bluuebunny/crossref_metadata_2025 huggingface dataset:
An assessment of the cloud signals simulated by NICAM using ISCCP, CALIPSO, and CloudSat satellite simulators
Authors: Kodama C. , Noda A. T. , Satoh M.
Published: May 2012

This study presents an assessment of three‐dimensional structures of hydrometeors simulated by the NICAM, global nonhydrostatic atmospheric model without cumulus parameterization, using multiple satellite data sets. A satellite simulator package (COSP: the CFMIP Observation Simulator Package) is employed to consistently compare model output with ISCCP, CALIPSO, and CloudSat satellite observations. Special focus is placed on high thin clouds, which are not observable in the conventional ISCCP data set, but can be detected by the CALIPSO observations. For the control run, the NICAM simulation qualitatively captures the geographical distributions of the high, middle, and low clouds, even though the horizontal mesh spacing is as coarse as 14 km. The simulated low cloud is very close to that of the CALIPSO low cloud. Both the CloudSat observations and NICAM simulation show a boomerang‐type pattern in the radar reflectivity‐height histogram, suggesting that NICAM realistically simulates the deep cloud development process. A striking difference was found in the comparisons of high thin cirrus, showing overestimated cloud and higher cloud top in the model simulation. Several model sensitivity experiments are conducted with different cloud microphysical parameters to reduce the model‐observation discrepancies in high thin cirrus. In addition, relationships among clouds, Hadley circulation, outgoing longwave radiation and precipitation are discussed through the sensitivity experiments.
Dissolved nutrient retention dynamics in river networks: A modeling investigation of transient flows and scale effects
Authors: Ye Sheng , Covino Timothy P. , Sivapalan Murugesu , Basu Nandita B. , Li Hong‐Yi , Wang Shao‐Wen
Published: May 2012

We have used a dynamic hydrologic network model, coupled with a transient storage zone solute transport model, to simulate dissolved nutrient retention processes during transient flow events at the channel network scale. We explored several scenarios with a combination of rainfall variability, and biological and geomorphic characteristics of the catchment, to understand the dominant factors that control the transport of dissolved nutrients (e.g., nitrate) along channel networks. While much experimental work has focused on studying nutrient retention during base flow periods in headwater streams, our model‐based theoretical analyses, for the given parameter combinations used, suggest that high‐flow periods can contribute substantially to overall nutrient retention, and that bulk nutrient retention is greater in larger rivers compared to headwaters. The relative efficiencies of nutrient retention during high‐ and low‐flow periods vary due to changes in the relative sizes of the main channel and transient storage zones, as well as due to differences in the relative strengths of the various nutrient retention mechanisms operating in both zones. Our results also indicate that nutrient retention efficiency at all spatial scales of observation has strong dependence on within‐year variability of streamflow (e.g., frequency and duration of high and low flows), as well as on the relative magnitudes of the coefficients that govern biogeochemical uptake processes: the more variable the streamflow, the greater the export of nutrients. Despite limitations of the model parameterizations, our results suggest that increased attention must be paid to field observations of the interactions between process hydrology and nutrient transport and reaction processes at a range of scales to assist with extrapolation of understandings and estimates gained from site‐specific studies to ungauged basins across gradients in climate, human impacts, and landscape characteristics.
Biomass burning as a potential source for atmospheric ice nuclei: Western wildfires and prescribed burns
Authors: Prenni Anthony J. , DeMott Paul J. , Sullivan Amy P. , Sullivan Ryan C. , Kreidenweis Sonia M. , Rogers David C.
Published: May 2012

The sources, abundance and nature of atmospheric particles that serve as ice nuclei (IN) for cold cloud formation remain some of the most important, yet poorly‐characterized, features of aerosol‐cloud interactions that indirectly affect climate. Although a great deal of effort has focused on characterizing the ice nucleating ability of mineral dusts, less is known about carbonaceous particles. A primary source for carbonaceous IN is from biomass combustion. Here we report new measurements of IN activity at −30°C and above water saturation from biomass burning generated particles from prescribed burns and wildfires in the western US. These measurements suggest a range of IN activity, with variability largely dependent on the intensity of the fire. Although the fraction of particles generated during burns which serve as IN is quite small, the large numbers of particles generated in fires make biomass burning a potentially important source of IN to the atmosphere.
Tracer transport during the Arctic stratospheric final warming based on a 33‐year (1979‐2011) tracer equivalent latitude simulation
Authors: Allen Douglas R. , Douglass Anne R. , Nedoluha Gerald E. , Coy Lawrence
Published: May 2012

During the 2011 stratospheric final warming (SFW), a large anticyclone rapidly encompassed the pole, displacing the polar vortex and establishing strong summer easterlies. Tracer Equivalent Latitude (TrEL) maps indicate low latitude air was transported by the anticyclone into the summer polar vortex. MLS nitrous oxide was anomalously high throughout the following summer, confirming the TrEL results. A 33‐year (1979–2011) TrEL simulation at 850 K potential temperature reveals a number of similar low‐TrEL events, which are often, but not always, associated with Frozen‐In Anticyclone (FrIAC) formation. The summertime TrEL values are highly correlated with zonal wind speed in the polar stratosphere following the SFW, suggesting that strong post‐SFW circulation favors polar trapping of low‐TrEL air. The 2011 event, classified as a large‐scale FrIAC, was unusual in having the lowest TrEL values and the strongest easterly vortex within the past three decades.
Joint inversion of Rayleigh wave phase velocity and ellipticity using USArray: Constraining velocity and density structure in the upper crust
Authors: Lin Fan‐Chi , Schmandt Brandon , Tsai Victor C.
Published: May 2012

Rayleigh wave ellipticity, or H/V ratio, observed on the surface is particularly sensitive to shallow earth structure. In this study, we jointly invert measurements of Rayleigh wave H/V ratio and phase velocity between 24–100 and 8–100 sec period, respectively, for crust and upper mantle structure beneath more than 1000 USArray stations covering the western United States. Upper crustal structure, in particular, is better constrained by the joint inversion compared to inversions based on phase velocities alone. In addition to imaging Vs structure, we show that the joint inversion can be used to constrain Vp/Vs and density in the upper crust. New images of uppermost crustal structure (<3 km depth) are in excellent agreement with known surface features, with pronounced low Vs, low density, and high Vp/Vs anomalies imaged in the locations of several major sedimentary basins including the Williston, Powder River, Green River, Denver, and San Juan basins. These results demonstrate not only the consistency of broadband H/V ratios and phase velocity measurements, but also that their complementary sensitivities have the potential to resolve density and Vp/Vs variations.
Decadal changes in the CaCO3 saturation state along 179°E in the Pacific Ocean
Authors: Murata Akihiko , Saito Shu
Published: May 2012

To assess degrees of ocean acidification, we mainly investigated decadal changes in the saturation state of seawater with respect to aragonite (Ωarg), which is a more vulnerable mineral form of CaCO3, along the 179°E meridian (WOCE P14N) in the Pacific Ocean. We found a maximum decrease of Ωarg of −0.48 (−0.034 a−1) at 200–300 dbar (isopycnal surfaces of 24.0–25.8 kg m−3) at 20°N. Between 1993 and 2007, the saturation horizon rose by 17 dbar (1.2 dbar a−1) at latitudes 10°N–50°N. Although ΔΩarg mostly reflected changes in normalized dissolved inorganic carbon (ΔnCT), it was larger than could be explained by anthropogenic CO2 storage alone. Decomposition of ΔnCT revealed that ΔΩargwas enhanced by approximately 50% by a non‐anthropogenic CO2 contribution represented by changes in apparent oxygen utilization. Our results suggest that ocean acidification can be temporarily accelerated by temporal changes in oceanic conditions.
Importance of capturing heliospheric variability for studies of thermospheric vertical winds
Authors: Yiğit Erdal , Ridley Aaron J. , Moldwin Mark B.
Published: May 2012

Using the Global Ionosphere Thermosphere Model with observed real‐time heliospheric input data, the magnitude and variability of thermospheric neutral vertical winds are investigated. In order to determine the role of variability in the Interplanetary Magnetic Field (IMF) and solar wind density on the neutral wind variability, the heliospheric input data are smoothed. The effects of smoothing the IMF and solar wind and density on the vertical winds are simulated for the cases of no smoothing, 5‐minute, and 12‐minute smoothing. Various vertical wind acceleration terms, such as the nonhydrostatic acceleration, are quantified. Polar stereographic projections of the variabilities of vertical wind and ion flows are compared to highlight existing correlations. Overall, the smoother, that is, the less variable the IMF and solar wind parameters are, the weaker are the magnitude and the variability of the thermospheric vertical winds. Weaker IMF variability leads to smaller variability in ion flows, which in turn negatively impacts the variability and the magnitude of Joule heating. Small‐scale temporal variation of the vertical wind acceleration, and thus the variability of the vertical wind, is dominated by the nonhydrostatic term that is controlled primarily by the temporal variation of the Joule heating, which in turn is related to ion flow variations that are shaped by the IMF in the high‐latitude thermosphere. Wavelet analysis of the vertical wind data shows that gravity waves of ∼5 and ∼10‐minute periods are more prominent when the model is run with high‐resolution real‐time IMF and solar wind data. Better capturing of the temporal variation of the IMF and solar wind parameters is crucial for modeling the variability and magnitude of thermospheric vertical winds.
A nighttime temperature maximum in the thermosphere above Saint Santin in winter
Authors: Oliver W. L. , Martinis C. R. , Hickey D. A. , Wright A. D. , Amory‐Mazaudier C.
Published: May 2012

The Saint Santin (45°N) incoherent scatter radar data base shows a local enhancement in nighttime ion temperature that occurs in winter only. Its amplitude can exceed 100 K and averages 40 K on the basis of a conservative computation. The enhancement peaks near 4 LT and has a duration of about 4 hours. We discuss two possible explanations for this feature: (1) it is caused by the convergence of global winds at the global pressure minimum, under which Saint Santin rotates at winter solstice, and (2) it is an extension or propagation of the well‐known low‐latitude midnight temperature maximum to midlatitudes, perhaps to that pressure minimum.
Stepwise changes in stratospheric water vapor?
Authors: Fueglistaler S.
Published: May 2012

The sparse data available of stratospheric water vapor since the 1950s suggests a positive long‐term trend that cannot be explained by the methane increase and what is known about temperature trends around the tropical tropopause, which constrain the amount of water entering the stratosphere. Here, we discuss the 1991–2005 time series of stratospheric water (and methane) measurements from the Halogen Occultation Experiment (HALOE). The high sampling, global coverage and measurement of methane render HALOE data ideal to check the data for self‐consistency and to pinpoint the time of changes in entry mixing ratios. In addition to the well‐known ‘drop’ in October 2000, the HALOE data at 10 hPa and less suggest a steep increase in entry mixing ratios shortly before the beginning of the HALOE measurements. Model calculations using simple representations of the stratospheric age of air spectrum in the tropics show that the very dry phase may be explained by a range of scenarios: A long (several years) dry phase followed by a step increase with amplitude 0.3 ppmv; a shorter (≥1 year) dry pulse with amplitude 0.6 ppmv; or steep linear trends over about 2 years with total increases similar to the step scenarios. The drop in October 2000 coincides with anomalously large eddy heat fluxes in the Southern hemisphere and low tropopause temperatures, but no such relation is found for the situation around 1991. The coincidence with the eruption of Mt. Pinatubo is discussed. The evidence for the results presented here is circumstantial, but they would imply that decoupling between stratospheric water trends and tropical tropopause temperatures can occur on short timescales.
Pigment Epithelium‐Derived Factor, Insulin Sensitivity, and Adiposity in Polycystic Ovary Syndrome: Impact of Exercise Training
Authors: Joham Anju E. , Teede Helena J. , Hutchison Samantha K. , Stepto Nigel K. , Harrison Cheryce L. , Strauss Boyd J. , Paul Eldho , Watt Matthew J.
Published: May 2012

Pigment epithelium‐derived factor (PEDF) is upregulated in obese rodents and is involved in the development of insulin resistance (IR). We aim to explore the relationships between PEDF, adiposity, insulin sensitivity, and cardiovascular risk factors in obese women with polycystic ovary syndrome (PCOS) and weight‐matched controls and to examine the impact of endurance exercise training on PEDF. This prospective cohort intervention study was based at a tertiary medical center. Twenty obese PCOS women and 14 non‐PCOS weight‐matched women were studied at baseline. PEDF, cardiometabolic markers, detailed body composition, and euglycemic—hyperinsulinemic clamps were performed and measures were repeated in 10 PCOS and 8 non‐PCOS women following 12 weeks of intensified aerobic exercise. Mean glucose infusion rate (GIR) was 31.7% lower (P = 0.02) in PCOS compared to controls (175.6 ± 96.3 and 257.2 ± 64.3 mg.m−2.min−1) at baseline, yet both PEDF and BMI were similar between groups. PEDF negatively correlated to GIR (r = −0.41, P = 0.03) and high‐density lipoprotein (HDL) (r = −0.46, P = 0.01), and positively to cardiovascular risk factors, systolic (r = 0.41, P = 0.02) and diastolic blood pressure (r = 0.47, P = 0.01) and triglycerides (r = 0.49, P = 0.004). The correlation with GIR was not significant after adjusting for fat mass (P = 0.07). Exercise training maintained BMI and increased GIR in both groups; however, plasma PEDF was unchanged. In summary, PEDF is not elevated in PCOS, is not associated with IR when adjusted for fat mass, and is not reduced by endurance exercise training despite improved insulin sensitivity. PEDF was associated with cardiovascular risk factors, suggesting PEDF may be a marker of cardiovascular risk status.
Axial and azimuthal spin-wave eigenmodes in rolled-up permalloy stripes
Authors: Balhorn Felix , Jeni Simon , Hansen Wolfgang , Heitmann Detlef , Mendach Stefan
Published: May 2012

We experimentally realized rolled-up permalloy stripes to form three-dimensional ring-like ferromagnetic structures. By means of microwave absorption spectroscopy, we find multiple resonances occurring above a demagnetization field threshold which depends on the ring’s axial width. Our experimental data can be well modeled by assuming both axial and azimuthal spin-wave confinement.
Analysis of a multi-machine database on divertor heat fluxes
Authors: Makowski M. A. , Elder D. , Gray T. K. , LaBombard B. , Lasnier C. J. , Leonard A. W. , Maingi R. , Osborne T. H. , Stangeby P. C. , Terry J. L. , Watkins J.
Published: May 2012

A coordinated effort to measure divertor heat flux characteristics in fully attached, similarly shaped H-mode plasmas on C-Mod, DIII-D, and NSTX was carried out in 2010 in order to construct a predictive scaling relation applicable to next step devices including ITER, FNSF, and DEMO. Few published scaling laws are available and those that have been published were obtained under widely varying conditions and divertor geometries, leading to conflicting predictions for this critically important quantity. This study was designed to overcome these deficiencies. Analysis of the combined data set reveals that the primary dependence of the parallel heat flux width is robustly inverse with Ip, which all three tokamaks independently demonstrate. An improved Thomson scattering system on DIII-D has yielded very accurate scrape off layer (SOL) profile measurements from which tests of parallel transport models have been made. It is found that a flux-limited model agrees best with the data at all collisionalities, while a Spitzer resistivity model agrees at higher collisionality where it is more valid. The SOL profile measurements and divertor heat flux scaling are consistent with a heuristic drift based model as well as a critical gradient model.
The thermal flash technique: The inconsequential effect of contact resistance and the characterization of carbon nanotube clusters
Authors: Mahanta Nayandeep K. , Abramson Alexis R.
Published: May 2012

This article presents a comprehensive mathematical treatment of the theory behind the thermal flash technique used to measure the thermal diffusivity of nanostructures. Analytical expressions predicting the temperature and its rate of change for various combinations of sample length and diffusivity confirmed that the presence of contact resistance between the heat sink/source or within a cluster of materials does not influence the measurement. Measurements on multi-walled carbon nanotube clusters provide further experimental evidence supporting the claim that contact resistance is inconsequential to this technique and yield a thermal conductivity of 2665 W/m K, which corresponds to an isolated nanotube and not the overall cluster.
High resolution detection and excitation of resonant magnetic perturbations in a wall-stabilized tokamak
Authors: Maurer David A. , Shiraki Daisuke , Levesque Jeffrey P. , Bialek James , Angelini Sarah , Byrne Patrick , DeBono Bryan , Hughes Paul , Mauel Michael E. , Navratil Gerald A. , Peng Qian , Rhodes Dov , Rath Nickolaus , Stoafer Christopher
Published: May 2012

We report high-resolution detection of the 3D plasma magnetic response of wall-stabilized tokamak discharges in the High Beta Tokamak-Extended Pulse [T. H. Ivers et al., Phys. Plasmas 3, 1926 (1996)] device. A new adjustable conducting wall has been installed on HBT-EP made up of 20 independent, movable, wall segments instrumented with three distinct sets of 40 modular coils that can be independently driven to generate a wide variety of magnetic perturbations. High-resolution detection of the plasma response is made with 216 poloidal and radial magnetic sensors that have been located and calibrated with high-accuracy. Static and dynamic plasma responses to resonant and non-resonant magnetic perturbations are observed through measurement of the step-response following a rapid change in the toroidal phase of the applied perturbations. Biorthogonal decomposition of the full set of magnetic sensors clearly defines the structures of naturally occurring external kinks as being composed of independent m/n = 3/1 and 6/2 modes. Resonant magnetic perturbations were applied to discharges with pre-existing, saturated m/n = 3/1 external kink mode activity. This m/n = 3/1 kink mode was observed to lock to the applied perturbation field. During this kink mode locked period, the plasma resonant response is characterized by a linear, a saturated, and a disruptive plasma regime dependent on the magnitude of the applied field and value of the edge safety factor and plasma rotation.
A high-resolution integrated model of the National Ignition Campaign cryogenic layered experiments
Authors: Jones O. S. , Cerjan C. J. , Marinak M. M. , Milovich J. L. , Robey H. F. , Springer P. T. , Benedetti L. R. , Bleuel D. L. , Bond E. J. , Bradley D. K. , Callahan D. A. , Caggiano J. A. , Celliers P. M. , Clark D. S. , Dixit S. M. , Doppner T. , Dylla-Spears R. J. , Dzentitis E. G. , Farley D. R. , Glenn S. M. , Glenzer S. H. , Haan S. W. , Haid B. J. , Haynam C. A. , Hicks D. G. , Kozioziemski B. J. , LaFortune K. N. , Landen O. L. , Mapoles E. R. , MacKinnon A. J. , McNaney J. M. , Meezan N. B. , Michel P. A. , Moody J. D. , Moran M. J. , Munro D. H. , Patel M. V. , Parham T. G. , Sater J. D. , Sepke S. M. , Spears B. K. , Town R. P. J. , Weber S. V. , Widmann K. , Widmayer C. C. , Williams E. A. , Atherton L. J. , Edwards M. J. , Lindl J. D. , MacGowan B. J. , Suter L. J. , Olson R. E. , Herrmann H. W. , Kline J. L. , Kyrala G. A. , Wilson D. C. , Frenje J. , Boehly T. R. , Glebov V. , Knauer J. P. , Nikroo A. , Wilkens H. , Kilkenny J. D.
Published: May 2012

A detailed simulation-based model of the June 2011 National Ignition Campaign cryogenic DT experiments is presented. The model is based on integrated hohlraum-capsule simulations that utilize the best available models for the hohlraum wall, ablator, and DT equations of state and opacities. The calculated radiation drive was adjusted by changing the input laser power to match the experimentally measured shock speeds, shock merger times, peak implosion velocity, and bangtime. The crossbeam energy transfer model was tuned to match the measured time-dependent symmetry. Mid-mode mix was included by directly modeling the ablator and ice surface perturbations up to mode 60. Simulated experimental values were extracted from the simulation and compared against the experiment. Although by design the model is able to reproduce the 1D in-flight implosion parameters and low-mode asymmetries, it is not able to accurately predict the measured and inferred stagnation properties and levels of mix. In particular, the measured yields were 15%–40% of the calculated yields, and the inferred stagnation pressure is about 3 times lower than simulated.
Development of a novel 3-degrees of freedom flexure based positioning system
Authors: Kim Hyo-Young , Ahn Da-Hoon , Gweon Dae-Gab
Published: May 2012

Flexure mechanisms have been widely used for nanometer positioning systems. This article presents a novel conceptual design of an ultra-precision 3-degrees of freedom (XYθZ) positioning system with nanometer precision. The main purpose of this novel stage design is for the application of measurement equipment, in particular biological specimens. The stage was designed as a hollow type and with a compact size for the inverted microscope. This stage includes piezoelectric transducer actuators, double compound amplification mechanisms, moving plate, and capacitor sensors. The double compound amplification mechanism was designed using a mathematical model and analyzed by the finite element method. Since the relationship between the variables of the hinge parameters and system performances are complicated, an optimization procedure was used to obtain the optimal design parameters, which maximized the system bandwidth. Based on the solution of the optimization problem, the design of the stage and FEM simulation results are presented. Finally, the stage was manufactured and tested.
Enhancing performance of polymer-based microlasers by a pedestal geometry
Authors: Lozenko S. , Djellali N. , Gozhyk I. , Delezoide C. , Lautru J. , Ulysse C. , Zyss J. , Lebental M.
Published: May 2012

Polymer-based micro-lasers have recently drawn attention due to their attractive features in terms of technological potential, while providing deeper physical insights. In this perspective, we are reporting a number of advances which are related to the practical implementation of a relatively new design whereby micro-cavities are set on pedestals, in contrast with earlier architectures where the resonators were set in full contact with the substrate. Such a pedestal structure is shown to be responsible for a spectacular increase in the lasing efficiency. Depending on the cavity shape, the output power increase can reach up to 3 orders of magnitude. The emitted spectra also exhibit an enriched structure revealed by more favorable lasing and output coupling conditions. Simulations support experimental results and designate the crucial role of the cavity edges in light output coupling processes. Perspectives towards sensing applications are outlined as well as insights into fundamental issues of great practical implications such as wedge diffraction or effective index approximation.
Hydrogen scrambling in ethane induced by intense laser fields: Statistical analysis of coincidence events
Authors: Kanya Reika , Kudou Tatsuya , Schirmel Nora , Miura Shun , Weitzel Karl-Michael , Hoshina Kennosuke , Yamanouchi Kaoru
Published: May 2012

Two-body Coulomb explosion processes of ethane (CH3CH3) and its isotopomers (CD3CD3 and CH3CD3) induced by an intense laser field (800 nm, 1.0 × 1014 W/cm2) with three different pulse durations (40 fs, 80 fs, and 120 fs) are investigated by a coincidence momentum imaging method. On the basis of statistical treatment of the coincidence data, the contributions from false coincidence events are estimated and the relative yields of the decomposition pathways are determined with sufficiently small uncertainties. The branching ratios of the two body decomposition pathways of CH3CD3 from which triatomic hydrogen molecular ions (\documentclass[12pt]{minimal}\begin{document}${\rm H}_{3}^{+}$\end{document}H3+, H2D+, \documentclass[12pt]{minimal}\begin{document}${\rm HD}_{2}^{+}$\end{document} HD 2+, \documentclass[12pt]{minimal}\begin{document}${\rm D}_{3}^{+}$\end{document}D3+) are ejected show that protons and deuterons within CH3CD3 are scrambled almost statistically prior to the ejection of a triatomic hydrogen molecular ion. The branching ratios were estimated by statistical Rice-Ramsperger-Kassel-Marcus calculations by assuming a transition state with a hindered-rotation of a diatomic hydrogen moiety. The hydrogen scrambling dynamics followed by the two body decomposition processes are discussed also by using the anisotropies in the ejection directions of the fragment ions and the kinetic energy distribution of the two body decomposition pathways.
Stroboscopic imaging of an alternating magnetic field from a perpendicular magnetic recording head by frequency-modulated magnetic force microscopy
Authors: Li Zhenghua , Hatakeyama Kodai , Egawa Genta , Yoshimura Satoru , Saito Hitoshi
Published: May 2012

The alternating current (ac) magnetic field from perpendicular magnetic recording head was imaged by using our developed frequency-modulated magnetic force microscopy (FM-MFM), which uses the frequency modulation of cantilever oscillation caused by applying ac magnetic field to a mechanically oscillated cantilever. The amplitude and phase signals (or orthogonal X and Y signals) of the ac magnetic field can be obtained separately by using the FM-MFM technique incorporated with a lock-in amplifier. A signal transformation technique to characterize the AC magnetic field source for frequency modulated magnetic force microscopy was proposed. Two-dimensional vector analysis together with the magnetization vector rotation of the perpendicular recording head was demonstrated using the FM-MFM method combined with the signal transformation algorithm. By taking advantage of this technique, the present method opens a possibility to stroboscopic analyze the AC magnetic field source and gives a very useful feedback for the development of advanced magnetic recording heads.
What are the internal field and the vortex density along the edges of a coated conductor or a superconducting bridge carrying current?
Authors: Bernstein P.
Published: May 2012

In this contribution, I show that, due to demagnetizing effects, the internal field and the vortex density along the edges of coated conductors and superconducting thin film bridges carrying current can be very large. To support this claim, using relations derived between the current and the self and internal fields, the self fields along the edges of YBa2Cu3O7−δ bridges and coated conductors are calculated as functions of the transport current. The resulting values are compared to those obtained from magneto-optical and scanning Hall probe measurements. The possible consequences on the behaviour of coated conductors in the critical state are discussed.
Reduction of crosshatch roughness and threading dislocation density in metamorphic GaInP buffers and GaInAs solar cells
Authors: France R. M. , Geisz J. F. , Steiner M. A. , To B. , Romero M. J. , Olavarria W. J. , King R. R.
Published: May 2012

Surface crosshatch roughness typically develops during the growth of lattice-mismatched compositionally graded buffers and can limit misfit dislocation glide. In this study, the crosshatch roughness during growth of a compressive GaInP/GaAs graded buffer is reduced by increasing the phosphine partial pressure throughout the metamorphic growth. Changes in the average misfit dislocation length are qualitatively determined by characterizing the threading defect density and residual strain. The decrease of crosshatch roughness leads to an increase in the average misfit dislocation glide length, indicating that the surface roughness is limiting dislocation glide. Growth rate is also analyzed as a method to reduce surface crosshatch roughness and increase glide length, but has a more complicated relationship with glide kinetics. Using knowledge gained from these experiments, high quality inverted GaInAs 1 eV solar cells are grown on a GaInP compositionally graded buffer with reduced roughness and threading dislocation density. The open circuit voltage is only 0.38 V lower than the bandgap potential at a short circuit current density of 15 mA/cm2, suggesting that there is very little loss due to the lattice mismatch.
Polarization of poly(vinylidene fluoride) and poly(vinylidene fluoride-trifluoroethylene) thin films revealed by emission spectroscopy with computational simulation during phase transition
Authors: Bystrov Vladimir S. , Paramonova Ekaterina V. , Dekhtyar Yuri , Pullar Robert C. , Katashev Aleksey , Polyaka Natalie , Bystrova Anna V. , Sapronova Alla V. , Fridkin Vladimir M. , Kliem Herbert , Kholkin Andrei L.
Published: May 2012

The electronic structure and self-polarization of P(VDF-TrFE) Langmuir-Blodgett nanofilms were analyzed under temperature-driven phase transitions, according to their thickness, composition, and structural conformation. Both thermo-stimulated exoelectron emission (TSEE) spectroscopy and computational simulation, including quantum-chemical calculations from first principles, were carried out. PVDF and composite P(VDF-TrFE) (70:30) molecular chains as Trans and Gauche conformers, as well as crystal cells, were modeled for these TSEE analyses. The quantum-chemical calculations and the computational simulation were based on the density functional theory (DFT) as well as semi-empirical (PM3) methods. It was demonstrated that the energy of electron states, as well as the total energies of the studied P(VDF-TrFE) molecular clusters during phase transformation, is influenced by electron work function and electron affinity. Analysis was performed by combining TSEE experimental data with the computational data of the molecular models, demonstrating the effectiveness of this joint approach. For the first time, TSEE was used for contactless measurements of nanofilm polarization, and characterization of the phase transition. The proposed new method can be widely applied in nanobiomedicine, particularly in development of new bone bio-implants, including built-in sensors (new smart nanotechnology).
Excitonic origin of enhanced luminescence quantum efficiency in MgZnO/ZnO coaxial nanowire heterostructures
Authors: Yoo Jinkyoung , Chon Bonghwan , Tang Wei , Joo Taiha , Dang Le Si , Yi Gyu-Chul
Published: May 2012

The effect of exciton transport on luminescence efficiency was investigated by time-resolved photoluminescence and spatially resolved cathodoluminescence spectroscopy. The internal quantum efficiency of ZnO nanowire (NW) increased from 45% to 56% due to formation of a MgZnO/ZnO coaxial NW heterostructure. MgZnO shell layer formation induced a decrease in the exciton diffusion length and diffusion coefficient from 150 to 120 nm and 9.8 to 6.4 cm2/s, respectively. The change in exciton transport characteristics indicated that exciton transport, in addition to the surface passivation effect, was an important factor determining the luminescence efficiency in the coaxial NW heterostructure.
Correlating whisker growth and grain structure on Sn-Cu samples by real-time scanning electron microscopy and backscattering diffraction characterization
Authors: Pei Fei , Jadhav Nitin , Chason Eric
Published: May 2012

Whiskers/hillocks grow out of Pb-free Sn coatings used in electronics manufacturing. To determine which grains form whiskers/hillocks, we use scanning electron microscopy and backscattering diffraction to simultaneously monitor the surface morphology and grain structure. To reduce surface roughness, we developed a “peel-off” method to prepare ultra-flat samples that were measured repeatedly while whiskers/hillocks formed. We find grains that form into whiskers/hillocks are present in the as-deposited film (i.e., not re-nucleated) and many have horizontal grain boundaries beneath them. Grain rotation during whisker/hillock formation means that measurements performed after the features grow do not indicate their initial grain orientations.
Acoustically enhanced boiling heat transfer
Authors: Douglas Zachary , Boziuk Thomas R. , Smith Marc K. , Glezer Ari
Published: May 2012

An acoustic field generated by a light-weight, low-power acoustic driver is shown to increase the critical heat flux during pool boiling by about 17%. It does this by facilitating the removal of vapor bubbles from the heated surface and suppressing the instability that leads to the transition to film boiling at the critical heat flux. Bubble removal is enhanced because the acoustic field induces capillary waves on the surface of a vapor bubble that interact with the bubble contact line on the heated surface causing the contact line to contract and detach the bubble from the surface. The acoustic field also produces a radiation pressure that helps to facilitate the bubble detachment process and also suppresses the transition to film boiling. The mechanisms associated with these interactions are explored using three different experimental setups with acoustic forcing: an air bubble on the underside of a horizontal surface, a single vapor bubble on the top side of a horizontal heated surface, and pool boiling from a horizontal heated surface. Measurements of the capillary waves induced on the bubbles, bubble motion, and heat transfer from the heated surface were performed to isolate and identify the dominant forces involved in these acoustically forced motions.
Rupture of a highly stretchable acrylic dielectric elastomer
Authors: Pharr Matt , Sun Jeong-Yun , Suo Zhigang
Published: May 2012

Dielectric elastomer transducers are often subject to large tensile stretches and are susceptible to rupture. Here we carry out an experimental study of the rupture behavior of membranes of an acrylic dielectric elastomer. Pure-shear test specimens are used to measure force-displacement curves, using samples with and without pre-cracks. We find that introducing a pre-crack into a membrane drastically reduces the stretch at rupture. Furthermore, we measure the stretch at rupture and fracture energy using samples of different heights at various stretch-rates. The stretch at rupture is found to decrease with sample height, and the fracture energy is found to increase with stretch-rate.
Enhanced ferroelectric, magnetoelectric, and magnetic properties in Pr and Cr co-doped BiFeO3 nanotubes fabricated by template assisted route
Authors: Das Rajasree , Gopal Khan Gobinda , Mandal Kalyan
Published: May 2012

Arrays of single phase perovskite-type polycrystalline pure, Pr and Cr doped, and Pr-Cr co-doped BiFeO3 (BFO) nanotubes (NTs) (∼50 nm wall thickness) have been synthesized using simple wet chemical liquid phase deposition template assisted technique. Spontaneous enhancement in the ferroelectricity, magnetoelectricity, and ferromagnetic ordering are evidenced in the Pr and Cr co-doped BFO NTs. Significant increase in the ferroelectric characteristics in co-doped BFO NTs suggests the lower leakage current due to the reduction of the oxygen vacancies in the structure. Strong magnetoelectric coupling is observed in co-doped BFO NTs, where the increase of the dielectric constant is noticeable with the increase of the applied magnetic field. Substantial increase in the ferromagnetic signature in the co-doped BFO NTs is believed to be due to the collapse of the space-modulated spin structure.
Red blood cell clustering in Poiseuille microcapillary flow
Authors: Tomaiuolo Giovanna , Lanotte Luca , Ghigliotti Giovanni , Misbah Chaouqi , Guido Stefano
Published: May 2012

Red blood cells (RBC) flowing in microcapillaries tend to associate into clusters, i.e., small trains of cells separated from each other by a distance comparable to cell size. This process is usually attributed to slower RBCs acting to create a sequence of trailing cells. Here, based on the first systematic investigation of collective RBC flow behavior in microcapillaries in vitro by high-speed video microscopy and numerical simulations, we show that RBC size polydispersity within the physiological range does not affect cluster stability. Lower applied pressure drops and longer residence times favor larger RBC clusters. A limiting cluster length, depending on the number of cells in a cluster, is found by increasing the applied pressure drop. The insight on the mechanism of RBC clustering provided by this work can be applied to further our understanding of RBC aggregability, which is a key parameter implicated in clotting and thrombus formation.
Transparent SiO2-Ag core-satellite nanoparticle assembled layer for plasmonic-based chemical sensors
Authors: Chen Tsung-Han , Jean Ren-Der , Chiu Kuo-Chuang , Chen Chun-Hua , Liu Dean-Mo
Published: May 2012

We discovered a promising sensing capability of SiO2@Ag core-satellite nanoparticles with respect to organic melamine when they were consolidated into a solid-type thin-film entity. A series of theoretical models were proposed which provided calculation outcomes superior to those of existing models for the localized surface plasmon resonance spectra of the solid-state assemblies. We envisioned not only that such a SiO2@Ag film is a potential candidate for a transparent solid-state optical nanosensor for the detection of organic molecules but also that the resulting plasmonic resonance model facilitates a better understanding of such a solid-state nanosensor used for a number of sensory applications.
Intrinsic characteristics of transmission line of graphenes at microwave frequencies
Authors: Lee Hee-Jo , Kim Eunho , Yook Jong-Gwan , Jung Jongwan
Published: May 2012

In this paper, we have quantitatively evaluated the effective surface conductivity of chemical vapor deposition-grown graphene through a full-wave electromagnetic method and also investigated the intrinsic characteristics of the transmission line (TL) of the graphene at frequency ranging from 0.5 to 40 GHz. According to the simulated data based on the measured S-parameters, the effective conductivity of single- and multi-layer graphene (MLG) was about 4.3 × 106 S/m and 1.2 × 106 S/m, respectively. Furthermore, we confirm that multi-layer graphene is more suitable for use in transmission lines compared to single-layer graphene in the observed frequency region.
The asymmetrical degradation behavior on drain bias stress under illumination for InGaZnO thin film transistors
Authors: Huang Sheng-Yao , Chang Ting-Chang , Lin Li-Wei , Yang Man-Chun , Chen Min-Chen , Jhu Jhe-Ciou , Jian Fu-Yen
Published: May 2012

This paper investigates behavior of drain bias stress and gate-drain bias stress under illumination for InGaZnO thin film transistors as the current-driver operated. Properties exhibit two-stage degradation behavior during drain bias stress. The photo-excited hole non-uniform trapping from illumination induces drain side barrier lowering and causes an apparent hump phenomenon of the subthreshold swing. However, the positive threshold voltage shift without a hump phenomenon after gate-drain bias stress is different degradation behaviors. It is reliant on whether or not an inversion layer exists in the channel. This work also employs capacitance-voltage measurement to further clarify the mechanism of degradation behaviors.
Spinel oxides: Δ1 spin-filter barrier for a class of magnetic tunnel junctions
Authors: Zhang Jia , Zhang X.-G. , Han X. F.
Published: May 2012

The orbital composition of the electrode wave functions and the complex bands within the barrier band gap are two important factors in deciding the spin-filter effect. This is illustrated in a class of spinel oxides, including MgAl2O4, ZnAl2O4, SiMg2O4, and SiZn2O4. Through first-principles calculations of the complex bands and electron transmission along the [001] direction, they are shown to have the same Δ1 spin-filter effect as MgO due to the combination of both factors. Due to better lattice match with typical bcc magnetic electrodes than MgO, these materials provide a broad spectrum of candidate materials for magnetic tunnel junctions.
Near infrared two-photon self-confinement in photopolymers for light induced self-written waveguides fabrication
Authors: Barsella Alberto , Dorkenoo Honorat , Mager Loïc
Published: May 2012

We present the fabrication of single mode light induced self-written waveguides using two-photon absorption in photopolymers. The measurements are compared to the finite element method simulation of the propagation and demonstrate that two-photon process leads to the confinement of light.
Cherenkov high-order harmonic generation by multistep cascading in χ(2) nonlinear photonic crystal
Authors: An Ning , Ren Huaijin , Zheng Yuanlin , Deng Xuewei , Chen Xianfeng
Published: May 2012

We propose a scheme for efficient Cherenkov high-order harmonic generation. Second to fifth order harmonic wave are observed in a single periodically poled ferroelectric crystal in our experiment. The noncollinear high-order harmonic generation is produced via enhanced Cherenkov second harmonic cascaded with successive multistep sum-frequency generation with simultaneously longitudinal phase-matching. The emission angle and power dependencies are analyzed in detail experimentally, which coincide with theoretical predictions.
Effects of intermolecular interaction on the energy distribution of valance electronic states of a carbazole-based material in amorphous thin films
Authors: Kwon Soonnam , Wee Kyung-Ryang , Kim Jeong Won , Pac Chyongjin , Kang Sang Ook
Published: May 2012

Effects of intermolecular interactions on the occupied electronic structure of amorphous solid of a carbazole-based material were investigated under an assumption that the organic solid consists of randomly oriented assemblies of dimers. The electronic energy states were calculated on the ensemble of large number of random dimers, of which geometries are relaxed using semiempirical van der Waals density functional theory. Intermolecular interactions result in splitting of energy level, and further disorders occur by aggregation of randomly orientated molecules. As a result, frontier occupied energy states can be represented by a superposition of Gaussian distributions, including (i) a main distribution with full width at half maximum of 80–110 meV, depending on the methods of relaxation and (ii) shoulders separated from the center of the main distribution with a value as large as 150 meV. A possible origin for the appearance of these shoulders was ascribed to the presence of molecular assemblies consisting of more tightly bound dimers compared with the others.
Femtosecond laser-induced modification of potassium-magnesium silicate glasses: An analysis of structural changes by near edge x-ray absorption spectroscopy
Authors: Seuthe T. , Höfner M. , Reinhardt F. , Tsai W. J. , Bonse J. , Eberstein M. , Eichler H. J. , Grehn M.
Published: May 2012

The effects of femtosecond laser pulse irradiation on the glass structure of alkaline silicate glasses were investigated by x-ray absorption near edge structure spectroscopy using the beamline of the Physikalisch-Technische Bundesanstalt at the electron synchrotron BESSY II in Berlin (Germany) by analyzing the magnesium K-edge absorption peak for different laser fluences. The application of fluences above the material modification threshold (2.1 J/cm2) leads to a characteristic shift of ∼1.0 eV in the K-edge revealing a reduced (∼3%) mean magnesium bond length to the ligated oxygen ions (Mg-O) along with a reduced average coordination number of the Mg ions.
Carbon mineralisation kinetics of poultry manure in two soils
Authors: Martín José V. , Miralles de Imperial R. , Calvo R. , Garcia M. C. , Leon-Cófreces C. , Delgado M. M.
Published: May 2012

Soil has an important role in the greenhouse effect as a net source or net sink of greenhouse gases. This study compared CO2 emission from broiler poultry manure (PMB) and hen poultry manure (PMH) in two different soils. A laboratory experiment was conducted to evaluate the decomposition of poultry manure by analysing carbon mineralisation. Jars were filled with soil, sealed, and placed in an incubator for 60 days, with periodic CO2 analysis. Higher emissions were found in soil amended with PMH; cumulative carbon released as CO2 was 800 mg C/kg in soil amended with PMH, and 600 mg C/kg with PMB. Data for cumulative CO2-C released from unamended and amended soils were fitted to four different kinetic models. With poultry manure, there were significant differences in the model parameters that represent the amount of total potentially mineralisable carbon and the mineralisation rate constant. After 60 days, the percentages of organic carbon mineralised for PMH were 40% and 26% for each soil, whereas the percentages were 20% and 12% for PMB.
Clay and biochar amendments decreased inorganic but not dissolved organic nitrogen leaching in soil
Authors: Dempster Daniel N. , Jones Davey L. , Murphy Daniel V.
Published: May 2012

Nitrogen (N) leaching from coarse-textured soils frequently leads to productivity losses and negative environmental consequences. Historically, clay amendment has been used on coarse-textured soils to decrease water repellence and nutrient leaching. More recently, biochar has been proposed as an alternative soil amendment to decrease N leaching while simultaneously storing carbon. As biochar has a greater nutrient-retention capacity, we hypothesised that biochar derived from Eucalyptus marginata would be a more effective amendment than clay at minimising N leaching. The soil used was a coarse-textured agricultural sand with the following treatments: (1) biochar incorporated homogenously into the 0–10 cm soil layer, (2) clay incorporated similarly, (3) biochar added as a layer at 10 cm depth, (4) clay added similarly, or (5) a control. Amendments were added at 25 t/ha and watered periodically over 21 days and watered with the equivalent to 30 mm. Clay and biochar amendments significantly decreased cumulative NH4+ leaching by ~20% and NO3– leaching by 25%. Biochar decreased NO3– leaching significantly more than clay, possibly due to decreased nitrification. Dissolved organic N leaching was not influenced by any treatment. Leaching of N was unaffected by amendment application method. We conclude that to decrease N leaching, land managers should apply the most readily available of the amendments in the most convenient manner.