bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermophysical properties of the MER and Beagle II landing site regions on Mars
Authors: Jakosky Bruce M. , Hynek Brian M. , Pelkey Shannon M. , Mellon Michael T. , Martínez‐Alonso Sara , Putzig Nathaniel E. , Murphy Nate , Christensen Philip R.
Published: August 2006

We analyzed remote‐sensing observations of the Isidis Basin, Gusev Crater, and Meridiani Planum landing sites for Beagle II, MER‐A Spirit, and MER‐B Opportunity spacecraft, respectively. We emphasized the thermophysical properties using daytime and nighttime radiance measurements from the Mars Global Surveyor (MGS) Thermal Emission Spectrometer and Mars Odyssey Thermal Emission Imaging System (THEMIS) and thermal inertias derived from nighttime data sets. THEMIS visible images, MGS Mars Orbiter Camera (MOC) narrow‐angle images, and MGS Mars Orbiter Laser Altimeter (MOLA) data are incorporated as well. Additionally, the remote‐sensing data were compared with ground‐truth at the MER sites. The Isidis Basin surface layer has been shaped by aeolian processes and erosion by slope winds coming off of the southern highlands and funneling through notches between massifs. In the Gusev region, surface materials of contrasting thermophysical properties have been interpreted as rocks or bedrock, duricrust, and dust deposits; these are consistent with a complex geological history dominated by volcanic and aeolian processes. At Meridiani Planum the many layers having different thermophysical and erosional properties suggest periodic deposition of differing sedimentological facies possibly related to clast size, grain orientation and packing, or mineralogy.
Variability in serpentinite mudflow mechanisms and sources: ODP drilling results on Mariana forearc seamounts
Authors: Fryer P. , Gharib J. , Ross K. , Savov I. , Mottl M. J.
Published: August 2006

Samples of metamorphic rock were collected from drilled holes on ODP Leg 195 and in piston/gravity cores collected with the Jason 2 remotely operated vehicle from S. Chamorro Seamount, a serpentinite mud volcano on the Mariana forearc. The recovered muds are approximately 90% serpentinite, including grit‐ to boulder‐sized clasts of serpentinized peridotites, but also contain a wide variety of small fragments of metabasic rocks. These metabasic fragments include high‐pressure, low‐temperature rocks derived from the subduction zone. Other serpentinite seamounts also have yielded metabasic rock fragments as small clasts in the serpentinite mudflows, but none have as wide a variety of rock types as S. Chamorro Seamount. The sources of the rock clasts, both serpentinized peridotites and metabasic schists, vary with the eruptive episodes of the mud volcanoes. Swath mapping of S. Chamorro Seamount shows that a sector collapse of its southeastern flank has resulted in debris flows from the summit region of the seamount that have traveled more than 70 km eastward toward the trench. These debris flows, however, have a very different morphology from mudflows observed at the summit. High‐resolution seafloor mapping of the summit shows both thin, presumably highly fluid‐ (or gas‐) charged serpentinite mudflows and a relatively viscous protrusion that has formed the main summit knoll. By comparison, the summit of Conical Seamount drilled on ODP Leg 125 lacks a distinct summit knoll and has numerous, relatively thin and widespread mudflows covering the flanks of the edifice. The style of eruption at a given seamount probably varies with time and with the amount of fluid or gas incorporated in a given pulse of mud. The greater diversity of metabasic rocks at S. Chamorro Seamount may be a consequence of recycling of forearc materials through tectonic erosion and subduction in the southern part of the forearc.
Implication for the solar wind effect on the Io plasma torus
Authors: Nozawa H. , Misawa H. , Kagitani M. , Tsuchiya F. , Takahashi S. , Morioka A. , Kimura T. , Okano S. , Yamamoto H. , Sood R.
Published: August 2006

Sporadic enhancements of [SII] 673.1 nm emissions from the Io plasma torus were found in ground‐based observations in 1998 and 1999. Just after the onset of the enhancement on September 21, 1999, narrow‐band kilometric (nKOM) radiation began to be observed by the Galileo/PWS in the Jovian magnetosphere. During this period, quasi‐periodic burst groups (Morioka et al., 2006) were also observed by the PWS, and Jovian “auroral flare” (Waite et al., 2001) events were found on the same day by the Hubble Space Telescope. The sudden appearances of both nKOM radiation and auroral flare suggest the arrival of a remarkable solar‐wind disturbance at the Jovian magnetosphere. In this paper, we present evidence that these enhancements are stochastic, related to solar wind disturbances.
Temporally resolved ammonia emission inventories: Current estimates, evaluation tools, and measurement needs
Authors: Pinder Robert W. , Adams Peter J. , Pandis Spyros N. , Gilliland Alice B.
Published: August 2006

We evaluate the suitability of a three‐dimensional chemical transport model (CTM) as a tool for assessing ammonia emission inventories, calculate the improvement in CTM performance owing to recent advances in temporally varying ammonia emission estimates, and identify the observational data necessary to improve future ammonia emission estimates. We evaluate two advanced approaches to estimating the temporal variation in ammonia emissions: a process‐based approach and an inverse‐modeled approach. These inventories are used as inputs to a three‐dimensional CTM, PMCAMx. The model predictions of aerosol NH4+ concentration, NHx (NHx ≡ NH3 + NH4+) concentration, wet‐deposited NH4+ mass flux, and NH4+ precipitation concentration are compared with observations. However, it should be cautioned that errors in model inputs other than the ammonia emissions may bias such comparisons. We estimate the robustness of each of these amodel‐measurement comparisons as the ratio of the sensitivity to changes in emissions over the sensitivity to errors in the CTM inputs other than the ammonia emission inventory. We find the NHx concentration to be the only indicator that is sufficiently robust during all time periods. Using this as an indicator, the ammonia emission inventories with diurnal and seasonal variation improve the PMCAMx predictions in the summer and winter. In the United States, future efforts to improve the spatial and temporal accuracy of ammonia emission inventories are limited by a lack of a long‐term, widespread network of highly time‐resolved NHx measurements.
Tropospheric Emission Spectrometer observations of the tropospheric HDO/H2O ratio: Estimation approach and characterization
Authors: Worden John , Bowman Kevin , Noone David , Beer Reinhard , Clough Shepard , Eldering Annmarie , Fisher Brendan , Goldman Aaron , Gunson Michael , Herman Robert , Kulawik Susan S. , Lampel Michael , Luo Ming , Osterman Gregory , Rinsland Curtis , Rodgers Clive , Sander Stanley , Shephard Mark , Worden Helen
Published: August 2006

We present global, vertical profile estimates of the HDO/H2O ratio from the Tropospheric Emission Spectrometer (TES) on the Earth Observing System (EOS) Aura satellite. We emphasize in this paper the estimation approach and error characterization, which are critical to determining the very small absolute concentration of HDO relative to H2O and its uncertainty. These estimates were made from TES nadir‐viewing (downlooking) thermal infrared spectral radiances observed on 20 September 2004. Profiles of HDO and H2O are simultaneously estimated from the observed radiances and a profile of the ratio is then calculated. This simultaneous, or “joint,” estimate is regularized with an a priori covariance matrix that includes expected correlations between HDO and H2O. This approach minimizes errors in the profile of the HDO/H2O ratio that are due to overlapping HDO and H2O spectroscopic lines. Under clear‐sky conditions in the tropics, TES estimates of the HDO/H2O ratio are sensitive to the distribution of the actual ratio between the surface and about 300 hPa with peak sensitivity at 700 hPa. The sensitivity decreases with latitude through its dependence on temperature and water amount. We estimate a precision of approximately 1% to 2% for the ratio of the HDO/H2O tropospheric densities; however, there is possibly a bias of approximately 5% in the ratio due to the HDO spectroscopic line strengths. These global observations clearly show increased isotopic depletion of water vapor at higher latitudes as well as increased depletion in the upper troposphere versus the lower troposphere.
Interactive dust‐radiation modeling: A step to improve weather forecasts
Authors: Pérez Carlos , Nickovic Slobodan , Pejanovic Goran , Baldasano José María , Özsoy Emin
Published: August 2006

Inclusion of mineral dust radiative effects could lead to a significant improvement in the radiation balance of numerical weather prediction models with subsequent improvements in the weather forecast itself. In this study the radiative effects of mineral dust have been fully incorporated into a regional atmospheric dust model. Dust affects the radiative fluxes at the surface and the top of the atmosphere and the temperature profiles at every model time step when the radiation module is processed. These changes influence the atmospheric dynamics, moisture physics, and near‐surface conditions. Furthermore, dust emission is modified by changes in friction velocity and turbulent exchange coefficients; dust turbulent mixing, transport, and deposition are altered by changes in atmospheric stability, precipitation conditions, and free‐atmosphere winds. A major dust outbreak with dust optical depths reaching 3.5 at 550 nm over the Mediterranean region on April 2002 is selected to assess the radiative dust effects on the atmosphere at a regional level. A strong dust negative feedback upon dust emission (35–45% reduction of the AOD) resulted from the smaller outgoing sensible turbulent heat flux decreasing the turbulent momentum transfer from the atmosphere and consequently dust emission. Significant improvements of the atmospheric temperature and mean sea‐level pressure forecasts are obtained over dust‐affected areas by considerably reducing both warm and cold temperature biases existing in the model without dust‐radiation interactions. This study demonstrates that the use of the proposed model with integrated dust and atmospheric radiation represents a promising approach for further improvements in numerical weather prediction practice and radiative impact assessment over dust‐affected areas.
Evaluation of SF6, C2Cl4, and CO to approximate fossil fuel CO2 in the Northern Hemisphere using a chemistry transport model
Authors: Rivier L. , Ciais P. , Hauglustaine D. A. , Bakwin P. , Bousquet P. , Peylin P. , Klonecki A.
Published: August 2006

The distribution of the fossil fuel component in atmospheric CO2 cannot be measured directly at a cheap cost. Could anthropogenic tracers with source patterns similar to fossil fuel CO2 then be used for that purpose? Here we present and evaluate a methodology using surrogate tracers, CO, SF6, and C2Cl4, to deduce fossil fuel CO2. A three‐dimensional atmospheric chemistry transport model is used to simulate the relationship between each tracer and fossil fuel CO2. In summertime the regression slopes between fossil fuel CO2 and surrogate tracers show large spatial variations for chemically active tracers (CO and C2Cl4), although C2Cl4 presents less scatter than CO. At two tall tower sites in the United States (WLEF, Wisconsin, and WITN, North Carolina), we found that in summertime the C2Cl4 (CO) versus fossil CO2 slope is on average up to 15% (25%) higher than in winter. We show that for C2Cl4 this seasonal variation is due to OH oxidation. For CO the seasonal variation is due to both chemistry and mixing with nonanthropogenic CO sources. In wintertime the three surrogate tracers SF6, C2Cl4, and CO are about equally as good indicators of the presence of fossil CO2. However, our model strongly underestimates the variability of SF6 at both towers, probably because of unaccounted for emissions. Hence poor knowledge of emission distribution hampers the use of SF6 as a surrogate tracer. From a practical point of view we recommend the use of C2Cl4 as a proxy of fossil CO2. We also recommend the use of tracers to separate fossil CO2. Despite the fact that the uncertainty on the regression slope is on the order of 30%, the tracer approach is likely to have less bias than when letting one model with one inventory emission map calculate the fossil CO2 distribution.
Tidal analysis of meridional winds at the South Pole using a VHF interferometric meteor radar
Authors: Lau Elías M. , Avery Susan K. , Avery James P. , Palo Scott E. , Makarov Nikolai A.
Published: August 2006

Atmospheric tides are perturbations driven by the periodic absorption of solar radiation. They manifest themselves everywhere in the atmosphere, and an understanding of their sources, propagation, and interaction with other waves is vital to comprehend the global atmosphere. In order to measure the horizontal wind field in the mesosphere–lower thermosphere (MLT) over the geographical South Pole and use these measurements to understand the large‐scale dynamics of this region, a VHF meteor radar was installed at the Amundsen‐Scott station at the South Pole in 2001. The radar operated for a few months in 2001 and with minor interruptions in 2002 and 2003. However, toward the end of 2003, receiver problems caused a drop in our meteor echo rates, preventing us from getting tidal results after October 2003. We report on the temporal behavior of the diurnal and semidiurnal tides observed in the meridional wind field at mesospheric and lower thermospheric heights in the vicinity of the geographic South Pole. With the interferometric capabilities of this radar, we also document for the first time the vertical structure of these tides. The zonal wave number one component of the diurnal tide shows consistency for all years that we analyze. On the other hand, the zonal wave number one component of the semidiurnal tide shows significantly more year‐to‐year variability. Our results are compared to previous observations and model predictions. A significant decrease in the amplitude of this oscillation from December 2002 to February 2003 is also observed and discussed.
Distinguishing ionospheric models using Schumann resonance spectra
Authors: Williams Earle R. , Mushtak Vadim C. , Nickolaenko Alexander P.
Published: August 2006

A number of models for Schumann resonance (SR) behavior in uniform approximations of the real Earth‐ionosphere cavity now populate the literature. These models are treated in terms of variously formulated propagation parameters: as the complex eigenvalue of the propagation problem, as the complex incident angle's sine, as the phase velocity and attenuation rate, or as a pair of complex characteristic altitudes. This study compares a priori theoretical propagation parameters with the corresponding quantities recovered from calculated Schumann resonance spectra by means of Lorentzian spectral fits. To estimate the ultimate accuracy of the recovery procedure, the influence of source‐receiver separation is excluded by assuming a globally uniform distribution of lightning sources. The comparisons show a practically acceptable agreement, within several percent, agreement between recovered and a priori parameters for all models studied. When judged against real Schumann resonance observations, these results shed light on problems with certain models. More importantly, the results reaffirm the ability of procedures based on SR observations to resolve global features of the ionosphere's state and structure.
Evolution of inorganic chlorine partitioning in the Arctic polar vortex
Authors: Wilmouth D. M. , Stimpfle R. M. , Anderson J. G. , Elkins J. W. , Hurst D. F. , Salawitch R. J. , Lait L. R.
Published: August 2006

The first simultaneous, in situ atmospheric measurements of ClO, ClOOCl, ClONO2, and HCl, which together nearly compose total inorganic chlorine, Cly, were obtained using the NASA ER‐2 aircraft, deployed from Kiruna, Sweden, during the SOLVE/THESEO mission. These chlorine measurements, along with Cly inferred from in situ measurements of organic chlorine source gases, offer an unprecedented opportunity to observe chlorine activation and recovery in the polar winter stratosphere and evaluate the inorganic chlorine budget, i.e., a test of the quantitative agreement between the sum of ClOx (ClO + 2 × ClOOCl), ClONO2, and HCl with Cly. Inside the Arctic vortex, inorganic chlorine is rarely fully activated with ClOx/Cly ranging from approximately 0.25 to 0.90. An apparent discrepancy in the inorganic chlorine budget for much of the midwinter correlates well with back trajectory solar zenith angle minimum and is consistent with the presence of Cl2, which was not observable. Evaluation of the midwinter inorganic chlorine budget, excluding data where Cl2 is present, yields (ClOx + ClONO2 + HCl)/Cly = 0.94 ± 0.07. In contrast, a shortfall in the late winter inorganic chlorine budget is the result of an apparent low bias in the HCl measurements. A diurnal box model constructed to analyze chlorine recovery rates highlights the importance of not only the Cl + CH4 reaction in HCl formation, but also OH + ClO and potentially HO2 + ClO. We find that significant HCl production accompanied net ClONO2 production in the inorganic chlorine recovery phase of this Arctic winter.
Electric field in windblown sand flux with thermal diffusion
Authors: Yue Gaowei , Zheng Xiaojing
Published: August 2006

A theoretical model considering thermal diffusion (TD) from a sand bed is suggested in this paper to account for the effect of both TD and the electric field produced by charged sand grains during the evolution of windblown sand flux, where the coupled interaction among wind speeds in the vertical and the horizontal directions, sand movement (saltation, suspension, and creep), and the electric field are taken into consideration. The numerical results show that during the evolution of windblown sand flux the electric field varies along with time and height. Then the profiles of the electric field produced by charged sand grains in windblown sand flux are quantitatively analyzed in detail and are compared with those without considering TD at different moments and different heights. Also, the results indicate that different conditions would produce different electric fields in magnitude: electric fields considering TD are more intense than those without considering thermal diffusion (NTD) at the same time and height. In the meantime, when the windblown sand flux reaches steady state, the mass flux profile and the transport rate of sand grains will increase, while horizontal wind speed will decease because of the effect of TD and the electric field.
Reactive nitrogen transport and photochemistry in urban plumes over the North Atlantic Ocean
Authors: Neuman J. A. , Parrish D. D. , Trainer M. , Ryerson T. B. , Holloway J. S. , Nowak J. B. , Swanson A. , Flocke F. , Roberts J. M. , Brown S. S. , Stark H. , Sommariva R. , Stohl A. , Peltier R. , Weber R. , Wollny A. G. , Sueper D. T. , Hubler G. , Fehsenfeld F. C.
Published: August 2006

Photochemical and transport processes involving reactive nitrogen compounds were studied in plumes of urban pollutants using measurements obtained from the NOAA WP‐3 aircraft during the ICARTT study in July and August 2004. Observations close to Boston and New York City were used to characterize urban emissions, and plume transport and transformation processes were studied in aged plumes located up to 1000 km downwind from the east coast of North America. Pollution was observed primarily below 1.5 km altitude in well‐defined layers that were decoupled from the marine boundary layer. In aged plumes located over the North Atlantic Ocean, the nitric acid (HNO3) mixing ratios were large (up to 50 ppbv), and HNO3 accounted for the majority of reactive nitrogen. Plume CO and reactive nitrogen enhancement ratios were nearly equivalent in fresh and aged plumes. Efficient transport of HNO3 explained the observed trace gas ratios and abundances. Without substantial HNO3 loss, the ratio of HNO3 to NOx was between 13 and 42 in most highly aged plumes and sometimes exceeded calculated photochemical steady state values. Box model calculations that include nighttime reactions that convert NOx to HNO3 reproduce the observations. Photolysis and OH oxidation of over 10 ppbv of HNO3 that was in the troposphere for days resulted in reformation of hundreds of pptv of NOx, which is sufficient to maintain photochemical ozone production. Efficient transport of HNO3 over the North Atlantic Ocean for days carried both HNO3 and NOx far from their continental sources and increased their photochemical influence.
Polarization coherence tomography
Authors: Cloude Shane R.
Published: August 2006

In this paper we introduce a new radar‐imaging technique, called polarization coherence tomography (PCT), which employs variation of the interferometric coherence with polarization to reconstruct a vertical profile function in penetrable volume scattering. We first show how this profile function can be efficiently represented as a Fourier‐Legendre series, with tomographic reconstruction reducing to estimation of the unknown coefficients of this series from coherence data. We then show that we can linearize this inversion by using a priori knowledge of two parameters, namely, volume depth and topographic phase. We further propose a new algorithm based on polarimetric interferometry to estimate these two from the data itself. To assess stability, we investigate both the single‐ and dual‐baseline conditioning of the associated matrix inversion and then concentrate on the single‐baseline case to demonstrate that for sufficient multilooking (around 50), stable retrievals of profiles can be obtained in the presence of coherence noise. Finally, we apply the technique to simulated L band coherent radar data to demonstrate its potential for new applications in radar remote sensing.
Enhancing random heterogeneity representation by mixing the kriging method with the zonation structure
Authors: Tsai Frank T.‐C.
Published: August 2006

This research develops a zonation‐kriging (ZK) method and extends the geostatistical theory to investigate the spatially distributed random field and obtain an optimal nonsmooth conditional estimate. In the ZK method the zonal structure honors the parameter measurements such that each sample location represents a distinct zone, while the kriging method also honors the same data set and results in a smooth distribution. The ZK method integrates the conditional estimates of the zonal structure and the kriged field over a set of weighting coefficients on the sample data. The extended geostatistical theory using the ZK method is applied to the intrinsic field, stationary field, and nonstationary field. The study shows that the conditional variance using the ZK method is bounded between the kriging variance and variogram. When estimating hydraulic conductivity by inversion of a groundwater model, the optimal values of weighting coefficients are determined via predictive probability of the Bayesian decision theory. The numerical examples show that the ZK method has less dependence on the semivariogram model. The ZK method outperforms the kriging method in both smooth and nonsmooth fields. The ZK method shows high efficiency to better the conditional estimate of hydraulic conductivity distribution with low conditional uncertainty and good agreement to the groundwater head observations.
Effects of upstream hydropower operation on riverine particle transport and turbidity in downstream lakes
Authors: Finger David , Schmid Martin , Wüest Alfred
Published: August 2006

Retention in upstream storage dams results in modified riverine water and particle discharge patterns. Particularly, suspended solids input and intrusion dynamics in downstream lakes are affected by dam operations. In a case study, size‐dependent particle budgets for peri‐alpine Lake Brienz (Switzerland), downstream of major hydropower installations, were determined for a recent 8‐year period (1997–2004) and compared to hypothetical no‐dam scenarios based on numerical simulations. For this purpose, current tributary particle loads, as well as lake‐internal sedimentation and turbidity dynamics, were assessed with in situ measurements. The analysis shows that hydropower damming drastically diminishes particle fluxes and minimizes (short‐term) peak discharges. Reductions of high‐flow events substantially cut the number of deep intrusions increasing particle supply to the lake surface layer. Furthermore, these hydropower operations shift particle inputs from summer to winter. As a consequence, such peri‐alpine lakes become more turbid during winter and less turbid during summer, influencing the seasonal light regime and subsequently the dynamics of phytoplankton growth.
Enhancement of the emission of mineral dust aerosols by electric forces
Authors: Kok Jasper F. , Renno Nilton O.
Published: August 2006

Climate forcing by mineral dust aerosols is one of the most uncertain processes in our current understanding of climate change. The main natural sources of dust aerosols are blowing dust, dust devils, and dust storms. Electric fields larger than 100 kV/m have been measured in these phenomena. Theoretical calculations and laboratory experiments show that these electric fields produce electric forces that can reduce the critical wind speed necessary to initiate dust lifting and can even directly lift mineral particles from the surface. Thus, we conclude that electric forces enhance the natural lifting of mineral dust aerosols.
Evidence for long‐range transport of carbon monoxide in the Southern Hemisphere from SCIAMACHY observations
Authors: Gloudemans A. M. S. , Krol M. C. , Meirink J. F. , de Laat A. T. J. , van der Werf G. R. , Schrijver H. , van den Broek M. M. P. , Aben I.
Published: August 2006

The SCIAMACHY satellite instrument shows enhanced carbon monoxide (CO) columns in the Southern Hemisphere during the local Spring. Chemistry‐transport model simulations using the new GFEDv2 biomass‐burning emission database show a similar temporal and spatial CO distribution, indicating that the observed enhancements are mainly due to biomass burning (BB). Large differences between the year 2003 and 2004 are observed in both the measurements and the model for South America and Australia. This study analyzes the origin of these observed enhancements in the Southern Hemisphere. The fact that SCIAMACHY is sensitive to surface CO allows for the observation of enhanced CO columns in both emission areas and in areas that are affected by long‐range transport of CO. Model results show a large contribution of South American BB CO over Australian BB regions during the 2004 BB season of up to ∼30–35% and up to 55% further south, with smaller contributions for 2003. BB CO transported from southern Africa contributes up to ∼40% in 2003 and ∼30% in 2004. The results indicate that differences between SCIAMACHY CO and the model simulations over Australian BB areas are probably not only caused by uncertainties in local emissions but also in overseas emissions.
Sinkhole structure imaging in covered Karst terrain
Authors: Kruse S. , Grasmueck M. , Weiss M. , Viggiano D.
Published: August 2006

Ground penetrating radar (GPR) and resistivity techniques have been widely used to map the locations of sinkholes in covered karst terrain. To determine whether a sinkhole is a likely preferential conduit for groundwater flow, however, requires higher‐resolution imaging than that used in conventional sinkhole mapping surveys. Field observations combined with simulated surveys for a 15‐m diameter 3‐m deep sinkhole in west‐central Florida are used to assess the resolution of GPR and resistivity surveys targeting the semiconfining unit that floors the sinkhole depression. 2D resistivity surveys clearly show the central depression as well as resistivity contrasts between the cover sediments within and outside of the sinkhole, but are inadequate for resolving breaches in the semiconfining unit or underlying conduits. A 3D GPR survey resolves vertical structure on the order of tens of centimeters within the semiconfining unit, as well as indicators of conduits that extend several meters beneath the central depression. 3D GPR thus holds promise for imaging hydrologically significant features of sinkholes.
Whistler instability threshold condition of energetic electrons by kappa distribution in space plasmas
Authors: Xiao Fuliang , Zhou Qinghua , Zheng Huinan , Wang Shui
Published: August 2006

Observational studies clearly reveal that natural space plasmas generally possess a pronounced non‐Maxwellian high‐energy tail distribution that can be well modeled by a generalized Lorentzian (kappa) distribution. In this study we consider the whistler mode wave instability driven by the anisotropy condition (T⊥/T∥ > 1) of energetic electrons modeled with a typical kappa distribution in the presence of a cold plasma population. We use a linear theory to study the instability threshold condition for two typical plasma regions of interest: the higher‐density (or a weakly magnetized) region and the lower‐density (or a strongly magnetized) region. We find that (1) as in the case for a regular bi‐Maxwellian, the energetic electron anisotropy T⊥/T∥ is subject to the threshold condition of this whistler instability, and the instability threshold condition obeys a general form T⊥/T∥ − 1 = S/β∥α, with a narrow range of the fitting parameter 0.25 ≤ α ≤ 0.52 over 0.01 ≤ β∥ ≤ 2.0; (2) the instability threshold condition in the higher‐density (or a weakly magnetized) region is generally lower than that in the lower‐density (or a strongly magnetized) region, specifically, with the fitting parameter range 0.3 ≤ S ≤ 5.0 in the higher‐density (or a weakly magnetized) region, while 0.32 ≤ S ≤ 6.94 in the lower‐density (or a strongly magnetized) region; and (3) the instability threshold condition for the kappa distribution generally decreases as the spectral index κ increases and tends to the lowest limiting values of the bi‐Maxwellian as κ → ∞. The results above may present a further insight into the nature of this instability threshold condition for the whistler mode waves in the outer radiation belts of the Earth, the inner Jovian magnetosphere, or other space plasmas where an anisotropic hot electron component and a cold plasma component are both present.
Secondary organic aerosols formed from oxidation of biogenic volatile organic compounds in the Sierra Nevada Mountains of California
Authors: Cahill Thomas M. , Seaman Vincent Y. , Charles M. Judith , Holzinger Rupert , Goldstein Allen H.
Published: August 2006

Biogenic volatile organic compound (BVOC) emissions, such as isoprene and terpenes, can be oxidized to form less volatile carbonyls, acids, and multifunctional oxygenated products that may condense to form secondary organic aerosols (SOA). This research was designed to assess the contribution of oxidized BVOC emissions to SOA in coniferous forests by collecting high‐volume particulate samples for 6 days and 5 nights in the summer of 2003. The samples were analyzed for acids, carbonyls, polyols and alkanes to quantify oxidized BVOCs. Terpene and isoprene oxidation products were among the most abundant chemical species detected with the exception of hexadecanoic acid, octadecanoic acid and two butyl esters of unknown origin. The terpene oxidation products of pinonic acid, pinic acid, nopinone and pinonaldehyde showed clear diurnal cycles with concentrations two‐ to eight‐fold higher at night. These cycles resulted from the diurnal cycles in gaseous terpene concentrations and lower temperatures that enhanced condensation of semivolatile chemicals onto aerosols. The terpene‐derived compounds averaged 157 ± 118 ng/m3 of particulate organic matter while the isoprene oxidation compounds, namely the 2‐methyltetrols and 2‐methylglyceric acid, accounted for 53 ± 19 ng/m3. Together, the terpene and isoprene oxidation products represented 36.9% of the identified organic mass of 490 ± 95 ng/m3. PM10 organic matter loadings in the region were approximately 2.1 ± 1.2 μg/m3, so about 23% of the organic matter was identified and at least 8.6% was oxidized BVOCs. The BVOC oxidation products we measured were significant, but not dominant, contributors to the regional SOA only 75 km downwind of the Sacramento urban area.
Observation of polarization dependent Raman scattering in a large scale plasma illuminated with multiple laser beams
Authors: Kirkwood R. K. , Moody J. D. , Niemann C. , Williams E. A. , Langdon A. B. , Landen O. L. , Divol L. , Suter L. J. , Depierreux S. , Seka W.
Published: August 2006

Experiments in plasmas produced with 2mm diameter gas filled targets preheated with 10kJ of laser energy have shown that the stimulated Raman scattering (SRS) of a high intensity, 351nm, beam is affected by the presence of a second, counterpropagating, high intensity beam and that has its polarization aligned to the first when the plasma conditions are relevant to ignition by indirect drive. Separate experiments with the crossing beam's polarization rotated to be normal to the first beam's polarization show little change in the SRS backscatter when the second beam is added, consistent with the reduction in the SRS being caused by low frequency waves driven by the ponderomotive force produced by the beating of the two beams.
High translational energy release in H2 (D2) associative desorption from H (D) chemisorbed on C(0001)
Authors: Baouche S. , Gamborg G. , Petrunin V. V. , Luntz A. C. , Baurichter A. , Hornekær L.
Published: August 2006

Highly energetic translational energy distributions are reported for hydrogen and deuterium molecules desorbing associatively from the atomic chemisorption states on highly oriented pyrolytic graphite (HOPG). Laser assisted associative desorption is used to measure the time of flight of molecules desorbing from a hydrogen (deuterium) saturated HOPG surface produced by atomic exposure from a thermal atom source at around 2100K. The translational energy distributions normal to the surface are very broad, from ∼0.5to∼3eV, with a peak at ∼1.3eV. The highest translational energy measured is close to the theoretically predicted barrier height. The angular distribution of the desorbing molecules is sharply peaked along the surface normal and is consistent with thermal broadening contributing to energy release parallel to the surface. All results are in qualitative agreement with recent density functional theory calculations suggesting a lowest energy para-type dimer recombination path.
Effect of confinement by porous carbons on the unimolecular decomposition of formaldehyde
Authors: Santiso Erik E. , George Aaron M. , Gubbins Keith E. , Buongiorno Nardelli Marco
Published: August 2006

As part of an effort to understand the effect of confinement by porous carbons on chemical reactions, we have carried out density functional theory calculations on the unimolecular decomposition of formaldehyde within graphitic carbons. Our results show that the interactions with the carbon walls result in a lowering of the reaction barrier. For larger pores, there is also a shift of the equilibrium towards the formation of carbon monoxide and hydrogen at low temperatures. This trend is reversed for small pore sizes.
Perturbation evolution started by Richtmyer-Meshkov instability in planar laser targets
Authors: Aglitskiy Y. , Metzler N. , Karasik M. , Serlin V. , Velikovich A. L. , Obenschain S. P. , Mostovych A. N. , Schmitt A. J. , Weaver J. , Gardner J. H. , Walsh T.
Published: August 2006

The first observations of the interaction of the Richtmyer-Meshkov (RM) instability with reflected shock and rarefaction waves in laser-driven targets are reported. The RM growth is started by a shock wave incident upon a rippled interface between low-density foam and solid plastic. The subsequent interaction of secondary rarefaction and/or shock waves arriving from the ablation front and the rear surface of the target with the RM-unstable interface stops the perturbation growth and reverses its direction. The ensuing exponential Rayleigh-Taylor growth thus can sometimes proceed with an inverted phase.
Fifth-order two-dimensional Raman spectroscopy of liquid water, crystalline ice Ih and amorphous ices: Sensitivity to anharmonic dynamics and local hydrogen bond network structure
Authors: Saito Shinji , Ohmine Iwao
Published: August 2006

The theoretical study of off-resonant fifth-order two-dimensional (2D)-Raman spectroscopy is made to analyze the intermolecular dynamics of liquid and solid water. The 2D-Raman spectroscopy is susceptible to the nonlinear anharmonic dynamics and local hydrogen bond structure in water. It is found that the distinct 2D-Raman response appears as the negative signal near the t2 axis. The origin of this negative signal for t2<15fs is from the nonlinear polarizability in the librational motions, whereas that for 30fs<t2<150fs is attributed to the anharmonic translational motions. It is found that the mechanical anharmonicity and nonlinear polarizability couplings among modes clearly can be observed as the sum- and difference-frequency peaks in the 2D-Raman spectrum (i.e., Fourier transforms of the response). The 2D-Raman spectroscopies of ice Ih and amorphous ices, i.e., low density, high density, and very high density amorphous ices, are also investigated. It is found that the 2D-Raman spectroscopy is very sensitive to the anisotropy of the structure of ice Ih. The strong hydrogen bond stretching band is seen in the 2D-Raman spectroscopy of the polarization directions parallel to the c axis, whereas the contributions of the librational motion can be also seen in the spectrum with the polarization directions parallel to the a axis. The 2D-Raman spectroscopy is also found to be also very sensitive to the differences in local hydrogen bond network structures in various amorphous phases.
Suppression of short-channel effects in organic thin-film transistors
Authors: Wang J. Z. , Zheng Z. H. , Sirringhaus H.
Published: August 2006

To improve the speed of organic thin-film transistor (TFT) circuits device architectures with submicrometer channel length are of interest. However, in conventional, submicrometer TFT structures the performance is degraded as a result of short-channel effects. Here we present an architecture for short-channel organic TFTs which is based on incorporating an insulating mesa structure in between source and drain electrodes. For submicrometer organic TFTs the mesa structure results in a significant enhancement of the on-off ratio and saturation characteristics. Device modeling shows that the mesa improves the ability of the gate electrode to modulate the carrier concentration in a submicrometer channel.
On the simultaneous presence of unilateral and kinetic constraints in time-dependent impulsive mechanics
Authors: Pasquero Stefano
Published: August 2006

The simultaneous presence of unilateral and kinetic constraints acting on a mechanical system with a finite number of degrees of freedom is framed in the geometric context of left and right jet-bundles of the classical space–time bundle of the system. The survey gives three main cases and several subcases, some of which are mathematically correct but physically meaningless. The existence of at least one frame of reference for which the whole set of constraints can be at rest is the criterion selecting the physically relevant systems. For these systems, the conservation of kinetic energy, possibly together with a standard Gauss’s requirement on the impulsive reaction, is shown to give a well posed criterion of ideality of the constraints. The application of the criterion to several examples is presented and the corresponding results are critically analyzed.
On solutions of the two-component Camassa-Holm system
Authors: Wu Chao-Zhong
Published: August 2006

Following the approach of [Chen et al.Lett. Math. Phys. 75, 1–15 (2006)], we continue the study of the two-component Camassa-Holm system by using its relation with the first negative flow of the AKNS hierarchy. We obtain a more general class of particular solutions including the multisoliton ones.
Electron doped (Sm1−x,Cax)MnO3 perovskite manganite as potential infrared thermochromic switch
Authors: Laffez Patrick , Zaghrioui M. , Reversat Luc , Ruello P.
Published: August 2006

We have synthesized (Sm1−x,Cax)MnO3 and related compositions to show their potential use as thermochromic switch in the infrared range. Depending on temperature or composition, the single phase is stabilized using the polyacrilamide gel process. Infrared transmittance was measured on selected samples in the 1,42–25μm range. Relative contrast up to 0.773 is measured in the 8–14μm range. Full opacity in the 8–14μm range occurs at temperatures between 273 and 300K, depending on the composition. The potential application of perovskites manganites as thermochromic infrared switch or coating is discussed.
Negative oxygen vacancies in HfO2 as charge traps in high-k stacks
Authors: Gavartin J. L. , Muñoz Ramo D. , Shluger A. L. , Bersuker G. , Lee B. H.
Published: August 2006

The optical excitation and thermal ionization energies of oxygen vacancies in m-HfO2 are calculated using a non-local density functional theory with atomic basis sets and periodic supercell. The thermal ionization energies of negatively charged V− and V2− centers are consistent with values obtained by the electrical measurements. The results suggest that negative oxygen vacancies are essentially polaronic in origin. They are likely candidates for intrinsic shallow electron traps in the hafnium based gate stack devices.
Molecular dynamics simulations of melting of perfect crystalline hexahydro-1,3,5-trinitro-1,3,5-s-triazine
Authors: Zheng Lianqing , Thompson Donald L.
Published: August 2006

The melting mechanism of superheated perfect crystalline hexahydro-1,3,5-trinitro-1,3,5-s-triazine (α-RDX) has been investigated using molecular dynamics simulations with the fully flexible force field developed by Smith and Bharadwaj [J. Phys. Chem. B 103, 3570 (1999)]. Sequential 50ps equilibration simulations of the constant stress–constant temperature ensemble were performed at 10K intervals over the range of 300–650K, corresponding to a heating rate of 2.0×1011K∕s. A solid-solid phase transition is observed between 480 and 490K, followed by melting, which occurs between 500 and 510K. The solid-solid phase transition, both displacive and rotational, is characterized by an abrupt decrease in the lengths of the unit cell edges a and b and an increase of the length of edge c. The molecular conformation in the new phase is AAE, although the axial nitro groups have different changes: one shift is more axial and the other is more equatorial. Phases other than α-RDX have been observed experimentally, however, there are insufficient data for comparisons to ascertain that the new phase observed here corresponds to a real phase. At the high heating rate (2.0×1011K∕s) used in the simulations, the melted RDX reaches full orientational disorder at about 540K and translational freedom at around 580K. If the simulation at the melting temperature (510K) is run sufficiently long complete rotational freedom is achieved in a few hundreds of picoseconds, while complete translational freedom requires much longer. These results show that given a sufficiently high heating rate, the system can exist for significant periods of time in a near-liquid state in which the molecules are not as free to rotate and diffuse as in the true liquid state. The bond lengths and bond angles undergo little change upon melting, while there are significant changes in the dihedral angles. The molecular conformation of RDX changes from AAE to EEE upon melting. The ramification of this for formulating force fields that accurately describe melting is that it is important that the torsional motions are accurately described.
Wide band gap photonic structures in dichromate gelatin emulsions
Authors: Ma Rui , Xu Jun , Tam Wing Yim
Published: August 2006

The authors report the fabrication of wide band gap photonic crystals with planar structures in dichromate gelatin emulsions using a two-beam holographic method. By exploiting the differential swelling of the gelatin, planar structures with gradient spacing are fabricated. The crystals exhibit high efficiencies and wide band gaps in the visible range. The authors model the planar gelatin system by an effective medium approach and use transfer matrix to calculate the reflectance and transmittance. Good agreement is obtained between theory and experiment.
Magnetic catalyst residues and their influence on the field electron emission characteristics of low temperature grown carbon nanotubes
Authors: Lee Yun-Hi , Kim D. H. , Kim Dong Hyun , Ju Byeong-Kwon
Published: August 2006

We report the electron paramagnetic resonance characteristics of catalytic residues for in situ grown carbon nanotube field electron emitter and present direct evidence that field electron emission in carbon nanotube sheets grown on various catalytic nanodots/SiO2-coated Si substrate with low-pressure chemical vapor deposition is influenced by the magnetism of catalytic metals and thus the electrical properties of the nanotubes. The nanotubes with weak trace of ferromagnetism, which originated from the catalysts, show lower turn-on emission field and higher electron emission current than those with distinct ferromagnetic properties. A strong relationship between the ferromagnetism of nanocrystalline catalysts and field electron emission characteristics of nanotubes can be utilized for the development of an efficient carbon nanotube based-field electron emitter.
Simple largely tunable optical microcavity
Authors: Kiraz A. , Kurt A. , Dündar M. A. , Demirel A. L.
Published: August 2006

The authors demonstrate more than 9nm tunability of the whispering gallery modes (WGMs) of rhodamine B doped water microdroplets resting on a superhydrophobic surface. Tunability was achieved by controlling the size of the microdroplets in a current controlled mini humidity chamber. WGMs were observed with quality factors of more than 8000 when kept stable. The sensitivity of the resonances to the size and shape of the microdroplet reveals opportunities for the use of this technique as a probe to characterize superhydrophobic surfaces and investigate liquid-solid surfaces.
Oblique electromagnetic instabilities for a hot relativistic beam interacting with a hot and magnetized plasma
Authors: Bret A. , Dieckmann M. E. , Deutsch C.
Published: August 2006

The temperature-dependent fluid model from Phys. Plasmas 13, 042106 (2006) is expanded in order to explore the oblique electromagnetic instabilities, which are driven by a hot relativistic electron beam that is interpenetrating a hot and magnetized plasma. The beam velocity vector is parallel to the magnetic-field direction. The results are restricted to nonrelativistic temperatures. The growth rates of all instabilities but the two-stream instability can be reduced by a strong magnetic field so that the distribution of unstable waves becomes almost one dimensional. For high beam densities, highly unstable oblique modes dominate the spectrum of unstable waves as long as ωc∕ωp≲2γb3∕2, where ωc is the electron gyrofrequency, ωp is the electron plasma frequency, and γb is the relativistic factor of the beam. A uniform stabilization over the entire k space cannot be achieved.