bluuebunny/crossref_metadata_2025 huggingface dataset:
Roaming zones of precipitation on ancient Mars as recorded in valley networks
Authors: Hoke Monica R. T. , Hynek Brian M.
Published: August 2009

The 10 largest valley networks in the Terra Sabaea, Arabia Terra, and Meridiani Planum regions of Mars were mapped, crater age dated, and analyzed by geomorphology, stream order, and drainage density to understand changes in fluvial erosion during early Martian history. All of these networks demonstrate characteristics consistent with formation by precipitation. Many appear to be in different stages of preservation, with both highly eroded and pristine valleys sometimes appearing in the same network. In some cases, the valley network morphologies and crater age dating indicate multiple periods of formation. The results from this research place precipitation‐driven formation of the Martian valley networks in Terra Sabaea, Arabia Terra, and Meridiani Planum in the late Noachian and early Hesperian epochs (∼3.6–3.8 billion years ago). Our age estimates do not extend into earlier or later Martian history, and the spread in these ages indicates they did not all form or cease formation at the same time. The difference in age between the oldest and youngest valley networks in Terra Sabaea, Arabia Terra, and Meridiani Planum analyzed in this work is ∼210 ± 50 Ma. Within this range are valley networks that have distinctly separate ages and those that appear to be coeval. This research suggests the late Noachian and early Hesperian were characterized by roaming zones of precipitation that occurred during either continuously warmer and thicker atmospheric conditions or intermittently clement conditions, with precipitation occasionally returning to previously rainy regions and overall continuing near Meridiani Planum longer than in Terra Sabaea.
Altimetry of the Venus cloud tops from the Venus Express observations
Authors: Ignatiev N. I. , Titov D. V. , Piccioni G. , Drossart P. , Markiewicz W. J. , Cottini V. , Roatsch Th. , Almeida M. , Manoel N.
Published: August 2009

Simultaneous observations of Venus by Visible and Infrared Thermal Imaging Spectrometer and Venus Monitoring Camera onboard the Venus Express spacecraft are used to map the cloud top altitude and to relate it to the ultraviolet (UV) markings. The cloud top altitude is retrieved from the depth of CO2 absorption band at 1.6 μm. In low and middle latitudes the cloud top is located at 74 ± 1 km. It decreases poleward of ±50° and reaches 63–69 km in the polar regions. This depression coincides with the eye of the planetary vortex. At the same latitude and hour angle, cloud top can experience fast variations of about 1 km in tens of hours, while larger long‐term variations of several kilometers have been observed only at high latitudes. UV markings correlate with the cloud altimetry, however, the difference between adjacent UV dark and bright regions does not exceed several hundred meters. Surprisingly, CO2 absorption bands are often weaker in the dark UV features, indicating that these clouds may be a few hundred meters higher or have a larger scale height than neighboring clouds. Ultraviolet dark spiral arms, which are often seen at about −70°, correspond to higher altitudes or to the regions with strong latitudinal gradient of the cloud top altitude. Cloud altimetry in the polar region reveals the structure that correlates with the thermal emission maps but is invisible in UV images. This implies that the UV optically thick polar hood is transparent in the near IR.
From climate model ensembles to climate change impacts and adaptation: A case study of water resource management in the southwest of England
Authors: Lopez Ana , Fung Fai , New Mark , Watts Glenn , Weston Alan , Wilby Robert L.
Published: August 2009

The majority of climate change impacts and adaptation studies so far have been based on at most a few deterministic realizations of future climate, usually representing different emissions scenarios. Large ensembles of climate models are increasingly available either as ensembles of opportunity or perturbed physics ensembles, providing a wealth of additional data that is potentially useful for improving adaptation strategies to climate change. Because of the novelty of this ensemble information, there is little previous experience of practical applications or of the added value of this information for impacts and adaptation decision making. This paper evaluates the value of perturbed physics ensembles of climate models for understanding and planning public water supply under climate change. We deliberately select water resource models that are already used by water supply companies and regulators on the assumption that uptake of information from large ensembles of climate models will be more likely if it does not involve significant investment in new modeling tools and methods. We illustrate the methods with a case study on the Wimbleball water resource zone in the southwest of England. This zone is sufficiently simple to demonstrate the utility of the approach but with enough complexity to allow a variety of different decisions to be made. Our research shows that the additional information contained in the climate model ensemble provides a better understanding of the possible ranges of future conditions, compared to the use of single‐model scenarios. Furthermore, with careful presentation, decision makers will find the results from large ensembles of models more accessible and be able to more easily compare the merits of different management options and the timing of different adaptation. The overhead in additional time and expertise for carrying out the impacts analysis will be justified by the increased quality of the decision‐making process. We remark that even though we have focused our study on a water resource system in the United Kingdom, our conclusions about the added value of climate model ensembles in guiding adaptation decisions can be generalized to other sectors and geographical regions.
Nonnormality and transient behavior of the de Saint‐Venant‐Exner equations
Authors: Camporeale C. , Ridolfi L.
Published: August 2009

Shallow‐water flows on fixed and movable beds play an important role in both hydrology and river morphodynamics, and several efforts have been devoted to investigating their stability. The analysis is usually conducted focusing the asymptotic fate of small disturbances, using normal modes. In this work we instead have tackled another aspect of the stability problem studying the disturbance behavior at finite times. Recent studies have in fact shown that nonnormality of differential operators can induce a nonmonotonic decay of disturbances in asymptotically stable cases and the occurrence of transient growths. We have investigated these aspects for the de Saint‐Venant‐Exner equations and discussed the transient behavior of the energy of disturbances for both fixed and movable bed conditions. We show that the former case provides weak levels of nonnormality; while the latter can give rise to important transient growths. These growths result from uniquely linear mechanisms, are potentially able to trigger nonlinear instabilities, and are physically due to a transfer of potential energy between the water stream and the bed. The results encourage revisiting the study of morphodynamics from a nonmodal perspective.
Apollo 11 Mission Commemorated
Authors: Showstack Randy
Published: August 2009

On 24 July 1969, 4 days after Apollo 11 Mission Commander Neil Armstrong and Lunar Module Eagle Pilot Eugene “Buzz” Aldrin had become the first people to walk on the Moon, they and Apollo 11 Command Module Pilot Michael Collins peered through a window of the Mobile Quarantine Facility on board the U.S.S. Hornet following splashdown of the command module in the central Pacific as U.S. President Richard Nixon told them, “This is the greatest week in the history of the world since the creation.”

Forty years later, the Apollo 11 crew and other Apollo‐era astronauts gathered at several events in Washington, D.C., to commemorate and reflect on the Apollo program, that mission, and the future of manned spaceflight. “I don't know what the greatest week in history is,” Aldrin told Eos. “But it was certainly a pioneering opening the door. With the door open when we touched down on the Moon, that was what enabled humans to put many more footprints on the surface of the Moon.”
Fiftieth Anniversary of the First Incoherent Scatter Radar Experiment
Authors: Robinson Robert M. , van Eyken Anthony , Farley Donald
Published: August 2009

In the 11 November 2008 issue of Eos (89(46), 458), Henry Rishbeth asked whether the years 2008–2010 feature any important anniversaries in solar‐terrestrial physics other than those he mentioned. One such milestone is the fiftieth anniversary of the first incoherent scatter radar (ISR) experiment.

At a Cornell University (Ithaca, N.Y.) departmental seminar in the spring of 1958, William Gordon showed that a powerful radar system could detect the uncorrelated and extremely weak scattered signals from individual ionospheric electrons. This process is called incoherent scatter, and studying the properties of the resulting radar echoes can reveal information about the density, temperature, and velocity of ionospheric particles. Gordon discussed this idea with Ken Bowles, a recent Ph.D. graduate of Cornell, and in a few weeks Bowles built a large but inexpensive antenna array that he connected to an existing transmitter near Havana, Ill. Using this crude radar (the data processing consisted of taking a time exposure photograph of the signal amplitude displayed on an oscilloscope), Bowles successfully measured an incoherently scattered signal on 21 October 1958. By a happy coincidence, 21 October was also the day that Gordon gave his first formal talk on the ISR concept at an International Union of Radio Science (URSI) conference at Pennsylvania State University. After calling Bowles for an update on his experiment, Gordon presented his research and added the dramatic and newsworthy note to the end of his talk on the success of the first ISR experiment!
Understanding Variability and Climate Impacts of Atlantic Meridional Overturning Circulation: First U.S. Atlantic Meridional Overturning Circulation (AMOC) Annual Workshopsemi; Annapolis, Maryland, 4–6 May 2009
Authors: Legler David , Lozier M. Susan
Published: August 2009

The new U.S. Atlantic Meridional Overturning Circulation (AMOC) program, with its international partners, aims to further develop abilities to observe, understand, and simulate the AMOC as well as characterize its potential impacts on climate (see http://www.atlanticmoc.org for program details). Its first workshop included contributions from more than 100 U.S. and international participants on a range of topics, including the current state of the AMOC, its coherence and connectivity, the influence of AMOC on climate and related impacts, and AMOC observing system requirements.

Presenters at the meeting described a number of significant, but disparate, AMOC observational efforts currently under way. Of these, only the U.K./U.S. RAPID/MOCHA (Rapid Climate Change/Meridional Overturning Circulation and Heatflux Array) mooring array at 26°N, which spans the basin at full depth, has provided direct measures of the AMOC. Results from this array have revealed significant intra‐annual variability in the heat and mass fluxes at this latitude, causing a reexamination of previous estimates of AMOC changes.
Helium systematics of cold seep fluids at Monterey Bay, California, USA: Temporal variations and mantle contributions
Authors: Füri E. , Hilton D. R. , Brown K. M. , Tryon M. D.
Published: August 2009

We report helium isotope ratios (3He/4He) as well as helium and neon abundance results for submarine cold seep fluids from Extrovert Cliff in Monterey Bay, California. Samples were collected in copper tubing attached to submarine flux meters operating in continuous pumping mode. Following instrumentation recovery, the tubing was sectioned to produce for the first time a high‐resolution time series of dissolved He and Ne variations over a time span of several days. Noble gas concentrations are variable and appear affected by interaction with a hydrocarbon phase within the aquifer. However, it is still possible to resolve the He signal into components associated with air equilibration, excess air entrainment, and terrigenic fluxes (both crustal and mantle‐derived). The mantle He contribution reaches ∼25–30% in some samples (up to 2.3 RA, where RA = air 3He/4He). Our quasi‐continuous He‐Ne record shows remarkable fluctuations over time scales of only a few hours and reflects the combined effects of gas stripping by hydrocarbons and an episodic input of mantle‐derived fluids.
An analysis of clear sky and contextual biases using an operational over ocean MODIS aerosol product
Authors: Zhang Jianglong , Reid Jeffrey S.
Published: August 2009

Clear sky and other cloud‐related contextual biases are critical yet unsolved mysteries for aerosol related climatological studies using satellite observations. For the first time, we simulated contextual biases over ocean using 2‐years of Navy Aerosol Analysis and Prediction System (NAAPS) products that include the Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD) assimilation. We compared model‐derived AOD in regions with and without observations, and found that sampling results in negligible seasonal globally averaged AOD bias (<5%). Biases are more pronounced in regions with frequent overcast skies and high aerosol loadings, such as Southeast Asia, and mid‐latitude South America. This suggests that contextual biases may develop from transport covariance and other observing biases. Lastly, we found that over remote oceans, under cloud decks, a slight increase aerosol optical depth values could exist, comparing with cloud free regions. But this is still small relative to cloud artifacts in the retrieval.
Parametric uncertainty effects on aerosol radiative forcing
Authors: Haerter J. O. , Roeckner E. , Tomassini L. , von Storch J.‐S.
Published: August 2009

Among the known radiative forcings, the fourth IPCC assessment report estimates the aerosol radiative forcing to harbor the widest range of uncertainty extending from −1.8 to −0.3 W/m2. The IPCC estimates focus mainly on structural uncertainties, including uncertainties in aerosol sources. Here, we study the uncertainty of the sulfate aerosol radiative forcing due to parametric uncertainty in a state‐of‐the‐art general circulation model (GCM). Numerical experiments were carried out by perturbing seven cloud parameters in the model. We find that the uncertainty due to a single one of these parameters can be as large as 0.5 W/m2, and the uncertainty due to combinations of these parameters can reach more than 1 W/m2. These numbers should be compared with the sulfate aerosol forcing of −1.9 W/m2 for the year 2000, obtained using the default values of the parameters. The uncertainty results from a high sensitivity of cloud optical properties to aerosol concentrations, which can be amplified by changing cloud parameter setting.
Does dust change the clear sky top of atmosphere shortwave flux over high surface reflectance regions?
Authors: Patadia Falguni , Yang Eun‐Su , Christopher Sundar A.
Published: August 2009

Using four stream radiative transfer calculations, satellite‐derived aerosol optical thickness at 558 nm and top of atmosphere (TOA) broadband radiative fluxes we examine the effect of mineral dust aerosols on the clear sky TOA shortwave (0.3–5 μm) fluxes over the Saharan desert [30E‐10W, 15N‐30N]. Over very bright surfaces (surface albedo > 35%), the TOA shortwave flux, from both satellite measurements and model calculations, is nearly insensitive to the increase in dust optical thickness. Below this surface albedo value, known as the critical albedo, mineral dust aerosols show scattering effects and above this they show absorbing effects. Therefore, over desert regions with a large range of surface albedo values, scattering and absorbing effects compensate each other thereby making the TOA shortwave aerosol radiative effect rather small.
A nonstationary index flood model for precipitation extremes in transient regional climate model simulations
Authors: Hanel Martin , Buishand T. Adri , Ferro Christopher A. T.
Published: August 2009

The generalized extreme value (GEV) distribution has often been used to describe the distribution of daily maximum precipitation in observed and climate model data. The model developed in this paper allows the GEV location parameter to vary over the region, while the dispersion coefficient (the ratio of the GEV scale and location parameters) and the GEV shape parameter are assumed to be constant over the region. This corresponds with the index flood assumption in hydrology. It is further assumed that all three GEV parameters vary with time, such that the relative change in a quantile of the distribution is constant over the region. This nonstationary model is fitted to the 1‐day summer and 5‐day winter precipitation maxima in the Rhine basin in a simulation of the Regional Atmospheric Climate Model (RACMO) for the period 1950–2099, and the results are compared with gridded observations. Except for an underestimation of the dispersion coefficient of the 5‐day winter maxima by about 35%, the GEV parameters obtained from the observations are reasonably well reproduced by RACMO. A positive trend in the dispersion coefficient is found in the summer season, which implies that the relative increase of a quantile increases with increasing return period. In the winter season there is a positive trend in the location parameter and a negative trend in the shape parameter. For large quantiles the latter counterbalances the effect of the increase of the location parameter. It is shown that the standard errors of the parameter estimates are significantly reduced in the regional approach compared to those of the estimated parameters from individual grid box values, especially for the summer maxima.
Phenoscape: Ontologies for Large Multi-species Phenotype Datasets
Authors: Midford Peter , Mabee Paula , Vision Todd , Lapp Hilmar , Balhoff Jim , Dahdul Wasila , Kothari Cartik , Lundberg John , Westerfield Monte
Published: August 2009

The Phenoscape project is developing ontologies and tools to integrate morphological and genomic data to address comparative questions in evolutionary biology. We are currently curating 81 publications describing ~5000 phenotypic characters in 4,000 species of Ostariophysian fishes, and will be making our database of ontology-based annotations concurrently with this meeting via a web-based interface at "http://kb.phenoscape.org":http://kb.phenoscape.org.
The plural of anecdote is not data: Rigorously testing a boreal forest chronosequence
Authors: Bond-Lamberty Ben , Wang Chuankuan , Gower Stith
Published: August 2009

"Forests appear stable because the ecologists who study them die." The chronosequence, with its space-for-time substitution, is a widely-employed workaround for a difficult problem: many interesting ecosystem processes occur at much longer time scales than researchers can afford to spend studying them. But their use is problematic, particularly for vegetation succession but also for biogeochemical cycling: having sites of different ages is only a necessary, and not a sufficient, condition. How do we test the validity and representativeness of a chronosequence, particularly given ecosystem variability in time and space? Here we use data from an intensively-studied group of stands in northern Manitoba, Canada, to assess the spatial and temporal variability of carbon fluxes in this boreal forest, and examine the suitability of a chronosequence study design for making larger-scale (in space and time) generalizations. This ecosystem is well suited for examining this question, being floristically simple, frequently disturbed by wildfire, and thus generally composed of even-aged forests of known origin. A number of techniques can be brought to bear: re-visiting chronosequence sites after a significant period converts single-point measurements into data vectors; measurements that integrate fluxes over longer time periods (e.g., tree ring cores) provide a similar capability, extending our observation window; replication of the chronosequence stands extends the spatial domain; process modeling may indicate site selection errors. We can also examine data at local, regional and global scales to ask, for any particular pool or flux, if replication in time or space is more useful. For example, global soil respiration studies indicate that spatial and interannual variability are of roughly equal magnitude; in contrast, boreal tree ring data suggest that carbon sequestration is more variable year-to-year than it is site-to-site, after controlling for forest age and soil drainage. Different sampling strategies may thus be appropriate for each flux; historical records such as databases of wildfire occurrence also help constrain this problem. We conclude that while unreplicated chronosequences provide anecdotes, not data, extending measurements in space and time lets us quantifiably assess their performance.
Assemblage-structuring force of species interactions varies spatially and temporally: Co-occurrence analysis of canopy arthropod distributions
Authors: Lau Matthew , Hagenauer Laura , Whitham Thomas
Published: August 2009

*Background/Question/Methods*

Understanding how interactions amongst species contribute to their distribution is central to community ecology. However, it is not understood how these processes may change under different environmental conditions. In this study, we present evidence that suggests interactions amongst canopy arthropods contribute to assemblage structure, depending on both the sampling time and location. We sampled canopy arthropod species abundances on individual trees in three adjacent, monospecific stands of Populus fremontii (Fremont cottonwood), which differ in planting year (2000, 2002, 2005). We then conducted null-model based co-occurrence analysis using the freely available software EcoSim (Kesey-Bear and Acquired Intelligence, Inc.) to test for patterns suggestive of interactions influencing assemblage structure. Environmental heterogeneity amongst trees is low within stands; therefore environmental gradients are most likely not contributing to co-occurrence patterns. Also, all stands were planted recently and closely enough such that evolutionary processes (e.g. allopatric speciation) have not occurred. For the analyses of each stand at each sampling date we used a fixed-row, equiprobable-column matrix permutation algorithm in order to simulate presence-absence matrices in which species co-occurrences are effectively random with respect to species interactions. We chose to use the C-score index of co-occurence because of its robustness to Type I Errors when used with this simulation algorithm. P-values and standardized effect sizes (SES) were based on 5000 simulated matrixes.

*Results/Conclusions*

We found significant variation in SES values across both sampling dates and stands; and three main patterns emerged. 1) The SES values in the youngest stand (2005) were all near zero and none were statistically significant. This could be the result of unresolved species interactions, meaning that species interactions have not had sufficient time to produce consistent distributional patterns. 2) The SES values were primarily negative, indicating a dominating force of facilitative interactions. 3) The 2000 and 2002 stands varied in the size and significance of their SES values with the oldest (2000) stand switching from positive to negative as the season progressed, suggesting a switch from competitive to facilitative interactions driving structure. These results suggest that species interactions are indeed important in structuring canopy arthropod communities, but that the efficacy of these forces can vary across both space and time.
Ambient induced degradation and chemically activated recovery in copper phthalocyanine thin film transistors
Authors: Park Jeongwon , Royer James E. , Colesniuc Corneliu N. , Bohrer Forest I. , Sharoni Amos , Jin Sungho , Schuller Ivan K. , Trogler William C. , Kummel Andrew C.
Published: August 2009

The electrical degradation (aging) of copper phthalocyanine (CuPc) organic thin film transistors (OTFTs) was investigated. Thick (1000 ML) and ultrathin (4 ML) channel thicknesses were used in bottom contact OTFTs to correlate the electrical effects of aging with film microstructure. Proper TFT saturation behavior was unattainable in thick devices subject to ambient aging; however ultrathin devices were significantly less susceptible and maintained good saturation and subthreshold behavior. Therefore 1000 monolayer (ML) CuPc OTFTs were characterized in ambient air, clean dry air, clean humidified air, and NOx environments to isolate the ambient components that induce aging. Thick channel devices which had been aged in ambient air to the point of losing all saturation behavior could be restored to proper saturation behavior by exposure to clean humidified air. The data are consistent with aging resulting primarily from adsorption of strong oxidants from ambient air within the grain boundaries of the CuPc films.
Morphology of RuO2(110) oxide films on Ru(0001) studied by scanning tunneling microscopy
Authors: Kim Sang Hoon , Wintterlin J.
Published: August 2009

Using scanning tunneling microscopy we have investigated the morphology of RuO2(110) films grown on Ru(0001). The films were prepared by dosing 2×105 to 1×106 L of O2 at temperatures between 650 and 850 K. It was found that the films are between 2 and 5 RuO2(110) layers thick, largely independent of the growth conditions. Within the temperature range investigated the perfectness of the films varied significantly. The morphology can be understood according to the habit of RuO2 single crystals, namely, the formation of extended (110), (100), and (101) surfaces. Upon annealing the films decompose by the formation of holes that go down to the metal substrate rather than in a layer-by-layer fashion. The Ru atoms released during decomposition form terraces with shapes similar to the terraces obtained by homoepitaxial metal-on-metal growth. Under the oxidation conditions used, we have not observed suboxides RuOx or the O–Ru–O trilayer that had been postulated to play a role for the RuO2 formation. The partially covered surfaces exclusively showed RuO2 and the known phases of adsorbed O atoms on the metallic Ru.
Fine calibration of the residual dissipation in a surface forces apparatus using a capacitive sensor
Authors: Leroy Samuel , Restagno Frédéric , Charlaix Élisabeth
Published: August 2009

The design of a dynamic surface force apparatus using a capacitive sensor has been useful in the past to study the nanorheological behavior of thin liquid films confined between a sphere and a plane. This allows a precise measurement of the hydrodynamical boundary condition of liquids down to some molecular sizes. However for thick liquid films, the viscous force is decreased and the dissipation due to the flow of air in the capacitive sensor becomes of the same order of magnitude than the force due to the liquid flow. In the present paper we present an original technique to characterize this residual force due to the capacitive sensor and we show that a precise subtraction of this force extends the precision of the device to the case of thick liquid films of low viscosity. This correction should be of major importance to extend the capability of surface forces apparatus to measure very large boundary slippage of simple liquids.
Color tunable phosphorescence in KY3F10:Tb3+ for x-ray or cathode-ray tubes
Authors: Zhang Jinsu , Hao Zhendong , Zhang Xia , Luo Yongshi , Ren Xingguang , Wang Xiao-jun , Zhang Jiahua
Published: August 2009

We report a persistent phosphor of KY3(1−x)Tb3xF10 (KY3F10:xTb3+) synthesized by solid-state reaction for x-ray or cathode-ray tubes. The phosphorescence consists of a group of blue and green emission lines originating from D53→F7J and D54→F7J transitions of Tb3+, respectively. The phosphorescent emitting color can be tuned from blue to green by gradually increasing Tb3+ concentrations, which is attributed to the enhanced D53-D54 relaxation through the cross relaxation between two Tb3+ ions, as described by of (D53,F76)-(D54,F70). The Tb3+ concentration dependent phosphorescence spectra are well simulated based on the analysis of luminescence dynamical processes using the Judd–Ofelt theory and rate equations concerning the D53 and D54 levels. The energy charge and release pattern of the phosphor are presented and a 10% decay time is 29 s. The measurement of the thermoluminescence glow curve gives convincing evidence for the traps analysis.
On the nonlinear stability of inviscid axisymmetric swirling flows in a pipe of finite length
Authors: Wang Shixiao
Published: August 2009

The nonlinear stability of columnar swirling flows in a finite constant-area pipe with periodic boundary conditions imposed at the inlet and outlet of the pipe is investigated by the Arnold energy-Casimir method. Szeri and Holmes [“Nonlinear stability of axisymmetric swirling flows,” Philos. Trans. R. Soc. London, Ser. A 326, 327 (1988)] applied the Arnold energy-Casimir method to the swirling flow and developed a general form of Arnold function, which forms the basis for the current investigation. It has been shown that for the base flow which has a uniform axial velocity profile, a reduced form of the Arnold function can be used to obtain nonlinear stability. This essentially extends Rayleigh’s linear stability theory to the nonlinear theory which is applicable to finite-amplitude disturbances, and leads to several nonlinear stability criteria which can readily be applied to swirling flows with various configurations. The nonlinear stability criteria are then applied to the Lamb–Oseen vortex and the Taylor–Couette flow, and crucial information about the disturbance’s size in terms of its kinetic energy has been obtained. A notable feature of the nonlinear stability is that it is applicable to a base flow which is linearly unstable, which was demonstrated by the linearly unstable Taylor–Couette flow.
Theoretical study of hierarchical structures and heredity effect of silicon solidifying on carbon nanotube
Authors: Li H. , Li Y. F. , Liew K. M. , Zhang J. X. , Liu X. F. , Fan R. H.
Published: August 2009

The growth of silicon atoms at the heterogeneous surface of carbon nanotubes (CNTs) is studied by means of molecular dynamics simulations. The results indicate that silicon atoms are concentrated to form an “annual ring” structure around CNTs. The structures of CNTs have strong correlation with the stacking sequence of silicon atoms. Heredity effect can be clearly observed during the heterogeneous nucleation. The uniform internal potential field around CNTs results in the formation of annual ring structures.
Investigation of the source-side injection characteristic of a dopant-segregated Schottky barrier metal-oxide-semiconductor field-effect-transistor
Authors: Kim Sungho , Choi Sung-Jin , Jang Moongyu , Choi Yang-Kyu
Published: August 2009

A unique characteristic of hot electron injection from the source side in a dopant-segregated Schottky barrier (DSSB) metal-oxide-semiconductor field-effect-transistor is investigated. A hot electron injection triggered by the sharp energy band bending near the source-side Schottky barrier is verified by the charge pumping method with numerical device simulations. With the aid of the charge pumping method, the lateral distribution of interface traps generated by injected hot electrons is analyzed. The results provide a guideline for the optimization of programming and erase operations in DSSB devices.
Nonlinear dust acoustic waves in a charge varying ion-ion-dust plasma
Authors: Tribeche Mouloud , Benzekka Moufida
Published: August 2009

The effect of nonthermal negative ions on large amplitude dust acoustic waves is investigated in a charge varying ion-ion-dust plasma. The proper nonthermal negative ion charging current is derived based on the orbit motion limited approach. Our results show that the negative ion nonthermality reduces the potential pulse amplitude and increases the net negative charge residing on the dust grain surface. The dust density localization is found to be more effective for lower values of the negative ion nonthermal parameter or higher values of the negative ion number of charges. Under certain conditions, the dust charge fluctuation may provide an alternate physical mechanism causing dissipation, the strength of which becomes more important as the nonthermal parameter increases or the negative ion number of charges decreases. The results are useful to understand the salient features of localization of large amplitude dust acoustic waves in cosmic plasmas such as the ionospheric D-region and the mesosphere.
Radiation hydrodynamic theory of double ablation fronts in direct-drive inertial confinement fusion
Authors: Sanz J. , Betti R. , Smalyuk V. A. , Olazabal-Loume M. , Drean V. , Tikhonchuk V. , Ribeyre X. , Feugeas J.
Published: August 2009

The one-dimensional theory of double ablation fronts is developed for direct-drive inertial confinement fusion targets. The theory is based on the subsonic ablation front approximation and includes the effects of both radiation and electron heat fluxes. It is found that the structure of the ablation front is determined by two dimensionless parameters: the Boltzmann number and the effective mean free path. The Boltzmann number represents the ratio of the convective thermal and radiation energy fluxes, while the effective mean free path is the ratio between the characteristic plasma temperature gradient conduction scale length and the radiation mean free path. The development of a double ablation front is determined based on the range of the above dimensionless parameters. Temperature and density profiles in double ablation fronts are derived from a simplified analytic model and compared with the results of numerical simulations.
Generation of warm dense matter and strongly coupled plasmas using the High Radiation on Materials facility at the CERN Super Proton Synchrotron
Authors: Tahir Naeem A. , Schmidt Ruediger , Brugger Markus , Assmann Ralph , Shutov Alexander , Lomonosov Igor V. , Gryaznov Viktor , Piriz Antonio Roberto , Udrea Serban , Hoffmann Dieter H. H. , Fortov Vladimir E. , Deutsch Claude
Published: August 2009

A dedicated facility named High Radiation on Materials (HiRadMat) is being constructed at CERN to study the interaction of the 450 GeV protons generated by the Super Proton Synchrotron (SPS) with fixed solid targets of different materials. The main purpose of these future experiments is to study the generation and propagation of thermal shock waves in the target in order to assess the damage caused to the equipment, including collimators and absorbers, in case of an accident involving an uncontrolled release of the entire beam at a given point. Detailed numerical simulations of the beam-target interaction of several cases of interest have been carried out. In this paper we present simulations of the thermodynamic and the hydrodynamic response of a solid tungsten cylindrical target that is facially irradiated with the SPS beam with nominal parameters. These calculations have been carried out in two steps. First, the energy loss of the protons is calculated in the solid target using the FLUKA code [Fasso et al., “FLUKA: A multi-particle transport code,” Report Nos. CERN-2005-10, INFN/TC-05/11, and SLAC-R-773, 2005; Fasso et al., Conference on Computing in High Energy and Nuclear Physics, La Jolla, CA, 24–28 March 2003] and this energy loss data is used as input to a sophisticated two-dimensional hydrodynamic code, BIG2 [Fortov et al., Nucl. Sci. Eng. 123, 169 (1996)], which is based on a Godunov-type numerical scheme. The transverse intensity distribution in the beam focal spot is Gaussian. We consider three different sizes of the focal spot that are characterized by standard deviations, σ=0.088, 0.28, and 0.88 mm, respectively. This study has shown that the target is severely damaged in all the three cases and the material in the beam-heated region is transformed into warm dense matter including a strongly coupled plasma state. This new experimental facility can therefore also be used for dedicated experiments to study high energy density matter.
Controllable resistance switching behavior of NiO/SiO2 double layers for nonvolatile memory applications
Authors: Choi Ji-Hyuk , Das Sachindra Nath , Myoung Jae-Min
Published: August 2009

Resistive switching characteristics of the double layer (NiO/SiO2) were studied for possible nonvolatile memory applications. The effect of SiO2 thickness variation in the memory device was investigated. A repeatable resistance switching behavior was observed with on/off ratio 105. The operation voltage of the device depended on the thickness of SiO2 layer and it increases with increasing SiO2 thickness. High-resolution transmission electron microscopy analyses revealed that the formation/rapture of Ni filament like percolation path inside SiO2 layer is responsible for the current transport mechanism.
In situ fabrication of cobalt-doped SrFe2As2 thin films by using pulsed laser deposition with excimer laser
Authors: Choi Eun-Mi , Jung Soon-Gil , Lee Nam Hoon , Kwon Young-Seung , Kang Won Nam , Kim Dong Ho , Jung Myung-Hwa , Lee Sung-Ik , Sun Liling
Published: August 2009

The remarkably high superconducting transition temperature and upper critical field of iron (Fe)-based layered superconductors, despite ferromagnetic material base, open the prospect for superconducting electronics. However, success in superconducting electronics has been limited because of difficulties in fabricating high-quality thin films. We report the growth of high-quality c-axis-oriented cobalt (Co)-doped SrFe2As2 thin films with bulk superconductivity by using an in situ pulsed laser deposition technique with a 248 nm wavelength KrF excimer laser and an arsenic (As)-rich phase target. The temperature and field dependences of the magnetization showing strong diamagnetism and transport critical current density with superior Jc-H performance are reported. These results provide necessary information for practical applications of Fe-based superconductors.
Impact energy and retained dose uniformity in enhanced glow discharge plasma immersion ion implantation
Authors: Lu Qiu Yuan , Li Liu He , Li Jian Hui , Fu Ricky K. Y. , Chu Paul K.
Published: August 2009

The implantation energy and retained dose uniformity in enhanced glow discharge plasma immersion ion implantation (EGD-PIII) is investigated numerically and experimentally. Depth profiles obtained from different samples processed by EGD-PIII and traditional PIII are compared. The retained doses under different pulse widths are calculated by integrating the area under the depth profiles. Our results indicate that the improvement in the impact energy and retained dose uniformity by this technique is remarkable.
Dynamics of water adsorption on Pt{110}-(1×2): A molecular dynamics study
Authors: Panczyk Tomasz , Fiorin Vittorio , Blanco-Alemany Raquel , King David A.
Published: August 2009

Recent experimental studies of water adsorption on Pt{110}-(1×2) using supersonic molecular beams [F. R. Laffir et al., J. Chem. Phys. 128, 114717 (2008)] have revealed that the translational energy dependence of the initial sticking probability is a stepwise function with a threshold energy of 5 kJ/mol. The initial sticking probability increases sixfold from ∼0.1 (at translational energies less than 5 kJ/mol) to ∼0.64 (at translational energies greater than 10 kJ/mol). The aim of this work is to study the adsorption dynamics of water using classical molecular dynamics simulation in order to assess what physical factors are responsible for the observed behavior of the initial sticking probability. The simulations were performed using a purpose-designed code; water molecules were modeled using the well-known TIP4P water model, whereas the water-platinum potential energy function was determined using the ab initio density functional theory calculations. We conclude that the main factor controlling the initial sticking probability is a relatively weak energy transfer between the water molecule and the surface substrate during collision. This energy transfer is enhanced when the total energy of the water molecule increases. The assumption of an exponential increase of the probability of the energy transfer as a function of total energy of water molecule gives initial sticking probabilities very similar to those experimentally obtained. The same model was applied for the simulation of the coverage dependent sticking probability using a hybrid method comprising molecular dynamics and kinetic Monte Carlo approaches. We found a reasonable agreement between our results and the experimental data. The sticking probability as a function of coverage initially increases due to an increasing amount of the adsorbate island edges; it reaches a maximum and finally decreases as the islands merge together at high coverage. The saturation coverage was determined to be 2.8 ML at surface temperature 165 K, where water forms a puckered almost regular lattice with each water molecule having four nearest neighbors. At the studied temperature we did not observe the existence of stable water multilayers on the surface which is consistent with the experimental findings.
Ultrathin lead oxide film on Pb(111) and its application in single spin detection
Authors: Fu Ying-Shuang , Ji Shuai-Hua , Zhang Tong , Chen Xi , Ma Xu-Cun , Jia Jin-Feng , Xue Qi-Kun
Published: August 2009

The morphology and electronic structure of ultrathin PbO films on silicon-supported Pb islands have been investigated with a low temperature scanning tunneling microscope. It is found that the PbO film acts as an insulating layer to electronically decouple the adsorbates from the metallic substrate. Due to the increased lifetime of spin excitation, the Zeeman splitting of individual manganese phthalocyanine molecules adsorbed on PbO could be detected with spin-flip inelastic tunneling spectroscopy. The ultrathin insulating films like PbO provide an effective way to control the electronic coupling in the nanometer scale.
The magnetic field reconnection site and dissipation region
Authors: Pritchett P. L. , Mozer F. S.
Published: August 2009

Magnetic field reconnection is said to involve an ion diffusion region surrounding an electron diffusion region. Because of uncertainties in the meanings of these terms and on the physical parameters that characterize them, this paper defines the reconnection site as a region having an electron scale size and containing magnetic fields from four topologies, and the dissipation region, as having an ion scale size and surrounding the reconnection site. Two-dimensional, asymmetric, open, particle-in-cell simulations, with and without guide fields, examine these regions. It is found that significant values of (E+UI×B) and/or (E+Ue×B) are not confined to either the reconnection site or the dissipation region. The reconnection site is uninteresting because, for asymmetric reconnection, it does not contain processes that serve to locate it, such as electron acceleration, parallel electric fields, super-Alfvenic electron flow, maximum electron beta, electron nongyrotopy, or demagnetized thermal electrons. However, the surrounding dissipation region exhibits these features.
Genome-wide location analysis reveals a role for Sub1 in RNA polymerase III transcription
Authors: Tavenet Arounie , Suleau Audrey , Dubreuil Géraldine , Ferrari Roberto , Ducrot Cécile , Michaut Magali , Aude Jean-Christophe , Dieci Giorgio , Lefebvre Olivier , Conesa Christine , Acker Joël
Published: August 2009

Human PC4 and the yeast ortholog Sub1 have multiple functions in RNA polymerase II transcription. Genome-wide mapping revealed that Sub1 is present on Pol III-transcribed genes. Sub1 was found to interact with components of the Pol III transcription system and to stimulate the initiation and reinitiation steps in a system reconstituted with all recombinant factors. Sub1 was required for optimal Pol III gene transcription in exponentially growing cells.
Structure and charging of hydrophobic material/water interfaces studied by phase-sensitive sum-frequency vibrational spectroscopy
Authors: Tian C. S. , Shen Y. R.
Published: August 2009

We have studied the hydrophobic water/octadecyltrichlorosilane (OTS) interface by using the phase-sensitive sum-frequency vibrational spectroscopy (PS-SFVS), and we obtained detailed structural information of the interface at the molecular level. Excess ions emerging at the interface were detected by changes of the surface vibrational spectrum induced by the surface field created by the excess ions. Both hydronium (H
3
O
+
) and hydroxide (OH
−
) ions were found to adsorb at the interface, and so did other negative ions such as Cl
−
. By varying the ion concentrations in the bulk water, their adsorption isotherms were measured. It was seen that among the three, OH
−
has the highest adsorption energy, and H
3
O
+
has the lowest; OH
−
also has the highest saturation coverage, and Cl
−
has the lowest. The result shows that even the neat water/OTS interface is not neutral, but charged with OH
−
ions. The result also explains the surprising observation that the isoelectric point appeared at ∼3.0 when HCl was used to decrease the pH starting from neat water.
Isotopic evidence for the diets of European Neanderthals and early modern humans
Authors: Richards Michael P. , Trinkaus Erik
Published: August 2009

We report here on the direct isotopic evidence for Neanderthal and early modern human diets in Europe. Isotopic methods indicate the sources of dietary protein over many years of life, and show that Neanderthals had a similar diet through time (≈120,000 to ≈37,000 cal BP) and in different regions of Europe. The isotopic evidence indicates that in all cases Neanderthals were top-level carnivores and obtained all, or most, of their dietary protein from large herbivores. In contrast, early modern humans (≈40,000 to ≈27,000 cal BP) exhibited a wider range of isotopic values, and a number of individuals had evidence for the consumption of aquatic (marine and freshwater) resources. This pattern includes Oase 1, the oldest directly dated modern human in Europe (≈40,000 cal BP) with the highest nitrogen isotope value of all of the humans studied, likely because of freshwater fish consumption. As Oase 1 was close in time to the last Neanderthals, these data may indicate a significant dietary shift associated with the changing population dynamics of modern human emergence in Europe.
Anomalously large anisotropic magnetoresistance in a perovskite manganite
Authors: Li Run-Wei , Wang Huabing , Wang Xuewen , Yu X. Z. , Matsui Y. , Cheng Zhao-Hua , Shen Bao-Gen , Plummer E. Ward , Zhang Jiandi
Published: August 2009

The signature of correlated electron materials (CEMs) is the coupling between spin, charge, orbital and lattice resulting in exotic functionality. This complexity is directly responsible for their tunability. We demonstrate here that the broken symmetry, through cubic to orthorhombic distortion in the lattice structure in a prototype manganite single crystal, La
0.69
Ca
0.31
MnO
3
, leads to an anisotropic magneto-elastic response to an external field, and consequently to remarkable magneto-transport behavior. An anomalous anisotropic magnetoresistance (AMR) effect occurs close to the metal-insulator transition (MIT) in the system, showing a direct correlation with the anisotropic field-tuned MIT in the system and can be understood by means of a simple phenomenological model. A small crystalline anisotropy stimulates a “colossal” AMR near the MIT phase boundary of the system, thus revealing the intimate interplay between magneto- and electronic-crystalline couplings.