bluuebunny/crossref_metadata_2025 huggingface dataset:
Global ray tracing simulations of the SABER gravity wave climatology
Authors: Preusse Peter , Eckermann Stephen D. , Ern Manfred , Oberheide Jens , Picard Richard H. , Roble Raymond G. , Riese Martin , Russell James M. , Mlynczak Martin G.
Published: April 2009

Since February 2002, the SABER (sounding of the atmosphere using broadband emission radiometry) satellite instrument has measured temperatures throughout the entire middle atmosphere. Employing the same techniques as previously used for CRISTA (cryogenic infrared spectrometers and telescopes for the atmosphere), we deduce from SABER V1.06 data 5 years of gravity wave (GW) temperature variances from altitudes of 20 to 100 km. A typical annual cycle is presented by calculating averages for the individual calendar months. Findings are consistent with previous results from various satellite missions. Based on zonal mean, SABER data for July and zonal mean GW momentum flux from CRISTA, a homogeneous and isotropic launch distribution for the GROGRAT (gravity wave regional or global ray tracer) is tuned. The launch distribution contains different phase speed mesoscale waves, some of very high‐phase speed and extremely low amplitudes, as well as waves with horizontal wavelengths of several thousand kilometers. Global maps for different seasons and altitudes, as well as time series of zonal mean GW squared amplitudes based on this launch distribution, match the observations well. Based on this realistic observation‐tuned model run, we calculate quantities that cannot be measured directly and are speculated to be major sources of uncertainty in current GW parameterization schemes. Two examples presented in this paper are the average cross‐latitude propagation of GWs and the relative acceleration contributions provided by saturation and dissipation, on the one hand, and the horizontal refraction of GWs by horizontal gradients of the mean flow, on the other hand.
On the temporal scale of the turbulent exchange of carbon dioxide and energy above a tropical rain forest in Amazonia
Authors: Campos José Galúcio , Acevedo Otávio C. , Tota Júlio , Manzi Antônio O.
Published: April 2009

The Large Scale Biosphere‐Atmosphere Experiment in Amazonia (LBA) project has been using the eddy covariance technique since 1998 to monitor energy, water, and carbon surface fluxes over Amazonia. The results obtained up‐to‐date indicate high level of uncertainties, especially regarding the role of the Amazonian ecosystem to the global carbon budget. Besides the problems related to the eddy covariance measuring system (systematic error and nighttime stable conditions), an extremely important factor is associated with the averaging time scale or “time window” used by the scientific community to determine the surface fluxes. This work presents initial efforts to determine the turbulence time scale for long‐term carbon and energy surface fluxes over the Amazon rain forest. A total of 198 nights and 218 days during 2006 were analyzed. The multiresolution decomposition technique was applied to project the signal into several time scales and determine when the spectral and cospectral gap occurred. This technique permitted evaluating and separating the real contribution from turbulent and mesoscale fluxes to the total surface fluxes at both diurnal and nocturnal periods. The average turbulence time scale was below 200 and 1200 s for all scalars at nighttime and daytime, respectively. In all cases, there is seasonal dependence. This result shows that the time scale commonly used to calculate nocturnal surface fluxes (30 min) includes a good portion of mesoscale flux in the estimates. The role of these mesoscale fluxes, in terms of seasonal dependence and the uncertainties they add to the estimates, is then analyzed.
Aerosol characterization studies at Great Smoky Mountains National Park, summer 2006
Authors: Lowenthal Douglas , Zielinska Barbara , Mason Brooks , Samy Shar , Samburova Vera , Collins Don , Spencer Chance , Taylor Nathan , Allen Jonathan , Kumar Naresh
Published: April 2009

A study was conducted during summer 2006 at Great Smoky Mountains (GRSM) National Park (NP), TN, to address issues related to estimating aerosol light extinction in the Interagency Monitoring of Protected Visual Environments (IMPROVE) network. The revised IMPROVE equation calculates PM2.5 light scattering (Bsp) from ammonium sulfate, ammonium nitrate, organic carbon mass, and fine soil concentrations; dry scattering efficiencies; and factors that account for hygroscopic growth. Organics are assumed to be nonhygroscopic. The organic compound mass (OCM)/organic carbon (OC) ratio is assumed to be 1.8. Experiments involving in situ and laboratory measurements were conducted to address issues related to (1) concentration‐varying scattering efficiencies; (2) aerosol hydration state; (3) the OCM/OC ratio; and (4) the organic hygroscopicity. Filter‐based measurements indicated that sulfate was acidic, with an average NH4+/SO4= molar ratio of 1.16. Ambient State Hygroscopic Tandem Differential Mobility Analyzer measurements of the ambient hydration state rarely indicated deliquescence. The frequency of hysteresis ranged from 29% to 46% for 0.05 and 0.2 μm particles, respectively. There was a clear relationship between dry particle mean diameter and volume at GRSM, supporting the assumption that an increase in particle size during transport increases both the scattering efficiency and concentration. Water‐soluble organic carbon (WSOC) was isolated from water extracts of high‐volume filter samples using XAD solid‐phase absorbents. The average ratios of OCM measured gravimetrically to OC measured by thermal optical reflectance in residues of isolated WSOC and dichloromethane (DCM) extracts were 2.4 ± 0.3 and 1.9 ± 0.2, respectively. Hygroscopic growth factors (GF) of aerosols generated from WSOC extracts averaged 1.10 ± 0.02, 1.13 ± 0.03, and 1.19 ± 0.04 at 80%, 85%, and 90% RH, respectively. These results indicate that, at GRSM during summer, at least some of the organic aerosol was hygroscopic.
An interdecadal American rainfall mode
Authors: Jury Mark R.
Published: April 2009

Low‐frequency climate variability across the American continents and surrounding oceans is analyzed by application of singular value decomposition (SVD) to gauge‐based rainfall and environmental anomaly fields in the period 1901–2002. A 5‐year filter is used to maintain a focus on interdecadal cycles. The rainfall regime of particular interest (mode 1) is when West Africa and the Caribbean share positive loading and North and South America share negative loading. Wavelet cospectral energy is found at ∼8, 24, and 50 years for Caribbean/West African zones and 16 and 32 years for North/South America. West Africa and South America exhibit antiphase multidecadal variability, while North America and the Caribbean rainfall exhibit quasi‐decadal cycles. The rainfall associations are nonstationary. In the early 1900s, Caribbean and South American rainfall were antiphase. Since 1930 low‐frequency oscillations of North American (West African) rainfall have been positively (negatively) associated with South America. Low‐frequency oscillations of North American rainfall have been consistently antiphase with respect to Caribbean rainfall; however, West Africa rainfall fluctuations have been in phase with the Caribbean more in the period 1920–1950 than at other times. Hemispheric‐scale environmental SVD patterns and scores were compared with the leading rainfall modes. The north‐south gradient modes in temperature are influential in respect of mode 1 rainfall, while east‐west gradients relate to mode 2 (northern Brazil) rainfall. The ability of the GFDL2.1 coupled (ocean‐atmosphere) general circulation model to represent interdecadal rainfall modes in the 20th century was evaluated. While mode 2 is reproduced, mode 1 remains elusive.
Continuous measurements of optical properties of atmospheric aerosols in Mukteshwar, northern India
Authors: Hyvärinen A.‐P. , Lihavainen H. , Komppula M. , Sharma V. P. , Kerminen V.‐M. , Panwar T. S. , Viisanen Y.
Published: April 2009

Particulate pollution of mainly anthropogenic origin is a widely spread phenomenon in southern Asia, influencing climate and causing adverse health effects on humans. In this paper, we analyze continuous measurements of aerosol scattering and absorption properties that were conducted in Mukteshwar, a remote site in the Himalayan Mountains in northern India, during September 2005–September 2007. While aerosol concentrations were somewhat lower than those measured closer to urban areas in India, some optical parameters had a noticeable resemblance to those measured elsewhere in India. The average value of the measured single‐scattering albedo was 0.81 at 525 nm, being indicative of a substantial amount of absorbing material. Annually, there were two periods when aerosol scattering and absorption coefficients were relatively low. These were the rainy season during July and August and the winter months December and January when particulate pollution seemed to reside partly below the altitude of the measurement station. During December and January, local cooking and warming of houses by biomass burning, normally not visible in the data, became evident yet weak sources of absorbing material.
Near‐IR oxygen nightglow observed by VIRTIS in the Venus upper atmosphere
Authors: Piccioni G. , Zasova L. , Migliorini A. , Drossart P. , Shakun A. , García Muñoz A. , Mills F. P. , Cardesin‐Moinelo A.
Published: April 2009

We present observations of both the (0–0) and (0–1) bands at 1.27 and 1.58 μm of the O2(a1Δg − X3Σg−) nightglow made with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument aboard Venus Express. The observations were conducted in both nadir and limb viewing modes, the latter constituting the first systematic investigation into the vertical distribution of the volume emission rate of the infrared oxygen nightglow in Venus' upper atmosphere. Limb measurements from 42 orbits covering the latitude range 7°S to 77°N are analyzed. The peak altitude of the volume emission rate occurs typically between 95 and 100 km, with a mean of 97.4 ± 2.5 km. The vertical profile is broader near the equator, with a full width at half maximum of 11 km, a factor 2 larger than at middle latitudes. A double peak is frequently observed, with the lower and upper peaks occurring near 96–98 km and 103–105 km, respectively. On average, the nightglow appears brightest in the vicinity of the antisolar point. This conclusion is consistent with past ground‐based observations and nadir measurements by VIRTIS. We mapped the global mean O2 nightglow intensity from VIRTIS data collected during 880 orbits. Patchy features of the nightglow intensity observed in nadir view are correlated with the thermal brightness at 4.23–4.28 μm. The observed positive correlation is consistent with downwelling (upwelling) of oxygen atoms accompanying compressional heating (expansion cooling) or with modulation by gravity waves. Finally, from simultaneous measurements of the 1.27 and 1.58 μm bands, we have estimated the ratio of the transition probabilities A00/A01 to be 63 ± 8.
Forecasting maximum solar flare magnitudes from photospheric magnetograms
Authors: Yamamoto Tetsuya T. , Sakurai T.
Published: April 2009

The purpose of this paper is to forecast the maximum solar flare magnitude in an active region and its uncertainty from photospheric magnetic field data. We analyzed 21 flare samples covering X‐ray flare magnitudes from A5.0 to X17.0. Photospheric magnetic parameters are obtained from vector and line of sight magnetograms observed with the Solar Flare Telescope and the Michelson Doppler Imager. Magnetic parameters are averaged axial field strength, averaged longitudinal field strength, and characteristic scale length. These parameters show linear relations with the X‐ray flare magnitudes. This enables us to forecast the maximum flare magnitude an active region will produce. The uncertainty in the forecast is estimated with a simultaneous tolerance interval analysis under 95% confidence level and probability. The minimum uncertainty is factor 3.7 with the data from high‐shear regions (shear angles larger than 60°). Therefore, log FX of the regionally largest flare is forecasted with an uncertainty of log (3.7) = 0.57. For example, an X7.0 flare can be predicted with an uncertainty between X1.9 and X25.9.
A nonlinear model for river meandering
Authors: Bolla Pittaluga M. , Nobile G. , Seminara G.
Published: April 2009

We develop a nonlinear asymptotic theory of flow and bed topography in meandering channels able to describe finite amplitude perturbations of bottom topography and account for arbitrary, yet slow, variations of channel curvature. This approach then allows us to formulate a nonlinear bend instability theory, which predicts several characteristic features of the actual meandering process and extends results obtained by classical linear bend theories. In particular, in agreement with previous weakly nonlinear findings and consistently with field observations, the bend growth rate is found to peak at some value of the meander wave number, reminiscent of the resonant value of linear stability theory. Moreover, a feature typical of nonlinear waves arises: the selected wave number depends on the amplitude of the initial perturbation (for given values of the relevant dimensionless parameters), and in particular, larger wavelengths are associated with larger amplitudes. Meanders are found to migrate preferentially downstream, though upstream migration is found to be possible for relatively large values of the aspect ratio of the channel, a finding in agreement with the picture provided by linear theory. Meanders are found to slow down as their amplitude increases, again a feature typical of nonlinear waves, driven in the present case by flow rather than geometric nonlinearities. The model is substantiated by comparing predictions with field observations obtained for a test case. The potential use of the present approach to investigate a number of as yet unexplored aspects of meander evolution (e.g., chute cutoff) is finally discussed.
Best unbiased ensemble linearization and the quasi‐linear Kalman ensemble generator
Authors: Nowak W.
Published: April 2009

Linearized representations of the stochastic groundwater flow and transport equations have been heavily used in hydrogeology, e.g., for geostatistical inversion or generating conditional realizations. The respective linearizations are commonly defined via Jacobians (numerical sensitivity matrices). This study will show that Jacobian‐based linearizations are biased with nonminimal error variance in the ensemble sense. An alternative linearization approach will be derived from the principles of unbiasedness and minimum error variance. The resulting paradigm prefers empirical cross covariances from Monte Carlo analyses over those from linearized error propagation and points toward methods like ensemble Kalman filters (EnKFs). Unlike conditional simulation in geostatistical applications, EnKFs condition transient state variables rather than geostatistical parameter fields. Recently, modifications toward geostatistical applications have been tested and used. This study completes the transformation of EnKFs to geostatistical conditioning tools on the basis of best unbiased ensemble linearization. To distinguish it from the original EnKF, the new method is called the Kalman ensemble generator (KEG). The new context of best unbiased ensemble linearization provides an additional theoretical foundation to EnKF‐like methods (such as the KEG). Like EnKFs and derivates, the KEG is optimal for Gaussian variables. Toward increased robustness and accuracy in non‐Gaussian and nonlinear cases, sequential updating, acceptance/rejection sampling, successive linearization, and a Levenberg‐Marquardt formalism are added. State variables are updated through simulation with updated parameters, always guaranteeing the physicalness of all state variables. The KEG combines the computational efficiency of linearized methods with the robustness of EnKFs and accuracy of expensive realization‐based methods while drawing on the advantages of conditional simulation over conditional estimation (such as adequate representation of solute dispersion). As proof of concept, a large‐scale numerical test case with 200 synthetic sets of flow and tracer data is conducted and analyzed.
Seminar 2.0: Learning With Skype and Video Podcasts
Authors: Wessel Paul , Anderson Tiffany , Austin Regan , Benediktsdottir Asdis , Chandler Michael T. , Conley Michaela M. , Kim Seung‐Sep , Michaud Robert L. , Rumpf M. Elise , Sleeper Jonathan D. , Weiss Jonathan R.
Published: April 2009

Graduate seminars typically involve reviewing key papers, ranging from seminal contributions by pioneers to the latest cutting‐edge results published in journals such as Nature, Science, and Geophysical Research Letters. Ideally, guest lecturers are invited to add specific expertise and stimulate discussions. However, the increasing costs for travel make this an expensive proposition. Recent improvements in free videoconferencing over the Internet make it possible to invite distant experts to participate in seminars without involving expensive and time‐consuming travel. Tools to record videoconferences allow anyone to combine narrations with slide presentations and prepare merged video files for distribution over the Internet (i.e., podcasts). This brief report discusses such an experiment in a graduate seminar on advanced plate tectonics in the Department of Geology and Geophysics at University of Hawai'i at Manoa's (UHM) School of Ocean and Earth Science and Technology (SOEST). The podcasts are freely available from iTunes (UHM; SOEST; Public Course Lectures) and from http://www.soest.hawaii.edu/pwessel/podcasts.
Assessing Sediment‐Related Effects of Dam Removals: Subcommittee on Sedimentation: Sediment Management and Dam Removal Workshop; Portland, Oregon, 14–16 October 2008
Authors: Wallick J. Rose , Randle Timothy
Published: April 2009

For a host of reasons including dam safety, maintenance costs, and ecological concerns, more dams are currently being removed each year in the United States than are being constructed. Because many reservoirs have accumulated sediments within their pools, dam removal can potentially impose a variety of sediment‐related risks, including downstream effects on habitat, water quality, infrastructure, and flood storage. Sediment‐related risks are particularly heightened when the sediment stored behind a dam is contaminated.
Chambers Receives 2008 Geodesy Section Award
Authors: Nerem R. Steven , Chambers Don P.
Published: April 2009

Don P. Chambers received the 2008 Geodesy Section Award at the 2008 AGU Fall Meeting Honors Ceremony, held 17 December in San Francisco, Calif. The award is given in recognition of major advances in geodesy.
Therapeutic Neutralization of the NLRP1 Inflammasome Reduces the Innate Immune Response and Improves Histopathology after Traumatic Brain Injury
Authors: de Rivero Vaccari Juan Pablo , Lotocki George , Alonso Ofelia F , Bramlett Helen M , Dietrich W Dalton , Keane Robert W
Published: April 2009

Traumatic brain injury elicits acute inflammation that in turn exacerbates primary brain damage. A crucial part of innate immunity in the immune privileged central nervous system involves production of proinflammatory cytokines mediated by inflammasome signaling. Here, we show that the nucleotide-binding, leucine-rich repeat pyrin domain containing protein 1 (NLRP1) inflammasome consisting of NLRP1, caspase-1, caspase-11, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), the X-linked inhibitor of apoptosis protein, and pannexin 1 is expressed in neurons of the cerebral cortex. Moderate parasagittal fluid-percussion injury (FPI) induced processing of interleukin-1β, activation of caspase-1, cleavage of X-linked inhibitor of apoptosis protein, and promoted assembly of the NLRP1 inflammasome complex. Anti-ASC neutralizing antibodies administered immediately after fluid-percussion injury to injured rats reduced caspase-1 activation, X-linked inhibitor of apoptosis protein cleavage, and processing of interleukin-1β, resulting in a significant decrease in contusion volume. These studies show that the NLRP1 inflammasome constitutes an important component of the innate central nervous system inflammatory response after traumatic brain injury and may be a novel therapeutic target for reducing the damaging effects of posttraumatic brain inflammation.
Signal Separation and Parameter Estimation in Noninvasive Dual-Tracer PET Scans using Reference-Region Approaches
Authors: Joshi Aniket D , Koeppe Robert A , Fessier Jeffrey A , Kilbourn Michael R
Published: April 2009

This is the first study to report results from a noninvasive dual-tracer positron emission tomography (PET) in humans not requiring arterial sampling, in which two radiotracers were injected closely in time within the same scan. These studies yield near simultaneous information on two different neuropharmacological systems, providing better characterization of a subject's neurologic condition. The noninvasive dual-tracer approach described in this study is based on the primary assumption that an appropriate bolus plus constant infusion protocol brings the reference tissue of the first radiotracer to steady state before injection of the second tracer. Two methods for separation of time-activity curves (TACs) and parameter estimation were investigated, namely (1) an extrapolation method, in which TACs of the first tracer were extrapolated over total scan duration followed by subtraction from dual-tracer TACs and (2) a simultaneous fitting method, in which reference-region models for both tracers were fitted simultaneously to dual-tracer TACs. Combinations of two reversible tracers ([11C]flumazenil and [11C]dihydrotetrabenazine) or one reversible and one irreversible tracer ([11C] N-methylpiperidinyl propionate) were used. After the dual-tracer scan, a single-tracer (ST) scan using one of the tracers was obtained for comparison of the dual-tracer results. Both approaches provided parameter estimates with intersubject regions-of-interest means typically within 10% of those obtained from ST scans without an appreciable increase in variance.
Evolution of non-Gaussian electron bunches in ultrafast electron diffraction experiments: Comparison to analytic model
Authors: Michalik A. M. , Sipe J. E.
Published: April 2009

We present a comparison of a three-dimensional analytic Gaussian (AG) model of electron bunch propagation with numerical simulations of quasi- and non-Gaussian distributions. Quasi- and non-Gaussian distributions are a good representation of electron bunches used in ultrafast electron diffraction (UED) experiments, and we show that the AG model is successful in predicting the evolution of such freely propagating bunches. The bunch parameters in our comparisons are the bunch size, the total momentum spread, and the local momentum spread. In the case of the local momentum spread, which is related to the bunch coherence length, we compare the predictions of the AG model with three methods for calculating the local momentum spread from numerical data. This comparison also highlights the difficulties of calculating the evolution of the local momentum parameter from N-body simulations. The AG model shows good agreement with N-body simulations of different distributions for all the bunch parameters and is therefore a convenient tool for refining the UED experimental design.
Amorphous to fcc-polycrystal transition in Ge2Sb2Te5 thin films studied by electrical measurements: Data analysis and comparison with direct microscopy observations
Authors: La Fata Pietro , Torrisi Felice , Lombardo Salvatore , Nicotra Giuseppe , Puglisi Rosaria , Rimini Emanuele
Published: April 2009

We experimentally investigate the isothermal amorphous-to-fcc polycrystalline phase transition process in amorphous Ge2Sb2Te5 thin films prepared by sputtering. The amorphous layers were either as deposited or formed by Ar+ ion implantation after crystallization at 300 °C. The kinetics of the amorphous-to-polycrystal transition are analyzed through electrical measurements, in which the Johnson–Mehl–Avrami–Kolmogorov theory is employed. The procedure to extract the kinetics of the phase transition from conductivity versus time data is carefully discussed and compared to data of cross-sectional transmission electron microscopy images versus anneal time. By following this proposed procedure, the nucleation and growth parameters, and the activation energies have been determined. Results indicate that the process of isothermal crystallization in Ge2Sb2Te5 takes place in two stages, in which the Avrami exponent changes in the range from 3 to 1. These results are understood in terms of modifications in the kinetics of the phase transition.
Heteroepitaxy of 3C-SiC on different on-axis oriented silicon substrates
Authors: Anzalone R. , Severino A. , D’Arrigo G. , Bongiorno C. , Abbondanza G. , Foti G. , Saddow S. , La Via F.
Published: April 2009

The heteroepitaxial growth of 3C-SiC films on on-axis (100), (110), and (111) Si oriented substrates has been investigated. A multistep growth process using low-pressure chemical vapor deposition with trichlorosilane as the silicon precursor was conducted at a growth temperature of 1350 °C. X-ray diffraction analysis (θ-2θ and polar figure) and numerical simulation have been shown to be a suitable method to investigate and understand the SiC film structural properties for each substrate orientation. Epitaxial SiC films with first order twins, at least for growth on (100) and (111) Si, were obtained. SiC growth on (110) Si, on the other hand, showed a change in the growth direction by the observation of first and second order twins from the ⟨110⟩ to ⟨111⟩ direction. This is due to the high growth rate of (110) 3C-SiC/(110) Si heteroepitaxial system which encourages the SiC film to grow in a direction with a higher packing density. It was observed that the 3C-SiC surface morphology and average residual stress depends strongly on the silicon substrate orientation, as confirmed by atomic force microscopy analysis and radius of curvature measurements.
Three-dimensional blast-wave-driven Rayleigh–Taylor instability and the effects of long-wavelength modes
Authors: Kuranz C. C. , Drake R. P. , Grosskopf M. J. , Budde A. , Krauland C. , Marion D. C. , Visco A. J. , Ditmar J. R. , Robey H. F. , Remington B. A. , Miles A. R. , Cooper A. B. R. , Sorce C. , Plewa T. , Hearn N. C. , Killebrew K. L. , Knauer J. P. , Arnett D. , Donajkowski T.
Published: April 2009

This paper describes experiments exploring the three-dimensional (3D) Rayleigh–Taylor instability at a blast-wave-driven interface. This experiment is well scaled to the He/H interface during the explosion phase of SN1987A. In the experiments,  ∼5 kJ of energy from the Omega laser was used to create a planar blast wave in a plastic disk, which is accelerated into a lower-density foam. These circumstances induce the Richtmyer–Meshkov instability and, after the shock passes the interface, the system quickly becomes dominated by the Rayleigh–Taylor instability. The plastic disk has an intentional pattern machined at the plastic/foam interface. This perturbation is 3D with a basic structure of two orthogonal sine waves with a wavelength of 71 μm and an amplitude of 2.5 μm. Additional long-wavelength modes with a wavelength of either 212 or 424 μm are added onto the single-mode pattern. The addition of the long-wavelength modes was motivated by the results of previous experiments where material penetrated unexpectedly to the shock front, perhaps due to an unintended structure. The current experiments and simulations were performed to explore the effects of this unintended structure; however, we were unable to reproduce the previous results.
Topological change and impedance spectrum of rat olfactory receptor I7: A comparative analysis with bovine rhodopsin and bacteriorhodopsin
Authors: Alfinito Eleonora , Pennetta Cecilia , Reggiani Lino
Published: April 2009

We present a theoretical investigation on possible selection of olfactory receptors (ORs) as sensing components of nanobiosensors. Accordingly, we generate the impedance spectra of the rat OR I7 in the native and activated states and analyze their differences. In this way, we connect the protein morphological transformation, caused by the sensing action, with its change in electrical impedance. The results are compared with those obtained by studying the best known protein of the G protein coupled receptor (GPCR) family: bovine rhodopsin. Our investigations indicate that a change in morphology goes with a change in impedance spectrum mostly associated with a decrease in the static impedance up to about 60% of the initial value, in qualitative agreement with existing experiments on rat OR I7. The predictiveness of the model is tested successfully for the case of recent experiments on bacteriorhodopsin. The present results point to a promising development of a new class of nanobiosensors based on the electrical properties of GPCR and other sensing proteins.
Magnetic grating produced by localized crystallization of amorphous Cu2MnSn thin film using femtosecond laser pulses
Authors: Baek Kwang H. , Kim Jung H. , Woo Hee J. , Lee Geon Joon , Lee Young Pak , Yoon Chong S.
Published: April 2009

A magnetic grating with a periodicity of 2 μm was generated by selective crystallization of an amorphous Cu2MnSn thin film using femtosecond laser pulses. By irradiating the amorphous Cu2MnSn thin film with two-beam interference pattern of femtosecond laser pulses, alternating bands of ferromagnetic and paramagnetic phases were produced. The crystallized region was composed of ferromagnetic Cu2MnSn grains, whereas the amorphous region remained paramagnetic. Because crystallized Cu2MnSn is the only ferromagnetic phase that can be produced by heat-treatment of the amorphous Cu2MnSn thin film, a magnetic grating with high definition was produced. Moreover, the periodicity of the modulated structure can be reduced down to a submicrometer scale and extended to two dimensions so that the technique could be potentially utilized for magnetic patterning.
Shape effects in graphene nanoribbon resonant tunneling diodes: A computational study
Authors: Teong Hansen , Lam Kai-Tak , Khalid Sharjeel Bin , Liang Gengchiau
Published: April 2009

The possibility of using graphene nanoribbons (GNRs) as the material for resonant tunneling diodes (RTDs) was investigated using a device simulator based on the nonequilibrium Green’s function with the π-orbital tight-binding approach. The double-barrier quantum well (DBQW) requirements of a RTD can be implemented by adjusting the width of a GNR to derive a negative differential resistance (NDR). The implementation of such a device is demonstrated in this paper and its mechanism was also found to be robust regardless of the eventual shape of the GNR patterned. Furthermore, the effects of the shape of the patterned GNR and the operating temperature on the performance of the device were explored by looking at the real space current flux of the device and the temperature dependency of the peak-valley ratio (PVR), respectively. Although the different shapes of GNR RTDs had a similar DBQW structure, their PVRs were different due to their conduction mechanisms which were dependent on the different geometrical shapes of each case. Lastly, the effect of thermal broadening, and width/length dependence of the central GNR between two barriers on the device performance, was further investigated in order to provide insights into the device physics of GNR RTDs for future study on performance optimization.
Tungsten oxide doped N,N′-di(naphthalen-1-yl)-N,N′-diphenyl-benzidine as hole injection layer for high performance organic light-emitting diodes
Authors: Wang Fengxia , Qiao Xianfeng , Xiong Tao , Ma Dongge
Published: April 2009

By introducing tungsten oxide (WO3) doped N,N′-di(naphthalen-1-yl)-N,N′-diphenyl-benzidine (NPB) hole injection layer, the great improvement in device efficiency and the organic film morphology stability at high temperature were realized for organic light-emitting diodes (OLEDs). The detailed investigations on the improvement mechanism by optical, electric, and film morphology properties were presented. The experimental results clearly demonstrated that using WO3 doped NPB as the hole injection layer in OLEDs not only reduced the hole injection barrier and enhanced the transport property, leading to low operational voltage and high efficiency, but also improved organic film morphology stability, which should be related to the device stability. It could be seen that due to the utilization of WO3 doped NPB hole injection layer in NPB/tris (8-quinolinolato) aluminum (Alq3)-based device, the maximum efficiency reached 6.1 cd A−1 and 4.8 lm W−1, which were much higher than 4.5 cd A−1 and 1.1 lm W−1 of NPB/Alq3 device without hole injection layer. The device with WO3 doped NPB hole injection layer yet gave high efficiency of 6.1 cd A−1 (2.9 lm W−1) even though the device was fabricated at substrate temperature of 80 °C. These results adequately indicated that WO3 doped NPB was a promising hole injection layer for high efficiency and high stability OLEDs.
Sputtered In2O3 and ITO thin films containing zirconium
Authors: Gessert T. A. , Yoshida Y. , Fesenmaier C. C. , Coutts T. J.
Published: April 2009

Additions of Zr to In2O3 (IO) and In2O3:SnO2 (ITO) sputtered thin films are studied. We find that Zr allows IO-based films to maintain optical transparency as oxygen partial pressure in the sputter ambient decreases, and it also maintains high carrier concentration as the oxygen partial pressure increases. Applying this guidance could indicate pathways to improve film properties in large-area deposition systems. We also find that for films deposited at optimum oxygen partial pressure, the optical transparency of the IO-based films improves as Zr is added, especially in the near-infrared spectral region. Analysis of these films using Drude theory approximations indicate that optical improvement is due to an increase in dielectric permittivity caused by Zr addition. We propose that controlling dielectric permittivity may be an important strategy in improving other transparent conducting oxides (TCOs), as well as indicative of an important pathway to developing new TCOs.
High accuracy subwavelength distance measurements: A variable-angle standing-wave total-internal-reflection optical microscope
Authors: Haynie A. , Min T.-j. , Luan L. , Mu W. , Ketterson J. B.
Published: April 2009

We describe an extension of the total-internal-reflection microscopy technique that permits direct in-plane distance measurements with high accuracy (<10 nm) over a wide range of separations. This high position accuracy arises from the creation of a standing evanescent wave and the ability to sweep the nodal positions (intensity minima of the standing wave) in a controlled manner via both the incident angle and the relative phase of the incoming laser beams. Some control over the vertical resolution is available through the ability to scan the incoming angle and with it the evanescent penetration depth.
Magnetism-driven anomalous surface alloying between Cu and Cr
Authors: Kádas K. , Lindquist M. , Eriksson O. , Johansson B. , Vitos L.
Published: April 2009

Cu–Cr contact materials are widely used as medium- and high-voltage vacuum interrupters. The microstructure of these materials is critical in their performance: the finer structure they have, the better are their physical properties. A solid solution of Cu and Cr could significantly increase the performance of such contact materials. However, Cu and Cr are practically immiscible in the bulk phase. Based on first principles density functional theory we show here that the solubility of Cr in Cu is dramatically increased on Cu surfaces already at room temperature and Cu–Cr alloys are formed on both the Cu(111) and Cu(100) surfaces. We demonstrate that the origin of this phenomenon is the unique magnetic properties of Cr atoms near surfaces.
Pore collapse in powder metal mixtures during shock compression
Authors: Reding D. J.
Published: April 2009

A multiscale modeling approach is proposed to simulate the mechanical response in porous energetic mixtures during shock loading. A spherically symmetric single pore model is developed that incorporates viscoplastic and temperature dependent effects for a mixture. Our proposed model introduces parameters that capture microstructural effects due to changes in mixture morphology, particle size, and magnitude of the shock load applied to the mixture. These parameters are used to describe geometric, inertial, and constituent interaction effects. The proposed pore collapse model is incorporated into a gas-gun simulation and the parameters are studied with comparisons to experimental results for an intermetallic powder mixture containing Ni+Al.
Electric-induced nanodamage in single ZnO nanowires
Authors: Yang Ya , Zhang Yue , Qi Junjie , Liao Qingliang , Tang Lidan , Wang Yishu
Published: April 2009

The electric-induced nanodamage in single ZnO nanowires was measured with a conductive atomic force microscope. The damage threshold voltage was estimated to be 7.0±0.5 V for the 5 nm nanowires. The thickness along a single nanowire during the damaging process can be accurately modulated by controlling the evaporation time and applied voltage in selected areas. The transverse conductance was found to increase as the heights of the single damaging nanowire increased, which is suggested to be attributed to the quantum confinement effect.
Incorporation of phosphorus donors in (110)-textured polycrystalline diamond
Authors: Lazea A. , Barjon J. , D’Haen J. , Mortet V. , D’Olieslaeger M. , Haenen K.
Published: April 2009

The incorporation efficiency of phosphorus was studied as a function of the surface orientation of grains in (110)-textured polycrystalline chemical vapor deposited diamond. Cathodoluminescence mapping of such films exhibits large local differences in relative intensities stemming from P-bound and free excitons. Combined with electron backscattering diffraction mapping, these data allow assessing of the donor concentration as a function of the grain orientation. While [P] can vary between 1015 and >1018 cm−3 within one film, misorientation angles of more than 10° with respect to the exact [110] axis assure an enhanced incorporation of P with concentrations surpassing 5×1017 cm−3. The role of the surface morphology in the observation of these large incorporation differences is explained.
X-ray fluorescence spectroscopy from ions at charged vapor/water interfaces
Authors: Bu Wei , Vaknin David
Published: April 2009

X-ray fluorescence spectra from monovalent ions (Cs+) that accumulate from dilute solutions to form an ion-rich layer near a charged Langmuir monolayer are presented. For the salt solution without the monolayer, the fluorescence signals below the critical angle are significantly lower than the detection sensitivity and only above the critical angle signals from the bulk are observed. In the presence of a monolayer that provides surface charges, strong fluorescence signals below the critical angle are observed. Ion density accumulated at the interface are determined from the fluorescence. The fluorescent spectra collected as a function of incident x-ray energy near the LIII edge yield the extended absorption spectra from the ions, and are compared to recent independent results. The fluorescence data from divalent Ba2+ with and without monolayer are also presented.
Femtosecond-laser-induced quasiperiodic nanostructures on TiO2 surfaces
Authors: Das Susanta Kumar , Dufft Daniela , Rosenfeld Arkadi , Bonse Joern , Bock Martin , Grunwald Ruediger
Published: April 2009

High-spatial frequency, quasiperiodic structures (HSFL, Nanoripples) of 170 nm feature size were induced in rutile-type titanium dioxide surfaces by focused 150 fs Ti:sapphire laser pulses at wavelengths around 800 nm. The ripple formation is distinctly visible for numbers of pulses of N=100–1000. At lower number of pulses (N=10), a significant surface roughening appears instead of ripples which is characterized by randomly meandering nanostructures. These observations confirm an essential contribution of early stage irregular material modifications to the dynamics of quasiperiodic ripple formation. The threshold fluence for ripple generation is estimated on the basis of the conventional theory of laser-induced surface structuring. The decrease in the threshold fluence from 0.34 to 0.24 J/cm2, as it was found for an increase in the number of pulses from N=100 to N=1000, is attributed to a damage accumulation effect. Nanostructuring of spatially extended regions was enabled by utilizing a controlled sample translation at optimized energy and repetition rate of the laser pulses. A significant enhancement of the periodicity of the nanostructures was confirmed by two-dimensional Fourier transform of scanning electron microscopy data. At second harmonic wavelengths around 400 nm, the generation of nanoripples even on the sub-100 nm scale was demonstrated.
Experimental realization of nearly steady-state toroidal electron plasmas
Authors: Stoneking M. R. , Marler J. P. , Ha B. N. , Smoniewski J.
Published: April 2009

Electron plasmas with densities of 5×106 cm−3 are trapped in the Lawrence Non-neutral Torus II (LNT II) for times exceeding 1 s. LNT II is a high aspect ratio (R0/a≳10) partially toroidal trap (270° arc, B0=670 G). The m=1 diocotron mode is launched and detected using isolated segments of a fully sectored conducting boundary and its frequency is used to determine the total trapped charge as a function of time. The observed confinement time (≈3 s) approaches the theoretical limit (≈6 s) set by the magnetic pumping transport mechanism of Crooks and O’Neil [Phys. Plasmas 3, 2533 (1996)]. We also present equilibrium modeling and numerical simulations of the toroidal m=1 mode constrained by experimental data. Future work includes the identification of the dominant transport mechanisms via confinement scaling experiments and measurement of the m=2 mode frequency and development of a strategy for making a transition to fully toroidal confinement.
On the structure of high-pressure high-temperature η-O2
Authors: Lundegaard Lars F. , Guillaume Christophe , McMahon Malcolm I. , Gregoryanz Eugene , Merlini Marco
Published: April 2009

In situ high-pressure high-temperature x-ray diffraction and optical studies have been conducted on solid oxygen between 10 and 20 GPa and up to 700 K. Optical observations and Raman spectroscopic studies have been utilized to confirm the existence of η-O2 and to identify phase behavior and phase boundaries of β-, ϵ- and η-O2 at elevated temperatures. Subsequent single-crystal synchrotron x-ray diffraction studies yielded the structure of the η-O2 phase at 15.9 GPa and 625 K.
Small amplitude electron-acoustic double layers and solitons in fully relativistic plasmas of two-temperature electrons
Authors: Lee Nam C.
Published: April 2009

A Korteweg–de Vries (KdV) equation for fully relativistic one dimensional plasmas of arbitrarily large streaming speed and temperature is derived by using the reductive perturbation method. For plasmas with more than two species of particles, the coefficient representing quadratic nonlinearity in KdV can vanish at critical values of certain parameters. To describe the nonlinear evolution at this critical parameter, a modified KdV (mKdV) equation that contains a cubic nonlinear term is obtained. Furthermore, a mixed mKdV equation pertaining to parameters in the vicinity of the critical values is also derived, in which the quadratic and cubic nonlinearities are both present. As an illustration of the results, the mixed mKdV equation is applied to a plasma comprised of cold ions and electrons having cold (T=0) and finite temperature components. For warm temperature T⪡mec2, it is found that electron-acoustic nonlinear waves in the shape of double layer (kink) and solitary waves can exist, which have phase speed 3T/(4+α)me in the rest frame of plasma, where α is the polytropic index of the equation of state of the warm electrons. The thickness of the transitional layer of the kink structure is of the order of Debye length λD. For extremely high temperature T⪢mec2, it is also found that double layer and soliton-type solutions can exist with phase speed α−1c, which is equal to the well known relativistic sound speed c/3 for α=4/3. The thickness of the transition layer scales as δ∼T−1/4, which is different from the T⪡mec2 case.
Miniature diamond anvil cell for broad range of high pressure measurements
Authors: Gavriliuk A. G. , Mironovich A. A. , Struzhkin V. V.
Published: April 2009

A miniature versatile nonmagnetic diamond anvil cell for diverse physical property measurement under cryogenic environments and high magnetic fields at high pressure has been developed. Several such cells have been manufactured and tested in the Physical Properties Measurement System (PPMS) by Quantum Design at high pressures and low temperatures. The cells have good pressure stability during temperature scans down to helium temperatures and back to room temperature. The cells have been tested in strong magnetic fields and demonstrated excellent nonmagnetic properties. The wide-angle side openings give the possibility to use this cell as a “panoramic cell” in synchrotron experiments requiring large angle off-axis access. The possible experiments, which may use this cell, include spectroscopic experiments (optical, synchrotron Mössbauer, Raman, x-ray emission, etc.), different types of x-ray diffraction experiments, transport measurements (resistivity, magnetoresistivity, thermoelectromotive force, etc.), measurements of susceptibility, and many other conventional and synchrotron experiments at very low temperatures and in strong magnetic fields.
Roto-translational Raman spectra of pairs of hydrogen molecules from first principles
Authors: Gustafsson Magnus , Frommhold Lothar , Li Xiaoping , Hunt K. L. C.
Published: April 2009

We calculate the collision-induced, roto-translational, polarized, and depolarized Raman spectra of pairs of H2 molecules. The Schrödinger equation of H2–H2 scattering in the presence of a weak radiation field is integrated in the close-coupled scheme. This permits the accounting for the anisotropy of the intermolecular potential energy surface and thereby it includes mixing of polarizability components. The static polarizability invariants, trace and anisotropy, of two interacting H2 molecules were obtained elsewhere [Li et al., J. Chem. Phys. 126, 214302 (2007)] from first principles. Here we report the associated spherical tensor components which, along with the potential surface, are input in the calculation of the supramolecular Raman spectra. Special attention is paid to the interferences in the wings of the rotational S0(0) and S0(1) lines of the H2 molecule. The calculated Raman pair spectra show reasonable consistency with existing measurements of the polarized and depolarized Raman spectra of pairs of H2 molecules.