring at birth in the lung render the newborn particularly vulnerable to the action of environmental agents. In fact, we demonstrated that cigarette smoke becomes a potent carcinogen in mice when exposure starts at birth and continues early in life. We investigated a number of chemopreventive agents by evaluating modulation of intermediate biomarkers and carcinogenicity. An optimal agent should not excessively alter the physiological patterns of gene expression, microRNA and proteome profiles, but at the same time it should be effective in inhibiting alterations induced by mutagens and carcinogens. It should be noted that most chemopreventive agents possess pleiotropic properties. The knowledge of mechanisms can be exploited to combine different agents working with complementary mechanisms. Like the therapy of important diseases, such as cancer, cardiovascular diseases, AIDS, etc., uses combinations of drugs, combined chemoprevention is a quite promising strategy. Although a large number of agents are potentially able to prevent cancer, we are in search of tools to predict, hopefully in the single individual, their efficacy and safety in humans.
Solitons against a pump wave background in an easy-axis ferromagnet
Authors: Kiselev V. V. , Rascovalov A. A.
Published: November 2010

Exact solutions of the Landau-Lifshitz equation are obtained for a ferromagnet with an easy-axis asymmetry which describe the interaction of a nonlinear precession wave of arbitrary amplitude with soliton-like objects such as breathers, solitary domains, and domain boundaries. Changes in the internal structure and physical parameters of solitons owing to their interaction with a magnetization wave are analyzed. Solitary domains and domain boundaries are shown to move counter to the wave. Conditions are found such that solitons are destroyed by a nonlinear magnetization wave.
Nature of the metastable boron–oxygen complex formation in crystalline silicon
Authors: Crandall Richard S.
Published: November 2010

Transient capacitance measurements reveal new physics of metastable defect formation in boron-doped oxygen-containing crystalline silicon solar cells. These measurements demonstrate that holes are deeply trapped during defect formation and removed during thermal annealing with activation energy of 1.3 eV. Previous theoretical models {Du et al., [Phys. Rev. Lett. 97, 256602 (2006)] and Adey et al., [Phys. Rev. Lett. 93, 055504 (2004)]} are supported by present findings that defect formation is a slow two-stage process with activation energies of 0.17 eV and 0.4 eV at high and low temperature, respectively. Repulsive hole capture by a positive oxygen-dimer determines the defect formation rate at low temperature {Du et al., [Phys. Rev. Lett. 97, 256602 (2006)]}. The high temperature process is governed by a structural conversion of the dimer {Du et al., [Phys. Rev. Lett. 97, 256602 (2006)] and Adey et al., [Phys. Rev. Lett. 93, 055504 (2004)]}. An abnormally low rate prefactor allows this low-enthalpy reaction to be observed at the higher temperature. This dimer conversion presents an excellent example of an “entropy barrier” that explains the low conversion rate. Disparate formation and annealing results published here and in other publications are related by the Meyer–Neldel rule with an isokinetic temperature of 410 K.
Surface alloy formation and two-dimensional vitrification in adsorbed monolayers on Molybdenum (112) surfaces
Authors: Mitryaev A. A. , Naumovets A. G. , Fedorus A. G.
Published: November 2010

Low-energy electron diffraction, scanning tunneling microscopy, contact potential difference, and Auger electron spectroscopy methods are used to observe the formation of surface alloys during annealing of Dy, Gd, Sr, and Be monolayers adsorbed on Mo(112) surfaces. Surface alloys develop as a nanodispersed system of oligomeric clusters in the Dy and Sr films and as a continuous covering in the Be and Gd films. It is shown that Dy films, which form a Dy-Mo surface alloy on annealing, will enter a two-dimensional glassy state after cooling (quenching) to low temperatures, while the surface alloys of Be and Gd are formed in a crystalline state.
Intergranular interactions in nanogranular (CoFeB)x–(SiO2)1−x films with temperature and angular variations in coercivity
Authors: Ryabchenko S. M. , Timopheev A. A. , Kalita V. M. , Lozenko A. F. , Trotsenko P. A. , Stephanovich V. A. , Munakata M.
Published: November 2010

The temperature (4.5–550K) and angular (in the film plane) dependences of the coercivity field for physically nonpercolated nanogranular (CoFeB)x–(SiO2)1−x films with an oriented intraplane granule anisotropy have some unusual properties compared to those owing to blocking of thermally activated reorientation of the magnetic moments of the granules. At temperatures above the blocking temperature Tb≈350–370K, the dependence of the coercivity on the measurement duration is weak compared to that below Tb. Its angular (in the film plane) dependence differs qualitatively from that expected with blocking of superparamagnetic particles. This behavior is explained by the appearance of superferromagnetic ordering of the granule magnetic moments at T>Tb owing to interactions among them. As the temperature is reduced below 100K, the coercive field Hc for magnetization in the easy direction increases significantly more than expected for a blocked superparamagnetic ensemble. Here Hc≠0 for magnetization along the hard direction in the plane. The angular (in-plane) dependence of Hc acquires two maxima, along the easy and hard (in-plane) directions. This phenomenon is explained by the appearance of superspin-glass correlations in the mutual orientations of the granule magnetic moments of the ensemble.
Quasiparticle theory of superfluid Bose systems with single-particle and pair condensates
Authors: Peletminskii A. S. , Peletminskii S. V.
Published: November 2010

A semi-phenomenological theory of superfluid Bose systems based on a quasiparticle description is examined. This theory makes it possible to study, from a unified standpoint, single-particle and pair condensates with repulsive, as well as attractive, forces. The resulting equations for the order parameters corresponding to these condensates are analyzed in the weak interaction approximation.
Spin-wave resonances in antiferromagnets
Authors: Krug von Nidda H. A. , Svistov L. E. , Prozorova L. A.
Published: November 2010

Spin-wave resonances with record high wave numbers (n∼100–1000), corresponding to wave vectors k∼105–106cm−1, have been observed in thin plates of FeBO3. Studies of the spin-wave resonances provide information on the spin wave spectrum. The temperature dependence of the inhomogeneous exchange constant has been determined for FeBO3. For temperatures higher than 1∕3 of the Neel temperature the magnon spectrum is observed to undergo considerable softening, apparently as a result of their interaction. The efficiency with which spin-wave resonances are excited is found to depend significantly on inhomogeneous elastic deformations that have been artificially created in the sample. A model is proposed to describe the experimental results.
Effect of cross correlations between inhomogeneities on the spectrum and damping of spin and elastic waves
Authors: Ignatchenko V. A. , Polukhin D. S.
Published: November 2010

This is a study of the dispersion relations and damping of spin waves in ferromagnets with inhomogeneities in their exchange and magnetic anisotropy parameters and of elastic waves in isotropic media with inhomogeneities in the density of matter and in the elastic force constants, with cross correlations between these inhomogeneities taken into account. A general behavior is found which is independent of the physical nature of the waves: the kind of effect cross correlations between inhomogeneities in any two parameters of a material will have on the wave spectrum depends on whether both parameters belong to the same (i.e., both belong to the kinetic part or both belong to the potential part) or to different parts of the hamiltonian. In the former case, positive cross correlations lead to a substantial modification of the dispersion relation and to increased wave damping, and in the latter case, to a smaller modification of these characteristics. On the other hand, negative cross correlations lead to the opposite effects in both cases. This behavior is explained qualitatively.
Quantum dynamics of vortices in small magnetic particles
Authors: Ivanov B. A. , Galkina E. G. , Galkin A. Yu.
Published: November 2010

A collective variables approach based on the Thiele equation is used to construct an exact solution for the quantum dynamics of vortices in small, round magnetic particles. It is shown that knowledge of the dynamics of vortices in magnetic particles can be used to create mesoscopic quantum systems with specified distributions of energy levels and to control the rate of transitions between these levels by varying the particle geometry.
Three-dimensional static vortex solitons in incommensurate magnetic crystals
Authors: Borisov A. B. , Rybakov F. N.
Published: November 2010

A new type of three-dimensional magnetic soliton in easy-axis ferromagnets is predicted by taking simultaneous account of the Dzyaloshinsky-Moriya interaction and an external magnetic field. The numerically obtained static three-dimensional solitons with a finite energy are characterized by a Hopf topological index H=0 and have a vortex structure. The structure of these solitons and the dependence of their energy on the external field are determined. The asymptotic behavior of these solitons is investigated and a necessary condition for their existence is found.
Magnus force and the inertial properties of magnetic vortices in weak ferromagnets
Authors: Zvezdin A. K. , Zvezdin K. A.
Published: November 2010

The Magnus force (gyroscopic force) acting on magnetic vortices (Bloch lines) within domain boundaries in weak ferromagnets is discussed. A general formula is derived for the Magnus force in weak ferromagnets. The Magnus force is found to be nonzero for most types of domain boundaries and is determined by the average sublattice magnetization and the constants for the Dzyaloshinsky interaction and the exchange interaction between sublattices. Generalized expressions are obtained for the effective Lagrange and Rayleigh functions in weak ferromagnets taking their vortex structure into account. The question of the vortex mass, which has been found to be on the order of m*∼10−14g∕cm in YFeO3, is discussed. The dynamic flexure of domain boundaries when moving vortices are present is analyzed. A formula is derived for the magnetic field dependence of the velocity of a vortex in a motionless domain boundary.
Resonance properties of domain boundaries in quasi-two dimensional antiferromagnets
Authors: Kovalev A. S. , Prilepsky J. E. , Kryukov E. A. , Kulik N. V.
Published: November 2010

The so-called “internal modes” localized near the domain boundaries in quasi-two dimensional antiferromagnets are investigated. The possible localized states are classified and their frequency dependences on the system discreteness parameter λ=J∕β, which describes the ratio of the magnitudes of the exchange interplane interaction and the magnetic anisotropy, are found. A sudden change in the spectrum of the local internal modes is observed at a critical value of this parameter, λ=λb=3∕4, where the domain wall shifts from a collinear to a canted shape. When λ<λb there are one symmetric and two antisymmetric local modes, and when λ>λb the modes are two symmetric, one antisymmetric, and one shear. For discreteness parameters close to the critical value, the frequencies of some of the local modes lie deep inside the gap for the linear AFM magnon spectrum and can be observed experimentally.
In situ contacting and current-injection into samples in photoemission electron microscopes
Authors: Heyne L. , Kläui M. , Rhensius J. , Le Guyader L. , Nolting F.
Published: November 2010

Studying the interaction of spin-polarized currents with the magnetization configuration is of high interest due to the possible applications and the novel physics involved. High-resolution magnetic imaging is one of the key techniques necessary for a better understanding of these effects. Here, we present an extension to a magnetic microscope that allows for in situ current injection into the structure investigated, and furthermore for the study of current induced magnetization changes during pulsed current injection. The developed setup is highly flexible and can be used for a wide range of investigations. Examples of current-induced domain wall motion and vortex core displacements measured using this setup are presented.
Single-magnon tunneling through a ferromagnetic nanochain
Authors: Petrov E. G. , Ostrovsky V.
Published: November 2010

Magnon transmission between ferromagnetic contacts coupled by a linear ferromagnetic chain is studied when the chain acts as a tunnel magnon transmitter. It is shown that depending on the magnon energy in the chain, distant intercontact magnon transmission can occur by resonant or nonresonant tunneling. In the first case, the transmission function depends weakly on the number of chain sites, whereas in the nonresonant case this function falls off exponentially with the chain length. Changing the direction of an external magnetic field at one of the ferromagnetic contacts blocks magnon tunnel transmission.
The scattering of surface plasmon polaritons by nanoscale surface defects
Authors: Maradudin A. A. , Leskova T. A. , García-Guerrero E. E. , Méndez E. R.
Published: November 2010

A rigorous computational approach based on Green’s second integral identity in the plane is used to calculate the transmission, reflection, and conversion into volume electromagnetic waves of a surface plasmon polariton incident on a nanoscale one-dimensional surface defect on an otherwise planar interface between vacuum and a lossy metal.
Magnetic properties of amorphous Co0.74Si0.26∕Si multilayers with different numbers of periods
Authors: Kakazei G. N. , Santos N. M. , Quiros C. , Velez M. , Martin J. I. , Alameda J. M. , Golub V. O. , Saliuk O. Y. , Pogorelov Yu. G. , Sousa J. B. , Carmo M. C. , Sobolev N. A.
Published: November 2010

Two sets of [Co0.74Si0.26(5nm)∕Si(s)]n amorphous films were prepared by magnetron sputtering: one in the form of multilayers with the Si spacer thickness s fixed at 3nm, and the number n of periods varying from 1 to 10 and the other with only two periods and s varying from 3to24nm (trilayers). In both sets, the Co0.74Si0.26 layer thickness t was fixed at 5nm. All the samples except the one with s=24nm manifest antiferromagnetic coupling. Their magnetic properties at room temperature were probed using the magnetooptical transverse Kerr effect (MOTKE) and ferromagnetic resonance (FMR). The relative increase in the saturation magnetization Ms (for trilayers, relative to a structure with s=24nm; for multilayers, relative to the single-layer structure) determined from the FMR measurements was compared with the exchange coupling strength HJAF obtained from the MOTKE studies. The dependences of HJAF and Ms on n and s were found to be very similar to each other. Possible mechanisms of this similarity are discussed.
AutoMicromanager: A microscopy scripting toolkit for LABVIEW and other programming environments
Authors: Ashcroft Brian Alan , Oosterkamp Tjerk
Published: November 2010

We present a scripting toolkit for the acquisition and analysis of a wide variety of imaging data by integrating the ease of use of various programming environments such as LABVIEW, IGOR PRO, MATLAB, SCILAB, and others. This toolkit is designed to allow the user to quickly program a variety of standard microscopy components for custom microscopy applications allowing much more flexibility than other packages. Included are both programming tools as well as graphical user interface classes allowing a standard, consistent, and easy to maintain scripting environment. This programming toolkit allows easy access to most commonly used cameras, stages, and shutters through the Micromanager project so the scripter can focus on their custom application instead of boilerplate code generation.
Perturbations of the Kerr black hole and the boundness of linear waves
Authors: Eskin G.
Published: November 2010

Artificial black holes (also called acoustic or optical black holes) are the black holes for the linear wave equation describing the wave propagation in a moving medium. They attracted a considerable interest of physicists who study them to better understand the black holes in general relativity. We consider the case of stationary axisymmetric metrics and we show that the Kerr black hole is not stable under perturbations in the class of all axisymmetric metrics. We describe families of axisymmetric metrics having black holes that are the perturbations of the Kerr black hole. We also show that the ergosphere can be determined by boundary measurements. Finally, we prove the uniform boundness of the solution in the exterior of the black hole when the event horizon coincides with the ergosphere.
Pulsating and traveling wave modes of natural convection in spherical shells
Authors: Scurtu N. , Futterer B. , Egbers C.
Published: November 2010

A numerical study is made of the natural convective fluid motion in the spherical shell geometry, i.e., the gap between two concentric spheres. The case of homogeneously heated inner sphere and cooled outer sphere is considered for the radius ratio η=0.714 and Prandtl number Pr=0.7. Patterns of fluid flow are established by the variation of the Rayleigh number Ra and its heat transfer is characterized by the Nusselt number Nu. For small values of the Rayleigh number, a crescent shaped axisymmetric vortex is formed and is regarded as the basic flow. By increasing the Rayleigh number, two transitions occur to a fully developed three-dimensional irregular flow. On the first bifurcation branch, a pulsating wave flow was found with petal-like formations pulsating in meridional direction. On the second branch, a traveling wave flow exists with an azimuthal rotation of the spirally distributed petal patterns. Various characteristics of the flow patterns are investigated as well as their transition to chaos. Both branches conjoin in the very supercritical domain, where the traveling wave dominates.
The Influence of shearing and rotary inertia on the resonant properties of gold nanowires
Authors: Olsson Pär A. T. , Park Harold S. , Lidström Per C.
Published: November 2010

In a previous publication [P. A. T. Olsson, J. Appl. Phys. 108, 034318 (2010)], molecular dynamics (MD) simulations have been performed to study the resonant properties of gold nanowires. It has been documented in the aforementioned publication that the eigenfrequencies of the fundamental mode follows the continuum mechanically predicted behavior when Bernoulli–Euler beam theory is used, whereas the higher order modes tend to be low in comparison to Bernoulli–Euler beam theory predictions. In this work, we have studied the resonant properties of unstressed and prestressed nanowires to explain why the eigenfrequencies of the fundamental mode follows the behavior predicted by Bernoulli–Euler beam theory while those of higher order modes are low in comparison. This is done by employing Timoshenko beam theory and studying the nanowire deformations for different modes. We find good agreement between the MD results and Timoshenko predictions due to the increasing importance of shearing and rotary inertia for higher order resonant modes. Furthermore, we argue that this type of behavior is merely a geometric effect stemming from low aspect ratio for the considered structures as a converging type of behavior is found when the aspect ratios fall between 15 and 20. Finally, we have found that classical Timoshenko beam theory that neglects nanoscale surface effects is able to, simply through utilization of the size dependent Young’s modulus, capture the dynamic properties of the gold nanowires as calculated through MD.
Electrical bistability in hybrid ZnO nanorod/polymethylmethacrylate heterostructures
Authors: Tseng Zong-Liang , Kao Po-Ching , Shih Meng-Fu , Huang Hsin-Hsuan , Wang Jing-Yuan , Chu Sheng-Yuan
Published: November 2010

A hybrid resistance switching device consisting of ZnO nanorods embedded in an insulating polymethylmethacrylate (PMMA) heterostructure sandwiched between a transparent conductive film and an Al electrode is proposed. The current-voltage characteristics of the device are discussed in terms of the formation and rupture of its conductive filaments. The hybrid device shows stable electrical bistable behaviors after more than 200 resistance-switching cycles. The hybrid ZnO nanorod/PMMA device presented in this work has potential applications in the field of bistable random access memory devices.
Raman study of Ca3Co2O6 single crystals
Authors: Gohil Smita , Iyer Kartik K. , Aswathi P. , Ghosh Shankar , Sampathkumaran E. V.
Published: November 2010

We report Raman scattering experiments on single crystals of Ca3Co2O6. The polarization dependent scattering was used to assign symmetry of the observed vibrational modes. The low temperature experiments show a subtle change in peak widths at 75 K. The increase in the peak widths is also accompanied by a gain in spectral weight for wave numbers greater than 1000 cm−1. We have associated the increase in peak widths to lattice distortion and the high frequency spectral feature to the inelastic light scattering processes involving two magnons. These observations are consistent with the reported extended x-ray absorption fine structure [Bindu et al., Phys. Rev. B 79, 094103 (2009)] and Mössbauer measurements [Paulose et al., Phys. Rev. B 77, 172403 (2008)] which suggests simultaneous presence of lattice distortion and short range magnetic order in the system well above the Néel temperature (24 K). Thus, our experiments highlight the usage of Raman spectroscopy as a tool to study systems which show precursor effects to magnetic transition.
Ultrathin, ultrasmooth, and low-loss silver films via wetting and annealing
Authors: Chen W. , Chen K. P. , Thoreson M. D. , Kildishev A. V. , Shalaev V. M.
Published: November 2010

We have demonstrated that a thermal annealing treatment can reduce the optical losses in ultrathin, ultrasmooth, silver films deposited on a Ge wetting layer to values as low as the bulk material value and at the same time maintain an ultrasmooth surface. The annealing effect is sensitive to the annealing temperature and time, both of which should be carefully controlled. This annealing treatment is also effective for Ag–SiO2 multilayer composite films.