Contribution Of Different Processes Research Articles

Forward Λ production and nuclear stopping power ind+Aucollisions atsNN=200GeV

We report the measurement of {lambda} and {lambda} yields and inverse slope parameters in d+Au collisions at {radical}(s{sub NN})=200 GeV at forward and backward rapidities (y={+-}2.75), using data from the STAR forward time projection chambers. The contributions of different processes to baryon transport and particle production are probed exploiting the inherent asymmetry of the d+Au system. Comparisons to model calculations show that baryon transport on the deuteron side is consistent with multiple collisions of the deuteron nucleons with gold participants. On the gold side, HIJING-based models without a hadronic rescattering phase do not describe the measured particle yields, while models that include target remnants or hadronic rescattering do. The multichain model can provide a good description of the net baryon density in d+Au collisions at energies currently available at the BNL Relativistic Heavy Ion Collider, and the derived parameters of the model agree with those from nuclear collisions at lower energies.

Magnetocaloric effect near the first-order phase transitions in compounds of rare earth and transition metals

The results of the calculations and the experimental values of the magnetocaloric effect (MCE) in a group of compounds that are promising for use in magnetic coolers are reported. In the materials studied, MCE reaches the largest values near the magnetic first-order phase transitions and is mainly determined by the evolving latent heat of the transition. Contributions of different processes, occurring at the first-order phase transitions, to the observed MCE value have been separated on the basis of the thermodynamic model.

Dynamics of nanoscale grain-boundary decohesion in aluminum by molecular-dynamics simulation

The dynamics and energetics of intergranular crack growth along a flat grain boundary in aluminum is studied by a molecular-dynamics simulation model for crack propagation under steady-state conditions. Using the ability of the molecular-dynamics simulation to identify atoms involved in different atomistic mechanisms, it was possible to identify the energy contribution of different processes taking place during crack growth. The energy contributions were divided as: elastic energy, defined as the potential energy of the atoms in fcc crystallographic state; and plastically stored energy, the energy of stacking faults and twin boundaries; grain-boundary and surface energy. In addition, monitoring the amount of heat exchange with the molecular-dynamics thermostat gives the energy dissipated as heat in the system. The energetic analysis indicates that the majority of energy in a fast growing crack is dissipated as heat. This dissipation increases linearly at low speed, and faster than linear at speeds approaching 1/3 the Rayleigh wave speed when the crack tip becomes dynamically unstable producing periodic dislocation bursts until the crack is blunted.

The role of the gluonic $gg\leftrightarrow{ggg}$ interactions in early thermalization in ultrarelativistic heavy-ion collisions

We “quantify” the role of elastic as well as inelastic \(gg\leftrightarrow{ggg}\) pQCD processes in kinetic equilibration within a pQCD inspired parton cascade. The contributions of different processes to kinetic equilibration are manifested by the transport collision rates. We find that in a central Au+Au collision at RHIC energy pQCD bremsstrahlung processes are much more efficient for momentum isotropization compared to elastic scatterings. For the parameters chosen the ratio of their transport collision rates amounts to 5:1.

Forward Λ Production and Nuclear Stopping Power in d+Au Collisions at RHIC

Using the forward time projection chambers of STAR we measure the centrality dependent A and Ā yields in d+Au collisions at √s NN =200 GeV at forward and backward rapidities. The contributions of different processes to particle production and baryon transport are probed exploiting the inherent asymmetry of the d+Au system. While the d side appears to be dominated by multiple independent nucleon-nucleon collisions, nuclear effects contribute significantly on the Au side. Using the constraint of baryon number conservation, the rapidity loss of baryons in the incoming deuteron can be estimated as a function of centrality. This is compared to a model and to similar measurements in Au+Au, which gives insights into the nuclear stopping power at relativistic energies.

Simulating low frequency changes in atmospheric CO<sub>2</sub> during the last 740 000 years

Abstract. Atmospheric CO2 measured in Antarctic ice cores shows a natural variability of 80 to 100 ppmv during the last four glacial cycles and variations of approximately 60 ppmv in the two cycles between 410 and 650 kyr BP. We here use various paleo-climatic records from the EPICA Dome C Antarctic ice core and from oceanic sediment cores covering the last 740 kyr to force the ocean/atmosphere/biosphere box model of the global carbon cycle BICYCLE in a forward mode over this time in order to interpret the natural variability of CO2. Our approach is based on the previous interpretation of carbon cycle variations during Termination I (Köhler et al., 2005a). In the absense of a process-based sediment module one main simplification of BICYCLE is that carbonate compensation is approximated by the temporally delayed restoration of deep ocean [CO32−]. Our results match the low frequency changes in CO2 measured in the Vostok and the EPICA Dome C ice core for the last 650 kyr BP (r2≈0.75). During these transient simulations the carbon cycle reaches never a steady state due to the ongoing variability of the overall carbon budget caused by the time delayed response of the carbonate compensation to other processes. The average contributions of different processes to the rise in CO2 during Terminations I to V and during earlier terminations are: the rise in Southern Ocean vertical mixing: 36/22 ppmv, the rise in ocean temperature: 26/11 ppmv, iron limitation of the marine biota in the Southern Ocean: 20/14 ppmv, carbonate compensation: 15/7 ppmv, the rise in North Atlantic deep water formation: 13/0 ppmv, the rise in gas exchange due to a decreasing sea ice cover: −8/−7 ppmv, sea level rise: −12/−4 ppmv, and rising terrestrial carbon storage: −13/−6 ppmv. According to our model the smaller interglacial CO2 values in the pre-Vostok period prior to Termination V are mainly caused by smaller interglacial Southern Ocean SST and an Atlantic THC which stayed before MIS 11 (before 420 kyr BP) in its weaker glacial circulation mode.

A calibration methodology and model‐based systems analysis for SBRs removing nutrients under limited aeration conditions

AbstractA methodology is proposed for the model calibration of nutrient‐removing laboratory‐scale SBRs under limited aeration. Based on in‐process measurements and influent wastewater characterization, the ASM2d model was modified by adding an organic nitrogen module incorporating a hydrolysis mechanism. After calibration, the simulation results showed that enhanced biological nutrient removal occurred during the fill period and under reduced aeration achieving so‐called ‘simultaneous nutrient removal’. A model‐based systems analysis was performed in terms of the contributions of different processes to overall oxygen, nitrogen and phosphate utilization. In each phase, simultaneously occurring biological reactions were compared using the calibrated model. According to the calibrated model, 61% of all denitrified nitrate is denitrified during the mixing/filling phase. On the other hand, 17% of all denitrified nitrate is consumed by simultaneous nitrification–denitrification during the first aerobic period. The aerobic and anoxic P‐removals were quantified as 73% and 12%, respectively. Copyright © 2006 Society of Chemical Industry

Influence of Reduction Conditions on H2 Adsorption in High-Surface Rh/CeO2 Catalysts as Deduced by Volumetry, Calorimetry, and 1H NMR Techniques

1H NMR spectra corresponding to H2 adsorption on high-surface Rh/CeO2 catalysts (S(BET) approximately 55 m2/g) are formed by two lines, attributed to hydrogen adsorbed on ceria (resonance line A) and rhodium-metal particles (upfield-shifted line B). The evolution of 1H NMR spectra as a function of temperature, time, and type of reduction (static or dynamic) allows the study of the progressive establishment of the strong metal-support interaction (SMSI) in Rh/CeO2 catalysts. As the reduction progresses, the mean adsorption heat and the amount of hydrogen adsorbed on the metal, deduced from volumetry, NMR, and calorimetry techniques, decrease considerably. As a consequence of the decrease in metal activity, the amount of hydrogen transferred to the support CeO2 is also reduced (spill-over processes). Outgassing of samples at 773 K eliminates hydrogen species retained at the metal-support surface, and oxidation treatments at 473 and 673 K eliminate the electronic effect and physical blocking of metal particles. The oxidation at 673 K recuperates the total adsorption capacity of metal particles. On the basis of these treatments, the contribution of different processes to the SMSI effect is analyzed. Electronic perturbation of rhodium particles is higher when reductions are performed in dynamic conditions; however, the importance of physical blocking of metal particles increases in static reductions. High reducibility of ceria strengthens electronic effects in Rh/CeO2 compared to those observed in Rh/TiO2 catalysts.

Λ production at forward and backward rapidity in d+Au collisions at

Using the forward time projection chambers of the STAR experiment at the Brookhaven Relativistic Heavy-Ion Collider, we measure the centrality-dependent Λ and yields and the inverse slope parameters in d+Au collisions at forward and backward rapidities y = ±2.75. The contributions of different processes to stopping and baryon transport are probed exploiting the inherent asymmetry of the d+Au system. Comparisons to model calculations show that the baryon transport on the deuteron side is due to multiple collisions of the deuteron nucleons with gold participants. On the gold side, the inclusion of initial-state nuclear effects or hadronic rescattering is necessary to describe the data.

Evaluation of CO simulations and the analysis of the CO budget for Europe

CO is a well‐suited indicator for the transport of pollutants in the troposphere on a regional and global scale. For the study presented here, simulations of CO concentrations from a global chemistry transport model (MOZART‐2), with the CO being tagged according to the emission type and the source region, have been used to diagnose the contributions of different processes and regions to the CO burden over Europe. Model simulations have been performed with both a priori emissions and an optimized set of CO surface emissions derived from the inversion of CO retrievals of the Measurements of Pollution in the Troposphere (MOPITT) remote sensing instrument. The annual mean difference between the modeled and the observed CO at 850 hPa over Europe is −38 ± 13 ppb with the a priori set of emissions and −7 ± 7 ppb when the optimized emissions are employed in the model. The general difficulties arising from an intercomparison of remote sensing data with model simulations are discussed. Besides data from MOPITT, ground‐based CO measurements have been employed in the evaluation of the model and its emissions. The comparisons show that the model represents the background conditions as well as large‐scale transport relatively well. The budget analysis reveals the predominant impact of the European emissions on CO concentrations near the surface, and a strong impact of sources from Asia and North America on the CO burden in the free troposphere over Europe. On average, the largest contribution (67%) to the anthropogenic (fossil and biofuel sources, biomass burning) CO at the surface originates from regional anthropogenic sources, but further significant impact is evident from North America (14%) and Asia (15%). With increasing altitude, anthropogenic CO from Asia and North America gains in importance, reaching maximum contributions of 32% for North American CO at 500 hPa and 50% for Asian CO at 200 hPa. The impact of European emissions weakens with increasing altitude (8% at 500 hPa).

Mosaicity reduction during growth of heteroepitaxial diamond films on iridium buffer layers: Experimental results and numerical simulations

Heteroepitaxial diamond films can be grown by bias enhanced nucleation on iridium buffer layers followed by an appropriate textured-growth step. Unlike epitaxial diamond films on silicon, the mosaicity reduction during textured growth includes tilt as well as twist. We conclude that different mechanisms causing the grain coarsening are working in the two cases. It is shown that the principle of evolutionary selection can be excluded as a decisive mechanism in the present films. Merging of neighboring grains by disclination formation yields an alternative explanation, that can convincingly substantiate the differences between the textured growth on iridium and silicon. From a Monte–Carlo type simulation describing the texture evolution due to merging of grains, a simple functional correlation between grain coarsening and mosaicity reduction is deduced. Comparison between simulation and experiment allows one to estimate the contributions of different processes. Finally, the general significance of the present findings for other materials is discussed.

Highlights of the tropospheric lidar studies at IFU within the TOR project

A summary of the ozone soundings with the tropospheric ozone lidar at IFU in the years 1991 and 1993 is given. The results cover vertical distributions obtained under a variety of meteorological conditions in different seasons such as during high pressure, before and after frontal passages and during stratospheric air intrusions. The lidar time series, carried out between typically 0.25 and 10 km and at intervals of about 1 h, are an excellent tool for transport studies. Quite frequently contributions of different processes may be observed even simultaneously which may yield insight on the troposphere as a whole. Although the time series were limited to single days during that phase information on a number of relevant transport processes could be extracted. In particular, the uplifting in the Alpine thermal wind system was investigated. The air in the valley is vented to heights in part even beyond 4 km a.s.l. during fair-weather summer days. The high efficiency of the underlying mechanism suggests a major contribution of the orographically induced transport in the Alps to the pollution export from the Central European boundary layer. A spectacular case of trans-Alpine ozone transport was examined which resulted in an ozone increase by about 40% after sunset. This case may, again, reflect the role of the Alps in the redistribution of air pollution in a larger area. In addition, episodes of long-range ozone and aerosol transport have been studied. In this paper, we present the example of intense Föhn with advection of dust-loaded air from the Sahara desert and beyond containing just 35 ppb of O3. A rather complex layering may be observed after cold-front passages associated with subsequent anticyclonic advection. The analysis of a two-day vertical-sounding series reveals that the air in different height ranges originated in the troposphere or stratosphere above rather different source regions, even in the lowermost 4 km above the United States. More recent studies have confirmed the reproducibility of the general layer pattern under such conditions. The in part considerable difference in ozone concentration makes the definition of a free-tropospheric background ozone level a difficult task.

Recent patterns and mechanisms of carbon exchange by terrestrial ecosystems.

Knowledge of carbon exchange between the atmosphere, land and the oceans is important, given that the terrestrial and marine environments are currently absorbing about half of the carbon dioxide that is emitted by fossil-fuel combustion. This carbon uptake is therefore limiting the extent of atmospheric and climatic change, but its long-term nature remains uncertain. Here we provide an overview of the current state of knowledge of global and regional patterns of carbon exchange by terrestrial ecosystems. Atmospheric carbon dioxide and oxygen data confirm that the terrestrial biosphere was largely neutral with respect to net carbon exchange during the 1980s, but became a net carbon sink in the 1990s. This recent sink can be largely attributed to northern extratropical areas, and is roughly split between North America and Eurasia. Tropical land areas, however, were approximately in balance with respect to carbon exchange, implying a carbon sink that offset emissions due to tropical deforestation. The evolution of the terrestrial carbon sink is largely the result of changes in land use over time, such as regrowth on abandoned agricultural land and fire prevention, in addition to responses to environmental changes, such as longer growing seasons, and fertilization by carbon dioxide and nitrogen. Nevertheless, there remain considerable uncertainties as to the magnitude of the sink in different regions and the contribution of different processes.

Mechanisms of double-electron ionization of atomic systems in a strong laser field

The field-induced double ionization of a model two-electron quantum system is investigated by direct numerical integration of the nonstationary Schroedinger equation. The contribution of different processes to a formation of doubly charged ions is analyzed.

Nitrification and denitrification as sources of gaseous nitrogen emission from different forest soils in Changbai Mountain

The contributions of nitrification and denitrification to N2O and N2 emissions from four forest soils on northern slop of Changbai Mountain were measured with acetylene inhibition methods. In incubation experiments, 0.06% and 3% C2H2 were used to inhibit nitrification and denitrification in these soils, respectively. Both nitrification and denitification existed in these soils except tundra soil, where only denitrification was found. The annually averaged rates of nitrification and denitrification in mountain dark brown forest soil were much higher than that in other three soils. In mountain brown coniferous soil, contributions of different processes to gaseous nitrogen emissions were Denitrification N2O>nitrification N2O>Denitrification N2. The same sequence exists in mountain soddy soil as that in the mountain brown coniferous soil. The sequence in mountain tundra soil was Denitrification N2O>Denitrification N2.

Calibration and identifiability analysis of a water quality model to evaluate the contribution of different processes to the short-term dynamics of suspended sediment and dissolved nutrients in the surface water of a rural catchment

A method that combines calibration and identifiability analysis of a dynamic water quality model to evaluate the relative importance of various processes affecting the dynamic aspects of water composition is illustrated by a study of the response of suspended sediment and dissolved nutrients to a flood hydrograph in a rural catchment area in the Netherlands. Since the water quality model simulates the observed concentrations of suspended sediment and dissolved nutrients reasonably well, the most important processes during the observed flood hydrograph could be determined. These were erosion, exchange between dissolved phase and bed sediments and denitrification. It is concluded that the method is very useful for identifying the most significant model parameters and processes that are essential for water quality modelling. © 1998 John Wiley & Sons, Ltd.

Calibration and identifiability analysis of a water quality model to evaluate the contribution of different processes to the short‐term dynamics of suspended sediment and dissolved nutrients in the surface water of a rural catchment

A method that combines calibration and identifiability analysis of a dynamic water quality model to evaluate the relative importance of various processes affecting the dynamic aspects of water composition is illustrated by a study of the response of suspended sediment and dissolved nutrients to a flood hydrograph in a rural catchment area in the Netherlands. Since the water quality model simulates the observed concentrations of suspended sediment and dissolved nutrients reasonably well, the most important processes during the observed flood hydrograph could be determined. These were erosion, exchange between dissolved phase and bed sediments and denitrification. It is concluded that the method is very useful for identifying the most significant model parameters and processes that are essential for water quality modelling. © 1998 John Wiley & Sons, Ltd.

Metallographic Indications of Creep Process in Double-Notch Specimens / Metallographische Indikationen des Kriechprozesses in Doppelkerbproben

The technique of double-notch specimens can generate a pronounced shear strain in a chosen crystal plane of copper single crystals only in the initial period of creep, before the high shear stress relaxes due to a deformation response of the whole specimen. A complex bi-axial stress field in the specimen is responded by a complex field of strain. Appropriate creep conditions must be chosen so as the strains in different regions of the specimen contribute time dependent creep components that can be distinguished. This would give a chance to separate contributions of different processes to the creep curve.

A simple‐model study of the interaction between cumulus and stratocumulus clouds in the marine boundary layer

AbstractDecoupling of the marine boundary layer beneath stratocumulus clouds and the formation of cumulus clouds at the top of a surface‐based mixed layer have frequently been observed and modelled. However, little is known of the details of the interaction between the two cloud types, how this affects the microphysical and radiative properties of the stratocumulus, and how the cloud‐topped marine boundary layer evolves in such cases. Recent observational studies suggest that the microphysical and geometrical characteristics of the stratocumulus layer can be modified significantly by interaction with cumulus clouds. In this paper, a preliminary assessment of the relative contribution of different processes and initial boundary‐layer conditions, as suggested by the observations, to the outcome of the interaction between cumulus and stratocumulus clouds is carried out using a one‐dimensional entraining parcel model, which has been modified to simulate a cumulus cloud which penetrates a stratocumulus layer. the results suggest that the change in droplet size at the stratocumulus top as a result of mixing with the penetrating cumulus clouds is particularly sensitive both to the amount of pollution in the air mass and to the vertical structure of the boundary layer, and that these may be more important in determining the outcome of the interaction than the local temperature. A simple coalescence calculation is then used to show that the introduction of cumulus cloud droplets into a stratocumulus layer may alter the potential for drizzle formation in the cloud layer by introducing droplets which are of a different size from those already existing in the stratocumulus. However, it is clear that more detailed dynamical, microphysical and radiative‐transfer models are required, in conjunction with further observations, if these effects are to be parametrized for use in large‐scale numerical models.

Temperature effect on proton-transfer equilibrium and IR spectra of chlorophenol–tributylamine systems

Binary solutions of chlorophenols in tributylamine (TBA) have been studied by UV and IR spectroscopy at temperatures down to the glassy transition state of TBA (123 K). The pentachlorophenol–TBA system has also been studied at 13–123 K in TBA matrices prepared by co-deposition of the gaseous components on a cooled window. 2,4-Dichlorophenol, 2,4,5-trichlorophenol, 2,6-dichlorophenol and 2,4,6-trichlorophenol in solution show proton-transfer (PT) equilibria which shift sharply toward the PT species on cooling. No PT is detected in the case of 2-chlorophenol. Pentachlorophenol appears entirely as a PT ion pair across the whole temperature range both in solution and in a matrix. Significant influence of ion-pair self-association on the IR spectra of solutions has been found by comparison with spectra obtained in rigid matrices. All systems studied reveal broad, intense, temperature-dependent bands corresponding to protonic vibrations. An extremely intense and broad absorption, with a maximum shifted to 700–500 cm–1, is observed when the PT equilibrium constant is close to unity. The contribution of different processes, e.g. hydrogen-bond strengthening, proton transfer and association of ion pairs, to the temperature transformations of IR spectra is discussed.